Sticky casts?

[sbarrett4]

Well,

My first mold came out okay, my first cast went well until... I demolded it. The shape is fine and there are no airbubbles, but it didn't fully cure, part of it is still wet - I even waited twice the recommended time before demolding. Will it eventually cure fully? Or stay perpetually sticky? Any help/tips appreciated. FYI, I am using Smooth-On's Smooth-Cast 300 liquid plastic.

[mslz22]

You may not be stirring it enough, I always count to 100 slowly when mixing resin (are you using the 3 minute one?) I always use the 305, allows a little more time. Also be sure you are mixing the right proportions, when I use the 305 I always pour the resin from the yellow into the resin from the blue bottle (measured of course)the reason is that the yellow has a lower viscosity and will not end up "clinging" to the vehicle from which you are pouring it and messing up the proportions. It may cure, but it may not. Good luck

[sbarrett4]

I probably didn't stir them enough. I was concerned with the short potlife so I mixed them for maybe 20 seconds and began to pour. I'll try again and stir it longer.

Thanks

[mslz22]

That will do it, I used the 3 minute stuff when I first started and will never use it again, you may want to cut that 100 I said down to 60 seconds but do it briskly and make sure to scrap the sides. Watch those eyes when stirring briskly.

[Valkyrie]

Yea, the 3 minute stuff sets up way too fast. Especaially if you're pressure casting.

But yea, mix thoroughly but quickly, if you're using SC-300. Also, with some times of resins, it's necessary to shake up the container of each part before pouring and mixing. The suff I'm using now won't cure for crap unless I shake them up real good RIGHT before I pour them. But this obviously introduces a LOT of air into the mix, making de-airing methods all the more necessary.

[kanata67]

Mix all two part compounds very well. Agitate individual components vigorously before mixing for best results.

I have another resin question though. I know many of the jetfire armor bits that have come through my hands have had stress marks. I also know that jesse's resin was brittle and prone to breaking rather than stressing. I don't know if this is typical of all resin or only specific mixtures. I know that I broke a tab off one of jesse's strike bosters and a tab off the cannon, though that was due primarily to my own stupidity of not dry fitting the last part I had to assemble. Robs resin on the other hand, which I have a lot more of, ha sonly suffered one break of a medium leg armor post during shipping so I can't be certain of the tensile strength. As all of robs stuff dry fits perfectly and I have no desire to break something just to find out, can anybody tell me if some smooth-on types are more flexible than others when cured?

I was also wondering if anybody has ever tried using extra metal for strength in their resin? From past concrete experince I know that laying steel down before pouring not only meets DOT standards, but with enough can support a school bus. I'm thinking maybe some copper wire strands might not prefent it from cracking, but might help it not break completely. Has anybody experimented?

Also... has anybody done any wax/disposable molds? I have a tube of some really nasty, really expensive commercial self leveling epoxy that is almost bullet proff when dried [depends on the calibur and thickness], but I am sure that the mold would have to be burnt off it when dried. Can a one-shot mold be made easily and cheaply, or am I better off waiting till a mold is only good for one more cast and then doing it?

[mslz22]

I was also wondering if anybody has ever tried using extra metal for strength in their resin? From past concrete experince I know that laying steel down before pouring not only meets DOT standards, but with enough can support a school bus. I'm thinking maybe some copper wire strands might not prefent it from cracking, but might help it not break completely. Has anybody experimented?

When I recast the additonal set of landing gear for Chris B's USV dioramma I used music wire to add strength. Works well if the part is straight like landing gear or head lazers.

[jwinges]

Another Question

Do you think that someone could make a mold and then scan it in a 3D scanner then have the mold replicated in Aluminum in a CNC lathe?

Better Yet do you think that an original part (or better yet an original part tree) could be 3D scanned then inverted on computer to make an Aluminum mold via CNC lathe?

I was watching that orange county choppers show on Discovery channel and saw them using a lathe to Cut out rims for their chopper. Could we use one of these to make permanent molds that could be used with real plastec rather then resin and getting the benefit of longer mold life?

Problem is would the 3D scan file be compatable with the lathe files?

[fulcy]

That's how most injection molded plastic molds are made - they are CNC'd out of billets of aluminum. Problem is, a mold that is around 5" x 8" x 3" deep will cost you about $2000 to $3000 - as such, the number of parts in a single mold is limited, and the total number of kits you'd need to sell to recoup the cost of the molds would be in the hundreds.

[EXO]

I was watching that orange county choppers show on Discovery channel and saw them using a lathe to Cut out rims for their chopper. Could we use one of these to make permanent molds that could be used with real plastec rather then resin and getting the benefit of longer mold life?

Man! My job just switched locations and I'm a few blocks from where they shoot that show. Maybe they would let me makes some molds there.

Yeah, right!!!

[kanata67]

LOL ... Thats something I've been thinking about for a while. Molds for a jetfire set were estimated at about $5000 including scan from daytona molds. They will give me a direct quote once/if I send them the parts. This still doesn't count getting a place to pour/press the kits from the finished mold. The nice thing is... for a bit more money a mold of ALL five 1/55 armor sets could be done in one mold and sets could be spit out every thirty seconds or so. How much would you pay for all the sets in one nice carded package? Seriously... I'm still thinking about doing this but doubt I would get the money back in a timely fashion.

[jwinges]

Interestingly I recently received a magazine that had mini lathes for you home. Cost about $3000 but they could do a 1' by 1' mold. However it wasn't computer operated. Get this...Joystick operated. Can you imagine how hard it would be to make a good, accurate mold with a joystick.

[Valkyrie]

What you're talking about is a milling machine, not a lathe. Lathes would be utterly useless in making molds

I have a small bench lathe, and I'm hopefully going to be getting a mill sometime in the near future. But they're just tools for scratch-building. Making injection molds is still way beyond me. And I really don't need the to do injection stuff, anyway. Everything I need to do, I can do with silicone.