Re: 1/14 CAT 390D LME
 

Hey JW, have you seen myfordboys video's on youtube? http://www.youtube.com/watch?v=l638qR0Y6YE Hope you find them usefull!

Cheer's, Neil.

Re: 1/14 CAT 390D LME
 

Thanks Neil. His videos were some of the first I came across when I first looked into casting. Lots of cool videos on sand casting. I'll definitely use this method for many other parts I need to make.

I did first try this way for the tracks with a 2 part flask with greensand but quickly abandoned the sand casting and never poured the one mold I made. Its just not possible to do such an undercut part easily with this method that I see. That's why I just tried a track pad but this alone is also undercut for the leading and trailing edges to mesh with each other track pad. So it didn't work out. What I want to be able to do is cast a track pad and links together without having to bolt the two together or have to machine each piece even more. Even if there is a way to do sand casting with the whole piece. I still don't think I'll do it. Its still such a long process to do just one sand mold for one piece. It would take me weeks for a set. My goal is to be able to cast a complete set of tracks in one day.

Jeff

http://i784.photobucket.com/albums/y...-59-24_638.jpg

http://i784.photobucket.com/albums/y...-58-15_651.jpg

Re: 1/14 CAT 390D LME
 

I really hope you get a decent solution for home metal casting because I believe that many of us would then try it too and that would make builds even more awesome!

But why I really posted was that I read on a local 3D printing site that they offer making molds. Maybe you can find a solution from there?

Just wanted to help, maybe you already know that option.


Keep it up!

Re: 1/14 CAT 390D LME
 

Hey Jeff, thick and thin area's in a casting will alway's be a shrinkage problem. What I'm wondering is, can you cast the edge thick, and clean it up on a belt sander, to get the curved radius, on the leading and trailing edge? Just a brain cramp!

Cheer's, Neil.

Re: 1/14 CAT 390D LME
 

It would be awesome if I get this figured out because I would like to share it with everyone. I've been looking at all you guys build all these great builds for a while now and when ever someone comes down to making home made tracks. It easily drives anyone nuts with all the machining, drilling and tapping. I was going to do all of them with my mill but after making just one I was done. You know what I mean. Time for casting.

Yes I've been looking into 3D printers for a while. I hope to get one of my own someday. If you had one of those you could design anything and easily cast the parts in sand. You wouldn't even need a mill or a lathe :D 3D printers just print plastic so it would be good to make a master that's it. Low production parts could be sand cast and high production could be plaster cast.


I should be good with molds though as I am now able to cast a part in plaster with zero cracks and zero bubbles. It just needs to be fired in my kiln, add a sprue and vent hole.

Thanks
Jeff

Re: 1/14 CAT 390D LME
 

Ah yes the shrinkage problem :D I designed my track pad and links .015" per inch oversize. To account for the 3/16" shrinkage per 12 inches for aluminum that I was going to use. Now though I will be using zinc, its 5\16" per 12 inches. So its now undersized just a hair.

About casting the edge thicker I think it might work but now you have to make sure you sand each leading and trailing edge on all pads to match each other perfectly so they mesh. That would be a job for someone with a really good eye and steady hands.

Re: 1/14 CAT 390D LME
 

I did some research on the plaster of paris and its moisture content. The plaster is calcium sulfate hemihydrate(contains water). So yes molten metal plus water equals mold failure and or a steam explosion but only until it is heated above 392°F, it forms into anhydrite(does not contain water).


First plaster mold with no imperfections.
http://i784.photobucket.com/albums/y...-23-49_289.jpg

Re: 1/14 CAT 390D LME
 

Jw.-sounds like you are stuck on making metal tracks but I think your goal of a complete set of tracks in 1 day is unrealistic. Have you considered other options? I made rubber molds from silicone rubber and cast my track pads from epoxy. With rubber molds you can have undercuts and just peel the molds away from the part and the epoxy parts are plenty strong for a model. I cast the hinge pin holes into the parts at the perfect size but depending on your part you still may have to do machine work. This is the master part ready to mold-

http://i305.photobucket.com/albums/n...100_0055-2.jpg
This is the rubber mold-
http://i305.photobucket.com/albums/n...100_0138-1.jpg
Here is the track pads-
http://i305.photobucket.com/albums/n...n/100_0108.jpg
Track pads assembled-
http://i305.photobucket.com/albums/n...100_0126-1.jpg
Something to think about ????

Re: 1/14 CAT 390D LME
 

Thanks modelman! Casting the hinge pin holes is a brilliant idea. Saves so much more machining time. I will try to incorporate that in to my next molds. What's the strength of the epoxy your using? How are they holding up on your shovel?

I have considered using resin or plastic but I'm hoping to get the metal tracks going if I can. I have some hard urethane plastic that I will try out later. It has a tensile strength of 5,840 psi.

Thank you for the pictures.

Re: 1/14 CAT 390D LME
 

Jw.-I don't know the physical properties of the epoxy but you can check it out if your interested-
http://www.smooth-on.com/Model-Making/c1290/index.html
I bought all my products from them. Quick shipping and okay prices. The epoxy is plenty strong for my use. I cannot break the pads with my bare hands. This type of shovel doesn't crawl as much as an excavator or a dozer so I took that into consideration. It took me 3-4 days milling to make the master part from aluminun so machining 70-75 track pads was out of the picture and I can not do metal casting so the epoxy was the only option for me. I have not crawled the shovel in the dirt which is the true test for a model but I think it would do just fine. The way the tracks and sprockets are made I don't think dirt would bother it.