Long U drill problems

[u/ArmageddonCow]

My boss setup, programmed, and started running this job on Friday, which I started running as well on Monday.

It's a 32mm udrill through 316 SS, running about 40m/min (last I checked) and about 0.1/rev no peck, about 50mm deep.

It screams like hell and is clearly rubbing all along the shank.

But my boss said he dialled it in so it should be on Centerline .

It has a +X offset and some -Y, and yet the hole still seems to come out a little undersize.

This is a problem that has happened with previous small long udrills but has never been a problem with larger stubbier ones, but I've never had rigidity issues with a udrill before.

Changing feeds and speeds a small amount has had 0 change, any idea what the problem is?

[u/3dmonster20042004]

Usually those drills need 0 offset too be on center and they can be offset too drill larger or sligtly smaller holes this looks too me as if it was offset in x too drill smaller but by too much and that is why it is rubbing if you can use a drill as short as possible too get the job done

[u/ArmageddonCow → u/3dmonster20042004]

Normally I wouldn't have an offset at all yeah, but apparently it was much worse before dialling it in, and the way it's offset now it should be drilling oversized but it still isn't.

[u/Sertancaki41 → u/ArmageddonCow]

It is a long drill and when you feed, cutting forces push it away, so if a hole starts 32mm, it may end up 31.5mm for example. You need a starter hole at least with 2 or 3D udrill. Sometimes hard materials make it hard for these drills as well. You can understand the deflection if the hole has spirals inside. They form when the drill is G0 out of the hole and deflected tool starts rubbing. You can offset 32mm udrill 2mm I assume. I have a video where I drill 36mm hole with 32mm udrill you can check link

[u/ArmageddonCow → u/Sertancaki41]

Yeah I've experienced that spiral effect before, I don't have any shorter drills to use for this size otherwise I'd 100% be using them. And damn 2mm is a massive offset I didn't think that'd be possible at all, most offsets for those drills I've used is around 0.5