View Full Version : 3C collets or MT3 collets?

11-08-2004, 02:56 PM
My lathe has an MT3 spindle. I can either get 3C collets, a 3C to MT3 adapter, and an open drawbar; or I can get MT3 collets.

About the only advantage (which can be a big advantage) I see is that the 3C collets allow long pieces to pass through the spindle.

Any other advantages for one type over the other? (cost, availability, functionality, etc.)


11-08-2004, 03:22 PM
I have the 3c collet spindle adapter for my South bend, however the cost of 3c collets is much greater than that of 5c collets. Dan, on my minilathe, I indicated the internal mt3 taper in the spindle, and it showed about .001 runout. You might want to do the same, because the main reason to use collets is for less runout. If its better than .001 or within what you want, (most likely is) then great.
I've been eying a 5c collet chuck, thats another way you could go as well.

Herb Helbig
11-08-2004, 03:46 PM
Let me chip in a collet question, if I may. Why doesn't everyone want ER collets? They seem very versatile. I'd like to have an ER-32 set for my #3 morse taper lathe spindle. Is that a bad idea?


11-08-2004, 04:11 PM
You can also get a Bison 5C collet chuck, or the Metal Lathe Accessories castings and make your own 5C collet chuck. The MLA castings are written up in latest HSM.

If possible, the use of 5C collets will be an advantage over MT3 or 3C as they are more readily available, hence cheaper, and cover a much wider range of sizes as well as hex and square.

11-08-2004, 04:19 PM

For the heck of it I checked the TIR of the side of my lathe chuck and it was less than .0005". I then checked the register part of the spindle and detected barely visible movement of the needle.

When using a 4 jaw independent chuck I can cancel out any spindle runout. A 3 jaw scroll chuck is not going to be as good as .0005" anyhow so spindle runout isn't the problem.

I should get high accuracy in my lathe with good collets but even if there is some runout it won't matter as long as turned piece is parted from the original piece in the collet. I'm happy with the accuracy.

On my little 7x12 I thought about adapting a 5C collet chuck but that would just eat up too much of the 'between centers' distance.

11-08-2004, 06:14 PM
Herb, I think the big drawback to the ER collets is the fact that you can't put long stock through them, the way you can with regular lathe collets (3C, 5C, or whatever). Except for that, I can't see anything wrong with the idea but for lathe work it can be a pretty significant drawback.

As far as 3C or Morse #3, Morse #3 goes up to 3/4", 3C goes only to 1/2", but Morse collets suffer the same limitation as the ER collets -- you can't put long stock through them. They are also not self-releasing, which means one would have to always be more or less gently flogging the end of the drawbar to get the collet to release...maybe not a good thing.

I think I'd be inclined to look into the Bison 5C collet chuck, as others have suggested. Or if you're feeling ambitious, Metal Lathe Accessories' kit.

[This message has been edited by SGW (edited 11-08-2004).]

11-08-2004, 06:18 PM
Dan, that is the kicker though, On my lathe spindle, the register and outside diameter read hardly any runout, but the morse taper inside the spindle read .001, maybe .0015.

11-08-2004, 07:49 PM
Herb Hilbig: funny you should ask about ER collets; I just finished making a 3MT to ER-20 collet chuck adapter. The collet chuck has a straight 1" diam. shank; I made a 3MT tapered piece to fit my lathe, and bored it out to a nice slip fit to the adapter. I designed 6 setscrews around the perimeter to allow a sort of "set true" capability, and also to hold the adapter's shank.

BUT... even though my bore turned out great, less than 1 mil TIR, and even though the collet chuck body itself maintains that tolerance, one I put in a collet and screw down the nut that pushes the collet into the chuck: the TIR goes to the 2-5 range.
The darn chuck nut, or the threads, must have a high spot that tilts the collet a bit. I can shim it to get the TIR back down, but that's a pain. I forget who I bought the chuck from, but it was probably an Enco special or the like.

11-08-2004, 08:30 PM
BillH, I'll have to check that out. I haven't checked the inside of the spindle...yet. http://bbs.homeshopmachinist.net//smile.gif

J Tiers
11-08-2004, 10:00 PM
<font face="Verdana, Arial" size="2">Originally posted by BillH:
Dan, that is the kicker though, On my lathe spindle, the register and outside diameter read hardly any runout, but the morse taper inside the spindle read .001, maybe .0015.</font>

If you make your 3C adapter, and mark position before removing it after boring for the collet, you can get much better, even if the taper is off. Just put it back in same position as when it as made.

That's what I did. No way was I buying a collet setup for $150-$250 and then paying large $$ for collets also. I don't use them that much.

Took 2 evenings to make the drawtube, closer, and nose protector/remover, and has worked fine when I use it.

A call to Sobel and I had a bunch of collets. I have not yet spent as much total as the closer and drawtube alone would go for.


MT collets require to be beat on to remove them. (self-locking taper)

You can't put stock thru, so you waste more drill rod, etc, etc.

They don't cost much less than the 3C in any case, so no big advantage there.

5C collets in your machine need a chuck:

It sticks out and may have runout itself.

Chuck costs even more than drawtube etc. May cost as much as drawtube and a set of 3C collets. Way more than if you make the adapter.

Collets are cheap, however, at maybe $5 for import.

You be the judge.

[This message has been edited by J Tiers (edited 11-08-2004).]

11-08-2004, 11:14 PM
I wish 3c collets were 5$ a pop. I was speaking of my mini lathe, not my southbend about the taper runout.

Herb Helbig
11-09-2004, 05:58 PM
SGW,jeastwood - Thank you both for your help; the pros and cons are much clearer now. The extended range of the ER collets appealed to my native cheapness, but no feed through looks like too high a price to pay for that convenience. I don't mind dialing in my 4-jaw chuck, and it will hold diameters down to ~ 0.140", so I'll save my $ for now. If I need to hold something smaller, I'll make a custom collet to hold in the 4-jaw.


11-09-2004, 08:14 PM
Herb: well, you actually CAN use the ER collets in a feed through mode: the chucks that I'm aware of use a nut to force the face of the collet into the chuck body; this means that a chuck that has a hole through it will accomodate long stock. The chuck I have has a plug in it, but I will probably bore that out.