Clamping drill bit flutes with ER collet?

[zoltan]

I heard that you can clamp the flutes of a drill bit with an ER collet. Is this true?

 

[Swifty]

You will find that the "land" on twist drills is not relieved like on cutters, so you could hold them with collets. But, I would be wary of it if you want to drill large dia holes, the amount of contact in the collet may allow it to slip, it may also not be very good for the collets.


Paul.

 

[zoltan]

What would you consider large diameter?

 

[bazmak]

I would say you can grip the drills to the limit of your collets.I assume you would want to do it to turn down the shank or the MT.Just take light cuts
The collets need to be medium tight,enough to prevent slip which will damage the collet but not enough to deform the collet.Have done it but its not common practice.Have reduced the MT to nom 12mm dia etc etc.Same as anything its suck it and see.There is no foreman looking over your shoulder

 

[Blogwitch]

Looking at it Z, I personally wouldn't even think about trying it, you will do more damage than good for the sake of a few bucks.

If you are running out of throat space with an ER chuck, you need to go for spindle collets, they should give you at least a couple more inches, or for cheapness for use with an ER chuck, go for stub drills, which are much shorter than standard drills and you could then reduce the length of the shank a little as well.

John

 

[Swifty]

John beat me to it, I also was going to suggest using shorter drills.

Paul.

 

[zoltan]

I was hoping to use the drill bits I already have without having to buy another set of stub drill bits.

 

[Swifty]

You may have to end up buying new collets if you damage them, so a few stub drill may be more advisable. As to how big a drill is too big for a collet will depend a lot on the material that you are drilling and your methods. Step drilling, working your way up to final size using smaller drills first, will ease the load on the collet.

A lot of things that we do, although not advisable, we can get away with, so it's probably worth a try. I often see pictures of people milling with the cutter held in a drill chuck, I cringe every time that I see that, but they get away with it, it's only 3 point contact on the shank and certainly not the way to do it.

Paul.

 

[MachineTom]

You will likely find the bit is not concentric when put in a collet by its lands. All drills have a back taper, about .0005-.400120. Per inch. It seems small but its enough to cause wobble. When set as you propose.

 

[velocette]

Hi Zoltan
There is another approach to drilling holes that does not require a drill bit with the lands held in a collet.
Drill a pilot hole with a stub drill with the job held firm and X and Y axis locked on the table.
Then enlarge the hole with a series of end mills of increasing diameter until the required size or slightly under size then finish with the boring bar or reamer for an accurate fit.

Eric

 

[Wizard69]

I was hoping to use the drill bits I already have without having to buy another set of stub drill bits.

Don't buy a set just buy the one you need! The other option is to clip a spare drill you have and re-grind it.