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Aciera F3, ER32 retrofit.

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NeoTech:
So most of you know by now i got a new machine with some collet issues.

So i got this ER32 20mm straight shank collet chuck.. Sweet. Standard stuff. It has a 50mm long shank with a M10 drawbar thread.
I was thinking cutting this thing and put it in a 20mm collet with a 24mm runout to hold with.. BUT.. then i struck me.. Why not make a new drawbar.


So i got this idea.. Its a new drawbar that mimicks the old ones dimension but with a 10mm thread in the drawbar end instead. And a small "collet" is made
so that the ER32 can sit in the W20 spindle without causeing wobble and other troubles.

One of the big concerns i have i slotting the ER32 chuck (see different thread under how do i). But on second note i have a concern about a 10mm thread holding
that badboy in place. Of course the small adapter collet could be slotted so some gripping force could be applied there. But still the major force would sit in the
drawbar threads itself wouldnt it?!

NeoTech:
So i went ahead and made this



And after everything assembled and i turn the spindle on i could see something were off.. terribly. The runout on the ER32 collet is off with a couple of 1/10mm, im taking an educated guess and would say 3-4 or so.. its a noticeable wobble.. I wonder what went wrong.

The brass on the drawbar is pressed on and machined to dimension its a slipfit with oil film in the head of the F3.
The other brass is just sitting in the end of the spindle to center the ER32 collet.. i drilled that with a 15mm drill and then took a boringbar, and took it up to the dimension of the  ER32 collet shank, it slips on and need some effort to get loose again.. BUT its not a slip fit in the spindle nose..its has about 1/100 of play, i'm thinking what if i made a compression version instead. that is oooh so slightly oversized but would be compressed in the spindle like the original schaublin collets.

Anyone wanna venture a guess?!

PekkaNF:
I think I finally got it :doh:: You are trying to locate the ER-holder front end with thin cone and back (far) end with draw-bar? If this is the case, please read on and comment, otherwise ignore my ramblings:

1) I hope you are not trusting the draw bar to center end of the collet holder? :palm:
* Most likely the thread on the collet holder is off-center and skewed. If the draw bar assembly is too good fit it might bend it out of alignment.
* You want both registers on the same piece (I.E. front cone and rear "ring". You don't want to trust thread to locate anything radially or axially.
* If I got this right you have three registers: Cone, ER-holder side draw bar and upper side of the draw bar. There is no practical way you get this straight repeatedly. You must put two registers on the collet holder and allow the draw bar collet holder side have will of it's own.

Believe me on this one one. Thread is great pulling stuff together but thread itself should not generally be trusted to loacte anything if it can be avoided.


2) How true is the collet holder? If you:
* clean up the collet holder, collet and nut
* chuck a piece of ground stock
* and turn the whole assy from ground stock (I.e. center the ground stock on lathe)
DO NOT support the collet holder on the far end - I'm guessing that the trouble is there

How would the collet holder turn out to be?

I think that objective should be to locate the front end of the holder with cone and far end with a "ring". And all these on the same integral part, to keep the stuff concentric. If you make these with sliding fit they will "live" when you put them under load.

I would machine the cone into ER-holder ( I need to bash these chinese holders all the time, because mu milling machine has MT3 with dogs). Measure carefully, but normally they have enough meat  in the end. If not see if this could me made out of ER32 MT4 or MT3 holder. The reasoning is that thing "rings" are not great idea under multidirectional loads. They will shift/turn. You either need strong enough "collet" closer to nominal 16 mm ID or such that was the design of this collet type

I also would check the diameter at the end, these collet holders don't always conform standard fits. I would machine there a recess and press strong enough bushing there (either press fit or strong "stud" loctite), and then I would skim the outside of this bushing on the same setting that the cone is machined to keep then concentric.

I would not trust the draw bar to locate the end of the holder. Too many variables. I actually would machine the end that comes next to ER-holder very much smaller diameter to allow the ER-holder far end to locate it's own.

Pekka

NeoTech:
 Ah ok, well i just tried to replicate what the original drawbar does atm. And that was a failure.

I did turn down the ER32 shank slightly and put a drive keyway into it. I hade some hope that the brass rings would locate it mosly cause they are turned on each axle so they sit concentric to it. But the slop on the ring sitting on the er32 collet itself i guess will make it wobble like crazy atm. Or im just so off centre that its sad. :D

Gonna give this another go. The drawbar itself is not centering anything atm, it just rides the bushing on each bearing position. But im thinking that the bushing sitting on the ER collet it self, it has a 15degree angle on it. It should be done in a slight oversize and slit open so that it will compress around the axle when its drawn into the spindle cone. So if i turn that on the ER collet shank and make the outside diameter like 1/100 to big so the cone will press down onto it. shouldnt that center itself "better" then?! Or im thinking wrong here.

NeoTech:
Addendum; there isnt enough material to machine the  cone into the collet holder itself. And i didnt buy a cheap chinese one. I went and bought an expensive one. (next time i buy the chinese... cause they are half he price  :doh:).

But been thinking, i could prolly tig some brass onto that shank and build up a machineable layer that could be machined to fit that cone and centrered on there.. could that be one way to go?

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