Epoxy granite mill head support beam

[RotarySMP]

For the Deckel G1L frame which I rescued from the scrappy for €20, I want to make a BT30 spindle and head.

The support beam for it is E/G over a steel weldment.

The mold was made from a bunch of layers of MDF, bogged and painted.

The E/G recipe is 8% epoxy, made up to an approximite fuller curve using 5 appregates to Thomas Z's spread sheet. I vibrated the mold with an industrial three phase concrete vibrator.

Mark

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[RotarySMP]

After hardening for five days, today I removed it form the mold. The three layers of wax failed to performed there job, as the paint and bog has stuck well to the epoxy. I should have filled more slowly, and vibrated out the air as I went, rather than filling it full, then vibrating. There are quite a few air bubbles, reducing towards the top (as poured). Only feature at the bottom failed to fill. Over all I am pretty happy with my first practical E/G casting.
Mark

[Zekyx]

What is the black stuff? Any chance to upload the spreadsheet which your based you aggregate calculation upon? Did you vibrate the whole structure or you used small vibrator inside the casting (similar as used for concrete)?

Sorry for so many questions, I want to gather as much info regarding EG as possible.

Thanks for sharing your work!

[RotarySMP]

The black stuff is carbon (toner from a laser printer cartridge). I added about 5g. Without it, the white powdered aluminium oxide which I my finest aggregate makes for an ugly light grey Polymer concrete.

This concrete vibrator was bolted to the yellow board, and then the mold bolted and clamped to it. The whole thing was stood up on a 100mm thick Styrofoam block to stop the vibration going into my house. It was vibrated for about 10 minutes. This made for a 400mm deep mold vertically.

In hindsight, lessons learnt are:
- don't try using clamps with such a mold. The vibration is so severe, that they just loosen and fall off. I was constantly stopping to put then back on. You need to bolt everything together.
- If you cant vibrate and pour at the same time, layer in the E/G, vibrating out the air every 50mm or so.

Thomas's Spreadsheet has been posted here:
http://www.cnczone.com/forums/epoxy-...ml#post1750730

The finest aggregate is the most important. Try to source some really fine alumina or quarz flour. I got mine from a pottery supply firm. The other aggregates are simply what I could get from the nearest hardware store. I posted them here to this thread:
http://www.cnczone.com/forums/epoxy-...ml#post1652212

The test piece I made with 8% epoxy tested out with a youngs modulus of about 50Gpa.
http://www.cnczone.com/forums/epoxy-...frame-406.html

Mark



Mark

[CaptainVee]

Thanks thanks for sharing your work and (maybe again?) sharing Thomas' spreadsheet, I'd been trying to find it.

I entered some values but in looking at the results a BIIIIG question mark appeared.

I entered the specific density of the sand in each row, at 1700 g/liter. It is a value I found at some point and should be more or less the same for each grain size.

But at the end I found that one litre of the mix of grains still weighing 1700 grams.

Shouldn't that be creeping towards 2700 (density of quartz), as the point of mixing the grains is filling all voids between the grain with smaller fractions?

[RotarySMP]

Good point. I didn't pick up on that, yet was wondering why I ended up about 20% short each time I used it. That explains it.
Mark

[CaptainVee]

Have you checked the density of your samples?
I'm curious how close it gets to the 2.7 density of quartz.

[RotarySMP]

I did back when I made the samples as my daughter was doing density in science at school and I helped her with examples. Unfortunately I can't remember what the value was and have since thrown out the samples.

Mark