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timh
11-01-2005, 01:37 PM
Which machines better plain 4140 or preharded? Advantages or disadvantages useing one over the other?

Rustybolt
11-01-2005, 04:02 PM
I'd say it depends on what you want to use it for.
As for easy machinig, that too depends on a few variables. Are you using HSS or carbide?

Forrest Addy
11-01-2005, 04:28 PM
I machine either with the same tools. I use slower speeds on the pre-hard but otherwise no biggie. I suggest you pick waht you need and make it from that. If you need harder than pre-hard go with the un heat treated stuff and haarden after machining.

timh
11-01-2005, 04:43 PM
I will be milling useing hss cutters i hope will this be possable? And would it be better to use anneled because of this also what about stress in this type steel. Thanks

Mcgyver
11-01-2005, 05:31 PM
<font face="Verdana, Arial" size="2">Originally posted by Forrest Addy:
I machine either with the same tools. I use slower speeds on the pre-hard but otherwise no biggie. I suggest you pick waht you need and make it from that. If you need harder than pre-hard go with the un heat treated stuff and haarden after machining. </font>

Forrest, how stable is this stuff? ie compared to tool steel how much movement would you expect from heat treating it? or for that matter how much is the pre hardened going to move from machining, ie how stressed is it?

I've not much experience with these alloys, but am wondering how different they are from tool steel where you'd usually want to grind after heat treating because of the potential movement. please enlighten.

canman
11-02-2005, 03:36 AM
Hello,
Years ago I used to make a lot of parts from 4140 annealed and pre-hard. What I found was that most of the movement I was getting at heattreat was created by the vendor. I made link pins that were 4" to 6" in diameter x upto 40" long. After heatreat I would run between centers and turn with ceramic to finish O.D. Finish was great. The movement at first would be around .080. They would just bearly clean up at .100 over. After "suggesting" to vendor that his process needed to be looked into, the worst movement (warpage) was .040 inclusive. That improved finishing time eminsley as I would now just leave the part .050 oversize. So make sure of your heattreat source. The type of 4140 used in this application (prehard) was determined by mangement. (That was the only type available in the sive needed and the "customer was charged by the hour".) I have worked for some nice ones over the years.................

KDRedd
11-02-2005, 03:22 PM
I at one time made so oil pump shaft from 4140. I was using carbide end mills and not getting any life from them. Some of the last ones I built I tried an experiment and used roughing HSS end mill. The roughing lasted longer but you will have to change out the cutter for a finish cut if finish is important.

Kent

Forrest Addy
11-03-2005, 01:33 AM
4140 is as stable as any steel alloy. Stability comes with consistancy of the metal, the heat treatment, any post treatment like stress relief, and finally the machining process.

Most barstocks have unavoidable stresses in them from the rolling process at the mill. A smart machinist making long skinny parts will place their neutral axes concentric with that of the bar they're machined from.

As for the kind of stability where stuff stays stright, that can only come from material that's stable to start with. 4140 is no better or worse than any other in this respect. Thermal cycle stress relieving will go a long ways towards ensuring the dimensional stability of precision parts.

If you're making blocks for a home brew quick change tool post, pre-hard 4140 is an excellent choice. So it is also with press brake dies 16 ft long. I've made many press brake dies and tons of other parts over the years and have come to appreciate prehardened 4140's virtues as a stable material suited for a wide range of products and parts where strength, fatigue resistance, attainable range of mechanical properties, resistance to elevated temperature, and machineability are desirable.

[This message has been edited by Forrest Addy (edited 11-03-2005).]

madman
11-03-2005, 10:56 AM
4140a ( annealed or drawn back) is easier to machine than 4140 heat treated as they seem to call it. We use both daily in the shop.