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Comment by Jonathan Kreilich on May 13, 2016 at 1:33am

I took my spar middle to a local metal shop and had it sheared, which gave me a nice side for the top and bottom.  Some of the rivets where a little hard to lay out, but I read that the spacing is maximum, so if it pitch 40 and you end up with pitch 35 that is good.  I have seen several 'C' rivet machines, I forget what they call them, but it holds the air hammer at a 90 degree angle to give you near perfect rivets every time, the other thing I was looking at was a rivet press, which I think would have worked very well.

The hammer technique worked alright, they are not perfect, but they are within spec as far as I can tell.  I tried an air hammer, but I think it was the wrong type and did not get good results with it on some test pieces, so I opted for the shoeing hammer, which gave me much better results.  I was able to hit the rivet every time, I have quite a bit of practice from shoeing horses, so that helped. 

As for work hardening, as I understand it that is caused by heat and then rapid cooling, like if you douse it in a bucket of cold water.  If you heat metal up, then let it cool at about the same rate the metal will form back to the original structure, to a limit with heat and cooling.  As little heat as is generated by using the hammer I do not see a problem.  If it was caused by the structure being deformed, any method you use would cause the crystalline to occur.  I am not worried about the metal being work hardened since it was not heated up very much and allowed to cool at a slow rate.

Good luck, just take your time and lay things out and then check it.  It took me longer then expected to build the first wing, but I did not follow plans exactly so I had to figure a few things out on my own.  A good idea is to build a jig for the rib rivets and the wing skin rivets, that way they line up and things look a little nicer.

Comment by michael w. mckosky on May 12, 2016 at 7:33pm

Jonathan,

Thanks for the reply.

I ask such questions since I will begin working on my scratch-build CH750 wing, and the spar construction is the high-risk item that I will do first, as a go-nogo step in the process.

I am making a simple jig that will hold the back-rivet tool normal to the spar web/angle stock, since I think errors that people make are due primarily to column buckling of the rivet, due to miss-alignment of the tool.

Is control of your hammer technique working out okay?

I plan on using either a rivet gun or an el-cheapo Harbor Freight air hammer. If the later is held normal with the jig I expect that it should yield perfect rivet sets.

When I was at the Sonex workshop several years ago, as I recall Monet suggested using a large bolt, with a large washer to use as a shield to protect the hand holding the bolt, and striking the bolt with a heavy hammer. It seemed to work well, but I am still a bit concerned about failure. Especially if one is really installing the rivets in the actual spar. I would not want the hammer to slip, or the bolt to slip sideways and ruin the spar itself.

How does it go with you so far? Hopefully no dings?

Is work hardening a function of temperature  as the metal is being deformed? Or due to the crystalline structure being reformed? I haven't yet found a good explanation for that. Darn, I should have taken a course in material science! Oh well.

Thanks

Mike

Comment by Jonathan Kreilich on May 10, 2016 at 10:01pm

I would say no Michael, it would be the same as using a pneumatic hammer, except I am using my muscles instead of air.  If anything it would be less likely to work-harden the rivets since my hammering is not as fast as a pneumatic hammer, there is a little more time between strikes, not a lot, but my hammering skills are not near as fast as a pneumatic hammer so little to no difference.

Comment by michael w. mckosky on May 10, 2016 at 7:03pm

Jonathan,

Is there any risk of work-hardening the rivets, with 20 strikes?