er25 collet

This topic has 8 replies, 7 voices, and was last updated 13 August 2021 at 18:12 by Graham Williams 11.

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13 August 2021 at 11:18 #558082
Graham Williams 11
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@grahamwilliams11
Never been really satisfied in the interchangeability Accuracy) between ER25 lathe chuck and my ER25 Stevenson's square. I usually turn a 1/2" long spigot on whatever I want to machine to fit say my 16mm collet. 1/2" long only so as not to waste to much very expensive metal. I'm beginning to wonder after this mornings episode that the spigot should be at or near collet length, does anyone have any advice on this?

Cheers

GW
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13 August 2021 at 11:18 #28307
Graham Williams 11
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@grahamwilliams11
13 August 2021 at 11:31 #558086
Steviegtr
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@steviegtr
I use the ER25 a lot ,but would try & get the holding a bit further in than 1/2". Also what are you using to turn the spigot. I.E is it accurate.

Steve.
13 August 2021 at 11:39 #558088
Ian Parkin
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@ianparkin39383
I would always put at least the length of any type of collet chuck..in the collet
13 August 2021 at 11:58 #558092
SillyOldDuffer
Moderator
@sillyoldduffer
I agree with Ian. The ER series are a tool-holding collet normally expecting a shank to go all the way through. I think work should be long enough to do the same. When the holder is tightened, the collet is pulled into a taper which compresses it equally on to the shank. If the shank is too short, the collet collapses unequally, losing grip and tipping the work in the collet, causing poor run-out. Might even damage the collet.

I sometimes use a stub-mandrel to save metal, supergluing the blank to it, and detaching the job later with a blow-lamp. Superglued joints are remarkably strong apart from a sharp sideways blow.

Dave
13 August 2021 at 12:07 #558095
Pete.
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@pete-2
Doesn't your collet block have a hole at the rear? Meaning you can just pass the bar through, say for arguments sake a 6" piece all the way in, then when finished the milling put back in the lathe and part off, not wasting any metal.
13 August 2021 at 12:11 #558096
not done it yet
Participant
@notdoneityet
ER collets are 35mm long. Not all of them grip that full length, particularly cheaper offerings.
13 August 2021 at 15:00 #558127
old mart
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@oldmart
I would feel safer using the full length of the collet. 16mm collets will always be full length inside.
13 August 2021 at 18:12 #558160
Graham Williams 11
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@grahamwilliams11
What I'm machining is the cylinder liner for an Owen Mate i/c engine, there are 4 transfer ports at 90 deg to each other. How I approached it was to put a length x 1 1/2" dia. of EN3 (from the scrap box) into the 3 jaw chuck and turn a 1/2" long spigot 16mm dia (using tipped tool) Switch the 3 jaw to a collet chuck, spigot into that and turn a diameter to enable marking out for the 4 ports when it's then transferred into the Stevenson's square fixture using the same 16mm dia collet. That's when the accuracy went. So I've now set the EN3 up in a 4 jaw chuck and machined the spigot tp 7/8" long (thats as long as I could go and still get the finished length I needed), tried in lathe collet chuck and and it's running true so as you've advised got to approach using er collets differently to my 'ordinary' morse 2 taper collets.

Thanks for all your input.

GW
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