Mini lathe conversion to CNC

Found a PC build video for LinuxCNC based on the J1900 motherboard here:


It's relatively inexpensive and I think I will follow the same route and perhaps run it with a Mesa 7i76-6i25 kit. What do you think?

TML:

I'm attempting to do the same with my Sherline Lathe. The log is on this forum here . Haven't posted for way too long, too many other projects have gotten in the way. I'm now working on the encoder mount and will post it soon.

I decided to use a Gecko G540 Driver board with the parallel port from a Atom Dual-Core D525 based computer. The G540 has four axis capability and may use the driver box to run a Sherline mill eventually. The Sherline CNC retrofit (motor mounts etc.) went on easily and I can recommend them. Don't know where you are with hardware selection but though this may be of some help.

I'll follow along now that I've found your log.

Thanks.
Hugh

Tom:

Yes, I'm attempting to use an encoder on the spindle. The Gecko 540 is for stepper motors, with steppers I don't see any reason to put an encoder on each axis? It would allow tracking axis location with the encoder, but with steppers it would be difficult to correct for lost steps. It could likely be set up to fault out with an error?

But yes, the encoder I'm using is for spindle position. I wanted this mainly for threading.

Thanks.
Hugh

Hi Hugh,
Thanks for sharing your log, I will definitely check it out. It's been slow progress for me too as I couldn't spend as much time on the project lately. Currently I'm looking into limit/homing switches. I've read that it's better to have them as a backup to the software limits. The Sherline is such a small lathe though, so I think any suitable limit/homing switches would have to have a very small foot print. I don't think the Sherline CNC-ready machines even use them, maybe because it's simply not practical. I'm not really sure how you would home the tool/cutter without any switches used for reference point. Maybe they depend on hard stop? So yeah, I don't know yet what's the best option here... Anyone care to share your thoughts?

OK, so I decided to use inductive proximity sensor for limit/homing switches. I bought this particular one from Automationdirect.com: www.automationdirect.com/adc/Shopping/Ca...g_(5mm)/DW-AS-504-M5
They also have much cheaper sensors but it's the only PNP Normally Closed proximity sensor I could find that also has good repeatability and accuracy.
As for hardware selection, I went with the Mesa 5i25 and 7i76 combination. I still have to figure out how to control the Sherline lathe motor. I'm going to try to stick with the stock Sherline 90-volt DC motor and speed controller ... Will be reading more on how the 7i76 works to control the spindle. If you guys have any inputs, feel free to discuss. Thanks

I've been running a Digispeed DC-04 on both my Sherline Lathe and Mill, with stock Sherline Spindles. Works great.
DC-04 DigiSpeed SL
It also has an input for the sherline tach encoder which gives reasonable spindle speed feedback.
I'm using that as-is on the mill, but on the lathe I made my own 60ppm encoder for the speed, and use the sherline tach for the index pulse.

Doing all this with a standard parallel port too, the 7i76 probably is better though!

Limit switches are on my list of things to do (so I'd love to know how you go), but are a "nice to have" rather than a necessity on such a small machine.
I suspect the reason sherline don't offer limit switches is the same as them not offering spindle speed control - cost.

FYI, the way I home my lathe (first time!) is to put in a tool that has zero offsets, then jog it to a known Z point (eg the spindle shoulder) home (Z). Then jog it to touch off the X on to say the spindle OD, then home (X) (with a spindle OD offset))

That's probably close enough - chuck a little scrap and reduce the OD and measure diameter to confirm, set x and z offset if required. I tend to send the machine back to home before shutting off, and then just hit the home all next time. Usually close enough.