Help selecting alloy for small shaft. hard surface, low load

[bob1111]

We are making a simple shaft with a bearing tolerance OD to +/- .0002" We want to keep the entire part in house because pricing is a concern. We are looking very hard at 17-4PH H900 but it is only HRC 38-42 and we really need to be around HRC 50. The shaft is roughly 7/16 diam and 3" long. I know 4140 is a good choice and just through harden it but some mfg problems exist.

We either need to machine complete for one lathe operation, or machine complete, then HT. H900 material runs good in a lathe as is. We can hold the tolerace with our machines and have a makeshift grinding setup that works to get the final OD we need. Problem is once we remove the part from the lathe and put it back in, (sa from heat treating it), we will have some runout. 4140 can achieve our hardness and would like to just make the parts complete, HT, and move on but the HT scale is what is concerning with that material. If we could air quench or something so that we would not have scale, it could work great. We plan to do the HT in house.

We will be applying a DFL coating on these parts which requires a light Alo2 blast just for reference.

 

[bob1111]

I would also add that we can certainly tumble these parts if that will remove the scale left on the 4140 parts from HT. In our experience, with the right media will not remove an appreciable amount of OD material to worry about. The scale is our only concern...

 

[desertfox]

Hi bob1111

Is it possible to rough machine, heat treat and then machine/grind to final size thereby getting rid of the scale. I am assuming of course you can eliminate any distortion due to residual stresses.


desertfox

 

[bob1111]

No, our goal is to have the parts on the machine 1 time. We can certainly adjust our process to adjust for HT variance in size and slight part distortion from HT will not be an issue. Only maintaining the OD size. If we can tumble and remove the scale or keep it from forming, we are good. We are aldo VERY open to other alloys for this part.

 

[unclesyd]

To start off I would look at a air hardening tool steel like A-2. If this is not cost effective then to purchase pins from Dowels Pins and Shafts, Even if the hardness is above your requirements you can draw it back. The same holds true for hardened drill rod. If your process won't allow this approach then I would look to Boston Centerless for ground rods. As to keeping your heat treating in house I would look at either one of the approaches afforded by Rose Mill or Sentry Furnaces' Carbon Block.

http://www.rosemill.com/default.asp?pageid=27391

http://www.sentryfurnaces.com/diamondblock.htm

http://www.bostoncenterless.com/materials.htm

http://www.dowelspinsshafts.com/

 

[israelkk]

Check Thomson linear bearing shafts, they come already surface hardened so you can cut from a long shaft or order to your length. I assume they heve the 7/16" it is called 60 case shaftings, see page 4 in

http://www.thomsonlinear.com/website/com/eng/img/brand/Thomson_Overview_v4_final.pdf