Vibration with large bit

[bmurph]

I have a mini mill and am trying to cut 4140 with a 1/2" end mill. It vibraites like crazy, and even when I'm not moving the table, the endmill is slaping the workpiece. I have milled 4140 allright with small endmills, but I need the reach of a large endmill.

I read on the internet that ceramic cutters are 8 times faster then carbide. Maybe if I use one of them it will be like my mill is 8 times bigger?

[broby]

Sounds like you have a loose spindle problem.
If the tool is "slapping" the job without moving, then that is first area that I would check.
As for ceramic cutters being 8 times faster... well they are certainly faster than standard carbide, but there is a whole lot of things that need to be taken into account first!
1. is the job stable?
2. is the Tool STABLE? i.e. NO chatter, as that will shatter the tool.
3. no huge cuts, these are generally finishing tools only.
4. Expensive, compared to ordinary carbide tooling.

As for making your machine like it is 8 times bigger... nope! definitely gets the job done faster tho
Cheers
Brian.

[bmurph]

How do I check that, I can't make it budge.

I tried plunge milling with a regular endmill, and the head wobbled, but I can't make it wobble by hand. So I can only assume that there must be extreme forces that are bending the metal of my machine.

[wendtmk]

What are you using to hold the endmill?

Mark

[bmurph]

a quick change collet set from grizzly

[wendtmk]

You might want to check the runout on those collets, especially the larger ones where you are having the problems with the larger endmills. They may be seating solidly into the collet chuck, but if the runout is large enough, it could cause problems.

Mark