jonbakerok

jonbakerok

Well Known Member
Anybody know a trick for building a dummy spar exactly 1-7/32 " thick?

Seems like it needs to be perfect. Otherwise the spar is either not going to slip into the spar box or it's going to be all loosy goosy. It's tempting to just make it 1-1/4", but 1/32" seems like too much clearance. Besides, the previous builder built my F-404 to exactly 1-7/32" and I don't see any way to make it bigger without rebuilding it.

I tried gluing two 1/2" MDF boards together and then adding a piece of pre-sanded 7/32" plywood. Even using contact cement, it came out to 1-1/4".

Sure wish I knew someone with a surface planer.
 
You could try building up a 1" piece out of your MDF, adding a 1/8"--3/16" of something, and using some aluminum scrap to shim the last little bit.

By shimming to fit, you can get around the variables in trying to make it up as a single unit.

Good luck.
 
aluminum bar stock

i used wood at first. measured it a while later found it to be compressed or shrunk?:confused: got a piece of barstock and machined it to the spec you mentioned...bolted a leg to it. worked better than anything ive seen yet.
 
Find a friend who has a woodworking hobby and get him to run a piece of 2 by six through his thickness planner. I did that seven planes ago and I am still using the same board.
 
Wood shop

Tom Martin said:
Find a friend who has a woodworking hobby and get him to run a piece of 2 by six through his thickness planner. I did that seven planes ago and I am still using the same board.
Click to expand...

Not sure about the 4 - but that won't work on a -6. There are nutplates sticking out of the bulkhead that the spar bolts against. These nutplates are in the center, between the spar strips.

I had a woodworker run some good 1x2 through his thickness planer, glued them to both side of a 1/4 plywood "spar web" and then had the whole thing planed to the correct thickness.

Then the blank was run through a planer to get one side dead straight, and then cut to the correct width on a table saw. It was then cut into left and right pieces with the correct angle in the middle.

Except for the gluing step, it was probably quicker to do than typing this message...:)

As Tom said, find a friend with a good wood shop.

gil A
 
I concur with az and Tom.
I did what they did. It isnt a big ask because to do the job with the thicknesser is the work of a few minutes and you will get it bang on. You can even offer it up to the spar to satisfy yourself that the dimensions look right.
 
Don't need no stinkin' dummy spar...

I didn't make a dummy spar. I built the 404 bulkhead around the actual spars.
 
I have a friend in the lumber business, he plained down a piece of doug fir for me. It is better a little to thick than to thin. I countersunk holes in the wood to clear the nut plates. Worked great, the wings fit.
Aaron
 
spar jig

Jon,
I am a wood worker more than a rivet and sheet metal guy so making the jigs is always a treat for me. A dummy spar is a very good idea for the 4. There aren?t any nut plates to interfere. You must have a friend around town that has a table saw and a few clamps? You can make a dummy spar spacer on a table saw. No planer needed.

I thickened the edges of a 3/4" piece of plywood (or MDF) rip cut on the table saw to the approximate width. Plywood is much more stable than solid stock planed to final thickness. Glue lumber store procured strips of 1/4" x 2.5" molding or whatever is available, along the top and bottom edges, both sides. Half-inch thick stock is much more common and would be fine. Also glue strips at the ends (perpendicular to the top and bottom edges). Then run it through the table saw standing up against the rip fence. Rip it down to exactly 1-7/32. You might have to make a cutting pass on one side, then adjust the rip fence and flip it over and make a rip down the other side. This should only take you about an hour or so. Maybe a little longer if you have a cup of coffee while the glue dries.

If my description is fuzzy I can sketch a simple drawing and email it to you. Let me know, glad to assist.
 
Simple way

I just took a couple pieces of fiberboard and added pieces of scrap aluminum sheet, cardboard, whatever it took to get the thickness just right. I used some wood screws to keep it all together - simple but it works! The "random" pieces were in the middle.

Worked great!

Rick
 
Brian Vickers said:
Jon,
I am a wood worker more than a rivet and sheet metal guy so making the jigs is always a treat for me. A dummy spar is a very good idea for the 4. There aren?t any nut plates to interfere. You must have a friend around town that has a table saw and a few clamps? You can make a dummy spar spacer on a table saw. No planer needed.

I thickened the edges of a 3/4" piece of plywood (or MDF) rip cut on the table saw to the approximate width. Plywood is much more stable than solid stock planed to final thickness. Glue lumber store procured strips of 1/4" x 2.5" molding or whatever is available, along the top and bottom edges, both sides. Half-inch thick stock is much more common and would be fine. Also glue strips at the ends (perpendicular to the top and bottom edges). Then run it through the table saw standing up against the rip fence. Rip it down to exactly 1-7/32. You might have to make a cutting pass on one side, then adjust the rip fence and flip it over and make a rip down the other side. This should only take you about an hour or so. Maybe a little longer if you have a cup of coffee while the glue dries.

If my description is fuzzy I can sketch a simple drawing and email it to you. Let me know, glad to assist.
Click to expand...

I guess I don't follow. Are you building a box instead of a solid board? Otherise, how do you rip something 8" tall on a table saw? My blade can't rip anything more than 3.5" tall. Yes, I'd appreciate a drawing if you don't mind going to the trouble.

Since I can't seem to find anyone with a planer, I've about decided to try my original idea again, only instead of gluing the two 1/2" MDF boards to the 7/32" plywood, this time I'll just bolt them together so I won't have any glue joints. I can countersink the bolts.

I guess using the spars would the ultimate jig, but since I'm building in my garage, there's not enough room.
 
Thanks Sam Buchanan!

Somebody on another thread mentioned that Sam Buchanan had an alternative for the false spar problem.

Sam's solution is Genius! When you read it you'll go "Duh! Why didn't I think of that?".

Instead of trying to build a piece of wood to some critical dimension that ought to be measured in thousandths, he just put a bolt through each spar bolt hole, with two nuts inside the spar box. Then he just adjusted the distance precisely by turning the nuts.

That got me thinking... You could improve on the idea by basically creating an adjustable false spar with two pieces of 1/2" plywood or MDF and a bunch of bolts, nuts, and washers.
 
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