5C minimum grip length

[colin hamiltonParticipant @colinhamilton16803]

Is there a minimum depth material that needs to be inserted into a 5C collet to ensure proper holding?

Thanks Colin

[colin hamiltonParticipant @colinhamilton16803]

[Martin ConnellyParticipant @martinconnelly55370]

As with many such questions there is not a simple yes/no answer. On the basis that it is a single taper I would suggest it does not have a minimum, as long as the part being held is sized to suit the collet and can take the pressure of all the closing force on a small area. If you look at ER collets for small diameters they do not support the part all the way along the collet but larger ones do and need something to be gripped nearer the back as well as at the outer lip. Also, don't try large cuts on a part held by very little contact or have a long, unsupported, stick out from the collet. If you use soft jaws for something like a washer it is a very similar work holding method apart from there being a shoulder behind the part that will also resist pressure from things like drilling. With a 5C you can add a back stop to resist pressure from the front.

Martin C

[Clive FosterParticipant @clivefoster55965]

General rule with collets is that the parallel, gripping, part inside the collet must be filled for proper, stable, grip.

In the absence of measurements its usually OK to assume that so long as the workpiece goes in a bit further than teh depth of the outer, large, taper things will work correctly on unambitious jobs.

Trying to hold a very short piece and ramping up the pressure to get things to hold is a quick way of messing up a collet. They are not as robust as they look at first sight. There don't seem to be any official figures but I imagine 20 ft lb would be as high as I could sensibly manage with the hand wheel closer on my lathes and the shoe C spanner with my collet block. What I actually use is less.

Clive

[JasonBModerator @jasonb]

As they are single taper you don't have to worry so much like you do with ER, I've happily worked on items held by 0.75mm 1/32"

[Clive FosterParticipant @clivefoster55965]

Jason

With only 1/32" held how the devil did you get the job running true?

Nearest I ever came to that was with an 3/32" long spigot on an asymmetric and non circular flange that needed the hole in the middle enlarged. I blessed the original maker for putting a teeny undercut at the junction so it sat flat against the face of the collet.

A job for one of the "gash" set of Harding 5C collets I bought for "£ not very much" in the days before I learned proper E-Bay caution. Clearly retired from production duties, probably from a Tier 3 shop, most have lost their spring and don't open properly, maybe half have internal taper in greater or lesser degree and some are so badly distorted that there is visible error in the angle between the main shank and the taper. Lord knows what they were tightening the things up with. Surprisingly concentricity was still very good but the various errors and tapers vastly compromised grip. Which I found out they hard way after a job that needed to be real nice spun! Concentricity great, I checked first, grip crap. Fortunately most of the 1/64 th s are still pretty good.

Clive

[JasonBModerator @jasonb]

I probably mostly use it like that for drilling an milling cylinder end covers holding by the short spigot that goes into the cylinder so can use the larger face to push against the end of the collet. If no step I will hold collet front end down against bench and push the item down from behind while tightening

Turning flat parts I'm more likely to use the soft jaws so there is something to push the work back against

[Bo’sunParticipant @bosun58570]

Hi colin,

Have a look at Joe Pie's latest model canon video on You Tube.

[colin hamiltonParticipant @colinhamilton16803]

Thanks everyone. I'm taking from all of this – grip as much as possible and go steady until you understand the loads involved

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