wooden car stand (cribbing) project

I wanted to work under the car/truck when I needed and I don't like the regular car stands that rests on frame...prefer to have them sit under the tires. If you haven't seen any example..here is one:



Old design - 12" height and weights 44.6 LBs per wheel.

So I wanted make my own, but slightly modified in the design...similar to housing construction where the 2x4 left standing up instead of laying flat as shown above. So here are my proposed design pictures:

Side View

Top View:

So this will give me 13" of lift under the tire or 21" total to work freely underneath stock regular cab truck. If I place it under the frame rails... it'll be 14.5" of lift total. The dimensions will be 14.5" height (including wheel choke), 12" width, and 24" length. The other design is 100% safe and with the 2x4 studs laying flat, but this way I get more height and I think just as robust. Since the height vs width is almost equal...I doubt there will be any worry of tipping over. This design will weight about 42 lbs per wheel stand.

If I need more height...I can use the current stand and add to it another 3" to 16" total and weight would be 54 lbs per wheel stand.

So any structural engineer, architect, or construction folks want to comment about my design? I like some professional opinions. Thanks!


P.s. 285 size tires are still under 12" width...so that's why I went 12", since I doubt I'll ever use 285 size tires.

 

As someone who does framing for Habitat houses, I would advise you to revise your plan slightly. The 2x4 studs that you put vertically should be doubled up and centered over each other instead of staggered as shown. It would probably be OK as is, but you will see some sag in the 2x6. Nice vette; 64?

 

One word, JENGA!!!!

 

I dont know why. but that seems sketchy as fuck.

 

As mentioned earlier by nasaengr I don't like the vertical studs being offset from one another , it puts too much load on the 2x material that is on the flat

 

I'm no engineer, but first thing I thought was JENGA (as mentioned by bigfoote13), but have a little knowledge in wood and construction.. I do know that wood is stronger when force is applied straight down the grain like as if it were still a tree standing vertical, (in this case) next strongest would be applying force while it would be on the nominal side of 2'' or actual of 1-1/2''. I see that you changed the original design, which had a lot of boards laying flat. Although they are laying flat I would think that it would be extremely strong (in the center especially) where there is no spanning, (I would think that the force if applied straight down the center of that would be fine). I would think that the changes you made, there is more spanning on the boards laying flat (in center areas), so they'd potentially be under more stress, if the weight wasn't distributed evenly, (even thought some are laying on the side).
I'm sure you could get real technical and dive deeper on this tho. If I were you and were going to use the new design I may just add some to the center areas .
That being said, I'd imagine either design would be stronger than you'd think.

Whenever you do build some, I would use wood glue in every joining of a piece/'s of wood and clamp them together tightly and allow to fully cure.

 

Ever seen wood cribbing holding up a house that's been moved or jacked up , or big boats when they are on land getting worked on ?

 

Another structural engineer's opinion here...I agree with the other posters about aligning the vertical supports directly above each other. You want to create a load path that goes straight down, if possible. With the verticals located mid-span on the 2x6s, you're introducing bending stress. I'd also use SYP rather than hem-fir.

How do you plan to get the truck up on those supports? Worst case scenario for loading would be if only 2 wheels at a time are up on the blocks. Once all 4 wheels are elevated, the load will be more evenly distributed.

 

you see what the Corvette is sitting on ?

duplicate that exactly. that is super solid

your new design needs double verticals if you use it

 

The truck is 3300lbs... more weight in up front, but figure about 1100 lbs for front wheels, and 550 lbs for the back wheels? Just guessing, but it's 1 ft span to the next support. If you look at the picture, there's no third support which I added.

I was going to use some decking screws...that uses a torx screw or hex head. I bought some titebond II wood glue. I heard it was better than liquid nails or regular wood glue. Is that GRK RSS something I can get at Lowes or Home Depot? I want to do this project this week.

Thank you for that...that's the reason why I wanted professional opinion...I researched this quite a bit, but I'm not an construction architect.... so appreciated when experienced woodworkers comments.

The reason why I didn't align the is...assembly... how do I screw in the vertical support when they are right on top of each other...I have to go in at a 45 degree angle. If I stagger them, I can make a pilot hole and screw in from the top and bottom (with glue inbetween). Regarding the staggering, if there's 1 ft span...how would there be any flex or compromise. This is where I wanted experienced advise...would this be so bad? If you look at the original picture, there's no middle support...I have it...just staggered.

Do you know what the max load of a 2ft x 6ft x 1ft laying flat under support of 2x4 vertical? The numbers will determine if this will work or not. It's been a long time since I had my applied dynamics class...that's why I wanted professional opinion who can do the math for me...it's not something I could easily find online.

I plan to jack the truck up with hydraulic jack, then slide the two front car stands under the wheel, then jack up the back...so yes...worse case is 2 wheels at a time.

There's no middle support on the design you the Corvette sitting on...just the top where the wheels sit; that has the middle support.

 

If gaining a little extra height/strentgh is one thing you're after~ Why not, just go with the original design layout/construction plan (in first diagram).. Except flip some centers on side and double up for extra strength, it's stronger that way anyway.. And 2x's are cheap.. You could slightly widen footprint of outer dimensions of over all support to make up for height increase, if you're concerned about tipping.

And never underestimate the strength of properly applied/cured quality glue.. Really, glue creates such a good bond, you technically really wouldn't really need screws/fasteners.

However~ I think concerning your Q about how to attach (w screws) without going in at a 45.. I would build each level individually allowing glue to cure, you could run screws up thru the bottom of horizontals connecting centers (or sandwiched boards). After there all complete.. I'd start stacking them, applying glue at every contact area, then screw in from the top of that level down to lower level. I'd clamp everything and allow full cure on glue. That way you have screws coming in from top and bottom, pulling all the structure together (vertical) in the way the load will be forced on to it. I would also use clamps on everything while the glue cured.

Hope that made sense.. Or I worded it well enough.

There's really so many ways you could go about doing this.

 

I'm not too concerned about tipping... 13" versus 12" it's not that far over. The original design is heavier. This design is a little less in weight, but gain another 1". I made a new drawing and it's actually only spanning 8.25" max. That was the reason why I staggered, so I can screw top down and bottom up.

If you look at the latest drawing, the difference between the old and new design is 6.75" span versus 8.25" span.

So would this be really a problem? I wish I had solidworks experience and be able to model this up and see the forces applied. I had hope someone with architectural or engineering experience to punch up the numbers and tell me. I did email my old professor and see if he will respond.

 

I wouldn't use screws at all unless they were structural types like the GRKs or similar , no shear value

 

Okay...I'll go buy some GRKs... I don't have experience in this area...so take your wood working advice. Thanks

Update: Damn those screws are expensive..$20 for 45 screws

 

If your verticals are only offset by 1 1/2" , they would offer nearly the same support as if they were stacked , essentially if the load path is only offset by a 45 degree angle through the thickness of your pieces on the flat ( ie 1 1/2" )

Obviously directly stacked has the best load capacity

 

Or nails

 

If Nails are okay to use...what's wrong with the deck screws I already have...I plan to screw in every 3 inches or so. Those GRK RSS are pretty pricey. maybe overkill?

 

OZ mentioned he wouldn't even use screws unless certain type, I agree.
That's how strong quality wood glue properly applied will join the wood.. The wood itself would more likely break before the site of where the glue was applied.

If you properly build/glue this thing together.. You really don't even need screws.. ~ ~~Screws would really be for your peace of mind, which is why I mentioned your Q about screwing at a 45, I knew you were concerned about screwing this thing together.. But if you still wanted you'd be able to screw it in from top and bottom without staggering, if you built it the way I mentioned above. You'd be basically keep original design (without staggering, like your design) but just adding strength and some height.

Nails? I wouldn't use nails.

 

I hear what you are saying. I did read good things about titebond II. It seems my way to make it a little bit lighter and taller may cost a lot more....I'm not sure if the original design would need any special screws. I may just abandon the idea of the new design and go traditional, since it'll cost less and less worry about racking...that was my main concern. I didn't think the 8.25" spans would cause the wood to collapse. Really appreciate everyone's inputs.

 

That's going to the other extreme. I was looking at these structural screws instead:

$27 Simpson Strong-Tie SD10212R100 #10 x 2-1/2" Structural Screw 100ct

http://www.amazon.com/Simpson-Struc...1441745285&sr=8-17&keywords=structural+screws

Like I said early...maybe I will stick with the original design and screw top down with decking screws that I already have and use the titebond II glue. lose an inch and 2 more lbs, but no question about structural doubts... Damn...wish I knew someone with structural modelling program to give the answer... the traditional way...no doubts in my mind.