OK, what am I doing wrong?
Posted 02 April 2012 - 02:48 AM
I have a few other parts and wheels that I have made that I also want to make copies of that will require two piece molds. How do I keep the air out? Should I inject the resin on one side of the mold and let the air escape on the other? Should I slush cast and have an area to let the air escape? I really don't want to go to the expense of buying a pressure pot just for what few parts I'm going to cast. Plus, I don't see how the pressure pot would help since the resin sets up so fast. Seems to me that once it starts setting up,the pressure pot isn't going to help anyway. Does the resin set up slower inside the mold? I will appreciate any info anyone can give me.
Posted 02 April 2012 - 03:04 AM
While mold design and air key ways play a big part in how easily the air travels in and out on a mold, the big culprit is the fast set resin, how fast is yours? I recommend a medium speed resin without pressure pots, heck smoothon makes a very slow resin also that will give you 20 minutes of MIXING time..which if I was a patient person who wanted to get the most out of my resin with more than enough time to knock out most of the air bubbles. id use it. It has a demold time of 2-4 hours but that can be a bit longer depending on size of item and air temp.
Checkout smooth-on smoothcast 305 and 310 if you wanted to try a new resin.
Now the molds themselves, have any pictures? how are they vented? ive found when casting tires using 1 vent hole that is both a fill port and vent. tap of the mold a few times on a hard surface when almost filled, will knockout the air pocket..however that's using smoothcast 305 medium set resin so i got enough work time, you may not have that.
You can try putting your resins in the fridge before you mix to buy you a minute or two, some folks do that..i never tried it though.
Posted 02 April 2012 - 03:55 AM
As Ryan stated, set time depends on a number of factors. What resin are you using? I started with alumilite's "hobby" kit - with the tan resin. It sets wry fast and is pretty thick, making it difficult for me to get everything in place before I could get the bubbles out. I switched to Alumilite's white resin and that helps some - it is closer to the consistency of water and gives you a little more working time. So check the viscosity and set time.
As for the mold - post some pics and the experienced casters here could throw some tips and ideas your way. I have made a few two part molds and usually have to do them twice to work out errors in layout, etc.
Bubbles are a pain.
Edited by Erik Smith, 02 April 2012 - 03:55 AM.
Posted 02 April 2012 - 04:26 AM
The other posters are giving good advice and with experience you'll find what works for you. I never had a lot of luck with Alumilite although now that my skills are better I could probably deal with it. Anyway, I prefer SmoothCast 305.
As far as mold design, I no longer have any "fill ports". The molds are designed so that you just pour a puddle of resin into the lower mold half and it squeezes out through the vents as you close the mold. That way you have pressure forcing the resin through the mold. Look at the squeeze out on these molds:
That's what you want to see when you close the mold. You can see in the picture below how each part has a "well" in the lower mold half to hold the resin.
Good luck! Just keep trying and you'll get it.
Posted 02 April 2012 - 06:23 AM
Posted 02 April 2012 - 08:12 AM
Ryan's suggestion about chilling the two parts does help,and you can also chill the mold. Some wheels are hard to cast,especially the ones with small detail such as the lug nuts.
Posted 22 April 2012 - 10:01 AM
My lunch is ready now, I will have to come back and finish this entry. YES Dear! I will be there shortly. Lunch is over and the wife left. ate SOS. Good stuff!
I pretty much have to get psyched up to make parts if I can't stay on track. Here is a pic of three molds that make a Judson Dual Supercharged engine from a 64 Olds Cutlass kit. You can see all the vents I cut in the mold top. The mold pictured above is a very nice mold to me. I first started making parts by setting them all on one flat surface and no venting. The flash around the parts was quite thick. Then I dreamed up the pyramid shapes and it was just what I was hoping for, flash that was as thin or thinner than some you will occasionally see still hanging on new kit sprues. I am probably not the first guy to dream this up but it was a big help to me. I use Task 8 because it will withstand higher temps than most resin. A club member bought a resin 57 Chevy convertible kit from someone. He had it in his car trunk for only a half hour under the Arizona summer sun and it was warped badly. I thought about my parts going out in the mail from here and thought the worst so I switched from the Smooth On 300 I was using.
Edited by Greg Wann, 22 April 2012 - 10:45 AM.
Posted 22 April 2012 - 11:12 AM
Edited by Greg Wann, 22 April 2012 - 11:35 AM.