What's the best way to fix this assembly table / cabinet?

[Curt Harms]

I would add a truss cable underneath about inch and a half back. Use a strip of wood across the middle a inch in height less than intended height. Use a turnbuckle to tighten the cable and raise center of the chest back up. Could do it with all thread also. Use two pieces that go from each end and meet in the middle. Use an angle iron in the middle of you use all thread.
Good luck
Ron

I was thinking about a truss arrangement as well. Alternatively, I wonder how channel iron attached the 'flat' way compares to angle iron for deflection.

[Malcolm McLeod]

.... Alternatively, I wonder how channel iron attached the 'flat' way compares to angle iron for deflection.

Using the lightest weight of 3" ASTM C3x4.1 (C=channel; 3= 'height' in inches; 4.1 = weight #/ft; flange 'width' would be ~1.41"), and making the same dimension and load assumption as in my last post:

• with the web (3") horizontal :: max deflection = 0.102"
• with the web vertical :: max deflection = 0.012"

Using the lightest weight of 4" ASTM C4x5.4 (flange 'width' would be ~1.58"), and making the same assumptions:

• with the web (4") horizontal :: max deflection = 0.063"
• with the web vertical :: max deflection = 0.005"

In the last case, you're up over 60lbs of steel (12' x 5.4#/ft), so may be a bit heavy - and pricey, but again demonstrates the advantage of keeping the 'long' dimensions oriented vertically.

If using plywood, or worse MDF, over this kind of span I'd worry about creep.

[Zachary Hoyt]

In my experience the need for portability/temporariness and the need for strength and precision push in opposite directions. I would think you may need to decide which is most important and that may tell you which advice to follow.

[Marc Fenneuff]

Ribs don't need to be attached via stopped dados though, right? I could just screw full length ones to the bottom of the cabinet and it should still work. Correct?

I don’t see why not. The dados are mainly to register the ribs. If you can get the cabinet [flat] on its back you can attach them however you wish.

I agree that swivel casters added at the center could be problematic. The more heavily weight-rated, the easier they will swivel. Also, depending on how you “steer” the cabinet around, fixed casters could potentially work in the center. Lastly, also related to steering, is that you could still lock the casters if they were moved inward, at least, the trailing casters could.

[Michael W. Clark]

Do you generally park it in the same place when in use? And only move it for using the planer? If so, how about a piece of 1/2” plywood on the floor, then a 3-1/2” spacer in center of cabinet that sits on the plywood and supports cabinet when in its normal position? Or you could do same concept with a 3” caster in middle and may be easier to move on/off floor spacer.

Just brainstorming and trying to thing of something different that hasn’t been suggested.

[Frederick Skelly]

Just an aside. For me, this thread is an example of what I like best about SMC - everyone pooling their knowledge and experience to solve a problem and help someone out. I mean, there are a half dozen ideas here that I hadnt even considered and most of them look viable.

You guys rock!
Fred

[Alan Lightstone]

Just an aside. For me, this thread is an example of what I like best about SMC - everyone pooling their knowledge and experience to solve a problem and help someone out. I mean, there are a half dozen ideas here that I hadnt even considered and most of them look viable.

You guys rock!
Fred

Absolutely. I'm thinking of steel of some sort on the bottom. And one of the members here has volunteered to step up to the plate to help with that, so awesome.

I try to jump in and help when I can here, although many members are far more experienced than me. More often, I'm the one asking questions and getting great answers.

SMC is an amazing resource!!!

[Alan Lightstone]

Do you generally park it in the same place when in use? And only move it for using the planer? If so, how about a piece of 1/2” plywood on the floor, then a 3-1/2” spacer in center of cabinet that sits on the plywood and supports cabinet when in its normal position? Or you could do same concept with a 3” caster in middle and may be easier to move on/off floor spacer.

Just brainstorming and trying to thing of something different that hasn’t been suggested.

I generally do park the cabinet in the same place. Almost always except for moving it for the planer.

The suggestion of raising the planer I think was great. Never thought of that (although in my defense, raising an 800lb planer in the air was never high on my list, and I'll likely have to modify the dust collection ducts), but I would rarely have to move the table then.

[Jim Becker]

I think the steel is the way to go, Alan. You're basically reinforcing a bridge here...stiffening it up to reduce the effect of gravity across the span, both with and without load on top.

[Alan Lightstone]

I think the steel is the way to go, Alan. You're basically reinforcing a bridge here...stiffening it up to reduce the effect of gravity across the span, both with and without load on top.

Great. Now I have visions of Tacoma Narrows....

I'm also totally leaning towards steel. It's really interesting that the two angle irons I put on the bottom haven't done the job. Amazing how much deflection you can have in a cabinet, despite planning at least somewhat for it (but clearly not enough...)

[Jim Becker]

If the angle stock you used isn't doing the job, it's worth going heavy duty to preserve the piece and give you the flat surface you need up top.

[Malcolm McLeod]

Great. Now I have visions of Tacoma Narrows....

I'm also totally leaning towards steel. It's really interesting that the two angle irons I put on the bottom haven't done the job. Amazing how much deflection you can have in a cabinet, despite planning at least somewhat for it (but clearly not enough...)

... give you the flat surface you need up top.

Now that I may have 'sold you a bridge', I feel compelled to manage expectations and step back and (help) ask, "So how can this go wrong?! ...In a Tacoma-Narrows fashion.".

The data I provided is for a simply supported beam, and while the deflections hopefully show you the relative strength of each profile, you are building a structure - not a simple beam. I tried to guess what your cabinet might weigh, based on what I'd probably put in it - - YMMV. Wildly.

You may get a dead flat x-y axis on 4" channel, but the y-z axis (=in/out of drawers) may then look canyon-esque? Make sure you look at the entire structure. The casters will try to flex this z-axis, and so twist any beams on their x-axis. This impacts the moment of inertia of the new beams, and may allow more x-axis sag as well. :: Make sure the beams can't twist.

Mr. Jones made a great point: A good 'strong-back' and a symmetrical structure help tremendously. His strong-back is now presumably the web of the steel you are contemplating. You may not see his kind of total rebuild as a recovery path, but it certainly might help in future. Consider what your strong-back (beams) will be in the z-axis (:: the cabinet dividers and end panels). How do the casters transfer their loads to them?

Mr. Hoyt's point on conflicting uses is good too. Mobility, storage, and flat-surface-you-need-up-top are generally not used in the same sentence. Can you compromise on any of them? I get the impression that you would list 'flat' as your #1 priority at this point, but maybe this is just me. And my mis-reading between the lines. (Mr. Becker may be on the same page with me here?)

Just me, but starting from scratch to meet all 3 requirements, I'd probably model this very much like a workbench:

• A top flat & rigid enough for assembly (torsion box or thick butcher block), supported by solid contact with the floor (legs?), nothing trying to twist it;
• Levelling casters or workbench style casters that allow movement, but only used when moving (get the table off of them when not moving);
• Storage has two options:
  
  1. A cabinet sub-assembly, on its own casters, that rolls out of the way under the assembly 'table'.
  2. Build another lower torsion box on casters (steel or wood) - the table and the storage cabinet both sit on the box, with storage again nested under the table.

Like I said earlier, just throwing shhhhhtuff at the wall, to see what sticks. Try not to get any on you!

[Alan Lightstone]

Malcolm:

I totally appreciate the information that you have been providing. Having gone to college with a ton of engineers (MIT), sweating the details is second nature.

I'm not sure I understand your canyon-esque concerns with the in/out of the drawers. Can you elaborate as my engineering classes are 44 years in the distant past.

A total rebuild is out of the question, but flipping the unit over and reinforcing the daylights of of the bottom with steel beams is certainly a possibility.

I'm also strongly considering removing the 3/4" plywood top and changing it out for a 1-1/2" end grain butcher block workbench top. My present workbench is one with 1" holes, which drive me nuts not being 3/4", although I did have a machinist make some bushing adapters for me. But not a clue why Sjobergs built them that way. But I digress...

I'll have to switch out the casters to 3" instead of 4", but moving it only happens rarely. I'll look into heavy duty workbench casters for those, with 4 thick legs instead (4x4"s?).

I'm also likely going to raise the jointer so that moving the cabinet / workbench will be a far less likely event.

[Malcolm McLeod]

.. canyon-esque concerns with the in/out of the drawers. ...

I used the drawer's travel direction just to illustrate the orientation of the axis I was referring to.

The canyon may be just one of perception. You may get one direction dead flat, and then realize the other is sagging, either previously unnoticed, or newly induced by the fix. If it's me, I'm now re-considering the ill-conceived re-construction of my re-designed semi-planned Plan B. Or was that Plan J? ...I forget.

I think anyone who's built much with wood has had to deal with movement like this at one time or another - evidenced by numerous good ideas so far - and perhaps why I have the proverbial bit in my teeth on it! Drag the %@*& thing to Texas and we'll steel torsion box the $#^* out of it!

Over a Shiner. Of course.

[Jack Frederick]

I knocked this together yesterday. I believe it will take care of sag. Twin 2” channel, 3/4x10 rod couplings and Bolts. End flanges to secure assembly to base. Also a jam nut to secure setting. Fun little project. Fingers crossed.