Modify an end-mill holder; cut off tang and add draw-bar threads....

[benmychree]

Those adapters are heat treated, do not assume that they are tapable.

 

[brino]

By the way, when I tried to put one of the tanged end-mill holders into my vertical spindle, it would NOT go.
So not only is there no drive slot for the tang, the tang won't even fit. They have to come off.

Those adapters are heat treated, do not assume that they are tapable.

Funny thing, I was trying to assume nothing.
I had already tested one of the end-mill holders with a file to the tang, and it seemed to cut fine.
I also had the back-up plan of welding on a nut if I could not tap them.

I have an immediate need for the 1" end-mill holder, so I loaded it into the 4-jaw chuck as @T Bredehoft and @JimDawson advised.
I used the centre in the end of the tang to help centre it with the tailstock, as @RJSakowski suggested, and a dial indicator near the chuck.
I had it mounted perfect, and then realized that I had only tested the other end mill holder with a file, not this one.

When I did the file test I couldn't cut this one at all! The file just skated off.
TANG it all!, wasted time.

I knew if I could not file it then even if I had a carbide drill the required size, I could never tap it.
So take it out of the lathe, and I grabbed the tang in a bench vise, mounted a thin cutoff disk on the 4-1/2" angle grinder and took off the tang, then cleaned-up the severed end at the belt sander, and slightly beveled the cut edge.

I was eyeing up what nut could be welded on, and not have fit issues (like the tangs did).
I took a chance and tried a file near the newly cut face. That filed fine!
So I blued the centre of the fresh cut end with a sharpie, used calipers to find centre, and used the optical centre punch to mark the centre.
Then it went back to the lathe using the new punch mark to centre it.

It still looked wrong with such a long work piece extending from the chuck, but it felt solid.
I first tried a small spot drill and that cut fine, so on to bigger.
I drilled up to 9/16 (the 50% thread drill from my charts) and then tapped 5/8"-11 (by hand) in the lathe.



What did I learn:
just because the tang is hard, it doesn't mean the entire part is un-machinable.
I guess it has to do with the thickness of the metal and the heat-treat cycle (heat and quench).
The thinner tang would heat faster and cool faster.

Anyway, the job is (half) done and I have that holder in the vertical spindle right now, ready to cut my first splined shaft.

Thanks for all the guidance and support!
-brino

 

[benmychree]

I don't think the heat treat was the issue, very likely it a steel was used that would be tough on the inside, and was likely carburized on the surface; when quenched and drawn, it would have a hard wear resistant surface and a tough interior; steel like 8620 is a good choice for such parts.

 

[ezduzit]

For a Suburban fly cutter I needed a 1" B&S #9 arbor, which was unavailable. Found a used one with a tang, cut that off and was able to tap for the draw bar.