power lead screw for 7x12 lathes - brian's workshop....

Power Lead screw for 7x12 lathes

A common complaint with mini lathes is that the slowest

saddle feed is to high to produce a good finish, so I added a

variable speed drive to cure this.

The motor is a 12 volt wiper motor. from a Fiat Panda with

it’s mounting bracket, free from the local garage.

As the tailstock end of the lead screw already had a hand

wheel fitted, I decided to fit the motor in the screw cutting

drive train.

T o achieve this I needed a 40 tooth gear, rather than using

one from the gear set, I decided to make one. First I made a

No1 module single point cutter from silver steel and

hardened it.

The gear was then cut from Polycarbonate sheet and fitted to

the motor shaft.

The motor was then bolted in position to line up with the

gears, yet be out of the way if I want to do screw cutting

To improve the location of the gears a support collar was

added to the plate that holds the gears.

A leaver/ pinch screw was added help move the gear

assembly in and out of gear, when I use the hand wheel.

The (hard to get at) plate locking nut, was replaced with long

tubular nut to make life easier.

Next problem was a power supply, wiper motors are

designed to run on just over 14 volts, this is the system

voltage when the battery in being charged, and will stand

considerably more than that without harm, so I wanted a

Supply of about 18 v. In the junk box I had a dead computer

back up unit, so this provided the parts.

The transformer, diodes, and the associated capacitor where

removed.

And used to make the power supply.

Not pretty but effective.

A box was then made with ventilation at the rear and a volt

meter added.

A PWM control unit was purchased on E Bay, and mounted

in a box with a switch to reverse the motor. this also drops

the voltage a further 1 volt

I am very pleased with this mod It is quiet in operation and

gives the option of a very fine feed to obtain a good finish to

the work.

Brian.