Thread: Measuring epoxy accurately by weight... can somebody please check my math please!!

That is assuming that the ratio by volume is 1:1.

An easier way to write the formula is hardener = 0.862 X resin by weight.

Champion! Thanks Bohdan. Yes, the ratio is 1:1 and H = 0.826 X R is a lot simpler.

Thanks for the speedy reply.
Cheers,
Ben

If you are using small quantities then why not buy it in the 24ml twin syringe pack which makes it unnecessary to measure anything.

BTW the price at Bunnys is also one of the cheapest way to buy it.

I like to finesse it a bit more based on work time/ temperature/hardness. EG add a bit more hardener for quicker/harder on a cold day set and a bit less for the opposite.
A set of $10 scales from eBay that allows you to work to about a small drop (~0.03g) will allow you to do that.

I just had to fill 3 , 40 mm by 4mm diam holes (1/2 mm per hole, 1.5 mm in total) in some carbon fibre rods and as it's pretty cold here today and I added about 10% more hardener. I draw it out of the bottles using disposable 3mL plastic pipettes and that allows me to put back what is not needed. The resin and hardener get put into a detergent scoop and mixed by sucking the mix back and forth into one of the pipettes and then use that to transfer the mix to the surfaces or holes. For bigger amounts I use 10 mL pipettes for even smaller amounts I have some 1ml Pipettes.

More cost than anything else Bohdan. The 200g pack is a fair bit cheaper.. I have scales on the bench where I glue up and thought I would give it a go. I know if you're careful the pre-packed syringes are great but I find they can cross contaminate if you're a little messy....mostly I'm just tight fisted!!!

Cheers Bob! I thought the araldite would have been a bit thick for the pipettes. I will order some and give that a go mate. What epoxy are you using?

One thing I noticed when mixing the 1:1 araldite is that if I did not 'guess' the volume correctly, the araldite would setup a little rubbery. It's one of the reasons I wanted to bring a scale into the confusion. I did not think you could mess with epoxy ratios the same way as you do with fibreglass resin and hardener.

I've always just measured it by volume by eye, both 1:1 and 2:1 resins, and I've never had a batch not set

Originally Posted by elanjacobs

I've always just measured it by volume by eye, both 1:1 and 2:1 resins, and I've never had a batch not set

Ditto. I understood the tolerance to be fairly wide. This document, which looks fairly authoritative, PTM&W | Epoxy, aeropoxy, vartm, rapid prototyping, and urethane tooling resins says 10%, but I seem to remember when using Boatcote to build boats that maker said 20%. Different formulations have different tolerances but I would think araldite would be at the wide end of the spectrum because not many people are going to be able to use those little syringes accurately anyway.

Cheers
Arron

The scales worked a treat! I should have added, the epoxy is for gluing handles onto machetes/knives and I was going for the maximum strength I could get out of the adhesive. Thanks for your input everyone.