"shade tree" surface plate?

[stephen wilson]

I need to do some frame repairs, a want to construct an inexpensive surface plate. It only needs to be frame sized, so I was thinking of using a 4x8 sheet of Melamine, shimmed with floor tiles. But I'm not sure if this material is straight enough for my needs. I could also us 1/8" or 1/4" steel plate. Thoughts & suggestions ?

Related question: what are the odds of replacing much of the bottom frame rails on an RF80 without it ending up like a pretzel ? The chassis tube are built up from these lower rails, so it doesn't look I can just un-braze and replace them, because you can't access the underlying joints.

Thanks,
Steve

[brownslane]

Steve, don't even try with melamine...it won't stay still as you are working on the car and you (ideally) need to clamp down on the surface plate.

Better off to find a flat and level piece of floor...use that for measurements. To actually keep the frame straight and true, go get some 2X2 1/4 wall tubing, longer than the chassis. Tack weld it to the chassis in a couple of places to keep the chassis straight, then install your replacement parts. Don't worry if you have to X-brace the cockpit area or something...Do it! The tack welds will remove easily later.

If you don't jig your chassis, you will never get it straight and true again, and by tacking the tubes right into the chassis, you can roll it up on its side or even upside down to weld the offending areas.

Best of luck, Tom

[john f]

Many years ago I built a cheap but very strong and straight table from 1/2" & 3/4" b-c plywood. I first sawed up 8" wide strips that I built an egg crate with centers of 12" x 12". I then screwed and glued on a top of 3/4" b-c plywood and then covered that with a layer of 1/2". I formed angle legs from 10 ga sheet for the corners and had slots cut in the legs so the table could be slid up and down at each corner to level the table. I bolted the legs to the floor with a single anchor so nothing moved. The table will be as straight as you cut the egg crate strips. You can either screw or thru-bolt your frame or mounting points to the table and mount the frame from tubes or susspention pick-up points. I used my to build a new tub for a T-590 lola S2000 and when done the tub was square within 1/64" and so lever that I could not measure any twist. I also built a 37 ford sedan street rod with 460 ford/C6 trans on that table and it had no problem holding the weight. Today my wife uses that table for her "farts and craps". Just my $0.02.

john f

[stephen wilson]

Thanks guys. It sounds like I have significantly more work than just cutting and welding a few tubes!

When jigging, what are the critical areas to brace, mainly the tubes adjacent to the one being removed? In other words, if I'm cutting out a lower frame rail, do I need to brace the upper rail?

[john f]

Personaly, I would fixture just past the ends of where i am cutting out. That is assuming that nothing beyond what is being removed is out of position. With that said, you must determine what points are really important. I think that the most important points are the suspention pick-up points. From there, does it realy mater if something is out of position a little or not? Your engine and transaxle points must line up but if a tube is slightly out of position side to side? Rack mounting is important but you should have some way to shim position if needed on that. Another $0.02 IMHO.

john f

[stephen wilson]

I'll have to make some more accurate measurements, but the pick-up points seem to be pretty good. I only found this problem because I wanted to replace/bond the floor pan. The tubes are so bowed, dented, and patched so much, I don't think bonding is possible.

[preform resources]

Stephan, one tool that will help you out a lot is a height gauge, you can find 24" on line fairly easy for $100/125. the digital ones are more, and if you build your base reasonably flat you can take measurements within the same range as the (sometimes better) factory dimensions. As far as a quasi surface plate, John's method will work well or use 1.250 industrial particle board egg crated , check for flatness as you assemble it . Also, you can use a laser transit to set and check for flatness/level.Of course the problem with using wood is that it is hydroscopic so if you can keep it in a dry place it helps the life expectancy, if it starts going away , pitch it out !
Dave Craddock

[stephen wilson]

Thanks Dave. Yeah, the flat surface to measure from is my problem. I want to check for chassis twist to a reasonable degree of accuracy, at least within 1/16th of an inch.

[Darrin Teeter]

Steve,

You can purchase a "suitable" urethane or epoxy resin & pour a perfectly level/flat surface plate. All you need is some decent edging material & RTV to make a leakproof rectangular basin, then fill it up to the desired depth. Keeping the flies, cats, dirt, etc. out until it cures can be the bigger issue. Of course, it becomes a permanent part of your floor. There are some commercially available flooring systems that can be cast up to 1/4" thick. It's not cheap stuff, but probably a lot cheaper than a metal plate.

[brownslane]

Thanks Dave. Yeah, the flat surface to measure from is my problem. I want to check for chassis twist to a reasonable degree of accuracy, at least within 1/16th of an inch.

Stephen, again the easiest way is to get two long pieces of tube (ideally 2" square or so) and build them into a square. Tack weld them enough to keep them stable, and verify they are flat. I use a digital level (smartlevel) With the square corners, you have established points of measurement...with long, flat and immovable surfaces on the tubing, you have the ability to level the chassis and have an ability to tack the chassis to the tubing to keep things stable while you are removing/adding chassis parts. Additionally, you have an ability to use a jack or come-a-long to straighten anything you identify.

Finally, when you are done, you can store the tubing just about anywhere...or cut the tack welds and stack the tubing in an even smaller space. Two-inch square tubing is the standard for trailer mounts, hitches etc, so you could even use it for a new trailer-receiver mounted carrying platform...

A good, solid, repeatable, strong and inexpensive quality table that costs less than a hundred bucks and can be reused. No egg crates, no giant wooden table that you can't guarantee is flat or level, no pouring a thousand dollars of epoxy...

Tom

[Reddog]

[FONT=Calibri][SIZE=3]A good flat tooling plate 120” x 24” x 1.25" thick will set you back $1700, just priced one..you can set on a pair of matching tool boxes[/SIZE][/FONT]

[john f]

[FONT=Calibri][SIZE=3]A good flat tooling plate 120” x 24” x 1.25" thick will set you back $1700, just priced one..you can set on a pair of matching tool boxes[/SIZE][/FONT]

And in steel will weigh 1018# or aluminum will be 350#. And, when supported at the ends will deflect .23" and .2" with nothing on it.

john f

[john f]

Stephen, again the easiest way is to get two long pieces of tube (ideally 2" square or so) and build them into a square. Tack weld them enough to keep them stable, and verify they are flat. I use a digital level (smartlevel) With the square corners, you have established points of measurement...with long, flat and immovable surfaces on the tubing, you have the ability to level the chassis and have an ability to tack the chassis to the tubing to keep things stable while you are removing/adding chassis parts. Additionally, you have an ability to use a jack or come-a-long to straighten anything you identify.

Finally, when you are done, you can store the tubing just about anywhere...or cut the tack welds and stack the tubing in an even smaller space. Two-inch square tubing is the standard for trailer mounts, hitches etc, so you could even use it for a new trailer-receiver mounted carrying platform...

A good, solid, repeatable, strong and inexpensive quality table that costs less than a hundred bucks and can be reused. No egg crates, no giant wooden table that you can't guarantee is flat or level, no pouring a thousand dollars of epoxy...

Tom

Tom:

The problem that I see with a pc or two pcs of 2" tube is they have no stiffness. If you look at a 2" x .120 wall steel tube, 120" long, it will weigh 3.084#/ft or 37# total. If you support that tube at both ends the tube will deflect .102" from its own weight. Trying to keep the frame straight by attaching it to the tube is more like keeping the tube straight by attaching it to the frame. Stiffness is a function of height cubed (floor joists are on end, not flat). Using a 2" tube is like taking a knife to a gun fight. The egg crate is a hell of a lot stiffer than that, IMHO. Just my $0.02.

john f

[brownslane]

John, I respect your point, but please remember what we are talking about; a shade tree chassis table! Let me assure you that I have been building cars for 30 years now, and the steel square works. BTW, I do not mount the square on anything. I leave it on the floor. So it is totally supported over its length. And we are tacking a chassis; there is no way that a race car chassis would deflect 2X2 1/4 wall tubing!

I thought we were building a temporary and sufficient support frame to allow a guy to repair a race car chassis....we are not going into production.

BTW, I built a series of Formula C cars with just this described frame. Of 6 chassis, not one was warped, bent or twisted....all were within spec (ie flat) and square. So you CAN go into production!!


Respectfully, Tom

[stephen wilson]

Well, I like the Epoxy idea, as it would also serve as a set-up pad later. What I ( and my wife ) don't like is the $600-1000 price.

John, not being much of a wood-worker, how did you fasten the egg-crate sections, just butt them and screw & glue ?

Tom, I will use tubing to jig before cutting, possibly bigger than 2x2, but the tubing doesn't give a actual reference plane to measure from, since not all of the pick-up points will fall in a straight line. ( ie, on the tube )

Due to time & budget constraints, I will probably just create level measuring surfaces with cheap Vinyl tile and an 8' level.

[john f]

I notched the strips 4" deep on both the long and cross sections. Slipped together with 1" blocking on two sides diagonally with glue and screws. When installing the top, I have the notches in the long sections on top so any loading tends to try to close the notch of the long sections onto the cross sections Hope that makes sense. As a side note, a single layer of plywood on the bottom would increase the stiffness at least two-fold. A table 24" x 96" would handle the frame and can be stood up in the corner or hung from the ceiling when not in use. It also makes a great work bench top. Just my $0.02 again.

john f