Lathe conversion from stock to CNC

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30 Sep 2012 16:15 - 30 Sep 2012 16:54 #24746 by RotarySMP
How is your lathe progressing? I converted on of the generic 7x12 lathes years ago, and it has been a handy tool.



After I blew up the little chinese motor, I now power it with a 550W 3ph and a VFD belt driving the man spindle.



I use the SFM chart on the littlemachineshop.com website for reference for cutting speeds, although with an infinite variable speed drive, you get a feel for the speeds, and can correct on the fly.

littlemachineshop.com/Reference/CuttingSpeeds.php

In my opinion, one of the most valuable aspects of a lathe CNC conversion is being able to enclose it and control the mess.


Mine is a never finished project. I have been thinking about putting the arceuro steel gears in the head, and getting a more torque at lower speed range which would be handy for cutting larger threads and drilling bigger holes.

Still need to make up a new spindle encoder, as LinuxCNC needs both the single pulse indexer, plus a multi pulse encoder, and I just have a the single pulse at present (TurboCNC didn't nee more). When I pull the head about for those two, I'll also install taper roller bearings (although I already replaced the cheap chinese bearings for SKF.)

I had home switches on it once, but never used them under TCNC. Since LinuxCNC has better tool management, I need to reinstall the limit switches and spend some time setting up a tool table.

The tail stock is rubbish on my lathe. Sooner or later I'd like to cast and machine up a new one.

The cross slide still runs of the original spindle. There is a far bt of backlash, but it is normally not a big deal for normal turning operations.
Last edit: 30 Sep 2012 16:54 by RotarySMP.

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30 Sep 2012 21:18 #24770 by PCW
You should be able to use a single pulse/turn spindle encoder for LinuxCNC by running the encoder in the counter mode and feeding both the count ('A') and index ('Z') from the same signal. Of course this will still not perform as well as a multi-count/turn encoder as LinuxCNC has to guess the actual spindle speed between index positions, and any load induced spindle speed variations during the turn are not tracked by the linear axis

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23 Oct 2012 12:17 #25664 by Soundreflections
Been traveling a bit more than I want, so have not been home long enough for much progress.

I am building a stepper driver, using a L297, with 2 L298's. I first did a veroboard build, which looks quite messy by the time one gets anywhere. It did work, though rotating quite slow I thought, then trying a higher current power supply I blew the system. I am now trying to make a PCB layout. One can get many designs using one L298, but that can only handle 2A, so I need to use 2, for 4A.

I will be making a shaft encoder, using 2 IR beams on a slotted disc, then a IR reflective sensor for indexing.

I might build a CNC dremmel router before finishing the lathe, opperational needs. I am though needing to get the drivers working and reliable before I go to mechanical modifications stages.

I am thinking of making a indexed table using a stepper as main drive, to be able to do some gearing.

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23 Oct 2012 12:35 #25667 by andypugh
Soundreflections wrote:

I am building a stepper driver, using a L297, with 2 L298's. I first did a veroboard build, which looks quite messy by the time one gets anywhere. It did work, though rotating quite slow I thought, then trying a higher current power supply I blew the system. I am now trying to make a PCB layout. One can get many designs using one L298, but that can only handle 2A, so I need to use 2, for 4A.

This sounds like a high-effort solution. Are you sure that the devices can work in parallel?
The THB6064 is allegedly toughter and more capable: www.linuxcnc.org/index.php/english/compo...id=27&id=21964#21964
There is a link there to several open-source driver designs too.

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23 Oct 2012 15:34 #25679 by BigJohnT
Have you seen what Jon did on his mill to make a spindle encoder?

pico-systems.com/bridge_spindle.html

John

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26 Oct 2012 12:54 #25835 by Soundreflections
I have now ordered some kits from piclist, thanks Andy for the link!

I don't mind spending time developing a driver, the data sheet assures me they can be paralleled, also shows how. I need a design program with an auto router to do the board layout, manual routing is too much like hard work. I have 2 programs with auto routing, they both have not got the L298 driver, I have imported it to Designspark, but there seems to be no PCB footprint in the model. I now have the diagram in KiCAD and Designspark, KiCAD is manual routing and I get stuck very quickly trying that.

Anyway - awaiting the driver kits, then see how it all comes together!

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30 Oct 2012 15:38 #26048 by Soundreflections
I have bought a basic machine, with cables to get the parallel and serial port outside the PC, which needs modification as the parallel port cable has a small size plug on and the serial a large size, whilst the main board has the opposite!

Amazing how hard it is to get a machine with serial and parallel ports these days! I now have LinuxCNC running, a basic config actually working, though I have settled on a 0-10V PWM conversion rather than serial MODBUS, as I chased the adaptor I had ordered for my drive only to find doubt if it will work and about 1000ZAR, instead of R300 I was expecting. I could also not see a simple way to tell LinuxCNC to reverse the Parport, so I will add a second port or get a expansion card at some stage. Now just waiting for drivers, then get the electronics sorted.

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30 Oct 2012 16:56 #26050 by andypugh

I could also not see a simple way to tell LinuxCNC to reverse the Parport.

Can you explain what you mean by that?

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31 Oct 2012 22:07 #26134 by Soundreflections
Apparently some parallel ports are bidirectional, reversing I&O. That would mean about 10 inputs and 5 outputs. I remember somewhere reading on how to test to make sure the port can do this, on my PC I was trying to resuscitate for LinuxCNC the parport actually had a "bidirectional" as a mode, but the machine is too unstable.
Looking at axis config I cannot see any way to reverse the port, though at the moment, nearly having all the hardware I am focusing on a plain, straight config to work, then perhaps start dabbling in to other setups.

Then of course my biggest challenge: Getting a CAM package, drawing my designs and figuring out how to get them to G-code! I have tried a few threads on the forum, hoping it gives me the steps / software (open source if possible) and procedures, but have not been that lucky so far.

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31 Oct 2012 22:14 #26137 by andypugh

Apparently some parallel ports are bidirectional, reversing I&O. That would mean about 10 inputs and 5 outputs

www.linuxcnc.org/docs/html/hal/parallel_port.html
It could be a little clearer about how to set direction (in that the section that tells you how to do that is the section that tells you how to access the port by address rather than index number)
I think Stepconf might only support reversing the second port. (the assumption perhaps being that you are not going to be able to move a machine with only 4 outputs.)

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