MDF torsion box..what fasteners?

[Jim O'Dell]

I'm going to build 2 10' long 14" wide 3" tall torsion boxes for my multistation tops out of 3/4" MDF. What should I use to fasten the pieces while the wood dries? I don't want to shoot anything through the top that I'll have trouble with when I go to put the laminate surface on. Don't cared so much about the bottom. Just toe nail some brads at an angle from the inside? Same from the outside bottom piece...shot in at an angle? I'' be able to use 2 other sheets of the same size MDF as weight for the curing time, and the first finished torsion box as weight for the second one. TIA!! Jim,

[Tyler Purcell]

Yellow glue and brads should get the job done just fine.

[David DeCristoforo]

If you are going to use MDF under PL, there is no need to worry too much. Use countersunk screws and glue (plenty of both) to attach the top. Then fill the screw holes with Bondo, sand flush and slap down your PL.

[Steve Aiken]

Have you already purchased the supplies? If not, I'm wondering if you are overbuilding it with 3/4" MDF skins. Check out a hollow core door -- a wonderful torsion box. It's made with cardboard strips inside and less than 1/8" skins. You can probably make this with 1/4" skins or 3/8" if you really want to beef it up. You could use 3/4" plywood or MDF for the webbing -- it's more than is required, but it will give you (a) lots of glue surface, and (b) lots of room to make sure the brads actually make contact with the webbing strips inside.

Make sure we get to see pics when you're all done.

Steve

[Jim O'Dell]

Thanks guys.
Yes Steve, a hollow core door is a torsion box, but you can deflect it just pushing in on the skin. Not enough there to be rigid, at least not as rigid as I want for what I'm doing. I thought at one time about using 1/2", and making 2 layers on top, one on the bottom, but then I came to my senses. :D :D Jim.

[Andy Haney]

FWIW, I constructed 3' x 5' TB, all from 1/2" MDF. The "web" was assembled @ 6" o.c. Then I glued a hardwood perimeter on. I did the whole this with glue, no hardware.

I found a flat(ish) spot on the concrete floor;
laid down one face;
assembled the "grid" on top of that surface (no glue);
glued the top surface over that assembly, held in place by sand tubesuntil glue dried;
flipped 'er over; and
glued the other face (the first one down).

Worked well for me.

Andy

[Mike Henderson]

That's going to be very heavy if you make the ribs from 3/4" MDF. 3/4" MDF would be good for the skin but you can make the ribs from much thinner stock and still get plenty of strength. I'd use 1/8" hardboard for the ribs and 3/4" MDF for the skins. You can use 3/4" MDF for the outside ribs where they might get hit.

The strength comes from the depth of the box, and how well you glue the ribs to the skins.

Good luck in whatever you choose.

Mike

[Rick Lizek]

Been making torsion boxes for years based on Ian Kirby's article in FWW from over 25 years ago. He pioneered the idea. He recently did a rewrite of the same article in American Woodworker.
You don't need to use 3/4" for the skins. The strength is in the height of the core materials. !/4" skins are plenty strong and the extra height of the core will be stronger in the long run. Staples are the best bet to hold the core together. The staples are plenty strong enough to keep the core together untill you glue the skins on. No need to use glue on the v\core pieces either. The glue will be plenty to adhere the skins to the core. I'm speaking from practical experience, not theory. The MDF core will be fine and 1/4" luan or hardboard will make a tremedously strong torsion box for your work tables.
http://www.amazon.com/Woodworkers-Essential-Facts-Formulas-Short-Cuts/dp/1892836211/ref=pd_bbs_sr_1/102-4987260-7982562?ie=UTF8&s=books&qid=1183462799&sr=8-1
Ken horner's book and Ian's article will tell you everything you need to know about torsion boxes. Kirby has the foundation and Horner has the mathematical aspects covered to explain how it works.

[Phil Thien]

No need to use glue on the v\core pieces either. The glue will be plenty to adhere the skins to the core. I'm speaking from practical experience, not theory.

So you can assemble the core w/o using any glue, and just use the glue between the skins and the core? Am I getting that right?

Any comments on thickness of core material?

Maybe I should get that article.

[randy street]

Jim,

Here is one that David Marks did, 1/2" for the ribs (glue and brads) and 3/4" for the top & bottom.

http://www.diynetwork.com/diy/ww_materials_products/article/0,2049,DIY_14442_2278182,00.html

Randy

[Rick Lizek]

So you can assemble the core w/o using any glue, and just use the glue between the skins and the core? Am I getting that right?
Yes...just glue for the skins is all you need. The great thing about torsion boxes is the strength and the speed to make them. Smaller grids in the core material also make it stonger. The other nice thing about making them this way is you can easily make round and odd curved shapes relatively fast. Folks that insist that one must notch the frame material are making a simple thing unnecessarily complicated. The staples are countersunk in the core material. One only needs to hold the core material in place until the glue sets with the gluing of the skins. Do both skins at the same time.

Any comments on thickness of core material?
!/4" skins are plenty strong. The strength of the core box is the height of the core material. 1/4" skins and 2-1/2" core material is stronger than 3/4" skins and 1-1/2" core material. I made a torsion box with 1/4" luan skins and 3/4" mdf core that got stored in a damp garage for 5 years and it is still as flat as the day I made it. If you need to screw legs or something to the torsion box add some built up blocking to key areas.

The torsion box is based on aircraft wing constuction.

Maybe I should get that article.
Get Kirby's article...FWW from 25 years ago so it might be in a reprint or someone will have it archived. The article in American Woodworker was from last month so it shoulf still be around. Get Ken Horner's book that I referenced in a previous post. Great book!

[Matt Benton]

I have so far made 2 torsion boxes, the last one just finished for my contractor saw and router/extension table.

I used (3) 2X4's lengthwise on end and a few pieces across for the ribs and 3/4 mdf for the top and bottom, screwed and glued. It is 6 feet long on 5" casters.

My saw now feels like a cabinet saw, even on the locked casters. Cheap, easy and quick.

[Jim O'Dell]

WOW!! Lots of information! Thanks!!!!! If I use 3/4", I can get both sides done with 2 sheets of MDF. If I use 1/2", then I'll need 3 sheets. But I'll look into that, especially with the strength coming from the height of the ribs, whick makes sense, since there would be less deflection on taller ones. I'll rethink this. Was going to go get MDF after work today, but just found out this am that the other guy in the office is not here today, and failed to notify me. In fact 2 days this week I get to work his late nights as well as mine. :( :mad: So with company here from out of town, I may bypass that for today and rethink what I'm going to use. The weight doesn't bother me.
New question: What would be best to use on the bracing? If I use the 1/2" skins, then my braces will be max 2" tall. Would 1/2" MDF or Plywood be best? Continued thanks for the information! Jim.

[Rick Lizek]

These are work tables right. I'd go with 1/4" skins with 2-1/2" MDF frames. I gather this is your first torsion box. If you use 4" or 5" grid spacing and 1/4" skins you will swear the the top is thicker than 1/4" if you rap it with your knuckles.
Don't forget this is aircraft technology. Think about a wing with dope covered canvas supporting thousands of pound stress in flight fighting gravity and heavy wind currents.

Find the article by Kirby and read Horners book. Why reinvent the torsion box? Sure Marks used 3/4" skins but for an assembley table it's overkill. The math proves the thick core along with the gluing of the skins to the frame is where the strength is from.

[Mike Henderson]

Just an added comment. I agree with an earlier poster who said that thin skins will provide plenty of strength for the torsion box. The problem is attaching tools to the box - if you use thin skins, you pretty much have to use bolts that go completely through the torsion box, and may have to use a backer board underneath to spread the pressure. If you use a thicker top skin, you can screw into it to hold your tools. But if you're not going to fasten tools to the torsion box, that won't make any difference.

The thing that will make the most difference in the strength of the box is the depth of the ribs - how thick the box is. To a large degree, the spacing between the ribs is chosen to limit the deflection of the skin between the ribs (the thickness of the skin affects this also).

I use torsion boxes for veneer pressing - where I have to handle the boxes to put one on top for pressing so the weight means a lot to me. An all MDF torsion box can be surprisingly heavy.

Mike

[Chris Padilla]

I made a torsion box as the BASE of my rolling workstation several years ago and just used 3/4" MDF all the way around. Yes, it is heavy like a mofo but being the base of my workstation, it works just fine. I half-lapped the grid and made the half-laps so snug that they didn't need any glue between them...just glued the grid to the 3/4" MDF skins and side pieces. But, the sucker is HEAVY!! Did I say it is HEAVY??!! :)

[Jim O'Dell]

Just for clarification, this is not for a true work bench. Think about them as being very long infeed/outfeed tables that will probably be abused, in manners unthinkable, while working in the shop. :eek: :D It is a multi uses station 23 + feet long, that different tools will "dock" in the center: CSMS, possibly RAS, down draft sanding, scroll saw, lunchbox planer, limited router station, I think I can even adapt the 6" jointer that is only about 28" long into this, plus ideas I'm still formulating. It won't be ideal for some purposes, as I plan to have the infeed side about 1/16" lower, but I hope to develop a work around for that. Maybe that information helps. I don't plan to hard mount tools to these boxes. I want the surfaces to stay smooth. And it will be abused, mark my words. That's why I lean toward thicker material. Plus the fact that I'm a bad shot. Get the pieces down to 1/4" and I'll never hit them with a brad! :D :D

[Chris Padilla]

Jim,

In that case it sounds like 3/4" might be good to use. The devil's always in the details! :rolleyes: Seal up any exposed MDF with poly so it doesn't swell over time on you. Even here in California I've had that problem and it caused my laminated surface to pop free over time. I now need to redo the top section of my workbench. :mad:

[Phil Johnson]

The Ian Kirby article is in the June '07 Woodworkers Journal. There is a follow-up segment on the web:
http://woodworkersjournal.com/articles/Ians%20boxes.pdf

The follow-up shows how to use Tricel (cardboard honeycomb) as the core which is probably better suited for shelves than work tops.

[Jim O'Dell]

Hey Chris, you still have your Santa hat on!! :D Please tell me you have your cyclone up and running! Jim.

[Chris Padilla]

Cyclone is up and running but sadly it doesn't run much because I haven't had much shop time in quite a while. :( However, I aim to amend that soon as some other things are finally wrapping up! :)

[Jim O'Dell]

Hi all. I went ahead and got 2 sheets of the 1/2" MDF. I think I can get just about all I need out of them for both torsion boxes I need to build. A suggestion on another forum said to use a 10" wide section to brace the 2 seams I'll have, to make 10' long boxes. I may have to get some more MDF, or if I have a piece of plywood, I may use that.
I also got 4 of the HF hand screw wood clamps to help with this. I have wanted some since I bought 3 for my dad for Christmas a few years back. They aren't Jorgensens, but for 5 smackers each with a coupon, I think they will work pretty good. 67489 Wish I had some more money and I'd have gotten a few more...ok, I would have wiped them out. :eek: :D
Hope everyone has a great weekend! I've been off today for a dog show, so it already seems like Sat. to me. Jim.

[Cliff Rohrabacher]

Is it too late for me to say: "10 penny nails." ??

[Jim O'Dell]

Never too late to say it. Being in time to get it implemented may be another story!:D :D My usual fare is to screw everything together. But I think I will use the brad nailer and do it "Nahm" style this time.:cool: The glue is what will hold it together, so whatever I use probably won't make too much difference. I do find that screws tend to hold tighter for a longer period of time without backing out, though. I prefer the top not to have any penetrations in it, so will attach it from underneath. The bottom I don't care, and might use screws, or shoot brads in from the outside. I could use the Kreg jig and drill holes to attach the grid to the top from underneath, but I'm afraid of the MDF splitting with the screws,eiven drilling a pilot hole. But we'll see what wins out in the end. Thanks for the note! Jim.

[Noah Katz]

"the strength coming from the height of the ribs, whick makes sense, since there would be less deflection on taller ones."

I think there may be some confusion here.

The strength/stiffness is a function of the total height and skin thickness, not just the core height.

For the same total thickness, thicker skins will give higher stiffness and strength.

For a given thickness, the stiffness/stength increase more or less linearly with thickness, i.e. 2X thickness gives 2X more stiffness/strength; for a given skin thickness, they increase with the square of the height, i.e., 2X height gives 4X stiffness/strength.

[Jim O'Dell]

Woah, Noah!! :D So using 3/4" skins would be stronger? Oh well, I'm not going to haul these things back to trade out.:D :D Actually, I think they will be plenty stiff for what I'm going to be using them for. But thank you for the information!!!! I'll store that back in the file cabinet for the next table I build.

New question: After waddling back home after supper, and letting the stomach bulge calm down a little, I've plotted out the cuts on graph paper. Need to try a cutlist program, but alas, I still don't have access to my computer (guest bedroom) yet. So I can get everything out of the 2 sheets of MDF with the exception of the 2 stiffening plates over the joints on the top and bottom pieces. Instead of purchasing more MDF, I'm thnking about using some of my left over 1/2" OSB. Any problems anyone can think of with doing that? TIA!! Jim.

[Alan Schaffter]

I didn't use nails, brads, or screws on the a torsion box assembly table I made except for the perimeter pieces. I used half lap joints and glue for the web. It worked great and required no cutting and piecing of the web. Here is a link to a thread on the process. (http://www.ncwoodworker.net/forums/showthread.php?t=2980&highlight=assembly)

http://members.cox.net/aschaffter/table-4.jpg

[Noah Katz]

"Instead of purchasing more MDF, I'm thnking about using some of my left over 1/2" OSB."

Actually OSB and ply are both stiffer, stronger, and more stable than MDF.

[Jim O'Dell]

Well, I was able to get everything cut out of the 2 sheets. Even the bracing for the joints. At least as long as I dont mess up cutting the braces! :D I had to change my original thoughts of staggering the joints to mke this happen. I had a left over piece that I thought would be 1 1/2" wide...it ended up 1 1/4" instead. Not wide enough unless I have the bracing on top of each other. Shouldn't be a big deal.
Oh, and a poster on another forum mentioned the trouble he had with laminating MDF and OSB. They react to moisture/temperature differently, and bow one way, then the other. So that's why I decided to use all MDF. I've stayed out of the shop for the last hour and a half. Neighbors had an outdoor wedding at their house. I figured I would create problems running my machines and the cyclone (exhausts outside) during the ceremony.:eek: Especially if they were video taping it. :D Jim.

[Monte Milanuk]

Has anyone here made a torsion box for a workbench top and used fillers/spacers in the edge? I'd like to be able to mount some heavy objects to the corner or edge of a workbench (think metal working vise and reloading presses), and I was wanting to make the top from a torsion box for stiffness. Seems like filling the front row or two w/ glued in spacer blocks *should* do the trick, as thats where any drilled holes are likely to be located.

Thanks,

Monte

[Jim O'Dell]

Monte, I would think that would work, but I'm learning a lot from posters in this thread and it's mate on another forum I participate in. I'd use whatever you make the top from, and just layer it in the holes where you want to mount the vice. Then I'd use long carriage bolts to go all the way through the top, and big fender washers under the nuts on the bottom side.

And an update...I don't have enough wood.:o I miscounted. I need the long grid parts for the second box, and a couple more short grid parts for it as well as 4 properly sized joint stiffeners. The 2 I cut were too small. Knew I should have dry fitted some to be able to measure. So I'll have to get one more sheet this week to finish up. It's not like I would have finished one this weekend anyway. Maybe I can do a little more prep work tomorrow after getting back from the dog show. Jim.

[Jimmy Newman]

Has anyone here made a torsion box for a workbench top and used fillers/spacers in the edge? I'd like to be able to mount some heavy objects to the corner or edge of a workbench (think metal working vise and reloading presses), and I was wanting to make the top from a torsion box for stiffness. Seems like filling the front row or two w/ glued in spacer blocks *should* do the trick, as thats where any drilled holes are likely to be located.

Thanks,

Monte

I've read some discussions on using torsion boxes as benchtops before - and while they work fine for a number of things, there is one main problem. One of the virtues of a big, solid wood benchtop is that its mass dampens vibrations. A torsion box (especially with ply instead of mdf) can be pretty "springy" and won't dampen vibrations as well. Of course, this only matters when you're pounding on things. One other thing that could be a problem is that the lighter table will be more prone to "walking" under heavy use.

On the subject of reloading presses, I have a 4-station turret press that I use pretty regularly and it is lag bolted down to a table with a 3/4" ply top. I screwed another piece of 3/4" ply about 8" wide and 6" deep under where I mounted the press (probably unnecessary), then lag bolted the press into both layers of ply. It's rock solid. If you have one of the big progressive presses, you may need more structure, but a single stage or turret press should be just fine bolted or lag screwed onto a 3/4" or more of ply.

[Monte Milanuk]

Maybe I'm leaning on mine too hard... or it's too far between supports underneath (18" between rails) but I've flexed MDF tops thicker than that with a single-stage six-hole Redding turret press. My Dillon RL550B w/ Strong Mount seems pretty easy on the bench it's on by comparison (I think it uses better mechanical advantage).

Current slapped-together top is three thicknesses of 3/4 plywood... 30" wide x 10' long, on top of an old kitchen counter base. Base is lag-screwed to the wall, and I've got a liberal number of figure-8 table-top fasteners attaching the top to the base. Eventually I plan on putting a laminate top and hardwood edging on it, but I'm in the middle of the competitive season so I need the real estate!

As I work on fixing up my shop, I'm going to be adding various benches and counters here and there, which is why I was interested in the torsion box option.

Thanks,

Monte

[Roland Chung]

Is there a problem with using Ultralight MDF? I picked up material yesterday and am about to start putting together an assembly table - possibly with some Brian Gray features.

Would I be better off using 1" for the top in regular or ultralight if I were to plan on routing 3/4" holes in the top and 4" access holes in the bottom? Or is a layer of tempered hardboard on top of a 3/4" top good enough?

[Al Willits]

"""""""
I've read some discussions on using torsion boxes as benchtops before - and while they work fine for a number of things, there is one main problem. One of the virtues of a big, solid wood benchtop is that its mass dampens vibrations. A torsion box (especially with ply instead of mdf) can be pretty "springy" and won't dampen vibrations as well. Of course, this only matters when you're pounding on things. One other thing that could be a problem is that the lighter table will be more prone to "walking" under heavy use.
"""""""""

Hasn't been my experience with the Marks version, 3/4" top and bottom and 1/2" cross pieces make a very stable base, I use it as a workbench all the time, run my Rigid belt sander on it, use it with the ez system, stack lumber I'm running though a jointer or planer on it or assemble just about anything from small pieces to 6' storage cabinets and it does not flex.

If I was to make another one just for a assembly table I would probably use 1/2" all the way around, but considering I just had 12'x8'x20 car port in pieces sitting on it, at over 600#, I'm sticking with 3/4".

Al

[Alfred Toy]

FWW Free video (http://www.taunton.com/finewoodworking/ProjectsAndDesign/ProjectsAndDesignArticle.aspx?id=28855) dead flat assembly table with torsion box.

Torsion Box Ultimate Tool Stand (http://www.christophermerrill.net/ww/plans/UTS/Tool_Stand_4.html)

Create a dead level surface to build a torsion box (http://www1.diynet.com/diy/ww_materials_products/article/0,2049,DIY_14442_2278181,00.html)

The Workbench: A Complete Guide (Torsion Box) (http://books.google.com/books?id=pks1lGO6zvYC&pg=RA1-PA73&lpg=RA1-PA73&dq=torsion+box+workbench&source=web&ots=WxB83so4vr&sig=F2a-kQcNRmrgLNB-2_LtnrdJhqw)- Google excerpt