Crawford multibore collet chuck

[chipenter]

I was lucky to get a Crawford multibore T980 chuck from a friend , I fitted this to a backplate this morning had to take it apart to set up for drilling and tapping as part of the chuck overlaped the mounting holes , interesting construction as the potos show , the collets are sticky and not all of the fingers come out and only eight collets nine in the set , the run out is a couple of thow but may inprove after I have cleaned the collets .

[Manxmodder]

Very nice piece of kit  .  Appears to be very similar to the Pratt Burnerd multi size collets and chuck which are available either as a key tightening model like yours,or the quick release lever lock type which I have for the Harrison.

Are your collets pushed open by hair springs or are they the rubber flex type?......OZ.

[chipenter]

It's a KC10 not a T980 only goes up to 1 inch , yes they are springs and quite stiff the collets are in penatrating oil overnight , they haven't been used for so long the oil has set .

[RotarySMP]

Very tasty bit of kit.

Mark

[chipenter]

Glad to report all collets are now free , a piece of 7/8" silver steel as a test piece gives just under 4 thow at 11 inches from the chuck , the chuck aperes to have been reground as there is engineering blue inside and on the outer lip , the collet left marks on the outer edge of chuck posably the grinding is a little out , now I have put a back plate on the lid of the box now longer fits .

[Manxmodder]

  Looking good chipenter.

I agree the ground finish does look rather coarse to be original. You could always true the cone area up by
taking a light cut on the taper with a indexable boring bar fitted with a cubic boron nitride (CBN) insert tip.

They work a treat for turning  hardened steel and would ensure concentricity to your headstock.

Link to CBN inserts I have used for such purposes in the past:
http://www.shop-apt.co.uk/cbn-turning-inserts.html

EDIT TO ADD: I emphasise only a light cut,a couple of thou may be all you need to get concentricity.

OZ.

[chipenter]

Put a clock on the taper zero run out , I have a toolpost grinder and a small diamond stone , but will try triple 0 emery first .

[seadog]

I wouldn't rely on the silver steel being ground true.

[Manxmodder]

Put a clock on the taper zero run out , I have a toolpost grinder and a small diamond stone , but will try triple 0 emery first .

Just re-read your earlier post where you say 4 thou run out at 11" from chuck.

It would be interesting to see what sort of run out reading you get with a shorter test piece and clocking closer to the chuck.....OZ.

[chipenter]

Put a clock on the taper zero run out , I have a toolpost grinder and a small diamond stone , but will try triple 0 emery first .

Just re-read your earlier post where you say 4 thou run out at 11" from chuck.

It would be interesting to see what sort of run out reading you get with a shorter test piece and clocking closer to the chuck.....OZ.


Les than half a thow , I cant find any info on this chuck as it's no longer made , the angles vary from 14 , 14.5 to 15 degrees for the outher collet sizes .

[chipenter]

Used some 1200 grit wet and dry on the taper only took a few minets to smooth it , tried two pieces of bar twenty thow cut if the taper was out I would get a rough finish , got a good finish so it can't be out , first is mild steel second is stainles .

[Manxmodder]

Half a thou runout is pretty good, I'd be happy enough with that.

 I have seen those collets  come up for sale individually on fleabay a few times so may be worth keeping an eye open for the one you're short of.

What size are you missing?.......OZ.

[chipenter]

It's a full set KC10 1/16" to 1" the T980 goes to 1 1/8" but I don't know if they would fit , each type of chuck seems to have a diferent angle it's a minefield .

[chipenter]

The taper is definetly out by 1 degree , blued up a capstan socket and fited it in by hand until I just couldn't turn the socket , and could get a .15mm feeler guage in the end , moved the compound and ground it out with the toolpost grinder , still neds a polish but the jobs a good un no rattle .