Slow Speed Feed for the Mini Lathe...Use a DC Gear Motor 1 to 5 rpm Lead Screw feed

[jjr2001]

Been wanting to do this for a long time and I finally got aroundtoit!

Found this gear motor on eBay:
https://www.ebay.com/itm/COLEMAN-GEA...B19y:rk:1:pf:0

Mine came with the mounting plate shown in the description photos.
I am powering mine with a 15VDC 1amp wall transformer. (wall wart?)
Used a variable dc power supply module from the bay also to control the low speed motor.

This was an easy build since I already had made up 4 banjos like this:
http://www.homemadetools.net/forum/m...2148#post75832

It was a simple matter to make an adapter to mate the 1/4" shaft to the smallest change gear I had.
Put the 80 tooth gear on the lead screw and there it was. Fine....That is Very Fine Feed.

With this setup the lead screw speed is independent of the spindle speed.

With the gears I selected the lead screw rpm is from 1 to 5 depending on the voltage being fed the motor.
Plenty of torque to drive the carriage.

I was able to take .0005" and have an almost polished finish on a piece of rather hard steel.

On the example picture of the turned shaft you can see the rough finish near the chuck.
That was done by hand and going slow. The right hand section was done at about 3 rpm on the lead screw.

Simple matter to put the change gears back on for threading or even the original banjo with the 80 20 80 20 gears
for a coarse feed.

So far so good.

Cheers, JR

[Toolmaker51]

Great adaptation jjr2001. DC motored feed screws are used on some expensive toolroom lathes. They use leadscrews for threading. Huge advantage considering lathe swing, varieties of material, tooling and operations. Any other system can only approximate ideal settings.

[DIYer]

Thanks jjr2001! We've added your Mini Lathe Slow Speed Feed to our Lathe Accessories category,
as well as to your builder page: jjr2001's Homemade Tools. Your receipt:

Mini Lathe Slow Speed Feed by jjr2001

tags: lathe, motor, power feed

[jjr2001]

Thanks Toolmaker51, I did not know that some machines used DC motors for the lead screw.
I thought all the professional tools used change gears.

Thanks for the info,
Cheers, JR

[wizard69]

Thanks Toolmaker51, I did not know that some machines used DC motors for the lead screw.
I thought all the professional tools used change gears.

Thanks for the info,
Cheers, JR

Hardinge HLV's used a DC motor for years and that is one of the finer toolroom lathes available. The feature is very nice for feed rate optimization as you can go from is that really moving to way too fast with ease. One of the goals I have on my 9x20 is to have a saddle drive that would allow for variabvle speed drive, one of these days it might even happen. A bigger goal would be electronic leadscrew functionality.

Come to think of it many milling machine use to come with a drive motor mounted on the knee saddle to drive the table there. On really large machines it becomes impractical to run a shaft to the lathes saddle so that is another issue.

In any event I suspect you will enjoy your machine even more now. Next up a DC feed for facing. Once you get use to variable speed it is hard to get away from it, it literally feels like a step backwards to go with mechanical drives.

One side note on surface finish ans feed rates, you don't always want to go slower. I was turning a bit of 4340 HT at work and got caught thinking my problem was somewhere else when the tool started to make a racket. The reality was my feed rate was too slow hardening the material and thus making for really ugly finish. It didn't take much of an increase in feed rate to cure the problem and the finish was gorgeous.

[Toolmaker51]

Thanks Toolmaker51, I did not know that some machines used DC motors for the lead screw.
I thought all the professional tools used change gears.

Thanks for the info,
Cheers, JR

To be perfectly accurate the lead screw depends on synchronization with spindle to produce threads. Lathes with one screw were common, but threading is less common than turning; wear on a single screw eventually may not thread as well.

A feed screw that can deviate from a prescribed rate, [ie DC motor] to improve or tune cutting conditions, time included. Most of us developed a sense what RPM looks right for so & do diameter, feed is less intuitive. What appears a good finish can be a result of rubbing, not cutting. Careful measurements might show an expected size reduction is less than what dial indicates. Just as possible, when a 'coarse' finish is precisely on size.

In general I judge a cut by a continual helix, somewhat thread-like. Finish in a pre-honed cylinder is another way to visualize it. As a cutting edge breaks down, the finish degrades. Rough or finish, a consistent appearance is near certainty one end is same as other, or tapers at prescribed rate
In job shops, we apply finishes according to intended use of a particular feature; a bearing bore deserves more attention than say, a shaft connecting two hubs. Too fine is a burden on shop rate just like too coarse requires secondary work.
When we re-open post holiday I'll get a picture to illustrate this.

[jjr2001]

Thanks guys, excellent information. Since I only have a lead screw it would second as my feed screw.
I had added a hand wheel to the right end of it for "fine feed". That was never fine or consistent enough for me.
Which is why I added the DC motor to the lead screw.

I have found that the speed can certainly be too slow for the steel I was testing it on.
I will have to experiment with other gears and speed it up a bit.

Thanks again,
Cheers, JR

[Toolmaker51]

jjr2001; Nice! Hoped this was helpful. I can offer another tip.
We haven't any DC lathe feeds, but our mills certainly do. Certain speed and feed combinations work like magic. Mechanical combinations are easily duplicated, DC not as readily.........so I mark off 1 or 2 feet, and time covering that distance with a stop watch. Setting a DC dial is now a lesser degree of approximation.

[jjr2001]

Thanks TM, great idea. I had thought about putting a 5 or 10 turn vernier dial on the speed control and then
calibrating it for threading rates. It will be a future experiment but I think it is worth doing.

Cheers, JR

[Toolmaker51]

Thanks TM, great idea. I had thought about putting a 5 or 10 turn vernier dial on the speed control and then
calibrating it for threading rates. It will be a future experiment but I think it is worth doing.

Cheers, JR

If you mean feeding rates, that is perfectly logical.
Threading rates will never occur motor-controlled other than CNC. Every pass of threading deepens [torque load], mechanical or programmed transit of carriage is only way to insure intended pitch rate is maintained.
We have an import mill with a multi-turn vernier [RPM] speed control. Belt slip, low voltage, tool loading; stalling doesn't reflect in the LED readout. Adjusting X.X TPI or metric pitch would take all day, without breaks or lunch. And late for dinner.