Duane's torsion box bench top build thread - Router Forums
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post #1 of 153 (permalink) Old 07-03-2015, 08:33 PM Thread Starter
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Default Duane's torsion box bench top build thread

Well I'm committed now!!!

I made another trip to the shop where I bought my router table a few weeks back and spent $330 while there today, and most of that went to materials needed for my new table top torsion box.

First, to go ahead and get it out of the way, I'll mention that part of that money went for a Kreg Jig K4 master kit. I will use this to connect the grid to the underside of the top of the new table with pocket hole screws. I picked up a box of 500 1 1/4" pocket hole screws for that (no, I'm not using the whole box ). I will also be using the PL adhesive that Stick suggested. I know he suggested countersink screws for the top also as a first choice over pocket holes, but I am not sure I have faith that I could hit solidly into the edges of the torsion frame every time I put a screw in.

Then I bought two sheets of 5' x 5' russian birch ply (I asked for baltic but my receipt says russian so I guess that is just the kind they sell) in 3/4" size to make the inner grid with. Yes, I know 3/4" might be overkill, but I know it will be strong that way, no doubt. Also, I will have a little bit more width to hit when I need to aim for it from outside through my ply skins with screws (I still might decide to do countersink on top). Having never built one before, I don't know what to expect and I just felt better with 3/4". At this point, I plan to run them through the table saw and make 3" strips for the depth of the grid, and make 8" squares internally. At least in one direction, I will have to do scarf joints to lengthen the strips longer than their current 5' length because the finished table top will be 6' long when completed.

I also bought two 10' long boards of hard maple for the outer edge banding. This is the first time I have bought any real hardwood besides what the big box stores sell. I had no idea what to look for, but since this is just for edge banding and to add stiffness and durability, I hope it doesn't matter all that much about imperfections and other things. I noticed after I got home that they were flat sawn, which I'd have preferred quarter sawn if I had thought of it, but I was too giddy at the time to think of it all. I have already cross cut these to lengths of 48"+ and 72"+ and that gives me room to work, being over just a tad. The wood is somewhat rough, but since I don't have a planer I will have to just sand it. It has been planed to a rough 13/16" as is, mostly smooth but a few rough patches, and all I plan to do is just joint it on my router table so I have a straight edge to use on the table saw to rip it to width, and then I'll sand it to remove the roughness and put the smoothest side out for looks.

I also bought two Amana 1/2" flush trim bits with 1" long cutters. One is 1/4" shank, and one is 1/2" shank. I was just gonna get a 1/4" shank bit so it would fit all my routers, especially the trim router, but I got talked into one of each by my wife again. All I need this for is just to trim the hardboard surface even with the plywood under surface after the torsion box is built. I can't think of any reason I'd need two of these, but I like having them.

Also, I tried my router table as a jointer today. Never did any of that before but it worked like a charm. First I ran a short piece of pine as an experiment before trying my maple. When that worked well, then I went to the hardwood. I had a nice straight edge on the edge of that maple in just a few passes. Checking with a square, it was dead on 90 degrees from edge to face, and ram rod straight, so now it can go through the table saw and be ripped to width accurately.

Ok, so from here on in, as I build this I will post pics and report my progress. I figure I owe you guys a build thread since I cheated you out of a router table build when I bought that Kreg.
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Last edited by Duane Bledsoe; 07-03-2015 at 08:58 PM.
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post #2 of 153 (permalink) Old 07-03-2015, 09:23 PM
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Duane, You may want to add 1/4" Masonite to the top of your bench. As it gets scared up you can just replace the Masonite. If you want to do this add 1/4" to your edge banding to hold it in place.
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post #3 of 153 (permalink) Old 07-03-2015, 09:25 PM
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If you use just the PL 400, 500, or 700 you don't need screws. There isn't anything that will get it apart in one piece once those set up. My son used to use those to build speaker boxes out of mdf and the only way they would come apart was with a sledge hammer. He used gyp rock screws to hold everything together until the glue dried. After that it didn't matter if you took them out. You could use a few cauls and clamps to hold it it on instead.
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post #4 of 153 (permalink) Old 07-03-2015, 09:28 PM
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Kreg Jig K4 master kit. I will use this to connect the grid to the underside of the top of the new table with pocket hole screws.
on the frame/rim install the screws from the outside of the frame/rim in...
watch the depth of the penetration of the screws into the top sheet very carefully....
too deep will telegraph through as pimples into top surface....


Then I bought two sheets of 5' x 5' Russian birch ply (I asked for Baltic but my receipt says Russian so I guess that is just the kind they sell) in 3/4" size to make the inner grid with.
Russian birch ply may be a knock off, may have voids and isn't an actual 60''...
if it's the real deal it's virtually indistinguishable from BB...
verify the sheet thicknesses... both of them... each sheet may be different...

Yes, I know 3/4" might be overkill,
no it's not...

but I know it will be strong that way, no doubt.
it will, no doubt...

Also, I will have a little bit more width to hit when I need to aim for it from outside through my ply skins with screws. Having never built one before,
I don't know what to expect and I just felt better with 3/4". At this point,
being comfortable is very important here...

I plan to run them through the table saw and make 3" strips for the depth of the grid, and make 8" squares internally. At least in one direction, I will have to do scarf joints to lengthen the strips longer than their current 5' length because the finished table top will be 6' long when completed.
remember to alternate the locations of the scarf joints and to plate them...
will you be doing half blinds or blocking???...

I also bought two 10' long boards of hard maple for the outer edge banding. This is the first time I have bought any real hardwood besides what the big box stores sell. I had no idea what to look for, but since this is just for edge banding and to add stiffness and durability, I hope it doesn't matter all that much about imperfections and other things.
shouldn't...

I also bought two Amana 1/2" flush trim bits with 1" long cutters. One is 1/4" shank, and one is 1/2" shank. I was just gonna get a 1/4" shank bit so it would fit all my routers, especially the trim router, but I got talked into one of each by my wife again. All I need this for is just to trim the hardboard surface even with the plywood under surface after the torsion box is built. I can't think of any reason I'd need two of these, but I like having them.
being redundant is a good thing... ask any of us...

Also, I tried my router table as a jointer today. Never did any of that before but it worked like a charm. First I ran a short piece of pine as an experiment before trying my maple. When that worked well, then I went to the hardwood. I had a nice straight edge on the edge of that maple in just a few passes. Checking with a square, it was dead on 90 degrees from edge to face, and ram rod straight, so now it can go through the table saw and be ripped to width accurately.
excellent...


Ok, so from here on in, as I build this I will post pics and report my progress. I figure I owe you guys a build thread since I cheated you out of a router table build when I bought that Kreg.

what thickness ply will you be putting on the bottom side...

Notes...
when you spline the top pieces together make sure the grain goes the same way nd not perpendicular...
after you build the grid verify that it is flat flat...
fine tune it w/ a LA plane if need be...
if the pockets for the screws annoy you in the rim plug them...
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This would have been the week that I'd have finished chewing thru the restraints...
If only new layers hadn't been added....

Stick....
Forget the primal scream, just ROAR!!!
"SNORK Mountain Congressional Library and Taxidermy”

Last edited by Stick486; 07-03-2015 at 09:30 PM.
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post #5 of 153 (permalink) Old 07-03-2015, 11:21 PM Thread Starter
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I doubt the pocket holes will annoy me. I was planning to build the full grid, rim and all, from the birch plywood, and attach the top and bottom sheets to it, and also add a top layer of tempered hardboard (and then flush trim it with one of the new bits), then add the hardwood edge band. I figured the edge band would cover the pocket holes up if any showed on the rim. As for adding the hardwood, how should I do it? I was just thinking of adhesive and countersunk screws.

As for the top sheet beneath the hardboard, does this have to be more baltic birch plywood? Because it would be a bit easier on me if a standard cabinet plywood available at the big box in 4x8 sheets could be used. Save me a hassle of joining plys together to lengthen them, especially since it will be PL bonded and screwed to the 3/4" birch ply framing anyway.

For the bottom piece, I know 1/4" plywood will work. However, I am thinking of using 3/4" anyway, simply because I need to secure it to the metal Kreg frame using the predrilled screw holes, and these may not line up with anything other than the bottom skin. I'd rather run a screw into thicker plywood than to only hit thin material, especially since I can now see how heavy this is going to turn out to be, and the only way to move it if needed will involve lifting it by the overhanging surface and letting the frame hang from below by the connecting screws. I also know I could place some strategically located wood blocks inside, but it is much simpler to just use thicker plywood instead.

On lengthening the frame strips to the needed distance, I figured on a scarf joint. If this is ok, my plan was to set each strip needing lengthened on the miter saw, edge up, as if I were just cutting trim, and use the saw's widest angle of 60 degrees and miter it. Make a matching piece and overlap them with PL glue and air nails. Have this joint positioned in the middle of one of the 8" squares in the grid (in other words NOT as it crosses another strip in the grid), and use birch ply blocking on both sides of the joint to reinforce it, also air nailed and PL glued. These blocking pieces will span the full 8" width of the square spaces they are in, from side to side. I will stagger these joints out across the grid so they're not all in a line.

At this point, I plan to do the half blind joints as each strip crosses another to form the grid. I don't know the method yet. I can make a stack from them and use the sliding miter saw set at a specific depth to make the cross cuts and form most of the cut outs, but then I will have to remove the material and finish squaring the joint cutouts by hand with a chisel. If I am accurate enough, I might first drill out the back of the cutout with a forstner bit on the drill press, then do the cross cuts and the material will fall away on its own, and then just chisel the corners to square them up. All of this means every drilled hole, every slide of the saw blade, all has to be spot on accurate. I hope I'm up to it. A dado blade on a table saw and a cross cut sled would be best I think, but I don't have those things and budget won't allow it. I'm into my wallet deep as it is now.

Last edited by Duane Bledsoe; 07-03-2015 at 11:28 PM.
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post #6 of 153 (permalink) Old 07-04-2015, 12:56 AM
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Duane I am curious what a single sheet of 3/4" Birch plywood is down there . 60"/60" is 89 bucks a sheet here before the 14% tax.

Btw good luck with the build . Looking forward to seeing your work station

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post #7 of 153 (permalink) Old 07-04-2015, 01:06 AM
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I doubt the pocket holes will annoy me. I was planning to build the full grid, rim and all, from the birch plywood, and attach the top and bottom sheets to it,
okay...

and also add a top layer of tempered hardboard (and then flush trim it with one of the new bits), then add the hardwood edge band.
I would make the torsion grid...
add the edge band...
add the ¾'' top over lapping the edge band so it's under the top...
since you have a sistered frame put the pocket screws on the inside...

I figured the edge band would cover the pocket holes up if any showed on the rim. As for adding the hardwood, how should I do it? I was just thinking of adhesive and countersunk screws.
you use adhesive and it's a forever deal...

As for the top sheet beneath the hardboard, does this have to be more Baltic birch plywood?
definitely not... I thought that is what you wanted to use...

Because it would be a bit easier on me if a standard cabinet plywood available at the big box in 4x8 sheets could be used.
go for it...
use an AB or BB grade APA (American Plywood Association) stamped ply w/ the more plys being a distinct advantage... AB or BB Fir would be an excellent choice...
Here a C faced plywood won't be smooth nor flat... the lesser side is the one you'll be fastening the grid to..
VOE says DO NOT use the plywood from china or S. America... trust me, you will become disenchanted when the plywood begins to delaminate...

For the bottom piece, I know 1/4" plywood will work. However, I am thinking of using 3/4" anyway, simply because I need to secure it to the metal Kreg frame using the predrilled screw holes, and these may not line up with anything other than the bottom skin. I'd rather run a screw into thicker plywood than to only hit thin material, especially since I can now see how heavy this is going to turn out to be, and the only way to move it if needed will involve lifting it by the overhanging surface and letting the frame hang from below by the connecting screws. I also know I could place some strategically located wood blocks inside, but it is much simpler to just use thicker plywood instead.
go for it... do the wood blocks too...
you said you were going to pound on the table...

On lengthening the frame strips to the needed distance, I figured on a scarf joint. If this is OK, my plan was to set each strip needing lengthened on the miter saw, edge up, as if I were just cutting trim, and use the saw's widest angle of 60 degrees and miter it. Make a matching piece and overlap them with PL glue and air nails. Have this joint positioned in the middle of one of the 8" squares in the grid (in other words NOT as it crosses another strip in the grid), and use birch ply blocking on both sides of the joint to reinforce it, also air nailed and PL glued. These blocking pieces will span the full 8" width of the square spaces they are in, from side to side. I will stagger these joints out across the grid so they're not all in a line.
yes on the scarf joint...
BUT!!!! because it's ply you are joining this scarf joint seems to work the best... see the picture...
TS and dado blade to the rescue..
block like you said you were going to but you'll only need to do a block on one side...
once the PL sets up you WILL NOT get that joint apart w/o destroying it...


At this point, I plan to do the half blind joints as each strip crosses another to form the grid. I don't know the method yet.
dado blade and TS to the rescue again...
layout the cuts on one piece...
make your stack and clamp them together... make sure the edge is square to the face....
make your 1st cut... (I'd do the cut 1-9/16'' deep.. this helps w/ easier flush fitting and hydro static glue pressures)...
use a precut piece 1½'' wide in to the dado and pin it in place... this keeps things lined up and square...
another way is to cut the 1st dado only using your miter gauge, fence and then adding the insert... clamp up and gang cut...
every time you cut validate that the edges are flush before you cut...
no TS/dado blade.. use your router...

I can make a stack from them and use the sliding miter saw set at a specific depth to make the cross cuts and form most of the cut outs, but then I will have to remove the material and finish squaring the joint cutouts by hand with a chisel. If I am accurate enough,
I believe that to use you mitersaw is an invitation for things not coming out as well as they could...

I might first drill out the back of the cutout with a forstner bit on the drill press, then do the cross cuts and the material will fall away on its own, and then just chisel the corners to square them up.
All of this means every drilled hole, every slide of the saw blade, all has to be spot on accurate. I hope I'm up to it.
that seems a bit over thought and a challenge to maintain accuracy...

A dado blade on a table saw and a cross cut sled would be best I think, but I don't have those things and budget won't allow it. I'm into my wallet deep as it is now.
use your router... treat the cuts like a mortise...

the hardboard...
take it to the edge of the top...
DS tape (I used carpet tape) and a BRASS screw in each corner will hold it in place for years to come till you flip it over to use the other side...
Brass is kinder to your cutting edges than steel should you clip one...
a holding frame makes for a seam and trash gets into the seam and then works it's way under the hardboard lifting it and negating your flatness... VOE...



This would have been the week that I'd have finished chewing thru the restraints...
If only new layers hadn't been added....

Stick....
Forget the primal scream, just ROAR!!!
"SNORK Mountain Congressional Library and Taxidermy”
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post #8 of 153 (permalink) Old 07-04-2015, 08:21 AM Thread Starter
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How long does that PL glue take to dry?
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post #9 of 153 (permalink) Old 07-04-2015, 08:49 AM
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About the same amount of time as most wood glues but it stays more flexible. It will stretch before it will fail which is one of the reasons that it makes such a strong joint. You would only need to worry about the extra flexibility in its early stages if you intended to flex your frame. Leaving pressure on it would be similar to clamping standard wood glues. In about an hour you should probably be okay to take them off.

Screwing the bottom layer on is fine too, if you have enough time. Screws are slower than clamping and in some cases you have to consider that in your plans if you are going to have a lot of them to put in.

One other attribute of the PLs is that they have gap filling capability. I used PL 400 to glue the subfloor in my house to the floor joists. It is capable of filling a 3/8" gap. Just as an example, if your frame had a few low spots among the inner members you could use some good stiff cauls along with clamps and the PL would leave a solid bond across the gaps.

Someone I consider a master woodworker once told me that a master woodworker is not someone who never makes mistakes. He is someone who is able to cover them up so that no one can tell.
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post #10 of 153 (permalink) Old 07-04-2015, 09:52 AM
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Quote:
Originally Posted by Cherryville Chuck View Post
About the same amount of time as most wood glues but it stays more flexible. It will stretch before it will fail which is one of the reasons that it makes such a strong joint. You would only need to worry about the extra flexibility in its early stages if you intended to flex your frame. Leaving pressure on it would be similar to clamping standard wood glues. In about an hour you should probably be okay to take them off.

Screwing the bottom layer on is fine too, if you have enough time. Screws are slower than clamping and in some cases you have to consider that in your plans if you are going to have a lot of them to put in.

One other attribute of the PLs is that they have gap filling capability. I used PL 400 to glue the subfloor in my house to the floor joists. It is capable of filling a 3/8" gap. Just as an example, if your frame had a few low spots among the inner members you could use some good stiff cauls along with clamps and the PL would leave a solid bond across the gaps.
Charles I never even thought of using PL , thanks for the heads up earlier . Funny thing is I've used it years ago too . When I get back to my torsion box router table I'll take that route.
Which one would be the best though as you mention three . Does one have a longer setup time?

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Ok ,I never insulate

Last edited by RainMan 2.0; 07-04-2015 at 09:56 AM.
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