[79FT]: Building Things
lots of grinding
|On:||Aug 31, 2019|
|In:||[Chickenhouse Charger] Electrical Rebuild|
|Tags:||6781G, MA5 Charger, alternator, 4130, fabrication, drilling, CAD, SWX|
With baffle support bracket done, the next step on the path to alternator happiness was the pivot arm.
... was that the default B&C's pivot arm did interfere with the front baffle hookup brackets.
That did actually make me pay attention to the very unusual old pivot arm.
Nice dogleg, isn't it?
Well, this bracket did not involve any bending, just needed to make the correct one to fit around all the other stuff there on the nose.
Hmm... so how do we do that? Well, first, we need...
This is not the real template, because (.. read on ;) ). It's the template for the Template.
Start with a piece of heavy paper
Cut around the alternator
All we need to do with this template is show the location of the hookup hole (top hole, the one that attaches the bracket to the motor); the location of the slot for the alternator to hook up to, and the general outline of the alternator
Alternator bolt location is being marked
Bolt imprints along the "pivot arc"
..and finally, some more "no go" zones to prevent interference with other brackets there:
Notice I also added some "imprints" of the B&C-supplied pivot arm in there, just in case I'd need them.
Okay. I'm lying to you. This template is not the one I used. It was done with the long belt that ended up not working out, so I had to redo the template (thanks God, just the template). The new one was done in the same manner as the one I described above.
Here it is:
The *actual* template used
Okay. So now, we know critical locations of things and where not to go - so, cue in...
It's magic, I keep telling people.
So, we take our template, and scan it on a scanner, along with a little metal ruler to give us physical dimensions. Then, we go to Solidworks, start a sketch, and insert the scan as "sketch picture". Using the image of the ruler that was scanned in, we tell Solidworks what "one inch" on this picture is. Boom! The image is now dimensionally accurate.
Then, we start drawing around it.
Above, I positioned the top hole, and the four 5/16" holes around bolt imprints. I then sketched a large circle and made it tangent to three out of four of those holes - it defines the "pivot arc". Then, offsetting it 5/16th gives me the other "side" of the slot; and offsetting it more gives me the "sides" of the bracket in the "pivot arc" area.
I also started sketching the "no go" lines around the top portion of the bracket.
More circles and lines are added, and off-set. They are not positioned or dimensioned - just made tangent to "no go" lines. You can almost see the outline of the pivot arm, yes? ;)
Now, we take this master sketch; and add arc elements with real lines that we care about.
Tada! We got the Solidworks Part.
By the way. How do you "measure" the round over of the B&C arm? Radius gauge? Calipers? Hmmm.. Or...
Measuring with Solidworks
Nice, isn't it?
Next, we print the drawing of our new part; making sure our holes' centers are marked (we'll use that later to drill them)
And, we got ourselves the actual template!
Now, the final test (Many thanks to USPS for providing material for this test)
Spray glue and cardboard
I wish I could cut 1/8" steel with X-Acto...
Okay, we have the real template now, and we know it'll work. And now, comes...
1/8" steel is no joke
Nice little sheet of 1/8" 4130 showed up from Spruce some time earlier... I used spray glue to put the print out of the bracket on top of it.
Template on steel
First, all the holes had to be drilled. The drill press I have at the moment is severely underpowered, so I had to step-drill them in four steps.
I got to admit, I am starting to become very fond of pretty steel curlies made by nice drill bits.
Also, lesson number one learned: drilling oil (I used TapMagic) gets under the template, and messes up the glue (and unglues it). I need to figure out a better glue.
I drilled the slot's "start" and "end" holes slightly undersized, and reamed the main attachment hole to 5/16ths exactly.
Next, the slot... I rough-drilled small holes around it's perimeter, thinking that a 1/8" shank carbide burr in an air die grinder (basically, Dremel) would work... Ha! It did... for a second ;)
Slot in the making
Okay, time to go old school... where's that...
I cut it out, and cleaned it out with a bastard file.
.. and cleaned up
And then, more and more hacksaw...
.. my right arm
.. is beginning to feel...
.. it ..
Yeah. The last few inches, I gave up, and used the jig saw. It did cost me 3 blades, but I was too ... done with the hacksaw. I figure, about a blade per 1 inch of cut in 1/8" 4130 with a jigsaw...
.. gave up.
Looks very ugly, right? Well.... to the grinder!
.. grind ..
.. grind away ..
Three belts I believe is what it took.
Well, now, the final cleanup on the slot. Yes, Dima, I used the rotary file here :).
Cleaning up the slot
..and, test fit
That was two evenings, folks; but I wasn't done.
The Three Brackets
Next, I had to prep the edges and sand out all the scratches, and paint. A deburring wheel on a bench grinder helped; and the most nasty marks were filed out and then polished out with the deburring wheel.
It has to be done because every scratch is a stress riser - on fittings, every edge needs to be rounded over, and polished.
Every airplane "paintjob" I've done so far was in my makeshift "paintboots". Like this one.
I sprayed both the pivot arm, and the baffle support bracket I made earlier, with self-etching primer, and some Rustoleum paint. White will make cracks more visible, if they show up.
So there we go. With this done, I can now install the alternator. Just measly 30 hours to get ready to install the damn alternator! ;)
I’m not speeding officer — I’m just flying low.
...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.
...I almost decided to make new nose baffles
|On:||Aug 16, 2019|
|In:||[Chickenhouse Charger] Electrical Rebuild|
|Tags:||6781G, MA5 Charger, electrical, alternator|
So most orders have been placed, and a lot of them have arrived already. (Note to self: need to take pictures of all the stuff).
The first thing to be worked on is the heart - the alternator.
Look at this little beauty!
Tiny, light as a feather, and cute as a button! No, sir, this thing has to get attached to the nose!
The old one needs to come off. Pivot arm bolt undone. Pivot bold undone.
Wait. The pivot bolt can't get out, because the flywheel gets in the way...
Pivot bolt and interference
Hmm.. No, I can't believe Remo pulled the flywheel off of crank just to install the alternator. There must be a better way.
The better way - bracket attach bolts!
Aha! This is case mount, and the bracket is attached to the motor case. Let's see... Yep! It came off.
Now, the new bracket... centers nicely!
See that ear on the right, that touches the starter boss? That one needs to attach to the starter, to prevent the bracket flexing left and right. It lines up great, but, problem number one (but I knew this one), the old alternator bracket didn't have that. Remo used that hole on the starter boss to hook up the front of the nose "ramp" part of the baffle:
Baffle attach bracket
No matter. I will just bend up a new one, to account for the thickness of the new bracket's "ear" that will get sandwiched between this baffle attach bracket, and the starter boss. Material already ordered!
Now, let's test fit the belt, and the new pivot arm. The belt, the belt.. oh wait. Yep. The prop needs to come off - but this is a non-event now (and I am not leaving the prop off again - learned that one already). I'm becoming quite good at this prop pulling business....
Belt on and prop back on, test-fitting the pivot arm... CRUD!
That black bracket to the left of it holds the hose "ramp" portion of the baffle..... and, it won't let the damn pivot arm go in! No way. And no easy modification here - it's interfering, seriously...
Frankly, at that point I went home (this whole note covers quite a few days of work), with thoughts of remaking the front baffle; and spent the evening researching how baffles are done on planes with similar nosebowl... Frankly, I don't like how this front baffle is done on this plane (see Cowling Conundrum), and thought of this as being a good chance to fix it. I moaned about this to my buddy and colleague Dima D (who's helping me here quite a lot with notes and advice)...
But next nite, I thought that maybe I can get away with remaking just the arm... I am absolutely not set up to do complicated sheet metal work at the moment...
The old alternator had this weird pivot arm that now made way more sense. It "doglegged" around the bracket with which the standard pivot arm interfered:
The old pivot arm
Notice how it has this portion that goes down, and then the pivot arm "turns" left to go under the nose baffle ramp attach bracket?
That corner is definitely a large stress riser... but this arm held a much heavier Delco-Remy alternator for almost 40 years... Granted, it's made out of 0.190 steel as opposed to 0.125 steel used in B&C bracket... but I can make a similar one for the new alternator...
We'll see if we can smooth out that corner so that it's arcing better, reducing stress. If I can, I will use 0.125 steel. If I can't, I'll settle with 0.190 - just like the old one. We know this works.
Thanks Dima! You were right. For now. I will redo this nose ramp when I'm redoing the motor, later :).
... and now, to the belt. Let's get this nose ramp back on. It has an opening for the belt to pass thru, and a fairing for the alternator pulley....
Damn. Yep. That one doesn't fit right, either.
Nose ramp back on
If you look real careful inside the red circle, you can just see the belt there. It will rub on the left edge of that hole. It has to go right, which means the alternator has to go down, which means longer belt.
I used a piece of wire to mock this up. Here are a couple of pictures from the back side.
B&C supplied belt - interference
Wire mocking up a longer belt - so that it's centered in the hole
I ordered a couple of longer belts from the same series, to try them out and see how they will work in the end...
So, where are we at?
Meanwhile, folks at B&C were extremely helpful and generous with their time, reading my long, ranty, emails, and responding to me with their thoughts. I really appreciated that!
"Leave five on the glide, have a nice ride, tower inside, twenty-six nine .... see ya!"
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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.