Question about making an endmill holder.

[D.sebens]

Hey I have a mini lathe and milling attachment. I am going to make an endmill holder out of a mt3 drawbar blank. I understand the limitations of milling on the mini lathe and if any thing this will just be an exercise at making a tool and the "idea" of milling. So I plan on drilling undersize in the mt3 blank and boring to 3/8(the size of bits I have). I plan on mic'ing the bits and machining the holder to a "precise" measurement to help eliminate the bit moving to the side when clamping with the set screw.

I have a few questions for this project,
What clearance should I shoot for on the hole? I feel like I could possibly get the bit stuck if it's too tight and it tries to spin a little.
If that is a possibility could I drill a smaller hole through it so I could insert something on the draw bar side to press out? I dont know if I will have a hard time once it hits the hardened end.
Last question is should I harden the end after this work or will it's annealed state be fine for this operation? Also I have used oil, oxy ace torch and could round up sand. I haven't hardened anything since highschool so I dont remember the exacts of it.

Thanks in advance.

 

[Ulma Doctor]

the more clearance you have, the more endmill wobble will be produced.
i would shoot for less than a .002" clearance (the tighter the better)
you could definitely drill a pilot hole to punch out a stuck endmill

if you are going to use this endmill holder under high load or extensive heavy work,
then yes i would harden the business end.
for occasional use, this is not 100% necessary

 

[FOMOGO]

You might want to get a .001 over size reamer to get your finish size, and keep things as true as possible. Mike

 

[D.sebens]

I don’t think the mini lathe can qualify for high load. I dont expect to do much more than aluminum. Also, I comfortable with running the lathe at various feeds and speeds, what is the best approximate speeds for 2 flutes with hand feeding?

 

[Uglydog]

you could definitely drill a pilot hole to punch out a stuck endmill

Excellent idea, especially if you get the highly desirable really tight tolerances (.001-.002) as you could potentially get some suction making it difficult to extract.

I'd also drill and tap the flank of the holder to capture the flat that many endmills have.

Daryl
MN

 

[Ulma Doctor]

It’s best done at relatively slow to moderate spindle speeds , depending upon material.

If you’re in for some experimenting,
try the slowest speed possible and take some test cuts.
Increase the speed and try again , ad infintium , until you get a clear idea of what your machine is capable of.

Carbide endmills need to be turned at higher speeds than HSS

Large endmills get turned at slower speeds than smaller endmills