Using 5C collets

[Mr Ron]

I find that some round bar stock is larger than it's nominal size by one and as much as 3 thous. That means if I try to put a piece of 3/4" bar stock in a 3/4" collet, it doesn't want to fit. I can jam it in a ways, but I don't like to do that. I could of course use a scroll chuck or a 4 jaw chuck, but that is time consuming. Has anyone had this problem and how did you solve it? I usually have this problem with 6061 round bar stock which I use a lot. I want the precision of collets and don't want to use a chuck.

[Harold_V]

Jacobs rubber flex collets are a respectable way to approach that issue. They grip over a wide range, and maintain concentricity quite nicely. Their one shortcoming is they don't hold short pieces very securely, even if you use the provided plug. I'd experienced pieces being pulled from them on occasion.

One other thing they could do was to provide a cut that wasn't round. Under extreme pressure (like when roughing), the part could deflect slightly when pressure was between steel segments. A finish cut would eliminate the problem, however.

They're really nice if you work with hot rolled materials, which are rarely on size, or round.

I don't have a set of these collets, but there was a complete set provided for the Monarch EE I once operated. That is my sole experience in using them. They are no longer available so far as I know, but they can be found on eBay. They are not cheap.

H

[Mr Ron]

I guess one thing I could do is mount a length of bar between centers and take a light cut to get it down to a nominal size and then use collets.

[GlennW]

While Import 5C collets are as you describe, some manufacturers, (Hardinge for one) "spring" their collets. This means that when relaxed, they are sprung slightly over size so the stock can easily slide through them.

I got rid of all of my Import (Chinese) 5C collets for the reason you describe.

[Mr Ron]

While Import 5C collets are as you describe, some manufacturers, (Hardinge for one) "spring" their collets. This means that when relaxed, they are sprung slightly over size so the stock can easily slide through them.

I got rid of all of my Import (Chinese) 5C collets for the reason you describe.

I wasn't aware that the collets were the problem.

[BadDog]

I have a Rubberflex chuck and complete set of the collets. They are very good for working with bar stock where you can hold a minimum of about 2". And they offer "plugs" that make it theoretically possible to hold sorter lengths. But in my experience, you better be real easy with a cut or it'll come out and trash your tool edge...

[tornitore45]

The most practical solution I have to offer is to develop a technique to center the work in the 4 jaws without trial and error but a set sequence that gets the part from eyeball centered to as dead on as the part roundness allows.
Unless I have to make over 10 parts with no concentricity requirement I do not bother to switch to a 3 jaws

[earlgo]

N0-one has mentioned yet that you could buy the brass unbored collets and make the sizes you use most. They are quite expensive though and may not be worth it if you need a lot of different sizes.
https://www.mcmaster.com/collets
Just another way to go.
--earlgo

[Mr Ron]

I only seem to be having the problem with 6061. I don't have that problem with 7075 or 2024. With 6061, it's hit or miss. Sometimes it works and other time not.

[ChipMaker4130]

A lot of aluminum stock has that problem, and a lot of it isn't round. A lot of tubing has irregular wall-thickness too, and this from reputable dealers. You have to check the specs. As for collets, they're available in 1/64th increments. Gradually filling the gaps in your collection with imports at 1/32nd increments will likely be cheaper than acquiring the 'sprung' Hardinge, etc.

[johnfreese]

ER collets have a wide gripping range. Not quite as wide as the Rubberflex. Neither ER or Rubberflex are good for really short work. The work needs to extend the full length of the collet. Rubberflex did provide rubber plugs to support the back end of the collet when holding short work. Conventional collets are only good for work that is "on size". That includes 5C, 3C, 6K, and all the others.