Would you buy one of these collets?

One of the 25mm R8 collets is back on ebay, for sale by a reputable vendor. I would not dare to try one for fear of a disaster, has anyone used one?

https://www.ebay.co.uk/itm/R8-Collet-for-Bridgeport-Milling-Machine-etc-25-mm/372791941387?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2060353.m1438.l2649

Edited By old mart on 05/10/2019 21:39:11

Quite possibly a perfectly servicable item.

But, at £19.95 postage to France, I wouldn't consider it.

ATB,

Daniel

I wouldn't buy one. One, the vendor is not a supplier I use anymore. Two, I don't see how the collet grips anything. Sure, at end nearest the taper, the collet will grip. But as you move away from the taper there's nothing compressing the collet fingers and making them grip. I'd imagine that a 25mm endmill would work loose in a very short time with any sort of cut.

Andrew

Agree with Andrew's comments re grip but may take a chance to hold a tool that needed light grinding to sharpen.

Emgee

Only way thats going to hold anything against cutting forces is if you tap tight fitting sleeve, or better, shrink fit, over the extended part after you've put the cutter in.

A semi permanent job. Which might be worth it if you have a suitably hefty cutter, flycutter, boring head or whatever on a 25 mm shaft sitting around doing nowt.

Considerable risk of the collet snapping where the taper runs out into the extended part.

Better to get a sidelock (weldon) holder and grind a flat on the cutter. At least the holder is all solid.

Although I have full sets of R8 in both imperial and metric I'm rapidly coming to the conclusion that sidelock is the better way for plain shank cutters. But Clarkson is my general purpose go to as I have plenty of screwed shank cutters.

Clive

You would need a very strong Jubilee clip on the end!

I have one of these as someone gave me several 50mm milling cutters i find if i clamp it in and also use a jublee clip at the end it works fine i have never tried to work the cutter hard though.

Bob

For my 1" cutters and i assume their is a 25 mm alternative i have a holder that looks like an oversize FC3 holder.Still oversized for an R8 spindle so light cuts and only used when nothing else will do

For me its a no ! When using larger cutters its far better to use a screwed shank cutter and a Clarkson [style] chuck. Better not to push beyond the design limits IMO.

However If you did choose to go there I would consider making a split collar that goes over the extended part of the collet and lock it in place with an allen screw thus supporting the thin walls and not allowing them to splay outwards. Still not the best option -- use the right tool for the job !

John

I suppose it would not be too difficult to screw-cut the outer diameter and turn a taper on the nose ... then add a closing nut.

Whether that’s worth the effort might depend upon how accurately the basic collet is made.

MichaelG.

At not more than £10 from most well known UK suppliers why would you?

Fizzy it's an oversize one, question is will it hold

Edited By JasonB on 12/10/2019 17:12:42

I dont have or use R8, but this one looks the same as the one Arc have so what is oversized about it?

Ian P

.

... the bore is oversized for R8

A rather dubious arrangement [whoever supplies it] methinks.

MichaelG.

Arc 1” : https://www.arceurotrade.co.uk/Catalogue/Collets/R8-Collets/R8-Collets-Round-1

Arc 20mm : https://www.arceurotrade.co.uk/Catalogue/Collets/R8-Collets/R8-Collets-Round-20mm

Edited By Michael Gilligan on 12/10/2019 17:09:39

If you also compare it to a standard R8 collet you will see that they grip in the tapered area but the oversize ones grip in the extended end so not as direct a closing force.

It's a bit like using a 5C step collet without the closing ring.

Edited By JasonB on 12/10/2019 17:14:31

I thought many people had migrated to the ER series of collets nowadays. Obviously not. The grip of an ER collet is parallel over a wide range.

For Crawford’s range of sizes, see p22 of this brochure: **LINK**

http://www.rotagriponline.com/datasheets/5C.pdf

[ ignore the file-name ]

MichaelG.

Yes I'd buy one if I needed it!

I have an over size C5 collet (30mm) that I bought for one job.

Jim

Using a big cutter [i.e. 25 mm / 1"] or above in an R8 spindled machine seems attractive but in practice you would get little or no benefit out of doing so.

Tony

Does allow you to get a decent cutting speed if the machines spindle speed is limited, I got 500m/min cutting speed earlier today