Material type choices for transportable workbench

[James Nugnes]

So I really have to ask this here cause I just don't know of a board better qualified to give an opinion.

I had posted recently that I was going to build a transportable workbench much like the Paults transportable benches but with some modifications all my own. One of those is that the total size, the two sections at 24" x 48" each combined would be 48" x 48" with a top and bottom in each case (four total panels built into two workbench sections). I end up with four 24" x 48" panels to do the job...was planning on 3/4" ply (tops) and 1/2" ply (bottoms).

Another question I asked here concerned the holes. I have settled on the 20mm bench holes throughout...meaning all sides, all panels....20mm holes with 96mm spacing. At one point I thought I might do one section in 3/4" hole and the other in 20mm. But I don't think I would really gain anything. So 20mm throughout.

So now that brings me to this question. I had been planning all along to get a template (probably 24" on a side)....and use it to cut the holes with a router....which I can do. I think the only downside doing that is the degree to which you can be perfect something like 60 times. That said I think I can be close enough to perfect to do it that way if I still want to. But assigning myself the perfection of a CNC machine is a bit much I think. So i really can't assign myself better than very good but not perfect.

However I now see that I can buy two 29.2" x 52.3" slabs in 3/4" MDF for what is not a terrible price. I can even get two MDF slabs at 24" x 48" for even less (about $200 total). I could use those for tops or use the aforementioned 29.2" x 52.3" MDF slabs for tops.

The two touchy points for me are weight and construction. If I use the 24" x 48" MDF slabs, each section with 1/2" ply bottoms will weigh in at about 34 lbs all in. If I do it in 3/4" ply tops with 1/2" ply bottoms each section comes in at about 24 lbs all in. Ten pounds per section isn't exactly chicken feed. That is a pretty big dif in weight. In most cases probably not that much as far as practical concerns go...but not nothing either.

The other concern is planning on using ply between the tops and bottoms for support much like the Paults transportable benches. So if I use MDF slabs for the tops, will pocket hole screws and glue do the job or is there a construction problem that will arise out of mating those two materials at right angles using such a technique? Was not planning on cutting dado's into the panels for the support pieces. I suppose that is an option but not one i really want to pursue unless truly needed. I would guess dados would completely kill any issue I would have as the increased surface area at the mating line would be significant. Am I worrying for no reason, in which case I would just process the material as planned regardless of which path I decided on for the material. Is there something besides dados that would improve the mating assuming some improvement is actually desirable? One thing we all know is that MDF does not like rework. Get it right the first time.

What I gain in using the MDF should be obvious. I get two perfectly cut slabs that will give me perfect alignment when using tracks and clamps to hold material for processing and I can use an MDF slab as a template to cut the holes in my 1/2" ply bottoms.

[Jim Matthews]

You'll be able the transport MDF once, maybe twice.
It's not an ideal material for this application.

Is this for a jobsite?

[James Nugnes]

Nope...I would never trust MDF to something I was actually moving distances, tossing in and out of a truck etc.Just using it to create a workbench or work-surface that I can take from the concrete platform outside my basement double doors to my garage so that I can have an outdoor workbench to take advantage of the good weather coming. I work in my basement workshop constantly and it just gets old. You begin to feel like a mole or a ground hog after awhile. Love being able to work in the fresh air but need a workbench that I can move between the two outdoor locations (garage and basement level concrete platform).

I suppose confirmat screws would be an option for mating the ply supports to the MDF top. The bottom surfaces will be ply in any case. So that ends up ply to ply no matter what I choose for the tops.

I wonder if using course kregs with pocket holes and glue would work to clamp the MDF to the ply and then take something like 1" x 1" stock, cut it into small blocks maybe 3" long and use Confirmat screws and glue between what will in effect be blocks and the MDF and ply. So I would drive a confirmat screw into the block and MDF in one direction and a wood screw into the block and the ply in the other direction. The screws would be at right angles to each other and the blocks would be glued as well. The Kreg system plus glue would be used to initially join the MDF to the ply but the holding strength would be significantly improved by the blocks and the Confirmat screws again with glue. Although it seems to me that I would be pulling against the initial joint when I battened down those Confirmat screws. Dados are beginning to sound better maybe using my block idea and dados. The ply and MDF could be friction fit together in a dado. Then when I went in with my blocks and Confirmat screws I would not be pulling against a glued and screwed joint. Again I don't have to worry about the ply to ply bottom to support joints....so there would be no dados there....maybe just glue and Kreg there. Dados would be in the 0.75 MDF.

The other option far simpler would be to just make the whole thing out of ply (which was my initial idea) and take as close to perfection as I can get on the accuracy and spacing of the 60 odd 20mm bench dog holes I will have to drill into the tops.

[James Nugnes]

One additional item that might help sway me to using the CMC cut MDF slabs is that the added weight if manageable might actually help. A standard MFT/3 weighs 54lbs. As neat as it might well be for power tools, 54lbs is clearly not enough mass to make any hand tool work feasible.

The base for my proposed bench will come in at about 55lbs. Each of the sections all in ply would weigh about 28lbs each for a total of 111lbs. The MDF slabs add about 10lbs per slab which would up the weight of the complete bench to 131lbs. At 38lbs per section that is still a manageable weight for hefting them around between the garage and the back platform. But the added 20lbs might make a difference in the stability of the complete bench when using hand tools. 131lbs total with the two sections weighing just under 40lb each might be as good as I am going to get for functionality mated to versatility and the ability to move the thing around.

One option that I just thought of that might be the best of everything while requiring that I use my noodle with regard to the assembly technique used would be to make one section with a 24" x 48" MDF top and the other 24" x 48" section all in ply. That would come in at about 121lbs total. Still substantial enough to allow for hand tool work with one section biased to power tool work and the other section biased to hand tool work. Certainly would be more comfortable with clamping vises and the like to the all ply side for working on workpieces with hand tools but would have a pretty large and very precise section in MDF for working with power tools.

That still leaves me trying to figure out the best way to mate the MDF top to the ply supports. So far at least the best idea I have come up with so far is to dado the MDF, friction fit the ply supports to the MDF using the dado and then using my 1" x 1" x 3" long blocks, Confirmat screws and glue to really mate the MDF to the ply. Maybe a block every 10" or 12" with Confirmat screws from block to MDF and regular wood screws from block to ply.....glue on all mating surfaces. The dado and some clamping should allow for an initial friction fit with just enough retention to get the permanent fixturing done. The dif between Kreg screws and glue and this method and glue is that the Kreg pocket screws are usually just acting as clamps for the glue. Here the dados, Confirmat screws, blocks and glue are equal partners in the permanent bonding. I don't think I would rely on either the Kregs or the glue in this application. But I think the combination of dado, Confirmats, blocks and glue will make for a solid reliable mating.

[Greg Hines, MD]

I guess I am not getting the picture of what you are trying to build. It sounds to me like plywood would be preferable to MDF in any event. I built my workbench top with 4 layers of 3/4" plywood, and used a router and jig to drill the holes, up the front and back, as well as more in front of my side vise. I can place dogs in any of them, as well as wonderdogs. I then lay a piece of 1/4" hardboard on it to protect it from glue when I need it.

If you are looking for a way to drill out the holes reliably, I would search for "AskWoodman" on Youtube. He builds what he refers to as the ultimate work table, the top of which is perforated with holes in a very regular manner, done with a drill and guide system. If it were me, I would use a router, but to each their own on that.

Doc

[James Nugnes]

Look at the Paults workbenches on Youtube. Shrink the base design down to 48" x 48" in total using two 24" x 48" sub-assemblies instead of the 24" x 96" sub-assemblies he uses and substitute 0.75" MDF slabs on top for the 0.50" ply he uses and you have the basic idea. The problem is mating an MDF top to the ply supports. In his design since it is all ply, he has no issues simply using Kreg pocket hole screws and glue. That is not a very good idea for MDF and ply. Some people use it....they have some success with it...I am not going to use Kreg screws and glue if I use MDF slabs on top. Just not going to do it that way and would have little confidence in it done that way if building it with a work surface in MDF.

I have a template for the 20mm bench dog holes, a router and correct router bits. So I can build the whole thing in ply if I want do so. I just think we are kidding ourselves if we think we can match what a properly set up CNC machine can do for precision and alignment hogging out 60 odd holes. You can do very well. You can do very well indeed. But you are not likely to match the precision of a CNC machine over that many drilled holes. The beauty of getting and using pre-cut MDF slabs is that you know the holes are perfectly aligned and positioned. Once you complete the workbench you can just drop your jigs and clamps anywhere on the surface and go, fully confident that if anything does go wrong it won't be because there was some misalignment in the bench dog holes that just kept multiplying itself out over however many workpieces you cut. The flatness and the mass of MDF offers some advantages over ply as well.

If however I was looking for the degree of portability that Paults gets out of his transportable workbenches I would without doubt use all ply. In my case, I just want to break it down and move it from my back basement double doors to my garage as once the good weather hits I am as likely to work in one place as the other. Working all winter in the basement shop is just about all of that I can stand. But I have more than one "fresh air" location that I will use,,,,Hence the desire to be able to break it down and move it from garage to back concrete platform. Also, I can probably convince myself that fixturing workpieces to MDF for hand tool work is not such a great idea. Hence I am thinking that one 24" x 48" side with an MDF slab top for power tool work and one 24" x 48" side all in ply using 3/4" ply for the top surface for hand tool work might in fact offer the best compromise of all:
1) Weight would be about 121 lbs for the whole unit...enough weight and mass to be able to do some hand tool work without the whole contraption walking or shaking or whatever (the one use the actual MDF/3 Festool table handles rather poorly)
2) Not so much weight in the heaviest of the sub-asssemblles that it discourages breakdown for moving (just under 40 lbs for the heaviest piece one would have to move)
3) One 24" x 48" surface in ply biased toward hand tool work given the rigidity of ply and the ability to ratchet down clamps and workpieces pretty hard without concern for damaging the top nor as much concern for possible damage to MDF via a slip of the hand tool.
4) one 24" x 48" surface in MDF with precision cut and aligned holes biased toward power tool work

Confirmat screws plus glue would appear to provide a solid process for mating the MDF to the ply supports. I think that if I cut a dados in the underside of the MDF I can slide the ply supports into the dados and they will hold it there well enough to go in with my 1" x 1" x 3" long blocks, Confirmat sccrews and glue to actually fixture the MDF to the ply supports using the method I described. But I have not done that before....I am not even sure anybody has fixtured MDF to ply in exactly that way (dado, blocks, confirmat screws, glue). But if I want one or both surfaces in MDF, I suspect what I propose would be better and stronger than Kreg screws and glue for a number of reasons.

[Greg Hines, MD]

That is an interesting design. I will probably make something similar one of these days. I would question why you would not want plywood for it, as it is significantly stronger and lighter than MDF. If you are concerned about it walking around if you are trying to use it, I would add some weight to the cavity inside the bench planks that you could then remove prior to transporting.

I liked how he perforated it with his router, though I would have done it with a strip of hardboard or mdf, across the width of the piece, and drilled with a 1-1 1/2" holes. The, use a router and bushing to center a 3/4" or 20mm bit wherever you want your holes. It makes it easy to drill them, and each row would be the same as all the others.

Doc

[Jim Dwight]

I plan to use the Woodrave router base and pegboard to make my holes. I'm not sure exactly how precise my holes will be but there should not be much error. I am not sure material yet but it will probably be plywood. I don't like working with MDF, it is relatively weak, and it is hard to fasten to. It's only significant advantages are price and flatness. With the stiffening ribs Paulk uses, plywood should be flat enough. And also much stronger and better to fasten together.

I also don't get your sizing. I would want the sub table to be useful separately. 2x4 seems a bit small. Maybe still useful. I plan a 3x6 foot table (one piece). But I don't have to move it up and down stairs. It will be on wheels in my shop and sometimes move out into the drive. I won't have to pick it up unless I want to throw it in the trailer and use it somewhere else. I will have a solid bottom so I can put tools on the bottom under the top. That seems like one of the best ideas in the Paulk design. Holes seems to take away from that.

[johnny means]

Where do you guys get the idea that plywood is stronger than MDF?

[Jim Dwight]

You can get there several ways. If you are not used to doing structural calculations you can just google up the "sagulator" and look at shelf deflection for different materials and you will find that MDF shelves deflect significantly more than plywood shelves (which deflect more than solid wood). If you are comfortable with doing the calculations you would know that deflection is controlled by the Modulus of elasticity. My quick search showed a value of 3.59 gigapascals for medium density fiberboard (MDF), 4.41-6.28 for oriented strand board, and 6.96 to 8.55 gigapascals for plywood. So plywood would deflect roughly half as much for a given load.

That doesn't mean MDF is bad material, only that it deflects more for a given load. It also tends to sag just from it's own weight when unsupported over a significant span.

[Greg Hines, MD]

Where do you guys get the idea that plywood is stronger than MDF?

I thought that was common knowledge, but here is an analysis:

http://www.diffen.com/difference/MDF_vs_Plywood

Doc