Thread: ER Collet Chuck Spindle Nose Blanks.

Originally Posted by Abratool

None of these could help me with the 64/90 compound gear & other gears required.
I contacted Hercus S.A who quoted me $680 for a set of gears & a delivery time of 10 weeks.

Pipeclay provided the 64/90 compound gear & the other 8 gears to complete the set for $325 a big reduction from the Hercus price of $680.

regards
Bruce
ABRATOOL

While OT, in case this comes up with anyone doing a search later I thought I'd just correct this area regarding transposing gears for the 260, as the above led to a lot of head scratching down my end. After chatting to Bruce we discovered there was actually a typo in the above, the correct 260 transposing gear is 60/63. Personally I'm quite surprised they went down that path as the conversion from inch to metric is 25.4 mm per inch. That can be divided by 2 to give 127, which is a prime number and can't be further divided. This is the reason 127 tooth gears are used in lathes to convert from inch to metric as they will give a perfect conversion. However 127 is quite a big gear, so instead some approximations can be made and this is what Hercus have done on the 260, 63 is approximately half 127 and will give a conversion that would probably be good enough for most people. However just looking at the machine I would expect a 127 would fit, and the previous model's gear chart can be used. If any member lives near me and has an imperial 260 they would like to see if the 127 would fit, I'm happy to swing by and we can try it. Not only would that allow a perfect conversion to metric, but the complete set of transposing gears is just over HALF the price quoted above!

Hope that helps.

Pete

Originally Posted by Swarfmaker1

The fine thread can be milled or ground in cast iron.



What's the justification for this? Anti-wear or a safeguard against shearing the threads due to excessive clamping forces? Are you referring to the nut threads or the chuck threads?

Please give us a reference to the site so that we might investigate further.

Hi Swarfmaker, the ER32 nut fenmale thread is 40x1.5mm and hardened. I am afraid but such fine male thread would be rather fragile on a cast iron collet chuck. I could imagine chunks of thread breaking off pretty soon. If you want to use something cast, maybe cast steel would last a little better than cast iron? It may be hard to get though as round stock.

All commercial ER collet chucks for lathe use that I know of are made of some steel, not cast iron. Maybe a free cutting stainless steel would be an otimal choice, as it finishes extremely well and as a bonus won't rust.

By the way, as far as I can tell ER coillets are not hardened as hard as the usual lathe collets. This is because ER collets were originally intended for toolholding, not workholding. And tools like mill cutters having hss or carbide shafts. In industry ER collets are consumables with a limited life, maybe 100 or 200 hours running time on a CNC machine.

I think the first to use ER collets in a lathe chuck were the Austrian EMCO. They made 3in1 lathes with a rear bed mounted milling head. The mill used ER collets, and having an ER collet chuck for the lathe spindle did let the users share the same collet set for milling and turning (thus saving money as 30 years ago there were no cheap Chinese collets). The idea has since become very popular for home/hobby shops.

Chris

Pete, many vintage lathes used the compromise 60/63 to convert between threading worlds. Not only the Hercus 260. The error is very small. I agree the error would be unacceptable if say making a leadscrew for a machine tool. But for just about any conceivable fastener application, the error is negligible. I personally do not care, as anything having to be accurate I do in Metric (I grew up in a metric country, I think in metric, I draw in metric, and anything imperial is at best like a third language to me). My metric Hercus 260's 60/63 gear set serves me well to do these for me rather rare but unavoidable imperial threads, like these odd NPT fittings for compressed air or Withworth for water pipes.... Chris

Hey Chris, I'm just a little surprised they decided to change it from 127 was the main point. Especially since they used the larger gear on the earlier models. I'm still keen to know if the 127 will fit on a 260 as it would certainly make life much easier for owners who needed a transposing gear.

Pete

What's the justification for this? Anti-wear or a safeguard against shearing the threads due to excessive clamping forces? Are you referring to the nut threads or the chuck threads?

Please give us a reference to the site so that we might investigate further.

the site is the home model engine machinist site

Building an ER collet chuck from scratch for a Myford ML7

the original poster found that with his rather indifferent piece of cast iron he chipped the 10x 1inch Myford internal thread and found that sections of the fine collet closer thread broke off when machining.

Anyway isn't it one of those old engineering maxims to use cast iron in compression rather than tension?

Thinking back to materials science, once you reach the Ultimate Tensile Strength with cast Iron, the sample tested broke quickly and with a loud bang and fractured along the crystal boundaries within the sample and did not show signs of ductility.

Steel on the other hand is ductile and for moderate loads is to a point elastic.

Getting back to the point with a chuck backplate thread is in compression but the collet closer nut exerts a tensile force onto the body of the collet adaptor through the fine thread.

My prejudices in this matter which is shared by chris (cba_melbourne) is that cast iron would not be a good material for this application due to the force exerted on a relatively weak collet closer thread on the cast iron body.

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Regards,
David