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Davek0974
08-21-2007, 05:24 AM
Just a quickie.

I need to make some simple t-bar wrenches.

7/32" square drive spigot on one end-about 3/8" long, 2.5" t-bar on other, it's a hand tool for tightening some locking clamps on a cutting machine so quite low torque usage hence the short t-bar.

I was thinking 1/2" mild steel with a case hardened tip. Mill the square tip straight from the round, bevel the handle end and pin the t-bar in, probably 15-20mins work each.

Is mild steel suitable or should i go for something a little more exotic? They don't need to last for life as they are semi disposable, usually last about a year. Too hard and they will destroy the locking screws which are hard to replace (also means i won't get so many repeat orders :-) ). Too soft and the end will twist off and it will give a crap image.

So is it worth case hardening?
Is Mild steel ok or what is better but won't last a lifetime?

I know you would probably like them but i don't have any torque figures, one-hand use only!

Thanks in advance
Dave

Forrest Addy
08-21-2007, 05:31 AM
I'd suggest a plain water hardenng tool steel or a high carbon steel. 4140 is also good. Then you can readily harden the end and draw it back to a spring temper like Rc45 or so. The bar of the wrench needs to be hardened to so it won't bend when tightenting up the wrench. Finally, don't mill the square with the end of an endmill so it has a sharp inside corner. Mill the square with the side so there is a big fillet to transistion the stresses into the body of the wrench.

Davek0974
08-21-2007, 06:18 AM
Thanks

I did a trial tool and using 3/16" mild steel for the t-bar seems ok. Using it at the normal torque shows no sign of twisting the tip or the bar.

Applying a painful amout of torque can cause some damage to the tip but not the bar. That is what made me feel that ordinary M/S is ok for the application, being a small handtool limits the amount of force you can apply under normal use.

I clamped the tool in a vise and gave it some elbow and only just managed to bend the bar, but it hurt like hell!

I concur with the milling, side-on gives a lovely fillet from round to square.

If i try another mock-up, is it worth case-hardening the tip?

Dave

DR
08-21-2007, 08:04 AM
1144, Stressproof, might a good choice of material. Pre-heat treated, machines well, not real hard. Readily available.

I have a couple of lathe chuck wrenches I made years ago out of 1144, they're still working fine.

wierdscience
08-21-2007, 09:32 AM
Case hardening will only give you a thin skin that is hard,possibly only .005" deep.That won't do much for strength.

Like said above I would use a good quality tool steel,even left soft it would be stronger than ordinary MS.

John R
08-21-2007, 09:56 AM
I make chuck wrenches from grade 8 bolts.
John R

Carld
08-21-2007, 09:56 AM
4140 may do the job. It's tough and can be hardened but is ok as is.

Mike W
08-21-2007, 10:07 AM
I made a torque wrench extension from the wrench to the nut you wanted to tighten that doubles the reading from the 150 pounds or whatever the limit of the wrench was. I used a piece of ms flat bar and brazed a socket for the wrench and a short 1/2 extension at the other end for sockets. It worked well.

lazlo
08-21-2007, 11:31 AM
I make chuck wrenches from grade 8 bolts.

Grade 8 bolts are pretty darn close to 4140 Pre Hard. I use Grade 8's in a pinch, if I don't happen to have 4140 stock that's the right size...