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Cutting Circles
« on: November 07, 2007, 08:56:47 PM »
Having a problem cutting circles. They don't come out exactly round. There will be a small flat spot on one side. The machine cuts squares within .002".

Offline Chip

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Re: Cutting Circles
« Reply #1 on: November 07, 2007, 10:08:15 PM »
Hi, Rkjohn

Check for backlash in the axis's, It's usually the cause.

Thanks, Chip
Re: Cutting Circles
« Reply #2 on: November 07, 2007, 10:21:12 PM »
I'm new to this. How do I do that?

Offline Hood

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Re: Cutting Circles
« Reply #3 on: November 08, 2007, 03:09:30 AM »
Put a dial against the quill (if a mill or router) and jog the table so that the plunger is pushed in. Either zero or take a note of both the axis and dial readings then change to step mode so that your axis jogs in small incriments and back off the dial, as soon as you see the needle moving stop and look at the DRO for the axis you are using and the difference between that and the previous noted reading is your backlash. Repeat for all other axis.
Hood

Offline Chip

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Re: Cutting Circles
« Reply #4 on: November 08, 2007, 03:48:00 AM »
Hi, Rkjohn

First theres a Jog/MPG Screen if you haven't found it, Under the Tab key, It may make it easer ? Learning curve.

Jog Mode, "Step", Cycle Jog Step, "click on it or to the right click to enter value.


Check for backlash in Axis's.

Best done with a dial indicator with 1 inch of travel,

Setup as Picture below, Jog left .750 then re-zero dial indicator 0 mark, Zero X on Mach3 Prog. Run Screen.

(this takes the backlash out to the left if any when your moving right).

Now jog .500 to the right, Dial indicator should read .500 and Mach will indicate .500, Record the distance moved.

(If the indicator shows above/below .500, Your steps Per. Unit  are incorrect in motor tuning for the axis).

I would repeat Above until you get units set as correct/close as you can.

Now Jog left .500, Mach will show 0 and indicator should read 0 again "if no backlash".

If the pointer didn't make it back to 0, The distance to go to 0 is your Backlash value.

Backlash can be turned on and set under Config, Backlash, Enter the value for axis, Check the Enable Box then OK, Re-start of Mach Required.

Where to start where to stop.

Hope this Helps, Chip

Offline jimpinder

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Re: Cutting Circles
« Reply #5 on: November 08, 2007, 08:17:31 AM »
Normally when operating a lathe/milling machine etc, one always tries to move the axis in the same direction, the problem being that the screws that move the tables have play in them, so when you reverse, the first part of the turn of the screw is lost by the thread moving across the gear to the opposite tooth, to move the table the opposite way.

This is not a problem in manual operation, because you do not tend to make such complcated moves - i.e. straight lines generally.
If you try and cut a circle using CNC, the table changes direction on both the x and y axis. You might start by moving the table from x0 to x1, but when you move back to x0, although your DRO's will say you have moved back by 1 unit, you may have only moved back by 0.995 i.e. 5 thousanths short. You can test this as outlined above - move from x0 to x1 - to make sure that any backlash is taken up in the positive direction.  (I use a G0 X1 command rather than jogging) and measure the distance you have moved. I use digital calipers to measure, and now zero them. Move from x1 to x2, then x2 to x1 and measure again. The calipers should read 0, but will not - they will read the "backlash" figure. Repeat for the Y axis. Repeat for the Z axis. (Actually repeat on the same axis several times to check your figures - if you are not getting the same figures consistantly (and it is difficult to accurately measure small distances) take a mean average.

It doesn't matter in which direction you actually do this - you could go 2 - 1 - 0 - 1 if you wanted, because , in theory, at any rate, backlash should be the same in both directions.

Under Config/Backlash enter the measurements and tick "backlash enabled". If you restart Mach3 these figures will be remembered.

This means that when Mach3 is traversing - if it hase to change direction on any axis, it will insert the extra pulses at the change of direction of the move to take up the "loose" movement of the screws, so that you maintain accuracy.

My lathe, when cutting a ball shape in the middle of a rod will traverse, then cut the G2 or G3 curve up to the crown of the ball and stop. Backlash is taken up (You can see the motors moving, but the table doesn't) and then it cuts down the other side of the ball. It leaves a faint mark on the work where it has changed direction. If the backlash was not enabled, there would be a flat area on the ball, where the Z axis (the main traverse) was still moving (because that has not changed direction) but the x axis was not moving because the backlash in the gearing was being taken up.
Not me driving the engine - I'm better looking.
Re: Cutting Circles
« Reply #6 on: November 08, 2007, 05:44:22 PM »
Thanks for your help. I just ordered a dial with a magnetic base. Don't know why, my table is wood. But thas all I could find.

Offline Chip

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Re: Cutting Circles
« Reply #7 on: November 08, 2007, 06:33:41 PM »
Hi, Rkjohn

Is this flat spot in line with one axis, Clock angle 9:00 3:00 X, 12:00 6:00 Y, or a combination of X,Y 1:30 4:30 7:30 10:30.

You could get started by enabling the backlash and putting in an estimated value's for X, Y or both X Y.

Thanks, Chip
Re: Cutting Circles
« Reply #8 on: November 08, 2007, 07:08:01 PM »
Chip
Thanks

The flat spots are on both X & Y. I'm in no hurry so I'll wait till I get the Dial...Just want to get it right so I can sell it. I'm about done with my new machine.

Ron
Re: Cutting Circles
« Reply #9 on: November 13, 2007, 01:46:55 PM »
I tested the X & Y with a dial & they both came out to "0" backlash. I built this machine very tight so I'm not supprised. Maybe I was running to fast. Any other suggestions?

Thanks

Ron