Great Dane excavating co.

[modelman]

Cooper-what you have so far looks really good. On molding, any imperfection in the tire will show up in the mold and on the molded part. But it is just a "dump truck tire" so I wouldn't be too concerned. The building technique you described is similar to what I did but I found by pouring the complete tire there will be problems with air. I even used a shaker table and still could not get all the air out but it was very minor and I turned that to the inside. The way I described the half mold idea will eliminate the air problem but I am sure you will work it out. Keep working!!

[Cooper]

I have not completely decided what method I'll do yet. One thing I have going is the highest part of the tire will be the sidewall. So doing something like yours I'm hoping to minimize air bubbles. And like you said that will be the back side. I even thought of having the mold at a 45 angle but that may make two of the treads capable of trapped air. Have to do a bit more knowledge searching . And that's my opinion on the imperfections, I thought about using a high build primer but I don't want to get any in the treads as they are not the easiest to sand and that's what the acetone flattened out. Once some real dirt gets on um I'm hoping they will blend right in. None of my stuff stays pretty for too long

I'm trying to get some pics of the frame that I can accurately scale off. This may change to a 785d, I can get one of the norscot die cast models. Anout the only difference I found so far is front end appearance. And those little models are pricey little buggers!!!! Have to go to the local cat dealer with the d11 and excavator, maybe they will sell me one cheeper. They don't get any trucks that size and biggest dozer they get in the lot is usually d9. Lots of adt trucks. But they have most of the toys, probably the 797 and not what I need. Everyone around has been telling me to take the toys up there anyway.

[Mikem]

HI Cooper if you are casting your tire horizontally why don't you put vents in the high part of the tire and then clip them of . I used .040 wire and my parts looked like a porcupine but it did get 99% of the bubbles out . The other thing we did was to put compressed air in our pressure pot about 60 psi . We also had the fill bigger so a little more resin would go where the bubbles were . Hope that helps . Mike

[bigford]

coop bought a vac pot. he should be able to vac out almost all the bubbles

[modelman]

Cooper-I think you will have a better chance of getting the air out if you have the tire lying down perfectly flat and level. I will show you a few pictures of what I did and maybe it will help you decide.

I used large vents but it still had air trapped but I think getting it filled just barely to the top would help let the air out easier. But the bad side of that is if it is not full the tire will be no good.

The nubs are easily trimmed off and sanded smooth.

Also be sure of the hardness you need. I thought this was good but with an extreme load on the truck there was no flex in the tire. I can send you more pictures if you want.

[modelman]

Originally Posted by bigford

coop bought a vac pot. he should be able to vac out almost all the bubbles

I don't think you can put a vacuum on a closed mold.

[Cooper]

Model man, I'm aiming for a casting just like you did yours. As far as the degassing, only the resin/urethane / whatever you are mixing gets vacuumed for about 90 seconds. Not the mold or poured mold. Once the resin pulls a vaccine (rises in the vacuume chamber and falls, like a bad loaf of bread, the resin is ready to be poured into mold. From what I've read so far just some well thought out pour holes and some hand tapping will release any bubbles on the mold. Most of the little bubbles are from mixing the resins together , that what the vacuume / degassing is supposta eliminate.
Modelman what hardness were those tires? I got stuff coming and the first one I'm starting with shore hardness of 60, it is said to be like sneaker tread. It may be a bit harder but it's a solid tire and pretty high sidewall.

[bigford]

wouldn't it draw the air out the 4 vent tubes?

[modelman]

Cooper-I used the "vyta-flex 30" urethane rubber from "smooth-on"on my tires. I thought I was good by how easily they flexed but when mounted on the rim they became very hard. I think because it was a solid tire. This is your decision but I think the 60 may be a bit too hard. I agree with what you are thinking though. I would prefer the tire be to hard than to soft. If it is to soft it might just roll right off the rim on a side hill drive.

[modelman]

Originally Posted by bigford

wouldn't it draw the air out the 4 vent tubes?

No, Vacuum is meant to be used on an open mold or table or a flat surface. Example-if you vacuum something down on a flat table, you seal the part around the edges and vacuum the air out from under the bag and atmospheric pressure pushes the material down against the table. The same thing happens when you pull a vacuum on an open mold. BUT-if you pour wet rubber into a rubber mold the vacuum will distort the mold and just force all the wet rubber from the mold. Most people don't realize that atmospheric pressure does all the work when bagging. The vacuum pump just pulls the air from underneath the part. Hope this makes sense

[Mikem]

Modelman I was doing ho scale buses vacuuming resin sucked but compressoring worked real swell . Mike

[Cooper]

Oh ok, I did not know about pulling a vacuume on the mold when casting. I am not planing on doing that. I got the pump to pull a vacuume on the materials before casting. To de gas the mold resin and casting resin after mixing but before pouring. I always thought that was more for carbon cloth or fiberglass mold forms, rigid stuff with vacuume bagging. Not casting stuff. The process I'm doing is something other than vacuume casting. I think it's called open mold casting.

[modelman]

Cooper-I was trying to explain to "bigford" how vacuum bagging works. I know what you are doing but I have no experience with de-gassing the resin or rubber. I have quite a bit of experience with open mold vacuum bagging (boat molds) and am quite familiar with that. I think what you are doing would be closed mold casting because you are putting-2-mold halves together and pouring a tire. And I could be wrong but I don't think vacuuming could be used in any way with this system. If so it is waaay over my head!! I like the k.i.s.s. method.

[Cooper]

Ok got ya, yup we are on the same page. The mold resin I'm using is best if degassed. And too the silicone rubber for the actual casting. All the boats I've worked on have already been joined. I could use some miniature hands!!!! Tuff reinforcing the seam on a 36" cat hull!! Speaking of I did get the maddcatt out a few times this summer all twice because I broke flex shafts. Punched it too hard , it's not user friendly, lol. Did hit the triple digits both times. But no fast runs.

[modelman]

Originally Posted by Cooper

. Did hit the triple digits both times. But no fast runs.

You don't think triple digits is fast!! You may need to back off sniffing the acetone fumes. When I see that smooth water in the background of your pictures I wonder why you don't have a boat each time you go there. I can give you a tip on glassing those seams on a boat if you need it.

[Cooper]

Originally Posted by modelman

You don't think triple digits is fast!! You may need to back off sniffing the acetone fumes. When I see that smooth water in the background of your pictures I wonder why you don't have a boat each time you go there. I can give you a tip on glassing those seams on a boat if you need it.

Nothing off topic at Great Dane ,,,,, lol!! Modelman this is a link from a couple years ago on the saw build of the madd Catt. I forget what my top speed was, I think just shy of 120. But not proven with pictures. She can run reliable 90-100 anytime decent water. I've got to get back to running her. We do play with the pursuit monos quite a bit. Set up an oval corse for summer till high water takes um .
http://forums.offshoreelectrics.com/...ight=MADD+Catt

[Supermario]

I've shared your video when you ran 102 mph with many friends and they all just love it and were amazed.

[bigford]

Kat vs dog

[Cooper]

Originally Posted by Supermario

I've shared your video when you ran 102 mph with many friends and they all just love it and were amazed.

Thanks, I really have to spend some time with her in the water next year, I built her for speed and to stay together. Hull has not been compromised yet, and been airborne several dozen times (at speed) so this one is doing no justice as a shelf queen. She would look better with a split hull if she has to live on the shelf!! So come next year I'll keep trying to go faster and find her breaking point. Usually the saw (straight-a-way racing) boats don't last past a couple 100mph+ crashes. She is heavy but heavily reinforced with carbon/Kevlar to take a few long jumps,,, and she has. !!

[Cooper]

Originally Posted by bigford

Kat vs dog

Lol!! Big babies!! Mine are same way, cats want to jump on and go for a ride!!