Mini lathe conversion to CNC

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20 Sep 2016 17:49 #80680 by tommylight
Where is your bike? Not in the shed i hope.
One of mine got out 2 days, the other is still outside, done 60km with both this summer. Bummer!!!
Congrats Andy, you do a magnificent job here.

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03 Oct 2016 02:28 #81165 by tml
Replied by tml on topic 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?

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03 Oct 2016 09:11 #81171 by andypugh

tml wrote: 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?


As a lathe only has two axes you might well find that the humble parallel port has enough IO.
The 7i76 gives you higher step-rates (which might not matter) and makes it easier to control a spindle VFD, however.

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19 Jan 2017 17:39 #86176 by currinh
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

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19 Jan 2017 17:54 #86181 by tommylight
FYI, encoders and Gecko 540 do not go together, if it is for the spindle that is all good.
Regards,
Tom

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20 Jan 2017 00:11 #86214 by currinh
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

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20 Jan 2017 00:54 #86217 by tommylight
Nice,
I am sorry to interfere, but beter to be on the safe side.
There are steppers with encoders and i am sure they can be added even to your setup using parallel port quite easily, but the only benefit would be to actualy alert you when missed steps hapen.
On the other hand, i never had much interest in stepers with encoders, the price is very near servo systems so why bother.
Again sorry for the barging in.
Regards,
Tom

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24 Feb 2017 07:01 - 24 Feb 2017 07:03 #88572 by tml
Replied by tml on topic Mini lathe conversion to CNC
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? :)
Last edit: 24 Feb 2017 07:03 by tml.

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16 Apr 2017 22:26 #91481 by tml
Replied by tml on topic Mini lathe conversion to CNC
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

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07 May 2017 10:57 #92768 by verticalperformance
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.
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