....the lab tech said while i was modifying some pliers to make a tube clamp for brazing. previously i had been using the tube jaws of a vise to hold a tube while i brazed:
this didn't permit good positioning of the joint--the vise being a bit too low and the tubes being quite short for these practice joints; loads of flux dripped all over the vise, which was a pain to clean up; and the lab tech, Bob, suggested that the vise may have been absorbing a lot of heat, which would be bad for the vise and would make brazing more difficult.
i got the idea for a solution from a buddy at school who directed me to instructables.com, where i found this set of instructions for a work stand. what interested me was this part on making the clamp. i made mine along the same lines, although i used regular "straight-jaw" vise-grips--not the brightest idea. what i made will probably work fine, but i imagine it would have taken a while less to make if i had used the type of vise-grips pictured in the instructable.
first i ground off the zinc plating/coating (to avoid nasty fumes) around where i welded the arm extension. i bench-ground a piece of square stock so one side was slighty concave to match the curve of the handle. i clamped the square stock to the handle, tacked, and welded in a couple places--just short welds so the pliers wouldn't get very hot. then i ground bevels into the square stock, and into a longer length of angle, tacked, and welded the angle on top of the square. next came a ~2' section of plack pipe, about 1/8" thick, which i welded into the angle. this pipe will get vised into the pipe jaws when i wanna braze; i left it long to give me lots of flexibility when positioning things.
last came modifying the jaw faces; this was damn tricky and took several hours. first i removed the hard jaw face from the top of the grips, the part that stays stationary when the jaws are closed. the face itself is too hard to cut with a bandsaw or hacksaw. i had to cut around it, into the softer steel that makes up the body of the pliers. to do the bottom, i attacked the jaw face with an angle grinder, and it was slow going to make the notch i wanted. the notch is to allow pieces of angle to be welded on as replacement faces.
the angle i used was some small scrap, 1/2" on a side, about a 2" length for each face. i spread the angle a bit by cold-forging: i sat the angle on an anvil with the apex up and hit the apex with a hammer. my metal teacher explained that hammering when forging is a lot different than other hammering; you hold the hammer up near the head and strike the work many times quickly, letting the hammer bounce up so you can recycle the energy you put into bringing it down. the angle deformed enough after a few minutes of hammering, although the apex was flattened, so i filed the outsides down to make it sharp again. i also rounded off the corners and made the inside faces a little convex--to hopefully prevent any damage to the tubes.
with the new faces done, i test-fitted them into the modified pliers around a 1.25" tube. the angles were a little off, so i did some more grinding and filing until everything clamped in right. i ground off the zinc coating before welding, but i didn't get it all so i wore a P100 respirator. i'm anal like that, plus the ventilation near the MIG isn't that good. to do the welds, i left the whole thing clamped together around the tube so 'twas all lined up. initial tests indicate the clamp will work down to 1" tubing. i think i'll plasti-dip the jaws once i'm done with practice brazing...until then i'll be putting some serious heat near the thing.
elapsed time: 4+ hours today, plus maybe 30 mins last week.
this is the "top," the stationary part, where i completely cut off the original face. note the cold-forged angle stock cradling (?) the tube. this will ultimately get coated with Plasti-Dip.
now the other side. i was worried about MIGing the hardened steel face, but it wasn't a problem. i would've cut it off, but i didn't think i'd be able to get the angle in there right without it.
the square stock between the pliers and the dyed angle is to offset the pliers so the adjusting bolt is still usable. also it was easier to put a concave radius on square than angle, and it was scrap.
the other side, showing the black pipe welded into the angle welded onto the square welded onto the pliers.
the school's tools are all marked with pink spray paint, so i've taken to marking mine with blue layout fluid to avoid confusion. goes on looking and smelling like nail polish.
end view showing the whole assembly.
the whole thing in the vise holding a piece of 1.25" 4130. previously i could've only held that tube about 2 feet lower than it's pictured. i'm hoping that 2 feet makes a difference.
i'll put it to use tomorrow afternoon. perhaps i'll blaze a joint and then braze a joint.
laminated maple blocks, ~3" square x ~5" long, waiting to become tubing blocks.