Lathe conversion from stock to CNC

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21 Aug 2012 11:30 #23470 by andypugh
Soundreflections wrote:

I was referring to the "motor to thread" interface. My current intension is to remove the adjustable dial behind the handle, which I have not found too helpful (Probably not figured out exactly how to read them), then fit a gear in it's place. I then want a gear on the stepper to mesh with it. Making more sense, or not the confusing part?

Still confused. Are you talking about how to get drive to the cross-slide leasdscrew, or something different?

I figure that if I can get an indexed head of some sort I can make a fitting to have my Dremmel cutting at 90deg.

Ah, OK, so gear in the lathe spindle/chuck, cutter on the tool slide?
When I was looking at this I was planning to have the gear cutter in the lathe spindle and the gear blank on a synchronised axis. But the angled feed required, and the need to adjust the depth of cut was too tricky, so I ended up modding the mill instead.

Making gears is quite complicated, when you get into it.

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22 Aug 2012 07:35 #23537 by Soundreflections
I am referring on how to get the drive to the cross slide lead screw. I have thought that I will make a mount for the Z motor to have a gear matching the normal lead screw gear. The X axis is giving me some more hassle, as I envisage the motor possibly getting in the way of the hand crank. I am thinking of 2 large gears, for physical spacing.

Hope I am making sense this time, otherwise just ignore it as ramblings, something I think I sometimes do. Thanks for the heads up on gear cutting being complex, I have thought of making a dedicated gear cutter at some point, maybe I will wait till I have a mill someday. I am impressed with your setup. Very similar to what I am planning with my encoder setup.

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22 Aug 2012 08:57 #23539 by andypugh
Soundreflections wrote:

I am thinking of 2 large gears, for physical spacing.


Gears add backlash, which is not ideal. Toothed belts work nicely. Here is an example (it's actually my lathe)
www.cnczone.com/forums/mini_lathe/63621-...ew-2.html#post509784
I moved the thrust bearings outboard of the tool slide travel, and could squeeze a small pulley and needle roller bearing into the available space under the slide.

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22 Aug 2012 12:54 #23544 by Soundreflections
I forgot about the backlash problem. You are lucky to have a mill available, even on the same machine. I have a drill press, which is probably not the worst, but no usable accuracy. I should investigate if I can get timing belt pulleys, that is my other consideration, I just happen to have all my change gears that will not be used unless I run manual.

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22 Aug 2012 13:56 #23548 by Soundreflections
I keep meaning to ask about gear changes. My lathe has a 6 speed gearbox, can LinuxCNC recommend correct gearing, or should I choose a gear, then run the program and evaluate how hard it is running the VFD to check if I need to change gears?

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22 Aug 2012 15:48 #23555 by andypugh
Soundreflections wrote:

I keep meaning to ask about gear changes. My lathe has a 6 speed gearbox, can LinuxCNC recommend correct gearing, or should I choose a gear, then run the program and evaluate how hard it is running the VFD to check if I need to change gears?


Both are possible.

What might be quick-and-easy would be to make a table of part diameter and material with the optimum gear. You want to use the highest gear which will still have a reasonable VFD frequency at max diameter so that you aren't running out of speed on the smallest diameter.

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23 Aug 2012 14:13 #23577 by Soundreflections
Any idea where I can get a table of recommended cutting speeds for different metals? I have found many requests for such a table, many people saying they will try and make one, but not yet any actual table. It is possible I am searching the wrong key words, but that would be helpful, in manual and CNC. Presumably I can then tell LinuxCNC what metal I am using, it can ask for the right gear combination. Lazy I know, but even a manual table would be fine. I often try to cut quite slow, finish as fast as possible. Not sure what to look for to find the correct speed. I have often thought video clips of CNC cutters are running very fast when they cut, so I thing I am on the wrong track.

I have now ordered a MODBUS interface for my drive, hoping I will have a reversible parallel port, but it won’t cost too much so I am happy with it, just need to figure out how to program HAL. I am first making my stepper drivers and then I will get the PC down and see if LinuxCNC is happy with it. Wish I had more free time for this!

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23 Aug 2012 16:11 #23582 by BigJohnT
Look for SFM calculators or charts...

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27 Aug 2012 14:51 #23684 by Soundreflections
I have found an ideal box among some stuff my work is throwing out. It has latches closing it and the hinges are slide off type. It also has a full metal insert on which all electronics can mount, it can then simply screw in to the box.


I have also started working on my PC. Finally got the thing to boot (long time been standing, looks like it now had a bad RAM and video card.). Looking through the BIOS settings I can set my parallel port to Bi-directional, so hoping I can believe that.

I am wondering how to configure LinuxCNC for serial MODBUS spindle speed. I am hoping it will all be clear and easy once I actually set it up. At this stage I get a black screen once Linux starts, need to play with VGA=778, to try and sort it out, just not had time yet.

Thanks for the SFM hint, I have now found some SMM? charts.
Attachments:

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27 Aug 2012 17:49 #23692 by BigJohnT
Soundreflections wrote:

Thanks for the SFM hint, I have now found some SMM? charts.


Ah metric would be Surface Meters? per Minute I guess. Also for the most part the charts depend on good tooling and rigid machine and are usually a good place to start.

John

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