Anyone know how to shrink a mold?

[Seachaser]

I saw the video on how to enlarge one, but is there a way to shrink one? I have a proto type that is a tad to large. Any suggestions without making a new mold?

[aka anglinarcher]

I asked that question once before. Larry and Mike both told me that they know of no way to do it.

To reduce the size of the "blank", I used my slightly oversized mold to mold a new blank with wax. Then I used hot carving tools and slowly worked the original down to the size I wanted. Once I was happy (had to do it several times; I am not a sculptor) I froze the wax and them made a new mold.

Sorry, not quite what you asked for, but maybe it will help.

[Mike - Alumilite]

Actually there is a way and I need to do a video on it for everyone but simply haven't had time. Here is the general idea ...

Odorless mineral spirits will swell a cured mold once it is cured when soaked in it for a period of time 12-24 hours. But lets flip this and shrink the mold using the same Odorless mineral spirits. Here is how you do it.

Say you need 125 grams of High Strength 2 silicone to make your mold. Mix 100 parts base, 10 parts catalyst, and then add 30 parts of Odorless mineral spirits and mix thoroughly. The mixture will be very thin compared to what you are use to when only mixing base and catalyst. Then pour your mold. At the 18 hour point, carefully remove the mold box and the original. Then allow the mold to sit out in the open for 2 days. The Odorless Mineral Spirits that were mixed in will flash out or evaporate from the mold and the mold will SHRINK. Its really cool! This will shrink approximately 20-25%.

Disclaimer ... feel like a politician ... this is very difficult to do in a 2 piece mold as it is difficult to have the exact same shrinkage occur which makes it extremely difficult line the two halves up perfectly. If you need to do a piece that would traditionally be a 2 piece mold, suspend it, mold it completely, cut it out, and then allow it to shrink as a 1 piece split mold. Then make a new original and make your production 2 piece mold for making parts. Another note ... dimensionally it shrinks pretty evenly HOWEVER if one part of your mold is thick and another thin, you may have some slight inconsistancies in the rate in which it shrinks and ends up. Typically its really close and good enough but it is something to keep in mind. Another note, I DO NOT recommend going more than 35% as it is a pretty drastic step. If you need to shrink it more, I'd recommend stepping it down by repeating the process more than once to make smaller scale drops.

Oh ... Odorless mineral spirits (I am pretty sure) can be purchased at Lowes, Home Depot, Menards or any other big box home improvement place. Check in the paint aisle near the paint thinner. Straight Mineral Spirits would work as well, it just stinks so I prefer the odorless.

Let me know if you still have questions on this or if it doesn't make sense and I'd be happy to elaborate.
Mike

[aka anglinarcher]

Thanks Mike.

I went back through my post using the search feature and I asked the question on Jan. 10, 2011. Wow, two years ago -- it does not seem that long.

To correct the record, Larry responded, Mike did not. Larry had some other ideas, but he had not tried them.

I think I am going to need to try this. I would never have thought that the Mineral Spirits would not inhibit the formation of the silicone.

[billh]

hi,
there is a product out there that shrinks, it is called hydro-shrink, but you would need to make your mold from it, then let it dry to the appropriate size that you want. then mold your fishing lure. hope this helps you, have a nice day!

bill h.

[Mike - Alumilite]

I have not needed to do this myself enough to dial in an exact plotted relation to the amount of Mineral Spirits to the % of Shrink yet but without opening up a huge can of worms on this I'd like to offer to make a mold or two of a couple lures that someone may have so we can play around with this technique. I'd film the process and then post it up on the site for everyone to view. So if you have lure, preferablly one that can be made with a one piece mold (even if we have to split it), please throw me an email at mike(at)alumilite(dot)com along with a pic of the lure and how much you'd like to shrink it and I'll pick a couple out to try. I'll then ask whomever to send me the lures and I'll get working on them. Please also make the lures original and not a commercially produced lure that you bought and would like a smaller size.

Thanks,
Mike

[aka anglinarcher]

http://www.sculpt.com/catalog_98/Castin ... Shrink.htm

Billh, interesting stuff, but I am not sure I like the fact that the stuff would be shrinking while I am trying to mold it. But, if I wanted to reduce something by 51%, this looks perfect.

I think Mike has the best method. I hope he can do the video soon.