Using cat 50 toolholder in NMTB taper

Rigor · Jul 5, 2018

I have an old K&T mill with NMTB 50 taper. I also have a dead Okuma mill that used Cat 50 tooling. So plenty of Cat 50 toolholders on hand.
Being that the drawbar of the K&T threads in perfectly into the Cat 50 tool holders and the drive dogs are also the same, I'm tempted to try and use them in the K&T.

You guys foresee any problems? After all the taper should be the same...right?

fmari --MariTool- · Jul 5, 2018

Yes you will be fine. The taper is the same. Just make sure you get at least 4 full threads of the drawbar thread before it clamps the tool holder. Don't want to strip the thread.

CatMan · Jul 5, 2018

Are the threads in the toolholders the same? Is the drawbar in the K&T long enough to engage a standard Cat 50 toolholder?

Ray Behner · Jul 5, 2018

Here's what I do. Just tig a piece of threaded 4140 to the top.

Rigor · Jul 5, 2018

CatMan said:
Are the threads in the toolholders the same? Is the drawbar in the K&T long enough to engage a standard Cat 50 toolholder?

Looks like I get around ten turns of the drawbar before it bottoms out in the holder so lots of engagement. I was mostly concerned about the taper but I just tried it and works like a charm.

Thanks to all...

gbent · Jul 5, 2018

Double check that the toolholder is seating properly in the taper. A Cat v-flange has one drive notch (the one with the dimple) cut shallower than the other. My K&T requires the removal (or shortening) of one of the drive lugs, and then the toolholder to be indexed to match the lugs.

I have a spacer I use on the back of the spindle to shorten the drawbar for NMTB holders, and I remove the spacer for Cat holders.

Limy Sami · Jul 5, 2018

When I saw this thread I was going to post that it worked for me on 30 taper, listing all the points others have made, and expecting the backlash

Then I saw Frank Maris post (#2) and shall we say ;- was mightily relieved, ……..if it's good enough Frank, it's good enough for me!

Mud · Jul 5, 2018

Rigor said:
Looks like I get around ten turns of the drawbar before it bottoms out in the holder so lots of engagement. I was mostly concerned about the taper but I just tried it and works like a charm.

Thanks to all...

Make sure it's not bottoming out, or nearly so, on the NMTB holders. The thread depth is different on a lot of my holders.

I had a Van Norman that had a drawbar with a nut on the outer end, so you could screw the bar into the holder by hand then tighten up the nut to prevent that.

Rigor · Jul 5, 2018

Mud said:
Make sure it's not bottoming out, or nearly so, on the NMTB holders. The thread depth is different on a lot of my holders.

I had a Van Norman that had a drawbar with a nut on the outer end, so you could screw the bar into the holder by hand then tighten up the nut to prevent that.

I have the same draw bar on the K&T. I blued up everything and all is well. Tapers are a perfect match. Drive dogs are also a perfect fit.

And yes, thank you Frank for chiming in earlier and confirming that this was doable.

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Using cat 50 toolholder in NMTB taper

Rigor

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fmari --MariTool-

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CatMan

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Ray Behner

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Rigor

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gbent

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Limy Sami

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Mud

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Rigor

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