Collet confusion.

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Collet confusion. Kevin(Bluey) 07-03-2008
Posted by Peter Fairbrother on July 4, 2008, 5:47 am
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 David Littlewood wrote:
>> David Littlewood wrote:
>>> The great advantage of ER collets is that their double taper means
>>> they can close down by 1.0mm (0.5 for the very small sizes) and
>>> still maintain excellent grip and concentricity. Collets with a
>>> single taper only work efficiently for material of the exact diameter
>>> of the collet; even normal mild steel (usually a few thou under
>>> nominal) can be a problem with single taper collets.
>>
>> I'm not sure that it's the double taper so much as the fact that there
>> are eight gripping segments, rather than three in a normal collet.
>>
>> In a three-segment collet the inside of the segments is round, and if
>> it is used to grip a tool which is slightly smaller than the hole then
>> each segment will only touch the tool on a thin line.
>>
>> With eight (or perhaps sixteen) segments an ER collet will grip on 8
>> or 16 lines, rather than 3.
>>
>> Also, as there are 8/16 gaps, they can close up more than i=f there
>> are three gaps.
>>
> The eight slits help improve grip, of course, but I believe it is the
> double taper and the fact that the slits are alternately from front and
> back. This means that on closing down the collet grips the work or
> cutter at front and back (indeed probably all the way along) instead of
> just at the front.

Yes, it's most helpful having the contact surfaces go all along the
length (rather than squeezing one end of the tool shaft at the point
where it leaves the collet, and leaving the other end inside the collet
wobbling about).

This happens because the inside of an ER collet remains parallel to the
tool when compressed, because the main taper acts along all the length
of the collet. Move the collet in a bit and both ends move in, rather
than just one.

A collet with a single taper would do this too.


I'm not sure what the second, front taper on an ER collet does? Makes
the front end grip hardest? angles the compressive force properly?

Anyone?



-- Peter Fairbrother



Some text books even show this diagrammatically.

You read the instructions?


>
> David

Posted by David Littlewood on July 4, 2008, 7:57 am
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>
>Yes, it's most helpful having the contact surfaces go all along the
>length (rather than squeezing one end of the tool shaft at the point
>where it leaves the collet, and leaving the other end inside the collet
>wobbling about).
>
>This happens because the inside of an ER collet remains parallel to the
>tool when compressed, because the main taper acts along all the length
>of the collet. Move the collet in a bit and both ends move in, rather
>than just one.
>
>A collet with a single taper would do this too.
>
>
>I'm not sure what the second, front taper on an ER collet does? Makes
>the front end grip hardest? angles the compressive force properly?
>
It may be that it allows easy changing of collets from the front without
need for a drawbar (apart from the one on the collet chuck, of course).
But I think the front taper, as you say, improves the grip at the front.
>
>Some text books even show this diagrammatically.
>
>You read the instructions?
>
Well, more that I just noticed it somewhere. Actually, there is a little
subtlety in loading an ER collet into the closing nut, so RTFM is not a
bad idea in this case.

David
--
David Littlewood

Posted by Kevin(Bluey) on July 4, 2008, 12:47 am
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Peter Fairbrother wrote:
> David Littlewood wrote:
>>> Hi ,
>>> I have been surfing sites like Chronos , RDG and RHR looking for some
>>> tooling and I noticed the number of different collets available ,
>>> this is leading to some confusion on my behalf.
>>>
>>> Just wondering why there are so many differnt collets , there are ER
>>> 32, ER35, ER40 etc and probably a heap more that I have not seen or
>>> heard off .
>>> What are differences and advantages one over the other.?
>>>
>>> The ones I remember from my trade days were threaded and were drawn
>>> into the lathe spindle using a draw bar and hand wheel on the out
>>> board end of the spindle.
>>> (Hope I'm not telling my age here.)
>>>
>>> I'm not looking to buy any , as I have a full set of what I think are
>>> Myford collets and a chuck that came with the Super 7 . There is one
>>> "ring in" in the set it has Hardinge stamped on it and is slightly
>>> different in the profile (concave)on the front face.
>>> I don't use them a lot ,but if you are machining lots of parts from
>>> small diameters they would make life easier.
>>>
>>> Thanks .
>>
>> The great advantage of ER collets is that their double taper means
>> they can close down by 1.0mm (0.5 for the very small sizes) and still
>> maintain excellent grip and concentricity. Collets with a single taper
>> will only work efficiently for material of the exact diameter of the
>> collet; even normal mild steel (usually a few thou under nominal) can
>> be a problem with single taper collets.
>
> I'm not sure that it's the double taper so much as the fact that there
> are eight gripping segments, rather than three in a normal collet.
>
> In a three-segement collet the inside of the segments is round, and if
> it is used to grip a tool which is slightly smaller than the hole then
> each segment will only touch the tool on a thin line.
>
> With eight (or perhaps sixteen) segments an ER collet will grip on 8 or
> 16 lines, rather than 3.
>
> Also, as there are 8/16 gaps, they can close up more than i=f there are
> three gaps.
>
>
> -- Peter Fairbrother
>
>>
>> This means that a set of ER collets will grip anything within their
>> range - you don't need a metric set and an imperial set, for instance.
>> They will grip milling cutters effectively. The collets themselves do
>> not need a drawbar as the double taper holds them in; it is the collet
>> chuck itself that needs a drawbar, at least when holding milling cutters.
>>
>> The different numbers are just sizes. ER25 (the set I use) goes from
>> 1.0 to 16.0 mm; the larger sets have a correspondingly larger range.
>>
>> David


David ,
Thank you for your in informative explaination ,its has been most helpful.
This news group is one of the best on usenet , and the people friendly
and helpful.

--
Kevin (Bluey)
"I'm not young enough to know everything."

bluey69@west.net.com.au

Posted by Hugh on July 6, 2008, 5:52 am
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hello Kevin,
just one thing to point out - although each closes down by up to 1mm - it a
good idea at the outset to decide if you are 'imperial or metric' - it isn't
true to say that a set will hold all cutting tools within the range of the
set.
If you look at the link below, you will see that the 14mm collet will close
down to 13mm, but the next one down is a 12mm collet - so there isn't a
collet to hold a 1/2" tool - ditto 1/4".
So you might need to buy extra collets to fill in - or go one way or the
other from the start!
http://cgi.ebay.co.uk/ER32-Collet-Set-12-Piece-MT3-Metric_W0QQitemZ320199826872QQihZ011QQcategoryZ12584QQtcZphotoQQcmdZViewItemQQ_trksidZp1742.m153.l1262

Hope that helps without adding to any confusion!
rgds
Hugh

> Hi ,
> I have been surfing sites like Chronos , RDG and RHR looking for some
> tooling and I noticed the number of different collets available ,
> this is leading to some confusion on my behalf.
>
> Just wondering why there are so many differnt collets , there are ER 32,
> ER35, ER40 etc and probably a heap more that I have not seen or heard off
> .
> What are differences and advantages one over the other.?
>
> The ones I remember from my trade days were threaded and were drawn into
> the lathe spindle using a draw bar and hand wheel on the out board end of
> the spindle.
> (Hope I'm not telling my age here.)
>
> I'm not looking to buy any , as I have a full set of what I think are
> Myford collets and a chuck that came with the Super 7 . There is one "ring
> in" in the set it has Hardinge stamped on it and is slightly different in
> the profile (concave)on the front face.
> I don't use them a lot ,but if you are machining lots of parts from small
> diameters they would make life easier.
>
> Thanks .
> --
> Kevin (Bluey)
> "I'm not young enough to know everything."
>
> bluey69@west.net.com.au



Posted by on July 6, 2008, 6:23 am
Please log in for more thread options
> hello Kevin,
> just one thing to point out - although each closes down by up to 1mm - it=
a
> good idea at the outset to decide if you are 'imperial or metric' - it is=
n't
> true to say that a set will hold all cutting tools within the range of th=
e
> set.
> If you look at the link below, you will see that the 14mm collet will clo=
se
> down to 13mm, but the next one down is a 12mm collet - so there isn't a
> collet to hold a 1/2" tool - ditto 1/4".
> So you might need to buy extra collets to fill in - or go one way or the
> other from the start!http://cgi.ebay.co.uk/ER32-Collet-Set-12-Piece-MT3-M=
etric_W0QQitemZ32...
>
> Hope that helps without adding to any confusion!
> rgds
> Hugh
>
>
>
>
>
> > Hi ,
> > I have been surfing sites like Chronos , RDG and RHR looking for some
> > tooling and I noticed the number of different collets available ,
> > this is leading to some confusion on my behalf.
>
> > =A0Just wondering why there are so many differnt collets , there are ER=
32,
> > ER35, ER40 etc and probably a heap more that I have not seen or heard o=
ff
> > .
> > What are differences and advantages one over the other.?
>
> > The ones I remember from my trade days were threaded and were drawn int=
o
> > the lathe spindle using a draw bar and hand wheel on the out board end =
of
> > the spindle.
> > (Hope I'm not telling my age here.)
>
> > I'm not looking to buy any , as I have a full set of what I think are
> > Myford collets and a chuck that came with the Super 7 . There is one "r=
ing
> > in" in the set it has Hardinge stamped on it and is slightly different =
in
> > the profile (concave)on the front face.
> > I don't use them a lot ,but if you are machining lots of parts from sma=
ll
> > diameters they would make life easier.
>
> > Thanks .
> > --
> > Kevin (Bluey)
> > "I'm not young enough to know everything."
>
> > blue...@west.net.com.au- Hide quoted text -
>
> - Show quoted text -


Hugh

Correct for the "part" set that you provided a link for but the normal
"full" set for ER32 includes 18 collets and does cover the full range
and the ER 25 full set includes 15 collets and does likewise.

http://www.chronos.ltd.uk/acatalog/Chronos_Catalogue_Sets_of_ER_Collets_131=
.html

Regards

Keith

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