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Author Topic: Accuracy and adjustment  (Read 3269 times)

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Accuracy and adjustment
« on: April 03, 2014, 03:25:09 PM »
Hi,

I'm new to all this CNC business, I've just got myself a router that came with Vcarve and Mach3. I've got to grips with the very basics and managed to cut my first 'shape' today which I'm rather chuffed about. Ok here comes the noob question! My second shape was a 50mm square, just to see how accurate it was ... it cut a 49mm square. I was using a 5mm cutter and a outside offset, all set in Vcarve. A couple of questions, what am I doing wrong and/or how do I compensate for missing mm?
I'm not making aero engines so I'm not that bothered about a quarter of a mm but I need to work out what's going wrong.
Any help would be much appreciated. Thanks in advance.

Offline ger21

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Re: Accuracy and adjustment
« Reply #1 on: April 03, 2014, 03:27:14 PM »
First thing you need to do is make sure the steps/unit are set correctly, and the machine moves the correct distance.

Lots of things can cause your square to be the wrong size. You need to start with the steps/unit.
Gerry

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Re: Accuracy and adjustment
« Reply #2 on: April 03, 2014, 03:32:06 PM »
Wow what a quick reply! Ok thanks, I'll try that tomorrow.
Re: Accuracy and adjustment
« Reply #3 on: April 05, 2014, 05:46:25 AM »
I checked the machine moved the correct distance and it was fine. I solved the issue by telling Vcarve I was using a 6mm tool, whilst using a 5mm tool. It's now bang on. I know it's probably not the proper way but it works for me!

Offline Tweakie.CNC

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Re: Accuracy and adjustment
« Reply #4 on: April 05, 2014, 07:08:03 AM »
If that solution works for you then that is the most important thing.  ;)

Just a thought - you could possibly have some 'run-out' on your spindle and the 5mm cutter is cutting oversize ??

Tweakie.
KEEP SAFE !

Offline Fastest1

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Re: Accuracy and adjustment
« Reply #5 on: April 05, 2014, 11:22:20 AM »
Though there are many ways to skin a cat as you have found out. There is still something wrong if you have to lie to the machine.

Does your code cut the square in 1 pass? If you cut to depth in a few passes, are the walls straight?In both the X and Y planes?

I want to die in my sleep like my grandfather, not like the passengers in the car! :-)
Re: Accuracy and adjustment
« Reply #6 on: April 05, 2014, 07:29:04 PM »
I'd cut the part again with tool compensation set to 0. Under that condition using a 5mm tool should yield a part exactly 5 mm smaller.  I'd also cut it twice, to remove as much tool deflection as possible from the measurement. If this works as expected then something is going on in the way tool compensation works. If it doesn't work then you've got something else going on.
Re: Accuracy and adjustment
« Reply #7 on: April 07, 2014, 10:03:43 AM »
I'd cut a 50mm square, then a 100mm square, then a 200mm square with the part zero at the bottom left corner of the parts and the same starting point on the machine.
The results should point to the error source,

 - Nick
Re: Accuracy and adjustment
« Reply #8 on: May 10, 2014, 05:35:44 PM »
Thanks for all the replies . I've been away and not been able to get on the machine. Very impressed with the level of help, thank you. I think I may of been a bit thick! I bought a couple of new tools and set a new preset in VCarve tried the above suggestions and they're just fine. The tool I was using was a old blunt(ish) thing that came with the machine just marked 'blunt'. I measured the end of the tool (cutting end) this was probably not the thing to do but I had nothing else to go on. It's a steep learning curve for me but it's good to know this forum will offer help when needed.