metric end mill in imperial R8 collet

**dspahn** · 02-23-2021, 03:15 PM

I was wondering if it would be feasible to create a split sleeve for a metric end mill such that the sleeve's ID = end mill OD, and sleeve's OD = R8 collet ID?

Example: You want to hold a 6mm shank end mill in a 3/8" R8 collet. So you create a sleeve with an ID of 6mm, and OD of 3/8" and then split the sleeve along the Z axis.

Do you think this would work? Thanks!

**Milland** · 02-23-2021, 03:49 PM

It'll work, just do a good job on ID and OD to ensure a true, straight, coaxial part. Good finish too, a rough finish will collapse somewhat and open up the tolerances. Make from a clean cutting steel, perhaps a 4140 pre-hard if you want it to last.

Leave a short shoulder on the end, which will prevent the sleeve from pushing up into the collet during assembly.

**Limy Sami** · 02-23-2021, 04:12 PM

Originally Posted by Milland

It'll work, just do a good job on ID and OD to ensure a true, straight, coaxial part. Good finish too, a rough finish will collapse somewhat and open up the tolerances. Make from a clean cutting steel, perhaps a 4140 pre-hard if you want it to last.

Leave a short shoulder on the end, which will prevent the sleeve from pushing up into the collet during assembly.

What he said + bore and turn the OD at the same setting, ......and it will have to be single point bored, a drill & reamer job ain't good enough.

**Illinoyance** · 02-23-2021, 04:15 PM

Buy the right collet. The time you invest will cost as much as the collet.

**Milland** · 02-23-2021, 04:35 PM

Originally Posted by Illinoyance

Buy the right collet. The time you invest will cost as much as the collet.

Bad advice - you need to keep the hobby guys occupied, otherwise they get into trouble...

**Hardplates** · 02-23-2021, 04:39 PM

Just buy a collet for a milling chuck and use a 3/4" r8 collet

**mhajicek** · 02-23-2021, 05:07 PM

Buying the correct collet is the correct answer. The sleeve can work fine, with some reduction in precision and rigidity, but will cost you more in time that the price of the correct collet. The only cases where it makes sense are when you can't wait for the new collet, or when your dead broke.

**Hardplates** · 02-23-2021, 05:14 PM

Originally Posted by mhajicek

Buying the correct collet is the correct answer. The sleeve can work fine, with some reduction in precision and rigidity, but will cost you more in time that the price of the correct collet. The only cases where it makes sense are when you can't wait for the new collet, or when your dead broke.

I was under the impression we had to come up with a solution that didn't involve buying a new R8 collet

I can't keep up with all these changing rules

**Limy Sami** · 02-23-2021, 05:44 PM

Originally Posted by Hardplates

I was under the impression we had to come up with a solution that didn't involve buying a new R8 collet

I can't keep up with all these changing rules

Join the club brother

**cyanidekid** · 02-23-2021, 06:04 PM

Originally Posted by Hardplates

I was under the impression we had to come up with a solution that didn't involve buying a new R8 collet

I can't keep up with all these changing rules

ok, braze a sleeve on the 6MM (carbide) end mill, grind to 3/8 dia. haha!! just kidding, buy the friggin collet!

**Booze Daily** · 02-23-2021, 06:10 PM

Drill chuck.

**Hardplates** · 02-23-2021, 06:12 PM

Originally Posted by Booze Daily

Drill chuck.

Son of a bitch, I knew there was an obvious solution, just couldn't put my figger on it

**mhajicek** · 02-23-2021, 06:57 PM

Originally Posted by Hardplates

I was under the impression we had to come up with a solution that didn't involve buying a new R8 collet

Ok, weld up the collet, then bore it out and grind the ID to 6mm. Now you can hold a 6mm endmill in your 3/8" collet!

**Booze Daily** · 02-23-2021, 07:06 PM

R8 emergency collet

**dspahn** · 02-23-2021, 07:35 PM

I appreciate all the responses. Yes, I'm just a hobbyist. And I figured that creating a sleeve would do a few things: 1) solve the problem for how to hold a 6mm end mill, 2) give me some good practice in hitting dimensions, and 3) save me a few bucks as my time these days is more plentiful than the contents of my wallet.

Re: shoulder on the end to prevent sleeve from going completely into collet : I would not have thought of this. Plan altered!

Re: drill chuck : Nope! I know enough to know that this is a no-no (although, something this small, going through 6061 you'd probably get away with it, but still Nope!)

Re: welding : I do not yet have any way to weld. But some day I hope to.

Re: grinding : My metal shop currently consists of a mill and a lathe. I would love to have a surface grinder and a d-bit grinder, but for now, same as welding... Hopefully some day.

So again, thanks for all the responses, even the less practical, funnier ones.

**car2** · 02-23-2021, 08:39 PM

It's a tough crowd here. If I had to adapt something like that, I'd use an r8 toolholder, not a collet. Start with a tight-tolerance piece stock (eliminates the need for turning the OD and cutting-off) drill and bore the ID, make one cut on the side (can be done on the bandsaw or hacksaw). Free-machining tight tolerance stock is cheap from McMaster. An asymmetric (2 tine to 3) adapter sleeve might not hold too well in an already rather wimpy R-8, particularly if the adapter is not really well-made. In any variation, it ain't gonna help the runout.

An r-8 to ER collet set will handle the rare cases the standard R8 collets won't work. cheers

**72bwhite** · 02-23-2021, 08:46 PM

R8 er20 collet holder is the way to go

**dspahn** · 02-24-2021, 01:14 AM

Originally Posted by car2

It's a tough crowd here.

Yeah. I knew I'd catch a bit of business for asking such a rookie question. But I figure that's just the price of admission to get help from a community with countless years of expertise and knowledge, given for free, and willingly. So it's all good. I figured it would work (assuming the sleeve is created well), but it's reassuring to know that the people who really know have said it's an okay thing to do.

**thermite** · 02-24-2021, 01:49 AM

Originally Posted by dspahn

Yeah. I knew I'd catch a bit of business for asking such a rookie question. But I figure that's just the price of admission to get help from a community with countless years of expertise and knowledge, given for free, and willingly. So it's all good. I figured it would work (assuming the sleeve is created well), but it's reassuring to know that the people who really know have said it's an okay thing to do.

You don't need to buy a collet OR modify it, OR make a bushing.

NONE of that waste of time need apply!

Stick the the Communist-Metric endmill up yer ass to remind you to NOT buy cutting tools you cannot hold. It will do that task EXCEPTIONALLY well if emplaced crosswise.

Acquire a proper US-dimensioned endmill. Side-lock holders, not Are-Ate collets highly recommended! Are-Ates are for drills. So you do not waste "daylight" on overly-optimistic "Jacobs-crutches".

No longer a problem?

What's not to like?

Oh.. the "reminder"?

No sweat. When you get USED to the feel of an endmill up yer arse, crosswise, and consider that just "same PITA, different day?"

You will have become a "real Machinashitist". No longer a "hobbyist"!

What's not to like about...?

**dspahn** · 02-24-2021, 03:27 AM

Originally Posted by thermite

Stick the the Communist-Metric endmill up yer ass crosswise.

I'll be honest. I hadn't considered that option. I'm assuming you're speaking from personal experience here.
And while I appreciate all of the replies, I'm pretty sure my tolerance for pain and discomfort must be lower
than yours, and as such, I think I'll opt to remain a hobbyist and not try this "solution". Thanks though!