# Drill bit in collet?



## JeffF (Mar 25, 2013)

All,

I have been working with my new 4" rotary table with a three jaw chuck mounted on it.  It works GREAT for milling out the face of a round piece (for a flywheel), but on my small mill there isn't enough headroom to mount a drill chuck in the mill for drilling the holes around the face.  Can I use a collet to hold a regular twist drill bit (which will give me the needed head room), or will the drill bit spin in a collet?

For that matter, should I just drill the holes with an endmill?  They are only about 1/4" diameter holes.

If I can't use a collet or the endmill to drill the holes, I can remove the 3 jaw check, but it is so convenient to have the piece mounted in the chuck that I would rather not have to mess around with getting the piece remounted directly on the table.

As always, thanks in advance for your help!

Jeff


----------



## Philjoe5 (Mar 25, 2013)

Jeff,
You didn't mention what type of collet you were using.  Based upon the size of your rotab, do you have a minimill with an R8 collet setup?  When I had this arrangement I was always looking for ways to get "z" axis space.

Use machine drills since they're shorter than their jobber drill counterparts.

Use R8 collets if you can closely match collet and drill size.  A 1/4" drill in a 1/4" R8 collet will work fine and gets you max "z" axis.

A 1/4" end mill will give you a hole larger than 1/4" based upon my experience with import end mills.  Sometimes 0.010"+ larger.  If that's not a problem, then that's a good combo also.

Hope this helps

Phil


----------



## rhankey (Mar 25, 2013)

Sure, you can use collets for holding drill bits.  I use collets with drill bits for almost all my mill drilling, as my mill also has somewhat limited vertical headroom.  If you are using 4C, 5C, R8 or like collets, you will need a 1/64" set of collets to hold the bits correctly, which gets a little annoying when have a bunch of operations to do through a lot of holes.

I understand from others and have generally found from my personal experiene that two flute milling bits are less likely to drill oversize holes than 4 flute milling bits.

Robin


----------



## JeffF (Mar 25, 2013)

Thanks guys!  I do indeed have the R-8 collet setup and since the size of the holes is not critical I can easily match up a drill bit and collet to make it work.

Learning a ton in this forum and really appreciate everyone's help!

Jeff


----------



## chipenter (Mar 25, 2013)

Collets will grip tighter than a Jacobs chuck but with only a small amount of tolerance , a BS3 centre drill is a 1\4 " with a 7\64 th pilot this has got me around a few problems in the past .


----------



## tornitore45 (Mar 25, 2013)

End mill are not rcommended for drilling, having no centering feature tend to chatter and drill oversized and not round.
Is ok to plunge to depth for a captive slot if using an undersized end mill and bringing the slot to size on multiple passes.


----------



## chrsbrbnk (Mar 25, 2013)

you could turn down the shanks on a batch of most needed sizes of drills to match a collet   or get one of those harbor freight  stepped shank drill sets


----------



## kvom (Mar 25, 2013)

Center-cutting endmills are fine for drilling, but typically are poor for chip evacuation.  You need to raise the spindle after each small increment.  Two flute endmills are best for this as there is more space between the flutes.  R8 collets have rather small size tolerance, so it's best to use them only with the correct drill sizes.  For tap drills, which are typically number series, always use a drill chuck.

Just remember that drills don't make round holes.  If you need the hole to be round drill undersize and use a reamer afterwards.


----------



## chrsbrbnk (Mar 26, 2013)

As a tool and die maker  for the last 30 some years  I generally don't drill with an end mill,. they have a tendincey to walk the work around  on almost anything less rigid than a fairly serious cnc mill. the walking seems to prematurely dull the end mill.  and make a crummy hole. try it on some  scrap  first find out if you machine and set up is rigid enough.  on the other hand a fairly well located and sized hole  can be made with plunging an end mill after drilling a hole  say .06 undersize


----------



## kvom (Mar 26, 2013)

To clarify my prior post, and in agreement with chrsbrbnk, I don't generally drill with endmills either.  But sometimes you have no choice.  My equipment is pretty rigid, so my holes come out fine.  The main reason to "drill" with an endmill is to make a flat in an inclined or uneven surface, so that a regular drill can then make the hole.

An endmill is also my choice when I need a flat bottom.


----------



## Trialnterror (Dec 25, 2016)

tornitore45 said:


> End mill are not rcommended for drilling, having no centering feature tend to chatter and drill oversized and not round.
> Is ok to plunge to depth for a captive slot if using an undersized end mill and bringing the slot to size on multiple passes.



I've looked all over the internet for information on drilling with endmills and could not find anything! I finally asked the machinist at work and he explained this very thing , that endmills are not self centering and a drill bit since it's self centering would be a better choice for making holes! 

I've been struggling making a cam housing for the hoglet build. It calls out 3 holes that are .250 radius (.5 diameter) and once drilled they are milled off half way. I was using a endmill to make the holes but once measured I can be off as much as .010! I've been looking all over to see how machinists make holes like this which was a pain. 

I will for the future when making accurate holes either 1. Step Drill up to just  1/64" under nominal size, then ream. 2. Step drill then plunge down with a sharp 2 flute endmill. (Although I have a very sharp 3 flute high angle endmill that I'd like to try on this (material I'm using is aluminum)


----------



## abby (Dec 26, 2016)

Use a slot drill , a Clarkson slot drill will cut a hole to within a thou of stated size ,  if using multi-flute endmills drill a pilot hole first then finish with the endmill , even if the pilot hole is out of true the endmill will still produce a hole true to the axis of the cut.


----------



## fcheslop (Dec 26, 2016)

Not sure what they are known as in the USA, I would drill to the nearest size then finish with a slot drill or a D bit
cheers


----------



## tornitore45 (Dec 26, 2016)

Trialnterror     You got good information.

The crux of the problem is that drill bits DO NOT cut on the Margins (Flutes)
The helix are ground cylindrical with a slight taper to reduce friction.
Once they have established Location they keep cutting on the front but not on the sides.  Of course drill bits are not known for making Round holes on size and location, that also depend from how symmetrical is the sharpening of the business end. 

End mills cut on front and sides, they are all to eager to nibble the hole edges at the slightest tremor or provocation.

In a pinch using an end mill as a reamer and/or flattening the bottom after drilling an undersized hole is not to bad solution, short of boring. In this case the entire length of the hole oppose resistance to side cutting the few thousands to clean out,

Spotting a flat before drilling as suggested is OK since is not really a precision operation, after all the spotted surface will be drilled out entirely or simply left as a landing for the bolt head.


----------



## Wizard69 (Dec 31, 2016)

Trialnterror said:


> I've looked all over the internet for information on drilling with endmills and could not find anything! I finally asked the machinist at work and he explained this very thing , that endmills are not self centering and a drill bit since it's self centering would be a better choice for making holes!
> 
> 
> > That is certainly the general rule.
> ...


----------

