Cat 777D Mining Truck

[Finster]

That's a great looking tire plug you made. Well done! I look forward to seeing the mold and tires it produces.

[td9clyde]

won't the lugs be stickin out ????or is that used to make the mold and then the casted tire??

[modelman]

TD9-this part will be used to make a two-piece flexible mold. Then the liquid rubber for the tire will be poured into the mold. Let it cure then hopefully I will have a tire.

[9W Monighan]

Do you have to coat the master with varnish like they do with sand casting? That would aid in releasing it from the rubber.

[td9clyde]

ahhhhh now i get it lol sorry i just didn't grasp the whole concept but now i do i wish i could make a solid mold so i can use it quite a few times like at a tire plant or something there is too much of a process for me to make tires i think unless i can buy solid rubber lol

[modelman]

Yes steve, This is the hard part. Varnish will not work but I have to finish it really smooth so it will release. I wanted to use glass filled delrin for the plug because it machines easy and you can mold directly from it but a 3-1/2" pc. cost over $200 with shipping and I only need a 1-1/4" slice and I probably would never use the rest of it so I went with the mdf but finishing it will take a while.

[modelman]

TD9-it is a long and time consuming process but I didn't think I had any other options. I e-mailed a couple of the foreign sites and although they did not have exactly what I needed I was going to buy their tires anyway but I never even got a response from them. Not sure how to deal with them maybe it has to be in their language, not sure?

[mog]

do you need some delrin i shere i got some liking around at the shop for you if all you need is a 1 1/2 pice think it 4" but that onlu take seconds to make it 3 1/2 lol let me know we got some scrap think there is some 6" around too

[modelman]

Mog-thanks-maybe I should have ask around before I started. I am too far along now to start over but if this doesn't work I may get back to you. I am waiting for the silicone & rubber to make the molds and tires so I should know something in a couple of weeks.

[D8R]

Great looking tyres, will follow progress closely. To find tyres that matches are a very hard part, Have had som thoughts of building a Pete with lowboy to transport my D8, but then it is the tyre problem again.
I you find a easy way of making those you will solve a lot of problems for us others.
Dan

[modelman]

D8R-thanks a lot-I agree tires can be a huge problem especially when you are not building by the common scales. I did not want to make my own tires but I felt like I had no other options. This is not an easy solution but there is not a lot of work involved just a lot of time. For me making the master part was the hardest job. The mold and tires just require some time & patience. A machinist would probably make the master part from aluminum and you could spray the release directly on that and make the molds. I spent several hours with the finish on the wood part I made so the silicone will release from it. Hopefully in a few days I can see the results of my work.

[tracksntreadslou]

Hi tom ..Not sure how far along you are with your tires but i did find this site with supplies and alot of free intresting how -to vids ..Any chance you could give us a bit of a tututial on how you are going about it...Cheers Lou

http://www.freemansupply.com/video.htm

[modelman]

T-n-T Lou-thanks for the link but I already have my supplies. I have the molds started and I am taking pictures as I go along so maybe I can do a how-to if everything works out okay.

[modelman]

Okay fellas, I have a tire! I will try to show how I did this. First step-I bedded the master part 1/2" deep in modeling clay. I put 4-3/8" steel balls in the corners and sprayed in the release wax.

Then I poured the top half of the mold-

After this cured for 16 hrs. I turned it over and removed the modeling clay and the steel balls and put the stems on for fill holes and air vents and sprayed the release wax on this surface.

I then poured the other half of the mold.

[modelman]

Aftter 16 more hrs. of cure time I separated the mold halves and this is how it looked-

This is the molds ready for pouring the tires-

I sprayed release wax on the molds and poured the black rubber mixture in the molds. To speed up this process I filled the bottom half about 2/3 full before closing the molds-

I had the molds on a perfectly level table to pour in the remaining rubber. I feel this is an important step to be sure the mold is full and to release all air. If air gets trapped in the mold the tire will be flawed.

[modelman]

After an overnight cure I separated the molds and this is the first tire right out of the mold-

Another-

I have these stems on the side of the tire from the pour holes and air vents but I can grind these off and turn this to the inside and I don't think it will be a problem.

Using this process I don't see any way to avoid this and I have a few tiny air bubbles on the fill side but I believe I can rig a shaker on the table and possibly solve this. I am happy with the results but will try to improve on the remaining tires. If anyone has any questions I will be glad to answer them.

[kerst]

Interesting! Thanks for sharing!

kerst

[9W Monighan]

WOW that is really nice. I think if you had a small autoclave that remedy the air bubbles. Can you put a ruler next to it for size?

[Iron Art]

Modelman, Those tires are looking good, I use a vacuum pump from Harbor Frieght and a garage sale pressure cooker as a vacuum chamber for moisture removal from Powder Coating powder, my thought is that would remove the air bubbles from the rubber. So far I haven't seen any problem with this lash-up. Fred

[pugs]

The urethane stuff I mold in my shop has do be "degassed", once mixed I place it in a vaccum chamber (with clear top) and pull a vac with a AC vac pump until it boils out. Then when molded you minimize the air bubbles such as you have in a simple hand poured mold.

The vac chamber I have is just a piece of 8 or 10" pipe with a bottom welded on, top machined flat and a piece of 1/2" lexan for a top sheet. Port in side for vac line from pump.

The tires came out very nice.