Making a shaft from D2 - What to look out for ?

[Doozer]

Making a shaft from D2 - What to look out for ?
This shaft is for the headstock of my Hendey T&G lathe.
It has 3 steps in it, 3/4, 5/8, and 9/16" over a 6" length.
Also has male 7/16-14 threads, a 1/8" woodruff keyseat
and a 5/32" keyway. I was going to cut the threads in the
lathe, and leave the step features (for needle bearings)
.010" oversize. Mill the keyseat and the keyway, then
heat treat and temper in an oven using stainless tool
wrap. I will grind to final size for the bearing journals
and where the gears go.
My question is, how tight do I make the male threads fit?
Will the D2 grow or shrink? I assume shrink.
Will my keyseats get tight ? I want the keys a light press
fit. Should I make the keyseats right on size and assume
they will close up a tenth or two? Is .010" oversize enough
grind stock? I don't know how much D2 will warp over 6".
I am not at all new to machining, but I do not heat treat
a lot of stuff. I typically use carbide tooling and buy pre-
hard stock in the 30Rc to 50Rc range, to get around the
need to heat treat. But this shaft had bronze bushings
that I would like to convert to needle bearings. Every
thing I read about needles say the shaft needs to be
at least 60Rc. I thought about buying Thompson shaft
but the needle bearings 3/4" and 5/8". Thinking if I
grind the Thompson shaft to 5/8" then it will be too soft
for the needle bearing. Hence my idea about making
the shaft from D2. Any cautionary thoughts before I
enter into this shaft adventure ?


Thanks,
Doozer

 

[Mtndew]

D2 shouldn't move but only a couple of tenths, but I haven't cut that stuff in years so I could be wrong.
Is 8620 carb & harden 58/62Rc an option?
You'd have to finish the diameters and lengths after heat treat though, just leave .01"-.02" on diameter.
But you can have them leave threads soft, you'll just take them about .005" undersize like you would oversize tap a hole before carb.

 

[eKretz]

I'd leave .020" on the diameters just to watch out for warpage. It's a small surface and a single part, so a little extra grind stock is cheap insurance. Try to keep the shaft vertical when going into the quench or it will warp worse. Once you're submerged position doesn't matter. The entry is the important part. Threads, slightly undersize, maybe .002"-.003" on small stuff. Key, on size. D2 can be tricky with growth/shrinkage sometimes. Occasionally I've seen it grow in one direction and shrink in the other. On small parts it's not going to be a whole lot though. The warpage is what you'll need to be careful about.

 

[gbent]

I'd probably use A2 and skip the quench. Can't predict the size change without knowing tempering temperature.

 

[Doozer]

Thanks for the replied so far.
I thought D2 was air hardening, is it not???
Yes, easy to leave .020" stock just in case.

-D

 

[eKretz]

Thanks for the replied so far.
I thought D2 was air hardening, is it not???
Yes, easy to leave .020" stock just in case.

-D

Yes, you're right, you can probably air harden for that thin section. I'm used to doing thicker sections, we'd often oil quench those.

 

[4GSR]

The QCGB on my Sheldon lathe is full of needle bearings running on soft steel shafts. Of course they don't turn that fast, maybe 100 RPM at most. I know they recommend running needle bearings with the harden steel bushings, I've used them without with decent run life.

 

[Goff]

Hudson Tool Steel at www.hudsontoolsteel.com, under technical data, select D2, has a graph showing size changes vs tempering.

 

[Doozer]

The QCGB on my Sheldon lathe is full of needle bearings running on soft steel shafts. Of course they don't turn that fast, maybe 100 RPM at most. I know they recommend running needle bearings with the harden steel bushings, I've used them without with decent run life.

The shaft hold a gear and a vee belt pulley.
The side load from the belt tension is what I believe
gave the bronze bushings a short life. I really think
I need to upgrade to needle bearings. But thank you
for the real world insight. Low speed and load they
would probably work ok.

-Doozer

 

[???]

Listen to those saying leave substantial extra stock. No one can accurately predict the movement, as ekretz said sometimes it shrinks sometimes it grows. The work of remaking the entire part is far greater than the extra finishing required. You can also rough after hardening with ceramic and then finish grind.

I should make a macro that puts in a standard response for hardening if you aren't really desperate and absolutely need to do it.

Go to a local toolroom and ask them to put it in with a batch of their hardening and buy them beers. Most hardening places have minimum charges and toolrooms often send out small pieces for rush maintenance jobs.

 

[BajaFire]

Doozer, you're in Buffalo. If you're not sure of your heat treating prowess, ship the shaft to Peter's Heat Treat. Or, take a scenic vacation to Meadville, PA, and drop it off. They've done single-piece jobs for me before. I don't remember their prices exactly, but I also don't remember falling out of my chair upon reading the receipt.

As a note, I'm not an expert heat treater. I usually do random bits and pieces made from 4140 or O-1 that are for inside projects. However, the one time I hardened D2, it was a breeze - just heat it and hang it in still air (made a chuck key from a piece of scrap - really just an excuse to experiment with this stuff).

The austenitizing temperature is up there, though - almost 2000 degrees Fraidofheights, I believe. Might have trouble getting that consistent (and not overheating/burning) without a decent oven.

 

[Doozer]

I am a bit of an amateur when it comes to heat treating too.
I do have access to a real deal heat treat oven at work that
the toolroom guys use. I can get the time and temp recipe
online for heat treat and temper for D2. We have stainless
steel tool wrap to, so I can bag my shaft. If something goes
wrong, I can make another one. It is not that complicated
of a shaft. Thanks for everyone's thoughts so far.

--Doozer

 

[gbent]

Be tempting to ask the tool room guys what they usually cook and make it from the same steel so they could run it with an existing job

 

[Doozer]

Be tempting to ask the tool room guys what they usually cook and make it from the same steel so they could run it with an existing job

I would be more successful asking a drunk homeless man
to solve a calculus problem......Sadly.

-D