Annoying milling cutter diving into the work

After taking the time to clean, square-up, mill to size and slot a part:

When it came to widening the slot (from 10mm to 22.8mm), the 10mm 4 flute milling cutter decided to dive into the work:

... and I have no idea why.

The part didn't move (it was still tight on it's parallels), so either the cutter was pulled from its holder or the quail was pulled down. However, although the quill was not locked (is this compulsory?) it was set to wheel (rather than big-pull-down-leaver-thing [scientific name]).

Any ideas?

Are you inserting the collet correctly into the nut before inserting tool and tightening it up? Are you doing it up tight enough?

Yes best to lock quill and head to column

How much did you move the cutter over per pass and what is the height of teh slot?

Edited By JasonB on 19/05/2020 13:52:04

Hi Lee

Lock all unused axis when milling, also if you are climb milling put a bit of pressure on the axis used gib to save it grabbing.

Emgee

Looking at the picture seems you were climb milling to increase the slot width.

Edited By Emgee on 19/05/2020 13:54:53

I believe I'm inserting it correctly. The collet is gripping the plain shank and I did it up pretty tight.

1mm DOC. The cutter was touching, but not cutting the bottom of the slot at the time.

I wasn't climb milling (at least I don't think I was). Which picture are you alluding to?

The bottom picture, looks like the tool grabbed as soon as it got into the cut with travel from left to right.

Emgee

No, that's the end of the cut. It started shallow then went progressively deeper.

The cutter started to spin in the collet near the end, then carried on going, then span at the very end.

I was cutting from right to left on the edge closest to me - I think this is conventional milling.

Edited By Lee Jones 6 on 19/05/2020 14:15:28

Bottom right to top left equals conventional milling.

Always lock the quill when it's not being used.

If the cutter span in the collet then it wasn't tight enough. But given it started cutting again I suspect it's a combination of a loose cutter and unlocked quill. Pretty tight is a bit vague, I'd suggest around 100Nm, ER collets need to be tightened rather more than you might think.

Andrew

This is how to insert the collet

Was it a 10-9mm collet you used for the 10mm cutter

Hi Lee, Guys,

You can get ball bearing collet nuts, much easier to tighten properly.

One other thing with cheap collets, check them very carefully for burrs and swarf in the slits. I use a Stanley knife blade to make sure that the slits are clean and burr free. It doesn't take much for a loaded cutter to pull down.

I thought that I had posted some pictures showing some of the worst of mine ! After cleaning properly they are fine.

This is the sort of thing that will cause all sorts of problems. If the collet has been used before checking, these bits of swarf will get squashed and be both hard to see and even harder to clean.

Edited to add pictures:

Edited By John Baron on 19/05/2020 14:56:26

I venture almost everyone using ER collets for the first time falls into the trap of not inserting them properly into the chuck collar. The collet goes in at an angle and then clicks into position vertically. It's slightly awkward to do and unexpected. Done properly the base of the collet will be almost flush with the bottom of the chuck.

It's impossible to tighten the collet on a cutter sufficiently unless the collet has clicked in. Then the collet needs to be good and tight: ball-bearing collars are easier to tighten than the ordinary type.

Now I've sussed ER32, cutters only pull into the work when I forget to tighten them up.

Dave

Oh my goodness. Talk about a case of you don't know what you don't know!

• A 10-11mm collet was used
• The collet was not properly inserted/clicked properly into place (at least not intentionally!)
• The collet needed de-burring

Right, what else do I need to know - tell me everything!

Never mill with the quill loose. Even on my Bridgeport, i have the quill nipped up. It can be forced up or down so, dont invite errors, keep them at bay.

ER collets were originally developed for tool holding. Tool shanks are normally hard. So when the collet is closed they do not 'give'. So if using a larger than needed collet the contact area becomes a line rather than a surface. Collet, and tool, runout and other parameters are only guaranteed if the collet is used at it's maximum value.

Andrew

Either the quill was unlocked, or the collet was not tight enough, or a combination of the two.

If it is any consolation, I have had an End Mill pull itself into the work because the ER collet was not tight enough, when I took a heavy cut..

The helix on the flutes of the cutter will act like a screw thread and try to pull the cutter into the work.

(Which is one of the reasons for not using a Drill Chuck to drive an End Mill! )

Howard

Just looking at the first picture I would guess that the collet nut is not fully home on the body (at least, mine screws on significantly more than that) which suggests that the collet was not properly installed in the nut.

You will now also find it a lot easier to change collets as when snapped into the nut they are pulled out of the main body when the nut is undone, usually the nut loosens first then another turn or so and it will "pop" loose, This is when you need to be ready incase the tool drops particularly if you are using a cutter less than the max size of the collet.

A good milling for beginner series may be worth reading

When I bought my ex=school Novamill with ER16 collets, there was a tool in the chuck that was a complete pig to remove. Turned out that the collet was not clicked into the nut but the nut was tightened EVER SO HARD so it didn't slip. From other evidence the teacher in charge of the machine didn't have a clue.

For a 10mm cutter you should chose the 9-10 mm collet not the 10-11. Yes the 10-11 will tighten to 10mm but it takes a lot of effort. The only time I chose a collet that is larger than the size of the tool is when it is imperial.

If you have access to the MEW archive, there was a series called Milling for Beginners which started in issue 261, then is in every other issue. It is very good.

Adrian

Edited By AdrianR on 19/05/2020 17:24:42