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Holding accurate length with a 5c collet

M

moonlight machine

Diamond
Joined
Nov 19, 2007
Location
marysville ohio
I'm making some parts that have a step on both ends and a tolerance of .001 between them. normally no problem but the OD is 5/8 nominal. the diameter varies between .6215 and .6240. I'm using a internal stop in the collet. the collet closer is a Royal lever action.
The OD variance causes the collet to grip deeper or shallower in the spindle. I use a stop on the carriage to set the depth of the cut. So you see how the distance between the steps changes with the diameter of the part. I ended up going through all the parts and grading them for diameter, and constantly adjusting the carriage stop. Any ideas how to get around this other than starting with 3/4 Dia and turning it to .625?
 
Limy Sami said:
Position them against a fixed stop on the ''outboard'' end before closing the collet?
Click to expand...

-No. The collet draws inward when closed and locked, you still get the length variations if the diameter changes.

The only "trick" I know of if you have a lot of OD variation, is to use a "dead length" collet (here and here.)

You might also see if you can get access to a machine with a Jacobs "Rubberflex" style collet assembly.

Doc.
 
If the part length and design permits...

Use an emergency collet (or clutch collet if you need the length) and bore to your larger diameter- and put a step in the bore for the part step to rest against.

Cut the face of the collet to be flat.

Select the depth from the collet step to the collet face to be a convienent number.
If possible make it short by the length of some feeler or shim stock you have handy.

Load the part to be agains the collet stop and tighten.
Move the tool bit up until it traps shim stock, remove shim, and take a test cut.

If needed- you can refine the depth of the face or the thickness of the shim stock.

If you have many to do, try and rig up fixed stop mounted on the carriage ( compound, or toolholder) to touch the face and you will not need the shimstock.
 
DocsMachine said:
-No. The collet draws inward when closed and locked, you still get the length variations if the diameter changes.

The only "trick" I know of if you have a lot of OD variation, is to use a "dead length" collet (here and here.)

You might also see if you can get access to a machine with a Jacobs "Rubberflex" style collet assembly.

Doc.
Click to expand...

Apologies, I worded it badly,. what I meant was the stop against which the part is set is fixed to the machine and not the collet.
 
You need a Hardinge "dead length" collet. Hardinge addressed this problem umpteen years ago. They weren't all that expensive ($65?) and I think I have some around here. You may be able to go to Hardinge's Workholding Solutions online catalog and read their write-up.

Here's a link to some information that may be helpful. I discovered the individual collets are around $57, but you have to have the "system" first. It looks like the "system" is around $150.

http://hardingeus.com/usr/pdf/collet/2285a.pdf
 
Hardinge has provided two solutions to the 5C collet length holding issue, and both work well. The dead length collet, an expensive special design collet, is the simplest, and works with any lathe. They also make a dead length stop which works with ordinary collets. But the dead length stops they sell only fit lathes with a Hardinge spindle nose, either taper or threaded. That design would be awkward to adapt to any other lathe. So that leaves the dead length collet, and there are used ones for sale out there. Actually, I have some.

My suggestion is to use an accurate adjustable 3-jaw chuck. I have two Buck 4 inch Ajust-tru chucks on 5C shanks that are quite handy for jobs where the stock size varies. Two chucks because I hate to swap jaws, so one is internal and one is external. The 5C shank can be fitted with an internal stop. Hardinge and some foreign makers sell 5C fixture plates. They are 5C shanks with a solid steel disk big enough to machine into a chuck mount.

Note that the length issue arises with any drawback collet, not just 5C type. Some screw machine collets, like B&S, are designed to be dead length. Hardinge even made a version of the DSM59 turret lathe with a spindle to take B&S collets just because they are better suited than 5C collets for many jobs.

Larry
 
"...spindle to take B&S collets just because they are better suited..."

Actually always wondered about the reasoning there, this explains it!

Another approach to the problem is to leave the stock a bit oversize,
and the first operation is to face off the ten or fifteen thou to get it
dead length. Then everything else follows from there as long as the
final cutoff happens before the collet gets unlatched. Yes another
operation but there are six on the turret, two on the cross slide, and
one more if you have a headstock cutoff.
 
As someone else mentioned a work stop inside the spindle will do what you want - something like the Aloris "Universal" Stop here: http://www.aloris.com/catalog/aloris_pg46.pdf (link to page pdf)

If the work is short enough and the collet is far enough from the spindle taper I've seen stops mounted in the taper - this works on the 10EE because the collet holder is mounted on the spindle face, leaving the taper free for this. Miller has a fairly inexpensive taper plug with a threaded holder for stop mounting.
 
rke[pler said:
As someone else mentioned a work stop inside the spindle will do what you want - something like the Aloris "Universal" Stop here: http://www.aloris.com/catalog/aloris_pg46.pdf (link to page pdf)
....
Click to expand...

But with a 5C collet and Royal lever closer, there is a draw tube inside the spindle. So your stop would grip the inside of the draw tube, not the inside of the spindle. And the draw tube is connected to the collet and moves to the left as the collet closes, so this type of stop is not a solution to length control. This type of stop would work with collet chucks that do not use a draw tube, like the Burnerd or Jacobs collet chucks.

Larry
 
On my hand turret lathes I use the simple process of taking a light facing cut on the part once the collet is closed, then all subsequent operations are in the right spots. Simple.
Brett
 
L Vanice said:
But with a 5C collet and Royal lever closer, there is a draw tube inside the spindle. So your stop would grip the inside of the draw tube, not the inside of the spindle. And the draw tube is connected to the collet and moves to the left as the collet closes, so this type of stop is not a solution to length control. This type of stop would work with collet chucks that do not use a draw tube, like the Burnerd or Jacobs collet chucks.
Click to expand...

You're right - I didn't notice that he was using a closer with a draw tube.

As Gilda Radner said playing Emily Latella: "That's very different. Never mind."
 
Brett by Portland said:
On my hand turret lathes I use the simple process of taking a light facing cut on the part once the collet is closed, then all subsequent operations are in the right spots. Simple.
Brett
Click to expand...

Yes, works fine on a first operation. But the original question was how to do a second operation and control length from a feature done on the first operation. Second operation means the part is cut off from the bar on the first operation and then the part is reversed and put in a lathe to perform additional work on the end that had been cut off.

Larry
 
I use a Kalamazoo 5C Collet holder to hold desired depth. This little guy can be centered in a 4 jaw chuck and you are good to go. It pushes the collet closer taper up around the collet while gripping the 5C collet securely at its base. These are nice!

Here's a link to some site selling them:
IndustrialTool.com

Usual disclaimer.
Jim

BTW - these are a made in USA item!

some more detail here:
http://www.practicalmachinist.com/vb/general/kalamazoo-collet-chuck-anyone-use-one-161891/

and

http://www.kalamazooind.com/products/5c-collet-fixtures/1cc-5c-collet-fixture-for-chucks/
 
collet stop

One other way we used to hold close lengths was to centerless grind od to size of smallest
part. Like to .620 dia.
Also used chuck soft jaws bored to stock size with shoulder to stop against.

Jim
 
The kalamazoo collet chuck is the way to the go. Once you have one, you'll use it for tons of stuff. I have one for the manual and cnc lathe, one mounted to a plate that can be clamped in a machine vise(vertically or horizontally), and one on a round plate to allow mounting on the 4th axis in the machining centers. If it's too spendy, bore some soft jaws with a step for your stop and go to town on those parts.
 
Third for the Kalamazoo

I also use the Kalamazoo collet chuck. I use mine in a 3-jaw set-tru chuck. I also have many other uses for this collet chuck.

Eric U
 
there are various other workholding devices offered, you can analyse all and select the best which can optimise your application.
 
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