Weldon Shank Tool Holding

MT2 collets minimize "stick out" from spindles etc and increase "daylight" between spindle and workpiece. However, under some conditions, a MT collet will allow a tool to be drawn out of the collet (also applies to R8 and certain other collets). The Clarkson threaded holder was the answer to holding tools, but the stick-out is greater.

Has anyone produced a (MT) collet modification that will retain a Weldon shank tool? Or, lacking that mod, a workable alternative?

Paul

Thought starter: Grind hole in side of collet and short T-headed-pin (pressed, epoxied, brazed into hole from inside the collet.)

Never had a tool drawn out of an R8 collet, obviously not trying hard enough.

TG and DA collets were made with a loose captive pin in the collet that when the collet chuck was tightened the pin went into weldon slot on the shank and stopped the cutter from pulling out and it worked fine,the only problem was when the collet was mistakenly used on straight shank cutters, chuck cutter etc could be damaged.

I use ER32 collets, not had a cutter incident....( touch wood...)

Like others I have not experienced cutter work out with ER collet system but concede the Clarkson holder screw in cutters are more secure in use by design.

Emgee

As others have mentioned I too have never had cutters move when using ER collets. It has happened to me when using MT collets. I have used Weldon end mill holders like these, and they have worked well for roughing.

Thor

But ER chucks stick out more which is missing the point of the MT collet question.

I suppose there is nothing to stop you making your own MT "collet" that could be drilled and tapped for a grub screw. Probably would not even need slotting as the weldon holders do not close up on the tool. So just a solid MT taper with an accurately formed hole, grub screw thread and drawbar thread, could unharden a blank end arbor and cut the blank end off.

Edited By JasonB on 30/04/2018 07:06:07

Paul,

Useful table of refererence dimensions, here: **LINK**

http://www.armstrongmetalcrafts.com/Reference/TaperShankDimensions.aspx#weldon

Assuming that you only intend to use the smaller sizes; it should, as Jason suggests be a simple matter to modify a plain MT2 arbor.

MichaelG.

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P.S. ... I should mention my personal distaste for the simple 'Weldon' fixing: The design is theoretically flawed, because in order to insert the cutter, there must be some finite clearance, and therefore the cutter will run eccentrically. ... The art is to render this flaw 'negligible'.

The likes of Kennametal have invented more accurate holders, but these are necessarily bulky and/or more complex.

This simple variant merits consideration:

https://worldwide.espacenet.com/publicationDetails/originalDocument?CC=US&NR=2004253070A1&KC=A1&FT=D&ND=3&date=20041216&DB=EPODOC&locale=en_EP

Edited By Michael Gilligan on 30/04/2018 08:55:31

Seems to be no reason why the retainer grub screw shouldn't be back up in the MT taper itself giving essentially zero extra stick out. Small flat with rounded edges so it doesn't interfere with or damage the machine taper.

Big disadvantage is that you need to pull the taper to change the tool.

In principle a set of shop made holders, one for each size of milling cutter you use, is not unaffordable compared to a new set of collets or collet chuck. If you went that way you could keep a cutter of each size permanently mounted with a note of the actual stick out. Works for the CNC boys. If I had an MT spindle mill I'd seriously consider this as making the holders is pretty trivial. But my lathe has a first class taper turning attachment so producing a batch of good tapers is basically shelling peas once set-up.

Although Michaels distaste is based on a valid point I think it is more theoretical than real. My Weldon holders are a sufficiently close fit on the shanks of good quality cutters that entrapped air can make it hard to insert the cutter so any shift when the screw is tightened will be miniscule. Contemplated drilling a relief hole more than once.

Theoretically they would be better made double bored with a smaller part bore intersecting the edge of the primary bore opposite the grub screw producing two line contacts about 20° or 30° apart. This would give true three point contact between holder and cutter. Two lines and screw. Standard set ups more two and a bit depending how well the cutter flat sits against grub screw. Worst case is simple single line on note bore immediately opposite the contacting "point" of the screw. In practice the screw point is of finite width so its more like one line and a narrow block. Although it generally works fine its somewhat unsatisfactorily indeterminate from a mechanical analysis point of view. Yet another issue to keep the Angles Dancing on the Head of a Pin debating society warm.

Clive.

Re eccentricity. The ones with a flat for the grub screw should be sharpened in a holder in which this flat governs the position - they would then be sharpened with an offset that allows for the error.

Isn't this similar to the cheap endmill holders readily available, particularly 'Over There'. The only possible difference is that with them, the grub screw is not in the taper but on a collar below the taper (I think). If there is a daylight issue, the collar could be trimmed back somewhat.

Dave
The Emerald Isle

Yes Dave, exactly the same principal except the hole and grub screw go into the actual taper rather than having a bit sticking out the end which would save 20-30mm. We can get them over here.

.

Rather like the patent that I linked, Clive

MichaelG.

As Clive said, this is angels and pinheads territory, strictly for the armchair experts. You may not have noted that Weldon / sidelock shank holders are commonly available in G2.5 balance ie fit for 25,000rpm with runout better than 3um. They are hardly going to sell stuff like that if the very principle is so deeply flawed. Certainly not an issue for some guy in a shed / armchair to worry about.

I prefer end mill holders like that. Unless you want to spend a few hundred quid on a really fancy set of collets, it's a more rigid, accurate and consistent way to hold cutters. And that's before you look at the runout on your spindle and the cutters themselves.....

Murray

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... and YOU may not have noted that I wrote: " The art is to render this flaw 'negligible' "

If I understand correctly; the discussion at that time was about DIY options.

MichaelG.

Paul​ in answer to the original question, from my own experience I'd say that it is quite practical to carefully bore a blank MT2 arbor to accept a Weldon shank and drill/tap for a retaining grubscrew, then I case harden the holes. I've made them in this manner to hold and drive Rotobor type cutters up to 48mm diameter to cut holes in thick plate and I do not see an issue with runout, though I must admit that I tend to be more interested in achieving a practical working result rather than fretting over theoretical perfection. Give it a try, the blanks are cheap enough and the result will be down to the accuracy of your boring.

Trevor.

I suspect that you might have been using MT3 shanks though. An MT2 one would have a negative amount of metal left is you stuffed a Rotabroach 3/4" Weldon shank up it.

Added:- or was that in the 'sticking out' bit of the arbor?

Edited By Mark Rand on 30/04/2018 22:02:21

yes Mark​ , you're quite correct, I was referring to my use of MT2 arbors with a soft stub that 'sticks out' Trevor

This is true Paul but are you that short of Z height? Or is it a large workpiece. Just interested.

The lack of “stick out” as you put it also makes things more rigid. Sometimes though I choose to use an ER chuck with small cutters because it’s easier to see the cutter simply because it’s not so much in shadow from the quill.

Sorry, I'd got my head stuck on Clive Foster's idea of having the grub screw back in the tapered part of the holder.

Got a trivial bit of milling to do on a too high item. Haven't got enough headroom even with zero stickout, so I've got to make a raising block.