Spindle material

[h3ndrix]

Hi ppl

I am in the process of making a spindle for the Mini mill head, I am going for a ISO 30 taper spindle but was wondering what type of material would you guyz recommend...my current thoughts were these;

-Stainless 416
-Low carbon Steel 1018
-Medium carbon (stressproof) 1144

Anyone got any ideas on this?

thx

H3ndrix

[HuFlungDung]

I would tend to stay away from stainless, because of the expansion rate being a bit higher, and the heat transfer capacity being less than carbon steel.

Stressproof is nice to machine, but is pretty soft.

I would use C4140 HTSR (heat treated stress relieved) because it is somewhat harder. This means cutting it at a bit lower speed, but you only do it once

The taper should last a bit better with C4140, as will the keyways or splines, and any threads on it, etc.

[h3ndrix]

thanks Hu, Ill look into that right now

[Stevie]

I used 4340 for my collet spindle in my self build lathe; seems quite good

[HuFlungDung]

Stevie, your choice is even better stuff Some guys get pretty discouraged when they try to drill it, though

[avsfan733]

4340's not to bad we do it on a speed lathe with a spray bottle of coolant and don't really have that man yproblems besides maybe one cooked part outta 35

[h3ndrix]

Hey

Thanks for the replies, I was able to find 4140 Heat treatted but i was only able to find 4340 in annealed state which I would need to get heat treated.. any ideas on how costly this treating process is?

[HuFlungDung]

Shop some more, its out there

The commercial "heat treated, stress relieved" C4140 and C4340 is stress relieved back down to about 35 Rc hardness I think. But, if you get a piece custom heat treated, it may be too hard for you to work, because this stuff will harden right up to 55 or 60 Rc

Or, it may bend a little bit after you have it heat treated. You have to be prepared to machine it back to straightness, so this might be asking a bit too much.

Most heat treaters charge by the pound, or a minimum charge of $50 or so dollars.

The main advantage of C4340 is it's toughness at low temperatures, which is likely not a big concern to you. It may also have slightly higher ultimate strength, but I wouldn't think you would be working this to its maximum capability, anyways.

[Klox]

Hu,
what's C4340?
I would use a high carbon steel that can be case hardened, or maybe something with a high tensile strength......

Klox

[HuFlungDung]

Hi Klox,

How's things burning (EDM)?

From memory,
C4140 = Chrome molybdenum carbon alloy

C4340 = same thing with nickel added

Yes, you could use a carburizing grade like C8620 if you have the wherewithall to machine it after its been heat treated.

[BIG AL]

I know if I was going to do a spindle I would look long and hard at 8620. It does not workharden as you machine it so their is no back and forth annealing going on while machineing, as I recall off the top of my head (without looking in Machinery"s Handbook, always dangerous) in the normalised state it's in the 90,000 psi area, it case hardens great with out distoration and leaves a great core for shock resistance. And of course it's in the chrome-moly family. But I'am bias in its favor, as I use it a great deal and love it in this type of situation where I need good machineablity, high or good wear chacteristics and ease of harding. Good luck with your project!

[h3ndrix]

thx BIG AL,

I will look into 8620 aswell...but I have one question, how well does it machine when doing free-machining rather than cnc machining?

Thx