Hey guys,
I've got a nice 9' long piece of 8/4 X 6" figured cherry with a sap edge I've been sitting on for years. I want to use it to build a glass top coffee table so you can see the wood through the table top. I'm gonna keep that part pretty simple but I want to do an arched base for it, as shown in the pictures below.
I'm still learning to use Scketchup so the model is crude but hopefully it shows what I have in mind right now. It's basically laminating together layers of 3/4" plywood or MDF to get a 2.5" thick base then cover it with some nice figured veneer.
What I'm thinking right now is I would make a long pivot out of 1/4" MDF to cut the first inner and outer radius with my router and a spiral bit. Then cut the remaining pieces roughly with a jigsaw and finish them with the router and a flush cut bit to perfectly match the first piece I cut.
I could make another jig to make holes with my little drill press in exactly the same place on each piece then use wood dowel to help align during glue-up.
But I'd really like to hear any ideas for making it easier. I'm fairly limited on big power tools. Table saw is just a portable Dewalt. No bandsaw unless I haul stuff 100 miles to borrow from my step-dad. I do have a decent router table with a fence.
Thanks a ton in advance for any help
-Chris
Here are a couple views of the table model and a shot of the cherry I plan to use for the cross beams.
You could make the curve with multiple layers of bending plywood. I made a curved door for a cabinet with it but used my vacuum bag during the glue up. It could get costly for you to do that, though, since it seems like you'll need ~60" of material to make that curve so you'll end up with waste.
Alternatively you could kerf cut MDF and bend it over a form. You could probably use ratchet straps to hold it in place while you glue it up. I have not tried this before but I think it could work. On the bottom side, you'd fill the kerf with bondo or some kind of filler then veneer on top. I don't know how the kerf cut method would work for strength, though.
That's an interesting design. It's going to be heavy, that's for sure.
Your idea for cutting the first one to shape with a trammel and then flush trimming subsequent layers is a good. Perhaps you would make the outer layers out of single pieces of ply. Maybe one or two inner plies could also be single pieces. The inner layers can be cut from narrow pieces. If you make the inner and outer curves the same radius, you could nest the inner and outer curves pretty efficiently.
I've built shapes similar to that in much the same way you propose. Your approach to do it will work, but there's an easier way. Make you master piece and then rough cut your others as you propose. Then glue/screw a layer of rough pieces on each side of your master. Then route them flush. Repeat until you get the width you want. You don't even need full pieces for each section; you can use shorter sections just butt jointed around the arch. Overlap the joints from by several inches with each layer and it will be just as strong as if you used full sections. FWIW, I would use plywood, not MDF.
Once you have the form made cover it on both sides with 1/8" bending plywood, glued and tacked on or weight it down with sand bags until the glue cures. Now you have a great substrate to veneer to.
No vacuum bag required, as nice as it is to have one.
John
atgcpaul said:
You could make the curve with multiple layers of bending plywood. I made a curved door for a cabinet with it but used my vacuum bag during the glue up. It could get costly for you to do that, though, since it seems like you'll need ~60" of material to make that curve so you'll end up with waste.
Alternatively you could kerf cut MDF and bend it over a form. You could probably use ratchet straps to hold it in place while you glue it up. I have not tried this before but I think it could work. On the bottom side, you'd fill the kerf with bondo or some kind of filler then veneer on top. I don't know how the kerf cut method would work for strength, though.
I thought about the kerf cutting but decided it wouldn't be so good in my case due to strength, just as you mentioned.
The bending plywood thing is interesting and I would like to try vacuum bagging as well. I built some fiberglass speaker boxes last year and I want to try laying up some carbon fiber at some point. But it seems like I would need a bunch of layers of plywood, even if I attach something to the outside edges to get my 2.5" thickness.
Chris
DaveR1 said:
That's an interesting design. It's going to be heavy, that's for sure.
Your idea for cutting the first one to shape with a trammel and then flush trimming subsequent layers is a good. Perhaps you would make the outer layers out of single pieces of ply. Maybe one or two inner plies could also be single pieces. The inner layers can be cut from narrow pieces. If you make the inner and outer curves the same radius, you could nest the inner and outer curves pretty efficiently.
Trammel. Thank you. For some reason I couldn't think of the right name for it.
One other potential advantage to having the same inner and outer radius could be drilling a series of holes in a straight line, 2.75 inches apart. Then I could attach my trammel to it with a pin and just move it down one hole at a time to cut each piece with the router and spiral bit. I'm not sure if it would be as precise as rough cutting then flush trimming though.
jteneyck said:
I've built shapes similar to that in much the same way you propose. Your approach to do it will work, but there's an easier way. Make you master piece and then rough cut your others as you propose. Then glue/screw a layer of rough pieces on each side of your master. Then route them flush. Repeat until you get the width you want. You don't even need full pieces for each section; you can use shorter sections just butt jointed around the arch. Overlap the joints from by several inches with each layer and it will be just as strong as if you used full sections. FWIW, I would use plywood, not MDF.
Once you have the form made cover it on both sides with 1/8" bending plywood, glued and tacked on or weight it down with sand bags until the glue cures. Now you have a great substrate to veneer to.
No vacuum bag required, as nice as it is to have one.
John
I do think your suggestion would be more efficient and I'll probably do it that way. I had it in my head that using the same "master" to flush cut all the other pieces would avoid error accumulation. But thinking about it a little more, that was probably a little silly since I have a nice flat router table and the plywood or MDF is going to be nice and flat.
I like the suggestions you guys made about leaving some gaps. I could probably cut down significantly on how much material I need that way and it will still be plenty strong.
mound said:
[blockquote]atgcpaul said:
You could make the curve with multiple layers of bending plywood. I made a curved door for a cabinet with it but used my vacuum bag during the glue up. It could get costly for you to do that, though, since it seems like you'll need ~60" of material to make that curve so you'll end up with waste.
That's how I'd probably do it today. You could also make only a handful of those MDF spines, and then make a curved torsion box skinning each face with a layer of bendy ply, then give it hardwood edges and veneer for the show face. A few years back I made this curvy gunrack using just that technique:
Similar for the base, shown below just to show you can use the technique to form any variety of multiply curved surfaces:
[/blockquote]
Wow, that's one hell of a gun rack. I like the frame you made for it. I was just planning to glue the veneer directly to my plywood or MDF edges but a combination of some shaped pieces and bendy plywood has me thinking.
Really glad I asked for some thoughts on how to do this. I almost just bought some plywood and started going at it.
The length of my table may be tweaked a little as well. I'm going to try to find a used glass top coffee table on Craigslist to get my glass. Hoping to find something around 26" X 50" for the measurements shown in the model. I might have to reduce it down a little if I can't find the right glass for the right price though.
If you buy a glass coffee tale top with the intention of cutting it a smaller size make sure the glass is not tempered. I think most commercial tops are tempered for safety.
John