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Author Topic: Cut parts are wrong size, CNC knee mill problem  (Read 21282 times)

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Re: Cut parts are wrong size, CNC knee mill problem
« Reply #20 on: July 26, 2012, 11:30:22 AM »
1000 line encoders
5TPI ballscrews, 0.2"
The number is somewhere around 1179-1184

The problem is that it cuts the inside too small now and the outside too big. The only way to fix it is to reduce the cutter diameter by 0.2mm in the solidcam. Because if I decrease the steps per mm, then the outside will be to size the inside will be even smaller. If I increase the steps per mm, then the inside will be fine but the outside will be too large. If the outside was too big and the inside was too big, than that would indicate that the steps per mm was off. It's hard to explain, but do you sort of understand what I was trying to say?

Sebastian
Re: Cut parts are wrong size, CNC knee mill problem
« Reply #21 on: July 26, 2012, 11:32:46 AM »
One more thing, should I turn off "Enchanced Pulsing" or increase/reduce the step & dir time in the motor tuning window?

Sebastian

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Re: Cut parts are wrong size, CNC knee mill problem
« Reply #22 on: July 26, 2012, 11:47:17 AM »
You could try with enhanced pulsing off but I would think it would be worse as 99.999% of people need it.
You could try increasing the pulse widths, try 10 and see or even enable sherline mode and see.
With your numbers I would say you have 1.5:1 gearing and that your steps per unit should be set to 1181.1023622

Hood
Re: Cut parts are wrong size, CNC knee mill problem
« Reply #23 on: July 26, 2012, 12:01:20 PM »
An interesting test.
 
Code and mill a circular slot like this sample.
If finished cut slot width is same as cutter dia., and the OD (boss) is correct, then how could the ID (bore) be too large ?  ? ?
...and vise-versa.
Here you are milling an OD and ID at the same time.
this will help to verify your measuring techniques as well as what the cutter is actually doing dimensionally.
Might lead to a clue.
Russ
Re: Cut parts are wrong size, CNC knee mill problem
« Reply #24 on: July 26, 2012, 12:11:51 PM »
My solidcam code test has been a horseshoe type shape as shown below. This allows me to pocket, lift z, lower z, and finish in one pass.

My plain circles have been generated by the mach3 cut circle wizard.

Sebastian
Re: Cut parts are wrong size, CNC knee mill problem
« Reply #25 on: July 26, 2012, 12:15:12 PM »
The horseshoe is the solid material left, revised pic.

Sebastian
Re: Cut parts are wrong size, CNC knee mill problem
« Reply #26 on: July 26, 2012, 12:30:54 PM »
Okay this is my idea of a game plan for tonight:

Brand new 3 flute 0.5" carbide ZRN coated bit (should be delivered today, says enroute)

Cut a 30mm circle with the following code that was generated by the Mach3 wizard:

F400
G00 Z10
G00 X8.55 Y0
G00 Z1
G01 Z-0.5 F50
G02 X8.55 Y0 I-8.55 J0 F400
G01 Z-1 F50
G02 X8.55 Y0 I-8.55 J0 F400
G01 Z-1.5 F50
G02 X8.55 Y0 I-8.55 J0 F400
G01 Z-2 F50
G02 X8.55 Y0 I-8.55 J0 F400
G01 Z-2.5 F50
G02 X8.55 Y0 I-8.55 J0 F400
G01 Z-3 F50
G02 X8.55 Y0 I-8.55 J0 F400
G01 Z-3.5 F50
G02 X8.55 Y0 I-8.55 J0 F400
G01 Z-4 F50
G02 X8.55 Y0 I-8.55 J0 F400
G01 Z-4.5 F50
G02 X8.55 Y0 I-8.55 J0 F400
G01 Z-4.9 F50
G02 X8.55 Y0 I-8.55 J0 F400
G00 Z10
G00 X8.65 Y0
G01 Z-4 F400
G01 Z-5 F50
G03 X8.65 Y0 I-8.65 J0 F400
G00 Z10
G00 X0 Y0
M30

Attached a pic below of the screenshot. Should I adjust my steps manually until this circle is exactly 30mm?

Then cut a 30mm profile circles with Solidcam gcode. If same size, then cut teh horseshoe?

Sebastian

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Re: Cut parts are wrong size, CNC knee mill problem
« Reply #27 on: July 26, 2012, 01:23:51 PM »
Have you adjusted the steps per unit to what I mentioned?
Hood
Re: Cut parts are wrong size, CNC knee mill problem
« Reply #28 on: July 26, 2012, 01:26:28 PM »
No I'm currently at work, will set it to that first then cut the circle with the posted g-code and see the result.

Can you verify that the gcode is fine?

If it's too small/big, should I manually adjust the steps? For example too big -> reduce steps, to small -> increase steps

Sebastian

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Re: Cut parts are wrong size, CNC knee mill problem
« Reply #29 on: July 26, 2012, 01:33:47 PM »
Code looks ok.
You have accurate ballscrews so if you have to adjust the steps from that calculated then you have something wrong and adjusting them by tweaking is not going to help in my opinion.
How are you measuring the ID and OD?
Hood