Jerry Feather

I will also dress the rough edges on the inside of the mold and will probably work the original mold joint marks out of the seam allowance grooves.

Rob Edwards

That's cooler than the other side of the pillow, Jerry.

Jerry Feather

Both of the bottom halves of the molds are pretty much finished. Next I have to set them up with the ***** and locate the top halves on them and then pour the top halves. I have the top halves pretty much ready. I have glued the respective bored pieces to them and when that sets I'll fit them together then locate several screws to fix their positions. Then I'll wax and apply mold release to the necessary parts and pour the compound into the top. I have three pour-holes milled into both top halves for that.

I finally got the registration notches milled in the aluminum pieces. They will have to register with the top halves of the molds, but I think that will work ok.

Jerry Feather

I have the first of the molds set up now and have the compound poured into the top half of it thru three pour holes I put in it for that purpose. I poured quite a bit of compound into the holes, but I can't see just how well it has filled. The holes stopped flowing but there may be some air pockets trapped inside. I wont know until it sets up fully and I take it apart. I suppose it there are significant bubbles trapped I can simply route it out and try again, maybe with bigger holes, and maybe some smaller additional vent holes.

It is still kind of cold out in the shop so I tried applying some heat to both the mold and the compound. That has the effect of getting it to flow more freely, but also it tends to cause the stuff to set up rather quickly, so I can't tell if it stopped flowing because it is full or because there is air trapped or because the stuff set up too much to flow freely inside, or likely some combination of all those.

Jerry Feather

I checked on the mold about an hour after the pour and found that the compound had settled a bit in two of the three pour holes. Then I noticed that somehow I had left a slight gap between the mold halves at one end of about 2mm. I'm not sure just how that happened. So, I tightened all the screws as much as I could while the compound was still soft and the gap mostly closed. It also forced some of the compound back up the pour holes and even produced a couple of air bubbles. I hope that was a good sign.

Then I decided that maybe heat would allow some continued flow, so I put the whole thing in the oven and set it at about 200 degrees F. I left it there for two and a half hours and when I checked, the compound on top of the mold was hard as a rock. I turned off the oven and left the mold in it to soak and cool off. Later this morning, after I finish my coffee, I'll go out and take it apart and see what I have.

Livio928

Many molding operations use vibrating tables which typically shake any air bubbles out of the molds or at least to the surface/entry point of resin/material. Easy to make - apply an electric motor with an off-centric cam that hits a plate on the table and creates a vibrating effect. Watch that your table doesn't start to walk away from you though. if you want to get elaborate, you could even isolate the table top with springs which only allows the top to vibrate while the legs remain stable. Tapping the molds for a few minutes after pouring also can create the desired effect but that can get tiring if you are molding more than one item.

hans14914

Jerry,

I am very keen to see how your molds turn out. I have great respect for the hand work you have done to make the molds.

If you do run into some air bubble issues with that product, I can recommend using Smooth-On brand 2-part products.

https://www.smooth-on.com/

I have been using their castable products for years, and they have always been reliable and easy to work with.

I also like the Mann brand of mold release agents. They have both wax and wax-free offerings depending on what material you are working with:

http://www.mann-release.com/erelease.htm

All the best,
Hans

Jerry Feather

I took the screws out of the mold and then brought it in to try to pull it apart. I could loosen the small end a little, but I couldn't get it apart. I took it back out to the shop and put the metal shaft piece in my mill vise and pulled it apart. That also pulled the original shift **** apart since the upper end of it seemed to be stuck in the mold. I finally got it out and find that it actually made a pretty good mold, and there is only one air bubble in it which I think I can patch and finish ok.

The application of heat the the mold, since it is wood, has shrunken the wood a bit and that has actually put a tiny crack in the first half of the mold. I think I can patch that also, or I may just leave it and maybe fill it with wax before I pour the rubber compound.

Jerry Feather

Thanks Livio for the suggestion about the vibrating. The guy that taught me about this mold making some time ago suggested that I simply put the mold onto my drill press table and let the motor run to settle the compound. I thought about doing that, but my drill press it out of service and I don't have another machine that I feel like leaving running for any significant time unattended, so I didn't do it with this mold.

Jerry Feather

Thanks Hans for your suggestions. I actually have a release agent that I used on the first half of the mold, but after I had waxed it three times with paste wax. On this second half I just used the paste wax and decided to try it without the release agent. That's what I had done before. I don't think I'll leave the release agent out on the next one.

If I don't have any success with the first try with the Devcon products I may try your suggested products. At this point I think the Aluminum F-2 is working just fine for the molds, and I have a small amount of their rubber, so I'll give that a try. Thanks again.

GT6ixer

That's good to know. I just bought some material from BJB Enterprises but was looking at Smooth-On. Do you happen to use a vacuum chamber to de-gas the silicone and casting material first? I bought a cheap vac to practice with.

GT6ixer

Nice work as usual Jerry. I look forward to seeing how these come out.

Jerry Feather

Another little success I think I had with this effort is that I filled the three or four small air bubbles in the lower half with compound before I put the mold bodies together for the second pour and they seem to have patched successfully. A little hand work and I think the holes will not even show in the final product.

Imo000

How about attaching the mold to a variable speed hand held electric sander? That should shake lose all the air bubbles.

Jerry Feather

Last nite I did the patching on the first mold and will check it later to see how that went.

I pretty much have the GTS mold ready to go except I think I'll open up the pour holes a little to both be able to pour faster but also to be able to see when the pour into one hole is reaching the next hole. Right now the holes are only 3/8 inch so I think 1/2 inch will be better. Then I am going to pour at room temp, which out in the shop is in the 50's, and not apply heat, even after the pour. It takes longer to set up that way, but I wont be shrinking the wood any more.

Oh, I see I still have to drill the screw holes to hold it together.