Different styles of 50 taper tool holders

A machine I recently got came with a good amount of tool holders. Pictured are three different styles.



The middle holder has a groove around the perimeter, does this serve a purpose?

I'm thinking the piece at the end of the taper on the one on the right is for clamping instead of a threaded drawbar? The machine (Cincinnati 2MI) just had the drawbar in it so I'm not sure how the holders with this clamp would have been used? Is there a name for this specific style of clamp? Pretty much all the images I've found searching showed a round style similar to:

There are three basic flange types (at lots of minor variations): NMTB, CAT and BT. The CAT and BT styles have (incompatible) V-grooves which are used with tool changers, and usually do not have the straight cylindrical tail of the NMTB. The middle holder in your photo is therefore both fish (CAT-type flange) and fowl (NMTB-type tail). BT style flanges are notably thicker to one side of the V-groove than your CAT example.

Any of these could be used with drawbar retention knobs screwed into the end. There are way too many different styles of retention knob; you must use the correct retention knob for your machine's automatic drawbar. Generally speaking NMTB machines pre-date automatic tool changers, so don't need tool changer grooves or automatic drawbar retention knobs.

Pretty standardized pull stud you have there. This works with a draw bar that pulls on the stud with fingers that interface with a taper inside the spindle. There are a couple varieties and angles, google machine tool pull stud. The 50 taper you have is called an nmtb 50 taper which if I remember correctly stands for National Machine Tool Builder. The groove around the perimeter of the one in the middle normally interfaces with tool changer arm or grippers but I haven't personally seen an nmtb 50 taper that had a tool changer.

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Thanks for the info. With some of the terminology in your post I was able to find a page with pretty much all the info I was after Machine Tool Shanks (Tapers).

This horizontal mill dates to 1955, so no tool changers for me.. still curious why some of the tooling had pull studs though.

Ah thanks, thats the term I needed – "pull stud". Maybe some of these holders came from another machine and I lucked into them with this purchase... Not sure what the guy was doing with them, this mill uses a threaded drawbar. Looks like I can probably just take them out and use them so long as the taper matches...

mindheavy said:

Ah thanks, thats the term I needed – "pull stud". Maybe some of these holders came from another machine and I lucked into them with this purchase... Not sure what the guy was doing with them, this mill uses a threaded drawbar. Looks like I can probably just take them out and use them so long as the taper matches...

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Ah...well. by convention, NMTB and CAT used a US thread for the drawbar. BT and Ericsson, Metric.

But. ISTR each standard actually has TWO threads permitted, same measurement race, even if one is a minority.

And then, makers will do a US thread or Metric thread even where it was NOT the expected one if you want to pay for that. As will a prior owner's shop, DIY in-house so as to not need two drawbars.

So.. Do not be surprised if not all of these fit your drawbar threads.

thermite said:

So.. Do not be surprised if not all of these fit your drawbar threads.

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I didn't even consider that some of these could be metric, interesting... About 10-15 holders came with the machine. I think tonight I'll sort them all out and check the threads, as I understand the SAE threads would be 1"-8.

One of the stories I got with this mill was that the guy worked at an aerospace company and when new tooling would come in, stuff that should have been replaced with new would just "go missing" sometimes... Several of the holders look much newer than the machine so I suppose it's possible they could have come home with him and don't necessarily fit this machine.

If you have older mills and you want to buy second hand tooling then you will probably need to think about making some extra drawbars. I have three alternative drawbars for each spindle (horizonal and vertical )in my Thiel. I can swap drawbars fairly quickly so although it is a bit of a nuisance I can use the wide range of 40 taper tooling I have acquired. You can make drawbars fairly easily (even for the Thiel which has a self ejecting feature for tooling). Some toolholders may require you to remove a drive tenon as well. If you need to do this I would suggest that you avoid really heavy cuts, although I have never had a problem in this respect.

billmac said:

If you have older mills and you want to buy second hand tooling then you will probably need to think about making some extra drawbars. I have three alternative drawbars for each spindle (horizonal and vertical )in my Thiel.

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Same here as to 3, and danged if I don't need two more arredy.

A shorty-short for a Dividing head, and a "coaxial" to manage a collet-within-taper draw-in, each component independently. IF I want to use it. Not even worth the bother, so far.