What is the rule to thumb for waiting to run the next toolpath when working with epoxy? Do you go off of demold, tack free or full cure times?
Any recommendations on epoxys that have shorter wait times and still give good results? I’m looking at MakerPoxy but I’m open to suggestions.
I usually wait 2-3 days. If you are going to carve into it you want it solid all the way through.
If the piece is small enough and the weather is good I will put the piece outside with a plastic box over it as a sort of green house. That speeds this up pretty good.
I tried UV curing resin but if you color the epoxy it never seems to cure under the outer shell.
I would love to find something that cures sufficiently in hours instead of days.
These will be be small pours. I’m using a coaster mold as the initial piece, the the following cuts will be for lettering which will all be .06-.1" deep. Then cut the final piece out of the coaster.
For small stuff if you don’t mind taking it off the machine you could get one of those pressure vessels to speed things up. I have not tried that myself though as even when I do coasters I typically do them 4-6 at a time on a single board.
2-3 days as @CullenS said is what I usually go by, but sometimes impatience wins and I’ll carve in resin after just 24 hours. I have not had any issues with that, but those carves have either been leveling of a single color, where clear is poured over it, or to insert a design element that will be filled, usually with another color.
If I’m going to level the top surface in preparation for final finishing, I’l wait the 2-3 days to prevent ‘smearing’ of any design elements across the surface.
There are way more experienced folks here who can probably offer better advice, but this is what’s worked for me so far.
So, I have done a fair amount of resin work over the last couple of years, and found that it is not necessary to wait for the resin to completely cure before machining it and pouring the next layer. Early on, using normal cure resin (like Total Boat or MAS Tabletop formulas) I typically waited ~15 hours . These days, I use fast cure resin (Total Boat 2:1) which hardens enough to machine in about 4-6 hours.
To be clear, the center of the pour will not be fully cured and will have a texture ranging from somewhat gummy to flaky. I’ve never had any problems making well defined edges/corners or with resin gumming up the tool.
Tips:
Ambient temp greatly affects the cure time. In the beginning I learned to bring my projects into the house if the shop temp was below 70°F. Now I use a heat mat, set to 80°F, under the stock to keep the temp up and speed curing. With an early start on a Saturday, I can usually cut and pour 3 layers.
My unscientific method of determining if a pour is cured enough is to gently tap on the surface with a tool or fingernail. It takes a couple of trials to get a feel for it but in general I’m listening for a sharp “click” vs duller “clack”. 
I’m also looking to see if my tool/fingernail leaves even the slightest impression. It kinda feels countertop hard, if that makes sense.
A more scientific method I’ve tried involves using an infrared thermometer to track the exothermic reaction. Theoretically, when the resin’s temp rises and then falls back down to ambient temp, the resin should be cured enough to cut.
Hope that helps.
Brian
That’s a lot of good information. I’ve worked with epoxy a little, but not where I was doing different color pours in epoxy. Looking to be efficient without ruing the project.
I read where MakerPoxy has a ~8hr wait time to sand. 6-8 hrs is more likely with what I’m planning and I can live with that.
I use MAS Table Top Pro for less than .25" depth. I can pour it by 10:00 PM and sand off t he over our the next day.
It depends on epoxy used. It is best to use the OEM recommendation about full cure time. Some deep pour takes a week and table top and other take 10-12 hours. Read the OEM instructions.