Molding An Hour Glass?

[Iceman065]

I am in the process of making the hour glass from the following picture.

I am making this for a local high school that is doing The Wiz. My college will be footing the bill on the molding materials but that doesn't mean that I am not on a budget!



Currently the plan is to make a Hershey Kiss shaped object for one half of the hour glass. It will have an extended top portion so that it can be cast twice using some Smooth-On 325 Amber Restin. The Positive "kiss" shaped object will be made out of foam that I will put 2 coats of Killz over to seal it then it will be painted with 30 or so light coats of spray paint in order to help smooth it out and also so that I can do any final touches to get it smoothed out.

The bottom squared off section is so that a circular ring can be carved into the wooden bottom for the entire piece to sit in securely once cast.



Right now the issue that I am having is trying to figure out the best way to cast it!



Currently I am thinking of making a barrier out of masonite that would make up the outer part of the soft mold. The inner part would have a dowel rod running down the center with a piece of rubber from a bike tire wrapped around it in order to use less molding material. The biggest issue is trying to figure out if the inner portion of the mold will be able to squeeze together enough (even if i make some kind of inflatable blatter)to come out of the mold. I have never worked with rebound before so I don't know if i need to be worried about it tearing if squeezed together.



The Smooth-On 325 resin will have some bubbles in because I dont have a vacuum chamber that I can put the entire mold into once the resin has been poured.



Please let me know what you guys think! I am open to all kinds of suggestions.

 

[NZTK]

Are you trying to make an hourglass with that exact configuration? or just a general hourglass. What size is it, and what is your budget?



If it were me, I'd have the glass portion turned on a lathe in wood which I'd then give a good thick clear coat to cover any wood grain, then make a two part mould and (roto) cast the part in water clear epoxy, be careful of the casting resins fluid resolution, if its too thick, you may loose your hole between the two sides... drill a small hole in the cast part and put the sand in, plug the hole. The three dragon frame supports are fairly straight forward, sculpt one cast three. the bases I'd have routed in MDF and texture added topically if required, though for stage purposes, effects painting (wood graining) is faster and will look just as good to the audience,

degassing is not usually done in mould btw

 

[Iceman065]

Are you trying to make an hourglass with that exact configuration? or just a general hourglass. What size is it, and what is your budget?

The piece will sit at a total height of 18" (the height of the plugs of the spindles is not included). Approximately 1.5" for the top and bottom bases (3/4" each) leaving the total height of the "glass" at around 16.5" which can be adjusted if needed. The budget is about $150 unless more free money becomes available in the near future. Idealy, the hour glass will function to some extent, but it can be rigged to function if necessary.



We don't have a lathe and we don't have a roto caster. The water clear resin is a bit to pricey for us but the amber tint to the resin will help to give the "glass" an aged look. Also, this is for High School kids so it needs to be durable.



We used to have a Vaccumformer but it broke down to the point that it could no longer be fixed. I could make a smaller version though using a few heat guns and the shop vac if we ordered a bit of clear Vaccumformer plastic. I would still need to do it in two pieces though.



I am sorry that I did not mention in the first post that I am planning for this to be in several pieces.



The top base, bottom base, top glass piece, bottom glass piece and the 3 spindles. We had planned on doing the spindles separately and then casting those independently, which in itself is a bit easier than this.

 

[NZTK]

Because its for a school project, you shouldn't have any trouble getting some parts machined for nothing, put out a message in the school notice asking for help from a wood worker, there is bound to be someone in you area with a lathe, if not not, hit up local workshops, tell them you'll thank them/advertise their logo, on the play's programme. A roto caster can be made for under $15 with scrap wood and some old bike parts (chain/cogs etc) It would be an hour or twos work for the schools shop teacher. It would be a very useful addition to your schools theatre/prop shop.

You really need to get into the whole beg/borrow/steal mindset when doing low budget effects, you'll be surprised how many people are willing to help if you ask

good luck with the project.



You could vac form the "glass" part cheaply so long as you don't mind a seam down the sides, just build up a quater form, and vac it four times. All you need is a plain domestic vacuum cleaner and some frames, the frames you can make from thin pinewood and just use wide painters tape to hold it together. measure them to fit you home oven. The form can be made with water clay, you should be able to get enough waterclay for about $5. The vac table itself is literally as simple as a flat surface with a hole in the middle, and you vacuum cleaner pipe stuck in the bottom. A local sheet plastics firm will most likely cut you 8 or so sheets of PETg for nothing (cause its for a school) or for a few dollars.