coefficient thermal expansion on disimilar materials (epoxy resin, steel, aggreggate)

[gregbest]

epoxy expands at a higher rate than that of steel for example. does adding filler to the epoxy (silica, aggregates) lower the coefficient of thermal expansion? I see eg machines using steel components (column bases,machines with steel heads/tables with eg base.

a machine made from all cast iron would expand at the same rate I am assuming, but is it ideal?

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[peteeng]

Hi - epoxy has an expansion co-efficient of around 45micron per deg per m. steel is about 13 aluminium is 26. If you have a mixture of materials it obeys the rule of mixtures. So if it was half steel and half epoxy by volume (not by weight) it would be (0.5x45) + (0.5x13) = 22.5+6.5 = 29 rocks and granite are on the low side about 9..

The expansion rates do not matter as long as they were set up in a consistent temperature and stay in a consistent temp. If you are trying to machine something today at 35C then tomorrow at 20C you will not produce thwe same result. By ideal are you asking if cast iron is ideal? Peter

[gregbest]

self leveling epoxy on steel, would the the epoxy expand to a greater volume causing de-lamination?

I have in mind is to build an eg column/base with steel for the mounting surfaces. In order to tram the column to the base, I will inject epoxy (with reinforcement fillers) between the steel.there are tram epoxies readily made that contain steel fillers. I want to make my own tramming epoxy, will using a filler that has a lower co-efficient than steel something i should aim for?

I was asking if keeping the all components of a machine the same material ideal for accuracy.

[peteeng]

Hi Greg - If the design has features that use multi materials in a way that when they expand conflict then its a problem, Some materials are used so they counteract each other. For accuracy a conditioned environment is a must. For instance a tool room quality workshop is air conditioned. Peter

[Eldon_Joh]

if your epoxy is 1cm thick then the thermal expansion of 10C would be 4.5 microns.

my guess is tramming epoxies are filled with various fillers to prevent creep. not restrain thermal expansion. 1cm gap is huge.