Manual machining: ER40 collets

I have been annoyed by the 5C collet system for my lathe for some time. It’s a pretty janky chuck anyway, and the design of the 5C set really doesn’t tolerate non-standard stock sizes well because the jaws are hinged at the back and end up clamping undersized stock non-parallel. By contrast, ER collets are hinged front and back and hold stock parallel through about a 1mm range per collet. They are also available in both metric and imperial sets so they can be a good, convenient fit for both metric and imperial stock. ER40 works all the way up to 26mm, which is fairly impressive. When Blondihacks put an ER32 on her lathe and it worked well, I started thinking seriously about ER, but figured with my larger lathe I’d rather go with the larger ER40 system.

I’d been haunting the Amazon listing for the Shars D1-5/ER40 set since last summer when it went out of stock, and when it came back into stock I immediately ordered it for my (comically large, 14x40 inch) lathe. Then I got a metric ER40 collet sets ranging from 0.5mm to 26mm and an imperial set ranging from ⅛" to 1", bought an R8/ER40 adapter for the mill, and a set of square and hex ER40 collet blocks, and some extra collet nuts to make it easy to quickly interchange tools.

The R8/ER40 adapter for the mill had 8 tenths of runout — four times its advertised max. I got a replacement, and it had the same problem. (The problem wasn’t in the mill spindle; that has less than a tenth of runout inside the nose on the mating taper — which is frankly awesome.) So both the original and the replacement are going back.

The D1-5/ER40 lathe chuck had an oversized D1-5 taper and can’t be made to register, so it’s going back. I got help from Hobby-Machinist to make that call:

About five minutes after I ordered the Shars D1-5/ER40 set, I discovered that Precision Matthews had one as well, and then today I discovered that they also have an R8-ER40 adapter. So I’ve ordered one of each, and hopefully soon I’ll have working ER40 system across the mill and the lathe.


The lathe collet set from Precision Matthews is sweet. Fully finished. Registration repeats perfectly. At about a tenth (one ten-thousandth of an inch, about .0025 mm) of runout I quit trying to improve it.

The R8-ER40 adapter is better than the more expensive unit from Amazon and more accurate, but still about 5 tenths of runout. I expect to use R8 collets most of the time in the mill anyway, and it’s easier to take 5 tenths TIR for $30 than 8 tenths TIR for $55. The lathe is my main reason for ER40 anyway.

Still waiting for the collet blocks. They haven’t arrived in the US yet…

1 Like