DIY straight edge with Epoxy+ aluminum profile. Will it work?

[ba99297]

Hi
I want to describe an idea that I had last days.
As it is very possible to use epoxy level for my machine and I will use a small amount of epoxy ( that will finally go to thrash) for some tests. So I was thinking if it reasonable to make the tests using two aluminum rectangular tubes 80X20 as follows.
We start with a 6 m long aluminum rectangular tube, cut into two pieces of 3m long each




We attach the two tubes with 2mm spacers( blue color)




At the edges we put two pieces of mdf as at the following pictures also with spacers between the mdf and aluminum profiles
We put the spacers so that we can cut the epoxy after cure.
Then we level the tubes, we fill with silicone the 2mm gap that the spacers will make and we pure epoxy.



After the epoxy get hard, we remove the spacers and we use a hacksaw blade to cut the epoxy

We now have (or we don’t have ????)two pieces of aluminum profile with a true surface.



MDF offsets are used to “absorb” the meniscus



We will need nearly 0.5*6.6*300=990ml of epoxy ( for this length )
1 X6m long aluminum rectangular tube
Spacers
Mdf strips
Of course somebody could use shorter tubes, even one only tube with mdf stripes left and right or cut the tube (after epoxy cure) to different lengths.

What is your opinion?
Does it worth to try?


I edit the post to make it more clear, ( after i read clives_s question that follows).
The main purpose of this DIY is to make a straight edge with low cost, instead of buying one that at this length will be out of the question.
The aluminum tubes that will be produced from the above process WONT be used as adjustable top beams where the rails will rest

[Clive S]

Then what are you going to do with them? You will end up with two rails that will bend when you move them.

One of the reasons for using epoxy is so that the rails that are fixed to the frame will be on the same plane.

Imagine a trough on the top of your rails that you fill with water it will be level in all planes it does not matter if the frame was twisted a little or out of level with the opposite rail.

[ba99297]

Then what are you going to do with them? You will end up with two rails that will bend when you move them.

O

I dont want to use them for constucting a machine, but to check the flatness of a machine, just the way i would do with a straight edge
The use of these rails is to use them as straight edge so that you can chek the flatness of a machine.
My question is if these aluminum tubes are reliable straight edges?

[GTJim]

Are you thinking of using these to get your rails straight?

[ba99297]

Are you thinking of using these to get your rails straight?

I already have a 1200mm long straight edge
It is enough to messusre my machine (1800mm long, 1160mm wide) between left and right sides.
For the distance of 1800 i will use the same straight edge in parts
If the above solution is reliable it will make my life easyer about messuring the flatness of 1800mm long rails
It is just a thought and i ask if somebody has an opinion about this
I dont think i am the first that has this idea
For me it sounds logical that it will work, unless i miss something

[GTJim]

Any straight edges above 1200mm that I have seen are very expensive. So I hope your suggestion works as I have yet to come up with a better one.
Jim

[Sasquatch]

It would never fly, even if epoxy came out straight whole thing would be hugely affected by temperature variations.