Re: Recommendations for stepper motors, controller, software
The single point threading cutters that Royce mentioned open up possibilities I think, even for a tiny machine like the Unimat 3.
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I can imagine a setup where the headstock spindle and leadscrew are both driven by stepper motors.? Some form of motorised holder for the cutter, that would mount on the slide.? The work (in the chuck) and the leadscrew can go as slow as you like (as long as they are correctly synchronised), while the cutter chomps away.
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Or do I have that wrong somewhere?
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Re: Recommendations for stepper motors, controller, software
On Wed, Aug 28, 2024 at 07:34 PM, John Dammeyer wrote:
Or just use taps and dies.
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If you find yourself in a dimensionally confused environment, as I am sometimes, with metric and inch threads, sometimes deliberately obscure (never did find ?" 27 tpi taps or dies when I needed them), and add in things like optical threads (large diameter, fine pitches), BSC (British Standard Cycle threads), Pg conduit threads and finally the oddity of BA threads - pitch is 0.9^(BA number) so it goes 1.0, 0.9, 0.81, 0.729, 0.6561, 0.59049, 0.531441 - and that only gets us to 6 BA - 16 BA has been seen in captivity. Yes, you can get taps and dies for all sorts, but the most obscure I have seen so far was a full set of taps and a die for M39.5 × 1.25 Left Handed. I dread to think what that cost. I also know, from looking at the job it was used on, that a much more standard thread could have done the job (using an M40 × 1.5 KM8 bearing retainer nut with a tab washer to lock it).
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So when screw cutting on the lathe? NC could give great flexibility in choice of diameter and pitch, well beyond all the drawers full of taps and dies my mate has accumulated in his workshop over the last fifty years. And saving hours searching for the odd thread you were sure was there, but in the end it wasn't.
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All this applies to thread milling, but I can't see how that would succeed on any of the small Unimats in milling format.
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Re: Recommendations for stepper motors, controller, software
Nope.? Not missing anything. ? Even with motors on the X and Lathe Z when the system is converted over to the mill making the ?axis now X and the X axis now a Y (from a CNC perspective) the motion of the vertical assembly (now Z axis) is very difficult to automate on the DB200 so it’s truly a 2 ? axis mill. ? The thing about automating and threading is the lathe part and because the motor is as underpowered as it is, any kind of cutting load causes motor speed change.? That pretty well disqualifies 1 PPR sensing for speed and therefore my ELS project.? But that project was started in 2005 when used encoders were $400 and stepper motor drivers were well over $100.? ? Now we have all the cheap stuff that could never be manufactured in North America or Europe being done in China at 1/10th the cost.? A Pi4 with MESA 7i92 can handle say a $35 360 line encoder connected with cheap toothed pulleys and belt to the spindle and full LinuxCNC to drive the Z and X.? If you don’t want the MESA card and just Pi4 I/O it’s still possible to do that with Pi4 I/O pins but there are limitations. ? To quote Sam Sokolk from the LinuxCNC forum: “Any way.. Let’s say you have a 25khz base thread. Encoders - You should be able to approach counting at 25khz if the quadrature signal is perfectly 50%.? (I might go 10% less) So - at 600 line encoder or 2400 count?? The absolute max counting rpm would be 625.” ? Drop that down to a 100 line encoder or 400 count then we’re up to 3750 RPM or if you can run the base thread at 50kHz then theoretically you can expect to handle at most 7500 RPM which now closer to the Unimat max speed.? In my case I was looking at using a 60 tooth sensor on my Gingery Lathe but this project was put on hold back in 2017 based on the photo and cad file dates.? With a 25kHz base thread the RPM range of this lathe would be easily handled.? ? But for the cost of the MESA product the encoder is counted in hardware so no longer matters.? And CNC is just a matter of the mechanicals;? mounting motors, encoders, power supplies and wiring. ? Or just use taps and dies. ? John
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From: [email protected] [mailto:[email protected]] On Behalf Of Andrei
Sent: August 28, 2024 10:44 AM
To: [email protected]; donmckee@...
Subject: Re: [Unimat] Recommendations for stepper motors, controller, software? If we are talking about thread milling on a unimat, i think this is a fool's errand, given the significant limitations of this tiny machine.? Just get the correct size dies and it is an easy job. Why reinvent the wheel? And why overcomplicate a simple task?
Are we talking about thread milling here? When thread milling the work-piece is clamped to the milling table and the X-Y motion of milling table can make any point on the work-piece follow a circular path.? The cutter in the spindle can then be used to mill an internal or external thread on the work-piece at that point.? The link that was provided looks an awful lot like what a thread milling cutter looks like. With thread milling you do not need to coordinate spindle rotation and axis movement like you do when cutting threads on a lathe.
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Re: Recommendations for stepper motors, controller, software
Andrei - in my case I’d like to be able to make adapters and flanges for large format lenses… I doubt if taps are available that big :-)
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The U3 may well not be up to the task but I’m quite happy to talk theoretically !
Don - I’m not sure what we’re talking about, it’s all new to me… I’m hoping Royce can elucidate a bit on how he has it setup.
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Re: Recommendations for stepper motors, controller, software
If we are talking about thread milling on a unimat, i think this is a fool's errand, given the significant limitations of this tiny machine.?
Just get the correct size dies and it is an easy job. Why reinvent the wheel? And why overcomplicate a simple task?
Am I missing something?
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Peter/Royce:
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Are we talking about thread milling here?
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When thread milling the work-piece is clamped to the milling table and the X-Y motion of milling table can make any point on the work-piece follow a circular path.? The cutter in the spindle can then be used to mill an internal or external thread on the
work-piece at that point.? The link that was provided looks an awful lot like what a thread milling cutter looks like.
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With thread milling you do not need to coordinate spindle rotation and axis movement like you do when cutting threads on a lathe.
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Don
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Re: Recommendations for stepper motors, controller, software
Peter/Royce:
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Are we talking about thread milling here?
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When thread milling the work-piece is clamped to the milling table and the X-Y motion of milling table can make any point on the work-piece follow a circular path.? The cutter in the spindle can then be used to mill an internal or external thread on the work-piece at that point.? The link that was provided looks an awful lot like what a thread milling cutter looks like.
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With thread milling you do not need to coordinate spindle rotation and axis movement like you do when cutting threads on a lathe.
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Don
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Re: Recommendations for stepper motors, controller, software
Thanks Royce, that’s very interesting, I didn’t know such a thing existed. My primary reason for thinking CNC is putting threads on things.
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From your description you need two things rotating at the same time (the work and the cutter) but I can’t see how you could get this arranged on a standard Unimat… have you built a drive unit for the cutter that fits on the slide (for instance)? ?Then the lead screw would feed it into the work. ?Just trying to envisage it.
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Re: Recommendations for stepper motors, controller, software
Mine are very old, a single cutting face and not so expensive.
Here is the first one I found on line. ?I think you can find less expensive ones.
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The work piece travels in a circle in the X/Y plane
The cutter rotates in the spindle and advances on the Z axis at the pitch rate.
GCode G2 or G3?
I used to make reproduction dust caps for classic French bicycles. ?As I remember the thread was 23.35M1. ?The Unimat did the whole job, turned the aluminum bar stock, cut the threads and engraved and polished the domed surface.
Good luck,
Royce
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On Aug 27, 2024, at 2:31?PM, Peter Brooks <peter@...> wrote:
Royce, could you possibly post a link to a ‘single point rotary screen cutting bit’ - I’m intrigued !
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Re: Recommendations for stepper motors, controller, software
Royce, could you possibly post a link to a ‘single point rotary screen cutting bit’ - I’m intrigued !
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Re: Unimat DB200 Dutch Motor Diagram
#db200
I finally got the induction motor apart. It wasn't too bad, just not much to grab to without scratching or crushing. It's a solid body and two end caps that protrude very little.
I bolted a wooden plank through motor mounting holes on the front cap (two M5), first drilling an opening in it to allow space for the shaft. Then twisted and pulled by hand. If you have unimat motor mounting bracket, you can use that too to provide more grip.
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Re: Recommendations for stepper motors, controller, software
Compared to the MESA cards like the 7i92 via Ethernet how well do you think it will handle say a 600 line quadrature encoder?? For a small Unimat or Sherline lathe running 8000 RPM is 8000/60 x 2400 = 320,000 edges per second for full quadrature. ? John ? ?
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From: [email protected] [mailto:[email protected]] On Behalf Of roycegb via groups.io
Sent: August 27, 2024 7:24 AM
To: roycegb; [email protected]
Subject: Re: [Unimat] Recommendations for stepper motors, controller, software? I use a parallel port mode for the stepper driver. ?The Raspberry Pi has a 40 pin header that can be configured to drive any such device. I currently use a Byte2Bot level shifter to drive a 25 pin cable that connects directly to all my steppers. I originally used a PC, then a Raspberry Pi 4 and currently a Raspberry Pi 5. ?It is a very compact setup.
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Re: Recommendations for stepper motors, controller, software
And if the load while cutting slows down the spindle how does the Z axis know to not move as quickly? ?
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From: [email protected] [mailto:[email protected]] On Behalf Of roycegb via groups.io
Sent: August 27, 2024 5:28 AM
To: [email protected]; keithsangus@...
Subject: Re: [Unimat] Recommendations for stepper motors, controller, software? NC Screw cutting can be done with the Unimat without spindle sensing. ?Use a single point rotary screen cutting bit. ?There is a single Gcode that cuts a helix path. ?It cuts any diameter, pitch or direction. ?It will cut inside and outside threads. ?The major limit is the Unimat's Z Axis travel since the tap or dye cutting must be vertical. G2 or G3 <X- Y- Z- I- J- P->
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Re: Unimat DB200 Dutch Motor Diagram
#db200
Good evening,
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I'm sorry but I have no experience with the type of motor on your lathe but had a similar problem with the older U90 motor.
It just would not come apart, in fact the previous owner had tried to knock it apart with a hammer using the brush holders as a contact point.
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Having ascertained that there were no wires holding it, it was just a case of brute force and plenty of sweating and cursing to pull it apart with my hands.
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Having got it apart it was obvious that it had been put together in a hydraulic press as there was evidence of large scratches inside the case.?
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Using a Dremmel and small grinding wheel I removed as much excess metal as required to ensure a looser fit.
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regards,
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David
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Re: Recommendations for stepper motors, controller, software
John,
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I use a parallel port mode for the stepper driver. ?The Raspberry Pi has a 40 pin header that can be configured to drive any such device.
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I currently use a Byte2Bot level shifter to drive a 25 pin cable that connects directly to all my steppers.
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I originally used a PC, then a Raspberry Pi 4 and currently a Raspberry Pi 5. ?It is a very compact setup.
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Royce
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Re: Recommendations for stepper motors, controller, software
Roy,
Could you elaborate on that a little more. I do not understand what you are describing.
Thanks,?
Dick
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Re: Recommendations for stepper motors, controller, software
NC Screw cutting can be done with the Unimat without spindle sensing. ?Use a single point rotary screen cutting bit. ?There is a single Gcode that cuts a helix path. ?It cuts any diameter, pitch or direction. ?It will cut inside and outside threads. ?The major limit is the Unimat's Z Axis travel since the tap or dye cutting must be vertical.
G2 or G3 <X- Y- Z- I- J- P->
Royce
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Re: Recommendations for stepper motors, controller, software
For NC screw cutting you will nee some sort of encoder on the main spindle (the Unimat PC had this). That then implies that the controller must have a suitable input, with a fast enough response.
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Re: Recommendations for stepper motors, controller, software
One thing to keep in mind.? Most of those modules are mostly for CNC routers or 3D printers.? Automating a lathe is slightly different.? Even MACH2/3 had a different user interface for the Lathe Option. ? John ?
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From: [email protected] [mailto:[email protected]] On Behalf Of McKee, Don {Quaker}
Sent: August 26, 2024 12:22 PM
To: Peter Brooks; [email protected]
Subject: Re: [Unimat] Recommendations for stepper motors, controller, software? To further muddy the already murky CNC waters, you have something like the DDCS 3 or 4 axis stand-alone CNC controller.? The DDCS was originally a very low-buck offering from China that went belly-up - it didn't really work that well.? This left most of the people that had purchased it high and dry.? A small-ish group of collaborators over on the Madmodder forum were given the original source code.? Over the course of several months/years that source code was de-bugged and re-written, then offered to anyone that wanted it, including the vendors that are selling the DDCS today.? (There is a thread over on Madmodder dedicated to the DDCS that spans several years.) With the DDCS you don't need a PC dedicated to controlling the CNC, you don't need the CNC control software, and you don't need any type of break-out board, that's all built into the DDCS.
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Re: Recommendations for stepper motors, controller, software
To further muddy the already murky CNC waters, you have something like the DDCS 3 or 4 axis stand-alone CNC controller.?
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The DDCS was originally a very low-buck offering from China that went belly-up - it didn't really work that well.? This left most of the people that had purchased it high and dry.? A small-ish group of collaborators over on the Madmodder forum were given the original source code.? Over the course of several months/years that source code was de-bugged and re-written, then offered to anyone that wanted it, including the vendors that are selling the DDCS today.? (There is a thread over on Madmodder dedicated to the DDCS that spans several years.)
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With the DDCS you don't need a PC dedicated to controlling the CNC, you don't need the CNC control software, and you don't need any type of break-out board, that's all built into the DDCS.
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Don
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Re: Recommendations for stepper motors, controller, software
Thanks John, your advice is much appreciated. ?A modular system certainly makes more sense, and LinuxCNC seems very full of functionality, with the various GUIs etc.
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As always it is the learning curve vs the available time - with a load of other projects already on the go !
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OldToolmaker