When is it "worth" making a mold?

[Sled Driver]

I see this question is indirectly asked in some of the threads on this forum and other forums. The way I answer this question is presented below, but I am very interested in hearing how other answer it.

"When is it worth making a mold?" is a question that I answer in two different ways. First, if I'm going to be making more eight parts and exactly what I want is not available commericially. An example would be SuperGee II DLG pod molds, since I'd make more than eight pods and there really isn't another pod that is as light and readily available. I would not however build a 3-meter TD fuselage mold, there are scads of TD fuses available that are adequate in my opinion.

The second reason that I'd make a mold is if I really want something and it isn't available anywhere in the world. An example would a fuse for an EDF F-105. I don't know of any electric ducted fan F-105's.

Regarding HydroCal mold, it works, it takes a little less time to actually make the molds, and the quality can be quite reasonable depending upon the application. Depending upon the subject, it might cause me to lower the my number of eight parts to five.

Hasta,

Jay

[Badger]

My break even number is three parts. The strength to weight advantage and better finish make it worthwhile for the extra time and effort to mold.

Regarding the 3m TD mold: I have not seen a 3m+ pod and boom available that is to my liking so I did build my own. The commercial 3m fuses are double the weight of a good pod and boom.

[davidfee]

I agree with all of the above. But I have a question... are you guys including the one or two parts you make to figure out the layup schedule? Or does the first one come out perfect? ;)

Actually, I am flying a couple first-part examples which were too heavy... but they were done. ;)

-David

[Sled Driver]

... are you guys including the one or two parts you make to figure out the layup schedule? Or does the first one come out perfect? ;)

You are right, it usually takes me a couple attempts to get a satisfactory part finish, seam, and weight-wise. I do not count those practices parts in my break even part count.

[Sled Driver]

Regarding the 3m TD mold: I have not seen a 3m+ pod and boom available that is to my liking so I did build my own. The commercial 3m fuses are double the weight of a good pod and boom.

I'd agree, most of the commercial 3-meter fuses are heavy. I was able to find a gentleman who made a Bubble Dancer pod with a lay-up for a TD plane. Saved me from having to build another plug and mold...

[SoarNeck]

I wish I had a logical "break even" point, but I don't really...I just make molds as the mood strikes me. The last two molds I made haven't even resulted in ANY parts yet (SuperGee II pod + Bubble Dancer pod), but have been carefully "archived" for later use (no, I don't want to sell them). The mold before that I only used for one part (S400 racer pod), which I coincidentally got right on the first try.

I usually make a mold when it's tough to replicate the part in wood, such as a small monocoque(sp?) structure.

My next project is still looking like an F3B sailplane, however, which will be my first try at a wing mold if all goes well. I have the design 99% complete now, and it's just a matter of starting to deform some appropriate composites.

I could use any one a dozen or so "good enough" F3B fuses...but I still plan to build my own mold there as well. The best reason for molding your own parts is still to take the exclusivity of scratch building to a WHOLE new level :cool:

[SoarNeck]

Oh, I forgot to mention another reason for molding: absolute repeatability. When designing a layup for a model, my rationale behind having a mold is that any changes in the behaviour of a model between versions can only be a result of differing weights and stiffnesses...no slight variations due to building errors. Given the finicky nature of modern airfoils, I would get a lot of peace of mind knowing that a mold was tightly controlling the aerodynamic profile.

[raptor22]

I was just wondering....about how much does a epoxy mold cost. Would like to try molding, just wondering about that....would it really be worth it.

BTW, do you think it would be best to try the first fuse in fiberglass first?

--Alex

[Badger]

The last two molds I made haven't even resulted in ANY parts yet (Bubble Dancer pod), but have been carefully "archived" for later use

Har Har, you call that making a mold? The hard part of the plug and splitter plate were already done for you. This another good way to justify a the effort, several people can get together and share the plug to make several molds for themselves. There was once a Allegro Pod plug going around until I think it got destroyed by a neophyte.

As far as costs go, an open class pod mold might run $20 to $30 in materials. Boom molds cost nothing to scrounge (pool cue or golf club shaft).

[raptor22]

That's not bad! Now that I know it I have to try it....

--Alex

[SoarNeck]

Har Har, you call that making a mold? The hard part of the plug and splitter plate were already done for you.

Not the hardest molding project I've ever done...I'll grant you that :D

My molds usually cost $30-40, since I don't go light on layers. I use a combination of coarse glass cloth and random-fibre matt to build up the thickness quickly.

[Bill Harris]

Here is an idea that I've toyed around with on making a mold for a composite fuse.

As an example, say I want to make a Killer Bird of Time. I have an old nostalgic BoT fuse. I make a splitter plate, coat the fuse with vasoline as a "release compound", and start making the mold out of plaster of paris/cotton bandage, with appropriate longitudinal reinforcement to keep it stable. After the plaster sets, split the mold, remove the original fuse and seal the plaster with epoxy/varnish. The fuse halves would be laid up with glass/epoxy resin and the two halves joined. I don't know how long the plaster mold would last, but it seems that it would be easier to fabricate than a 'glas mold.
--Bill

[Joedy]

I've used commercial FG fuses as plugs for molds. Just seal and tape up any potiential places where the epoxy slug will seep... and trust me, it WILL seep into the smallest of cracks and crevices.

Forget about plaster - it won't last and it's three times the work. Epoxy, milled CF and FG are still the way to go for quick and easy molds.

I find that going to about 400 grit on a poplar plug and then several layers of paste wax is faster to the finished mold than by perfect plugs.

I wet sand my "bumpy" mold surfaces to a mirror finish. A little bit of Dupont #7 is all that is really needed in additional to some 1000 wet/dry sandpaper.

I estimate that it takes about 30 minutes to polish both mold halves after popping them apart from their initial cure.

As far as value : mold ratio. I'll make a mold of any part that I anticipate wanting another one of if the landing is a little "too rough".

-joedy

[Tony D.]

I know this might sound crazy but I like making molds, and producing something unique doubles the fun.

I just finished a pod for a new TD ship and while I did not keep close track of cost I bet there is no more than $20CA in materials in the finished mold.

For me it is worth it to make a mold even if I only take one part out of it.



T.D.

[Haldor]

My criteria is "I want to"

[erikdahlchriste]

Hi,

A brak even point can be looked at from a work wiev or from an economical wiev.
But I don't know the figures :o

I make molds when I want something that I feel I can make better, smarter, more fancy or just plain better looking, than anything I can buy.
I also make molds just to see if I can.

I once read a thread on a yahoo group abot the cost brake even point of making things your self instead of buying it, and among others Jay Decker (Monkeytumble) wrote that the cheapest way of aquiring goods is to buy them. I you want to make it yourself by any means do it, but don't do it because you want to save mony. Most people will not reach the breake even numbers of items taken from a mold, hence it is cheaper to buy it.

If you are going to make molds or make anything yourself, do it because you HAVE to.

cheers

Erik Dahl Christensen
Denmark

www.gliders.dk

[Sled Driver]

Erik and the other guys bring other excellent perspectives. I realize that how one answer the original question seems to depend not only on econmics and how an individuals personality is wired, but also largely where they are in their life.

I have the career, house, and family including two kids with one still in diapers. So, effective utilization of my available time is the key criteria at this point in my life, because I have enough money to buy the toys I want, but don't have enough time to build what I want and can't buy...

Jay Decker
Kennewick, WA

[Prof. Maneuver]

Erik and the other guys bring other excellent perspectives. I realize that how one answer the original question seems to depend not only on econmics and how an individuals personality is wired, but also largely where they are in their life.

I have the career, house, and family including two kids with one still in diapers. So, effective utilization of my available time is the key criteria at this point in my life, because I have enough money to buy the toys I want, but don't have enough time to build what I want and can't buy...

Jay Decker
Kennewick, WA

I pretty much agree with this although there are things an individual can do with a mold that would not be commercially viable, thus unavailable. Have the following other suggestions should you decide the take the plunge :

1) try to make the mold somewhat universal at the expense of more secondary operations to get a flyable part. Example : a glider fuse with the nose cut off can be an electric glider fuse. A fuse without airfoil fillets can adapt to any wing/airfoil.
2) pool the labor among lots of folks whom would likely be the beneficiaries of the mold. One well made mold can make enough parts to keep 50 people happy if that many want to be involved.
3) consider commercial use of the mold after the plankholders have had thier fill. Maybe someone in the group wants to establish a side business?

V/R

Steve Manganelli AKA Prof. Maneuver