Author Topic: Question about Mach 3 Turn  (Read 1598 times)

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Offline carls

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Question about Mach 3 Turn
« on: October 22, 2014, 05:19:31 PM »
This post is to ask for opinions on my plan. I have been using Mach3 on my home made milling machine. I'm now building a simple CNC lathe/mill hybrid (for wood). The turning of the lathe spindle will be controlled by a stepper motor, and cutting will be by a router traveling on the X axis.

 My first test will be to make threaded dowels, using only the X and Y axis. I'm planning to write simple G code to do this. I think I can have it move along X using a normal command.  For rotation I'm planning to trick it into thinking the Y parameters are very large, and let it think it is moving along Y while it is actually rotating the lathe spindle.

If I haven't been clear enough, here's more detail. The whole "machine" is a platform clamped to the bed of a wood lathe. The X will control the left-right motion. The Y is a stepper motor with a pulley and belt rotating the lathe spindle by another pulley on the lathe shaft behind the chuck. (The lathe's motor will be disconnected)  If the test works, I plan to add a Z axis to raise and lower the router for use with objects that are not dowels.  A simple first version may not use a stepper for Z, as I could add a bearing to follow templates matching the form of the piece. Templates will be a simple way to do decorative detail such as spiral flutes on a spindle already shaped by traditional turning. The Z axis stepper when added will allow roughing out the shape before adding finer detail.

I know this has already been done on much more sophisticated machines, and eventually, for making and embellishing complex shapes,  I will need to have a direct way to command the spindle to turn, since it will be doing more than thinking the X and Y are causing a diagonal line across a table 2' (X) by 20' (50'? 100'?)  but I don't see a version of Mach 3 that controls rotation in this way.

Any comments?


Offline RICH

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Re: Question about Mach 3 Turn
« Reply #1 on: October 23, 2014, 08:45:59 AM »
Quote
turning of the lathe spindle will be controlled by a stepper motor

That is ok if you are only indexing and the stepper is adequate for holding position.
For continous turning of the spindle use a servo..... DO not use a stepper.

I suggest you do a search on 4th axis as you will find a lot of info.

RICH

Offline DICKEYBIRD

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Re: Question about Mach 3 Turn
« Reply #2 on: October 23, 2014, 10:42:19 AM »
I'm curious Rich about the stepper/servo spindle issue.  I understand the problem with stepper spindles/fixed tooling but he's using a router to make the cuts & just turning the work in the spindle.  Wouldn't it be about the same as routing the work using a round "table" instead of a flat X/Y table?
Milton from Tennessee ya'll.

Offline carls

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Re: Question about Mach 3 Turn
« Reply #3 on: October 23, 2014, 12:38:08 PM »
Thanks Rich, I think I understand what you mean. As Dickeybird mentioned, I see it more as routing than turning. I've only recently realized that servos have a place in CNC, always thought of them as too limited.

I do plan to use the lathe configuration only for positioning, not using the rotational force for cutting.  Are you saying that the higher torque of a servo is needed only if cutting as a normal lathe? As a traditional woodturner, I see the need for rotational Horse Power when the cutting force comes from the material to be cut,  rather than the cutting tool.  My plan is to use the lathe only to achieve symmetry, the only force needed is to turn the spindle (almost zero) and to overcome the resistance of the wood pushing against the spinning cutter.  Btw, the steppers I bought for this are 400+ ounce/inch.

My limited CNC experience is with steppers, but I will start learning more about servos, if not now, I'll eventually have a need for them.