Tightening collets

[David Clark 13Participant @davidclark13]

[David Clark 13Participant @davidclark13]

Hi There

I have a question from a reader who would like to know how to tighten the 2 Morse taper collets, the ones with 3 slots, so he can turn bar down.

At the moment, they tighten up so far then rotate when he puts on a cut.

 

I have used them for back stops but never turned or held cutters in them.

Can anyone help?

regards David

 

[CirclipParticipant @circlip]

Trying to clamp too small dia.??  Worn bore??

 

  Collets seem to have taken over as the universal “must have” clamping system, (bit like DRO’s make super machinists) The clamping “Range” is a misnomer, as the collet can only Truely grip its “Bored” diameter and the only near universal collet is the “Rubberflex” (No affiliation).

 

   Regards   Ian

 

 

[Ian S CParticipant @iansc]

I’v got one 1/4″ collet,it will grip +0.005″ and – 0.010″. it rarely gets any use, but Davids idea of using it for a back stop sounds good. Ian S C

[KWILParticipant @kwil]

I have a full set of Imperial and Metric 2MT collets for my Myfords. They work without any problem for the designated size. As Ian SC says the tolerance to tight.. I also use drawbar 2MT and 3MT collets to hold a spigot for for centering on a faceplate.  ER series collets will hold a wider range of diameters quite succesfully. Personally I would never hold a cutter in any of them.

[chris stephensParticipant @chrisstephens63393]

Hi Kwil,

Do I take you to say you would not hold a cutter in an ER collet. If so, you have it slightly back to front, ER collets were made, and are only recommended by the makers, to hold cutters, not work.

Or do you mean not to hold cutters in Morse collets? 

chriStephens 

[RobboParticipant @robbo]

Hi David,

 

I may have missed the point here, but surely the simple answer to how to tighten a 2MT plain collet is to use a drawbar and tighten it up.

 

As others have said, the collet bore must match the OD of what’s being put in it.

 

Robbo

[RobboParticipant @robbo]

Hi David,

 

I may have missed the point here, but surely the simple answer to how to tighten a 2MT plain collet is to use a drawbar and tighten it up.

 

As others have said, the collet bore must match the OD of what’s being put in it.

 

Robbo

[KWILParticipant @kwil]

Chris,

 

I would not hold cutters in MT collets, I do use ER for cutters on small jobs.

 

[Jim WhetrenParticipant @jimwhetren72358]

Hello David,

 

To return to the original query, I would have thought that if the work was spinning, then either the MT socket was too short and the collet was bottoming before it fully closed, or the drawbar thread was too short; and binding before the nut was fully tightened.

 

I would fit an empty collet and see if the slits start to close up if the drawbar is tightened.

 

Jim

[Clive FosterParticipant @clivefoster55965]

Further to the comment from Jim W

 

Due to the small taper angle MT collets need a lot of drawback to grip.  Taper angle is near enough 50 thou per inch so a 10 thou contraction needs getting on for 1/4″ drawback hence the need to keep close to the designated size.  I’m amazed by the + 5 to -10 thou range reported by Ian.  The small taper also means they are very inefficient at gripping things. Much of the draw bar effort goes in overcoming friction as the collet draws back into the socket. 

 

Be worth checking that the bore behind the collet is a bit larger than the standard small end MT 2 diameter of 0.572″ so the collet can pull back into it.  Something like 0.59″ to 0.6″ would be desirable.

 

Clive 

[Hugh GilhespieParticipant @hughgilhespie56163]

A slight variation on the collet tightening theme. I checked the runout on a piece of silver steel held in an ER32 collet on my mill today. The collet was a 7-8 mm size and I used 8mm silver steel in it so that the minimum tightening was needed. i tightened to my usual extent and was shocked that the TIR was 8 thou. The mill spindle TIR is about 0.2 thou and the collet holder was also around 0.2 thou, so it was all from the collet itself. I had to tighten much harder than I normally do to reduce the TIR to under 2 thou. OK, it’s an Asian collet but even so I am surprised that it needs to be bullied so much. Lesson learned and I will take more care in future.

 

Hugh

[chris stephensParticipant @chrisstephens63393]

Hi Hugh,

Welcome to the cynical “world of disappointment club”. Regrettably just because it is a nicely ground collet, it does not mean it is a nicely ground accurate collet.

Luckily for our end of the market, if you use a slightly naff collet in your mill you will not notice it. The odd thou or two run out of a cutter will not show up because you will almost certainly measure what you are making and alter the cut accordingly.

CNC machining folks might have a different idea, but if they can afford CNC machinery they can easily afford top quality collets to match. (if you detect a note of jealousy, you are clearly quite perceptive)

Where cheap and nasty collets are a real pain, is when you use them to hold work in your lathe. If the collet is not concentric it defeats the object in having one. The only exception to this is if you want a firmer grip than a 3 jaw can give. Even a dickey collet will hold work more firmly than a chuck, great if you want to cut a large and coarse thread with a die.

The voice of experience has spoken.

chriStephens 

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