• June Project of the Month (Click "x" at right to dismiss)

Lemons, sugar, water, and Ice

[10] Like what you see?
Click here to donate to this forum and upgrade your account!

Mitch Alsup

Active Member
Active Member
Nov 17, 2017
I ordered some a Hex and Square collet holder for general purpose work in my shop.
I ordered ER-40
After waiting 28 days they finally arrived.
When I opened then they did not fit my ER-40 collets.
They looked big enough to fit ER-50 collets, but there was something about the taper that looked strange.

After I measured the taper it was clear they were not of the ER family, but something else.
I considered sending them back, but shipping back to China was as expensive as what I originally paid !?!

After fretting for a while, I decided to make a collet adapter for them.

So I chucked up some 2" round in my 3-Jaw and turned it down to appropriate outside dimensions.
In order to keep concentricity, I removed 3-jaw and inserted 4-jaw.
I mounted the collet holder in the 4-jaw, and dialed it in on the interior taper.
Then I set up the compound with an indicator until there was no movement on the dial over the entire stroke.
I pulled the 4-jaw, and reattached the 3-jaw on the same chuck to spindle marks.
I cut the outside taper.
I pulled the 3-jaw, mounted the 4-jaw, and inserted 1/2" long pin.
After indicating the pin, I slid a tightly fitting 1/2" ER-40 collet on the pin, checked for runout,
Then I set up the compound to the taper on the ER-40.
Off with the 4-jaw, on with the 3-jaw.
Drilled the largest hole I can (3/4"),Then bored the hold out until it had the innermost dimension.
Then I bored in the interior taper.

With no way to measure if the 2 tapers were even close,....I cut the pair of tapers off the stock.

The exterior taper was a good-to-excellent fit to the collet holder.
The interior taper had a lip on it that prevented the ER-40 from going in far enough.
So I mounted the taper adapter in the 3-jaw and worked it until it was round, flat, and centered
Then I bored the interior edge until the lip went away.

Near success, ER-40 collets would slip into the adapter, the adapter would slip into the <whatever> sollet holders.
But the collet bolt would not go on--crap.

So I mounter some 1/2" stock in the 4-jaw, slipped an 1/2" ER-40 collet on the stock and pressed the adapter on the ER-40 collet and whacked the thing with a rubber mallet.

Then I spent the better part of an hour indicating the assembly until it was true, round and square.
I indicated the outside taper to the compound and turned 0.020 off the outside.
And now the collet bolt has at least 3 threads to grab before closing the collet on the stock.


The adapter is the second item from the left.


Runout looks to be about 0.00075 which is fine for my purposes with these holders.

Presto:: Lemons into lemonade.

T Bredehoft

Active User
H-M Supporter-Premium Member
Dec 27, 2014
I made a similar adapter to put ER40 collects in a C5 hex/square block set. It works, but I'm planning on buying an ER 40 set, too, eventually.


If you are gonna be stupid, ya gotta be TOUGH!
H-M Supporter-Premium Member
Mar 29, 2017
Well done, indeed! I have orders of magnitude more patience than I did years ago. Still, for me that job would have been a struggle to maintain the patience required. Vodka would not have been optional.
[5] [7]