ER40 vs. 5C collets accuracy in a lathe?

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Alan H.

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I am trying to sort out my direction in terms of buying a collet chuck for my PM1340Gt lathe. I am trying to decide between a ER40 or 5C collet system.

I have read and studied here and found a lot of information. I have evaluated the numbers of collets required, cost, etc. In addition, I have reached out to a few of my friends via pm and as usual, gotten good insights as to what one can buy and where as well as some of their experience.

So meanwhile, one direct question here -
Which will achieve the most accuracy in a 1340 D1-4 mount lathe with readily available hardware, ER40 or 5C?
 
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That is a loaded question with too many variables. Both are capable of excellent accuracy when well made and accurately fitted to the lathe. They can be more accurate than the lathe spindle. Assuming a lathe spindle with great accuracy, including the internal spindle taper, all of the accuracy of the finished work will be determined by the runout in the tooling. With a hand wheel 5C (or other size) collet closer, the only additional sources of inaccuracy are the collet adapter and the collet. With a 5C or ER collet chuck then the mount to the spindle and the collet holding stuff determines any loss of accuracy. Any of the systems, finely built and properly used and maintained, can provide accuracy better than you can cut on the work. What matters beyond that?
 
Well said, Bob.
My input would be: given equal accuracy, ER40 is more usable with far fewer collets. The collets were designed in the metric system, supposed to accept one mm variation in size with no loss of concentricity. that's .040 in Imperial measure. That works out to be about 1/4 of the needed collets relative to 5C series.
 
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T Bredehoft said:
Well said, Bob.
My input would be: given equal accuracy, ER40 is more usable with far fewer collets. The collets were designed in the metric system, supposed to accept one mm variation in size with no loss of concentricity. that's .040 in Imperial measure. That works out to be about 1/4 of the needed collets relative to C5 series.
Click to expand...
Adding to Tom's post, the 5C collets are perhaps more suited to production type work. They will only really hold work properly within .005" of the nominal size. They are however, faster to put work in and out of, or advance material from longer bar stock through the spindle for repetitive work.
 
Did not intend to be funny or put forward a "loaded question". I am putting forward a serious inquiry. So Bob, what is it that you use?
 
I use 5C collets on the lathe, R8 collets in the mill. Old school. I was not aware of ER collets when I bought them. If I had known about them I might have changed my mind, or maybe not. It really depends on what you are trying to do, and that changes often in many of our shops. The safe answer is that you need to have both!
 
What do you mean by "accuracy"?

I use 5C collets on the lathe. I have a set of ER32 and half a set of Er40 (for use with a T&C grinder). I also have a set of OZ25 (perhaps a precursor to ER40?). I certainly have not experienced any issues with the 5C that make me wish I had an ER chuck. The biggest issue with the 5C seems to be the narrow clamping range - I have never run into a problem with this. Most tooling and material stock comes in standard sizes - so the collets work fine. For the occasional issue I suppose one could skim what need be to fit the next size collet (I have reduced drill shanks for various reasons, though not to make them fit a collet). Also, for an occasional odd ball issue you can usually use a 3 or 4 jaw chuck (for small stuff, I'll use a drill chuck in the head stock).

My vote would be for 5C because the drawbacks are so easy to work around. What I like about the 5C is there is a large selection available (sizes, and shapes), you can also get soft collets and cut them to fit the job (i.e. to hold washers), you can also get oversize collets for quite large short items, you can get/make ID gripping collets (with an expander plug) and can easily set up an internal depth stop on 5C collets. I have never seen them, but you can probably get square holding ER32 collets or soft collets for cutting in unusual shapes - and all the above advantages I described above, but they certainly are not common.

If you get 5C you will not be disappointed. Like Bob says, you will end up with multiple collet systems anyway.

Pretty well any collet system will be pretty accurate. With the typical machines and tools folks hear are working with, any short coming in accuracy (to +/- 0.0005") is because of the operator. If you want better than 0.0000x" then you need to rethink your entire game plan.

What sort of accuracy are you after?
 
Another advantage of 5C collet system is that small chucks are made to fit into the 5C collet holders. If you are in the middle of doing work with the collets, you can switch to a small chuck just as easily as changing a collet to get a task done, then back to collets again, easily and quickly -- without breaking down the collet setup. That is a definite advantage, and I plan to purchase a collet chuck so I can do that. I am not aware of any ER equivalent to that.
 
Neither are more accurate over the other, as mentioned, too many variables but it comes down to the quality of the collect chuck, closure, etc as well as the quality of the collets, thay are not all equal. Each has their advantages & disadvantages which you have to decide what suits you better.

I have ER40 for use in the lathe but only cause I use ER40 in the mill & don't have a set of 5C collets. If I didn't use ER40 in the mill, I might have ended up using 5C for the lathe or if I had to do it over I would use TG150 collets for the lathe.

ER collets were not designed for workholding, they were designed for toolholding, the same for TG collets. But of course that doesn't matter or stop anyone. The use of ER for workholding seems to be popularized by hobbyist. You don't often see ER collets being used for workholding in machine shops if at all.
 
Alan
With limited experience I offer the following observations.
My recommendations would be a ER 40 or ER50 Collet chuck for your lathe. Why?
1 ER collets have a much greater ability to hold a range of diameters in the same collet( >1mm) Need less collets.
2 The size of bar that can be held in a ER40 or ER50 is greater than 5C
3 ER collets are split back and front and grip the workpiece along the full length of the collet. I believe ER collets were developed for holding cutters etc in Mills which requires a very strong grip.
5 While 5C can be held in the spindle taper, to use either collets with through bar, you need some sort of collet chuck. A 5C collet closer is quick for production work but of limited relevance in a hobby shop.
6 A ER50 collect chuck can be made into a set true using a D1-4 backplate so it is easy to remove replace and can be adjusted to negligible runout depending on the skill of the operator.

At present I use an ER32 collet set in a MT5 collet chuck in my lathe. I have the ER32 collets from my mill. The chuck uses a draw bar and I cannot use through bar which is a pain. Changing up to an ER50 gives a much larger range of diameters that can be held 1-32mm or up to 1 1/4 " I think you can obtain special oversizeER collets that are even larger.
I intend to purchase a cheap ER50 Chuck and machine the D1-4 backplate with the locating spigot turned slightly undersized so I can use it as a Set Tru quick adjust. Hopefully being a collet chuck, once set it will rarely need further adjustment but for critical work the option is there.
Ron
 
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