help again? ideas?

help again? ideas?

Postby 101179567skltd » Fri May 18, 2018 2:20 am

Hello guys, I have a 25x36 half home built half old dyna cnc machine. I was just cutting some cabinet sides for one drawer bases. The short x axis is deflecting(maybe) about 1.5mm in the middle of the cut then returning to 0. They are non supported rails but i have just put an extra bearing to stabilize the z. The cuts before and after the install are the same.
Could this be just the 5mm compression bit deflecting or a router issue?
Any one think i could just program an arc on those two sides to compensate?
Speeds are 20 ipm at about 8000 rpm.
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Left side one drawer base revised 1.txt
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Re: help again? ideas?

Postby IslaWW » Fri May 18, 2018 2:55 am

It's simple. Your toolpath parameters are allowing the bit to generate more force than the frame of the machine can withstand. You have 2 choices; slow down the cut speeds or reinforce the frame's motion components.
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Re: help again? ideas?

Postby 101179567skltd » Fri May 18, 2018 5:22 am

Thank you for a direct answer! These are new bits to me from centurion tools and i'm mostly trying not to have them burned up but not have it take all day either. i could speed the router up to 20000+ rpm or take the the travel down to 6 ipm or any combination of the two . Would you have any recommendations?
Thank you
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Re: help again? ideas?

Postby Leo » Fri May 18, 2018 1:03 pm

High RPM and Slow feedrate is not a good combination on wood. That WILL certainly burn the cutters.

There are tool calculations available to find the correct "chipload". The manufacturer will have some recommendations on chip load for the cutter.

When cutting there should be chips being made and not dust. Dust means heat is being generated.

I generally run my spindle 10,000 - 12,000 RPM and around 150-250 IPM. My machine is very solid and I can go much faster, but why? I like to be conservative.

Your machine may not be as solid, so the chipload calculations will need to be made to accommodate your machine
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Re: help again? ideas?

Postby ger21 » Fri May 18, 2018 1:36 pm

Even at 20ipm, your going to burn up your tools, as that's just way too slow for wood. If your machine is that "loose", all you can really do is take shallower passes.
For the machine to be useful, you're going to want to make it more rigid. I'd consider 100ipm to be the minimum that you should shoot for.
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Re: help again? ideas?

Postby 101179567skltd » Fri May 18, 2018 5:12 pm

Well I tightened the x bearing up a bit and can get the machine up to 60 ipm and the drift is down to about a little over .5 mm in the center. Still to much for me but better! I think i'm going to do a final pass slower and take off .0197 inch to try and straighten things up . I don't know if that's too much in one pass though?
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Re: help again? ideas?

Postby ger21 » Fri May 18, 2018 6:36 pm

No, it shouldn't be.
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Re: help again? ideas?

Postby Leo » Fri May 18, 2018 6:39 pm

Rule of thumb is Depth of cut to be 1/2 the diameter of the cutter.

Really - consider what I said about chip control -- you can turn your RPM down a bit.
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Re: help again? ideas?

Postby ger21 » Fri May 18, 2018 7:29 pm

Leo wrote:Rule of thumb is Depth of cut to be 1/2 the diameter of the cutter.


Not sure who came up with that rule, but I don't use it.

I use depth = diameter for 1/4" and smaller bits, and no depth limits on larger bits. But machine rigidity plays a role here with larger bits.
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Re: help again? ideas?

Postby 101179567skltd » Fri May 18, 2018 8:34 pm

I guess my machine is not rigid enough or fast enough to keep up with proper chip load and I can only make the best compromises to get this job done without going through $150 in bits. Vectric has been a lifesaver in getting things programed though after fighting with cabinetparts pro for two months. I think it is time to put out some money for a 4x8 machine that I don't have to find work arounds for every new project I do. I Appreciate all you guys advice and will be back for more!
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Re: help again? ideas?

Postby 101179567skltd » Fri May 18, 2018 10:03 pm

Back so soon! I have just encountered a new problem!! I have moved the speed up to 75 ipm and the pockets have now missing corners that look like the tool took a shortcut to speed up. Just looking at it i wood say it missed steps but when I rerun it the holes are exactly in the same position and the pockets are more or less the same maybe a little better. Do you figure a mach 3 problem?
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Re: help again? ideas?

Postby IslaWW » Fri May 18, 2018 11:17 pm

Most likely Mach CV settings
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Re: help again? ideas?

Postby 101179567skltd » Sun May 20, 2018 3:05 pm

Interesting, this is the next chapter of the story. I had to turn the acceleration down the faster I run. The y will run 150 ipm but looses steps like mad with a high acceleration and so does the x at the end of travel (where I think the machining is a little out) do to lack of motor power. I will have to read up on the best settings to run.
Thank you again!
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Re: help again? ideas?

Postby 101179567skltd » Tue May 22, 2018 5:16 pm

During my reading I found that G100 Adaptive NurbsCV is obsolete I don't really know what it does but it is checked on in the settings . Should it be off? Also it its set for 100 units and i can't find a hard rule of what it should be. Turning it down to 1 wouldn't slow this machine down too much but then maybe I should just turn ES on. Thought?
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