Collet Accuracy

[fizzy]

Well I am very disappointed. After a long time searching I bought a pair of Jacobs Rubberflex collet chucks in L1 spindle mount.
First time fitting one today. I don't think the Triumph 4 jaw chuck had ever been off.
Good news the spindle mount is in mint condition. Key looks like new.

Mounted the chuck. Runout less than a thou on the body next to the spindle.. Great I thought. I have tried a few different collets now and a few different bits of bar. Runout of between 2thou and 5 thou depending on where I measure.

And there was me thinking collets are supposed to be super accurate.

The chuck is lovely to use but not happy with the runout. I haven't tried the other one yet but this is supposed to be the better of the 2.

 

[pressbrake1]

Could be wear, trouble is everything is ancient now.
Check the collet receiving taper in the collet Chuck.
A careful tickle with a internal tool post grinder could bring it back

 

[mtt.tr]

Could be wear, trouble is everything is ancient now.
Check the collet receiving taper in the collet Chuck.
A careful tickle with a internal tool post grinder could bring it back

That's what i would be seriously considering, cant make it worse

 

[fizzy]

One thing I haven't tried yet.
It does say in the manual to tap the locking nut with a lead hammer until it's spot on.
Maybe I should do that and measure off a test bar in a collet rather than off the chuck body?

 

[mtt.tr]

One thing I haven't tried yet.
It does say in the manual to tap the locking nut with a lead hammer until it's spot on.
Maybe I should do that and measure off a test bar in a collet rather than off the chuck body?

Id ignore the od as you only care about the id of the chuck.

 

[Brad93]

OD of my chuck is out but I can get my three jaw to repeat within two or three thou on a bit of drill blank

 

[roofman]

The 1st cut and its bang on..4 jaw if you want to have zero runout

 

[fizzy]

Id ignore the od as you only care about the id of the chuck.

Yes reading the manual helps!
It says to measure runout inside the cone and keep whacking the draw nut with a babbit hammer until the required accuracy is obtained

It just seems alien to me talking in tenths of a thou and using a bloody big hammer to achieve it

 

[Dr.Al]

It just seems alien to me talking in tenths of a thou and using a bloody big hammer to achieve it

When I started working for Renishaw, I was amazed that despite having lots of clever ways of centring angle encoder rings, the most accurate rings of all (for the sub-arc-second accuracy rings) are installed and adjusted with a hammer (and a DTI): have a look at page 8 of this PDF.

 

[sako243]

I thought I had similar when I acquired my small lathe. Checked the outside of the chuck and was a couple of thou out - quickly turned a piece down without the tailstock and was within a thou and as circular as I could tell. The run-out on the surface of the chuck was a very slight coating of surface rust on one side.

 

[Kram]

Put an indicator on the collet chuck taper and if its out then recut it. Ive done on both my chinese ER chucks.

 

[fizzy]

I am happy at last.
After a lot of tapping and fiddling it is now accurate to within half a thou. I bet if I keep fiddling I could get it better but it might go the other way

I think I need a smaller 4 jaw - the lathe didn't like 1000rpm with that lump on it. Finding one with an L1 spindle won't be easy though. 4 jaws the only way to go for zero runout - or perhaps a griptru.
I am sure this will be fine now. Now I just need plenty of practice actually using it

 

[Hood]

I am happy at last.
After a lot of tapping and fiddling it is now accurate to within half a thou. I bet if I keep fiddling I could get it better but it might go the other way

I think I need a smaller 4 jaw - the lathe didn't like 1000rpm with that lump on it. Finding one with an L1 spindle won't be easy though. 4 jaws the only way to go for zero runout - or perhaps a griptru.
I am sure this will be fine now. Now I just need plenty of practice actually using it

Soft Jaws are your friend

 

[Shox Dr]

I don’t think an adjustable collet in an old lathe is ever going to be that accurate, or get repeated readings. Better off machining a collet blank to suit each job. Or soft jaws as Mr Hood says

 

[fizzy]

I don’t think an adjustable collet in an old lathe is ever going to be that accurate, or get repeated readings. Better off machining a collet blank to suit each job. Or soft jaws as Mr Hood says

Well I have just tried several ground blanks of a few sizes from 12mm up to 20mm. Used a few of the collets and they are all very consistent.
One problem though. Rubberflex is a very good name! You can see the work piece move sideways when you put pressure on it. Just A tad but it does flex and that is just on a piece say 10" inches long. It looks like the tailstock will be essential.

 

[Brad93]

These look like nice chucks.

 

[Agroshield]

...One problem though. Rubberflex is a very good name! You can see the work piece move sideways when you put pressure on it. Just A tad but it does flex and that is just on a piece say 10" inches long.

That's not the collet. That's the laws of physics (Jim). Look up deflection of a cantilever beam (delta = P * L ^3 / 3 * E * I).

Have a close look at the collet. The one and only thing the rubber does is to keep the steel fingers aligned and separated. Burnerd used springs for the same thing in their collets.

 

[zx9]

Well I have just tried several ground blanks of a few sizes from 12mm up to 20mm. Used a few of the collets and they are all very consistent.
One problem though. Rubberflex is a very good name! You can see the work piece move sideways when you put pressure on it. Just A tad but it does flex and that is just on a piece say 10" inches long. It looks like the tailstock will be essential.

At ten times diameter it will flex.

That's not the collet. That's the laws of physics (Jim). Look up deflection of a cantilever beam (delta = P * L ^3 / 3 * E * I).

^^^^^^^^^^^^ far more learned than I could have put it.

 

[Hood]

These look like nice chucks.

They are ok I have one, think the collets go to 2" on mine, hardly ever use it though. Occasionally I will use it clamped in the CNC chuck for small dia stuff, the CNC hard jaws only go down to about 14mm or so.

 

[fizzy]

That's not the collet. That's the laws of physics (Jim). Look up deflection of a cantilever beam (delta = P * L ^3 / 3 * E * I).

Have a close look at the collet. The one and only thing the rubber does is to keep the steel fingers aligned and separated. Burnerd used springs for the same thing in their collets.

You are spot on of course.
Yes the metal fingers actually do the gripping.
Maybe I should use my degree more. In fairness it was astrophysics and quantum dynamics