Need help with my bench build

[Dustin Keys]

I am in the process of building this bench:

http://americanwoodworker.com/blogs/projects/archive/2009/03/04/tom-s-torsion-box-workbench.aspx

This is my first significant project, and I'm doing it with a minimum of tools (circular saw, drill, beltsander, sawhorses, some basic layout tools, etc) and a lot of patience. Things have gone really well considering my basic skills and tools. The base lined up and assembled correctly on the first try, and there have been no major problems along the way. I've made a few minor mistakes, but I was able to correct them easily.

All was well, until last night. I have the base completed and assembled and the top completed and assembled. I set the top on the base, and discovered that the top rocks. I could have probably stomached a little bit of wobble, as the lag bolts should pull everything together nicely, but this was too much for my tastes. So, I need some advice on how to correct this before I attach the top to the base. When everything is positioned properly, there is a 1/4" of wobble at the front right corner.

Here are some observations I made:

1. The floor is level
2. The height of the 2x4s that the top will attach to are 29 13/16" from the floor on both sides of the front and 30" at the back.
3. Setting a straightedge and level across the 2x4 arms that the top will attach to reveals that the 2x4s are level across the base in both the front and back.
4. The base is rock solid - it doesn't squirm or budge at all
5. The top is reasonably flat. It doesn't wobble at all on the floor. When I sight down it with enough light in the right places, I do see some imperfections but they are very small.
6. The top of the base is not level in that the plywood skins and 2x4s aren't always perfectly aligned along the top of the base.

I think #6 is my main culprit. I was tempted to grab the belt sander and start trying to knock down the various 2x4 and plywood edges that I thought were high. I decided against it because it was late, I wasn't completely convinced that was the best solution, and once I've sanded the material off I can't add it back if I was wrong.

Since I'm new, I don't know what I don't know. The two most obvious solutions to me are to knock down the portions of the top of the base that I think are high or to add a shim to get rid of the wobble and attach the base. My problem with the shim is the size of it. I wouldn't be bothered by the idea of the shim if it was a small one, but it would have to be a pretty substantial shim to make things sit totally flat before I bolt the top to the base.

You guys have far more experience than I do and may have some better ideas, so before I start hacking on anything I was hoping for some advice.

Thanks for your help,
Dustin

[Carl Beckett]

Hi Dustin,

A great project, and once you get through the bumps along the way, you will enjoy the final results.

A couple of thoughts/questions:

How do you 'know' the floor is level? This is rare (especially if a concrete floor of a garage). One way of checking this might be to set up a new reference surface (say, mid way up each leg), and either with a laser level or a regular level check each point level to this by measuring back down to the floor. It seems circular logic, but if a particular leg is sitting on a low spot it might not be as easy to catch it. Or if each leg is truly the same length, maybe just level across the top surfaces (looks like what you have done in #2 - but check and recheck).

Also note that you can have a square workbench, and it will still wobble on the floor (this means the floor really isnt level), so lack of wobble doesnt necessarily mean level/square construction. Just something to keep in mind. If the base doesnt rock - this only means its on solid contact at each leg. It doesnt mean it isnt racked or tilted or one end higher than the other. (note a surface is defined by 3 points - so its impossible to get 4 points to be in a plane if you assume there 'has' to be variation/tolerance).

Look for forum threads on using 'winding sticks'. set these up on both the base as well as the top and see if there is any twist from end to end. This could be the case and you might not notice it.

Check for the squareness of cut on the plywood panels. If the plywood isnt cut square - you will by definition be building a non square structure. Measure diagonally across each plywood panel and be sure both diagonals read the same value.

It might be worthwhile trying to assemble this upside down. The top will first set a plane by touching only on the high spots of the floor. Then assemble the sides/legs onto the top (where the bottom surface of the top is the reference plane). It doesnt really ensure a flat surface, since the top can flex/twist - but it might help a little

1/4" off on one leg is pretty significant, so by going around it all again I bet you can find one of these items in error and close this gap significantly, if not completely.

Finally - dont hack! If the legs are identical lengths, and the plywood skins cut square on the corners - trust this first. Heck, maybe shim the legs up to allow the plywood edges to align flush to the frame and ASSUME the floor isnt level. Build a square and flat workbench - then shim under the leg to the floor to prevent rocking. Oh another test - just rotate it around 180. If it rocks in one orientation but not when you rotate it - again that means the floor isnt level.

Just some ideas....

[Dustin Keys]

Thanks Carl!

I did check the floor as you were describing, but I rechecked it anyway and it is level (at least in the area where my bench is currently resting). The garage is part of the original house slab foundation, so that may contribute to why it's fairly leve (may just be dumb luck too).

The way the base assembles, it would be incredibly difficult for it to tilt or do much of anything to throw the top out of alignment, but I tried everything I could to make sure. I can't find any evidence to indicate this is a problem.

I tried the winding sticks as you suggested, and this is where things got interesting... The base appears to be fine. The legs are ever so slightly out of alignment at one point, but certainly not 1/4".

I then tried placing a straight 1x6 on edge across various points of the base (especially the areas I thought were out) checking the alignment with a level, and even at the places I thought were the worst the base was barely off. Roughly 1/16" at the worst position, and that position wasn't really fair because it wasn't critical to how the top adjoins to the base.

Completely lost, I decided to investigate the top further. The skins are square. Actually they're perfect as far as I can perceive measuring them with a tape. Still lost, I set it on the ground to try winding sticks on the top while it was resting on the ground. The sticks weren't necessary, as I noticed it rocking as soon as I set it down. The top has moved somehow and is no longer flat. That's where my 1/4" is... Somehow it moved after it was glued and screwed. It was flat that night when I finished. I left it to dry the next day, and when I got home last night I immediately picked it up and put it on the base. It must have moved as it was drying.

This is really frustrating as I haven't the foggiest idea what can be done to salvage things now. I had options when I thought my problem was the base, but I can't think of anything to fix the top. Is there any hope, or did I just waste three days of work and $250?

D

[Joe Angrisani]

.....The top has moved somehow and is no longer flat. That's where my 1/4" is... Somehow it moved after it was glued and screwed.....

My first thought is Borg lumber. Were the 2x4s dried and straight, or were they fresh (and "dripping") from the store? My guess is one or both of the top's long 2x4s has warped, taking the plywood with it.

Any reason why you can't shim between the end leg assemblies and the top assembly before screwing it down?

[Kevin Presutti]

It wouldn't happen to be a parallelogram in either the front or the back, that would do it, unless you have the legs gussetted square to the base. That's where I would look first and since the front is 3/16" shorter in the front are the legs cut on a taper. A little wave in the top, a tick out of square, and angle on the top of the legs could easily be 1/4". Check the obvious stuff first, most of the time it is something very simple that gets overlooked.;)

Kevin

[Dustin Keys]

My first thought is Borg lumber. Were the 2x4s dried and straight, or were they fresh (and "dripping") from the store? My guess is one or both of the top's long 2x4s has warped, taking the plywood with it.

Any reason why you can't shim between the end leg assemblies and the top assembly before screwing it down?

I really have no way of knowing. The 2x4s are douglas fir and the ones I used for the top were the straightest and clearest of the lot (and I dug through two piles of boards to find the 17 I brought home - they appeared to be great choices). I don't know how to judge their moisture content. I did put some back that seemed good except they were heavier than the other boards which I took to mean they had a higher moisture content. I was also under the impression that the torsion box design would minimize these kinds of issues.

I have two options that I can think of unless someone has a better suggestion. One is I shim the space in that one corner as you're suggesting and attach the top to the base. In this case my top won't be flat, but I could mitigate that some buy making sure that the high corner is the tool tray corner on the face vise side of the bench. The other option I might have is turning the thing upside down to assemble it as Carl suggested. My hope in that situation would be that I could apply enough weight and pressure along with the lag bolts to pull the top back flat, but I don't know if that's even possible at this point.

Anyone have thoughts on these two possible solutions or another one that I haven't considered?

D

[Joe Angrisani]

....One is I shim the space in that one corner as you're suggesting and attach the top to the base. In this case my top won't be flat, but I could mitigate that some by making sure that the high corner is the tool tray corner on the face vise side of the bench.....

Yeah....scratch my shimming idea. You want the bench top to be flat and square. You NEED the bench top to be flat and square. A good bench becomes a fundamental reference surface in the shop. Was it Borg plywood? Lord knows that stuff "tacos" if you look at it crooked.

Have you tried assembling the whole thing? If the base pieces are square and even, and you are able to pull the top's torsion box down snug to the legs, the top should/could go back to flat.

Doesn't help you, but this is the main reason I don't like plywood-based bench tops. I'd rather have solid 2-by's that I can resurface to flat and true. If screwing it down doesn't pull it flat, I'd be half tempted to take the top back to the Borg, show them the warping, and get a refund on the plywood and 2x4s. Then I'd redo the top with doug fir boards I'd let dry, machine square (perhaps find a local woodworker with a kind heart and a jointer and planer), and laminate up. Pick quartersawn boards if you have to redo anything.

[Carl Beckett]

Some thoughts:

The path forward might depend on just how stiff/rigid that top really is. If you can set it on the frame (and you know the frame is square) - and pull it down with the lag bolts and the top conforms to the frame - then do that and be done. It doesnt matter whether you assemble it upside down or not, just that the top is the part that deflects to meet the frame (since the frame is square and the top is not). Now - if there is a clever way of clamping (with shims, clamps, braces, etc) to deform the top close to flat first, and then bolt to the frame - it will help. the question is how much springback will there be when clamped (and if a leg lifts off the floor - you know the frame conformed so not the path to go.

If this doesnt work - personally, I would go ahead and take one of the surfaces off the top. It will mess things up a bit, but get one side of it apart (maybe the underside of the top) - sand it smooth for a new mating surface - and apply a new piece. Once you have one side of the top off it should be quite flexible so deforming flat shouldnt be a problem. It means a new replacement piece on one side.

You could always try building up a layer of glue/goo - like construction adhesive - then putting a new layer on top of this and letting the glue accommodate the flatness gaps. This sounds messy and prone to other problems though

I agree with the others here that its much much better just to get the bench built square to begin with - it will be a reference surface for many projects to come.

This project isnt even close to being lost so dont despair - its just these things that woodworking is all about (when I built my last bench the solid lumber cupped and split my legs apart! Major reset on that one.

Also - read this thread:

http://www.sawmillcreek.org/showthread.php?173999-How-long-for-borg-KD-fir-to-dry


(http://www.sawmillcreek.org/showthread.php?173999-How-long-for-borg-KD-fir-to-dry)

[Dustin Keys]

OK. First I'll see if I can clamp it down flat. I'm afraid the top is too rigid to do that, but you never know until you try.

On replacing a skin, wouldn't the problem just reappear? If I'm understanding things right up to this point, the problem is that the 2x4 frame warped as the top was drying. Am I missing something?

[Carl Beckett]

OK. First I'll see if I can clamp it down flat. I'm afraid the top is too rigid to do that, but you never know until you try.

On replacing a skin, wouldn't the problem just reappear? If I'm understanding things right up to this point, the problem is that the 2x4 frame warped as the top was drying. Am I missing something?

This could be Dustin - the solution to this is to let it acclimate - even if still attached to a sheet on one side. Im wondering also if it might help to clamp it to the base before gluing/screwing the final surface on it.

Oh a thought - concrete, and large surfaces laying on concrete are prone to moisture problems. If you had this on the concrete floor to store or glueup dry, etc - it may have absorbed moisture that way (never store lumber on a concrete floor). Of course - you need a bench to build a bench!

[ian maybury]

This is untested and probably more than a bit unorthodox Dustin (thoughts/experience/cautions anybody?), but may offer some potential for a fix.

I'd be a cautious that the top (unless it's heavy enough to push everything down on the floor) may be stiff enough to pull the base/leg assembly out of true. I've also found that it takes considerable persuasion to remove the 'set' from plywood that's been badly stored - that storing it flat/under weights for a long period isn't alone enough to get the 'set' out of it.

If the base won't pull the top straight then my instincts would be to set to and arrange four or possibly six or more carefully positioned (as needed to pull the warps out) and levelled pads on a concrete floor - and set to to see if it can be persuaded to stay flat.

Stick them down using double sided tape or something. Level pad to pad using an accurate spirit level. Edge banding veneer is a very handy shim material in that successive layers can be ironed to each other. Then drill holes in the floor at each corner, and using expanding bolts and cross beams/cauls try cautiously pulling the top down flat. Go carefully in that you don't want to break anything

If the fir is still not fully dry it might just take on the required new set. It might be worth helping it all along with some heat and humidity, or it might need to be over corrected and let spring back. As in place some sort of temperature resistant waterproof fabric over it to form an enclosure, seal it down with tape and turn it into a steamer - use steam to do the heating before switching to a portable air conditioner to dry. The ply would need to be water and steam proof , and care would be needed to avoid any risk of fire though.

PVA, Titebond and the like will creep when heated - although it requires decent temperatures, and the sooner after initial application the better. There's temperature/time reactivation info for iron on use of those sorts of adhesives here: http://www.webherrera.com/blog/2009/04/19/titebonds-franklin-internationals-iron-on-instructions/ The fancier versions need higher temperatures and to be got earlier.

It could take quite a while to complete this process, in that while the initial steaming could be done in a few hours, it'd take quite some time for it all to get back down to the required moisture content. (days to weeks depending on how it's dried) There's no guarantee of success, or of not damaging what you have either.....

Plan B might be to strip off the top skin to let it straighten, and then re-skin it clamped down as above as everything dries and settles.

ian

[Dustin Keys]

Of course I had it on the concrete to dry after the glue up, so I may be to blame for this one. My reason for doing that was it was the only flat surface I had to put it on that could handle the weight. You really do need a bench to build one...

Joe, I did consider the laminated 2x4s and that was my original plan, but I just didn't have the tools to pull it off. At a minimum, I would need tons of clamps (I only have 4 small ones) and a big plane to make and level the top that way. It would have been much better to have a jointer and planer as well. The lumber alone was going to cost a chunk, so I couldn't let the tool cost get out of hand. The plan that I followed has been built successfully by a lot of people, met my bench criteria, and could be built mostly with the tools I already had. It seemed like a real winner at the time. Hopefully I can still salvage it!

D

[Dustin Keys]

This is untested and probably more than a bit unorthodox Dustin (thoughts/experience/cautions anybody?), but may offer some potential for a fix.

I'd be a cautious that the top (unless it's heavy enough to push everything down on the floor) may be stiff enough to pull the base/leg assembly out of true. I've also found that it takes considerable persuasion to remove the 'set' from plywood that's been badly stored - that storing it flat/under weights for a long period isn't alone enough to get the 'set' out of it.

If the base won't pull the top straight then my instincts would be to set to and arrange four or possibly six or more carefully positioned (as needed to pull the warps out) and levelled pads on a concrete floor - and set to to see if it can be persuaded to stay flat.

Stick them down using double sided tape or something. Level pad to pad using an accurate spirit level. Edge banding veneer is a very handy shim material in that successive layers can be ironed to each other. Then drill holes in the floor at each corner, and using expanding bolts and cross beams/cauls try cautiously pulling the top down flat. Go carefully in that you don't want to break anything

If the fir is still not fully dry it might just come straight. It might well be worth helping it along with some heat and humidity, or it might need to be over corrected and let spring back. As in place some sort of temperature resistant fabric over it to form an enclosure, and introduce some water (spray mist?) to up the moisture content again. Then heat the space up with a heater (it would need some experimentation to avoid overheating and the risk of fire) with an eye to getting the presumably fairly fresh glue to creep a bit before drying it all out again.

Even more off the wall - turn it into a steamer, and use steam to do the heating before switching to a portable air conditioner to dry. The ply would need to be water and steam proof though.

It needs to be fairly fresh, but PVA, Titebond and the like will creep when heated - although it requires decent temperatures, and the sooner after initial application the better. There's temperature/time reactivation info for iron on use of those sorts of adhesives here: http://www.webherrera.com/blog/2009/04/19/titebonds-franklin-internationals-iron-on-instructions/ The fancier versions need higher temperatures and to be got earlier.

The fir would hopefully take up a new set too.

It could take quite a while to complete this process, in that while the initial steaming could be done in a few hours, it'd take quite some time for it all to get back down to the required moisture content. (days to weeks depending on how it's dried) There's no guarantee of success, or of not damaging what you have either.....

Plan B might be to strip off the top skin to let it straighten, and then re-skin it clamped down as above as everything dries and settles.

ian

That's definitely an unorthodox approach, but it might be worth a try. I'm curious to see if anyone responds that has tried something similar. I used Titebond, and I glued the top up on Monday night. I'm not sure how long it takes to fully cure, but maybe it's not too late to try to coerce it a little?

[Jim Matthews]

A photo please, I have an idea...

[Dustin Keys]

A photo please, I have an idea...

Here it is. The corner closest to the camera or across from it diagonally are the ones that are 1/4" high depending on how you place it. I did try using clamps to pull it straight tonight, and while it works it also pulls the base out of alignment somewhat as there is a little bit of a perceptible rock if I step on the foot closest to the camera when it's clamped. There is zero rocking in the base without the clamps.

210019

D

[Carl Beckett]

Dustin,

If you do decide to take off the top, you might just run a circ saw down the length and take out the sections between the framing, leaving the plywood that is on top of the framing where its glued/screwed in place. Since you cut the plywood all the way through on each side of a frame member, there wont be any strength to it which will allow it to flex. And some panels/pieces will fall out this way.

Let it sit a week to acclimate. Pull it all down flat. Then just skin a new layer onto the top with glue/screws.

[Jim Matthews]

I posted this earlier, but don't see it here.

I suggest kerfing the bottom side, and applying a counter twist at the narrow ends.
The kerf in each case would follow the long axis, to free the skin effect from the bottom.
This would require two long spars, temporarily screwed into the ends. With some stout friends (or heavy weights suspended from the spars) twist the works beyond flat, as it will likely spring back slightly.

When you have the torsion box fully flexed (each high end down) affix it from underneath.

If this idea is repellant, the prior suggestions to shim the top so it does not rock, and laminate another skin at the surface should work.

jma
wpt, ma

[Dustin Keys]

I posted this earlier, but don't see it here.I suggest kerfing the bottom side, and applying a counter twist at the narrow ends.The kerf in each case would follow the long axis, to free the skin effect from the bottom.This would require two long spars, temporarily screwed into the ends. With some stout friends (or heavy weights suspended from the spars) twist the works beyond flat, as it will likely spring back slightly.When you have the torsion box fully flexed (each high end down) affix it from underneath.If this idea is repellant, the prior suggestions to shim the top so it does not rock, and laminate another skin at the surface should work.jmawpt, maA few questions on this idea. First, if I make that cut the top is no longer a torsion box, correct? Will it be strong and stable enough if I do that? Second, to bend it beyond flat wouldn't I have to insert some sort of spacer under the center of the top to make that possible? If so, would I or should I remove that spacer at some point and how would that affect things since the top is attached?Thanks, D

[Jim Matthews]

My recommendation is that the base becomes the point of fixation for the torsion box.

The stressed skin effect will be compromised by the kerf lines, so that you can get the works flat.
The alternative is to mount the T-box, as is, with shims and lay on a new sacrificial top that is flat and level.

[Tim Morton]

because I am lazy...i would build out the edges of the table with some 3/4" ply sides that were level, and throw an MDF top on. it would raise the bench an inch+. maybe even get fancy and build it so i could add an inlay of masonite that i could change when it got messed up.

[Jim Matthews]

D'oh!

Simple, easy to verify and within the realm of reason.

[Chris Parks]

If you were inclined to remove one skin, be damned if I would but you may think it is feasible, fix the bottom skin and frame assembly to the base and then fasten the top skin. The bottom skin and internal frame should bend enough but then I am only surmising there. Wouldn't building a level apron and installing a new top leave air gaps where the original fell away?

[Dustin Keys]

OK, here's my plan:

I'm going to make a cut through the bottom skin (maybe a few cuts if one doesn't do it), and try to pull the top flat to the base. I'm hoping that making those cuts like Jim suggests will free the skin effect enough to allow me to pull the top flat without bringing the base out of true. If it works, I'm going to bolt it to the base and call it a day for now. That will get me a working surface and allow me to get some projects caught up. If it doesn't work, I'll try removing a skin with cuts like Carl explained (leaving the ply strips on the frame), bending the rest flat, and adding a new skin. If that doesn't work either, I'll shim it and deal with the top not being flat for a short period until I can build a new top.

Ultimately, I'll probably build a new top, but I would like to salvage this one and get things going for now. My plan with this bench was that it would be something I could build with what I have now that will work for a few years as I'm acquiring the clamps, tools, and skills to build a good laminated bench. I still have hope that that is possible...

Thanks for all the help guys, I definitely wouldn't have come up with all of these ideas left to myself!

D

[Carl Beckett]

A good plan Dustin.

And I will bet a quarter (ok, a dime), that you use the heck out this bench and someday just make a new one, and keep this one as a secondary work surface. At least that is how it usually works out for me.

:)

[Dustin Keys]

A good plan Dustin.

And I will bet a quarter (ok, a dime), that you use the heck out this bench and someday just make a new one, and keep this one as a secondary work surface. At least that is how it usually works out for me.

:)

Funny you should mention that. The other reason I chose this bench design is that I thought it would be a decent assemply table if I do build a nice laminated bench later as the top would be flat "because it's a torsion box." But we all see how that worked out.... Oh well, you have to start somewhere and aside from this problem the project has gone well and I've learned a lot.

D

[Jim Matthews]

It bears mentioning -
this twist in the road says more about the quality of lumber used than your method.

Your methods are sound, and you're obviously careful. The same can't be said for the people that sold your stock.
Haunt Craigslist in your neighborhood for old guys moving out and selling their lumber.

If there's a boat builder nearby, they'll have offcuts.

Better still, bring coffee to a real lumberyard on quiet (not weekend) days to get help from the pros - they need your business and you need their expertise.

[Dustin Keys]

Last night I cut a kerf in the bottom skin of the top, and it didn't make any real difference when I tried to clamp the top down (one of the base legs lifted off the ground significantly). So, I cut another kerf between the two other stretchers on the bottom skin and had my wife lend a hand so I could tighten the threaded rod that pulls the base together as tight as I could get it. That combination did the trick! When I put the top on and clamped it down this time, I was able to pull it flat to the base. That leg of the base did raise off the ground ever so slightly (seems to be roughly 1/32"). I stacked a bunch of weight on top of the bench (christmas tree, cast iron vise, etc) to lend a helping hand and left it clamped down. After adding the weight to the top, the base legs are all flat to the ground again.

I left it that way last night, and I'll see how things are when I get home tonight. If everything appears to be good tonight, I'll spend the weekend building the front rail of the top with the dog holes and mounting the vises.

D

[Carl Beckett]

Great Dustin - the satisfaction/joy of woodworking. Solving problems is part of it.

But did you say one of the items you used to 'weight down' the top - was a Christmas tree?

(am imagining this tree growing out of the corner of your bench... in mid Oct no less!)

:p

[Dustin Keys]

Great Dustin - the satisfaction/joy of woodworking. Solving problems is part of it.

But did you say one of the items you used to 'weight down' the top - was a Christmas tree?

(am imagining this tree growing out of the corner of your bench... in mid Oct no less!)

:p

You read that right, but I probably should have clarified. This is an artificial tree still in the box. I was looking around the garage for heavy stuff, and the tree box is about the same size as the bench and heavy, so it seemed like an obvious choice. No live tree growing out of the bench at this point...

D

[Greg Portland]

Joe, I did consider the laminated 2x4s and that was my original plan, but I just didn't have the tools to pull it off.Dustin, I've built this exact bench and there is NO need for a laminated top... the torsion box is extremely strong and you'll be very happy when you've got the problems sorted out.

[Dustin Keys]

Great news... Last night I took the clamps off; and while it did spring back, it was reduced somewhat and more pliable than before (I could clamp it back down without the base lifting off the floor). So after routing the front of the top flush and positioning everything, I bolted the top down successfully and it's nice and flat. I did leave some weight on it as it will be a few days before I can attach the front rail and vises, but everything came together great.

Thanks for all the help! I'm really glad to have this sorted out without needing to throw the top out and start over. Once I had it bolted down, I worked it over pretty hard to see if it was going to rock, rack, shake, wobble, etc, and I'm happy to say it's solid as a rock.

D

[Jim Matthews]

Here's what I'll build after my dinner table project wraps up in November...

Ron Paulk (http://www.youtube.com/watch?v=sJoGTf6KL8s&feature=related) built something I'll adapt for an assembly table.