[79FT]: Building Things
...I am Bender, insert girder
|On:||Aug 25, 2019|
|In:||[Chickenhouse Charger] Electrical Rebuild|
|Tags:||6781G, MA5 Charger, alternator, 4130, fabrication, bending|
As I have thought before, I would need the new nose baffle support bracket, to replace this one:
Old baffle support bracket
...because it would have to now be shorter, fitting in front of the new case mount alternator bracket, over it's right "ear" over here:
Alternator mount ear and starter
However, prepping to set up to do it, I found this.
Gap between starter boss and alternator bracket
See that gap between the starter boss "ear" and the new alternator bracket?
Hmmm, methinks.. Maybe, maybe, I can get away without bending up a new, 0.090 steel bracket with weird geometry (it's not a simple "couple bends and you're done" - you'll see later).
Well, let's see.
Old bracket fits nicely in that gap
But it was just a touch too "low". Didn't fit right - and I couldn't raise it (that would raise the holes to which the nose baffle itself attaches, and make the whole thing just not work).
Oh well, I guess we're bending steel after all.
Around that time, my strip of 4130 I ordered from Spruce some days back showed up.
I needed a vice, and a couple more pieces of steel for bending block and such. Picked those up at big box stores (and I will admit, that included a trip to Harbor Freight..).
I also fished out my old small belt sander, and air grinder, from the storage (all my tools are packed up aside from simple hand tools - I am rebuilding my shop; and thanks God I had them close so that I didn't have to rummage thru boxes).
Cutting off a small chunk of an approx. 1/4" thick strip for a bending block is no joke...
My compressor would run out of air, and I'd have to stop, and, while waiting for it to get back to pressure, use hacksaw ('cause I didn't have anything better to do).
Then, I attempted to get away with shoddy bevel grind on the bending block...
Very poorly made bending block
I hoped that that little "cavity" in the middle would work enough to handle bending spring-back - the roundover was fine, just the bevel was uneven.
Ha! Bending a couple of test bends proved me wrong; and that one never gets away with shoddy workmanship.
I re-ground the block to have a nice, even section (all that on a 1x30 belt sander by the way - which I have discovered is perfectly adequate for handling steel with a ~40 grit belt).
A much better bending block
Cut my 4130 strip to width:
... and clean up that edge
Edge to be cleaned up
I kinda gave up on it, frankly - got too tired to get it straight and even; and decided to temporarily switch my mind to something else.
Instead, I cut another, test strip, of 4130, without making it to proper width - and attempted to replicate the bracket's geometry on the now much better bending block.
Thinking about how to replicate bend lines, I couldn't think of anything better than... just roughly folding a piece of paper over the old bracket.
Old bracket, test bend, paper pattern, and strip prepared for the new bracket
The key was, rather than bending the strip over the block by hand, instead, start the bend by hand, and then finish it with the hammer. I used another piece of 1/4 strip that I cleaned up as an "interface" between the hammer and the material bent, to avoid hammer marks. This way, the bend was much tighter radius (equal to about material thickness, which is what you need for steel), and much easier to control and nudge in the proper direction.
The geometry of the bracket was close enough; the angles were off a bit, but those could be tweaked.
All that bending was one day. I felt done, and left.
Next time I was over at the hangar, I thought, "to hell with it", and decided to use my real strip that I cut out for final bracket.
Used a nice square to draw a reference line, and cleaned up and straightened that edge left over from cutting, marked the first bend line using the paper template left over from my test bend:
Bend mark one
... put it into the vice
and bent, using the old bracket for angle reference. That worked out okay, so marked and bent the second bend
See the problem? Yep, the first bend is not right on the mark - I did not clamp it right for that first bend. No problem though, I had enough spare length on both ends, so I just moved the location of the second bend accordingly.
Final tweaking by hand
The hole is made, the "ear" is about to be
The hole was drilled with a Unibit, and all the cutting off of small pieces was done with a 3" cutoff wheel on an air die grinder, followed by final tweaking on the 1x30 belt sander.
And now, the first try.
Did it... work!?
Wow. It might've worked!!! Maybe.. just maybe.. the final test will be if I'll be able to make the holes for the baffle in it.
But for that, we need to position the baffle, and then mark out the holes.
Bolt on the old bracket, and hook up the baffle to it. Use anything, whatever, for reference (I used the starter conveniently sticking thru the baffle):
Reference marks set
Then, unbolt old bracket, put the new bracket in, and mark out the holes, while having the baffle back to position marked by reference marks.
Marking new bracket
Okay, here it is. The final test.
The Two Brackets
Not bad! Given the messed up geometry, me using the paper pattern, my first attempt at bending, it's not that bad at all! Hey, my holes are also not on the center; but the old bracket doesn't have it's holes particularly centered either (and it won the Golden Lindy ;) ).
I guess I'm keeping mine.
I pulled out my nice Cobalt bits I got at Oshkosh to make those holes. At that point I have obtained an old small drill press for the hangar (I had to drill the first, large, hole in the "ear" free hand - even with Unibit that was very annoying).
Sweet metal shavings
... and, trimmed to size
Emery cloth the whole thing, and it's done.
By the way - you must say - but it's just two bends! How come your holes are not lining up nicely, and such?
Well, this thing has a very messed up geometry. It's two bends, at a non-even angle. This picture probably illustrates this best:
Meanwhile, I also had to figure out the alternator's belt length - to make sure it clears all the brackets, and holes in the nose baffle.
I wrote a bit about it in the previous post. Initially I thought that just mocking up the belt, measuring the length of the mockup, and ordering the right size would work - ha!
New belt was too long, and didn't clear the newly made bracket.
Ooookay. Well, I had the belt that's too long (the one I ordered after making the mockup of belt length with a chunk of wire). And, I had the belt that was too short (the one that came with the alternator).
So, I bought all the sizes in between.
The one that worked? 7320 :).
... and just to make sure that everything will fit with the new bracket, I ended up putting the nosebowl back on. Didn't want to discover that the nose baffle was sticking out, or not fitting in any other way, when putting the cowling back on.
Bracket - final cut (still temp hardware)
Fit check with nosebowl
OKay. Next - the pivot arm! No bending here. Just lots and lots of grinding.
Meanwhile, all my electrical hardware started showing up! It's like Christmas in August!
There are some flight instructors where the student is important, and there are some instructors where the instructor is important. Pick carefully.
© Copyright "79FT". All rights reserved. Feel free to cite, but link back to the pages cited.
This website only shows how I did things in my various projects. These pages are for information and personal entertainment only and not to be construed as the only way, or even the perceived correct way of doing things. You are responsible for your own safety and techniques.