Thread: 4 facet sharpening problems, ER40 collet block doesn't hold the drill concentric

I've been messing about with 4 facet sharpening, using a 3-way vice and a 4 sided ER40 collet block to hold the drill in a T&C grinder

Most frustrating trying to get the facets to cross nicely and the drill to drill on size - the resulting hole is about 22.24 (worst case) for a nominal 22 mm drill (actual measurement about 21.95)

It looks like the collet block won't hold the drill concentric, seems to be that the collet only covers about 80% of a full turn of the flutes

Anyone used ER collets to hold relatively large drills with any success or otherwise ?

Maybe I'll need to make a long v-block with a registration finger and length stop to mount in the vice

Success... 16mm drill is fine, looks like an er40 collet is only good for 19mm of so sized drill

I tried with a 16mm drill, it's held concentric, pretty much. Facets turned out fine, resulting hole is about .04 mm oversize - good enough for me

Originally Posted by johntopp

Success... 16mm drill is fine, looks like an er40 collet is only good for 19mm of so sized drill

I tried with a 16mm drill, it's held concentric, pretty much. Facets turned out fine, resulting hole is about .04 mm oversize - good enough for me

Your collets must be crap if the 16 mm is OK, but the larger ones are not, in the same chuck.

To suggest ER40 is only accurate for small sizes is absurd.

I've only ever used ER32, but never had a problem with anything through the full size range.

Rob

Originally Posted by johntopp

I've been messing about with 4 facet sharpening, using a 3-way vice and a 4 sided ER40 collet block to hold the drill in a T&C grinder

Most frustrating trying to get the facets to cross nicely and the drill to drill on size - the resulting hole is about 22.24 (worst case) for a nominal 22 mm drill (actual measurement about 21.95)

It looks like the collet block won't hold the drill concentric, seems to be that the collet only covers about 80% of a full turn of the flutes

Anyone used ER collets to hold relatively large drills with any success or otherwise ?

Maybe I'll need to make a long v-block with a registration finger and length stop to mount in the vice

Hi John,
Apart from the problem that I found with my ER16 collet chuck, I think that for a drill of that size, nicks or burrs on the drill edges would cause the type of run out that you describe. Equally there could be a burr on the inside of the collet. I've recently purchased an ER32 / MT3 collect chuck for my mill and discovered that a couple of the collets have rough edges on the slits at one end which makes it hard to push a cutter in. I've used a diamond file to take the edges off and 800 grit emery paper in the slits. Not easy on a 1/2" collet !

I think you will find it is not that the collet is crap.

More likely a result of gripping the drill close to the business end.

That means it is only gripping a relatively small section of the spiral cutting edge. Probably not a full 360 degrees of cutting edge.

A lot different to gripping a solid 22mm bar as the ER collet was designed to do.

Absurd is a strong word to use without thinking about what the OP is trying to use the collet for.

Originally Posted by Greolt

I think you will find it is not that the collet is crap.

More likely a result of gripping the drill close to the business end.

.

Where does the OP say that ?

If the OP is trying to grip on the flute section of the drill (LOL) that's something no ER collet was designed to do.

ER collets can grip all or part of their length.

I've used ER collets for many years and know what they can and should be able to do.

The OP made an absurd statement about ER40 collets - regarding larger sizes.

Rob.

Originally Posted by nearnexus

Where does the OP say that ?

ER collets can grip all or part of their length.

I've used ER collets for many years and know what they can and should be able to do.

The OP made an absurd statement about ER40 collets - regarding larger sizes.

Rob.

That would be this from the first post Rob.

seems to be that the collet only covers about 80% of a full turn of the flutes

The larger the drill bit is the longer a full turn of the flutes are, so the collet does not grip enough flute to hold it concentric.

Dean

Trying to grip on the flute section is madness.

Rob

Originally Posted by nearnexus

Trying to grip on the flute section is madness.

Rob

Yes, well I don't think I would want to do that to my collets. Too damn expensive.

Dean

I checked the collet / block with a piece of bright bar, it was true, or pretty close

Then I did the same with the drill, maybe with the point protruding 30 mm or so, it was a bit out, not much, but seemingly enough to mess up the point

Did the same check with the 16 mm drill, it was concentric, and a good result with sharpening

I didn't attempt to mount the shank in the collet, I assumed the runout at the point would be unacceptable

If you look at the various drill sharpening jigs, the drill is held in a v-block or similar close to the pointy end (on the flutes. or maybe I should say lips, but who calls them that down the pub) - I don't recall a drill held for sharpening at the shank end

Anyway, I thought the the collet would average out over the lips, regardless of size, but it seems that the grip is unreliable if the collet doesn't cover a full spiral twist

Maybe it's a bit of a watchit for people building sharpeners using ER collets, perhap you can't hold drills to the full range of the collet capacity and have reliable concentricity. maybe the old-fashioned v-block and indexing finger is the go

Originally Posted by nearnexus

Trying to grip on the flute section is madness.

Rob

I'm curious, where else would you grip the drill ?

Originally Posted by BaronJ

I'm curious, where else would you grip the drill ?

On the shank. That's why it's there.

Rob

I was emulating the GadgetBuilder setup (link below) but using a vice and collet block in the grinder

The geometry is easy enough to achieve, but accuracy and repeatability not so easy

I had the drill held similarly to that in the picture (business end held in collet, little bit of stickout, just for wheel clearance)

http://www.gadgetbuilder.com/4_Facet_Overview1.jpg