Ball Nose end mill ok in a Jacobs chuck?

[usamech]

All,

Newbie here. For my Bridgeport, I’m turning a 15/32 radius on the bottom of large adjuster screws. And I also need to turn a matching concave radius in the 3/8” base plates the screws will seat on.

My question is on set up for turning (vs milling) the concave radius on base plates.
I’ve read a number of posts about never using end mills in a drill chuck because of rigidity, etc. And it makes perfect sense.

However, is it ok to peck drill a radius with a 15/16” ball nose end mill in a Jacobs chuck in the tailstock in this set up? Only going in the plates about .200”. In this case, aren’t the forces on a ball nose end mill basically the same as a drill bit? There shouldn’t be any forces 90 degrees to the drill chuck like a normal end mill.

Anything wrong with this?

Thanks!
Gordon

 

[jwmay]

While I can’t promise anything, it sure seems like it’d be ok.

 

[GrifterGuru]

To be honest, if it were me, and I mean if it were me, I would use a tailstock ER collet holder to hold the end mill.

A Drill chuck holds only on 3 points 120 degrees apart around the diameter of what it is gripping, whilst an ER spring collet grips the entire diameter.

As to chuck Vs ER collet, accuracy can become a wash depending on quality.

The other point here is that end-mills usually have hardened shafts and as such can not be gripped well by a 3 jaw drill chuck, resulting in slippage of the end-mill within the chuck jaws through the forces being imparted. This is also, to a degree, dependant on the flute count of the end-mill.

All of that said, if you are not worried about accuracy too much, maybe try a test on a scrap of the same material you intend to turn the radius into using light pressure, patience and you **may** be ok.

 

[Ulma Doctor]

While I wouldn’t recommend the practice to others, but I have successfully gripped ball endmills from 3mm up to 5/8” in my jacobs chuck on my drill press

 

[extropic]

You'll be fine because the cutting forces are torsional + axial (not transverse).
You're using the ball end mill in the same manor you would use a twist drill.

 

[chip maker]

In the amount of time it took you to take the pictures, post the question and wait for replies you could have done this, and the job would be done. !!! Just Kidding but I feel it will work out if you don't push it and take your time.

 

[Flyinfool]

When I need to do something like what you are doing I will start the hole with a drill bit leaving just enough for the ball end mill to clean it all up.
Ball end mills while they are center cutting do not do center cutting efficiently and they do not track well. Use a starter drill that is at least the diameter of the web of the ball mill. You will end up with a much more accurate hole.

 

[mmcmdl]

You'll be fine because the cutting forces are torsional + axial (not transverse).
You're using the ball end mill in the same manor you would use a twist drill.

@extropic is correct here . This is the same as drilling as the forces are torsional . Never use an end mill in a drill chuck to mill is the rule of thumb , although I will admit to doing it with very small endmills .

 

[woodchucker]

it has nothing to do with rigidity.
Drill bits have soft shanks so you can grab the drill bit. End mills are hard shanks.
So the jaws of a drill chuck don't get a full grip. There is a danger of the end mill spinning.

That said, we all have probably grabbed an end mill in a chuck because there was something we needed to do that it made sense for.
Just don't put too much pressure on it.

I didn't read the rest of your post.. so only answering the end mill in a chuck.

 

[usamech]

All,

All very good answers. I sort of knew the outcome, but I’m not too proud to ask questions on machining subjects that I have very little experience with. Not so much a matter of safety, as it is the expense of destroying a 16N Jacobs chuck.

Will definitely pre-drill. Plus I think this is similar to a first step drill which is typically larger than the chisel, dead center of a drill bit. Centers better.

Thanks again!
Gordon