Power Lead screw for 7x12 lathes

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.