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Thread: 4140L or 4140 TG&P?
04-19-2011, 10:09 PM #1
4140L or 4140 TG&P?
I need to buy some 4140, 3/4" dia., for threading on either end and used as a draw-bolt. I would like to find something like a cold-finished 1018, pretty much to size. So, I have been told about cold-drawn 4140L at $43 per 12' length or 4140 TG&P at $100 for 20'. Is 4140L of approximately equivalent strength as regular 4140? Are these prices reasonable? Thanks, KQ
04-19-2011, 11:08 PM #2
You don't have to get fancy. A draw bolt is just a long bolt. TG&P is a waste of money. 4140L is also a waste of money and it attracts rust eventually. 1040 or 4140 hot roll is plenty good enough. Machine it. Try it for fit. Harden and draw to suit.
This place you can get a 3 ft piece of pre-ht 4140 for $12.75
4140 Cold Rolled Steel Alloys Pre Rounds, 4140 Cold Rolled Steel, Cold Rolled Steel
or you can get oil hardening drill rod from Enco (3' length for $6.82.
Do you want a 12 ft length of 4140? Check with your local specialty steel yard. Many will have a minimum charge but sometimes they will vaive that.
04-19-2011, 11:12 PM #3
The bolts are 10" long, threaded 1" long on one end and 1 1/4" long on the opposite end. They need to fit a hole quite closely, only about .010" clearance on the entire length.
04-20-2011, 12:19 AM #4
You might consider 1144 or stressproof- either one will machine much easier than 4140 annealed or 1040. Od tolerance and finish should be ok also. what kind of material properties do you actually need- that should determine what you use as the primary criteria- could be that 1117 would work.
04-20-2011, 11:24 PM #5
These draw-bolts go through a piece of phenolic and screw into 4140 caps on either end. I would like to have the equivalent or close-to-it strength in the bolt as in the 4140 end caps. The rod will be tightened and then reamed/pinned with a tapered pin. (#5).
04-21-2011, 07:51 AM #6
This is an interesting problem, and your question and additions communicate the issue well. You are experiencing the "PM Mind Shift". You ask a simple question like "Would material 'A', or 'B' be a better match to this application, and where would I find the better material?". The answers you get range from literal, to "you shouldn't use either A or B", to "You really ought to buy an older DeVere lawnmower off eBay and restore it, not one those new cheap Chinese jobs". Completely off topic.
In that spirit, I offer the following.
My understanding is that the point is to take a 3/4 inch 4140 rod about 10 inches long and stick it into a hole in phenolic 10 inches long, torque it tight, and drill, ream and pin it. The hole is 0.010 oversize, leaving 0.005 on either side?
My thought was that phenolic will deform in the region around the hole long before you get to a torque value anywhere near the bolt strength. So unless there are other factors, I would think you have more design flexibility in choosing the shaft material. "The same strength as the nut" is probably not operative, as the phenolic will fail first (phenolic compressive limit (10% strain) is 36000psi, 4140's yield stress is ~60000psi, if I recall).
The second point is related to the first. If you tighten that bolt at all, the hole is going to distort, right? Is there a valid engineering or marketing reason to have a nice, shiny TG&P shaft for this application? If you are pinning the bolts, this is for relatively permanent installation, right? So the customer never even sees the shaft surface?
I mean, if customers see the surface finish, and it matters enough (as in customers will like the neato finish and are willing to pay more) to up the cost maybe TG&P is worth it. Otherwise, I trust Mr. Addy's suggestion of HR. Worst case, you have a little friction fit which should not be a problem in phenolic, right? And since you are tightening a high-strength steel bolt in plastic, you are willing to accept distortion anyway, right?
Plus, you really should buy an old, American-made lawnmower and restore it. It will last, like 300 years.
04-21-2011, 10:01 AM #7
There are two possibilities here.
A The OP doesn't know what he is doing and he should post a complete set of prints, useful life estimates, environmental impact study and cost analysis so we can do a design study.
B He knows what he is doing, in which case we should answer the damned question.
04-21-2011, 11:40 AM #8
Everybody's right. I used to do a lot of stuff like that from A-2 drill rod. For a 10" long piece, you can machine 1" hot rolled pre-hard for less than they want for TG&P.
For a lawn mower, find one of these:
04-21-2011, 01:40 PM #9
04-21-2011, 01:56 PM #10
I go to a reputable steel warehouse and buy 1144 stressproof (or stress stabilized) for practically all projects in my shop. It is easy to machine, comes in accurate sizes like cold drawn steel, has been normalized at the mill (hence the black color), has great strength properties and is resistant to bending, can be heat treated by heating and quenching, does not have surface tension (resistant to warping when the surfaces are machined unevenly). Plus the cost is reasonable. I have to go get another supply this spring. It does have some sulfur in it which aids machining, but may not be suitable for welding.
04-21-2011, 10:40 PM #11
I think I'll increase my hole dia. by a 32nd. and get hot-rolled material and thread it in a pipe threader with bolt dies. I have redesigned my mating pieces on either end so the outside of the phenolic will fit into a recessed registered (redundant) fit in the caps on either end so hole size doesn't really mean anything now. Thanks, KQ
04-21-2011, 10:57 PM #12
Some industrial fastener houses keep B7 round on hand for making DE studs. It is hot rolled, and cheap, relative to TG&P and certainly you wouldn't have to buy a 12 foot piece. For all I know, McMaster or Grainger carries B7 also. Not looked.