The Hunt For Big Fish with Larry Dahlberg

Hey all,
After seeing Larry's video, I've decided to try the mineral spirits trick on my rtv mold.

I make my rtv mold in a solo cup. This prevent clamping and allows an even distribution of pressure around the conical mold.

I have a couple questions before I do this though.

Will the mold return back to the exact original size? About how long does this take? Is there any warping on the original mold when it shrinks back?

The reason why I ask these is that I have to make 2 molds instead of 1 if the original doesn't return back to the exact size it was previously (since I won't be able to use the solo cup as a "clamp" anymore.

Appreciate any info! Thanks!

yes, the mold will return to original. Time depends on temp and humidity. The mineral spirits literally have to evaporate out of the rtv.
Just be careful with the expanded mold. It will tear much more easily than prior to wetting with mineral spirits.
best
L

A-Mac, let me know how you make out, I have a 2 pc lipless crank mold I would like to make bigger for a heavier saltwater version.

Thx

John

It only takes a couple hours to see it start to swell. Don't submerge it and walk away from it for the day or even overnight. Keep an eye on it and as soon as you start to see the mold deform or warp, you are about at the limit of growth without keeping your dimensional stability. I would expect a 10-20% growth rate ... anything more and you are pushing the envelope of what is manageable with this process without deforming it.

Thanks guys!

And thanks for the timing tip. If it's alright, I'll post some pics in a couple days of the process and turnout.

If you grow your mold too much, simply let it air dry back down to the point where it is not warping and deforming. Then pour a new master or soft plastic bait just to test it. If the bait looks good, then pour a new master. If it doesn't look good, recycle the soft plastic, and continue to grow or shrink the mold which ever way it needs to go.

Mike

I picked up some odorless mineral spirits and the mold is now soaking.
And since when is mineral spirits white???

I was skeptical about it working, but the mold does appear to be swelling a little after 1 hour of soaking.

Is there any special preparation that is necessary for the inside of the mold before pouring the resin? Would it be necessary to use a mold release? I'm just trying to prevent damaging the mold as much as possible, since there are some small details in the lure.

Thanks!

Yes, I would use UMR in the mold but more importantly, make sure the mold is completely dry with no left over mineral spirits left in the mold.

And yes, OMS should be clear???

Mike

Avoid the KleenStrip brand from home depot. From other people I've talked to, all of this brand OMS is white.
I was able to get a little swelling from this (after soaking about 27hrs), but it was more like a 5-10% increase. In addition, it has been 3 days and the OMS has still not evaporated from the rtv.

I decided to try a pour anyway. The pour came out alright, but I didn't care for the look of the details. With this being only a marginal increase in size, I figure I would have more dislike in the outcome at a 20% increase. I'm sure this has an appropriate place, just not with what I was working with.

Eh, what is lure building without failure?!

Just an fyi,
Perhaps it is the mineral spirits brand I used, but my mold never went back to the original size and is warped. I suppose I'll chop it up as filler for the next mold.

Hi A
Thanks for the update. Sorry it didn't work for you. I think you're correct about the mineral spirits. When I've done it worked out pretty well. I used clear KleenStrip that came in a big plastic gallon jug. The key was having the wall thicknesses in the mold fairly similar plus putting weights on the mold so it all stayed submerged.
Using the leftover mold as filler is a great idea.
best
L

I tend to not use more than about 30% as filler, but I think you could go higher. I just chop the mold into small cubes and throw them in as I start to fill the mold. I think if one could grind it into fine particles than you could use 60-70% of total volume and probably mix into a more homogeneous solution before pouring. I'm debating on taking my belt sander to it and collecting the particles in the attached dust bag. I guess worse comes to worst, I'll have a clean belt!

What is the best for re-sizing the mold? Would the Amazing Mold rubber, or HS3 be better? I have some lures that I would just like a larger version of, and the company is no longer in business.

Thanks,

Lance

I've used both high strength 2 and 3 and they worked fine. After they've expanded they are more prone to tearing so you have to be careful if you're expanding a one piece or squish mold, so you don't tear it when removing your part.
best
L

Also, don't leave it too long in the Minerals Spirits as it will start to grow rapidly after 30-60 minutes and will blow up like a balloon after hours. So don't put it in and forget about it. You might also want to measure it before you put it in as the first 20% is difficult to notice without something to measure it against.

Mike