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Pressure pot vs vacuum chamber for alumilite resin casting

Breck Whitworth

Breck Whitworth

Joined
Nov 1, 2013
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Location
Gulfport, MS
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www.woodtreasuresbybreck.com
Which of these systems would you recommend for resin casting around wood for turning.I am researching because I just love what I've seen of many of the pieces where resin is used. The colors are beautiful. The alumilite seems to be very popular. Is it possible to just pour resin around a piece without using either pressure or vacuum and still get a decent bubble free result? Also is there a web site where you can purchase either of these type systems? Best resins to use? Thanks
 
100% chance you will have bubbles in the finished piece if you don't use a pressure pot. Lots of good info on YouTube about Alumilite and casting processes. Here's a video on making a pot:
View: https://www.youtube.com/watch?v=FJvsHP-wFSM

Most people who do this kind of thing a lot will tell you that if you're going to cast resin around wood, the wood itself should be stabilized first, which is a whole different process, normally using a product called Cactus Juice and a vacuum pot.

You might find it less expensive and frustrating to get someone experienced in all of these techniques to do it for you. I think the guy in this video (Casey Martin) will cast your wood for a fee.
 
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Alumilite is a urethane resin and a very short pot life. Most will put it under pressure to make the bubbles too small to see. Polyester resin has a long pot life and bubbles will in the most part float to the surface. Both have little tolerance for moisture in the wood. The wood must be bone dry for Alumilite, or it will react and foam. There is no "best". Alumilite is crazy expensive, but very easy to turn and doesn't stink too badly. Polyester resin is cheap, but can be incredibly brittle and chippy when turning, when using the recommended amount of catalyst. Polyester resin has a horrible smell and a lot of air movement is a must. If you shop is in the house, do your casting somewhere else! Most pen casters use far less catalyst so the pen won't shatter when dropped, but it can come out of the mold and still be sticky. A few hours in direct sunlight usually sets it up. Thick pours can be problematic as the resin really builds up some heat. Both are sensitive to ambient air temp and with winter coming it becomes an issue for many. Curtis is a great guy to start with with Alumilite. https://www.turntex.com/product/casting-with-alumilite

You have a lot of experimenting and youtube watching ahead of you. Unfortunately with the cost of Alumilite, learning and experimenting will be costly! I'd suggest going to pen turners.org Pen guys have been casting about the longest of any turners.
 
I use Alumilite and for my first attempt I tried to remove air with a good vacuum pump. The problem was the Alumilite began to set before I got all the bubbles out. My next project I used a pressure pot and i had success. You don't have long to work in either case so plan out your moves and have everything you need at hand. As well, if the piece of wood I am using is dry and not too large I don't use cactus juice to stabilize it before putting the resin to it. I prefer Alumilite over epoxy. I have never used the resin without a pressure pot except on flat work like a river table.
 
I have another question, go figure. I have seen people do alumilite or a clear resin pour into what looks like a plastic mixing bowl. Can heavy duty plastic wear work for a mold for a resin pour cured in a pressure pot? Is there a specific material besides expensive silicon bought molds that will work?
 
Breck Whitworth said:
I have another question, go figure. I have seen people do alumilite or a clear resin pour into what looks like a plastic mixing bowl. Can heavy duty plastic wear work for a mold for a resin pour cured in a pressure pot? Is there a specific material besides expensive silicon bought molds that will work?
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If it keeps its shape and is sturdy enough to hold the liquid resin any vessel will work in the pressure pot. However, if you don't use a mold release spray then your cured mold and the vessel will be permanently united and the vessel will need to be turned away on the lathe. I often use some small paper cups for for molds and they turn away easily.
 
The one thing different with Alumilite is that it doesn't shrink as much as polyester resin. So casting in a square container will result in you possibly cutting the mold open to get it to release. Not all plastics are compatible with Alumilite and other resins. Here is a good short article that may help. I also know that many casters use cheap UHMW cutting boards from Walmart to makes rectangular molds. They hold them together with wood screws so they can be opened up to get the casting out of it.
 
Richard Coers said:
The one thing different with Alumilite is that it doesn't shrink as much as polyester resin. So casting in a square container will result in you possibly cutting the mold open to get it to release. Not all plastics are compatible with Alumilite and other resins. Here is a good short article that may help. I also know that many casters use cheap UHMW cutting boards from Walmart to makes rectangular molds. They hold them together with wood screws so they can be opened up to get the casting out of it.
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Where is the "good short article"?
 
HDPE, the smooth version is what I'm going to work with for making my own mold(s). Silicone is a good alternative choice. Tap plastics or Amazon sell these materials or you can find pre-made molds from sources including Turntex, Turner's Warehouse, etc.

I can recommend the California Air Tools 5gal pressure pot (Woodcraft stocks them), though a Harbor Freight paint pressure pot version can be used w/ some minor modifications. I chose the 5gal because I wanted capacity to turn larger resin and wood-resin projects. The 5gal is plug&play right out of the box. I run it w/ just a small pancake compressor just fine.
 
Breck Whitworth said:
I have another question, go figure. I have seen people do alumilite or a clear resin pour into what looks like a plastic mixing bowl. Can heavy duty plastic wear work for a mold for a resin pour cured in a pressure pot? Is there a specific material besides expensive silicon bought molds that will work?
Click to expand...
i use white mdf wood Or called melamine . Screw together and use hot glue gun to seal all edges. Or you can use any wood box and use the red or blue insulation poly tape to line mold.

you are going down a big rabbit hole, have fun, the possibilities are endless.
 
I bought the California Air Tools - Pressure Pot from Woodcraft ($249). It is ready to go right out of the box. No matter which resin I have used so far I put them under pressure.

​

 
Glenn Lefley said:
i use white mdf wood Or called melamine . Screw together and use hot glue gun to seal all edges. Or you can use any wood box and use the red or blue insulation poly tape to line mold.

you are going down a big rabbit hole, have fun, the possibilities are endless.
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I am looking forward to what I will find and what I can DO with what I find down that hole. woo woo
 
Bill Blasic said:
I bought the California Air Tools - Pressure Pot from Woodcraft ($249). It is ready to go right out of the box. No matter which resin I have used so far I put them under pressure.

​

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It's in my plan also, thanks
 
Tom Albrecht said:
If it keeps its shape and is sturdy enough to hold the liquid resin any vessel will work in the pressure pot. However, if you don't use a mold release spray then your cured mold and the vessel will be permanently united and the vessel will need to be turned away on the lathe. I often use some small paper cups for for molds and they turn away easily.
Click to expand...
Mold release spray I am assuming (even though) I know that is dangerous. Can be purchased easily?
 
Tom Albrecht said:
If it keeps its shape and is sturdy enough to hold the liquid resin any vessel will work in the pressure pot. However, if you don't use a mold release spray then your cured mold and the vessel will be permanently united and the vessel will need to be turned away on the lathe. I often use some small paper cups for for molds and they turn away easily.
Click to expand...
Tom I have another question for you if you will be so kind to help me with an answer. Would you recommend 2 to 1 deep pour epoxy or 1 to 1 epoxy for a relatively deep pour for a woodturner?
 
Breck, stabilizing the wood is not necessary but having dry wood is. Any moisture in the wood will react with he urethane and make foamy white bubbles. I highly suggest drying your wood in an oven at low heat and then allowing it to cool back to room temperature.
Any kind of resin is expensive so doing what you can to eliminate waste is time well spent. If you are turning pens or pepper mills then rectangular molds are fine. If you are doing hollow forms and vessels etc that will take a considerable amount then creating a mother mold or shell around the piece that fits it well is time well spent. Pvc pipe is a great solution many times. I get scrap pieces from the water district people up the road up to 8" diameter.
A final safety note, there is no reason to run the pressure on the pot above 60-65lbs even if the pot is rated for more. You tube is full of videos of what happens when people exceed the pressure rating. You are creating a bomb if the latches fail. I have a 55 gallon pot with a lid that weighs 95lbs. I don't even want to think about what would happen if things went south.
Alumalite is a common brand but Smooth-on has good products too as well as many others. Go with a slow cure product so you have at least 20 minutes of pot life. (From the time you mix til the resin sets up you have 20 min). This will mean you will keep the pressure pot under pressure til the next day 12-16hrs later. The slower the pot life the lower the exotherm that the resin creates as it sets. The larger mass you pour the more exotherm is created. A huge difference between 1/2" thick and 3" thick.
 
DON FRANK said:
Breck, stabilizing the wood is not necessary but having dry wood is. Any moisture in the wood will react with he urethane and make foamy white bubbles. I highly suggest drying your wood in an oven at low heat and then allowing it to cool back to room temperature.
Any kind of resin is expensive so doing what you can to eliminate waste is time well spent. If you are turning pens or pepper mills then rectangular molds are fine. If you are doing hollow forms and vessels etc that will take a considerable amount then creating a mother mold or shell around the piece that fits it well is time well spent. Pvc pipe is a great solution many times. I get scrap pieces from the water district people up the road up to 8" diameter.
A final safety note, there is no reason to run the pressure on the pot above 60-65lbs even if the pot is rated for more. You tube is full of videos of what happens when people exceed the pressure rating. You are creating a bomb if the latches fail. I have a 55 gallon pot with a lid that weighs 95lbs. I don't even want to think about what would happen if things went south.
Alumalite is a common brand but Smooth-on has good products too as well as many others. Go with a slow cure product so you have at least 20 minutes of pot life. (From the time you mix til the resin sets up you have 20 min). This will mean you will keep the pressure pot under pressure til the next day 12-16hrs later. The slower the pot life the lower the exotherm that the resin creates as it sets. The larger mass you pour the more exotherm is created. A huge difference between 1/2" thick and 3" thick.
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Thank you for the info Don, I appreciate it.
 
I of course have other questions for any of you with experience. The type of epoxy resin to get. I have seen deep pour 4" and regular 2" pour? What about 2 to 1 or 1 to 1 resin mix types for bowls with various items of course inside to give character or a hollow form. Any recommendations from experience would really be appreciated. So much to learn I am excited again to try new stuff.
 
I use Alumilite Clear/Slow ... it is 1 to 1 by weight (not volume)
 
When using deep pour epoxy, you need to be careful. The deeper the pour the hotter the resin will get to the point of cracking. For anything over 3" deep, I use Aulmilite Clear/Slow. It is a polyurethane bases acrylic and seems to be able to take the deeper pours better.
 
Scales are cheap but very accurate in the process. I have been playing around lately with UV resins and what is nice if the pour is too big for the UV lights I have I can just set the piece in the sun for finishing. Great for filling cracks, can be colored and is bubble free.
 
Breck, There are three types of resins to choose from, polyester, urethane or epoxy. Polyester is fiberglass resin and sold in stores labeled "Clear Casting resin". It takes a small amount of harder to set it off . It is very volume sensitive and gets excessive temps easily and it really really stinks. I don't recomend it.
Epoxy resins are what is typically used for the table pours where gallons of the product are used. It can be a 1-1, 2-1, 3-1 mix depending on the type and brand. It can be used without pressure potting but pressure potting will improve the results. Guys usually use a heat gun or torch to make the bubbles pop as they come to the surface.
Urethane resins are sometimes a 50-50 mix but some of the more expensive crystal clear varieties are a 1-4 which makes calculating volume more problematic. Alumalite, Smooth-On, Polytek, and others have variations of these. The cheaper ones will have a slight amber tone, the better ones will be optically clear. The amber tone is not a problem if you are mixing metallic flake or other colors into the mix. The ones that are optically clear usually have more warnings on the sheet that they are for professional use only. Alumalite slow is a good place to start. Urethanes need to be pressure cast to minimize bubbles. Pressure casting does not remove the bubbles it just reduces the size of them .
 
The more I learn the more questions I seem to have. When using a pressure pot, can a bladder of some kind be used on the inside of a hollow form? My first impression would be NO because the pressure would compress the bladder and make a mess but I would like to hear from someone who knows a little more than me. Just looking for ways to limit the amount of resin needed for a pour inside a hollow form.
 
Make an inner form and cast around it if you will be doing any kind of hollowing out of the piece as wood is cheaper than the resin not to mention the mess of cutting resin. Here is a blurry pic of some resin turning.
 

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The alumalites are clear but some of the less expensive smooth on products like 325,326 and 327 are clear with a slight amber tone. Their 200 series products are crystal clear but higher priced.
 
Thank you Don and Frank you both have been a great help as I learn before wasting.
One more Question if I may:

When polishing resin and wood turnings is there a polishing compound that has proven to work better than say Yorkshire grit. I read where when using OB shine juice after using Yorkshire grit a mild cloudiness can develop that shows fingerprints. Any experience with creating that stunning high gloss finish I really would love to learn before having to try various things that may or may not work.
 
Breck Whitworth said:
Already ordered the California pressure pot a couple hundred dollars worth of Aluminite I already have the mica powders, just waiting on delivery my friend. Thanks again Tom, and all that answered all my questions. I can't wait to get started.
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You may already have a simple plan, so please don't take offense at this suggestion. I would recommend starting out with some simple projects like a pine cone in a small paper cup-- that could be turned into a bottle stopper. I see that you have plans to fill voids in some stock, but before you tackle your big projects, play around with it on a few smaller bits to get the hang of it.
Do you plan to make a shelving system for your pot so you can make several smaller pieces at a time?

What size pot did you get?
Where'd you buy the Alumilite?
 
Tom, I got the 5 gal. California pressure pot that was recommended to me on this forum. I bought the Alumilite from their web site.
I have another question maybe you can help me or someone else on here.
I poured a 1/4" deep 3/8" wide groove I cut into the top of the rim of a large bowl. I used the A + B clear cast, their instructions say to leave it for 48 hours before cutting it down and sanding. This seems like a lot longer time to wait before working it. But I am being safe rather than sorry. If it can be worked after 24 hours please let me know guys.
Breck
 
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