CNC Workshop CNC Lathe Build

[kvom]

Gang tools are great for production, something i don't intend to do.  In general, i expect to use it for decorative turning for model engine parts, and also for threads that are too long for thread milling.

[RonGinger]

I have started to build a small gang tool holder for this lathe. I had hoped to have it at the class but didn't make it.

I really think a CNC lathe without quick and repeatable tool changes is not very useful, even for one-off parts.

[Dave Otto]

I agree Ron

I work in a R & D shop and we rarely ever make more than a few parts of anything; definitely not production quantities. I just thought I would throw that out there as not everyone might be familiar with this type of tooling set up.
Omni-turn makes some nice tooling and its what we are using on the Sharp, along whit ER holders form Maritool

http://www.omni-turn.com/Pages/Tooling/Tooling%20page.html#Anchor-OmniTurn C-8655
http://www.omni-turn.com/index.htm
https://www.maritool.com/

Dave

[Hugh Currin]

That looks like a very nice, clean design. It's good and bad that you can put it on the milling table. It's good that you can lift it and it fits. The bad part is it won't take "large" parts. The Little Machine Shop 7x16 lathe seems a good candidate for conversion. I would hate to discarding all the irrelevant parts though.

I'm still converting a Sherline lathe to CNC. The basic machine is functioning but I need to mount the encoder. The Sherline CNC kit was easy to install but they have no mounting scheme for an encoder. Have been taken away by travels and now "restoration" of a basement wall. (Had a friend and structural engineer look it over. Expected to hear it's ok OR call these guys and get it fixed. He said you should put in some steel support beams but, oh, you could do this yourself handing me a set of plans. More time away from the shop!)

I'm mainly doing the Sherline to see how useful a CNC lathe will be in a hobby shop setting. It is a little small, but should answer the question. If I'd known about this 7x16 design I'd have been real tempted. The Little Machine Shop 8.5x20 looks like a good size if CNC is found to be useful. I've stated to use CamBam for lathe G-code generation. They have an experimental plug in that's marginally useful. I expect it will rapidly get better. Till then I expect a good bit of hand coding.

My plan is to use a quick change tool post. This, I think, will be similar to the Tormach mill tooling, consistent manual tool changes. I don't think gang tooling would be useful for a one off parts. But hey, I have no experience with CNC lathes. I'll be real interested in your experiences.

My reasons for a CNC lathe include fancy round profiling and threading. Round profiles like columns for model engines. Also threading a dozen parts or so, like studs or special screws. It'll be interested to see what uses others find.

Please keep posting and let us know what uses you find. Thanks.

Hugh

[Flyboy Jim]

That looks like a very nice, clean design. It's good and bad that you can put it on the milling table. It's good that you can lift it and it fits. The bad part is it won't take "large" parts. The Little Machine Shop 7x16 lathe seems a good candidate for conversion. I would hate to discarding all the irrelevant parts though.

I'm still converting a Sherline lathe to CNC. The basic machine is functioning but I need to mount the encoder. The Sherline CNC kit was easy to install but they have no mounting scheme for an encoder. Have been taken away by travels and now "restoration" of a basement wall. (Had a friend and structural engineer look it over. Expected to hear it's ok OR call these guys and get it fixed. He said you should put in some steel support beams but, oh, you could do this yourself handing me a set of plans. More time away from the shop!)

I'm mainly doing the Sherline to see how useful a CNC lathe will be in a hobby shop setting. It is a little small, but should answer the question. If I'd known about this 7x16 design I'd have been real tempted. The Little Machine Shop 8.5x20 looks like a good size if CNC is found to be useful. I've stated to use CamBam for lathe G-code generation. They have an experimental plug in that's marginally useful. I expect it will rapidly get better. Till then I expect a good bit of hand coding.

My plan is to use a quick change tool post. This, I think, will be similar to the Tormach mill tooling, consistent manual tool changes. I don't think gang tooling would be useful for a one off parts. But hey, I have no experience with CNC lathes. I'll be real interested in your experiences.

My reasons for a CNC lathe include fancy round profiling and threading. Round profiles like columns for model engines. Also threading a dozen parts or so, like studs or special screws. It'll be interested to see what uses others find.

Please keep posting and let us know what uses you find. Thanks.

Hugh

Hugh, I hope that maybe you will start a thread dealing with your Sherline CNC conversion.

Jim

[Hugh Currin]

Hugh, I hope that maybe you will start a thread dealing with your Sherline CNC conversion.

Jim

A CNC build thread is a little off topic here. I also hate to document the retrofit in several places. I am documenting the process on the LinuxCNC forum. I hope anyone interested will follow the thread there. It includes all the nitty gritty ugly details showing my ignorance. I will post the final result here and, certainly, how I end up using it in making engines.

It's good to see interest in CNC here. I know how useful a CNC mill is. I have more doubts about a lathe but there's some interest in this also. I'll be interested in everyones experiences, and hopefully add a little.

Thanks.

Hugh

[Flyboy Jim]

Hugh, I hope that maybe you will start a thread dealing with your Sherline CNC conversion.

Jim

A CNC build thread is a little off topic here. I also hate to document the retrofit in several places. I am documenting the process on the LinuxCNC forum. I hope anyone interested will follow the thread there. It includes all the nitty gritty ugly details showing my ignorance. I will post the final result here and, certainly, how I end up using it in making engines.

It's good to see interest in CNC here. I know how useful a CNC mill is. I have more doubts about a lathe but there's some interest in this also. I'll be interested in everyones experiences, and hopefully add a little.

Thanks.

Hugh

I can see your point Hugh. Thanks for the link..............I skimmed over your thread and will look at it in more detail later. CNC seems to be a whole subculture unto itself.

Jim

[kvom]

After some trial and error, I finally did a test turning job using the lathe.  I have had some Mach4 issues that have gotten in the way, and as well I have found a number of problems with the lathe operation offered by CamBam.  This week I discovered a reasonably priced and simple CAM program for lathe that I am trying out: eCam.

http://ecam.altervista.org/

The hobbyist price for lathe functionality is 75 euros, which at current exchange rates is about $83.  The full download gives a 2 week trial period, and except for a few minor issues I had little problem getting working gcode is less than a day.

Attached are a photo of the part and a screen shot of the program window.

[kvom]

The workflow for external turning is pretty simple.  Draw the profile in the upper half of the screen, either using eCam's CAD facility, or else import it as a DXF.  Then select a tool and fill in machining parameters for roughing and finishing.

The program has a pretty good visual postprocessor facility, so I was able to get proper code for Mach4 easily.

My test part was machined using .01" steps, but because lathe is in diameter mode each cut was only .005".  I will need to determine what cuts the lathe can stand in various materials, but for a small one-off part I'll likely tend to be pretty conservative.

I did find a reasonable workaround for the fact that M4 doesn't allow direct setting of the X DRO but instead requires you to rely on tool table offsets.  Since the tool post I'm using isn't consistent across changes, a tool table makes no sense.  So the first solution is to not specify a tool change in the g-code or else tool 0.  Next I either take a skim turn off the stock with the tool or else jog until it touches.  Then zero the X DRO, jog it away, measure the stock, and then issue a G0 X-nnn command, where nnnn is the diameter measured.  The tool will then move to the spindle centerline.  Now zero the X DRO again, and issue G0 Xnnn to move back to the stock diameter.  Obviously in radius mode you'd use the radius and not the diameter in the moves.

[kvom]

After several tries I managed the first complete profile turning.  In the case I a frame spreader from the Ouzof Coventry as the example.  A photo is attached.

Next I attempted to cut a thread using a series of G32 passes since I couldn't get the G76 canned procedure to work as documented.  In attempted to cut a 5/16x24 thread using 10 passes at 1500 RPM, I got good looking threads but the TPI appears to be less than 24.  Unfortunately I can't tell whether M4 or the lathe electronics are to blame.

[Admiral_dk]

Looking good to me 

[kvom]

It appears that the motor tuning steps calculate for the Z axis may be off.  I spent some time tonight trying to tune, but didn't get repeatable results across all Z lengths.  More tomorrow.

[Dave Otto]

So if it is not consistent you are missing steps maybe? Have you tried lowering your acceleration and speed?
Looks like your are making good progress though.

Dave

[kvom]

The motor tuning requires entry of a "counts per unit" field for each motor.  Basically how many step pulses needed to move the avis one inch.  Of course, the pitch of the ball screw figured into this.  I've been using the number supplied in the class.  So when  just testing that moving in one direction and then reversing the same amount yields the same reading on a DTI, I have just verified no steps being lost.

So now I need to use a gauge block between the carriage and the DTI;  zero both the DTI and Z DRO, and then command a move equal to the gauge block length.  I found that a 3" move was short by about 30 thou.  So now I need to try to adjust the count field to get the correct feed distance.

Whether the error was enough to effect the thread pitch I was cutting will be know when I retry it.

[kvom]

I have been able to adjust the count field on both axes to what I hope will be reasonably accurate.  I did find a problem with the Z axis where the pillow block had worked slightly loose screwing up the results. I'll need to cut another thread to verify if the pitch will come out properly.

The adjustments took a lot of trial and error, plus setting up DTI and gauge blocks to accurately measure travel.