ER25 collets

[Doug J]

I have just bought a set of ER25 collets and a closing nut and wish to make a collet chuck for the lathe. My problem is that I can't find the included angle of these collets in order to make the chuck body. The second problem is how deep to make the internal taper to ensure that the collets can be closed properly without the closing nut fouling the end of the chuck. A few dimensions from anybody with a commercial chuck would be appreciated.
Doug

[NigelMuskett]

There was an article in Engineering in Miniture about making an ER32 collet chuck for the Myford lathe.

AFAIK each size of ER collets are bigger versions than the last. The angle if I remember is 8⁰ .

The fit is very important so using the angle is not much help anyway. Put a length of silver steel in the chuck and slide a suitable ER collet onto it. Stick your mag base and clock on the top slide and adjust the top slide to give a Zero deflection on your clock when running up and down the collet. It is then exactly the right angle.

(remembered from reading the article) I have a set of ER32 collets and intend one day to make a collet chuck and not be lazy a buy the Warco chuck

Nigel

[Doug J]

Thanks for the reply Nigel, I like your idea for setting the taper. The only problem may be finding a suitable diameter of rod to match one of the collets.
Doug

[SteveW]

I went down a similar route as outlined in the 'Make a ER32 Collect Chuch for a Myford' article. I got as far as making a dummy Myford nose and screwed up twice on making the female thread on the chuck body. Could never get that hang of women.

In the end I bought the ER32 chuck from Warco/Chester and a couple of back plates. I also notice the Chronos do something along the same lines (ER25 I think).

Just a thought on setting the cross slide angle. If you do simply stick a bit of silver steel in the chuck and slip a collet over that to get the angle and do it successfully then you've got a chuck good enough not to need a collect chuck. I might be better to stick a bit of rod in the chuck and then take it down to fit one of your collects and then match the angle with a DTI.

[houstonceng]

Doug

There was an article in MEW (IIRC #42) about making a fixture for 4 facet drill grinding using ER25 collets as the holding medium.

That article refers to another one in MEW about setting up for the 16 degree included angle using the method of turning a bobbin with known distances and then measuring the major and minor diameters - ie trial and error from the nominal setting of the compound rest.

Personally, I bought the Warco version. Life's too short for making tools. I'd rather make steam engines, however, each to their own.

A. N. Other Andy

[Doug J]

Thanks to those who have replied to this thread. The second part of my original question remains unanswered however, namely the distance that the collet protrudes from the collet holder when in its fully open state. Even info about an ER32 collet holder might help to give me an approximate guide for my ER25 holder.

[Tim Bayliss]

O.K. Doug,
Here's a nice convoluted way to answer your question about collet standout, it's a straight forward trig. problem.
Although ER collets are manufactured to an upper diameter they are designed to close a full 1mm on diameter, therefore if you take the largest ER25 collet marked 16-15/5/8", at 'rest' it accepts a bar of 16mm dia. but is able to close down to 15mm (taking in 5/8" on the way) when fully compressed, this makes them more useful than other types of collets.
Knowing that the included angle is 16 deg. we can produce a right angled triangle where the smallest angle is 8 deg. (half of the included angle) and the OPPOSITE side is 0.5mm (half the total closure). The hyponenuse being redundant in this case, we can calculate the ADJACENT side from Tan 8 deg = 0.5mm devided by the ADJACENT. This transposes and calculates to a linear compression of 3.56mm, this being how far we have to press the collet into the chuck to close the collet by the full 1mm on diameter.
Now give it a bit extra for luck (or lack of it more like!) and machine your taper to allow your collet to stick out of the chuck far enough to be able to compress it about 5 or 6 mm with the nut. Do not overtighten when empty as this will permanentlly damage the collet.
Phew! I hope you got all that.
Best of luck,
Tim Bayliss

[Doug J]

Thanks Tim - sorry for the delay in replying, I have been away for a few days. I just had a "why did I not think of that" moment on reading your reply - quite brilliant, thank you. I am always amazed at the number of sharp minds out there willing to lend a hand.

[lancelot]

Hello Tim,
correct me if I am wrong,but I think that ER25 collets work,by locating on a locking flange inside the chuck[this allows for withdrawal of the collet from the headstock spindle].
Pick any collet ,and insert it with a slightly slanted screwing motion into the collet chuck,the [locking flange]locks it in position so that it can not pull out with a straight pull nor can it push forward to protrude from the front of the chuck.
As my set is for MYFORD lathe and the collets load directly into the headstock spindle,when the chuck and collet assembly is screwed on to the headstock spindle ,the locking flange in the chuck pushes the collet BACK into the headstock spindle,thus locking any material located within the collet.With collet chuck tightened,the collet should not protrude from front of collet chuck.
I think that your theory may be correct,but possibly the wrong way round.0}} I am no maths expert.
All the best for now,
John.

[Tim Bayliss]

Hi there,
The ER range of collets use the very simple expedient of pressing a taper (the collet) into a matching taper (the chuck). There are no ridges or flanges in the chuck, just a plain taper, and when the collet is pressed into this taper by the nut, axially, it of course is compressed radially by the action of taper on taper, thus holding the workpiece, or whatever.
What you may be thinking of is the withdrawal ring that is machined into the nut. The collet/chuck tapers are 'self holding' (like morse tapers) so the collet can stick in the chuck. The withdrawal ring machined in the nut draws out the collet as the nut is unscrewed, this aids removal if it has become stuck in the chuck during use. This ring is machined off centre relative to the collet/chuck axis to facilitate collet insertion into and removal out of the nut.
Hoping this has clarified things for you.
Tim

[lancelot]

Hello Tim,
You are right,of course.
Transpose CHUCK for NUT in my post,as the nut and collet assembly fit directly into my lathe headstock spindle,and the nut screws onto the end of the spindle driving the collet into the spindle[or CHUCK]as it should be called in this instance? thus clamping the work located in the collet,although any collets that I have used so far did not protrude beyond the face of the nut.
I wonder if Doug's system has the separate ER25 chuck which fits into his headstock spindle{ie/mt2] so would both setups be relevant to your theory ?
All the best for now,
John.

[Doug J]

I have now made my collet chuck. Rather than using the morse taper to locate the chuck body I machined the inner end to screw onto the headstock nose and this has produced a much more rigid set up. The end result is superb and I am hoping that the unhardened inner taper will not wear too much in use.
The machining of the taper was a bit of trial and error but the end result has made it all worthwhile. Machining the body while fitted to the headstock had made it extremely accurate in use.
Doug