G Code dropping

G Code dropping

Postby Pete Howlett » Sun Jul 16, 2017 1:15 pm

We have had a problem with two machines and are finding it hard to identify. We do not suppose it's a hardware issue because the CNC we had and have now, when functioning worked well. The problem however has been the same in use with each machine. We can have components being routed perfectly and then suddenly. the toolpath drifts and the machine does not know where it is. When we return to zero all axis are out. I have a video of the problem on private view if anyone knows what the problem may be and would like to help us out. You would need to send me your email address to be put on the distribution list to view it as this is a private YouTube video - I don't want this to be out there in the public arena.

We use a simple CAD programe and Vectric software to design. File import into Vectric software is usually a dwg file. We then use Vectric software to plan the cutting regime and generate the GCODE. As recommended by our supplier this is done on a separate laptop. We use a USB stick to transfer the generated GCODE and load into MAC 3 on a laptop operating in airplane mode and with screensaver etc turned off. In most cases the error occurs part way through the cycle...

Thanks in advance

PS: If you could reply in words of one syllable that would be a great help - I am technologically challenged (I'm an Artisan craftsman building ukulele -http://petehowelttukulele.com) and my assistant is German with a fairly good command of English as a second language. We both however are geekless when it comes to computers and technology. I know this is a big ask but if anyone is in the North Wales area and is familiar with this software I would pay them for a day with us and our machine :)
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Re: G Code dropping

Postby IslaWW » Sun Jul 16, 2017 1:47 pm

Pete...
You can send a link to my gmail address in my signature panel, lower left. I would also request bit size, type, feedrate, rpm and material type, if not stated in the video.
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Re: G Code dropping

Postby ger21 » Sun Jul 16, 2017 2:01 pm

If the laptop is running Mach3 through a USB connection, then the PC is likely not the problem.

My guess is that it's mechanical? Possible a lack of lubrication? Or the motors may just be setup too soft.
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Re: G Code dropping

Postby Pete Howlett » Sun Jul 16, 2017 4:09 pm

Machine is brand new and the axis run very smoothly. Could it be a laptop issue - app working in the background?
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Re: G Code dropping

Postby Pete Howlett » Sun Jul 16, 2017 4:18 pm

YouTube link sent. I'm in the workshop tomorrow and will do a run and film the entire process for you. We are running an 8mm cutter at 20mm/sec at a speed of 22000rpm, depth of cut 4mm and a 6mm stepover. I ran it previously at 10mm sec. I did not that there were some 'hard stops'/jolts at the higher speed when the cutter changed direction.... Speed to high maybe? Is there a standard chart for cutting speeds in wood?
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Re: G Code dropping

Postby Adrian » Sun Jul 16, 2017 4:47 pm

Which make of bits are you using? Most manufacturers supply chip load figures which would give you the starting point for the feed and speed rates. You can use other manufacturers tables to get you in the ball park as well. For example https://www.vortextool.com/images/chipLoadChart.pdf - as one of many that are available.

The feed rate does depend to a large extent what your machine is capable of though. For my machine your RPM would be way too high and the feed rate way too low at that sort of cut depth. I'd say you're going to wear your bits out very quickly with the RPM that high.

The jolts/shocks can be a sign that the acceleration/deceleration of the machine in the controller software hasn't been setup correctly.
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Re: G Code dropping

Postby Pete Howlett » Sun Jul 16, 2017 5:38 pm

This is very helpful. However I am not very good with written explanations and find that link to a completely incomprehnsible data sheet. I use a twin fute 8mm spiral downcut solid carbide cutter. I have a cut depth of 4mm with a stepover of 6mm. My router can run at anything froom zero to 20,000. It would really help if those who know about these things could simoly say - yep a rate of 10mm/sec is good but 18mm/sec would be better... because if it is not a hardware issue (our machine was factory installed for us and it has had just 3 hours use) it must be totaly down to our programing toolpaths and feed rates?
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Re: G Code dropping

Postby ger21 » Sun Jul 16, 2017 6:41 pm

Do you have a link to your machine?
On issue is that different machines have different capabilities, so what works on one machine may not work on another.
I ran it previously at 10mm sec. I did not that there were some 'hard stops'/jolts at the higher speed when the cutter changed direction.... Speed to high maybe?


This may be a limitation of your machine. You may be pushing it to hard.

Could it be a laptop issue - app working in the background?


It shouldn't be, because the USB controller should be handling the motion control. But one thing to check is to open Task Manager while the machine is running and monitor CPU usage.
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Re: G Code dropping

Postby Pete Howlett » Mon Jul 17, 2017 9:43 pm

Well I lowered the feed rate, reduced the stepover and depth of cut and hey presto, after a very long time a successful electric ukulele body was cut out.https://www.facebook.com/photo.php?fbid=10155482079446031&set=pcb.1586894458010087&type=3&theater. Thanks for helping me think this through.
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