©2015 Nashua, NH USA. All rights reserved

A QC LATHE TURRET

Photos and drawings by the author

By John Manhardt

Page 1 of 27

BACKGROUND Soon after I acquired my minilathe some years ago, I coveted a quick change tool post. However, the financial

cupboard was bare, so I started out with the stock tool post, using shims to adjust the cutting tool height to the lathe

axis center. Then I spied an ingenious design by Andy Lofquist1 for a simple, shop-built QCTP (Quick Change

Tool Post. I built one (Photo 1) which has served me well for seven years. Recently I needed to make a number of

duplicate parts, each of which required a half dozen or more machining steps, most at fixed angles. Although I

ground those lathe tools as simple plunge forming tools, my QCTP had no indexing feature, so every time I

changed a tool holder, I had to carefully align the tool either parallel or perpendicular to the lathe axis for each

duplicate part. That cost a lot of time. Also my QCTP had two problems I was eager to solve. The first was the

seam, needed to lock tool holders to the rotatable body by spreading the body dovetails, was wide enough to allow

ingress of fine chips, which occasionally jammed the slot open, interfering with removal of the tool holder. The

second problem was finer chips, which found their way between the bottom of the body and its mounting base, and

damaged the base when the body was clamped to the compound slide. I had used unhardened flat ground O1 tool

steel for the mounting base, but it became badly dented and burred (Photo 2.) Although unhardened, the 1144 steel

body did not suffer any damage.

I researched shop-made indexable lathe turrets, but none of the four-sided lathe turrets I had seen had the quick tool

change feature. They also appeared difficult to machine accurately when it came to the ratchet indexing mechanism.

Even the renowned George Thomas advised the builder to identify the tool slot which most accurately aligned the

tool relative to the lathe spindle axis. Even the expensive Aloris tool post specified a one-degree angular tolerance

between its two 90° tool holder dovetail mounts.

After about a year’s worth of on and off doodling, I was satisfied with a concept I thought would solve the two

problems I had with my QCTP by shrouding the mounting base, providing a zero-width seam to minimize entry of

chips, act like a turret by quickly and accurately aligning the dovetails both parallel and perpendicular to the lathe

axis and, at the same time, providing the quick change tool holder feature. Andy Lofquist wanted to design a QCTP

of minimum complexity; he succeeded most admirably. My QC turret uses his brilliant basic concept but required

much more complexity to achieve my objectives. None of the parts are hardened. Andy built his entirely on a lathe

with a milling attachment. I needed a lathe plus a bench-top mill equipped with a rotary table to make my QC

Photo 1. My version of the Lofquist QCTP Photo 2. The damaged O1 mounting base

Page 2 of 27

Turret (Photo 3). There are as many approaches to building my design as there are machinists; this article describes

how I built mine. The version described here is 2.0. The version 1.0 prototype visible in some photos was used to

build it.

DESCRIPTION Referring to the Figure 1 ASSEMBLY, a MOUNTING BASE, 5, is clamped to the compound slide by the POST,

4. The mounting base is doweled into the compound slide to prevent its rotation. The three-piece BODY assembly,

1, overhangs and shrouds the MOUNTING BASE to deter entry of chips between them and rotates on the POST, 4.

It consists of two mirror halves, 1A and 1B, aligned by dowels, 2, through the TIE PLATE, 1C. Ten socket button

head screws, 3, flanking the seam between 1A and 1B pull the tie plate into shallow bevels machined into the

abutting ends of 1A and 1B to spring the seam closed and lock the three body components together. A ROTATION

STOP, 8, is bonded into the mounting base to limit body rotation. A quarter-circle slot machined into the body

clears the rotation stop. A tapered PLUG, 6, is forced vertically into a matching taper machined into the BODY by

rotating the HANDLE, 7 to spread the dovetails, simultaneously locking the tool holder firmly onto the body, and

clamping the body firmly to the mounting base. The STOP ADJUST screws, 9, can be adjusted to stop body

rotation at positions exactly parallel to- and exactly square to- the lathe axis. Two STOP LOCK screws, 10, lock

those adjustments. Photo 4 shows the major components.

Photo 3. My QC Turret

Photo 4. Major components

Page 3 of 27

BILL OF MATERIALS

PART NO. NAME DESCRIPTION QUANTITY

1A, 1B Body Half 1144 bar, 2¼”Ø x 6” long 1

1C Tie Plate O-1 Ground Flat 1/8” thick x 1-1/2 x 2-1/2” 1

2 Dowel ⅛”Ø x 1/2” long 6

3 Screw Socket Button Screw, 4-40 x ⅜” long 10

4 Post W1 drill rod, ½”Ø x 5” long 1

5 Mounting Base 1144 bar, 2¾”Ø. x 2” long 1

6 Plug Cast iron bar, 1¼”Ø x 2” long 1

7A Handle 12L14 bar, 1”Ø x 5” long 1

7B Handle Ball 12L14 bar, ¾”Ø x 3” long 1

8 Rotation Stop W-1 drill rod, ¼”Ø x 2” long 1

9 Stop Adjust Socket set screw 8-32 x 1” long 2

10 Stop Lock Socket Set Screw, 6-32 x ¼” long 2

1B

1C

1A

7

5

9

1

6

7B

2

3

10

9

AA

VIEW ON A-A

COMPOUND SLIDE

9

8

7A4

Figure 1ASSEMBLY

Page 4 of 27

DRAWINGS Detail drawings for the QC Turret are shown on pages 16 and 17. Parts 2 and 3 are not detailed.

PART 1, BODY, first operations The body halves were made from 1144 steel, which has high tensile strength, free machines to a good finish, is

wear resistant, and is harder in its annealed state than CRS, HRS, and 12L14. I could not find a source for rectangle

or square bar, so I machined a 6” bar of round stock on my mill (Figure 2) using a shop-made face mill (lots of

chips!) I gripped the entire bar atop a round parallel in the mill vise and roughed the rectangular cross section one

side at a time (Photo 5.) I made sure that all four sides were squared to a blackout fit to my Class N bevel-edge

square before taking it to the 1.095” x 1.630” cross section (0.020” over finished dimensions.) The face which will

become the seam face must not be convex. After squaring (Photo 6) and marking the ends (Figure 2 arrows, Photos

1.095

1.6

30

2.355 2.3550.0

03"

taper

SEAM FACE SEAM FACE

1.0

95

1.630

Figure 2. Rough Machining Parts 1A and 1B

Photo 5. Milling round to rectangle section Photo 6. Squaring the saw cut end

Page 5 of 27

7 & 9 (circled.) I hacksawed it in half crosswise (Photo 7) and milled the saw-cut ends together with the seam faces

in contact (Photo 8) to 2.355” overall length (0.010” over finished dimension.) These two pieces eventually became

parts 1A and 1B. Next I milled a 0.003” taper along the 1.095” dimension of the unmarked end of each piece (Photo

10) using the marks to orient the taper on each piece so that when assembled, the seam would orient the bevels

correctly.

The ⅛” thick tie plate, Part 1C, was milled to a 1.630” x 2.190 rectangle, and the three pieces, 1A, 1B, and 1C were

clamped together in the mill vise with the tie plate facing up. 1A and 1B were set on thin parallels, aligned by a

machinists clamp and clamped together by a Kantwist clamp with the tapered faces uppermost. A strap clamp held

Part 1C on top in register with 1A and 1B and locked the assembly to the mill table (Photo 11.) One hole at a time, I

located a dowel center, drilled No. 31Ø x 0.550” deep, reamed ⅛”Ø, and installed a 1/2” long dowel pin flush with

the surface of 1C. None of the dowels were bonded in place.

Leaving the three body parts clamped together, I rotated the assembly 90° on the mill table, indicated one edge

parallel to the mill X axis, and clamped the assembly to the mill table with a strap clamp. I drilled and tapped the

ten holes for the 4-40 socket button head screws one at a time (Photo 12) drilling through the 1C tie plate No. 43 x

Photo 10. Milling the 0.003 in. tapers Photo 9. Witness marks orient abutting seam faces

Photo 7. End and saw cut line marked out Photo 8. Squaring the saw cut ends

Page 6 of 27

0.500” deep, counter drilling No. 33 x 0.125” deep, and tapping 4-40 x 0.400” deep. I used a spiral fluted tap to

help extract the chips and installed a ⅜” long screw snug tight immediately after tapping each hole. After the tenth

screw was installed, I gradually tightened each of the screws in turn until the tie plate was pulled down flush with

the bevels on 1A and 1B. After unclamping from the vise and verifying the absence of any gap along the seam

between 1A and 1B, I milled the five flat faces to finished dimensions (Photos 13 & 14) taking care to keep the

seam centered. I put this part aside temporarily.

PART 2, POST The diameter of the drill rod used for the post should measure at least 0.500” to insure a great fit in the hole to be

reamed in the body. I chucked a 31/4” length of half-inch W1 drill rod in a collet chuck with 1” exposed, faced the

end, turned the end 0.385”Ø x 0.750” long to a sharp shoulder, plunged a 0.300”Ø, 0.070” wide thread relief groove

0.530” from the end, leaving 0.150” smooth up to the shoulder, turned 0.580” of the 0.385”Ø down to 0.381”Ø, and

Photo 12. Installing the screws Photo 11. Reaming for dowel pins

Photo 14. Milling to finished dimensions Photo 13. Milling to finished dimensions

Page 7 of 27

screw cut M10 X 1.5 taking out the last thou with a M10 X 1.5 die. I reversed the part in the collet chuck with 11/4”

exposed, faced the end to 3.040 overall length, and formed a ½” radius on the end by the incremental cut method

illustrated on page 17 (still don’t have a ball turning tool.) Photo 15 shows the roughed out radius on the post. I

turned the end 0.489”Ø x 0.830” long to a sharp shoulder, plunged a 0.420”Ø, 0.160” wide thread relief groove at

the shoulder, and then screw cut the end ½-20, taking the last thousandth with a ½-20 die (Photo 16.)

PART 8, ROTATION STOP This was a straightforward turning job needing no further comment.

TRANSFER PUNCH With a length of 3/16ӯ W1 drill rod in a collet chuck, I turned the exposed end to a 120 degree point, reversed the

part in the collet chuck, faced the part to 1.400 ” overall length, and formed a ½ ” radius with a file by eye on the

end. This piece was not hardened. Since this tool was not a component of the finished QC Turret, no part number is

assigned. It was left unhardened as it only had to make a single punch mark.

PART 5, MOUNTING BASE, first operations I use my compound slide in conjunction with a saddle stop to machine features to preset lengths as with the Post. I

keep the compound slide locked parallel to the lathe axis to facilitate that method of working. I made two mounting

bases because I have always screw cut threads with the compound slide swiveled 61 degrees to the lathe axis, and

that angle will be impossible to obtain without disturbing the rotation stop adjustment of the turret. I rejected the

idea of a removable rotation stop out of concern for its rigidity. So when I thread, I will accept the extra effort and

time required to replace the “stock” mounting base with one that doesn’t have a rotation stop. (Others might wish to

keep their compound at an angle suitable for threading all the time and will have no need for a second base or the

bother of installing it for taper machining. They will need to revise the location of the rotation stop to suit.) A short

length of 2¾”Ø 1144 bar stock was chucked in the 4-jaw lathe chuck, centered, and faced to clean up. The central

hole was drilled Ltr. “U” x ¾ ” deep, bored to 0.385”Ø for a locational fit on the Post, and two slices parted from it,

each 0.200 in long. I turned an expanding stub arbor on a piece of scrap to a snug fit in the 0.385ӯ hole in the

mounting base. One disk at a time, I turned the OD of the mounting base to 2.060”, and faced both faces to 0.1875”

Photo 16. Screw cut ½-20 thread Photo 15. Roughed out Post radius

Page 8 of 27

overall thickness (Photo 17.) I generously chamfered the OD of one face. I repeated that procedure with the second

base. I was careful to face the two parts to the same thickness, to avoid having to readjust my tool holders to lathe

center height when I swap one for the other. I positioned one mounting base with the chamfer facing upward onto

the lathe compound slide and screwed it tightly to the compound slide using the Post as a fastener. I tightened the

post using two ½-20 jam nuts, taking care to avoid contact between the lower nut and the shoulder on the post.

Moving to the mill, I centered the mounting base under the mill spindle, moved the mill table to center the mill

spindle 0.200” from the tailstock edge of the mounting base, drilled No. 14 through both base and compound slide,

and reamed 3/16ӯ through. Next I dowelled the mounting base to the compound slide to prevent its rotation. One at

a time, two holes located diagonally opposite each other and 0.707 ” from the mounting base center were drilled

No. 31 x 0.525 ” deep and reamed ⅛”Ø x 0.525 ” deep. As each hole was completed, a ⅛”Ø x ½” long hardened

steel dowel pin was pressed in just below the mounting plate surface. This part was then used as a drill jig to drill

holes for the two dowels in the other mounting base.

PART 1, BODY, second operations I measured the body assembly for squareness and outside dimensions. After verifying dimensions and squareness, I

laid out and lightly center punched the location for the central hole on the bottom face of the body 1.190 in from the

outside face of the tie plate and centered on the seam between the two body halves.

Photo 17. Facing the Mounting Base

Page 9 of 27

With sheet brass pads protecting the body from the chuck jaws, I chucked it in the 4-jaw lathe chuck with the

bottom face toward the tailstock, centered the punch mark using a dial indicator near the part bearing on a tailstock-

center-mounted wobbler (Photos 18 & 19,) drilled, bored, and reamed the 0.500ӯ hole right through (Photo 20.) I

then bored out a recess 2.060”Ø x 0.156” deep to fit the mounting base (Photo 21.) The bottom of the recess MUST

be flat and have a smooth finish. I then lightly faced the bottom face of the body to just clean up. While still gripped

in the chuck, I test fitted the assembled Post and mounting base. A locational fit is ideal. If the post is too tight, it

should be lapped to a close fit with the reamed hole in the body.

At this point one should have the cast iron bar handy for making the plug. The taper to be machined into the body

and that of the plug must match, so they should be machined one after the other before the compound setting can be

disturbed. I also made and fitted a stop2 (Photo 3) to the cross slide before starting this operation to make this job

and threading easier. I ask experienced readers to please forgive the elementary detailed description that follows. I

work these details out ahead of time for my own personal benefit and follow them to the letter. I hope they will be

useful to the less experienced readers like myself. I chucked the body in the 4-jaw, with brass pads between body

and chuck jaws, with the top of the body facing the tailstock, and centered the 0.500ӯ hole. Using the prototype

QC Turret with the new, plain mounting base, I swiveled the compound clockwise at a 20 degree angle to the lathe

axis, locked its rotation, retracted the compound slide toward the tailstock to the minimum feed position (the middle

Photo 20. Boring the body for the post Photo 21. Boring the recess in the body

Photo 18. Centering the body Photo 19. Centering the body

Page 10 of 27

gib screw aligned to the end of the compound slide,) and locked it. I used the cross slide and apron hand wheels to

counter bore parallel 0.880”Ø x 0.440” deep. With the lathe rotation stopped, I locked the cross slide at the 0.880”

tool tip diameter, locked the saddle to the lathe bed at the 0.440” tool tip depth, and zeroed both the compound slide

and cross slide feed dials. I set and locked the cross slide stop to prevent further movement of the cross slide toward

me. To position the boring tool to machine the taper, I unlocked the cross slide, fed it toward the lathe axis,

unlocked the saddle from the lathe bed, advanced the tool tip into the 0.500” bore using the apron hand wheel, and,

using the cross slide, touched up the tool tip to the near side wall of the 0.500” bore ID. I retracted the saddle

toward the tailstock to withdraw the tool tip from the bore, retracted the cross slide 0.020” (toward me) and locked

it. I then advanced the saddle toward the headstock to contact the part, verified the dial had returned to zero, and

locked the saddle to the lathe bed. From now on, all cuts were fed solely by the compound slide. With the lathe

rotating, I used the compound slide to advance the boring tool until the tool tip cleared the ID of the 0.500” bore.

With the lathe stopped, I positioned the tool for the next cut by retracting the compound to clear the tool tip from

the work, retracting the cross slide another 0.020”, and locking it. With the lathe rotating, I advanced the compound

slide until the tool tip cleared the 0.500” bore ID. I continued this sequence until the cross slide contacted the stop

and its dial reached the starting reading of zero. I then lightly faced the top surface of the body to just clean up.

Leaving the compound angle undisturbed for machining the taper on the plug, I removed the boring tool and the

body from the lathe and put this part aside temporarily.

PART 6, PLUG I centered the cast iron bar in the 4-jaw with 2” exposed, faced the exposed end, drilled and reamed 0.500”Ø x

1.510” deep, and verified its fit on the post. I then turned the OD parallel 0.880”Ø x 1.590” long using a knife tool

with a 1/32” tip radius to get a smooth finish. I aligned the tool tip by eye perpendicular to the taper about to be cut. I

chucked a ⅜“Ø wood dowel in the tailstock chuck and positioned it in the plug bore to catch the plug when it parted

from the parent bar. After using the apron hand wheel and cross slide to position the tool tip and then locking both

the saddle to the lathe bed and locking the cross slide, I used only the compound slide to make the cuts (Photo 22.)

The taper was turned until the part fell off the parent bar. Then I faced the small end to 0.970” overall length and

chamfered the junction between the parallel and tapered surfaces with a file to clear the radius on the internal body

taper.

Photo 22. Machining the taper on the plug

Page 11 of 27

PART 1, BODY, third operation The Lofquist QCTP was my dovetail machining baptism. To my surprise and delight, working slowly and carefully,

I didn’t scrap any of them. That experience gave me the confidence to take on this project. To mill the dovetails, I

dialed in the mill vise stationary jaw parallel to the mill X axis and clamped the body in the mill vise with the

dovetail face up on a single parallel (1/8ӯ drill blank) to clear the button head screws and oriented with the seam

parallel to the mill Y axis (Photo 23.) Figure 3 clarifies the machining sequence much better than mere words alone.

The first cuts (step 1) were made with a four-flute end mill, 15/64“ deep and 15/32“ wide on each side, leaving a

plateau 1.250“ wide centered on the seam. Then I milled one side at a time full (15/64“) depth with a ¾“Ø, 60 degree

dovetail cutter, taking incremental sideways cuts with the X and Z mill axes locked. I made the first cut 0.025” X-

axis feed, but had to reduce that for subsequent cuts to avoid stalling the mill spindle as the width of the chip

increased rapidly with each sideways increment. My mill is seriously torque limited, so my final cuts are usually in

0.001” increments. I have read that, to get the best finish, the final cut should be made with only one face of the

cutter in contact with the work, but I found I get the best finish with both faces touching. First, to provide a

reference for me to gage my progress and avoid having to switch from one side to the other and losing my bearing

(no DRO) I measured across 3/16 “ dowel pins before I made my first dovetail cut (Step 1: 1.625”) Then I cut the

first dovetail, periodically measuring across the two dowel pins. I stopped (step 2) when that measurement equaled

1.566” (half way between the reference measurement (1.625”) and the target final measurement (1.506”.)

(1.625+1.506)/2 = 1.566

Start Step 1

1.250

1.625

0.235

Step 2

1.566

Step 3

1.506

Figure 3. Sequence for Milling Body Dovetails

Page 12 of 27

I then cut the opposite dovetail, again periodically measuring across the dowel pins until the measurement equaled

the target value of 1.506” (Step 3.) At that point I checked the fit of all of my existing tool holder dovetail sockets

before removing the body from the mill vise. I machined the excess width at the dovetail end at a 45 degree angle to

discourage buildup of chips that might interfere with tool holder mounting or removal, but that step is best left until

after the stop adjust screws have been fitted.

Next I inverted the body in the mill vise, not on parallels, with the seam oriented parallel to the mill Y axis and

milled the tie plate in line with the seam 1/16” deep with a ¼”Ø ball end mill to adjust the effort needed to clamp

my tool holders securely. When a typical tool holder was clamped solid, the seam accepted a 0.004” feeler gage but

would not admit a 0.005” feeler gage. All of the tool holders I made to fit my Lofquist tool post clamped up solid.

I drilled and tapped the body for the stop adjust and stop lock set screws and machined 45° chamfers on the four

vertical corners for handling comfort (Photos 24 & 25.)

Photo 23. Milling the dovetails

Photo 24. Swiveled for turning Photo 25. Swiveled for boring

Page 13 of 27

PART 1, BODY, fourth operation After returning the compound slide parallel to the lathe axis and locking its rotation, I loosely assembled the

mounting plate, post, and body to the compound slide. I used a ½-20 hex nut and ½” washer to clamp the body

firmly in place to prevent its rotation. Before clamping up tightly, I indicated the dovetail end of the body square to

the lathe axis, clamped tightly, and verified squareness. I removed the assembly from the lathe, inverted it on a hard

surface, inserted the transfer punch, and gave a firm tap with a dead blow hammer to mark the center of the rotation

stop on the body recess. I removed the body and clamped it, inverted, on parallels in the mill vise. I centered the

punch mark under the mill spindle, drilled Ltr.”D”Ø x 0.190” deep (full drill flute Ø) and reamed ¼“Ø x 0.190”

deep.

To mill the slot for rotation stop clearance, I first made a ¼” thick, ½”Ø centering disk for my 6 ” RT (rotary table,)

installed it on the RT, clamped the RT to the mill table, and centered it under the mill spindle. I then placed the

body, recess upward, over the centering disk and lightly clamped it to the RT table. I rotated the RT table to zero

indicated degrees and locked it against rotation. Then I indicated the dovetail end of the body parallel to the mill Y

axis and clamped it solidly to the RT. I then turned up a ⅜”-to-3/16” centering pin, gripped it in the mill’s ⅜” end

mill holder, moved the mill table to center the 1/4“Ø hole in the body recess under the mill spindle, and locked the

mill table axes. I replaced the centering pin in the ⅜“ end mill holder with a ¼“, two-flute end mill (⅜“ shank)

touched up, and milled a slot while rotating the RT between 179 and 271 indicated RT degrees, taking incremental

cuts of 0.010” depth to gradually deepen the slot to 0.200” depth (Photo 26.) I then widened the slot 0.002” radially,

cutting 0.001” radially full depth on each wall. Before unclamping, I verified free transit of the rotation stop over

the full range of the slot.

At this point I went nuts removing all external machining marks using 400 grit abrasive paper taped to my surface

plate. I did not touch the dovetails, but all other exterior surfaces, being in the wind, were fair game.

Part 5, MOUNTING BASE, second operation I finished one mounting base by cleaning the rotation stop and the 3/16ӯ hole in the mounting base and bonded the

stop in place with Loctite 609 Retaining Compound. After the Loctite cured, I installed the mounting base and post

on the compound slide, using two ½-20 jam nuts to tighten the post. I clamped across the free ends of the body,

slipped it and the plug over the post, loosely clamped it down using a ½“ washer and ½-20 nut, and verified the

Photo 26. Milling the clearance slot for the rotation stop

Page 14 of 27

body rotated over its full range. With the body rotated fully clockwise, I verified the dovetail face was beyond

parallel to the lathe spindle axis and, when rotated fully counterclockwise, beyond square to the lathe spindle axis.

PART 7, HANDLE I used a handle design and machining method described by George H. Thomas.3 I drew the components I made but

have not described how I machined the parts as those details are available in his book (available from

Amazon.com) which is a treasure trove of information, well worth having, that has enabled me to become a much

better machinist. Use your ball turning tool to form the balls if you have one. For those like me, who lack a ball

turning tool, I have included cutting tables for roughing out the balls by the incremental cut method4 and detailed on

pages 18 and 19 and Photos 27 thru 32. I faced 1/16” off the top of the plug to adjust the tightened position of the

handle. You may need to remove more or less, depending on the how the post and handle threads align axially.

PARTS 9 &10, STOP ADJUST & STOP LOCK SCREWS I shortened the 8-32 Stop Adjust screws and converted their cup points to dog points which contact the rotation stop

with a solid thunk. Note that they are different lengths. The one sunk into the dovetail end needs to sit below that

face. I used a spiral-fluted tap to facilitate chip removal. The 6-32 Stop Lock screws (Part 10) were also given dog

points and shortened to bring them nearly flush with the outside surfaces of the body. Pads of 1/16” Ø copper

electrical wire were placed between the locking screw tips and the stop adjust screw threads to avoid marring the

threads on the latter. In the past I have used punched disks of 1/16” lead sheet roofing for that purpose, but I was

unable to locate my stash of that material for this project. Note to self: get better organized.

A WORD ABOUT LUBRICATION

Those familiar with boundary layer behavior of fluids will appreciate that, when the zero-gap seam is spread to lock

the body dovetails into those of the mounted tool holder, any free fluid in the vicinity of the seam will immediately

be drawn or injected into the opening gap. The resulting boundary layer of fluid in the gap will have a much higher

viscosity than the free fluid and may even succeed in preventing the seam from closing and freeing the tool holder

when the handle is loosened. That happened to me. If it happens to you, don’t panic. Tightening a toolmakers or

Kantwist clamp across the seam behind the tool holder will expel enough of the fluid to free the tool holder. No

need for a hammer. To avoid that irritant, I recommend a minimum of lubrication confined to the locations where it

is needed. Those locations are the post and handle threads, matching tapers on the body and plug, and the contact

surfaces between handle and plug. The metallurgy specified has served me well on my version of the Lofquist

design tool post for seven plus years without wear or galling. I am using CRC Sta-Lube “Moly-Graph”

moly/graphite grease applied sparingly with a finger, rubbed thoroughly into the texture of the machined surfaces,

and the excess wiped off with a lint-free cloth (old cotton tee shirt.) Enough lubricant remains in the surface nap to

be effective. The tapers on the plug and body rub hard against one another every time the handle is tightened, but

after 7 years of that the tapers of my Lofquist knockoff have burnished one another to a very smooth finish without

galling or apparent wear.

ALIGNMENT Finally I approached the finish line. With the compound slide locked in my preferred position parallel to the lathe

axis, the Stop Adjust and Stop Lock screws loosely installed, and the handle very lightly snugged, I rotated the

body CCW against the rotation stop and, while manipulating the cross slide to sweep the dovetail end past a dial

Page 15 of 27

indicator, adjusted the Stop Adjust screw near the tie plate to bring the dovetail end just square to the lathe axis and

tightened its locking screw. Then I rotated the body CW against the rotation stop and, while manipulating the apron

hand wheel to sweep the dovetail end with a dial indicator, adjusted the Stop Adjust screw at the dovetail end until

that end was parallel to the lathe axis and tightened its locking screw. I repeated those operations, lightly snugging

the handle after each body rotation, and sweeping the dovetail end to check alignment. I adjusted the stop adjust

screws until I obtained repeatable results.

Questions and/or comments? Email me at jayman03062@gmail.com. Please type “QC Turret” on the subject line to

avoid consignment to my SPAM black hole. Happy machining!

REFERENCES 1Lofquist, Andy. An MLA Toolpost. The Home Shop Machinist. May/June, 2006.

2Ralph Patterson. Yahoo Groups. 7X12minilathe/files/C-S Stop Mod.pdf ,Jan. 27, 2014

3Thomas, G. H. (1992). The Model Engineers Workshop Manual. Hinckley: TEE Publishing (available from

Amazon.com and other online sources)

4Lautard, Guy, The Machinist’s Bedside Reader, pp. 72-77 (addictive reading and available from the author at

www.guylauard.com)

Page 16 of 27

0.250

0.7100.040

HANDLE BALL7B

0.750

0.300Ø

POST4

0.580

0.383

0.7203.015

1/2-200.500Ø

0.6700.1700.070 0.500R

0.489

0.420ØM10X1.5 0.385Ø

0.540

PLUG6

20

0.880

0.500" ream

File to clear boring bar tip radius0.970

BODY ASSEMBLY1

0.390

Drill No. 36, tap 6-32

0.440

5/32

0.1

70 15

64

typ.

1/8"Ø dowel pins, 4 pl.

532

5/32

1.000

Drill No. 43, C'drill No. 33, & tap

4-40, 10 places

532

0.2

65

0.830R

0.270

1.190

0.390

1C

1A

1B

45

0.350 0.090

0.360

0.090

0.750

1564

2.480

2.355

Mill here to adjust clamping force

3/16"Ø dowel pin

2.190

1.506

1.250

0.460

2.060

18

5/32

1.630

0.2000.265

0.880

0.500

0.480

0.520

Drill No. 29 & Tap 8-32 0.360

0.99

HANDLE7A

Drill 29/64thread 1/2-200.500R

4.210

0.250

0.250

0.337Ø0.475Ø

3.020

0.170"

1/4"Ø

3/16"

3/16"

ROTATION STOP8

Page 17 of 27

START (n=0)

CUTTING TABLE FOR ROUGHING OUT THE 1/2" RADIUS ON TOP END OF THE POST

x

}yR-y

R-x

RR=0.5000

0.0646

END (n=6)

i} r = 0.250

Step No. x y i

START n n*w r-y

0 0.0000 0.0000 0.2500

1 0.0100 0.0995 0.1505

2 0.0200 0.1400 0.1100

3 0.0300 0.1706 0.0794

4 0.0400 0.1960 0.0540

5 0.0500 0.2179 0.0321

END 6 0.0600 0.2375 0.0125

Ball Radius, R = 0.5000

Post Radius, r = 0.2500

Blank Width, W = 0.0646

No. of steps, nmax = 6

Step Width, w = 0.0100

Virtual Ball Width, 2R-W = 0.9354

TRANSFER PUNCH

1.390

0.1875Ø

0.500R

120

STOP ADJUST9

3/4"

1"

8-32

8-32

MOUNTING PLATE5

Ø1/8",2 pl.

0.200

Ø0.385

0.500

0.500

Ø3/16

2.060

3/16

STOP LOCK10

1/4"

6-32

3/16"

6-32

Page 18 of 27

Ball Radius, R = 0.3750

Shank Radius, r = 0.1685

Blank width, W = 0.7100

no. of steps, nmax = 71

Step width, w = 0.0100

Virtual ball width, 2R-W = 0.0400

Step no. x y Step no. x y

n n*w n n*w

END LEFT 37 0.3700 0.0000 75 0.7500 0.3750 START RIGHT

36 0.3600 0.0003 74 0.7400 0.2890

35 0.3500 0.0008 73 0.7300 0.2542

34 0.3400 0.0016 72 0.7200 0.2280

33 0.3300 0.0027 71 0.7100 0.2065

32 0.3200 0.0041 70 0.7000 0.1879

31 0.3100 0.0057 69 0.6900 0.1715

30 0.3000 0.0076 68 0.6800 0.1568

29 0.2900 0.0098 67 0.6700 0.1435

28 0.2800 0.0122 66 0.6600 0.1313

27 0.2700 0.0150 65 0.6500 0.1200

26 0.2600 0.0181 64 0.6400 0.1097

25 0.2500 0.0214 63 0.6300 0.1000

24 0.2400 0.0251 62 0.6200 0.0911

23 0.2300 0.0292 61 0.6100 0.0828

22 0.2200 0.0335 60 0.6000 0.0750

21 0.2100 0.0383 59 0.5900 0.0678

20 0.2000 0.0433 58 0.5800 0.0610

19 0.1900 0.0488 57 0.5700 0.0547

18 0.1800 0.0547 56 0.5600 0.0488

17 0.1700 0.0610 55 0.5500 0.0433

16 0.1600 0.0678 54 0.5400 0.0383

15 0.1500 0.0750 53 0.5300 0.0335

14 0.1400 0.0828 52 0.5200 0.0292

13 0.1300 0.0911 51 0.5100 0.0251

12 0.1200 0.1000 50 0.5000 0.0214

11 0.1100 0.1097 49 0.4900 0.0181

10 0.1000 0.1200 48 0.4800 0.0150

9 0.0900 0.1313 47 0.4700 0.0122

8 0.0800 0.1435 46 0.4600 0.0098

7 0.0700 0.1568 45 0.4500 0.0076

6 0.0600 0.1715 44 0.4400 0.0057

5 0.0500 0.1879 43 0.4300 0.0041

START LEFT 4 0.0400 0.2065 42 0.4200 0.0027

3 0.0300 0.2280 41 0.4100 0.0016

2 0.0200 0.2542 40 0.4000 0.0008

1 0.0100 0.2890 39 0.3900 0.0003

0 0.0000 0.3750 38 0.3800 0.0000 END RIGHT

xy

R2 = (R-y)2+(R-x)2

y = R-√(2Rx-x2 )

CUTTING TABLE FOR ROUGHING OUT THE HANDLE BALL

0.710

0.7500.337

ST

AR

TLE

FT

ST

AR

TR

IGH

T

r-xr-yr

Page 19 of 27

Ball Radius, R = 0.5000

Shank radius, r = 0.2375

Blank width, W = 0.9400

no. of steps, nmax = 94

Step width, w = 0.0100

Virtual ball width, 2R - W = 0.0600

Step No. x y Step No. x y

n n*w n n*w

END LEFT 50 0.5000 0.0000 100 1.0000 0.5000 START RIGHT

49 0.4900 0.0001 99 0.9900 0.4005

48 0.4800 0.0004 98 0.9800 0.3600

47 0.4700 0.0009 97 0.9700 0.3294

46 0.4600 0.0016 96 0.9600 0.3040

45 0.4500 0.0025 95 0.9500 0.2821

44 0.4400 0.0036 94 0.9400 0.262543 0.4300 0.0049 93 0.9300 0.244942 0.4200 0.0064 92 0.9200 0.2287

41 0.4100 0.0082 91 0.9100 0.2138

40 0.4000 0.0101 90 0.9000 0.2000

39 0.3900 0.0123 89 0.8900 0.1871

38 0.3800 0.0146 88 0.8800 0.1750

37 0.3700 0.0172 87 0.8700 0.1637

36 0.3600 0.0200 86 0.8600 0.1530

35 0.3500 0.0230 85 0.8500 0.1429

34 0.3400 0.0263 84 0.8400 0.1334

33 0.3300 0.0298 83 0.8300 0.1244

32 0.3200 0.0335 82 0.8200 0.1158

31 0.3100 0.0375 81 0.8100 0.1077

30 0.3000 0.0417 80 0.8000 0.1000

29 0.2900 0.0462 79 0.7900 0.0927

28 0.2800 0.0510 78 0.7800 0.0858

27 0.2700 0.0560 77 0.7700 0.0792

26 0.2600 0.0614 76 0.7600 0.0729

25 0.2500 0.0670 75 0.7500 0.0670

24 0.2400 0.0729 74 0.7400 0.0614

23 0.2300 0.0792 73 0.7300 0.0560

22 0.2200 0.0858 72 0.7200 0.0510

21 0.2100 0.0927 71 0.7100 0.0462

20 0.2000 0.1000 70 0.7000 0.0417

19 0.1900 0.1077 69 0.6900 0.0375

18 0.1800 0.1158 68 0.6800 0.0335

17 0.1700 0.1244 67 0.6700 0.0298

16 0.1600 0.1334 66 0.6600 0.0263

15 0.1500 0.1429 65 0.6500 0.0230

14 0.1400 0.1530 64 0.6400 0.0200

13 0.1300 0.1637 63 0.6300 0.0172

12 0.1200 0.1750 62 0.6200 0.0146

11 0.1100 0.1871 61 0.6100 0.0123

10 0.1000 0.2000 60 0.6000 0.0101

9 0.0900 0.2138 59 0.5900 0.0082

8 0.0800 0.2287 58 0.5800 0.0064

7 0.0700 0.2449 57 0.5700 0.0049

START LEFT 6 0.0600 0.2625 56 0.5600 0.0036

5 0.0500 0.2821 55 0.5500 0.0025

4 0.0400 0.3040 54 0.5400 0.0016

3 0.0300 0.3294 53 0.5300 0.0009

2 0.0200 0.3600 52 0.5200 0.0004

1 0.0100 0.4005 51 0.5100 0.0001 END RIGHT

0 0.0000 0.5000

r2 = (r-y)2+(r-x)2

y = R - √(2Rx-x2)

CUTTING TABLE FOR ROUGHING OUT THE HANDLE

0.940

1.000

ST

AR

TR

IGH

T

ST

AR

TLE

FT

0.475

x

r

r-x

y

r-y

Page 20 of 27

1. Face end of 1.250"Ø brass bar & turn OD 1.160" X 0.531" long.2. Drill 5/8"Ø X 5/8" deep full drill dia.3. Cut off 0.600" long.

4. Reverse in chuck & face end leaving flange 1/16" thick. Mark dot on rim alignedwith center of jaw 1.

5. Bore 5/8"Ø hole out to 0.670 thru. Bore ID out to 0.985/0.990" x 0.500 deep

with flat bottom.6. Saw out the 0.500" wide slot inside layout lines opposite the dot; then mill slot

to width.

7. Make two saw cuts 60 each side of dot to weaken rim.8. Debur.9. Snap handle ball into holder, chuck the holder, support plain end of handle with

tailstock center & turn handle taper and 1/4"Ø.10. Rotate handle in holder to nestle shank end between chuck face and one jaw.

Face off 0.250", drill, & thread 1/2-20.

BALL HOLDER FOR FINISHING HANDLE

*0.010 - 0.015" below ball diameter

0.090

0.5900.531

1.2

40

1.1

60

0.6

70

0.5

00

0.2

50

0.9

85*

0.9

90

120 0.500

1. Face end of 1.250"Ø brass bar & turn OD 0.910" X 0.437" long.2. Drill 3/8"Ø X 0.530" deep full drill dia.3. Cut off 0.520" long.

4. Reverse in chuck & face end leaving flange 1/16" thick. Mark dot on rim aligned with center of jaw 1.

5. Bore 3/8"Ø hole out to 0.495 thru. Bore ID out to 0.735/0.740" X 0.406 deep

with flat bottom.6. Saw out the 0.375" wide slot inside layout lines opposite the dot; then mill slot

to width.

7. Make two saw cuts 60 each side of dot to weaken rim.8. Debur.9. Snap ball into holder, chuck the holder, support shank end with tailstock center,

cut off, & face to length.10. Drill 1/4"Ø, 0.710" deep.

BALL HOLDER FOR FINISHING HANDLE BALL

*0.010 - 0.015" below ball diameter

0.070

0.040

0.4

95

1.0

00

0.4

06

0.7

35*

0.7

40

0.9

10

0.4800.420

0.375120

Page 21 of 27

References

1Ralph Patterson, Cross Slide Adjustable Stop modification for 7x** Mini Lathe,

http://groups.yahoo.com/group/7x12minilathe/files

2George H Thomas, The Model Engineers Workshop Manual, 1992 England, Tee Publishing, Edwards Centre,

Regent Street, Hinckley, Leicestershire LE 10 0BB. Widely available (Amazon.com) ISBN 1-85761-000-8.

Photo 27. Handle, start left Photo 28. Handle, end left

Photo 31. Handle, after smoothing

Photo 30. Handle, end right Photo 29. Handle, start right

Photo 32. Finishing the handle

Page 22 of 27

QC TOOL HOLDERS As with clamps, one can never have too many tool holders. Photo 33 shows my current stock of tool holders. They

were made up two or three at a time as the need arose from 4140, 1144, hot rolled steel, and 12L14 to fit my

Lundquist-designed tool post and its successor, my QC lathe turret. I haven’t noticed any difference among the

various steel alloys in either performance or wear of my tool holders. Since 12L14 is the easiest to machine of the

alloys I’ve tried, I plan to make all future tool holders of that one. The single common dimension is the dovetail

socket, so I will describe how I machined that on each piece. Figure 4 will clarify the sequence (the dimensions fit

my QC Turret.) Machine a groove (Step 1) and measure across 3/16“ Ø dowel pins by jamming an adjustable parallel

between them and measuring the parallel with a micrometer (Step 2.) Take full-depth (0.240”) cuts on one

1.0200.240

Step 1

0.640

Step 2

0.700

Step 3

0.760

Step 4

Figure 4. Sequence for Milling Dovetail Sockets

Photo 33. My current stock of tool holders

Page 23 of 27

wall of the groove with a ¾“Ø, 60° dovetail cutter in incremental steps until the measurement across dowel pins

equals 0.700”, half way between the Step 2 measurement of 0.640 ” and the Step 4 target of 0.760 ” (Step 3.)

(0.640 + 0.760) / 2 = 0.700

Touch up the dovetail cutter to the opposite wall of the groove and take incremental cuts until the measurement

between the dowel pins is a little shy of 0.700 ” (Step 4.) Before removing the part from the mill vise, test the fit of

the body dovetail in the socket just machined. If too tight, take incremental 0.001 in. cuts on the second wall until it

fits. If you go too far, give yourself an “awshoot” and start over.

Don’t be intimidated by the drawing dimensions. We are not working to tenths here. For example, the dimensions

of my holders vary as follows: the 0.240 drawing dimension varies between 0.236 and 0.245, the 1.020 dimension

between 1.016 and 1.031, and the 0.760 dimension between 0.759 and 0.763. They all clamp up just fine. That is

not to say it’s OK to be sloppy. I worked as closely to the Figure 4 dimensions as I was able. I just measured after

each step and adjusted the next step to suit. What counts most is the step 4 dimension. Most of the variation among

the holders occurred during the “cut and try” stage before I developed the Figure 4 sequence.

TURNING TOOL HOLDERS My holders for turning tools are identical except for overall height and dimensions of the tool slot (Figure 5.) I

made holders for 3/16, ¼, and 5/16“ square tool bits. I use a 3/16” holder for 1/8” bits. A holder for ¼” square tool bits

is drawn. Dimensions for all sizes are shown in the Figure 5 table. The hand-tightened height adjuster (Figure 6)

consists of two knurled nuts which I made up in batches of six or so. They are common to all tool holders.

Figure 5. Turning Tool Holders

Tool DimensionBit A B C D

3/16" 0.400" 0.200" 0.200" 0.110"1/4" 0.380" 0.255" 0.255" 0.140" 5/16" 0.340" 0.318" 0.318" 0.170"

0.750

C

0.282

1.120

0.562 0.5620.562

8-32

0.375

10-32

2.240

0.6200.750

D

1.00

0.160

A

B

Page 24 of 27

BORING TOOL HOLDERS My tool holders for boring bars use cotters to clamp the bars. Although they are a bit more trouble to make, the tool

tip does not rotate when the cotter is tightened. Other methods of clamping I have tried always seem to rotate the

tool slightly as I clamp the bar in the holder. I usually carry out boring operations with the tool inverted and cutting

on the far wall of the hole. This encourages chips to fall away from the frantic activity at the tool tip. The cotter

alignment pins are a time saver when changing bars and are worth the extra effort expended to make them.

I made three holders for boring bars of ¼, ⅜, and ½” diameter. I made the three cotter blanks first (Figure 7.) Each

holder has a dedicated cotter. To make the cotter blanks, I faced one end of a 3/8ӯ 12L14 bar, and cut off three

different lengths to dimension G (Figure 8.) I Drilled and tapped each one 10-32 thru, milled the 1/16” wide x 1/16”

deep groove for the alignment pin, and deburred. I made the alignment pins from 1/16”Ø drill rod, 0.270” long.

Figure 8 details the boring bar holders. The 1/2” boring bar holder is drawn. The outside dimensions, dovetail

sockets, and height adjusters are common to all three. The table lists the dimensions unique to each holder. I milled

the three blanks to finished outside dimensions, machined the dovetail sockets, test fitted them to the QC Turret,

and then drilled and tapped 10-32 for the height adjusting stud. I laid out the cotter hole on the top face of the blank

and the centers for the boring bar and cotter alignment pin on the end of the blank closest to the cotter. I drilled No.

11 thru the cotter center and then counter bored No. 10 0.175” deep for the screw head. On the bottom face of the

blank I counter drilled the No. 11 hole Ltr. “U” x dimension F deep and reamed 3/8”Ø for the cotter. I drilled the

face 1/16ӯ for the alignment pin, inserted the pin, and clamped the cotter tightly in place with a 10-32 socket head

cap screw. I clamped the assembly to the QC Turret and swung it parallel to the lathe spindle axis, adjusting the

height to center the boring bar hole on the lathe spindle axis. Then I step drilled through the blank and reamed the

boring bar hole to size. Next I removed the cotter, deburred, reassembled the cotter in the holder, installed a boring

bar, and tested for solid lockup and free release of the bar when the 10-32 screw was slacked. If it was reluctant to

release the bar, I took light facing cuts on the thin end of the cotter until it released the bar freely.

Figure 6. Height adjuster for all holders.

0.750"Øknurl 96DP,

0.016" penetration

10-320.650Ø

0.1000.050

3/16

0.450

1.350

lock nut

height adjuster

fixed 10-32 stud Loctite

in place

0.160

10-32

0.750Ø; knurl96 DP, 0.016"penetration.

Page 25 of 27

CUT OFF TOOL HOLDER Used with my QC lathe turret, this tool has solved all of the problems I had previously experienced with that

operation. It uses a 0.040 ” wide blade with a T-shaped cross section and presents the tool to the work upside down

with the lathe spindle rotating in reverse direction to encourage exit of the chip ribbon from the groove. It has

proved to be very rigid in use and has a two-inch diameter capacity. If I need to cut off a larger-diameter bar (Photo

34) I plunge a groove as deep as possible, stop the lathe spindle rotation, and saw the rest of the way through using

a jeweler’s saw (Photo 34.) The absence of blade clearance taper in plan view means the blade must be aligned

exactly square to the lathe axis. Easy peasy with the QC Turret! When cutting off, rotate the turret against its stop,

rotate the handle to lock it to the cross slide, lock the compound slide, lock the saddle to the lathe bed, and set lathe

spindle RPM at about half the usual turning RPM for the material. With steel, I apply thread cutting oil liberally at

the top of the blade during the operation. Brass, cast iron, and plastics are cut dry. It works reliably on everything

from Delrin to drill rod.

The part consists of a 0.020” thick rectangle of brass sheet sandwiched between two steel rectangles (Figure 9.) The

top and bottom blanks were milled slightly oversize from 1¼” square hot rolled steel. The hot-rolled steel is a bit

soft for this application. If I ever make another one, I will use 1144 steel alloy. The blanks were milled to cross

sections of 0.900 x 0.945” (bottom) and 0.900 x 0.545 (top) making sure the mating faces were not convex. These

were clamped together on the mill table with the brass sheet in between. I drilled, tapped, and counter bored for the

four 6-32 socket head cap screws and installed the screws. Next I drilled and reamed the ⅛”Ø x 1.050” deep holes

Figure 7. COTTERS

3/8"Ø

D

3/8"Ø

10-320.062"

0.062"

Bar Ø A B C D E

0.250" 0.672" 0.925" 0.367" 0.367" 0.506"0.375" 0.754" 1.054" 0.372" 0.375" 0.534"0.500" 0.786" 1.150" 0.419" 0.420" 0.430"

Figure 8Boring Bar Holders

1.000

1/16 Ø

0.400

0.977

1.1

84

C

B

A Ø

E

D

2.450

0.375" Ø

1.125

10-32

0.430

0.600

0.370

No. 11

Page 26 of 27

1.380

0.470

0.895

0.020

0.895

0.900

Figure 9Cutoff Tool Holder Assembly

0.620

0.413

1.1250.282 0.5620.562

6-32

0.180

0.68010-32

2.250

0.562

⅛ ø x 1 dow el

pin (2 pl)

1.380

0.714 0.950

0.020

7

13/4

3/16

10-32 Jack Screw/Height

Adjusting Screw

0.488

10-32

0.3800.475

0.0300.0365

1.390

Page 27 of 27

for the dowels and pressed the dowels in about 0.020” below the top surface. I then milled the outside surfaces to

the final dimensions, machined the dovetail socket through the sandwich, and drilled and tapped 10-32 for the

height adjusting stud which, in this case, was a 13/4” 10-32 socket head cap screw. Only the upper half of the holder

was tapped to provide a jacking screw action. Before cutting the slot for the blade, I mounted the holder on my QC

turret and took a light facing cut with a spindle-mounted fly cutter to provide an accurate reference surface square

to the lathe axis. My cutoff blade, made by A.R. Warner, has very consistent dimensions end to end. After

measuring the top and bottom widths and depth of my cutoff blade at both ends, I milled the 0.475 ” wide tool slot

in one face of the sandwich at a seven degree angle to horizontal by slewing the mill vise at a 7° angle to the mill Y

axis. The slot depths in the top and bottom halves are different to keep the blade perpendicular to the lathe axis, and

the wider top edge of the blade projects 0.003 beyond the outside face of the holder. I separated the sandwich, put

the brass sheet aside, and assembled the top and bottom halves with the cutoff blade trapped between them. I

extended the thread on the 10-32 jack screw/height adjusting stud with a die as close as possible to the head,

screwed the height adjusting nuts onto it, and screwed that assembly into the tool holder. After snugging the four 8-

32 SHCS and the 10-32 SHCS they were then tightened gradually in sequence, maintaining a uniform gap between

top and bottom halves of the holder until the blade was snugly gripped. Next each screw was tightened in sequence

about 1/16 of a turn at a time until they were all tight and the gap was uniform all around. I sharpen the blade while it

is mounted in the holder. A T-square style jig positions the holder square to the straight cup wheel, the table is tilted

upward at 13 to 14 degrees, and the tool is presented to the rising side of the wheel while maintaining firm contact

between holder and table. I keep a close eye on the corners of the blade cutting edge and sharpen it at the first sign

of corner rounding.

Questions and/or comments? Email me at jayman03062@gmail.com. Please type “QC Turret” on the subject line to

avoid consignment to my SPAM black hole. Happy machining!

Photo 34

Cutting off a slice of 3” Ø steel bar