Fuselage Jig

[WingsOnWheels]

I'm just about done building the fuselage jig. I was wondering what is the best way to ensure that the builhead supports are at an even height (the 2X4s that sit on edge - not attached in the picture, you can see them on the workbench)? Do you lay the longerons across them (before bending) and look for gaps?

Ignore the extra 2x6s in the picture, those are the first set I bought that I decided were not straight enough.

Since my garage floor isn't even close to flat or level, I added adjuster screws to the bottom of the legs. Has anyone else done this? How did it work out for you?

Just for fun: I have been playing around with panel layouts - a bit premature...

So far I like this one.

 

[flion]

Who cares? It's just a fixture. Your primary concern is that the thing doesn't shift or warp while you build. When you put the longerons and bulkheads into your fixture, you will shim them to accurate position (I actually used wood shims bought cheap at Home Depot under the longerons at the points where it was fastened to the fixture).

While building, you will not trust your fixture and will check the parts often to be sure the alignment has remained stable. The procedure for checking alignment quickly becomes a habit and doesn't take long. I drilled a large hole in the center of the particle board used to support the baggage compartment bulkhead (the firewall did not have the recess installed) and used a laser level along the center-line of the fuselage. A level across the longerons at the bulkheads gave me a quick check for both twist and height (the level should just touch the laser line except the forward area where the longerons are deflected), the same level placed on the face of the bulkhead gave me a check for vertical orientation, and a tape run between the longerons quickly verified that the bulkheads were laterally centered on the laser line. Took just a few minutes to check at the start of a work session and adjustments were seldom necessary.

Rules:
1) A fixture is not a jig.
2) It is possible to build crooked assemblies in a straight fixture.
3) Conversely, it is possible to build straight assemblies in a crooked fixture.
4) From 2 & 3 above, only the relative alignment of parts matters.
5) No matter how stable the fixture, it is important to check part alignment often.

 

[C-GRVT]

take the time to get it straight

I used adjuster screws just as you did.
I think it is worth the effort to get the jig/fixture (whatever) as straight and level as possible. I found it necessary to add a shim in a few spots under the longerons to get everything absolutely level.
It is useful before you clamp any bulkheads in place to draw a straight line down the centre of the jig, front to back, to use as a reference in centering the bulkheads. The other important thing is to have the firewall at an absolute right angle to that centreline - I used various methods to determine that and crosscheck - strings diagonally across, long square....
Also, ensure that the rearmost bulkhead is installed perfectly vertical.
When installing bulkheads, use strings front to back along the bulkhead flanges to ensure the skin will lie flat, and reinforce bulkeads as necessary to hold their shape (but you probably know all that). I had to modify one of the bulkheads (608 or 609) to reduce its height to make it fit.
Bill Brooks
Ottawa Canada
RV-6A finishing kit

 

[jsharkey]

I used taught string to make sure every thing was straight and level. I shimmed under legs and the transverse 2x4s to get it as best as I could. The fuselage went together well and the plane flies straight and true.

Jim Sharkey
RV6

PS - I also Bondoed the feet to the basement floor to keep it stable.

 

[Ironflight]

My experience:

To get the tops of all the cross-bars level, I used right-angle framing braces screwed to the long side pieces, and put the 2x4 cross-pieces up next to them. Laid the long straight longeron stock on top and raised and lowered the cross-pieces with standard building shims until they were perfect, then put screws through the angle braces and into the cross-pieces to lock them in.

I like your adjustable legs, but I found I liked the stability of the entire 2x4 leg on the concrete floor. Again, I used regular cedar building shims to take up the "slack" between an uneven floor and the legs.

To keep warping from being a problem, push to get the fuse out of the jig/fixture as quickly as possible - don't give it all time to warp!

Paul

 

[Jerry Cochran]

Thanks

Colin,

Just what I need, pix of jig for RV-6's. I will soon be doing the same thing with a project I bought. So please continue to post progress and pix as you go along.
It will be very much appreciated.

I built a 6a but was a QB so no jig.


...

 

[WingsOnWheels]

Jim and Paul,

Both those ideas are great, consider them used.

Paul,

Stability is also my main concern. I do like having the extra surface area on the ground to keep things in place. I'll have to play this one by ear.

 

[jsharkey]

Jim and Paul,

Both those ideas are great, consider them used.

Paul,

Stability is also my main concern. I do like having the extra surface area on the ground to keep things in place. I'll have to play this one by ear.

When I had finished a quick whack with a hammer released the bondo from the floor.

Jim

 

[WingsOnWheels]

When I had finished a quick whack with a hammer released the bondo from the floor.

Jim

I was going to use some calking, but the bondo is a much better idea.



On a side note: I moved the jig into place in the shop yesterday, but have not done any leveling yet. I was just out there a minute ago to grab something and tossed the level on it. The jig was dead-level, so that is a good sign.