The number after the ER is based on the outer size of the collets and the bigger the outside the bigger the internal hole can be. For work holding I would suggest ER32 or at a pinch ER25 if you have a small machine.

This shows where the size “D”is taken from and also the available size ranges “d”of the collets for each ER size.

If you are only going up to 16mm then ER25 is ok for that but you can also get oversize to 20mm. One problem is they dont cater for boys with desktop size machines so I made blocks for ER16/11 and 8, they come in handy. The ER no refers to the largest dim of the mouth of the taper.

If you google ER taper specs its quite informative and it might help to make your mind up. by the way the oversize collets are not always available you just have to keep your eyes open. No ChatGPT used here.

Yes Jason the 5c indexer is the go to thing and with the adaptor much more useful but again its the size hence the ER16 size one I made which is good on small machines

For info my set of Arc Stevenson’s ER25 Collet Blocks have 18.5mm through holes.

I have an Arc 5C/ER spindex, but if you are short on space be aware they are not very small. I have no collet blocks…

1 important mod is to add a key to the index plate so it can’t slip on the spindle (damhikt…)

Dave

Rather Cute :

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although it’s only a block.

MichaelG.

Yes Paul “enjoy your Machining” is definitely what its all about. Heres the Er16 version

First job to do after getting a spindexer is to true up the base sides so they are exactly in line with the spindle. Assuming the three I’ve had through my hands are typical they are generally close but not dead on. Makes alignment far easier.

For non critical jobs I just drop a parallel into an appropriate Tee slot on my Bridgeport and push a (trued up) side of the spindexer against it before clamping down with step blocks and bars out of my import clamping kit. Making a sub base so i can simply bolt it down in the slots has been languishing on the “must get round to it” list since about a week after I bought it. Over a quarter of a century now so I probably won’t live long enough! Just don’t use it quite enough for the extra inconvenience of setting up clamps over simple Tee nut and stud to hit the red mist, arm powered satellite on launch pad, level where it will get done right now.

I find the standard clamp adequate, albeit upsetting to my feelings of engineering aesthetics, but I have other means to handle anything needing heavier cutting. There is an envelope with a sketch of an adapter to fit a split collet clamp in place of the standard device lying around in the “do it one day” file. Fundamentally simple but it does need proper drawing out to make due mostly to needing an add on part for the split collet to work in.

I agree that the index plate does get in the way at times and have contemplated reversing things so the plate is at the other end. No engineering reason why it couldn’t be done. I think a careful Internet search will find details of how to do it, possibly a write up of American origin also including and improved clamp.

Shortly after buying mine I purchased a small 3 jaw chuck on a 5C mount for £ very reasonable. The Chinese made chuck is decently accurate, unreasonably so given the price and the limited number of turns on the scroll. It’s very useful, probably sees more use that collets, more so since trading up the my Smart & Brown 1024 with its 5C native spindle nose bore. Nice to have a small chuck for fiddly jobs. But I’d not trust it beyond about 1,500 rpm, short scroll must limit the ultimate grip.

Getting back to collet blocks a bed stop of some description is pretty much essential for getting the block back into the vice after turning without upsetting the job position. Due to the overhang relative to the vice base some care is needed when tapping down to ensure the block is flat and level. Very easy to inadvertently put a bit of tilt on.

Clive

On 23 October 2024 at 16:12 Bob Said:

If you do try a collet block double check its concentricity and flatness/ parallel of the faces. I have one of ‘uncertain origin’ and it was a long way out.

 

Bob

 

Excellent point Bob.

However I thought I had that issue but eventually the penny dropped that I was only getting tapers on the machined, top, surface. Further investigation revealed that my tapping down technique was inadequate so creating the error. Interestingly the error was very consistent which at least demonstrated my, inadequate, technique was repeatably wrong.

On reflection i don’t think I’ve ever worked on anything other than the top surface of job held in a collet block. Working on the side is perfectly feasible, but to my recollection I’ve never done it over my quarter of a century or so ownership of collet blocks.

Clive