Manufacturing Tolerance on HR Bar Stock?
Manufacturing Tolerance on HR Bar Stock?
(OP)
I am trying to figure out what size (thickness) bar stock to order for machining a 100" long rail whose final thickness will be 1.875"+/-.003; material will need to be 4140 normalized (i think). We have seen bar stock come in that is bowed and twisted but has not been a concern for us since we generally can cut these into shorter lengths for our typical small piece production. But these long rails are new to us and so I am not sure what bar stock thickness to order so that I can be assured that we can mill away the twist and camber. How will I know that I can get 1.875"+/-.003 of usable thickness over a 100" length if I start out with 2" thick stock? or should I buy 2.25" stock? or 2.5" stock? What are the rules?
Thanks for helping.
Thanks for helping.





RE: Manufacturing Tolerance on HR Bar Stock?
for diameter 5/8" over, and length < 15 feet, and C > 0.28% the straightness tolerance is 1/8" for any 10 foot portion of the bar.
That means theoretically a 2" bar would suffice if the diameter was exactly 1.875". Your cold-finished bar supplier should be able to tell you if they can meet tighter straightness requirements than those specified in ASTM A 108.
RE: Manufacturing Tolerance on HR Bar Stock?
RE: Manufacturing Tolerance on HR Bar Stock?
Ornerynorsk provides good advice - a little straightening can replace a lot of machining.
RE: Manufacturing Tolerance on HR Bar Stock?
What you receive will _always_ be on the low side of the tolerance range, even though you pay for nominal weight.
Mike Halloran
Pembroke Pines, FL, USA
RE: Manufacturing Tolerance on HR Bar Stock?
http://www.associatedsteel.com/pdf/07-08.pdf
Another approach would be to get the bar to where it could be finished ground to size. This approach minimizes the distortion caused by machining a HR bar.
h