Red Oak for Roof Spars

[Larry C]

Here is a sketch (forgive my rough drawings) of the "plan".



I think Larry could make it work with his current side laminations but it would be a bit tight. You laminate the walls up and then do the rabbeting.

Hope this helps.

Cheers,

Gus

Gus,
Thanks for the sketch. I do see how it works, however, my laminations are already done and measure 3/4x1-1/2" My spars are also 1-1/2" If I rabbeted the laminations I would have to reduce the spars to 1" or less.
It could work, but my spars are only 5/8" thick. 1" x 5/8" x 5' spars would be pretty weak.

If I had made my laminations 2-3" vertically, this could probably work.
I do think the method is a good one if it's planned for. That's the problem with me not knowing what I am doing and finding out later there was an easier way

[eamarquardt]

That's the problem with me not knowing what I am doing and finding out later there was an easier way

I don't think you're entirely alone on this count. We're fighting the Subaru to VW transplant right now. This won't clear that, etc.

I do, however, find that a couple of rosebuds, a hydraulic jack, and proper application of "brute force" can increase clearances to the desired amounts!


Rosebuds do, though, take a toll on anything fabricated out of wood so the "rosebud fix" is not recommended for projects made from wood or wood byproducts.

Cheers,

Gus

[Larry C]

Here is a sketch (forgive my rough drawings) of the "plan".

That's pretty much how it is in Steve's shop notes. And that's the way I built mine. It's very easy to lay in the ceiling, then the spars and then the roof. I screwed my spars down into the wall framing because my sides were already finished. Ended up very solid.

Worked very well for me.

Would be more difficult to do with the laminated frame though.

Hi Mark,
I have Steve's shop notes and would have used this method if I had it earlier. It's probably not the best choice for my present situation. I think Tom's method may be my best choice right now, but that could change

Larry

[eamarquardt]

If I rabbeted the laminations I would have to reduce the spars to 1" or less.
It could work, but my spars are only 5/8" thick. 1" x 5/8" x 5' spars would be pretty weak.(

I think you'd be fine. The strenght added by the spars is nominal compared to the strenght of the two skins being held apart by the spars. As long as the spars are well glued to the interior and exterior skins (I plan on stapling the top skin to the spar) the completed structure should be pretty stiff. Split the 3/4 inch width of your laminates to 3/8" for the interior skin and 3/8" for the top skin to rest on. If you rabbet 1 1/8" out of your 1 1/2 beam you'd have 3/8" to attach your interior skin to. Maybe a bit tight but if you added a few staples or brads, given the total surface area of the laminate to interior skin I think it would work. Maybe you could add a bit more to the inside of your beam. The outside would still be 1 1/2" thick even if you didn't add to that side.I think laminated ribs are the way to go for galley hatch ribs. I"ll have lots of 1/8" BB left over and will make a test beam out of that. Anyone have any experience laminating 1/8" BB into beams/ribs?

Good exchange of ideas.

Cheers,

Gus

[dh]

Dang Gus, a quad post. I heard you the first time

[mikeschn]

I fixed that quad post for you guys!

Mike...

[Larry C]

If I rabbeted the laminations I would have to reduce the spars to 1" or less.
It could work, but my spars are only 5/8" thick. 1" x 5/8" x 5' spars would be pretty weak.(

I think you'd be fine. The strenght added by the spars is nominal compared to the strenght of the two skins being held apart by the spars. As long as the spars are well glued to the interior and exterior skins (I plan on stapling the top skin to the spar) the completed structure should be pretty stiff. Split the 3/4 inch width of your laminates to 3/8" for the interior skin and 3/8" for the top skin to rest on. If you rabbet 1 1/8" out of your 1 1/2 beam you'd have 3/8" to attach your interior skin to. Maybe a bit tight but if you added a few staples or brads, given the total surface area of the laminate to interior skin I think it would work. Maybe you could add a bit more to the inside of your beam. The outside would still be 1 1/2" thick even if you didn't add to that side.I think laminated ribs are the way to go for galley hatch ribs. I"ll have lots of 1/8" BB left over and will make a test beam out of that. Anyone have any experience laminating 1/8" BB into beams/ribs?

Good exchange of ideas.

Cheers,

Gus

Gus,
You have me thinking. I had originally thought along the same lines but I was concerned about the spar dimensions, but the spars will be added after the skin and as you pointed out, are only really just separating the skins.

In Steve Fredrick's method, he fills the space between the spars with rib segments. Are they actually needed? Maybe the same reinforcement could be done with glass tape and some narrow wood strips to help support the top skin as the outer ribs will only have 1/2" surface to anchor the top skin to (3/8" rabbet plus 1/8" outer skin)

What I do like about your idea is it saves weight over Tom's method and light weight is paramont in my build. However, I won't have the advantage of bench building my modular panels in my basement for later attachment.

Also, trying to cut a 3/8" X 1-1/8" rabbet on a narrow curved rib seems a bit difficult to this mostly hand tool woodworker. I did cut a similar rabbet in the wall base to match my floor, but I did that on my table saw.

Maybe I could mount my cheap router table to the edge of my building bench and run the profile rib through the table mounted router instead of the hand held router above the narrow rib.

I might need some hand holding with this one

I don't think its worth the trouble cutting thin plywood strips, but give it a try. I have cut miles of wood strips from 1- by lumber and it's pretty easy and fast. Strip laminatons are easy and cheap and are probably one of the strongest methods to use. I will probably use laminations for my hatch as well.

I have even considered using 5 profile ribs and only a few spars between the
these ribs.

Great exchange of ideas.........Larry

[kennyrayandersen]

I’m thinking something very similar for the composite build I’m working on. Make the perimeter from fir then Rabbet the corner out and then use it as a form to wrap the cut (slits across the foam every inch or so that would go through ¾ inch deep in the 1 inch core) of the thickness foam/glass lower skin around. After the foam/glass is glued down, I’ll fill the gaps with microballs, smooth it and then glass over the top. I’ll follow with a radius filler on the inside corner and then a couple of fabric tape plies to reinforce the corners.

It the same basic layout though. They used to make cars the same way – build the frame (wood or metal) and then form the body over it (using the body as the tooling).

[eamarquardt]

"Quads"! Not sure how I did it! Pretty soon I'll be up with "octamom" (a big story here).

Larry,

I'm not sure I'm clear on what you are proposing. Maybe a sketch would help. As I say, hollow core doors have cardboard separating the skins so the internal structure doesnt have to be heavy, just enough to keep the skins properly separated. More thin ones would be better than a few thick ones.

The trick to routing the rabbet is to build a larger base plate with a fence for your router so it won't tip. The interior skin will suport the extended base, the fence will keep the router bit the right distance from the outside edge, and away you go.

Cheers,

Gus

[Billy K]

Larry, you mentioned 5 profile ribs(PR) and this is what jumped into my head.....

6 PR ..you already have the first 2; you could set one to each side of the roof vent dimensions; then one each inside your exterior PR.
This would , if my brain is working...

1) allow for short spars, as needed
2) allow minimal chance of roof sag
3) when the extra 4 are set; you'd have all of your hatch spars in place
4) you could use glue and 1" screws straight in for the outside sets of
PRs, allowing @ 1 1/2 inch for attaching the roof and ceiling

just some thoughts as I read this morning....

[Larry C]

I’m thinking something very similar for the composite build I’m working on. Make the perimeter from fir then Rabbet the corner out and then use it as a form to wrap the cut (slits across the foam every inch or so that would go through ¾ inch deep in the 1 inch core) of the thickness foam/glass lower skin around. After the foam/glass is glued down, I’ll fill the gaps with microballs, smooth it and then glass over the top. I’ll follow with a radius filler on the inside corner and then a couple of fabric tape plies to reinforce the corners.

It the same basic layout though. They used to make cars the same way – build the frame (wood or metal) and then form the body over it (using the body as the tooling).

Kenny,
I like your plan. However, I do have a few comments. I have used glass over foam on a few projects. I don't think 2 layers of glass (outside) are going to give you much impact strength. Also, I found it difficult to get a smooth surface compared to glassing over plywood or faired wood strips. You may need many fill coats of epoxy (added weight) with lots of sanding to get a smooth surface.

You may have some professional method I am not familiar with to solve the above conserns. I just thought I would add my thoughts..........

Are you vacuum bagging the panels?

I assume you are building this way to save weight. I wonder if you will actually save much over using 1/8" or thinner plywood. 3mm marine plywood is really light and 1 layer of 3.25oz tight weave fiberglass only requires the epoxy wet out coat and maybe one fill coat. The epoxy used is the same weight as the glass., 6.5 oz total per yard (weight of glass plus epoxy).

The rest of your method is the same as mine, including the fillets and bias cut strips on the edges.

BTW/ if you dont already know, but your drawing looks like you do. Cut the 2 bias cut (hope your not using FG tape) fillet strips different widths, say one at 3" and one at 2", lay the 3 " into the fillet and add the 2" on top of it after the first one sets up. This way you won't be dealing with trying to blend 2 edges at the same location. The top edge will be 1/2" away from the bottom one.

.

The money saved by using less epoxy could go a long way paying for light weight plywood. Also, using light weight woods such as cedar for internal framing will further save weight.

I am enjoying this exchange of ideas with everyone.

Larry

[Larry C]

Larry, you mentioned 5 profile ribs(PR) and this is what jumped into my head.....

6 PR ..you already have the first 2; you could set one to each side of the roof vent dimensions; then one each inside your exterior PR.
This would , if my brain is working...

1) allow for short spars, as needed
2) allow minimal chance of roof sag
3) when the extra 4 are set; you'd have all of your hatch spars in place
4) you could use glue and 1" screws straight in for the outside sets of
PRs, allowing @ 1 1/2 inch for attaching the roof and ceiling

just some thoughts as I read this morning....

Billy,
Your plan is the same as mine except you suggest 1 more rib. I had thought about just using one center rib and boxing in the vent support and cutting the rib out of the box center. I would use double spars in this area.

Your 6 rib plan is probably better though. I could even reduce my rib depth to 1" from 1-1/2" and cutting my spars from 5/8" X 1-1/2" to 5/8" X 1" as they would only be short fill in supports.

Having the hatch spars already cut would be the frosting on the cake!!


Lots of great ideas, keep em commin!!

Larry

[Larry C]

"Quads"! Not sure how I did it! Pretty soon I'll be up with "octamom" (a big story here).

Larry,

I'm not sure I'm clear on what you are proposing. Maybe a sketch would help. As I say, hollow core doors have cardboard separating the skins so the internal structure doesnt have to be heavy, just enough to keep the skins properly separated. More thin ones would be better than a few thick ones.

The trick to routing the rabbet is to build a larger base plate with a fence for your router so it won't tip. The interior skin will suport the extended base, the fence will keep the router bit the right distance from the outside edge, and away you go.

Cheers,

Gus

Gus,
I guess what I was proposing was doing the rabbet before the skin is on I told you I would need some hand holding Anyway, it now makes perfect sense, but I dont have a rabbet bit as deep as needed.

[eamarquardt]

I dont have a rabbet bit as deep as needed.

Because you are using a fence against the top of your side to set the distance you're routing the rabbet into the side, any straight bit will work. You can make multiple cuts to get the depth you need. I like to use two flute endmills as router bits as they seem (but maybe it's all in my head) a little easier to control as they are a helix cut versus a straight cut.

How did you "plane" down the laminations after glueup? A router on a platform? Planer?

As nice as your laminations came out, I'm sure you'll choose a method that gives equally nice results.

Cheers,

Gus