Cut dimensions are wrong

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Re: Cut dimensions are wrong

Postby AlanAndrews » Mon May 28, 2018 10:23 am

Thanks Bernie,

Looks like the gcode and material setup is in inches, yet you seem to be working with mm for your original model dimensions and cutter. Is this correct?

Why are you mixing between inch and metric? Most confusing
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Re: Cut dimensions are wrong

Postby BernieNUFC » Mon May 28, 2018 11:06 am

Hi Alan

Yes you are right, i have been mixing 'in' and 'mm', i have been trying both in and mm posts to see if it helps, also my Router setup is in 'in' so i try to build the models in 'mm' and then at final part i change it to 'in' and then post.
you are right it is confusing but i am at early doors and finding my feet, i am at an age where i schooled in 'in' and converted to 'mm' so i dont find it too bad :-)
well spotted that man
thanks malc
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Re: Cut dimensions are wrong

Postby Adrian » Mon May 28, 2018 11:13 am

It doesn't matter what you use when designing as long as the post processor you matches what your control software is set to. If your control software expects to see files in inches then you need to save with an inches post processor.

I mix units all the time with most of the tools being metric with the speeds in inches per second but my ShopBot is set to millimetres so I always save using a mm processor. Some post processors and control software are setup to automatically switch units but I always find it easier to make sure the two match so it's one less thing to worry about.

If your other software is cutting the piece ok then you should be able to compare the two files to see what the difference is.
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Re: Cut dimensions are wrong

Postby BernieNUFC » Mon May 28, 2018 12:50 pm

Hi Adrian
My control software is mach 3 in inches, the xml that came with my CRP setup is that way unfortunatley. I dont have enough experience to change it or reset it to mm.
I have to say one of the reasons i like VCarve so much as you are able to produce good quality and variety of work from the outset and just gets better the more you use and develop with it.

Trouble is i need now to understand G Code so i can see how to resolve issues, always a challenge :D :D :D

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Re: Cut dimensions are wrong

Postby AlanAndrews » Mon May 28, 2018 1:36 pm

Bernie, can you provide the vcarve file that matches with the sample g-code you have already provided please. Only with these 2 files can we attempt to highlight any potential issues that may attribute to this dimensional mismatch.

Many thanks
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Re: Cut dimensions are wrong

Postby BernieNUFC » Mon May 28, 2018 3:02 pm

Hi Alan
Here is the file i generated the g code in vectric.
i would have also added the g code generated from other software, it may have helped it may make things a whole lot worse :-), but .tap is not allowed and i thought better of renaming it at this stage

New.crv
(139 KiB) Downloaded 9 times
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Re: Cut dimensions are wrong

Postby adze_cnc » Mon May 28, 2018 5:14 pm

Fascinating. In the "new.crv" file the bit is specified as having a 3.15mm diameter. The bit name mentions 60-102 which looks suspiciously like an Onsrud part number. Sure enough there is an 1/8 inch Onsrud bit with that part number.

So, in your tool database why are you not specifying the bit as having a 1/8" diameter? 3.15mm is approximately 0.124 inches rather than 0.125 for 1/8". No wonder the cuts are smaller.
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Re: Cut dimensions are wrong

Postby BernieNUFC » Mon May 28, 2018 5:44 pm

i see that level of accuracy is not achievable in my mind with wood so i can live with .001 x 2 :-), as soon as the temp changes a degree so the wood expands or contracts.
the other is that i mentioned that the outside cut of the object was spot on (not to the .001 but close enough) the cut outs and circles we are talking about 1.5mm diff
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Re: Cut dimensions are wrong

Postby adze_cnc » Mon May 28, 2018 5:58 pm

My apologies.

I saw 3.15 and was thinking in 1/100s. When I compared 0.125 with 0.124 I was thinking the difference was an order of magnitude off of what it is. Had I seen 3.150 I might have kept my decimal places in concert.

Still. Enter the tool as 1/8" and let the software deal with things. Or, if you must use mm, then use 3.175 mm and 6.350 mm for 1/4".
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Re: Cut dimensions are wrong

Postby BernieNUFC » Mon May 28, 2018 6:12 pm

I can not argue with your comment there, thank you for the heads up
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Re: Cut dimensions are wrong

Postby AlanAndrews » Tue May 29, 2018 1:34 pm

Hi Bernie,

an update.

I have loaded your test file in to my machine. I use a 1/2" shank, 3.2mm straight cutter - this is the smallest cutter I go to.

I generated a new g-code file (fanuc mm) and run the test piece.

I then zoomed to one of the joint slots and overlaid the profile outside toolpath. I established the positioning points for the 4 corners of the slot toolpath, and confirmed that these were within the g-code file.

I then loaded a piece of scrap material g-code file. Everything has worked out true to your dimensions.

So I'm convinced that the error lies with your machine....either the bit is flexing (doubtful this amount), the motors are dropping steps (doubtful as your other dimensions are true, but perhaps as a result of material build-up in the confined cavity of the slots and small holes), and/or there is some backlash in the machine drive.

I suggest that you try a couple of things....

1. do an extremely fine cut and measure the output. A cut that is just sufficient to cut and mark the upper surface so that you can measure.

2. redo the toolpath so that the cutter is moving in the opposite direction to that you normally use. repeat 1.

Let us know if you find anything.

Al

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Re: Cut dimensions are wrong

Postby Adrian » Tue May 29, 2018 1:50 pm

I would think the same were it not for the fact that the same parts are coming out correctly when generated from different software. It would seem to point to a speed, unit, G code macro etc problem in the output file rather than a physical issue.
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Re: Cut dimensions are wrong

Postby BernieNUFC » Tue May 29, 2018 3:53 pm

Thanks Al and Adrian

Its all relatively new to me at this depth so if do not reply straight away its becasue it takes me time to do a setup and get it all running.

Thats a great way to test if the cutter is the issue Al

i need to establish some base lines to work from as i have changed a number of things now to chase this so a start from the beginning might help.

I will certainly let you know

The machine is brand new, that said it was me who set it up, but i had good help from CRP and i think its about as good as it goes, but its still at the settling in period :-)

Cheers Malc
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Re: Cut dimensions are wrong

Postby Adrian » Tue May 29, 2018 4:17 pm

Probably the quickest way is to go through what you've done in VCarve and what you've done in your other software and then look at the parameters etc when those files are loaded into your control software. If one cuts perfectly and one doesn't as you say then there should be something that stands out as being different between the two files.
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