Fixing my mistake

[shell70634]

I bought the wrong size. Boring head is 3/4. Bit holder 3/8. Shank of new tool 1/2.
My choices:
1. turn shank down to 3/8 and shorten
2. bore bit holder to 1/2 ( I have another)
3. Make a new bit holder.

I think #3 is my best choice. Your opinion? Would 4140 be an acceptable material? How about 304 stainless. I've got both handy.

I hate returning things when it's my fault.

 

[NC Rick]

Seems like a new holder will be the best answer.

 

[aliva]

I'd make a new holder from 4140 and harden.

 

[graham-xrf]

I'd make a new holder from 4140 and harden.

On the subject of hardening 4140.
I have a rod of EN24T , and a choice for EN19T. These are European designations for an air hardening steel very like 4140 in makeup.
The intended use is a replacement tailstock quill.

The hardness I have listed for these is the pre-tempered value the have as supplied. 4140 is supplied as 18-22 HRC.
My rods are range 24.2 - 32.1 HRC.

Heat treatment of 4140 is to heat slowly up to 840°C-875°C, and soak (how long). Those would be 1544°F - 1607°F equivalent.
Then cool in air.
Then re-heat slowly to (some temperature??) between 550°C and 700°C depending on how hard you want it to end up, and soak for 2 hours per 25mm of ruling section. Those values are 1022°F - 1292°F.
Then again, cool in air.

I lack the final bit of information. How hard does it get? What is a good final hardness value to have for a tool holder? What temperature do you need to get it there?

I understand that second heating (tempering) value should not use values between 250-375°C because the Izod impact toughness value would be adversely affected. I guess it would still be "too hard", and a bit brittle.

 

[T Bredehoft]

I anneal, (second heat) 4140 at 450ºf in my oven, one hour per inch (or less) of thickness, turn off the oven and let it cool. I figure this leaves it about 60C, but no documentaiton on this, just feel. The last I made was a drill jig for .035 inch drills.

 

[ericc]

On the subject of hardening 4140.
I have a rod of EN24T , and a choice for EN19T. These are European designations for an air hardening steel very like 4140 in makeup.
The intended use is a replacement tailstock quill.

The hardness I have listed for these is the pre-tempered value the have as supplied. 4140 is supplied as 18-22 HRC.
My rods are range 24.2 - 32.1 HRC.

Heat treatment of 4140 is to heat slowly up to 840°C-875°C, and soak (how long). Those would be 1544°F - 1607°F equivalent.
Then cool in air.
Then re-heat slowly to (some temperature??) between 550°C and 700°C depending on how hard you want it to end up, and soak for 2 hours per 25mm of ruling section. Those values are 1022°F - 1292°F.
Then again, cool in air.

I lack the final bit of information. How hard does it get? What is a good final hardness value to have for a tool holder? What temperature do you need to get it there?

I understand that second heating (tempering) value should not use values between 250-375°C because the Izod impact toughness value would be adversely affected. I guess it would still be "too hard", and a bit brittle.

4140 is not air hardening. Cooling in air will probably produce poor results. A fast oil (warm a bit) would be better. S-7 is air hardening with about the same amount of carbon, but does not get all that hard. It's great for hot cutting and punching tools.

 

[graham-xrf]

4140 is not air hardening. Cooling in air will probably produce poor results. A fast oil (warm a bit) would be better. S-7 is air hardening with about the same amount of carbon, but does not get all that hard. It's great for hot cutting and punching tools.

Eric - if that is the case, then all my info is wrong! I have attached the stuff I have.
4140 is a chromium - manganese - molybdenum - nickel alloy with up to 0.4% carbon. It does not harden and temper like carbon steel.

 

[ericc]

That is correct. It is not like simple carbon steel, but it does not have enough chromium or molybdenum to air harden. Also, it shouldn't be used past about 50 RC. For cutting tools, use another tool steel.

 

[NC Rick]

Why not use pre-hard 4140, i like that stuff.

 

[NC Rick]

I bought the wrong size. Boring head is 3/4. Bit holder 3/8. Shank of new tool 1/2.
My choices:
1. turn shank down to 3/8 and shorten
2. bore bit holder to 1/2 ( I have another)
3. Make a new bit holder.

I think #3 is my best choice. Your opinion? Would 4140 be an acceptable material? How about 304 stainless. I've got both handy.

I hate returning things when it's my fault.
View attachment 362427

I apologize for not reading your post carefully enough. Making a new holder would be a fun exercise. If you have another unused holder indicating the existing hole and boring it out to 5/8 seems like a reasonable option to me. If a file will cut into the nose of the holder (which I assume it will) i would try a carbide boring bar to get it within a few thou and maybe ream it to size? I wouldnt have real good confidence in my ability to hold size down the length of that bore with such a small boring bar. Others will be more experienced than I.