Question on Atlas lathe endmill holder...

[56type]

I picked up a milling attachment for my Atlas 10100 Mk.2 and am about to make some of the sleeves to adapt the holder for different size in endmill shanks. I've seen it written that the weldon shank endmills are NOT to be used with a sleeve using the set screw on the flat as it may sieze the endmill in the holder. After searching and watching several videos I'm a bit confused as to why ?? The information I keep turning up advises not using a chuck (3 or 4 jaw, drill chuck) as both the endmill and chuck jaws are hardened, and so won't grip reliably and the endmill can draw itself out of the chuck while in use.

The milling attachment endmill holder for the Mk.2 has a set screw provided for what I assume is to engage the flat on the weldon style endmill shanks. The original setup also included IIRC 4 adapter sleeves (mine were missing) for use of smaller than 0.500 endmill shanks. If the weldon shank endmills were meant to be used with this holder and it's included adapter sleeves why all the warning not to do so ?? What I'm struggling to understand is if a regular 3 or 4 jaw chuck cannot reliably hold the endmill due to both the jaws and endmill being hardened, and I'm supposed to ensure that the slotted shank weldon endmills are not lined up with the set screw in the endmill holder adapters...then what exactly is supposed to be holding the endmill in place when all you have for retention is a set screw bearing against a smooth hardened shank instead of the slot cut into the weldon shank endmill which would allow the set screw to bear against the flat locking the endmill in place. What am I missing here...??

If the weldon style endmill shanks WERE NOT meant to be used with this endmill holder then what is providing the retaining force keeping the endmill in place instead of allowing it to draw itself out of the holder while in operation similar to what is said to happen if an endmill is used in a chuck ??


It's a bit hard to grasp how a smooth shank hardened endmill could be locked firmly in place by a single set screw so that it wouldn't rotate in the endmill holder in operation when the clamping force of a 4 jaw chuck isn't up to the task from what I've read.

Here's a mr. pete video where he talks about thsi at the 6:40 mark...

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[benmychree]

Sounds like foolishness, with a real milling machine, end mills are commonly held by Weldon style holders, hardened and with setscrews, if used in the lathe, they should have a drawbar.

 

[56type]

Sounds like foolishness, with a real milling machine, end mills are commonly held by Weldon style holders, hardened and with setscrews, if used in the lathe, they should have a drawbar.

I do have the drawbar, my setup was missing a vise flat jaw for the milling attachment and the adapter sleeves for the different endmill size shanks. I'll eventually pick up a mill when the right size machine comes along at the right price to fit in the limited space I have available.

 

[mmcmdl]

Can someone post a pic of an Atlas drawbar and end mill holder ? I think I found one stashed in a drawer from one of the smaller lathes . TIA .

 

[cross thread]

 

[mmcmdl]

That was quick ! Mine looks like the one on the right . Love to know more about the sleeve shown in the pic . I most likely have it but wouldn't know what to look for .

Edit . Just figured out the sleeve is for the lathe bore .

 

[cross thread]

Set screw in the Morse Taper is what you want . I use my little 3 jaw to hold an end mill all the time , . In theory Mr. Pete is right a 3-4 jaw should not be used , but you can't take a heavy enough cut with the milling attachment to make it slip anyway . Here is a little vise I mounted on my milling attachment .

 

[56type]

Set screw in the Morse Taper is what you want . I use my little 3 jaw to hold an end mill all the time , . In theory Mr. Pete is right a 3-4 jaw should not be used , but you can't take a heavy enough cut with the milling attachment to make it slip anyway . Here is a little vise I mounted on my milling attachment .
View attachment 406679

I have the same set that's ID'd as M-6-945 in the ad pic above. I have exactly one 1/2" endmill that I bought specifically to mill the T-slot plate for QCTP. Since I would only be milling the edges of the nut I figured the 1/2" endmill would be fine for that but now I've started to branch out a bit and am looking at smaller endmills with 3/8" shanks in order to machine the locking notches for these...

I just didn't want to be so close to completing a part only to have a cutter go cattywhompus and ruin it while cutting the last feature. Or Ruin the arbor on the cutter holder by having an endmill sieze in place with no easy way of getting it out of there without causing damage. So thought it best to check in here and see what other's thought were on the matter.

ETA: The little red arrows are pointing to the notches I'll be attempting to cut. They engage with a spring loaded locking pin that keeps them from backing off once threaded on by hand. No tools or torque needed to hold them in place, just thread on "finger tight" and locking pin should engage the nearest notch. Notches look to have been cut using a 4 mm. endmill on the factory made examples I'm looking to reproduce.

 

[wa5cab]

56type,

AFAIK, I am the one who posted the warning about NOT using the Atlas cutter holder and reducing bushings with the Weldon style shanks. Or if you do, turn the Weldon flat 180 degrees around so that the set screw does not try to go down into the Weldon flat,

The reason is because of how the flats are cut in the reducing bushings. If the shank diameter is 1/2", it will work fine because for that size you do not use a reducing bushing. But look at any of the reducing bushings. They each have a flat cut across the outside of the bushing that leaves a slot at the bottom, not a round clearance hole. The nose of the set screw doesn't actually ever touch the bottom of the slot because the cutter shank sticks up through the slot just a few thousands of an inch and that is what the set screw is tightened against, not the bottom of the slot.

However, if you stick a Weldon shank into the bushing and orient the Weldon flat with the set screw and start tightening the screw, you will begin to deform the bottom of the slot in the bushing into the Weldon slot cut across the cutter shank. And of course you make sure that the set screw is good and tight. Right??? Later, after using the milling cutter to do whatever it was that you needed to do, you will want to return the bushing and the cutter to wherever you store them so you loosen the set screw and go to pull the cutter and bushing out of the 2MT or 3MT adapter and discover that it won't come out. Because you have exceeded the elastic limit of the steel in the bushing and it now protrudes out into the space above the Weldon flat.

After several weeks or months of trying, I eventually got the cutter and bushing out of the 3MT holder but the bushing is still stuck on the cutter.

 

[56type]

56type,

AFAIK, I am the one who posted the warning about NOT using the Atlas cutter holder and reducing bushings with the Weldon style shanks. Or if you do, turn the Weldon flat 180 degrees around so that the set screw does not try to go down into the Weldon flat,

The reason is because of how the flats are cut in the reducing bushings. If the shank diameter is 1/2", it will work fine because for that size you do not use a reducing bushing. But look at any of the reducing bushings. They each have a flat cut across the outside of the bushing that leaves a slot at the bottom, not a round clearance hole. The nose of the set screw doesn't actually ever touch the bottom of the slot because the cutter shank sticks up through the slot just a few thousands of an inch and that is what the set screw is tightened against, not the bottom of the slot.

However, if you stick a Weldon shank into the bushing and orient the Weldon flat with the set screw and start tightening the screw, you will begin to deform the bottom of the slot in the bushing into the Weldon slot cut across the cutter shank. And of course you make sure that the set screw is good and tight. Right??? Later, after using the milling cutter to do whatever it was that you needed to do, you will want to return the bushing and the cutter to wherever you store them so you loosen the set screw and go to pull the cutter and bushing out of the 2MT or 3MT adapter and discover that it won't come out. Because you have exceeded the elastic limit of the steel in the bushing and it now protrudes out into the space above the Weldon flat.

After several weeks or months of trying, I eventually got the cutter and bushing out of the 3MT holder but the bushing is still stuck on the cutter.

Since I'm making my own bushings can I avoid that scenario by using a transfer punch in the existing 1/2" arbor set screw hole location to mark the reducing bushing, then drill it slightly oversize to ensure the set screw actually bears against the slot in the Weldon flat ?? My thinking is that by locating the set screw hole with the reducing bushing inserted .and drilling a clearance hole the set screw would have a minimal chance to displace any metal into the Weldon slot of the endmill. Alternatively I had thought of drilling the set screw hole to the correct size of the hole in the MT2 arbor, then using the set screw hole in the arbor as a tap guide, tapping the threads into the reducing bushings as well so that the set screw would "see" only the bottom of the weldon flat as a bearing surface to retain the endmill in place. Am I correct in this line of thought or is it just a spectacular way of adding complexity where none is needed ?? Thanks for taking the time to clear this up so I can get it right the first time.