Would you buy one of these collets?

[old martParticipant @oldmart]

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

[old martParticipant @oldmart]

[DanielParticipant @daniel]

Quite possibly a perfectly servicable item.

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

ATB,

Daniel

[Anonymous]

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

[EmgeeParticipant @emgee]

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

Emgee

[Clive FosterParticipant @clivefoster55965]

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

[old martParticipant @oldmart]

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

[Bob AstillParticipant @bobastill76884]

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

[old AlParticipant @oldal]

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

[JohnFParticipant @johnf59703]

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

[Michael GilliganParticipant @michaelgilligan61133]

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.

[nigel jones 5Participant @nigeljones5]

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

[JasonBModerator @jasonb]

Posted by fizzy on 12/10/2019 15:57:31:

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

[Ian PParticipant @ianp]

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

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Ian P on 12/10/2019 16:53:13:

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

[JasonBModerator @jasonb]

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

[Brian OldfordParticipant @brianoldford70365]

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.

[Michael GilliganParticipant @michaelgilligan61133]

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

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

[ ignore the file-name ]

MichaelG.

[jimmy bParticipant @jimmyb]

Yes I'd buy one if I needed it!

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

Jim

[Tony Pratt 1Participant @tonypratt1]

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

[JasonBModerator @jasonb]

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

[old martParticipant @oldmart]

The shank of an R8 toolholder is 15/16", (23.8mm) and the length of the tapered end is 1", if you use a standard collet for a 20mm cutter, the depth is limited, a 3/4" size is the biggest that gives a decent choice of fitted depth.

I use up to 80mm shell mills regularly with R8, but don't bother with any solid cutters above 20mm, and 16mm with ER25 collets. The threaded shank cutters used in the small series Clarkson, Osborn and Acramill go up to 16mm shank with cutting diameters up to 20mm. The larger threaded shank holders in R8 go up to about 32mm.

ER collets in 32 and 40 sizes are ok except, the limitations of the R8 only allow a relatively short amount of shank just the depth of the collet length.

[Nigel Graham 2Participant @nigelgraham2]

I can't see that collet as illustrated having much holding power at all. The grip on an R8 collet is given by the portion of the taper within the spindle, and it's hard to see what that protruding section can really achieve.

I prefer the Autolock for most work, keeping the R8 collets only for small diameter cutters, centre-drills and the wiggler.

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