JohnMac

Hi Guys, I am looking for some help in moulding tyres for a scale Viggen. They are a very unusual shape and nothing commercially available is going to fit. A friend has made a metal 2 part mould for me on his lathe but its the material for the tyre itself that I am stuck on. Obviously it needs to be a pretty tough rubber material when its finished and in black, but so far the only thing I have been albe to find is in the form of a thick paste applied with a mastic gun.
What I really need is a 2 part liguid that I can pour in that will set in the absence of air. The paste stuff would be ok except it will not set!.
Any ideas or help would be appreciated.
Thanks,

John.

ps2727

John,
I too have been on the lookout for a tire molding material. I've tried a two part urethane product which set up great but was too soft. That material is available in "harder" forms ( they are measured in units of durometer or on the Shore scale) but I haven't tried another type. I suspect urethane will not be the answer as I don't think it will hold up under use. I would like to find a hard foam material but I don't know if it needs high temp or pressure equipment. It may not be practical for a home shop. If you come across any suitable product please let us know.
Paul

eraysa

John,
Being a tyre producer, I can tell you that it's almost impossible to do at home ...
You practicaly need unvucanized Rubber-compound and this in a suitable form of a slab plus heat of at least 120 degrees celcius 250 F..
Eray

JohnMac

Thanks for the input Eray. I could apply that kind of heat but I imagine there might be toxic side effects. On top of that if i were to screw
up the oven in the kitchen my wife would become pretty toxic too.
I have read in the magazines that people have moulded there own tyres from a 2 part mix in the past , but I no longer have the articles.
Rehgards,

John.

JohnMac

Hi Paul, thanks for the feedback,
The paste I mention in my original post is certainly durable enough, if I could only get it to set. It is intended to repair rubber pond liners. I also tried layering the paste in the mould, letting one layer just about go off before adding another. If it were less viscous this might work. I might try some kind of thinning solution.
best regards,

John.

eraysa

John,
the kitchen oven would work theoreticaly,however I have serious concerns about your wife letting you do it..
The fumes are of horrible odor and would take 2-3 ours to cure with nprobably at least 3-4 trials until you have reached the optimum quantity of rubber in the mold...
What are the dimensions of the tire?

Rgds
Eray

Gordon Mc

My Feedback: (11)

If the oven would work and your only concerns are the smell in the kutchen & the reaction of the wife, couldn't you just get yourself a cheap portable "toaster oven" and do the work in your garage or even outdoors ?

Gordon

Vampire

My Feedback: (2)

Hello John:

McMaster Carr Supply (www.mcmaster.com) has several 2 part, Black Urethane's with a 60, 80 & 94 durometer which I have used for years with great success. It is air cured and will harden in 1-2 hours and will achieve max hardness in several days. (the 94 p/n is 8644K11)

After it solidifies, remove the tire from the molds as it has some flexability before it fully cures, expand over a wheel lip. (with a bit of force) I have madeup tappered wood plugs for this purpose.

Hope this helps.
Regards:

eraysa

Gordon,

I said only 'theoretically' .Actually one would have to apply pressure so the rubber can take form in the mold.

Rgds
Eray

F86_SABRE

Sorry to butt in guys.

I have a set that Eray has done and its really premium quality tyres. These are going to be used in my Kangaroo and hopefully it would be flying soon.

In my opinion and believe me I am no expert in tyre making but anything like this which involves fumes etc that might be harmful to the person is best left for the pros. After all we spend a bunch of money on these planes so why would we skimp on this detail....for health reasons.

Again guys....sorry for butting in but I wanted to air my opinion on this matter.

Thanks

Regards

Reuben

rpmtech

My Feedback: (6)

I suggest that you vacuum cast it if you can, as most 2 part urethanes are pretty thick and dont release all the air bubbles from mixing. When I make silicone molds I mix the silicone then pour it in a large container and put in the vacuum chamber,it will bubble fiercly under vacuum so you need a container about 4 times the volume of the batch. You dont have to vacuum it, but it makes it way more uniform and stronger than just mix and pour. It does depend on the thickness of the resin too, so you might not need to vacuum it of it is thin enough.

As for material 2 part Urethane is pretty tough but I would be afraid of it chunking in use.

Good topic

Kevin_W

My Feedback: (1)

If you can find a two part silicone or urethane I would suggest you spin the mold while it is curing, the centrifugal force will cause the heavier material (liquid silicone or urethane) to migrate to the outside of the mold, and the lighter material (whatever small trapped air bubbles are in there) to be forced to the center (where it doesn't really matter anyway). I have heard of people using old record (phonograph) players for this purpose.

I was going to try molding the nose tire for my Aeromacchi but I was not able to find a suitable compound to mold them out of. Instead I found that a Dubro tire was approximately the right dimension (although not nearly stiff enough to handle the weight), and I used a large syrenge (sp) to inject some two part urethane that I had for mold making. Then I spun them on my lathe while they were curing. It worked surprisingly well !!

If you are able to locate a good compound for molding your tires out of please let us know what it is and where to find it.

Good luck.

JohnMac

Hey Thanks guys. Some relly interesting ideas here. I think I will try the cold cure urethane sytem, but since I own a vacuum sytem for wing bagging, I might turn the grey matter to utilising this system for a batter, bubble free moulding.
I will come back with the results, but I am open to any other ideas please.

Modelman

My Feedback: (7)

I own a Rapid Prototyping / RIM shop and here's what I would recommend.

PMC-790 Urethane

PMC-790 urethane rubber cures to a Shore-A 90 hardness, but pours at only 3000 cps. (maple syrup). Air entrapment is minimal, so vacuum degassing is usually not required.

The natural color of the material is a clear amber, so you will need to add a colorant. I recommend Vantico PIM Black available from White Pine Lumber, Inc.

If air entrapment does become a problem (depending on the configuration of your tool) - I would recommend pressure casting over vacuum casting for those whom haven't tried this before.

The issuue with vacuum casting is that your tool needs to have been made with degassed silicone. If you simply mixed the silicone and made a mold, your mold will likely have entrapped air. Put this mold into a vacuum chamber and the air bubbles will expand deforming your mold and possibly rupturing.

Pressure casting is easier on the tool, especially if the tool was made with hand-mixed silicone. Pressure chambers can be purchased or made from old Pressure cookers. Just hook it up to your compressor (a little rigging required) . Place your filled mold into the chamber, close it and ramp the pressure to 60 psi. Any trapped air in the Urethane will still be there - however, it will be compressed into microscopic bubbles.

If you have any specific questions, please feel free to PM me. We'll exchange phone numbers and talk about it.

Here is a list of materials that I would recommend:

Mold material: OOMO 30 silicone - A very friendly Additivr cure Silicone that measures 1:1 by volume and fully cures in 6 hours.
$22.00 / Quart from www.smooth-on.com

Tire Material: PMC-790 Urethane - A hard, tough Urethane. Measures 2:1 by volume and pours very easily (cures in 16 hours). Requires colorant.
$25.00 / Quart from Smooth-On

PIM Black colorant for the Urethane. "Just a dab will do ya'". One container is probably a lifetime supply for the hobby user.
$25.00 / 400g (pint) jar from White Pine Lumber Industries - http://www.wplindustries.com/index.html

Hope this helps...

Craig

JohnMac

Hi Craig,
Yes it certainly does, thankyou. You clearly know your onions on the subject. I will take a look at the websites you mentioned. The only thing is that I am in the UK, and I could do with trying to find a local supplier. If not I will try to get these companies to export the materials to me. I may well call you when I have done a little more reaserch on the materials.
Thanks again,
John.

Modelman

My Feedback: (7)

Hi John,

UK distributors of Smooth-On products:

Bentley Chemicals Ltd.
Rowland Way
Hoo Farm Indust. Estate
Kidderminster, Worcestershire DY11 7RA
England
011-44-1562-515121
Fax: 011-44-1562-515847
Contact: Peter Bentley Turnoc
www.bentleychemicals.co.uk

Bentley Chemicals East London
54 Gordon Road
London
E4 6BU
Tel : 011-44-020-852-9099
Fax : 011-44-020-852-90999
Mobile: 07760 177700
Contact : Chris Warren

Alec Tiranti Ltd.
70 High St.
Reading, Berkshire RG7 5 AR
United Kingdom
011-44-118-930-2775
Fax: 011-44-118-932-3487
Contact: J. Lyons
[email protected]
www.tiranti.co.uk

UK Vantico Distributor:

John Burn & Co (B'ham) Ltd

74 Albert Road
Stechford
Birmingham
B33 9AJ
UK

t: 0121 508 4144
f: 0121 508 4145
e: [email protected]
w: www.johnburn.co.uk


Hope this helps!

Craig

JohnMac

Hi craig,
Thanks, I also got the info from their web site. I have emailed for info but no answer yet.
Thanks for your help.
Best Regards,

John

cactusflyer

My Feedback: (4)

Hello John,

What size is your Viggen? I might also be in the market for a few tires. I used to fly a Learjet for a tire manufacturer. I learned that it takes "rubber, heat, pressure, and time" to make a tire. Who knows, maybe I could cash in a few favors and get them to mold a few....your metal mold is a definite "plus".

Regards,

John

JohnMac

Hi John,
This model is built from the Jim Fox kit 1/9th scale if I remember correctly. It was built for DF but never flown. I got the scale retracts that were availble at the time but skipped the brakes. Trouble is tyres are made of foam rubber and useless for jet use. The design is ultra slim so no way will any commercially available tyres fit.
Best Regards,

John.

JohnMac

Well Guys,
The first Tyre is curing as I write. It should be ready to turn out of the mould in the morning. I used the Smooth-On product as suggested. I bought the smallest packs available of PMS 780 and 860, slight softer than that suggested, but the samples of 790 that I got from Bentley Chemicals in the UK were rock hard. I reckon that the 1.3kG packs should do dozens of tryes. At this stage I merely pored the liquid into each mould half, waited for the liquid to start to thicken and joined the halves together. Whether this is a satisfactory technique, only time will tell. However, If it should prove not to work the have to drill some hole in the mould to inject the liquid and release the air. All interesting stuff. I will report the results tommorow.
Regards,

John.

Woketman

My Feedback: (6)

Please do report as I find this VERY interesting. Thanks for the info.

mr_matt

My Feedback: (10)

Tad at Golden West Models is an expert at molding tires as well.

Good luck with the project.

TimD.

My Feedback: (207)

Another alternative to molding.

In the past I have taken black boat roller's, you can get them up to 3 1/2" and turn them on a lathe to make the tires. The compound works very well and is easily manulipated on a lathe. You can find the roller's at any local boat supplier.
When you are done put the tire in a bowl of water put in the microwave for 1:30 min this will soften the rubber to put them on . Wear some kind of glove's it will be hot.

I like the ideas in this thread and thought I would share one of mine.

Tim D.

JohnMac

OK guys,
The first tyre is out of the mould as clean as a whistle, small, black and pefectly formed. That's the good news. The bad news is that it is very soft, much softer than the sample of the cured material that I have. You will remember that Craig recommended PMC790. I chose to try PMC 860 and 780 because the sample of 790 was as hard as as rock.
So, the question is will the material harden up with time and is that what has happened to make the samples so hard? If so how much time is required to reach full hardness?
Also the instructions make it clear that the material can be heat treated post cure @150 deg c for 4-8 hours. So my friend (the one with the machine shop who machined the moulds for me), also has a portable digital control oven, so thats the next step (in the garden shed I hasten to add, lest I be laid low by razor sharp tongue!). In the meantime I have a batch of the harder PMC 780 in the mould. I will try to get some pictures as well i the next few days.
Any comments would be appreciated at this stage.
Regards,

John.

JohnMac

Ok Guys,
The latest instalment. I now have the original tyre that i moulded hardened off to the point where it is quite viable for use. This is made from the Smooth On PMC 680. However I have also moulded 3 tyres from the PMC 780 and these have moulded perfectely. Morover these 3 780 tyres are that bit harder than the 680 one and more suited to jet use.
So just to recap, I started by drawing the tyres in Autocad, having moulds turned in metal (just happens to be bronze), a register pin inserted in the centre to ensure accurate positioning of the mould halves. One tip, ensure that the opposite face (the outside face) of the mould is parallel to the inside face and find an absolutely level surface for pouring the solution into the mould. It's important to get the levels right.
Bentley Chemicals here in the UK sold me 2 1.3Kg starter kits, 2 cans of release agent and a small qty of colourant called So-Strong.
This lot cost me about £87 including shipping.
The instructions are very clear and the process is very simple. Mix the correct ratio (2:1), mix for a few minutes, add the colourant and allow to stand for a few minutes. This allows the air bubble to rise to the surface. Then the solution is pored slowly and carefully into each mould half. Now leave the job for about 30-40 minutes, checking the remaining solution regularly. When the solution is rweaching the end of its pot life it begins to thicken. It is necessary to judge just the right moment when the mould halves can be brought together without the solution running out. A little excess will squeeze out, this is ok. Leave at room temparture for 24 hours. The mould should part easily and he flash just pulls away with your fingers.
So there we have it guys, a system to make tyres that really works.
I just need some brakes now and my gear is complete.
My thanks to all who provided input and especially to Craig who put me straight onto the right track.
Regards,

John.