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Depth cuts

3/7/15       
Jerry Newman

I use Vortex 3/8" compression bits for most of my CNC cutting. My machine is old, slow, and I gave up on the vacuum and simply use screws at the corners now. So, for 3/4" sheets I do 2 passes, the first at 1/2" and the second a through cut.

My problem is that I end up with a line on my parts at that 1/2" initial depth cut after just a few sheets with a new bit. I'm sure part of the problem is that my feed rate is too slow. But my machine (Digital Tool) isn't designed to run as fast as the feed rate should be. So, aside from bumping up my feed rate, is there any setting in MasterCAM I could use to improve my cut results and/or get better life out of my tools?

3/7/15       #2: Depth cuts ...
Gary B.

Jerry,

What is your feed speed? Cutting is all about finding the appropriate chipload for the cutting edge. If you can't speed up the feed speed, try slowing down the rpm of the spindle.

3/9/15       #3: Depth cuts ...
Mark

You have a couple of unique problems.
With no vacuum, onion skinning (which is a little different than what you are doing but the principle is the same), that is using 2 passes is difficult since there will be vibration pulling the sheet up and down in the middle some. At the same time making a full thru cut Is going to be harder for you because your parts will have a lot of side force and want to move.
All this is usually exacerbated by machine flex, making the bit is a few thousandths away from it's true programmed position. This is especially true with a small light machine, and even more so with poor or no vacuum.
3 things to try:
First, be sure you are separating the parts in the nest by say 30 thousandths. Many times a cut from one part is interfering with a cut from the next not due to bad programming but due to the machine flexing and the sheet vibrating.
Second is making the first cut 5 to 8 thousandths larger than the second cut. This will trim away whatever line would have been left on the second pass.
Third is try cutting the first pass in climb and the second conventional. In climb, any flex in the machine or in the sheet will pull the bit slightly away from the part. The second conventional pass will run truer, or in your case even bias it toward the part slightly, eliminating the line. If none of these work alone try all of them together.

3/9/15       #4: Depth cuts ...
Jerry Newman

Mark,
I do keep 1/16" gap between parts. I like the idea of doing a wider first pass and then a true final pass. There is a setting in MasterCAM where I can do that. I'm also thinking that a climb cut for both passes might help.

Thanks

10/13/15       #5: Depth cuts ...
Joe Fitzgerald

A bad lead in/lead out can cause a dead spot in a bit, which I believe is what you're saying you have. That and a lack of rigidity of your parts will wear them out quickly as well. Had seen similar issues on a old multicam a few years ago that ran painfully slow compared to my new scm universal 20. He was using less aggressive cutters. I can't recall the number but it was a basic onsrud cutter...


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