Portable Wood Rack Stability

[derek labian]

I have a small workspace and so I attempt to put everything on wheels. In an attempt to make better use of my, low to the ground, wood storage space, I decided to build a rolling wood rack. Hardwood would be stored on the front, and sheet goods on the back. I can wheel it out from the wall when needed.

A few specs before I get to my question.

Its build of 2x6 pine and 4x4 fir. The pine is the body and the cedar is the bracing.
Each leg and post is 3x2x6 with an actual dimension of 5x4.5 or so. I used lag replacement screws for tensioning the frame. I used SPAX screws to reinforce. The frame joints are assembled with 4 4x28x140 mm dominos. The uprights are assembled with 2 of the same dominos along with a 6" lag replacement bold through the back side to the base frame to support the dominos. The front bracing is also assembled with a combination of lag replacement screws and SPAX #8's in various lengths.

The arms of the storage rack are 13 ply Russian birch 3/4" with 2x6 pine blocking. The pine blocking is also against and screwed into the the uprights for additional support. They are mounted to the upright with 8x1.5" SPAX #8's.

I have somewhere between 500 and 700bf of white oak on it.

My concern is, now that I have it assembled and the wood loaded on, is how strong those arms are going to be. I put the highest weight closest to the upright. Looking at it, I can see a cascade collapse happening etc. Thus far, it seems rock solid, i see no flexing of the shelves or anything else. Incidentally, it rolls easily too.

My thought is, I'll give it about a week to settle with all the weight and see if anything sags, or if it collapses or cracks. With that much wood and weight, it would be hard to see surviving it falling on you.

Thanks for any opinions!

[derek labian]

Btw, I didn't go with supported brackets because I didn't want to loose the storage under the brackets. I did go with steel supported L brackets for the storage at the top.

[Jim Becker]

Looks like a nice solution, Derek.

I don't see an issue with using the bracket design. They engage the uprights front and sides tightly and that helps with the stability, too. There is a small enough space between them that you're less likely to overload I would think.

[Lee Schierer]

The problem I see with your design is the size of the casters. They are quite small and all appear to be swivel casters. As you move the rack around you may have trouble controlling where it goes depending upon how level your floor is or isn't. The other problem may occur if your floor isn't perfectly clean. Those small casters are not going to want to roll past any small hard object on the floor. Your rack is going to be pretty tippy with such a narrow foot print. You will want to keep the heavier loads lower on the rack. Lighter wood and shorter pieces on upper levels. Please be careful moving it.

[derek labian]

Thank you for the feedback Lee and Jim.

[Ron Selzer]

Gotta agree with Lee
It will help when you load sheet goods on the back side
Definitely sweep the floor before moving this rack
Ron

[Scott Winners]

I don't know how good your climate control is, but lag screws versus Doug Fir, the Dough Fir will lose if you have much in the way of annual humidity swing inside the shop.

Good looking rack though. I do agree about sweeping the floor or installing biger casters next time the rack is empty. SOmtimes you gotta just pull the trigger, so kudos for stepping up.

[derek labian]

Thanks for the feedback.

I chose those small casters because I wanted the lowest center of gravity possible since the uprights work like a lever and the lower the center of gravity, the harder it is to tip to tip. I wasn't going for the easiest movement. I did add sheet goods to the back side but the weight isn't meaningful. This is a climate controlled space. It rolls easy enough although movement is limited and I'm going to add hooks to the base to allow it to be pulled from the base, instead of pushing on the uprights.

My primary concern is the shelves failing. As they say... So far so good... but I'll give it another week and check for and movement or sagging.

[Zachary Hoyt]

I made a movable lumber storage cart, but with uprights at the corners lag bolted to horizontal members, so the wood has to go in and out from the end. It's built on an old furniture factory cart with two big wheels and two swivel casters. I built it 6 years ago and have never moved it

If you have to move your cart a lot I would look for bigger casters, but if it's just every now and then it probably isn't worth the trouble. I don't think that pulling from hooks on the base will give you much directional control, especially if all 4 casters swivel.

[Kevin Jenness]

I have made several stationary lumber racks with plywood arms screwed to lumber uprights, but the arms are made stronger by being cut out of continuous vertically oriented strips. I don't see your arms failing, but they may sag over time unless glued.

That is a lot of weight for a moveable rack at about 4#/bd ft. I have a commercial shopcart 22" x 60" with 6" swivel casters and it is all I can do to move it alone when fully loaded with sheet goods (1/2 ton or so), especially when reversing direction. Loading sheet goods on the back side, leaning against the uprights, will increase the load on the front braces. It wouldn't be a bad idea to add some plywood gussets down there. I would be careful about overloading that rig. A sudden stop against a piece of scrap on the floor could be a real problem, especially with much weight up high.

This is the lateral parts cart I have, very useful when bringing in sheet stock for a project and organizing cut parts for assembly https://shopcartsusa.com/Product-LateralPartsCart.html

[Tom Bender]

Where the arms connect to the uprights I see two potential failures, one in tension and one in compression.
. the top of the arm is in tension and the few screws look inadequate, they could tear out or the arm could split thru the screws. This could be improved by adding 12" x 1" x 1/8" steel straps. Put a 3/8" bolt thru the post and at least 4 screws into the arm.
. the bottom of the arm is in compression and also looks inadequate. This could be improved by adding blocking there.
. I suggest making a quarter size model and testing it to failure

The height is concerning. You could install a shelf about 5' above the floor and use it only for storing light boxy stuff. I'm sure you have a good supply of that.

To stiffen the frame you could add a 1 x 3 stretcher across the base, preferably a few inches back from the front, on the bottom or recessed into the top. Same at the top if you don't do the shelf thing.

[Robert L Stewart]

I agree with Kevin and Tom, more re-reinforcing would help. I would not stand in front of the lumber side especially when moving it.
The total weight of solid stock can be deceiving. A quarter size model could be a revealing project.

[derek labian]

Since so many of you mentioned tipping, i ran some calculations. Depending on the weight of the wood, and assuming a velocity of near zero, ie just tipping it, and assuming mostly equal distribution of weight, would require a substantial amount of force, even applied high up. I expect at least 400 lbs assuming the wood is near 3000 lbs. if the wood is heavier, more force. If it's rolling rapidly, less force. I think it will be ok. Rough calculations, but I tried to calculate on the safe side. Based on where I think the actual center of gravity is and the actual weight, I think it requires more like 700 lbs.


I agree with Kevin and Tom, more re-reinforcing would help. I would not stand in front of the lumber side especially when moving it.
The total weight of solid stock can be deceiving. A quarter size model could be a revealing project.

I think that would actually be a pretty fun project. I think I'll give it a go. (stationary since I can't scale down the casters)

[derek labian]

Hi Robert,

I built a scale'ish model and it proved out the math effectively. I tested at the top of the upright so I could its the worst case scenario. In real life, you would be applying pressure mid-way.

The empty model tips over backward easily, no surprise since the uprights are skewed to the rear of the base. It doesn't tip forward easily at all. I doubt I could tip it when its an empty rack.

The math showed the heavier the mass on the rack, the harder it was to tip. Suffice to say, if it couldn't tip easily empty, it wouldn't tip loaded. I put white oak scraps on the rack to test. Indeed, it was significantly harder to tip, forwards or backwards. The amount of torque required goes up as the mass increases.

So I think the calculation was probably accurate, 700lbs of force applied to the top of the post to tip a 3,000 pound rack in the configuration I have. Easier to tip backwards, but still not a risk.

This was a static test, if the object was rolling, it would reduce the force needed to tip it. I didn't calculate that, however the rate of movement I plan won't significantly change these numbers.

While I didn't build shelves, the effect of the test is the same, all the weight from the uprights is bearing down on the legs at the same point.

I could have done more to test this, but my goal was just to prove out that the more mass that I added to the rack, the harder it would be to tip even at 8' tall. For the full size rack, it was very stable when it was empty, I checked it for tip-ability before adding the shelving.

[Kevin Jenness]

You're going to move a 6 1/2 foot tall rack around that weighs as much as my car on small swivel casters, with brackets and bracing that even you have doubts about. What could go wrong?

My dad used to work with an older guy, more experienced and set in his ways. When Dad tried some novel approach Milton would say, "Go ahead and do as you've a mind to, you're going to anyway- you goddamn nut!" Good luck.

[derek labian]

You're going to move a 6 1/2 foot tall rack around that weighs as much as my car on small swivel casters, with brackets and bracing that even you have doubts about. What could go wrong?

My dad used to work with an older guy, more experienced and set in his ways. When Dad tried some novel approach Milton would say, "Go ahead and do as you've a mind to, you're going to anyway- you goddamn nut!" Good luck.

What is your point, that you don't like my design? You are seeming to imply that I dismissed your concerns or comments. I can't see how this could be further from the truth.

I did the math and it looks very safe.

I built a scale model, very stable, more weight, more stability, just like the math.

If you read my OP, my concern was mainly around cantilevered shelf stability. That is still my honest concern, but no sagging as of yet.

Here's the feedback you provided, although I felt it was already addressed.


That is a lot of weight for a moveable rack at about 4#/bd ft. I have a commercial shopcart 22" x 60" with 6" swivel casters and it is all I can do to move it alone when fully loaded with sheet goods (1/2 ton or so), especially when reversing direction.

As stated in my previous post, the additional weight makes the rack more stable, and not less stable. Yes, its very difficult to move, and reversing the direction isn't ideal, but not bad enough to change them out.


Loading sheet goods on the back side, leaning against the uprights, will increase the load on the front braces.

I believe it's negligible, to the point of being irrelevant. I just don't think that much force, in comparison to the cantilevered shelves with white oak, is applied. It might be worth while to reinforce the uprights with steel L bracket though on the sheet good side. The uprights are glued, lagged, and tenoned into place though.


A sudden stop against a piece of scrap on the floor could be a real problem, especially with much weight up high.

Yes, I agree, and I addressed this in my previous post which was a static calculation. Moving something with that much weight has to have very low velocity. It also safest to move from the base. I'm adding a pully system to make it easy to push and pull from the base.

I will say again that I'm not wheeling this all over, its being moved like 2' at most once in a while (once every month or two).

[Kevin Jenness]

If it works, it works. Time will tell. The idea of moving that much weight around on the rack you have built leaves me skeptical, but it's your call. It doesn't hurt my feelings in the least if your judgment is different from mine. Milton wasn't always right, he just had an amusing (to me) way of expressing his disagreement. I meant no disrespect and I hope your solution works out long term.

[derek labian]

If it works, it works. Time will tell. The idea of moving that much weight around on the rack you have built leaves me skeptical, but it's your call. It doesn't hurt my feelings in the least if your judgment is different from mine. Milton wasn't always right, he just had an amusing (to me) way of expressing his disagreement. I meant no disrespect and I hope your solution works out long term.

Fair enough. I'll post an update in a year. If I don't post, you know it didn't work out so well :D

[Tom Bender]

Hi Derek
Nice job on the model. Actually I was suggesting making a model of the arm to upright joint and test that to destruction. My concern is mostly with the potential for a failure which could cascade like the World Trade Center.

And my concern about height is getting lumber on your head.

[derek labian]

Hi Derek
Nice job on the model. Actually I was suggesting making a model of the arm to upright joint and test that to destruction. My concern is mostly with the potential for a failure which could cascade like the World Trade Center.

And my concern about height is getting lumber on your head.

That is also my concern. Very time consuming to build a scale there. I think it would almost certainly cascade if it failed. I mentioned I may reinforce the 2x6 brace against the upright with an additional 4x4 wedge. Right nownimnjust going to check for sagging.

I think it would be easier to take a full size shelf and check the failure load. You can scale that out. Maybe I'll that.

[Steve Tripp]

I also agree with bigger casters. I have almost all of my tables and storage on wheels and they are the first things I'm going to upgrade. In my case, 4 inch wheels "may" be large enough.