Resin molding - can it be one big lump of resin?

I would think it's doable.resin does create heat but I dont see 3/4 inch square causing much of a problem. As mentioned in another post,you will have to vent

As mentioned in another post?  

I agree that the heat from something that size is not a problem.  RTV is a reasonably high temp material.

The venting mentioned is to allow air to be forced out of the mold cavity by the incoming resin.  Best way is to design the mold with a J-shaped pouring sprue, with a straight vent tube coming up from the highest point in the cavity up to the top of the mold.  I use a wire like 1/16, or a straightened paper clip. If you do not have good vent(s) you will get bubbles in the casting.

Other than heat, the remaining problem is cost of resin, why some folks like to make a mold for hollow parts, makes your resin bottle last longer :-)

Thanks, Don.  I think I understand your pouring sprue thoughts, and will consider that.  I tried the pouring sprue thing on my first project, but the working time of the resin was so short, that it would set in the sprue.  Luckily, the pieces I was casting were small enough I could just pour a lump of resin into the bottom half of the mold and smash the two mold halves together with great results. I'm still mulling this over as to whether or not to put the engine mostly together or copy it as cast by the manufacturer.  There's a lot of flash to deal with so I'm already having to cut the pieces off the sprue to clean them up.  That, and some of the pieces are plated, so I'll be stripping those first, too.  We'll see.  

Oh, and I work in such small batches, my resin usually gets old before it gets used, the ultimate cost!  I actually had one use kit get too bad to use, so I bought another kit.  That kit sat around so long it leaked and set up in the box.  I have yet another kit, and am trying to get to the point where I make a big 'pour' soon.  

I'll post up results soon....   I hope.  :-)

Gene Beaird,

Pearland, Texas

I do not like the five minute and other fast setting resins for that very reason. I like the working time and stay with the longer setting stuff.  I do like to mix the stuff thoroughly.

I have had resin last for just over a year before it goes bad.  Keep cap on immediately after pouring, and for the resin itself, it must be pre-mixed before pouring. It tends to separate into two components when it sits for awhile. I invert and return the bottle about six times before I pour it.  Much better than shaking.  I also do this sometimes for the hardener, though I am not sure whether anything separates out in that or not- just easy enough to do, so I don't risk not agitating.

Yeah, it's the 5-minute stuff.  I even keep the resin and hardener in the fridge to slow the set times down some, but it's not much of a help, especially if you really mix the resin.  

Do you have any recommendations for stuff that has a longer working time?  Thanks.

Gene Beaird,

Pearland, Texas