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So I have a bit of a question about using a CNC to clean up the outer contour of a specific shape. The first image is a bunch of the test runs I did and what the profile is.

Now the second image is what my boss wants to be the finish quality of it. Now we just bought a very cheap as CNC from someone who got it from an auction. Now one of the thing that my boss want the CNC to be able to do are these profiles which are wall brackets, there is another profile like this that he wants me to do but is more complicated. The way we usually finish these wall brackets is sanding it and then routing the edge with a cordless router. The other wall bracket profile my boss had a custom made 5-6" diameter bit for a shaper/router table that finishes the surface and routing the edges in one pass. My boss wants to see if I can do the same surface finish using the CNC just for faster production and if you see how he has to set up the shaper and the jig he using is very sketchy and no one in the entire shop wants to do it so my boss is the only one that does it and he wants it so he doesn't have to do it.

Ok back to the question. Now the second picture is what it looks like once its been sanded and routed. The third picture is what I'm getting with the CNC. There are some part of it where the bit chatters creating bumps and ridges on the surface almost like bit is bouncing on the surface. Last picture is the bit I'm using which is a straight bit. It is a clockwise turn and I have it running at about 12-14000 rpm and roughly 100in/min. The wood is poplar. On the first image is the path that I take on my test runs. The bottom left curve usually is smooth-ish but once it starts doing the curve of the second path around the center of the curve where it moves down the curve is usually where the chattering and vibrations start.

Now I have tried to change some settings on Mach3 like CV feedrate making sure Constant Velocity is one and all that kind of stuff. I've been going through multiple forums seeing if anyone my have an answer for why it starts to vibrate when it does a curve. My boss now suggested for me to try flipping the profile and going the opposite way I was going. I don't know if I should speed up the bit or lower it or speed up the bit and lower the feed rate. I'm planning on buy this bit which is a compression bit, same diameter and length but it is expensive and I'm buying this on behalf of the company on my own card so before I buy it to see if it will give me a much cleaner and smoother finish I want to know what your guys' thoughts if I can make the straight cut finish it like the sanded down version.

A little note: I an not cutting this wall bracket piece. I am only running the bit along the contour of it and only taking out 1/16 - 1/18th of an inch or 1 - 3 mms of material to try and smooth out the surface from the band saw and I am using the entire length of the bit along the contours of the bracket.

TLDR: I want to use the CNC to create a similar surface finish to the sanded down version of the wall bracket with a straight bit but encountering problems with the bit vibrating and chattering parts of the wall bracket. Boss said I should try flipping/mirroring it on the y-axis to see if the problem is "climb cutting". I want to buy an expensive compression bit on my behalf of the company but holding off to see what your guy's recommendations are.


Thanks,




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Hi. Have you thought about breaking your profile vector up so you can do climb milling on some parts, and conventional milling on others. If you use the same technique throughout on a part like you picture, you will on some curves be picking the grain up.
 
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