Holding milling cutters in a drill chuck

I have used a 3/4" end mill in a 3 jaw chuck to clean up the sides and bottom of main horns held in a vertical slide. I did that because I have read it in one or two of the old construction manuals. I used the same procedure to clean up the slots of the steel frames before fitting the gunmetal horns.

I also use end mils and slot drills in the tailstock chuck to clean the sides and bottom of pre drilled holes.

I don't quite understand why this is such a problem.

Phil H

It's OK by me. I do all my milling that way - up to a 7/8" diameter endmill used to clean up the edges of some 1" steel plate. You do have to nip up the chuck key good and tight but no pipes on chuck key involved.

There is no real issue when using milling cutters like this as the loads are no different to when drilling. There is a possible risk of the cutter comming loose when it is used as a milling cutter and sideways forces applied which can also cause a vibration as each flute takes a cut.

I also expect the condition of the jaws in both the drill chuck and 3-jaw lathe chuck play a part, if you have got bell mouthed old jaws then the grip won't be as good.

J

You have to look at this two ways - is it a safety issue or is it about getting the best results?

Chucks are not designed to take side loads and are less accurate.

The risks are two-fold:

1. The big one is the cutter walking out of the chuck or being pulled out by the work or even the chuck itself dropping off its taper. This is only likely with larger cutters and could pose a hazard if the cutter could be thrown out of the machine or snap.
2. The smaller risk is that the inaccuracies could lead to spoilt work or chipped cutters.

The danger of a flying or snapped cutter is always present in ordinary milling operations, if not as likely - has anyone here NOT snapped a cutter in a proper milling chuck? A chuck falling off its taper rarely causes anything to fly around. If you avoid using large cutters or heavy cuts you make these problems less likely. The ordinary safety gear you probably use already (guard, goggles) should protect you from serious injury from a smaller cutter if it came out. So we can manage that risk.

The risk of spoiled work/chipped cutters is much greater and is something that each person can only judge according to their equipment and the job in hand.

In summary, it's not best practice to use a drill chuck, but common sense can mitigate the safety risks and experience can tell us when other problems might occur.

Neil

P.S. holding cutters in three-jaw lathe chucks is a special issue - hardened cutters are not held as securely by hardened jaws.

The not suitable for side loads is an interesting thing.

As some of you know woodwork is my thing and I have had a couple of what are known as Combi machines on which a slot morticer takes its drive from the end of the planer/thicknesser cutter block. The cutters which can be upto 1/2" dia and 4-5" long are held in a 3-jaw "drill" chuck that fits onto the cutter block (screw fitting) and then get spun up at several thousand reves. These are then plunged into the wood which is then moved sideways agaist the cutter.

Never had one of those come loose either

I quite happily use a milling cutter in a drill chuck (in the drill press) to counter bore holes on occasion. Perhaps this might deemed to be a 'legitimate setup'.? There are not any side loads and the hole is sized with a standard twist drill first for location so the milling cutter is just cleaning up the bottom of the hole. (They are called slot 'drills' after all).

regards Martin

Difference between a slot and a hole? Clue's in the name?

My point about runout was related to uneven loading of the cutter leading to breakage. This is particularly relevant to small diameter cutters. Bludgeoning a large slot with a 1/2" cutter in a Jacob's chuck isn't what I had in mind.

Difference between a slot & a drill, clue is in the name

They can be plunge cut -No probls in a drill chuck

They can also be used to cut a slot - problems for some in a drill chuck not others

.

^^^

An obvious, and very appropriate, use for custom-machined Soft Jaws.

MichaelG.

re uneven loading Jacobs specify 4thou tir at 38mm so is that really a problem?

Martin

They will hold them well enough to cut. The advantage of the soft jaws is that they will run as true as the machine does. The catch really is that many lathes turn a taper but that wont matter either providing it's marginal. How much taper would be ok is debatable but it obviously needs to be very small.

John

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That would depend on several things, Martin ... Not least which product [?] and how long does it hold that tolerance before it wears ?

Whether 2thou of offset is really a problem might depend on the size of the cutter, the depth of cut, and whether [say] 4thou over-size hole or slot is 'really a problem'.

Therefore: Short answer to your rhetorical question = I don't know

MichaelG.

The question was regarding uneven loading ? The figure quoted was for 1 1/2 inches from the chuck so at that runout the cutter is not going to be tiny and its also max expected TIR too. So I suggest runout as far as the cutter is concerned is tilting at windows.

Martin

Seems to have turned into a great debate.

Really the answer is that if some one needs to do it try it bearing in mind that it might go wrong but is unlikely to harm any one - it might "harm" the work.

It probably helps going on the various posts to use a good quality Jacobs chuck that isn't made of Chinese toffee. Lathe chucks used to be a separate part of Jacob's repertoire. Probably still is.

In the past it wasn't all that unusual to see drill chucks being used to hold small work in a lathe instead of a collet. Drill chucks really do have a min grip length that is very close to the length of the jaws or longer. This includes those rather strange looking very old ones that have a very steep taper on the outer nose of the body.

John

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Or rather a great "bait".

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Edited By Muzzer on 06/10/2016 10:20:40

The main problem with milling with a drill chuck is the method of holding the chuck in the machine. The chuck is held in the spindle by friction alone, were as a collet chuck has a draw bar, also the drill chuck is attached to the MT arbor with a (in many cases) Jacobs taper, sometimes held in by a screw from the inside. Also, compared to the collet chuck, the jaws are fairly weak, particularly if they are used side ways as in milling.

Ian S C

It was not my intention to bait anyone - just to establish what is, and what is not 'good practice'.

I draw two major conclusions from the debate:

1. that there is a clear distinction between cutting endways (ie drilling) with a slot drill or end mill in a drill chuck, which is OK, and cutting sideways as this is what tends to cause the tool to walk out of its location.

2. the examples shown to us all, beginners and experts, need to be in line with 'good practice' and should not assume that all readers will know what they are about. Knowing that you can get away with something in some circumstances relies on us having the skill, & experience, to know where the limits are.

So, I would have expected some sort of editorial comment on the lines of 'don't try this at home' - or, better, a little panel explaining that this might be OK for narrow slots in the hands of an expert, or when deepening a hole, etc, but not otherwise.

And I see no distinction between a column drill and a column mill, in relation to this problem. It is the chuck that is the concern, not what drives it.

Cheers, Tim

Or just wrap the cutter with some brass shim. That's what I used to do when using a vertical slide on the lathe.

Russell.

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But you still haven't identified the Jacobs product, Martin

& personally [despite being a Mac user] I would tilt at Windmills

MichaelG.