Watch lathe CNC conversion

[N4NV]

I know, I have too many projects already, but in case I am off work for any length of time, I am trying to gather the items I will need to convert my Levin watch lathe to CNC. The attached picture shows the basic layout of my Z axis. Besides the mess of my watch bench, in the picture you can see a Taig cross slide I made to fit the lathe. I had do some special machining to get it low enough to fit under the spindle. There is also I micrometer XY slide I put together. I have two ball slides that are going to be the Z axis. In the bottom of the picture you can see a spare lathe base that I will use for this conversion so I don't have to drill holes in my chromed Levin bed. I am pretty good at hand scraping now and will make sure it is better than .0001" flat.

In between the ball slides you can see the precision ACME screw I got from NOOK. It was cheaper than a ball screw but has better tolerance than most rolled screws. NOOK guarantees better than .0001" per foot. It is 1/4x20 thread. The little stepper at the end of the screw is 200 steps per revolution. This will give me an accuracy of .00025" per step. With micro stepping it will be ever better. I purchased 4 of these little steppers from eBay for $25 total with the encoders! The guy was selling the encoders and the steppers were something he threw in because he did not want to take the encoders off.

I also got some plastic ACME nuts from NOOK for the screw. I plan on cutting them in half and installing a spring between the two halves so I can get zero backlash. The loads on this lathe will be so light that it won't take much preload. The X cross slide will look similar. I have one more ball slide that I will cut in half to get me the X direction. The total X movement will be about 2", it looks like I will get almost 5" on the Z though 2" would be more than enough.

I hope to be able to make custom balance staffs when it is all completed. A balance stall might be 3mm long, 1mm at it widest, and have pivots that are .12mm.

Vince

[N4NV]

I scraped the watch lathe bed today. I was lucky enough to find a Biax scraper on eBay a while ago so it went pretty fast, less than an hour. The process of scraping is pretty simple to say but takes a lot of skill to do. You just put some Prussian blue or high spot paint on a surface plate, put the surface of the object you want to scrape face down on the surface plate, move it around a little, then just remove the blue by scraping. The blue will be the high spots. I will not go into scraping very deeply, that is a subject for a book, namely "Machine tool reconditioning" by Connelly. There are a few quick tips. Make sure you don't have any big burs on the surface you want to scrape or you could gouge your surface plate. After each session of scraping, run a file lightly across the surface to remove any burs that are brought up by scraping. Make sure you put even pressure on the surface that you are marking. When done properly, the surface you scrape will be just as accurate as the surface plate you used to mark. With the three plate method you can easily get an accuracy of 50 millionth of an inch. This was done in the 1800's.

I think I did about 10 marking and scraping steps even though there are only 6 pictures. You can see the dark blue on the ends of the lathe bed at the start. The blue get lighter and lighter after each step, not because there is less blue left on the surface plate (I actually added more about half way through), it is lighter because the surface is getting flatter and flatter and there is less room for the marking blue. At the last picture, the lathe bed is flat within the limits of my surface plate +-.00005". I have a black granite surface plate. The marking blue will permanently stain your surface plate. You can barely tell on my black plate, but I would think twice about using a pink surface plate.

Vince

[N4NV]

I found some anti-backlash nuts on the web that have the same 1/4-20 acme thread as my screws. The manufacturer claims they are backlash free up to 6 pounds. Since I will be operating in the oz range, they should work fine. In the picture they are the red part, the round disk is the mounting flange that I will have to machine smaller to fit.

Vince

[SherlineGuy]

Wow,
Those little Levin lathes are like gold these days...
In the 80's I worked at CCCL making contact lenses and we had a whole room full of those little lathes. I remember actually taking to Mr. Levin by phone once.
Oh, the memories.
Good luck with this project, sir.

[Karl_T]

I watched you take a CHNC from what i thought was a hopeless basket case to a fine machine tool. I know that one wasn't your first rebuild. So, what machine number is this one?

Karl

[N4NV]

I watched you take a CHNC from what i thought was a hopeless basket case to a fine machine tool. I know that one wasn't your first rebuild. So, what machine number is this one?

Karl

Number 6. In order it was a Brute from scratch from the Crankorgan guy, then a Bridgeport series 1, Taig lathe, Yamazen knee mill, Hardinge CHNC, and now the watch lathe.

Vince

[zephyr9900]

Ah, so then you are a devotee of the simple linear progression...

Seriously though, I'm greatly looking forward to this build. Hand scraping--you're already on a higher plane of existence than I... I will add my admiration for your CHNC rebuild!

Randy

[thien_le93]

Hi all,
I have just bought 3 used CNC machines :
- Cincom F16
- Cincom G32
- Tsugami NP 17-2
Please help me to have manual instructions of these machines.

Thanks in advance and best regards,

Thien Le

[N4NV]

I have been busy with other projects. I just about finished my Miser stirling engine. You can see that here:

"http://www.youtube.com/watch?v=vdBYzzhe_To"]YouTube - Miser stirling engine

I laid out, drilled and tapped the holes in the lathe bed for the Z axis linear rail. I made lots of measurements with my Mill prior to drilling the bed and found that it was straight and parallel to at least .0005" (my mill has about .0002" repeatability). After drilling and tapping the holes I put the bed back on my surface plate and marked it with high spot to check to see if any of the holes pulled up some high areas. I had to do a little touch up scraping around three of the holes, but other than that it stayed flat to at least .0001".

I have to find some special metric screws to proceed so I can attached the cross slide to the "trucks".

Vince

[Jason3]

Vince, fantastic work on the engine! I'd love to make the time and have a go at something like that...

What size screws do you need? Let me know if you get stuck, I have a ton (not literally ) of metric stainless SHCS.

Best regards,

Jason

[zephyr9900]

Vince, beautiful work on the LTD Stirling engine indeed. I have a free sample Airpot cylinder/piston saved for just such a use, but have not gotten around to it yet. What are you using for your displacer? It looks like pink Styrofoam...

Randy

[N4NV]

Jason, thanks for the offer. We have a place in San Jose that carries just about every type of fastener. I picked up what I needed today.

Randy, the displacer is polystyrene building insulation from Owens Corning. I had to buy a 4' x 2' piece so I have plenty for more displacers. I melted my first one by trying too much heat. I still have some friction issues I need to work out. It takes at least 45 degrees differential to run. It should run on a 15 degree differential.

Vince