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Machining relief problems
« on: July 26, 2019, 04:08:42 AM »
Hi guys,

I'm trying to machine a relief designed with Fusion 360 derived from a jpeg, what I'm finding is the tool continually goes deeper into the job, where it should be carving at a maximum of 3mm its cutting down to more like 17mm and not much of a profile to be seen.

I'm using a small Chinese cnc machine and I don't have any trouble engraving shapes and text.

I recently bought a mach1 license hoping that would make a difference but that only allowed more lines to be processed.

I don't know if its the CNC or mach3 settings at fault

I have attached what I think is the config xml, the Confcheck text and the item .tap file

Thanks for looking at this for me
Regards Chuck   
« Last Edit: July 26, 2019, 04:10:55 AM by ChuckAustralia »

Offline Tweakie.CNC

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Re: Machining relief problems
« Reply #1 on: July 26, 2019, 05:01:12 AM »
Hi Chuck,

Welcome.

Your Gcode and Mach3 set-up seems to run just fine here with a maximum Z depth of -5.848 mm in your test Gcode file. If your cutter is going deeper than that then two possibilities spring to mind...

1) Your cutter could be loose in the collet and it is moving during the cutting operation.
2) You could be loosing steps on the +Z axis moves - try reducing the Z axis Velocity and Acceleration (in Motor Tuning) by 50% and save the changes - does it still cut too deep ?

Tweakie.

Another thought comes to mind - is your spindle motor tight in it's clamp ?
« Last Edit: July 26, 2019, 05:03:46 AM by Tweakie.CNC »
Success consists of going from failure to failure without loss of enthusiasm.  Winston Churchill.
Re: Machining relief problems
« Reply #2 on: July 26, 2019, 06:05:33 AM »
Thanks Tweakie,

Both the cutter and Spindle are tight, I can actually watch the Z axis (spindle) move down while in operation, it almost bottomed out onto the work piece.

I will try reducing the Velocity and Acceleration and let you know how it went.

Cheers Chuck
Re: Machining relief problems
« Reply #3 on: August 21, 2019, 02:34:57 AM »
Finally got a chance to reduce Z axis Velocity and Acceleration, but still cutting too deep, the cnc seems to be cutting at an ever increasing depth each row, starting at approx. 2mm to 13mm halfway through the job where I cancel.

Could it be the control board for the cnc not understanding the commands, although I can engrave and cut shapes without any problems.

Could there be any differences between .tap .nc files that could be causing this?

There are no problems when run through a simulator.

Thanks Chuck

Offline TPS

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Re: Machining relief problems
« Reply #4 on: August 21, 2019, 03:38:10 AM »
what does the z-axis DRO Show, allways the same value or is it also increasing?
anything is possible, just try it.
if you find some mistakes, in my bad bavarian english,they are yours.

Offline Tweakie.CNC

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Re: Machining relief problems
« Reply #5 on: August 21, 2019, 03:49:59 AM »
Does you Z axis have weight - ie. could a counterbalance or gas strut reduce the mass when it is travelling in an upward direction ?
Success consists of going from failure to failure without loss of enthusiasm.  Winston Churchill.
Re: Machining relief problems
« Reply #6 on: August 22, 2019, 01:29:50 AM »
what does the z-axis DRO Show, allways the same value or is it also increasing?

It shows the same values as the gcode
Re: Machining relief problems
« Reply #7 on: August 22, 2019, 01:36:51 AM »
Does you Z axis have weight - ie. could a counterbalance or gas strut reduce the mass when it is travelling in an upward direction ?

I'm at a loss with this Tweakie, I would have thought to remove weight if that would be the answer, there is only the weight of the spindle and minimal weight from the Z axis casting.

Offline TPS

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Re: Machining relief problems
« Reply #8 on: August 22, 2019, 02:46:45 AM »
so if the Z-DRO Shows correct value, there are IMHO following possibilities:

-z-axis machanical loose
-z-axis loosing step's during Lifting
-additional steps are indicated by electric noise

for a test you can run following simple GCode

Code: [Select]
M98 P123 L100
M30

O123
G90 G1 Z-5 F250
G1 Z0
M99
%

it will only run Z-axis a hundred times to -5 and 0 (you can stop it any time).
here you will see wether your z-axis moving down or not when it is running "standalone".
if not i would run the same test with spindle turned on (electrical noise).
and then with X/Y movement added.
 
anything is possible, just try it.
if you find some mistakes, in my bad bavarian english,they are yours.
Re: Machining relief problems
« Reply #9 on: August 23, 2019, 04:22:32 AM »
Thanks TPS,

I ran the code with and without the spindle running and it didn't go any further than 5mm (not up on programming X/Y movement)

Do you think it could be due to computer power 2ghz processor, 3gb memory, Vista operating system.

I don't have any problems with simple tasks such as engraving and cutting shapes