Reduce chatter in deep mortice

[rmueller1]

What is the best strategy for cutting deep mortices? I need a 1” x 4” mortice 3” deep I am cutting with a 1/4 end mill that is 3.5” long spiraling out from the center 1/16 at a time but there is still lots of chatter and backlash making it difficult to get a smooth accurate cut because the bit is so long.

[jfederer]

I strongly suggest you move up to a half inch cutter, They will be enormously stiffer at that length. Both Freud and Amana make long half inch diameter straight cut bits.

[Leo]

I agree with Joe. Use a 1/2" cutter - or bigger if possible.

You could maybe drill out the majority of the material first.

[adze_cnc]

Cross-linked to: viewtopic.php?p=271793#p271793

[ger21]

Even a 3/8" tool would be much better.

[jerry carney]

Try a 1 in. fly cutter , light cuts.FYI

[GEdward]

but there is still lots of chatter and backlash

I agree with the above comments to the extent that the larger the diameter of tool the stiffer and more resistant to flexing it is. Other factors that play into vibration and chatter include the pitch angle of the cutting flutes, the number of flutes, rpm, feed rate, material being cut, the sharpness of the cutter, how rigid the machine is etc. etc. You also mention backlash as an issue. Many controls will let you compensate for backlash to accurately position the axis' but that does not eliminate backlash. If you have excessive backlash in the mechanical side of the axis drives then perhaps it would serve you well to reduce it to the extent that you can. It is my hope that simply increasing the diameter of your end mill, as suggested above, takes care of your issue. But if it doesn't, then these are some of the other considerations you might investigate.

Ed

[adze_cnc]

Your post ("Drilling out mortices") cross-linked above is pretty much the solution I'd use if all you have is a 1/4" cutter. (see attached file) It's based on how we used to do things manually: drill a bunch of holes and clean up the sides with a chisel but in this case the chisel is a profile toolpath.