Collet Imperial - Cutter Metric

[smallbrother]

Will a 1/2" collet grip a 12mm shank or is the difference too great?

Pete.

[stevep]

It depends on the type of collet. For example, I wouldn't try it with an R8 collet, but an ER32 would probably be OK.

Look at this video from Joe Pie for an explanation.

www.youtube.com/watch?v=7ENSGgeiOVI

[David]

An ER-32 collet might just do it, they're meant to have a range of 1mm. A 5C one won't. I don't know about other systems.

[Deleted]

I mix imperial with metric all the time...as David states there's a 1mm range on metric collet's.... for example right now I'm holding a 1/2" cutter in a 13mm collet... no problem at all, all of my collets are metric.

Pete

[silverfox]

Peter
I splashed out on a set of 4 imperial 1/4, 3/8 1/2 and 5/8 for the cutters Have a nice case of metric as well and several ER 25 (or they masy be 40) ones up to 27mm

[smallbrother]

I have morse taper collets which are secured in the mini-mill with a draw-bar.

Pete.

[uuu]

Sounds unlikely then. I had those in my old Centec mill and I was none too happy gripping the right size shank, let alone anything that much smaller.

Wilf

[jasonb]

Don't try it with MT finger collets

[Deleted]

Jul 3, 2020 11:56:44 GMT silverfox said:

Peter
I splashed out on a set of 4 imperial 1/4, 3/8 1/2 and 5/8 for the cutters Have a nice case of metric as well and several ER 25 (or they masy be 40) ones up to 27mm

I have both metric and imperial for threaded shanks in my Clarkson's auto-lock, these days though I mainly use my ER sets for plain shank cutters. IIRC mine is the ER25 with collets 6,8,10,12,14 and 16, I added a set of metric collets to this that goes in increments of 1mm, again IIRC 2mm up to 16mm, so it has all of the odd-numbered collets which is handy for the imperial sized cutters... I also have a set that my son bought me for the finer stuff.. think it's an ER 16 but not really sure... it's small.

Pete

[simplyloco]

Jul 3, 2020 14:25:24 GMT jasonb said:

Don't try it with MT finger collets

Agreed. Absolutely hopeless.

[stevep]

Pete (Smallbrother),

Just to add some more detail, milling cutters are subject to lots of odd forces when milling, and even a cutter held in a properly sized morse taper collet will 'walk' out if you are not careful. (Hence Wilf's discomfort, even using correct sized cutters and collets).

Holding a milling cutter in a chuck is an almost certain recipe for disaster.

The system Pete (Greenlade) uses is the best solution - threaded shank cutters held in a Clarkson (or similar) autolock chuck. The cutter is held by the collet, but is also screwed against a stop inside the holder. This locks everything together solidly.

I have one with a morse taper that I used in my old mill. It is now in an R-8 adaptor for my current mill.

ER system collets (as the video from Joe Pie explains) have a much better and bigger contact area with what they are holding - hence a good grip. 3-way split collets (like morse, or R-8) have a less precise contact area - even on correct size cutters. Holding undersized ones will almost certainly result in a wobble, and they may work their way out.

[smallbrother]

I have now ordered the appropriate metric collet. (And checked I have the right draw-bar for it).

Hopefully i can get on with the counter-bore operation. Tried to make a shallow angle on a drill bit - works partially but not brilliant and I am concerned that I will make a mess of this slender coupling rod if I continue with a half-baked method. The cutter is 11.5mm diam which is slightly oversize and should allow the bush to sit nicely in the recess. As with many procedures I have been caught out with lack of pre-planning but no point getting older if you don't get wiser.

Thanks for the advice everyone.

Pete.

[smallbrother]

Well all the necessary bits and pieces have arrived and I got up today determined to complete the coupling rods.

Then my back went into a spasm.

Horlicks!!!!

Pete.

[stevep]

Pete, If you are doing a counter-bore, have you though about making a pin-drill?

I have a number that I have made over the years, and for the amount they get used, last quite well. Just use silver steel, turned to the necessary diameter, and drill and ream a hole up the middle that's the size of the bore that your are counter-boring.

It's easy to file a couple of teeth (or 4, depending on the diameter), then harden and temper. Pop a piece of silver steel in the hole in the cutter, and then use it to direct the counter-bore. The pin ensures the cutter cuts concentric with the hole, and with care and a reasonably slow speed, they cut well.

[smallbrother]

Jul 8, 2020 17:08:46 GMT stevep said:

Pete, If you are doing a counter-bore, have you though about making a pin-drill?

I have a number that I have made over the years, and for the amount they get used, last quite well. Just use silver steel, turned to the necessary diameter, and drill and ream a hole up the middle that's the size of the bore that your are counter-boring.

It's easy to file a couple of teeth (or 4, depending on the diameter), then harden and temper. Pop a piece of silver steel in the hole in the cutter, and then use it to direct the counter-bore. The pin ensures the cutter cuts concentric with the hole, and with care and a reasonably slow speed, they cut well.

Thanks Steve.

My next project is a 3.5" Mona and on checking the drawings I can't see any counter-bores being needed.

Obviously having put that in writing I will find one all too soon.

I'm hoping my back will ease off a bit tomorrow and let me finish the job off.

Pete.