Reducing end mill shank size

[Grinderman]

Hello,
I have a few double sided 3/4” end mills that are in good condition. I cut one in half to use as a stubby, but need to reduce the shank from 3/4 to 1/2”. I tried turning it on the lathe with a carbide insert but that wouldn’t even touch it, very hard stuff. Any diy ideas on accomplishing this? Annealing, grinding?? Do you think just the surface would be hard or the whole thing? I do have an oxy/ acetylene torch.

 

[markba633csi]

Grinding is pretty much the only way, they are harder than woodpecker lips
Could you make an adapter instead? You can't use heat on them or you'll ruin the temper

 

[gard]

It would be interesting to try to anneal it, you heat it up with the acetylene torch until a magnet no longer sticks to the section you want to anneal, then stick it in wood ashes to cool. I have only tried this a couple of times and it may be possible to anneal only the end you want to machine. If the whole thing gets too soft supposedly you can harden and heat treat the part after machining, I did that years ago but do not trust my memory. If it was me I would not expect a high confidence that it would work the first time but what do you have to lose? I have also made old end mills into boring bars to use in a lathe. Let us know how you make out,

 

[pontiac428]

Grinding in a spin fixture is the only rational way to reduce a tool shank. It's easy to do, but you won't be replicating a tool grinder in the lathe.

 

[tq60]

Amazon has adaptors cheap, either get correct collet or adaptor.

Reducing gas shaft is not worth effort unless you have centerless grinder, then not worth it

Sent from my SM-G781V using Tapatalk

 

[Grinderman]

Thanks for the replies. An adapter won’t work because of the added length.My current collet setup only goes to 1/2”. I have nothing to lose so I may try heat. This will only be used on 6061 or plastic.

 

[benmychree]

HSS cannot be annealed as suggested, and cannot be successfully rehardened by any method available to an amateur, white hear and very slow cooling is required for annealing, and also required for rehardening, and heat damage would effectively destroy the tool. Grinding is the only method to reduce the diameter and would not be practical for that much reduction in diameter.

 

[Grinderman]

Ok, thanks for the info

 

[Bi11Hudson]

Heat is a wonderful thing where it applies. But to draw the temper of the tool will probably likely cause distortion. In addition to re-tempering, which will be marginal at best. In my early days (when I didn't know any better) I have used large milling cutters in a drill chuck. It wasn't for real accurate work, and cutting mostly p;astic or aluminium. But it did the job to my satisfaction. For "one off" jobs, it might be an answer. . .

.

 

[MrWhoopee]

@benmychree is correct. The whole point of HSS is that it can take the heat and not lose its hardness.
Here's how to anneal it.

"Heat at a rate not exceeding 400°F per hour (222°C per hour) to 1525-1550°F (829-843°C), and hold at temperature for 1 hour per inch (25.4 mm) of thickness, 2 hours minimum. Then cool slowly with the furnace at a rate not exceeding 50°F per hour (28°C per hour) to 1000°F (538°C). Continue cooling to ambient temperature in the furnace or in air. The resultant hardness should be 248 HBW or lower."

Difficult to do to just the shank.
They do make reduced shank endmills.