Has anyone tried fiberglass?

[martinw]

Originally Posted by JerryFlyGuy nope.. had a reply thinggy in me' inbox and replied.. who reads the dates anyway?

LOL, likewise.

Anyway, thank you Jerry for the negative CTE info for carbon fibre. I still think that if you use an epoxy resin to laminate CF, or polyester resin with glass, you may have problems. The resin CTE has to manifest itself somewhere, even if constrained by a very inert matrix.

Best wishes,
Martin

[JerryFlyGuy]

Don't tell Nasa... they use very specific fibre orientations for highly specialised dish's [say on the space station] which would have highly degraded performance due to the huge tempurature fluxuations in space.. [sunny side to dark side can be over delta 200deg F and they use this stuff 'cause there is very very little movement due to Delta T. If they ever found out it wasn't so!... imagine all of a sudden those dish's wouldn't work.. they'd be screwed haha.. ok all joking aside.. the resin portion of the matrix is usually less than 40% in pre-pregs etc.. there ARE some plastic's which have extremely high Coef of Thermal exp. UHMW is a good example.. the stuff will move 1/8" over 5ft w/ a 30deg C temp change.. but it's good to remember that not ALL will exibit the same ..... hey.. it's what makes life interesting..

[martinw]

Dear Jerry,

It is absolutely clear to me that I will have to "run up the white flag" before "painting myself into a corner" of increasing BS.. LOL.

Thanks for the composite information. Good stuff.

Best wishes,

Martin

[Robert For]

Interesting post this one. Are you missing a trick though by covering a board like MDF with glass.

I am well through sourcing bits and pieces for a 3-axis router project and have thought quite a bit about the material to build the frame out of. I have decided to build out of e-glass faced aluminium honeycomb boards which are availble comercially.

I have looked at the various home built machines and can see that as we do not have access to heavy steel fabrication equipment or castings then rigidity is going to be a problem. Since, generally smaller stepper motors or servos are being used, inertia balanced against rigidity is the key to a high performing machine.

It seems to me that honeycomb preformed flat panels are the way to go for a light weight rigid frame. These can be simply fabricated into rectangular tubes and boxes using cut and fold techniques. The boards can be cut using standard carbide router cutters. The boxes can be easily reinforced using egg crate internal bracing and then joined to form the 3d shapes required to build a machine (using epoxy resins). These panels can be ordered at any thickness at time of order. My idea is to provide local reinforcement for linear rails by bonding tufnol strips to the surface of the structure where needed. The tufnol would be drilled and helicoiled to provide rail mounts.

Have a look at the following website for info on this class of materials

http://www.technicalresinbonders.co....ructuralPanels

I use these boards ( there are many other suppliers ) regularly in the building and woodworking trades.

I am working on the frame design at the moment (3d model in Rhino) and would be interested to here comments on the idea. The catch is that the material is more expensive than MDF/plywood, I think the gains however would be massive in terms of machine performance. Careful detailing in the design of the structure ( see 80s and 90s f1 car chassis as best practice ) can yield amazing performance.

My machine is based around Mach3, a smoothstepper and a set of Mitsubishi drives and motors I have aquired. ( MR-J2S 400 and 750 watt motors ). I am looking at a 1100x800x300 working envelope with a fixed gantry moving table design

Many thanks

Rob