Flanging those lightening holes

[Chris In Milwaukee]

HI all,

I was so inspired by N3UW and his squishy hole flanging technique that I thought I'd give it a try myself. I really like the quality of the flange.

A good friend of mine is a local dairy farmer, so I asked him if there was anything around the farm that could meet the squishy requirement. He handed me a big chunk of cow mat, a dense rubber mat that cows stand on in the milking parlor. I figure if the cows can stand on it all day, then it would be durable enough for this job.

I got out one of my extra ribs, routed out the hole on my routing jig with a 45-degree chamfer bit, and threw it under the press for a squeeze. The results were wonderful! I just need a couple of steel plates like he used instead of the material I had in the shop, and route a little wider so the flange goes a bit wider and deeper. It could use another 1/8" or so.

Otherwise, I'm pleased! That, and I'll probably go buy some fresh mat before I do a whole load of them again

~Chris

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[DRLPatrol]

Looks good. I did similar.

http://bearhawkforums.com/forum/bearhawk-patrol-plans-build/10579-more-rubber-press-forming-ideas

Doug

[Chris In Milwaukee]

That cow/horse mat is a heck of a lot cheaper, for sure. Looks good!

[Bcone1381]

Chris,

I see you flanged your lightening holes before flanging the edge of the rib. It looks real straight coming out of the press. Am I seeing this right?

I am making my form blocks now and look ahead towards this step. Other flanging methods I've seen result in a potato chip distortion of the rib blank that requires post flanging correction, and am a bit surprised yours turned out so nice and straight.

[Chris In Milwaukee]

Yes, you're seeing it correctly. My first round of ribs was a bear to get straight since I did the edges before the holes. I saw this other method from N3UW, and he did his holes first and left the edges flat. Then he went back and bent/fluted the edges. I really liked the way that turned out. Just a little bit of tweaking to the holes to get them to lay flat.

This rib was just a test from one of the extras I had, "just in case". I really like the way it turned out.

[BTAZ]

For my LSA, I flanged the lightening holes using the rubber press method before forming the edge flanges. I just free-handed circular reliefs in the form block to clear the hole flanges. Worked great.

[Bcone1381]

I don't have a hydraulic press and so my preferred lightening hole flanging method at this point is a mallet applied to a male plug. I am trying to visualize the reaction that rib blanks have to the stresses which it encounters during the flanging process, and understand why the rubber forming method has such good results. Because you have little deformation, there must be little stress taken on by the rest of the blank. So, I must conclude that your method confined the stress to the bend radius area, while other methods do not.

Lets take this theory one step further and apply it to my Mallet/Male Plug flanging method, Would application of a non slip surface to the form blocks followed by torquing the form blocks together as tight as can be, help limit the deformation? Would this limit the stresses from being transferred to the rest of the rib blank leaving a more perfected part after the flanging is complete?

Feedback?

[Glenn Patterson]

I think a large carpenters vise would press the plug in fairly evenly and well controlled to take the plug to the right depth. We bought a big carpenter's vice that was on sale for about $30 and put hardwood faces on the vice. The advantage to the carpenters vice is that they have a large throat so work pieces can be set well into them. The vice has been well used over the year and is kinder to work with than the mechanics vice.

Another method of pressing the plug is using a piece of steel or wood to bridge the back side and run the plug in with a nut,bolt and washers. An electric impact driver would speed up the process.

Glenn