Need help with square pockets


I have been unable to get an almost square in my attempts to make a small piano keyboard I use bone as
the material for the keyboard and ebony wood for the keys for a jewelry piece i need to square up the pocket as much as possible for the aesthetic and for the fit of the inlay.
Here are pics of what happens when the cnc machine is cutting the pockets.
I am more of a crafter than a machinist and would appreciate help.

What feedrate are you cutting at? What size is this pocket? What size tool are you using? What controller? And what machine are you running this on?

A quick guess would be:

  • cutting too fast causing tool deflection (for small tools)
  • machine not rigid enough for how fast its cutting
  • controller smoothing/contouring mode set too high causing rounded corners

There are many things that could cause this…we will need more info to help you track it down. Post up some more info and I’m sure we can get you squared away.

first thanks for responding, I am working on a 3040 3 axis cnc machine its controlled using Mach3 my feedrate is 4673.60 using a 1.52 metric end mill for rough and a 0.32 end mill for finishing the pocket size is 4mm X12mm for the keys on the keyboard the spindel speed is 8000 rpm and advice would be welcomed.

I would recommend slowing down, especially for the finish pass. A tool that small will deflect/bend when cutting and cutting that fast with Mach3 I am betting that the CV distance is giving some some rounding based on the Acceleration/Deceleration to reach that speed.

You want to watch the way the tool cuts in the different materials you normally work with and observe the results when climb vs. conventional cutting. Conventional on a finish pass on an inside profile will sometimes pull the tool into the corners causing not so great looking results. I don’t believe that is what has happened here, to me I think that it’s simply running too fast. OR the machine simply is not rigid enough to keep the tool from wandering while cutting. Without being there and seeing it cut and inspecting the equipment…these are my best guesses as to what is causing your issue.

So, things to try:

1 - leave plenty material on the rough passes so your finish pass can clean up any variation left due to roughing.
2 - Slow the finish pass down so that you feel confident you are not running the machine too fast. Experiment with this on scrap stock and you will find the sweet spot.
3 - I am not sure if you are taking multiple depth cuts, but you could try doing multiple depths for the finish also to reduce the load on the tool to keep if from wandering. Wandering is my non technical term for Tool Deflection. I am not sure if that is what is happening or if it’s the CV that’s causing it. You will have to test to find out.

HTH Alex

Would just like to say that everything sounds reasonable to me I will , try some of your suggestions and let you know my progress,

Again thanks

You get a chance to work on this? Curious to know how its going.