# Question on Atlas lathe endmill holder...



## 56type (May 10, 2022)

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 (May 10, 2022)

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.


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## 56type (May 10, 2022)

benmychree said:


> 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.


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## mmcmdl (May 10, 2022)

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 .


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## cross thread (May 10, 2022)




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## mmcmdl (May 10, 2022)

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 .


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## cross thread (May 10, 2022)

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 .


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## 56type (May 10, 2022)

cross thread said:


> 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.


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## wa5cab (May 11, 2022)

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.


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## 56type (May 11, 2022)

wa5cab said:


> 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,
> 
> ...



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.


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## mmcmdl (May 11, 2022)

This looks like the M6-945 , I think .


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## wa5cab (May 11, 2022)

Using a tapped hole through all of your "made by you" reducing bushings instead of a drill-through hole would work I suppose but (a) it would be a lot of extra work for zero gain and (b) assuming that the thread start would have to match the thread finish in the holder within one degree, the odds are 360:1 against you ever finding another cutter holder that those bushings would work with.  So if you use a hole instead of a slot, use a drill-through hole, not a threaded one.


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## 56type (May 11, 2022)

wa5cab said:


> Using a tapped hole through all of your "made by you" reducing bushings instead of a drill-through hole would work I suppose but (a) it would be a lot of extra work for zero gain and (b) assuming that the thread start would have to match the thread finish in the holder within one degree, the odds are 360:1 against you ever finding another cutter holder that those bushings would work with.  So if you use a hole instead of a slot, use a drill-through hole, not a threaded one.



Thanks, I'll go with the drill-through hole instead of taking the extra trouble of trying to tap the set screw hole.


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## epanzella (May 11, 2022)

Not sure if I understand exactly what you're doing but If you're making something why make a bushing to be used with a holder. Just make the holder to fit the end mill and put a set screw in it for the Weldon flat. I use a straight shank for the lathe and stick it in a 3 jaw. The reason you shouldn't stick an end mill into a 3 jaw is that they're both hardened. A mild steel adapter works just fine.


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## 56type (May 12, 2022)

epanzella said:


> Not sure if I understand exactly what you're doing but If you're making something why make a bushing to be used with a holder. Just make the holder to fit the end mill and put a set screw in it for the Weldon flat. I use a straight shank for the lathe and stick it in a 3 jaw. The reason you shouldn't stick an end mill into a 3 jaw is that they're both hardened. A mild steel adapter works just fine.



Since the end mill holder I have was missing the bushings it originally came with I was looking to make replacements initially. I had avoided using the 4-jaw to hold the end mill for the reasons already mentioned. I was planning on using the original end mill holder since it located in the MT of the spindle and so would be centered each time it was used with no need to dial it in with the 4-jaw ( haven't gotten a 3-jaw yet).

Also, my thinking was that the setup once installed, would be easier to swap out different size end mills by just loosening the set screw and pulling the bushing in current use and swapping it for the next size needed.


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## wa5cab (May 12, 2022)

epanzella,​
The milling cutter holders marketed by Atlas had a 1/2" inside diameter by 2MT (for the 6" lathes) or 3MT (for the 9"' 10" and 12" lathes) that was drilled and tapped for the 3/8-16 common draw bar.  And for smaller diameter  cutter shanks they supplied a set of four reducing bushings in 1/16" increments down to 1/4". They were NOT intended for use with Weldon style cutter shanks.  As I discovered  the hard way.

They also sold several types and sizes of end mills and milling cutters that were suitable for use in their holders.

As far as using milling cutter holders made for smaller diameter shanks, that would be OK except that all of them that I have personally ever seen had the tanged style of Morse Taper, not the draw bar style.  Do NOT use these unless you first convert them to draw bar style as they are guaranteed to pull loose and ruin your work.  And your day or night!


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## wa5cab (May 12, 2022)

Also, the reason for using one cutter holder and several reducing bushings is that although not cheap, the bushing are much cheaper than the holders.


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## 56type (May 13, 2022)

I have the original Atlas part with the 3/8-16" thread draw bar. Just need to make the suitable reducing bushings to use it with smaller shank endmills. I planned on making both imperial & metric sized bushings to use with the endmill holder. I had noticed in the Atlas ads for accessories that various cutters were offered, though I have no idea of the contruction of those particular cutters (i.e. were the shanks not quite as hard as the cutting surfaces ??). Seemed to me a round hardened shank endmill being held in place by only a set screw could spin as easily as if it were held in a 3 or 4 jaw chuck, henca why I was asking about the bushings with the weldon shanks. With the weldon shanks having a flat surface for the set screw to bear against I saw no way for the endmill to rotate in the holder. 

That's what I hoped to accomplish with this thread, to get a best case design for making reducing bushings that both work with the endmills on the market today and that wouldn't sieze themselves to the bushing/holder. So far it looks as though I'll make the reducing bushings from O-1 or W-1 drill rod, with a clearance hole to allow the set screw to pass through and contact the flat weldon shanks on the endmills.  

If anyone thinks this won't work or will cause the siezing problem of the endmill locking itself into the bushing and holder, or the choice of material is wrong, let me know and I'll make changes. Thanks.


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## mmcmdl (May 13, 2022)

No need to use tool steel , they are just bushings . If you do harden them , and they spin , it'll wipe out your original arbor . I would go with something soft . JMO .


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## epanzella (May 13, 2022)

wa5cab said:


> epanzella,​
> The milling cutter holders marketed by Atlas had a 1/2" inside diameter by 2MT (for the 6" lathes) or 3MT (for the 9"' 10" and 12" lathes) that was drilled and tapped for the 3/8-16 common draw bar.  And for smaller diameter  cutter shanks they supplied a set of four* reducing bushings in 1/16" increments down to 1/4". They were NOT intended for use with Weldon style cutter shanks.  As I discovered  the hard way.*


If you use a bushing inside an end mill cutter with no setscrew how do you hold it in? All the end mill holders I bought or made had a setscrew for the weldon shank. If the endmill didn't have a flat  already I ground one in. The MT holders all had draw bar threads, the untapered holders were soft and did not. I used them in a lathe chuck. The holders for my mill have R8 taper and draw bar threads. So does my ER32 collet chuck. I also have a 1 inch straight shank ER32 chuck for my lathe but It's hard so I have to tape it for chucking.


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## 56type (May 13, 2022)

mmcmdl said:


> No need to use tool steel , they are just bushings . If you do harden them , and they spin , it'll wipe out your original arbor . I would go with something soft . JMO .



Thanks. I just picked up a 3 ft. length of cold rolled 5/8" diameter steel from Tractor Supply while I was out earlier


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## wa5cab (May 14, 2022)

@epanzella,​* reducing bushings in 1/16" increments down to 1/4". They were NOT intended for use with Weldon style cutter shanks.  As I discovered  the hard way.*

First, I haven't actually looked for any MT equipped cutter holders threaded for draw bar as I already have two of the Atlas holders and bushing sets (had three sets until I ruined one set).  I merely wanted to warn of the consequences of not using a draw bar to secure holders in spindles (applies to lathes and mills, both vertical and horizontal).  I don't recall where I acquired the tanged holders but I must have nearly a dozen of them.

Second, you can use Weldon style cutters with the reducing bushings if they have 1/2" dia. shanks as you won't for this diameter use a reducing bushing.  But you will probably need to use a longer set screw.  

Third, you can also use them with smaller diameter shanks and factory style reducing bushings  but you will have to rotate the cutter 180 degrees and pretend that they have plain shanks.  I should have done that.


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