LocostUSA.com

Thanks to all for the excellent advice thus far!

I've been traveling like crazy for work and haven't gotten much done. This past week I workied on the build table some; 18ga 2X6 steel studs welded into a grid and then polysulphide glued and screwed to a 3/4" plywood base. When the glue has set I'll polysulphide glue the 3/4" MDF top on.

I haven't touched the Mustang yet. It's too cold outside, and who knows, maybe I'll sell it and use another doner for parts as has been suggested.

Here are some table pics;

It's definitely going to be strong enough. It's nice to get started, isn't it?

Cheers,

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Damn! That front slip angle is way too large and the Ackerman is just a muddle.

Build Log: viewtopic.php?f=35&t=5886

Yes! It is great to get this part going! I'll be buying steel soon.

How far out on Long Island are you from BNS? Just curious, my nephew lives in Oakdale and my biggest client has their offices in the Brooklyn Navy Yard.

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"There are times when a broken tool is better than a sound one, or a twisted personality more useful than a whole one.
For instance, a whole beer bottle isn't half the weapon that half a beer bottle is ..." Randall Garrett

Great progress on the build table. A note of caution, though, on mixing the MDF and plywood. The MDF top will be more humidity/moisture sensitive than the plywood bottom. The results will be a noticeable puckering of the table top over time. It doesn't take much swelling of the MDF to do this and the growth difference between the MDF and the plywood creates substantial bending forces. (Don't ask me how I know, and yes, I had steel studs in between. )

It's a real PITA to work with a "dome'd" table and I had to add a new (plywood) top in order to have a flat work surface.

As you already have the plywood bottom, I would recommend a 3/4" plywood top. You can get plywood with a nice "paper" top layer (I forget what its called) that makes a nice work surface.

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Cheers, Tom

My Car9 build: viewtopic.php?f=35&t=14613
"It's the construction of the car-the sheer lunacy and joy of making diverse parts come together and work as one-that counts."
Ultima Spyder, Northstar 4.0, Porsche G50/52

Hey Oldejack!

I'm in Bay Shore, about 15 minutes west of Oakdale and about 45 minutes drive from the Navy yard. Not too far out.

Seattletom - Wow.....I really want to go with the hardness and smoothness of the MDF top!

The plywood is 5-py with crossing grain, so I figured it's pretty stable. I've built a few cabinets with a combination of plywood and MDF and haven't seen any big expansion issues. Do really think that the MDF and plywood combination will bend my welded steel frame? I'm bummed

Ok, so After bit more research I am more comfortable with my plywood /MDF torsion table.

I agree that I did the wrong thing; it should have been MDF on the bottom. I had this plywood kicking around the garage for 2 years and needed to find a use for it!

I did some research and was directed to this pdf;

http://www.compositepanel.org/userfiles/filemanager/83/

Long story short, in the 96" direction they will expand about the same amount. In the ~48" direction the plywood may expand .10% more than the MDF from 40%-85% humidity. For the 48" that's 48 X .001 = .048" greater in length than the MDF, or +/- .024" from average humidity to super dry to nearly raining in my garage.

That's not too bad I don't think I can make the table any flatter than that, 100% MDF or not.

What did learn is NOT TO SEAL THE MDF ON ONE SIDE!!! This will cause uneven moisture in the MDF and surely cause buckling. I'm just going to leave it uncoaged and keep it out of the rain and not spill my unsweet tea on it (I hope!) I was going to paint/seal the top side with white lacquer.

Was your MDF sealed? Is this perhaps why you had such a pronounced buckle? Was your metal grid welded like mine?

That small change in dimension converts to a chord change with radius and results in bowing .... caveat emptor!

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Warren
Isuzu Pickup/SR20DE, +401 COLD frame
Build Log: viewtopic.php?f=35&t=11601

Paint all sides of the mdf and minimize the expansion/contraction?

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mobilito ergo sum
I drive therefore I am

I can explain it to you,
but I can't understand it for you.

The MDF was not sealed, the garage itself is/was quite dry, but rainy outside. The steel grid was not welded but held together with stout screw-in cleats and the top and bottom were screwed and glued to the grid. The table started billiard-table flat and quite strong, but after a few months the ends were at least 1/8" lower than the center and it bowed side-to-side as well. The top-center was the high point, and that was carrying most of the load.

Warren nailed it here. If you run the chord calculations, it doesn't take much differential to create a spherical patch with a non-infinite radius.

After weeks of constantly shimming the chassis to keep it level I added a sheet of the ply to the top, put one screw in the very middle and shimmed the entire perimeter. It is now billiard table flat again and I can adjust the perimeter shims to keep it that way. The resin-infused paper finished plywood is quite hard and smooth and nicer to work on than the MDF was.

But its your build and your results might vary.

Looking forward to following your build log. My wife's from Oceanside, L.I.

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Cheers, Tom

My Car9 build: viewtopic.php?f=35&t=14613
"It's the construction of the car-the sheer lunacy and joy of making diverse parts come together and work as one-that counts."
Ultima Spyder, Northstar 4.0, Porsche G50/52

Put a real engine instead of a plastic one on there and there's a good chance that high spot won't be so high anymore. At least that's what happened on my build table...

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Marcus Barrow - Car9 an open design community supported sports car for home builders!
SketchUp collection for LocostUSA: "Dream it, Build it, Drive it!"
Car9 Roadster information - models, drawings, resources etc.

Carguy - Yes, total encapsulation would be good, but I didn't want to paint the side I'm gluing to the steel studs, because I want a good bond to the steel and MDF and I'm afraid that the paint would interfere with the bond. I think I'm best off leaving uncoated.

Warren - yes, you are correct. I did do some cord pondering but my feeing is that at +/- .012" per foot the cord change is neglable, especially when you consider that the the plywood and MDF are not laminated together. They are separated by 6" of a welded steel structure that is cross braced. I can see how a small change in in length would make a big change in bow of the MDF if they were restrained together, analogous to a bimetallic thermometer strip. Somehow I can't see this bottom plywood piece affecting the top so far away. Of course; I could be wrong! Then I'd let the readers of my build know, make another table top with full MDF top and bottom, and then see what happens

Seattletom - thanks for the details! Wow...1/8" is a lot! Your steel webbing between the panels must have moved a lot too then? I'll look into the resin infused paper covered plywood, however it may have even greater stability than the MDF, therefore amplifying the problem you guys are anticipating for me.

To minimize MDF drooping at the edges, I'm running my steel studs right to the edge of the panels. This is one of the reasons I'm not using screws; I want nice clean steel areas for clamps to slide around.

Please don't take any of my comments back as argumentative I really, really do appreciate all the thoughts. I enjoy it

Hmmm, a pre-stressed build table might be a good thing...

Sorry for the hijack, LI-L. More on your build plans, please. Rod's 5.0 is a great choice for a reference. His build got my thinking started.

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Cheers, Tom

My Car9 build: viewtopic.php?f=35&t=14613
"It's the construction of the car-the sheer lunacy and joy of making diverse parts come together and work as one-that counts."
Ultima Spyder, Northstar 4.0, Porsche G50/52

Yes!!! Rod's build log got me started too! I must have read it 10 times, saved many of his photos for future reference, and even wrote him here but he never responded. I guess he's not much involved with the Locost these days. I saw he had many other cool projects.

So far I'm sticking with my plan to just "get it built", using as much as I can from the SVT Cobra, 442 frame upsized to 1.25", solid axle, pretty much like Rod's but with 4 link locating for the rear and normal coilovers up front. I'm also considering a rolled sheet steel tunnel instead of the 3/4" tubes. I read that chassis stiffening article

For now, I'm going to ditch the fuel injection and go with a carb. In the future, I'd like to do the ITB like Rod and Megasquirt. I'm going to stay pretty simple and cheap now and see how much I like and use the car. If it becomes a big part of my life then I'll invest in the works (408, Tremec, IRS, big brakes,etc.)

As far as the budget is concerned, I've saved up plenty. My troubles are;

I travel a lot for work, weeks at a time (petrochemical industry), so lots of interruptions and lot of time to think too much of changes!

Confusing rules to get it legally on the road in New York.