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Messages - Scott-tbs

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1
General Mach Discussion / Re: X Axis slowly goes wrong, every time.
« on: July 05, 2012, 12:54:14 PM »
Been busy!

Wrote some GCode that is basically G0 X0 Y0, G0 X30 Y30 in a loop, 200 times.
At the end I move to 0, 0 and then actually move to 0, 0 to see how far the machine has walked.

After 200 moves the machine had walked 2.5mm on the X axis.

I calculated 0.0125 mm backlash but after a retest it was still 2.5mm out. So it's not backlash.

I had some wobble on the bench from inertia from the motors so I broke out the welder for some angle supports. Solid now but a retest shows 2.5mm out.

Why always 2.5mm after 200 moves??

Changed Look-ahead to 1 move (Read this somewhere) No change, 2.5mm.....

Modded my CnC board to give some breakout wires, put these in to a new m542 driver board and...

Perfect!, no idea how a board was giving me 2.5mm error yet move the motors what seems perfectly.

So... Thead closed... Faulty control gear.

Thanks for your help.

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General Mach Discussion / Re: X Axis slowly goes wrong, every time.
« on: July 02, 2012, 01:41:14 PM »
Should have posted fully,

I'm milling a handle, a basic rectangle with 4 dips in it to make it more finger comfortable.

I've tried:
Pulse width from 1 to 5
Dir width from 0 to 5
Changing decimal places from 4 to 2
Acc/Dec time from 0.5 to 2 seconds
Feed speed from 3500 to 1500 and up to 6600 mm/min (I'm milling an expanding foam type material, Hardly any resistance)
Checked mechanical fittings, all tight

Noticed:
I'm always cutting clockwise, so always cutting in to the material and the handle bumps as it mills from X- to X+ cause an angle to appear on the Y+ side. So every time around its more Y+ than it should be. And milling the "mountain" shapes which should be the same on both sides has a steep incline on the Y- side and a shallow incline on the Y+

I'll try to upload a photo to show it in detail.

Can it be backlash? I though this would cause errors on both the + and the - of the movement? not just on one side?

3
General Mach Discussion / X Axis slowly goes wrong, every time.
« on: July 02, 2012, 01:07:22 PM »
Hi,

2 1/2 axis machine built up and everything runs ok in terms of keyboard movement. X Y Z all great.

Produced some G-Code from VisualMill and start the machine running.

But slowely, it drifts away on the Y Axis, in the same direction everytime.
As in, After milling around doing a curved handle shape the top edge has hardly no curve and the bottom has an increased curve.

A bit like, G01 Y100 and it moves 100, G01 Y0 and it moves 99, G01 Y100 and its now 101...?? Make sense?

The numbers I think are right on the screen but my Y axis is drifting further away all the time.

X is the same settings etc but it works lovely.

Any Ideas?

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