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

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

Attachment 17496


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

Attachment 17497Attachment 17498


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.
Attachment 17499Attachment 17501Attachment 17500


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.
Attachment 17503Attachment 17502


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

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.

Quote:

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Originally Posted by 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.

O

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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?

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

Quote:

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Originally Posted by GTJim

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

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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

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

Hi Don't see much of a problem here, you say width of rails 1160 so your straight edge will span that distance, to ensure the 1800 rail is straight set the master rail onto the grout leveled frame member and lightly clamp both ends, drill and tap the frame for the hole in the centre of the rail, work your way from the centre of the rail to the ends drilling tapping correcting and fixing the rail as you go, you will have a section of rail that can be verified straight with the straight edge, all you have to do is extend the straight edge 200mm each end to set the remaining portions of rail. the second rail can be set using a fixture with carriages set on the master rail and on the one your trying to bring into spec, most find that using the gantry works OK.
Regarding drilling and tapping you need a couple of jigs that will align in the countersunk holes of your rail, one to align the drill and one to keep the tap vertical.
Regards
Mike

Hi,
I have had exactly the same idea in my head for a week now :)
I will try to make my straight edge out of the "bridge" when leveling my long axis.

The two 3m aluminum tubes one way or another i should had bought them for general measuring use
Assuming that the extra cost is only the 500ml extra epoxy ( as for the above project will be needed 990ml), i will make a try
I Know that the result will be disputed
Of course i will use my straight edge against the epoxy surface to check the result
Mean while any advice will be welcome.
Thanks for your participation

Vagelis Personally I wouldn't waste the time or Money. You have decent length straight edge and using Technique Mekanik suggested will work for checking flatness of 1800 rails.

Did you made the straight edge?

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