Sieg C3 mini lathe - My shot at a CNC conversion

[Guldberg]

So it begins...

After making a CNC router, now comes the turn to converting a mini lathe into a small CNC machine.

Here is how it looks almost disassembled and ready to go, notice the fine homemade paper bellows:-) :



Here are the plan:

1
Change leadscrews and fit steppers.
Already have a HobbyCNC board lying around, needs to buy some steppers still.
Bought some TR16x4 and TR10x3, gonna have to make some taps for making the leadnut, we'll see how thats going to work. These are the babies


2
Way cover

3
Full enclosure

4
Change to digispeed control of the motor

5
Automatic toolchanger turret

6
Some kind of cooleant system

7
We'll see when we get there:-)

Im planning to tilt the lathe 45 degrees to allow the chips to fall down to the bottom of the enclosure. Does anybody knows if that could be a potential problem?

[PIngels]

Nice lathe! I especially like the bellows!

I just completed my (holefully) final mini-lathe conversion with the help of Mark and Sean (both on this Forum, they'll surely drop in).

We decided to go for ballscrews as the tries Mark and I made using TR screws gave only bad results: especially backlash and maximum speed limitations.

Should you go ahead using the TR screws, make sure to integrate some very good anti-backlash nuts, specifically for X.

Attached is a picture take today of my lathe: it works fine, but I just dismantled to mount a chip guard for Z and I want to refinish the tailstock ballnut support. (Please disregard the mess!)

I'll be watching closely your progress, especially for the Auto Toolchanger! My enclosure will be built in the next Week-ends using aluminium profiles and lexan panels that I got free.

Pierre

[Guldberg]

Looking sweet, maybe you should make a thread with some pictures. Would like to see some close-ups. Feel free to share your knowledge:-) Speed limitations with the TR? I would guess that there should be plenty of speed for those small distance:-) How did you fit a ballscrew in the cross slider, somebody on the forum told that they couldn even fit the ballnut for a 8mm ballscrew. As i just said, a couple of closeups would be the thing:-)

[Guldberg]

What a constructive day:-) I made the bearing mounts for the Z leadscrew and one of the plates on the carriager to hold the stepmotor. Still need to bore out the bearing for the hole though





Oh, i also learned, dont try to force a bearing in the radial way with a arbor press:-) One could proberly have told one self before trying

[PIngels]

I'll try to make some better pics and post them.

I talked of speed because the TR screws eat tons of power (efficiency of TR is 10% while ballscrews reach 90% +).
If you use Nema23 steppers you'll be limited in power. I'm running 1.75Nm steppers in a 2 to 1 ratio.

You'll easily discover that the mini-lathe is all but well finished and it'll need a lot of fine adjustment to get everything to get well...

The X ballscrew is a real challenge: the ballnut fits barely in the slot with less than a mm space. I also had to deepen and slightly enlarge the slot.
Using a 3/8" Rockwell screw and ballnut. The threads for that ballnut are very exotic so I used my cnc mill to threadmill the thread If you have a need here, I could help you out.

I'll work on the close-ups

[Guldberg]

I already discovered it, im still trying to adjust the cross slider so it doesnt bind nor can tilt but im having a hard time. The giant lathe in the students workshop im using runs much smoother and the carriager alone weighs more than the mini lathe itself. Im thinking maybe sometime ill check all surfaces for parallelism and smoothness.

Im in Denmark, ill remember to drop by next time i get to Belgium:-D (which would be my first time)

Btw, i think 10 is set a bit to low:-) as far as i know its around 20%-60% depending of the state. Ill, give it a shot with some polymere nuts and see how it goes:-) For a start im satisfied with cutting from one side, facing, side turning, tapers etc., later on ill either change to ballnut or give it a go on some anti backlash nuts

[RotarySMP]

Hi Guldberg, I have been collaborating with Pierre and Sean to convert our three lathes.

I had a Nylatron nut on my Z before I changed to Ballscrew. The most important thig to do is to address the bed thickness. Although Pierre and I tried the filing method recommended by Rick Kruger, I found I couldn't get accurate results, and ended up scrapping. Dumped the horrible saddle gib adjusting set screws and used shims. Not the saddle is snug and smooth. Well worth the effort.

[Guldberg]

I read about the filing method, but actually so far it seams to run pretty smooth, but ill have to do some mesuring. If its to much off i think i'll mill it straight and use shims. Anybody tried this method?
RotarySMP, please fill in with pictures, knowledge or link built log if you have a such:-)

[Guldberg]

Totally stripped down, i wonder if ill ever get it back to normal again:-)

[Guldberg]

Im back. Converting both a lathe conversion, finishing a router and studying at the same time, takes up some time.
I somehow managed to bore out the bearing block to a perfect fit for the angular contact bearings and turn the leadscrew down to a size where it fit perfectly inbetween the bearings with no play.


Also manage to make a lead nut, unfortunally i forgot to clean the leadscrew for small barbs, so it chew up the nut in no time:-)

[Trapper14]

looking pretty slick! I will try and put some pics up of mine (the same as Rotary, and PIngels) Oh its even more depressing when u have the headstock removed with the spindle out of it haha, trust me

[ngr1]

Gentlemen, your conversions look great!

Pingels, what size ballscrews are you planning to use on the X and Y axis?

Guldberg, what size ballscrews are you planning to use on the X and Y axis?

I am in the process of choosing ballscrews for my mini lathe conversion. 3/8” is the smallest size ballscrew available from NOOK so that will be used for the Y axis. The challenge with the 3/8” BS is that a sleeve will be needed at the stepper end to accommodate the ID of the smallest available angular contact bearing 7200. .500” or .621” can be used for the X axis.

Thanks