Straightness of steel/alumunium box section

[ecat]

Brain is starting to fry, again!

This guy had problems with the concave surface of his ali profiles...
http://www.cnczone.com/forums/showpo...7&postcount=33

... his fix was a mix of long t-nuts and epoxy to flatten the face, but the area he was dealing with was quite small.

This got me thinking, could epoxy be used to to flatten all mounting surfaces on steel box and smooth over the dimension issues with ali profile? The above thread makes for good reading and at some point leads to this build...
http://oneoceankayaks.com/madvac/madvac_index.htm

This epoxy is amazing stuff, the two linked builds make heavy use of it to ensure the joins in the steel frames are true.

So, with enough epoxy, a precision level and a thick sheet of glass do you think it possible to true ali profile? The end result must be better than building with 1mm irregularities?

Two big problems:
1) The cost of ali epoxy, http://uk.farnell.com/araldite/arald...0ml/dp/1759545, need to add in the cost of a dispensing gun too, I think.
2) The fact that even with surface prep the special epoxy is not a guaranteed strong, long lasting join.

Since all I'd be using the epoxy for is to make the filling between two lumps of metal is it necessary to use ali epoxy? And indeed, am I obsessing over trivial detail ?

[Jonathan]

Not got time to look at those links now - about to go into school to make a few bits I can't do at home :)

Try this site for epoxy:
http://www.ecfibreglasssupplies.co.u...k/default.aspx

Maybe reinforce it with some of there glass/carbon fibre?

I've sortof assembled mine with just the box section as it is...and it seems ok. I'll have it assembled properly later on today, then we'll see!

[FatFreddie]

Two big problems:
1) The cost of ali epoxy, http://uk.farnell.com/araldite/arald...0ml/dp/1759545, need to add in the cost of a dispensing gun too, I think.
2) The fact that even with surface prep the special epoxy is not a guaranteed strong, long lasting join.

Since all I'd be using the epoxy for is to make the filling between two lumps of metal is it necessary to use ali epoxy? And indeed, am I obsessing over trivial detail ?

Hopefully you shouldn't need much epoxy, where you need to fill anything over a few tenths of a mm you could put glass fibre cloth in the space. It will be better to use a thixotropic or fairly viscous variant than the west system stuff which is designed to wet out composites and is a pretty thin liquid. I don't think you need to worry too much about bonding if it's trapped in a clamped interface - using epoxy to actually make the join is another matter and you would need very good surface prep and glue / material selection in that case.

I've a length of 3" square 1/4" wall aluminium that I'm intending making my router out of but I haven't had chance to do any measuring on it. I'm hoping it will be close enough that I can just use a thin layer of epoxy on the interfaces and by initially clamping the rails down very lightly until the epoxy sets ensure that they are not deformed by the box section. It'll be at least a couple of months before I get to that stage so I'm looking forward to reading how you get on

[Jonathan]

It will be better to use a thixotropic or fairly viscous variant than the west system stuff which is designed to wet out composites and is a pretty thin liquid.... It'll be at least a couple of months before I get to that stage so I'm looking forward to reading how you get on

Something like gelcoat then?

Just been to the local fasteners shop so now I can get these rails fixed down. I'm going to just try it without epoxy first and see what happens.

[FatFreddie]

Something like gelcoat then?

Gelcoat is usually polyester and relatively weak, I was thinking of one of the thixotropic epoxys like the 2015 you originally mentioned - the west system stuff is very good but rather thin for this application.