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darryl
09-18-2012, 11:40 PM
ok, an actual metalworking question- :)

I have a mechanism to build which is two pieces of sheet metal crossing each other, pinned but free to pivot. One piece is 3/32 thick and the other is 1/16. I have less than 1/4 inch of space for this to slip into.

The thinner piece is the actuator for the thicker piece, which is a latch of sorts. My plan is to drill a hole in the thicker piece and a smaller hole in the thinner piece. With the two aligned together, I would hammer a tapered rod through the smaller piece which would enlarge that hole and force the metal to become somewhat like a rivet. If I continued to form the smaller hole, I could actually use it to rivet the pieces together, but the object here is for the pieces to stay together but pivot easily.

I know if I hammer it down it will be riveted and tight. If I take two pieces of thin steel, like tape measure thickness, and grind a half hole in the end of each piece, then push those together around the 'rivet', then hammer it down, then pull out these pieces- hmm, what are my chances that the joint will be free?

Any other ideas? This needs to be very low profile, so that's why I'm not considering working with a normal rivet. With nothing sticking out the 'bottom', I can afford about 1/16 or a bit less of a bump at the 'top'. I will probably have to grind that a bit in order for it to slip into the space where it needs to be.

The other thing that concerns me is that this is stainless. The hole might want to rip and tear before it stretches much. I could try to upset the hole by punching a pair of crossed lines across it so it would open up along those lines, but again this isn't easy to do in stainless. In any event, because this has to be a pivoting join, it should have a fairly tight but smooth action.

My latest thought on this is to make a jig to expand the small hole into, then have a slightly larger hole in the mating piece. I'd still have to make sure I could expand that result into a rivet, and make sure the pieces are still free after that.

J. R. Williams
09-18-2012, 11:43 PM
Check out the rivet design on a soft drink "Tab Top".

Evan
09-19-2012, 12:00 AM
Put a slip of paper between the pieces. It will disintegrate quickly when you move the joint after riveting.

CCWKen
09-19-2012, 12:02 AM
Your method is used often to assemble parts. Sometimes on a single layer to form a roll around a wiring feed-through hole. It would probably work as a pivot but it's going to be trial and error to get it snug and movable. I think I'd use a stepped rivet instead. Counter-sink both sides and use a flat head rivet. Use the 3/32 stock as the bucked side for the fixed pivot pin. Both sides could be ground flush if necessary.

darryl
09-19-2012, 01:10 AM
Ok, so I tried punching the hole out to form the rivet. By the time I got enough metal sticking out to fold over, the mating hole would have to be 1/2 inch diameter or more to make a fit. I don't think this is going to work. Ken, I think I'll have to go with your idea.

I just realized that I can cut a relief into one part of the housing for the head of a rivet to nest into. That will make it easier. I'll see if I can find some stepped rivets tomorrow.

oldtiffie
09-19-2012, 01:20 AM
Try biffercated rivets - they have been a "tinsman's" (sheet-metal worker's) - and many others - solution for many years.

http://www.google.com.au/search?q=bifurcated+rivets&hl=en&qscrl=1&rlz=1T4IRFC_enAU360AU360&prmd=imvns&tbm=isch&tbo=u&source=univ&sa=X&ei=MFVZUM5G6K-JB-DegKAE&sqi=2&ved=0CCQQsAQ&biw=1920&bih=851

http://www.google.com.au/webhp?sourceid=toolbar-instant&hl=en-GB&ion=1&qscrl=1&rlz=1T4IRFC_enAU360AU360#hl=en&sugexp=les%3B&gs_nf=1&cp=13&gs_id=c&xhr=t&q=bifurcated+rivets&pf=p&qscrl=1&rlz=1T4IRFC_enAU360AU360&sclient=psy-ab&oq=biffercated+r&gs_l=&pbx=1&fp=1&ion=1&biw=1920&bih=851&bav=on.2,or.r_gc.r_pw.r_qf.&cad=b

You can get a similar result with a "spiked" hole and a flat washer.

J Tiers
09-19-2012, 08:28 AM
Tog L Loc..... that's what you are talking about, whether you know it or not.

http://www.btmcorp.com/toglloc.html

darryl
09-21-2012, 03:05 PM
Just an update on this. First a quick re-cap- one strip of 1/16 thick stainless steel strip is an actuator rod for a latch made from 3/32 thick stainless. To attach the two I used a stainless steel rivet, the largest diameter they had in stock, which is 3/16. These are pop rivets, so I've ditched the pin and just cut the rivet short to suit. I drilled out the strip with a .190 bit, and the latch with a .187 bit. Rivet goes through the strip first, then two layers of parchment paper (for a total of .003 or so) go on as spacers, per Evans suggestion. Then the rivet is pressed into the latch piece, which is tight but can be done by fingers. A tapered rod is hammered into the cut end of the rivet to expand it, then it's hammered down. I took some care to hammer all around the edges of this expanded end to put the sharp edges lower than the 'button'. One drop of TriFlow is added, and the join worked around a bit.

It works PERFECTLY! There is no play, and the paper washers seem to want to stay in place. There is just enough freedom of movement ie no binding.

The parchment paper is not waxed paper, it's silicon impregnated I believe. It seems to be just the thing to keep parts separated in an application like this. It's supposed to be waterproof, so that's a bonus, and it's quite slick so it keeps friction to a minimum. I don't know if it will work itself out eventually, but no matter anyway in this case.

The total thickness of the 'package' is .200 as measured, so it fits within the space it has to occupy. This is the result I was looking for, so I'm happy.