How do I get a flat base....help

[mk1]

Ok, im going to hold my hands up here, Ive done a lot of work on my chassis and it is pretty much completely tacked together.....However I had a flood in my garage and didnt realise that to some degree this had warped the base board meaning it wasnt flat! Dumb...yes!

I have checked the dimensions and am not happy that it is accurate enough and realise that to spend more money on it i will need to take a backward step and rebuild it...after I have taken it to pieces.

Where I need the help is....how can I get a properly flat base? I have tried making a second one from timber but it is difficult to get timber also which is flat and checking it with an inclinometer shows this isnt quite right.....

Anyone who can lend some advice on this (or a flat base), your help would be very much appreciated.

Many thanks in advance,

Martyn

[Enoch]

I made mine out of timber. I constructed the frame and then used lofting chipboard to make the surface. Each piece was checked for level and where required thin pieces of ply were used to get it absolutely correct. I found that by the end of the build there was a very slight sag in the middle but it did not affect the chassis itself. It does seem like even the sturdiest of constructions will settle over time. My chassis was made in about 2-3 weeks so the settling was quite minimal. If I was doing it again I would use dexion or similar and would put in more vertical supports. Having said that my chassis appears to have come out as close to spot on as I can measure with tools that I have available to me. a mm here or there is going to make very little difference, I would say even 3mm would be nothing to worry about. Any more than that and I would be looking to redo it, others may have a different view.
Hope that helps a bit.
Enoch

[mr henderson]

The other approach is to not bother with a flat base! Yes, I know it sounds daft, and it won't work unless you have a laser that does horizontal beam, ideally mounted on a tripod.

Anyway, if you are so lucky as to have one, or can borrow one, then you can use it to good advantage in 2 ways. The first is to only bother to level up the bits you are actually working on, the chassis members themselves. Use the level ot project a horizontal beam across the board, hold a rule upright so it hits the beam, and find the highest spot (where the measurement on the rule is shortest, and mark it. Then any chassis part that rests on that spot is ok, and you just wedge up the other parts until they are level.

I have 2 RSJs that rest parallel to each other on blocks, they are levelled with the laser (they are not very level, because RSJ isn't perfectly straight).

The I have several lengths of decently straight 40x40x3 box which lie across like a ladder. Each of these is wedged up until perfectly level (usng the laser), and clamped in that postion.

Then all I have to do is to clamp each chassis rail to the cross rails, and we are taliking skooker table degrees of flatness.

If the laser does a vertical line as well (most do) then you can use that to project a centreline along the jig. Just fond the centre of each tube that goes across the chassis, get the laser shining along the centreline of the jig, then centre up each cross rail. Especially useful on the upper tubes as it iwill keep everything dead square, that way you know all your uprights have stayed vertical.

I'll post a pic if I can find one

[mr henderson]

This is from a couple of years ago, and before I had the laser, but it shows the basic idea. 2 rails welded on to keep everything stable, and so they can be marked for the centreline. Note the plastic wedges packing the RSJs level. Then the other rails are clamped on where needed.





Not necessary to do it to this level, of course, and it could be made of wood too, but all I'm trying to say is that as long as you have a means of checking for level, each and every time you use it, and you can wedge chassis parts (or even the board itself as needed) then you don't need a dead flat surface espeically as the chassis doesn't touch most of the board anyway.

The Dwewalt level I use is listed at £190 ish but I got mine from ebay for £150. I use it a lot, bloody good value and you would be surprised how many car building uses there are for it.

For instance, you want to set up a car, fist thing you need is a level floor. Garage floor, flat? you cannot be serious!

Anyway, shine the horizontal beam over the car, use a rule taped to a pole to find the hightest corner, measure the drop on the other three, then pack those corners up with cheap vinyl tiles from Wickes, almost exactly 1mm thick each. Result, car is on a dead flat surface.

Then you can use the vertical beam to check the camber on eacn wheel. I know there are other ways of doing it, but once you've got a laser you won't go back to those.

[Bonzo]

Nice informative post Mr H

I too used a tripod mounted laser level & as you say, 1,000 & 1 uses, very handy tool indeed

Me ?
Was lucky enough to have a stack of heavy duty 3" X 3" angle iron at my disposal .... Made a very sturdy frame supported by 6 legs, laid 3x2 timber accross the top, covered the whole lot over with water proof t&g floor boarding & finally capped the whole lot off with a full sheet of 2mm thick Zintec steel sheet ( Also laying about in the workshop )

It ended up as flat as you could expect in the home enviroment .... I expect that the wooden element of the table would have warped over an extended period but in my case the chassis went together quickly so I never had that problem to overcome

If you don't have loads of spare cash for expensive levels, you might be able to make good use of a plasterers feather edge.
Wickes do a good selection of them & some very long ones too .... They'll not tell you if something's level but it will tell you if it is all flat

[mk1]

Hi guys,

Thanks for all the advice. will have another look tomorrow. its only a few mm out here and there but I am a bit of a perfectionist and want it to be right.

Regards,
Martyn

[MikeB]

I think this is common with the wooden frame.
I made my table as per the book, it sagged in the middle i checked with the longest straightest edge I had. I added some legs to the middle of the span and tweeked until there was little or no gap under my straight edge.
Is used a long spirit level acros the width at various points to check it was consistent and not warped.
I'm now happy its good for a home build, I guess its accurate to 1-2mm.
A good check is when you tack the uprights to the base frame and lay the top tubes on do they all meet up reasonable well when cut to book dimensions and meet up with the seat back without too much tweeking.

Again I check all the top tube with my spirit level until I'm happy.

I had to take about 5 boards off the rack at B&Q until I found one that looked flat, that got me some odd looks and a lot of heaving! Think I bought the planed timber that was tightly bound into a stack of 4 or 6 that showed no obvious signs of splaying out between the pieces of timber.

Hope you sort it

[Headshot]

I have used 18mm marine ply and 75mmx50mm kiln dried planed timber to make a frame to attach the ply to, I then stood this on a pair of draper metal trestles, I leveled up using a laser level and a 3m long bubble level.

It took me ages to find straight enough timber and flat enough ply!

its still on the piss!!