Scratchbuilding tires

[Herman]

I cannot help you with proportions. They are manufacturer and prduct related. I have had several different silicones, all with an other mixing ratio, and curing times.

Your enemy is air. Best is to vacuum this out, but you need a high-vacuum pump for that. (no, the vacuum cleaner does not work). Also the mould should have undergone a vacuum treatment, otherwise the airbubbles in the mould will show.

I will see if I can get my old vacuumpump rolling again, I need to cast a rubber mould, and some resin parts. If I can repair it, I will make photos of the process.

[ScaleMotorcars]

Thanks Herman that would help out allot.

He's right. For the best results you need to either vacuum or pressure cast. Both methods work great.

He's also right that the molds need to be made in the same way or your going to get imperfections when you go to cast.

I really don't recommend hand casting tires. Its very hard to get all the details of the tread and lettering. If you want Ill break down a little tutorial on it.

As for the RTV rubber I use its a 10 to 1 mixture "by amount". Be careful because if its not right your going to have a big mess. Some are mixed by weight others by amount. If you let me know what brand and what type of rubber it is Ill find out your mixing ratio. :D

[hot ford coupe]

Thanks Herman. That's a lot of the kind of info I need. I should have realized about manufacturer's recommended proportions but the bottles I have didn't come with instructions. Typical. I think I know where I can get a strong enough vacuum. In my residency, we used to watch the laboratory technicians make some of the artificial face parts for people who had facial cancer surgery. We used medical grade silicone with a bell jar and a vacuum pump. Since that's the way you make the tires, I'm going to see if I can find a used setup. Again, thanks for the help. :) :) :)

[ScaleMotorcars]

Jeff, for best results get a pump that can pull at least 28 lbs of mercury. It might not seam like allot if you were pressure casting but in vacuum terms its huge. Must small vac bumps max out at about 14 to 18 and cant de-air the rubber. Makes nice big bubble on the surface but they don't pop. Also if you were going to cast resin another big thing to look for is the CFM (Cubic Feet per Minute) vacuumed. The unit I have is 10 CFM, most are 6 or less. Depending on the size of chamber your using will require bigger or smaller pumps. Labconco makes a nice small chamber that can be found on ebay from time to time. New its over $1500.00 but on ebay anywhere from $50.00 to $200.00 is normal. With this chamber you can use a smaller pump in the 3 to 4 CFM range and its small enough that when your not using it you can store it away out of sight. Hope this helps ya Jeff.

Theres allot more to it then this so once you get your equipment let me know and Ill walk you through it. :D

[Herman]

For a degassing barrel, also take a look at pressure vessels used for spraying larger amounts of paint.
Or take a look at the "vacuum overflow vessel" at www.airtechonline.com

I use a batch of Rhodorsil silicone now, mixing ratio 20:1

However, we now deal with Smooth-on, the Mold-Max 20 and 30 have a mixing ratio of 10:1

Indeed not all vacuum pumps work. You really need a suitable pump. I have 4 pumps available, but only one works. (a Leybold Trivac 10). The rest of the pumps are high volume pumps, but less vacuum...

A am making a vacuum chamber right now from a piece of epoxy piping , with a thick bottom and lid. A picture follows in a couple of days.

[hot ford coupe]

$1500 borks for a new pump!!??:eek: I didn't know how expensive it could go. Thanks guys for the help on this before I went and screwed up a lot of work or spent a lot of cash on something that wouldn't work. I'm going to have to save up for some kind of pump. Looks like tires are way in the future.

[ScaleMotorcars]

$1500 is just the chamber. (no pump) :eek: Like I said anywhere between $50 and $200 is normal and a good pump on ebay around $250.00. Under $500 for a complete outfit for sure. Used stuff even less.

Herman's got some good ideals on the chambers to save big $$$ Thanks...

Don't get me wrong guys you can hand cast the stuff I just want you to get the best results. Usually hand casting gives a tire with allot of bubbles in the tread. Slicks are the exception... :D

[hot ford coupe]

I'm just going to have to go out and buy a piece of rubber tubing, hook it up to a piece of my wife's old Tupperware, exhale real hard and inhale incredibly hard. After that they'll probably call me Ol' Rubber Face.:(

[ScaleMotorcars]

LOL...:D Maybe supermodeler can help you out. What happened it him anyway? Did Slick take over and lock him in the shed again?? Crayon overdose??? You know being a superhero can be a little overwhelming. :p

[Gluhead]

Hahahaha! I gotta admit I'd like to see that...

:D

Glu