Torsion Box Design

I have everything cut. Need to drill holes in the ribs closest to perimeter to route cables inside the box then I need to make a level assembly table from saw horses and planed 2x4 and then finally build this damn thing. Day job been kicking my but so it’s only every few days I can get in the shop.

I see everyone beefing up their torsion box at the corners to screw down the cnc’s feet. I hadn’t given that any thought. As I’ve already made my box from 1/2" ply thinking that would be adequate, I can’t do that. Will the top be strong enough as is or should I add a layer of thicker ply on top? I’m not planning on moving the machine seasonally so once in place , it’s staying there.

My thinking … the 1/2” plywood should be fine. I’m adding to the corners of mine because I chose MDF for the whole thing and the screws to hold down the machine may not hold securely in MDF.

Mine is 1/2" ply as well and I haven’t had any problem screwing the machine down to it.

Screws into 1/2" ply should be fine. It only has to keep it from shifting around on the table, correct?

I think there are a lot of frankly over-engineered designs on here. I built a Paulk Workbench (one of the original torsion box workbenches) a number of years ago from 1/2" ply and pocket screws. It’s held up through insane conditions, a cross-country move, and has been hacked into 3 different configurations and it’s still going strong as a miter and router table station. The Paulk plans only have 1/2" ribs every 24" where some here have 4x that amount. Paulk ribs are hollowed out to allow access as shelves, most of these are solid. I wouldn’t sweat screwing the OF into 1/2" ply just to keep it stationary on the table.


Thanks for the reassurance, bitrunner. Coming as I’m just putting the finishing touches on my cabinet and enclosure, I was getting a bit nervous. Tomorrow, electrical and actually installing the CNC. Trying not to get ahead of myself but anticipation is killing me!

I am 100% over-engineering LOL. This is my first torsion box so it’s a bit of fun for me too and I’m going to use it to build an assembly table before the 1F arrives.

Looking back I think 1/2” ply would be my preference but the price of good plywood by me is crazy compared to MDF.

I hear you. Frankly the price of even bad plywood is outrageous. I’ve spent years ordering 5 sheets for projects I only needed 3 for and this collection is what I’ve been using to make my torsion box and enclosure. I shudder to think what it would cost if I were to buy all this material at today’s prices. I’m using 4 different drawer slides in the same bank, 2 different kinds of hinges on the doors enclosing the vacuum, 3 different thicknesses of styrofoam to quiet the vacuum cabinet. I’m really cleaning up my rather tight shop. You just wind up designing around what you have. One thing I didn’t have was some acrylic for the window on the front of the enclosure. $186.00 for 2x4 1/4" at HD. That hurt.

I just paid $75 per for 3/4” luan plywood. Didn’t think that was too bad and that’s in NJ where everything is expensive.

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True, but if I had made my paulk workbench out of mdf it wouldn’t still be around today. That could be just a factor of my particular environment but if it’s needed to be in service for awhile, you have to factor in longevity and replacement costs with mdf much more so than with plywood.

Where I am at the big box stores 3/4" MDF is now upwards of $60 a sheet which is unbelievable considering a year or so ago it was $30, and is nothing more than scrap and glue :wink:

Even at that it’s still $40 less per sheet than 3/4" Baltic Birch at the lumber yard.

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Hey all,

what is a sheet’s size in your country?

Since plywood has often been the subject here in the forum lately, the day before yesterday when I was in a hardware store, I took the opportunity to see what it costs here today:

Plywood birch 12 mm (≈15/32″): 42 €/m² (ouch)
(that’s 3.90 € / sq ft or
35.12 € / sq yd)
(On 2022-06-23, 1 USD = 0.94891 EUR, 1 EUR = 1.05368 USD)

That means the price has doubled since I last checked and that it has more than doubled since I last built something with it (a few years ago).

But it was a hardware store, wasn’t at a lumber yard this week.

I recently read a report that hardware stores are now buying forest plots to become their own suppliers.

Lately I’ve been building mostly things out of glued laminated timber. I’m glad I still have enough wood that I bought years ago!

I agree with you … I wouldn’t build a workbench from MDF. This table is the only thing I’ve built from all MDF and I think it’s a good use case for MDF and I also think there aren’t many good use cases for an all-MDF project.

20 years ago when I made the cabinets for my workshop they were made with MDF. When I was done, I pretty much swore off ever using it again. All that fine dust gets everywhere I don’t care how good your dust collection is. However, I can’t think of anything else that will work as well for a waste board so I’m going to use the leftovers for drawer fronts and cabinet doors on my enclosure. 20 years later and I’m matching up my original cabinets.

Here in Canada, everything is pretty much in imperial still, at least as far as wood products go. Most likely comes from being next door to the largest market for them. Sheet goods are 4’ x 8’ although oddly the thickness is often given in metric. Baltic birch is available in metric sizes but at 5’x5’ ( see what I did there?) it’s difficult to transport and handle in my small shop. I hear on price rises, just about have a heart attack to buy anything now. That’s why I’m making everything from stockpiled lumber. Don’t know how much longer I can do that, this project is pretty much cleaning me out of sheet goods.

Hey Charles,

you say you get the baltic birch in the sheet sizes it is produced in europe (which is 150 x 300 cm = approx. 5′ x 10′) :slight_smile:?

I understand that if your sheet goods usually are 48″ wide it exactly matches Onefinity Journeyman workarea width (and that it does not match 60″ wide european sheets)

The whole series of One-finity machines are sized based on a multiple of 16". So you can break down a 4’x8’ sheet with no waste. For the Woodworker, you could break down a 5’ x 5’ sheet into 30" x 30" squares and Bob’s your uncle.

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Hey Charles,

Although a 60-inch wide Journeyman would be a nice thought :slight_smile:

Most real Baltic Birch ply here (U.S.) is 5x5 and is made for cabinet makers. It’s actually very nicely made and is the only ply that’s consistent enough for use in a CO2 laser cutter.

Standard plywood is in 4x8 (although you can special order 4x12) and sold in imperial sizes of fractional inches. except that they’ve shaved one ply off starting a few years ago so it’s no longer really a 1/4, 1/2, or 3/4" thick (it’s no longer 96" long either - it runs 1/2" short now). The thickness is shy a 32nd of an inch of the nominal measurement. The only real standard is for the face plies and what goes inside can be anything including stuff like automotive body repair Bondo. It’s acceptable for building purposes but not for anything where you want consistency through the material.

Sheathing plywood (used for the initial exterior layer of a house before housewrap & siding) is running about $44 for 1/2" (15/32) or 57 for 3/4". That’s CD graded - knots, voids on one face, etc.

BC graded plywood which has knot/void free surface plies (but allowable football patches on one side) about $5-$7 more per sheet.

The veneers are some variety of pine.

Hardwood plywood (usually 3/4" and 7 plies) runs substantially more but it’s good for cabinets, bookcases, etc., and priced based on the species. Birch runs about $84, oak is $90 and poplar is $75 locally (northeast U.S.). This is for C-3 grade (not the same standard as the A/B/C/D of the previous types) -

The prices of plywood and lumber in general are dropping to pre-pandemic levels. Right now the futures prices (for material to be delivered in 60-90 days) is running less than a third of its peak and not much more than a hundred dollars a 1000 board feet more than prior norms. The Fed’s interest rate hikes have stopped the “free money” that was the norm for the past 15 years and mortgage rates are back to pre-Great Recession levels which has reduced somewhat the frenetic demand for new houses. But we’re (the U.S.) still about 4-5 million houses short of demand so it’s not like lumber, etc. are going to crash.


We’re still working on getting them to offer a 48" x 48". You’ll have to get in line.

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