Author Topic: Sherline CNC Lathe  (Read 4046 times)

Offline Hugh Currin

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Sherline CNC Lathe
« on: February 07, 2017, 06:09:08 AM »
I'm not sure where to put this so decided to start a new thread. I mentioned I was converting a Sherline Lathe to CNC here. I've taken another step and it seems to be working.

The basic machine is a Sherline Lathe with the Sherline CNC conversion, NEMA 23 stepper motors and a Gecko G540 drive. I'm only using two of the four axis in the G540 but it was an easy way to go and I may need them for another project some day. I'm using LinuxCNC through a parallel port. I put the 50V power supply, a 5V supply for the encoder and the G540 in a nice driver box.


I designed and built an encoder system. It uses a 60 ppr encoder with index on a 1:1 timing belt to the spindle. (If anyone wants the drawings for the encoder mount let me know.)




In setting up LinuxCNC for the Sherline I was amazed to find encoder settings in the Stepper Wizard. This made set-up very simple. Some of the LinuxCNC diagnostics showed the encoder was being read by LinuxCNC. Woo Hoo!

Long story short, I turned a short piece of AL to .25". Then with great faith and a prayer I typed in a threading G-code (G76) and pressed the go button. I was amazed and mesmerized that it cut a thread.


In fact I was so mesmerized that I got around to adding more lubricant just after the last pass. Anyway, there is progress. Now I have another neat tool, I just have to learn how to use it. Oh yeah, also add spindle control and home switches. But it works. There is a write up on the LInuxCNC forum with more blow by blow descriptions if anyone has an interest. Glad to answer questions here though.

Hope this is of some interest to you. Thanks for looking it.

Hugh
Hugh

Offline 10KPete

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Re: Sherline CNC Lathe
« Reply #1 on: February 07, 2017, 06:25:36 AM »
Nice lathe, Hugh!! Next thing, you'll be turning out not only small parts but complicated ones with all sorts of curves...

 :cheers:

Pete
Craftsman, Tinkerer, Curious Person.
Retired, finally!
SB 10K lathe, Benchmaster mill. And stuff.

Online Vixen

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Re: Sherline CNC Lathe
« Reply #2 on: February 07, 2017, 09:28:11 AM »
Hello Hugh
Nothing beats that feeling of cutting your first thread on a CNC lathe. I still find it hypnotic after many years.
I am about to convert my second lathe to LinuxCNC, so I am pleased to hear it is straightforward.
I found your thread on LinuxCNC gave lots of background and encoder specs.
Omron 100P/R encoders are cheap and plentiful on E-bay. Do you think they could work? I bought the same Intel Atom Dual-Core D525 as you

Nice work

Thanks

Mike
« Last Edit: February 07, 2017, 03:12:14 PM by Vixen »
It is the journey that matters, not the destination

Offline zeeprogrammer

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Re: Sherline CNC Lathe
« Reply #3 on: February 07, 2017, 11:28:27 AM »
Hope this is of some interest to you.

It is.  :ThumbsUp: Thanks.

Did you have a project in mind when you started this?
Carl (aka Zee) Will sometimes respond to 'hey' but never 'hey you'.
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Offline Niels Abildgaard

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Re: Sherline CNC Lathe
« Reply #4 on: February 07, 2017, 11:46:42 AM »
Very,very interesting and giving an old,useless man ugly ideas what to do with his old not quite useless Boxford




If I understand it no DRO but only counting bits for steppers?
What is accuracy of that?

Offline tvoght

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Re: Sherline CNC Lathe
« Reply #5 on: February 07, 2017, 03:16:20 PM »
That's a really neat looking conversion Hugh, including the driver box. Congratulations on your first threading job!

--Tim

Online b.lindsey

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Re: Sherline CNC Lathe
« Reply #6 on: February 07, 2017, 03:41:54 PM »
That looks great Hugh.!  I have always been curious though, if you still want to use the lathe manually, I see you still have the handwheels outboard of the stepper motors, but how easy is it to still turn the wheels with the stepper motors in the drive system?

Bill

Offline Niels Abildgaard

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Re: Sherline CNC Lathe
« Reply #7 on: February 07, 2017, 04:43:24 PM »
Can the software compensate for backlash?If it was measured once per halfyear 3 or 4 places within travel an ultraprecise  lathe can be had for peanuts.It wil even be possible to compensate for bed wear.

Offline Hugh Currin

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Re: Sherline CNC Lathe
« Reply #8 on: February 07, 2017, 05:38:58 PM »
Thanks all for the positive feedback.

Mike: I learned barely enough about various encoders to pick one for my project. You should ask on the LinuxCNC forum about a particular encoder, lots of CNC knowledge there. Selecting mine I learned that many don't have an index signal which is needed to synchronize the spindle motion. I also found a calc to match encoder ppr with computer input speed. For mine it turned out nice to have 60ppr with 100ppr a little too high. Mine hooked up directly, given 5V excitation, to the Gecko G540. Going directly to the parallel port may require pull-up or pull-down resistors. I was lucky that the Stepper Wizard configuration program let me set up an encoder. I thought I'd have to get into the HAL configuration files but didn't for the encoder. May still have to for spindle control and home switches. So we may still be fooling ourselves about it being "easy". But the LinuxCNC folks are very helpful.

Niels: I think the hardest part of a lathe conversion is cramming a ball screw into the cross feed. Once you get this and the motors mounted it's not too bad. I like steppers since they are easier to set up than servos. Steppers give some 200 steps per revolution (or more). You can add a reduction between the motor and lead screw with timing pulleys and/or adjust the pitch of the lead screw. Accuracy quickly becomes dependent on the mechanical side rather than the electronics, accuracy depends on lead screws, bearings, ways, etc more than stepper function. The computer readout is just like a DRO and as accurate as the machine. With ball screws very accurate.

Bill: I had the hand wheels and the end of the stepper was a good place to store them. I should probably take them off so they don't catch on "things". It's not functional to turn the hand wheels with the steppers engaged. Hard to turn and doing so would cause lost steps negating the computer DRO. You could turn the drive off and use the hand wheels, but again losing the DRO function. I never planned to use the lathe "manually". I've found that I no longer use the hand wheels on my CNC converted mill. LinuxCNC, and I'm sure the other controllers, give full control of motion through the computer. I use the jog buttons a lot and find it nicer than hand wheels. You can set the feed rate and push +/- X/Y/Z buttons to move as a hand wheel would, just smoother. It also gives the function of moving a specified amount, like 0.05" or 0.001". Then using MDI commands I can enter G code directly. Nice for moving to a specific numerical location or cutting an angle. So I've migrated to not even having hand wheels on my mill. I expect it to be the same with the Sherline lathe. But like you I hesitate to abandon hand wheels on the lathe. My solution was to convert a Sherline Lathe and see how I get along with it. If it's like the mill I may migrate to a single larger CNC lathe. Till then I'll keep my 14" Goodway manual lathe and the CNC Sherline. Hey, don't you now have two small lathes, a Sherline and a Cowells? Great time for a Sherline conversion?

Niels: In LinuxCNC there is backlash compensation. It takes out a certain backlash when the axis changes direction. This is easy to implement. I remember something about lead screw compensation in LinuxCNC but have not pursued it. It's not common so I suspect not a panacea. Then LinuxCNC is open source so you could modify the internals. I use the first (backlash comp) but the second two I fear are beyond my meager capabilities. Your mileage may vary.

The Sherline seems to be quite accurate and repeatable. It doesn't use ball screws but the pitch of the lead screws is pretty fine. I think this increases accuracy, accuracy being a % of pitch? I've just started to use it so a long road ahead. From what I'm seeing it'll be a combination of hand G coding and CamBam outside profiles. Good CAM packages for turning are very expensive.

Thanks again for the nice comments. I'm sure the Sherline will show up in future build logs.

Hugh
Hugh

Online Vixen

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Re: Sherline CNC Lathe
« Reply #9 on: February 07, 2017, 08:30:18 PM »
Hello Hugh,

As ever, I am following along with everything you do. You are my guinea pig.

I bought the same Intel Atom Dual-Core D525 as you and installed LinuxCNC 2.7. Actually I now have three, a local tech collage was throwing them out. I could not resist the price.

I have two mills running on LinuxCNC and the third micro PC is destined for my Colchester Chipmaster lathe conversion. I already have the two axes running well and have started to look for an  encoder to enable thread cutting.

So along comes Hugh, he has done the research and has found an inexpensive encoder and got it to work with LinuxCNC on his Sherline. It seems logical that I should follow his advice once again.

Your Base Period calculations show that a D525 using an Omron E6B2-CWZ6C 60P/R encoder should be good for screw cutting at up to 2800 RPM with a safety factor of two. I found the same Omron Rotary Encoder E6B2-CWZ6C as you are using, on e-bay with 100P/R at a give away price and have ordered one. I recon that 2800 RPM is unbelievably fast for thread cutting. Using you Base Period calculations, I figure a 100P/R encoder should be good for thread cutting up to 1680 RPM with the same safety factor of two. I will be connecting it directly to the parallel port so will have to figure out the pull up/ down resistors. It is good to know that the Stepper Wizard is there ready to help me set up the encoder in the same way it set up the stepper drives.

Thanks for doing all the hard work up front, while I cruise along copying you.

Regards

Mike
« Last Edit: February 07, 2017, 09:37:30 PM by Vixen »
It is the journey that matters, not the destination

Offline Dave Otto

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Re: Sherline CNC Lathe
« Reply #10 on: February 08, 2017, 01:12:44 AM »
Hi Hugh

This is really great! A project and tool that I definitely want to add to my shop some day; I think that I would do as you did and use a short bed machine and leave my long bed lathe stock.
I would like to have a copy of the encoder bracket drawings or CAD models if you don't mind.

We have a Sharp CNC Tool Room lathe that I run at work, and that has got me thinking about someday having CNC lathe capability in my home shop.

Now you need to start thinking about a gang tool set up; this is what we use on the Sharp and if you don't have a turret tool changer it is real nice for setting multiple tools for a job. Then you don't have to deal with a tool post and its repeatability issues along with constantly changing tools. Once all the tools are set you can rock and roll!

I see that Sherline has recently come out with some gang tool holder blocks. http://sherline.com/product/5930-38-gang-tooling-tool-post/
The tricky part is getting it all set up so that everything clears, and you don't have tools running into things that they shouldn't. :wallbang:

I plan to head over to the Linux CNC forum and see the rest of the story.

Great work!
Dave

Offline Hugh Currin

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Re: Sherline CNC Lathe
« Reply #11 on: February 08, 2017, 04:29:26 AM »
We have a Sharp CNC Tool Room lathe that I run at work, and that has got me thinking about someday having CNC lathe capability in my home shop.
You are way ahead of me. I have about an hour, maybe two, running a CNC lathe. Steep learning curve so far.

Quote
Now you need to start thinking about a gang tool set up; this is what we use on the Sharp and if you don't have a turret tool changer it is real nice for setting multiple tools for a job. Then you don't have to deal with a tool post and its repeatability issues along with constantly changing tools. Once all the tools are set you can rock and roll!

I see that Sherline has recently come out with some gang tool holder blocks. http://sherline.com/product/5930-38-gang-tooling-tool-post/
The tricky part is getting it all set up so that everything clears, and you don't have tools running into things that they shouldn't. :wallbang:
I think I'll use the quick change tool post for awhile. It seems to be consistent. I'll need to come up with some additional tool holders though. Need some small drill chucks, which I don't have, at least. Also a couple of angled holders to keep the tool post square for drilling and cut off tools while angling a diamond insert tool. Maybe a rear cut off tool holder also. To my feeble mind this seems more flexible for a few parts than gang tooling. I know I'd not have what I wanted in the gang for the part I want to make. For production I can see an advantage to a gang of tools.

But again I have little experience so far.

Quote
Great work!
Dave

Thanks.

Hugh
Hugh

Offline Flyboy Jim

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Re: Sherline CNC Lathe
« Reply #12 on: February 08, 2017, 04:54:09 AM »
It's good to see you moving ahead with this, Hugh. I can see that CNC is a whole hobby in and of itself!

I'm sure you're aware of Ken Toonz on YouTube and his Sherline CNC system: https://www.youtube.com/channel/UC05j92cRyO6GvUAUu-EJgjA Actually, I should say the Sherline system he used to have.........he's since sold that system and gone to a Tormac mill and a big Grizzly lathe. His hobby certainly got way more expensive!

Jim
Sherline 4400 Lathe
Sherline 5400 Mill
"You can do small things on big machines, but you can do small things on small machines".