End Mill wandering under load?

Hi All,

I’m looking for a list of things to check when see the end mill being pulled off track by the load on the end mill.

I was conventional milling some oak and the load should not have been too much on the end mill. By the path it was taking it seemed to be pulled off course to the point were it ended up breaking.

The spindle is the one that ususes 3.17mm end mills.

I’ve done the 30 minute stiffening mod already. Given I’ve had good results in the past, I’m thinking the machine needs some maintinence.

What are your suggestions?

Please share the easel file or the details of your carve settings.
I suspect a cut depth that was too aggressive.

1 Like

You should also tell us about the bit you are using. We understand that it’s the 1/8" (3.17mm) shank.

I was snapping a lot of very thin bits in oak as well. There can be several causes. If the bit is quite long and your are taking shallow passes, that makes for a lever action that can break bits near the collet. Another factor is if you are cutting deeply and the bit begins to grab along the channel it is cutting, that puts a lot of torque on the bit which can snap the bit on the shank.

I found that be small bits could deflect quite a bit and that they wanted to follow the grain.

The cut that ended up snapping the end mill was supposed to be a finishing pass on a face. The depth was 17mm but the amount to mill off was only 0.5mm and I set the maximum stepover to 0.303mm. Other cuts were only 1.5mm deap and still wondered. I was milling oak.
The endmill was a single flute spiral upcut.
Cutting feedrate: 1270 mm/min (Hmm that’s a point perhaps I need to recheck the recommended hardwood feedrate).

My generic data sheet suggest a chip thickness of 0.03mm per tooth per revolution for Hardwood.
With 16k RPM as a basis this equal approx 480mm/min for feed rate.

What diameter is your cutter, 1/8"? We know your shank is, but the actual tip)

Hmm perhaps I’m pushing it too hard as you say. I still need to check the cutting data. the tip was in fact 1/8 too.

Last few projects have been MDF and Pine.

Time to check the data sheets for hard wood. that woudl explain something.

I definatly saw it follow the grain. at the beginning i did a facing pass and instead of cutting all the way through I say it split slivers of wood along the grain lines.

Do you think that perhaps climb milling might help? I read in the fusion help that climb milling was for more rigid machines, but in this case it may have saved the job.

OK at least one problem is the chipload for hardwood for the type of cutter is about 0.002 - 0.004.

At .0.004 the feedrate should have been between 1000 and 800mm/min. Given I know the machine isn’t rigid like an industrial one, I should have been more conservitive with a .0.002 chip load. and set to 75% of the rated feed rate I should have set the feed rate to 400mm/min.

Bummer - I guess it’s user error then.

Thanks for the help!

If tools of larger diameter than 3mm break its usually due to excessive chip thickness.
Either the rates are poor or the bit is allowed to deflect, causing thickness deviations = feed rate + flex + deflection
This is the main bit killer, assuming cutter is still good and not dulled down/bogged up…

Goood thinking to start with 75-80%, but more importantly reduce your depth per pass. You may have good results at 100% but shallower passed. Thickness is theoretically the same regardless (at a given feed rate/rpm) of depth per pass, but chip load increase with deeper passes.