OOZnest CNC router going off course

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Re: OOZnest CNC router going off course

Postby ger21 » Mon Jun 05, 2017 3:45 am

mplsartist wrote:That's something I didn't know! I thought that the general rule of thumb was to have pass depths at half of the bit diameter.

My personal rule for bits 1/4" and smaller, is cut depth = tool diameter, unless the machine is not rigid enough. In some cases you can cut deeper. Your machine will likely flex way before the tool does.

I've accidentally cut corian with a 1/16" bit using a 1/4" depth of cut, with no problems. Chip evacuation is a bigger concern with smaller bits.

As for whether or not your spindle has enough power, you'll need to try it and see. Does your control software have a feedrate override feature, where you can adjust the speed while cutting?
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Re: OOZnest CNC router going off course

Postby Leo » Mon Jun 05, 2017 5:14 pm

The general rule of thumb that the cut depth of 1/2 the cutter diameter is generally for steel, not wood. Wood is easier to cut than steel, so the 1/2 the cutter diameter in wood is really conservative, but, what is really the issue is the rigidity of the machine. Carbide cutters do flex, but not very much. They will break, because they are very brittle. If you notice distortions due to flexing it is most likely in the machine.
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Re: OOZnest CNC router going off course

Postby mplsartist » Mon Jun 12, 2017 1:11 am

I thought I had solved the problem by replacing my shop vac hose for dust extraction with a lighter and more flexible clear vinyl and wire hose purchased from Woodcraft. I had several successful runs but now have a similar problem with a new file that occurred twice in the same spot at the front of the table. I then changed my overhead hose support by adding a second source of support (3/4" PVC t-joint sliding on a 1/2" metal pipe) but got the same result. I then took a photo of that set up (see attached). Upon looking at the photo, it looks like I may have too much hose hanging down on the right side of the router (hard to see in photo as it is hidden by the router). I'll try to adjust this so that there is not so much slack hanging down.

I also reduced my feed rate to 75 ipm. I noticed that this deviation also has a lot of compacted chips in the tool path while the one next to it does not. This has been common with previous attempts as well. Some paths are clear of chips while others are clogged ( no deviations on those ). I'm wondering if I should use an up cut bit instead of a compression bit (I'm cutting Baltic Birch from the back side as I have plastic laminate on the front). I'm also doing a climb cut and wonder if a conventional cut would be preferable as someone had mentioned previously.

Thanks for any help you can provide.

Toolpath deviation.jpeg

Toolpath deviation.jpeg
CNC hose set up.jpg
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Re: OOZnest CNC router going off course

Postby mplsartist » Fri Jul 07, 2017 11:20 am

I just wanted to give an update on my situation. I have now done 4 sheets of 4'x4' Baltic Birch, each sheet consisting of 2-3 dozen individual pieces without error. I decreased by feedrate to 40 ipm climbcut, switched to a spiral upcut bit (as someone suggested), and increased my nesting gap between pieces from 0.5" to 1.0". My OOZnest 1500x1500 is now cranking out the pieces like a workhorse without complaint. I still need to do some fine tuning because I'm still getting a lot of chatter marks on the cuts especially on the long straight cuts. I slowed it down to 25 ipm but with very little improvement.

I will need to cut some MDF soon as was wondering what the feed rate should be for that. I've heard some horror stories about combustion etc. Any suggestions?
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Re: OOZnest CNC router going off course

Postby shedman » Fri Aug 04, 2017 11:31 pm

On my 1000x500 ooznest machine I cut at 79ipm but only use a shallow cut never more than 1/2 bit dia and only use 3mm up cut bits, I've manly cut lite ply and mdf board and a little bit of birch ply. I too suffer from chatter marks on the cut edge and I think they relate to the pitch of the belts as the drive is one to one, I have just converted the X axis to a 3:1 reduction drive and will do the Y axis when I get time, just converting the X axis with the 3:1 gear box has inproved the cut finish and accuracy but it still wont cut a true circle this I am hoping will be ok when the Y axis has been done
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