Bowl Casting 101

[Dave Bell]

A few months ago at a wood turning guild meeting (TVWG) there was a partially turned bowl placed on the draw table. The bowl was marked as being Silver Maple. It was a burl piece that had missing pieces around the bowls rim that had apparently come off during turning. My best guess is that the person who brought it to the meeting did not want to proceed further with the turning. Much to my surprise I was lucky enough to get through several draws before one of my tickets came up. I immediately picked up the bowl with full intentions of casting the bowl to replace the missing rim pieces. Here is the method that I followed to make a mold which lead to a new casting experience.

The first step was deciding how to fill the internal bowl section and figuring out just how much of the bowl needed casting. I decided to make a pine core to fill the inside completely. While I was making up the internal core I was faced with two additional problems. The first was how do I hold the bowl after casting to turn it again? The second problem was how do I pour the casting medium and fill the inside and outside at the same time? The bowl needed to be cast upside down in order to get the medium to the rim of the bowl. The bowl needed to be held at the rim end of the mold. The mold design was taking on the form of at least 3 pieces to encapsulate the entire mold.

The first piece of the mold was the internal core, which was followed by a transition piece that attached to the core and to the third piece which I will call the outer mold body. The core was turned to suit the internal bowl form and allow for a 1/8” gap for the casting medium. The transition piece needed to allow for a face plate to pass through it. The outer body was then turned to allow a 1/8” gap for the medium to flow through to the bowls rim.

After the core was turned a new problem developed and I was faced with the problem of turning the outer body of the mold. I decided to use the transition piece as a faceplate to hold the outer body and secured it by means of wood screws. The outer body was laminated together to build up a partial thickness of the bowls height. The inside of the outer body was cut on the scroll saw removing a large portion of the waste material. Once the cutting was completed, the remainder of the outer body was formed on the lathe and trial fitted to the bowls outer shape. The last piece of the outer body was added and hollowed out to fit the outer portion of the bowls base.

After the pieces were turned and shaped the entire bowl mold and the bowl were fitted together for one last inspection. When everything fitted properly the thought of air being trapped inside the bowl during casting came to mind. To solve this problem I drilled a vent hole through the core of the mold in the center. The mold and bowl were assembled and to help the casting medium flow better to the inside of the bowl, I added spacers (toothpicks) between the bowl and the mold at the rim. The bowl was then glued (CA) onto the mold core/transition piece with the aid of the tailstock to ensure the bowl was centered for turning after casting. With the bowl secured into the mold I added the outer body of the mold with wood screws and wood glue and clamps. After the glue was cured, the bowl was ready to be cast.
After the bowl was cast, I began to turn away the outer mold until I found the bowls form.

Stay tuned for more photos as the bowl reaches completion.

Dave

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[Donny Lawson]

I hope it turns out great. Cannot wait to see pictures.

[Chris Burgess]

Awesome idea. I have some super wormy Oak and this is exactly what I want to do to it but have not had time to really sit down and figure it out. Very creative. Thanks for sharing.

[David E Keller]

Looks like it's gonna be a neat looking piece! Alan Trout could provide a wealth of information about this kind of project... He likes to cast and turn really crappy wood!

[Scott Hackler]

Thats really interesting. I would be curious to the process you went through to prevent bubbles and voids. I know Alan uses a pressure pot and I have often thought that a vacuum chamber would work also. Also, what was/is you resin source. If its not super expensive I wouldn't mind getting some to experiment with a small chunk of wood.

[Dave Bell]

Thanks for the comments.


Thats really interesting. I would be curious to the process you went through to prevent bubbles and voids. I know Alan uses a pressure pot and I have often thought that a vacuum chamber would work also. Also, what was/is you resin source. If its not super expensive I wouldn't mind getting some to experiment with a small chunk of wood.

I cast worthless wood or fusion burl pen blanks and wine stoppers on a regular basis, so this is only new to me because it's a bowl. The resin is Alumilite and the dye is Alumilite Blue and the pigment is PearlEx Silver. The rule so to speak about pressure versus vacuum is that Alumilite is cast with pressure and PR is cast with vacuum (well it used to be for some folks). The reason for using pressure with Alumilite is that the resin sets up within about 5 minutes, so there is really no time for a vacuum to be created and draw out air bubbles. Another good practice is to avoid creating bubbles by stirring the two part resins/dye/pigment with a violent stirring action. This draws air into the mixture and this now makes the air bubbles a real problem. There are times when I do find air bubbles, but they are usually very tiny and can be fixed with some CA glue. My thinking is that any air bubbles associated with casting Alumilite are all due to the mixing process. Pressure does not remove air, it only compresses it down to a microscopic size if it is successful.

Contact Alumilite Corp and they can help you out with the dyes and two part resin. (Water Clear Alumilite) The pigments can be found at a lot of places that deal with art supplies. PearlEx can be found at Micheals, but it's expensive on their part. Look in the scrap booking section.

Dave

[Dave Bell]

Looks like it's gonna be a neat looking piece! Alan Trout could provide a wealth of information about this kind of project... He likes to cast and turn really crappy wood!

Thanks David. My source for working with Alumilite has been under some great advice from Curtis Seebeck (IAP) He also has a great knowledge on casting other things as well. He does a great Cactus pen blank as well as his usual pen blank process. He also has a new product for stabilizing crappy wood and it is called Cactus Juice. This allows the average user a way to stabilize their own materials. If you can afford a product made by loctite it is called Resinol 90C for stabilizing, but it is expensive.

I will look for Alans work.

Dave

[Alan Trout]

I now have a very large pressure pot so all my stuff is cast under pressure. I have done resin pours in excess of 160oz some are pretty big pieces. The pressure also aids in the bonding to the wood as it forces resin into the pours of the wood which I feel is very important. I know Curtis and I do some things different as I have found the tricks that work for me and the pieces that I make, particularly casting larger pieces. It really is not quite like casting pens. I have been requested to do a article for a magazine on casting these larger pieces and I will get into more specifics. Not sure when it will come out but I still have to write it.

Good Luck

Alan

[David E Keller]

Thanks David. My source for working with Alumilite has been under some great advice from Curtis Seebeck (IAP) He also has a great knowledge on casting other things as well. He does a great Cactus pen blank as well as his usual pen blank process. He also has a new product for stabilizing crappy wood and it is called Cactus Juice. This allows the average user a way to stabilize their own materials. If you can afford a product made by loctite it is called Resinol 90C for stabilizing, but it is expensive.

I will look for Alans work.

Dave

I know Curtis too! Great pen blanks and a heck of a nice guy! I've seen the cactus juice, but I've yet to try it... It sounds like those who have used it are having success. I'm looking forward to seeing that bowl of yours finished.

[Dave Bell]

Thanks Alan and David.

Alan I went back into the older posts and found your forms. Excellent work on them. I have a large PP myself (5 gal.) and I have about a dozen bowl blanks that can only be saved by casting. None of them are quite as fancy as yours, but they all deserve some sort of justice to make them usable forms. I'm looking forward to the next cast and to your article when you get the time to finish it.

Dave

[Dave Bell]

Well I finally had a break in my busy schedule to get this bowl finished.

Comments welcomed.

Dave

[Norm Zax]

Very NASA like! Beautiful!

[Donny Lawson]

Awesome looking bowl. I love the Earthly look to it. I would love to try some turnings from the "Trash wood" catagory. I bought some resin and a few colors and now I need to make some time. It looks like alot of time went into the making of the set up for your bowl so I will probally work with smaller items such as pen and maybe stopper blanks.

[Dan Hintz]

I'm still trying to figure out why someone would get rid of that owl in the first place... newbie turner, maybe? It was nice to begin with, but the blue swirl really complements the natural color.

[Bernie Weishapl]

Wow that turned out really nice. Beautiful piece.

[Dave Bell]

I'm still trying to figure out why someone would get rid of that owl in the first place... newbie turner, maybe? It was nice to begin with, but the blue swirl really complements the natural color.

Dan, tomorrow evening I am taking the finished bowl back to the guild and hopefully the individual who placed it on the raffle table can answer that question. I took note of a few things obvious when I fixed up some of the original roughness. There were several cracks with CA glue on them, there were missing pieces from the bowls edge and the foot for the chuck was very small, plus the bowls overall thickness was starting to get thin. Lots of vibration was encountered when the rim of the bowl was final turned also. Hopefully I have an answer tomorrow evening.

Dave

[Tim Rinehart]

Dave, very nice thread in total and a real complement to the casting techniques and some of the upfront work required for molds, etc to minimize resin and other tips to maximize outcome.
The finished piece came out really well...surprised to see it's maple, as it looks more like buckeye burl from a side angle with the color of the eyes. Probably the effect of the blue and reflections.
Really a gorgeous piece. Look forward to hearing reaction from original turner who started the piece when they see this!

[Dave Bell]

Well the bowl was mentioned as a highlight at the guild meeting tonight. Well received and a ton of compliments and a lot of questions about the casting process. However the person who placed it on the raffle table was not present (or didn't own up to it) tonight, so I can only assume the reasons they didn't want to finish this bowl off for one reason or another. I'm just happy to be lucky recipient and even happier it turned out so well. Thanks for all of the great comments and suggestions from all. I can't wait to post a few more already in the making.

:D

Dave