Sandwich wall frames

[QueticoBill]

I'm trying to move along and have a basic direction - based on the Grumman 2 in the design library - but am working on wall layout, blocking, etc. Planning on 1/4" ply skins and 3/4" ply framing, and plan to finish both inside and outside clear, so fasteners are a concern. I can cut the whole wall frame out of a 4 x 10 sheet - so two sheets - or I can cut up a single 4 x 8 and join 9 biscuits or pocket screws or both. I'm leaning towards the stick frame as it seems easier to handle the pieces, albeit at the expense of the joints, and partly because I'm comfortable with my table say and miter saw.

And do most cut the profile with a router, trammels, and other guides and fences (an elliptical router jig); or a jig saw, follow a line, and belt sand?

[bobwhite215]

As far as cutting the profile, I think I am going to lay it out on the plywood, and then cut as close as I can with circular saw. Then sand to the line with a belt sander. I will do both sides at the same time. I don't like using a jig saw as the blade just doesn't stay vertical.

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[QueticoBill]

Ditto to vertical. Why I was leaning towards router for finish cut - but the circular saw to rough might make sense - either full panel or stick and joined. Thanks.

[aggie79]

As far as cutting the profile, I think I am going to lay it out on the plywood, and then cut as close as I can with circular saw. Then sand to the line with a belt sander. I will do both sides at the same time.

Circular saws are designed for straight cuts. When cutting radii using a circular saw, you stand a good chance of binding the blade and getting kickback.

I don't like using a jig saw as the blade just doesn't stay vertical.

Depends upon what type - or better said - brand of jig saw you are using. A Bosch jig saw with its integral blade guide easily makes 90 degree cuts.

[bobwhite215]

Not going to cut on a curve with the circular saw. Just a bunch of straight cuts to get close to the profile.

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[bobwhite215]

I also have a rotozip, but just don't trust it. It spins at like 30,000 rpm, and if your not extremely careful it just kind of takes off on its own. I have ruined some contour cuts with it in the past.

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[tony.latham]

can cut the whole wall frame out of a 4 x 10 sheet - so two sheets - or I can cut up a single 4 x 8 and join 9 biscuits or pocket screws or both. I'm leaning towards the stick frame as it

I've built using both "sticks" and plywood for the internal frame. Using plywood is much less labor intense. I spline-join the skeleton with a 1/8" router cut and a piece of 1/8" ply. A biscuit jointer will do the same of course. Here's how I do a ten-foot wall:



If I ever build again, I'll remove more wood from the skeleton than in that photo. (And I don't attache fenders to walls. That was plan A with the last 'drop but I don't want a disintegrating tire ripping a fender off a wall.)

And do most cut the profile with a router, trammels, and other guides and fences (an elliptical router jig); or a jig saw, follow a line, and belt sand?

I use a jigsaw but have found that creating a 1/4" plywood pattern as the first build step–-with all the details laid out on it–-is a big help.

Tony

[yrock87]

I used minimal 1x framing stick built. I didn't biscuit or dowel the joints. Only glue and pocket holes /screws. The bond to the ply makes for an incredibly strong structure though. The second page of my build shows my floor/wall construction. It is plenty string. Just take sure you know where everything going to be so you can pplace blocking on the wall at that location.

As far as profile cuts, I did not use stick frame on my curves. So I just had to worry about the ply skins. For those I cut a template out of 1/2 osb with a jigsaw, smoothed it down perfect. Then used a router and flush bit off that osb template.

[QueticoBill]

Thanks yrock. That makes sense. I was leaning toward using 3/4 ply ripped to 2" for straights and 6 for curves where it would be trimmed.(hard to explain)

I'm comfortable with biscuits - have a good cutter and a seemingly lifetime supply of biscuits - and never used the pocket screws - so will have to decide. I agree that the glue and skin is most of strength.

PS: Went through your whole build journal. I think you convinced me to use 3/4 ply ripped instead of sawn lumber. Just way more stable and flat it would seem. Still debating biscuit vs pocket screw. And I see I have to spend more thought on wiring.

Would you use the 3m Fastbond 30 again?

[yrock87]

Thanks yrock. That makes sense. I was leaning toward using 3/4 ply ripped to 2" for straights and 6 for curves where it would be trimmed.(hard to explain)

I'm comfortable with biscuits - have a good cutter and a seemingly lifetime supply of biscuits - and never used the pocket screws - so will have to decide. I agree that the glue and skin is most of strength.

PS: Went through your whole build journal. I think you convinced me to use 3/4 ply ripped instead of sawn lumber. Just way more stable and flat it would seem. Still debating biscuit vs pocket screw. And I see I have to spend more thought on wiring.

Would you use the 3m Fastbond 30 again?

I would not use the 3m again. Maybe it was user error, but a few others on the forum have expressed similar disappointment. Some love it, some say it is overpriced and doesn't work great. After completing my build (well, campable anyeays) I would have spent the $130 I spent on fastbond on doubling my epoxy order from 1.5 Gallons to 3. The epoxy, after the initial learning curve, is much easier to work with and provides a reliable bond.

The 3m fastbond just didn't give a great bond and was very finicky.

As far as the pocket vs biscuts. I purchased the $35 kreg Jr for this build. A biscuit slot cutter was a little of let of the budget. Also, I can't speak to joining frames with biscuit, but the kreg screws pull everything in tight and square. Or at least as square as your cuts...

Hope this helps, happy building

[tony.latham]

Think twice about using sticks to frame your skeleton. This was a frame I built for my first teardrop.



If I've counted right, it has 21 joints. I think all have biscuits in them. It's not a strength issue, it's the fact that each joint takes time. I'll guess thirty minutes and then there is the time it takes for the glue to dry (for those that I couldn't use Kreg screws in). Also, even though I had a 4' x 8' bench to work off of, few if any of the joints came out perfectly flat. I had to take a block plane and clean them up to make a good glue surface for the skins. And then there's the adding material to the inside of the square doorframe...

Do the math. 21 joints x 30 minutes = about eleven hours to build one of two stick-built frames. (Plus you still need to get a jigsaw and cut the outline). That's close to three full days to build your skeletons.

Cut them out of 3/4" plywood and be done with it. Building a teardrop takes months or work. No sense adding to the labor end.

Here are a couple of my build videos using both sticks and plywood:







Tony

p.s I'm also getting a sense that you're going to attempt a traditional shaped teardrop without a jigsaw. There $30-$90. Go buy one. Tools save labor.

[bobwhite215]

I ordered some Starrett blades for my jigsaw. Kind of pricey, but they get good reviews. Hoping a better blade will stay straighter. I'll let you know how they work.

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[tony.latham]

I ordered some Starrett blades for my jigsaw. Kind of pricey, but they get good reviews. Hoping a better blade will stay straighter. I'll let you know how they work.

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Build a pattern out of 1/4" ply. Mark your parts and cut within 3/16" of your line with your jigsaw. Clamp your pattern on your part and finish the cut with a router and pattern or laminate flush chut bit. You'll have a nice square cut––that's perfect. Here's my wife making the final cut:



Tony

[QueticoBill]

I like that Tony. I was leaning toward making a pattern that was the appropriate undersized for router table and bit, as I find that is a little steadier and more immune to voids in the pattern than using a guide. Whether or not I rough trim or just use the router to cut it will be determined. The right bit in my 1/2" router ought to be fine.

[QueticoBill]

While we're on this, does the thickness of XPS - I think a full 3/4" but not sure - work OK with nominal 3/4" ply, usually a thirty second under 3/4"? I was afraid it could cause ply to bulge ever so slightly.