Poor edge finish on CNC router

[Dean Flannery]

Hi folks,
I just got a cnc router and am trying to make some parts with little sucess.
The parts are made from cherry, walnut and oak ranging from 1/4" thick to 3/4" but the finish on the edge is terrible, it looks like a series of fine sawtooth marks and when its running it makes a lot of noise almost like a squeel.
I am running a 1/4" dia 2 flute spiral upcutting bit at 16,000 rpm and 40 ipm feed rate.
The finish on the thicker parts is better than the thinner parts. (? why)
Any help would be appreciated.

Thanks, Dean

[Mitchell Andrus]

Sounds like you're getting "chatter" or tool bounce. Try making the "cut" pass leaving the part 1/16" larger than needed. Then make the "cleanup" pass the correct size to knock off the last 1/16", and the tool marks.

Mitch

[Doug Jones from Oregon]

Dean, how are you holding down your parts? Is it possible that they are moving slightly?

I would suggest going to a larger bit, less chance of bit deflection.

Doug

[Ed Lang]

If I did my math right, your chipload is 0.00125 which is way too small. I work in inch/sec but I would want a chipload of 0.005 to 0.020 in hard woods and 0.002 to 0.020 in softwood.

With a .25" 2 flute cutter and 16000 RPM on the router/spindle I would be running about 5 to 5.5 inch/sec or 300 inch/min. I would then vary the speed/feed from that starting point.

Part hold down is a BIG factor as was said above.

Another think to look at is where is the best edge? On the part or the scrap? You might be running your toolpath in the wrong direction.

Let us know how you hold the work and how speeding up the feed rate does.


https://www.onsrud.com/xdoc/ChipHardwood

The above link might help as well.

[Dean Flannery]

Hi folks,

After reading these posts and talking to a couple of cutter reps it appears my feed rate is way to low. I am using a vacuum table to hold the parts down and will try increasing the feed rate as long as I can hold the parts down.

Regarding the better finish on the thick parts vs thin, one rep told me the length of the cutting edge should be no more then half the thickness of the wood you are cutting for the best results.

Thanks for the help.

Dean