[petestrike]

i've just given myself quite a headache trawling through the "how to" threads. i am contemplating having a go and i think i've got the basic idea of the process now , but the selection of materials seems to be a bit of a minefield. ideally , i would like to source them from the uk (preferably from one supplier) at reasonable cost. i have been looking at the mbfg.co.uk website , which seems pretty comprehensive , but i thought before i e-mailed them and made myself sound like a gibbering idiot i would see if anyone has used them and if so what specific materials (and grades) to use. i would be , mostly , making small slix tyres for classic scaley mini/escort/260z too run on new sport track. from what ive read , i think , i would be looking at a shore 40 eurathane? initially i would be looking at approx 20/30 units. please be gentle with my delicate brain......its just taken a beating!!!

 

[Mr Modifier]

Hi Petestrike,

I have used MBFG for my tyre making stuff in the past.

Use the general purpose silicone mould making rubber. I used to use this but actually bought my last batch from another supplier because it was a bit cheaper.

For the tyres themselves I have used the Polytek T Flex 20 and PT Flex 50 rubbers BUT they have hellish short curing times so don't mix more than 40 grammes in TOTAL or it will thicken and set before you finish pouring.

Using a syringe to put the urethane in the moulds makes life a little easier BUT the pot life is too short to make it easy.

My next batch will be done using urethane mould making rubber from a different supplier - this has a pot life of 15-20 minutes rather than 2 minutes and will be far less stressful.

If you do mix only 40 grammes then the best way to measure the pigment is to dip a lolly stick about 10mm into the pot then lift it straight out - this tiny amount of pigment will give you jet black tyres. Make sure you pre-mix the pigment thoroughly into the correct part before combining parts A and B of the urethane.

If you are making small superslix - do not go softer than Shore A 40 - I made some in Shore A 20 and the tyres peel from the rims under cornering and acceleration - urethane stretches more than standard rubber. Shore A 40 or 50 is perfect for these little tyres.

If you make large superslix then Shore A 20 is great - the tyres are really thick so the tyres do not peel off and they are super sticky and actually quite controllable on the edge of adhesion.

I am going to order my next batch of stuff from tiranti.co.uk as they have some shore A 40 slow curing urethane rubber that will make the whole casting process a little less rushed (I hope!) and they are cheaper than MBFG for the stuff I want.

 

[petestrike]

mr modifier, how do you do it? top advise , as always. you manage to make every answer sound like one syllable , however many words it takes! it took me reading one of your posts in another thread about the actual technique before i finally got the drop on it. i take it that the mould making material is not particularly critical. i also notice from that other thread that you run my kind of cars (mini/escort/zed) on sport track (snap)...ideal for comparison. thanks!

 

[Mr Modifier]

Hi Petestrike,

You are most welcome!

You are right - the silicone mould making material is not particularly critical - a high tensile strength is handy because that makes it more resistant to tearing.

The silicones I have used are all around Shore A 25-27 and are all billed as general purpose mould making material.

On my first attempt at making a mould I forgot to shake the red catalyst. I sweated on it for days before taking the plunge to take the moulds out of the mould boxes only to find they were perfect!!! It seems the red stuff that settles at the bottom is only pigment because the silicone came out white not pink and I have used that mould at least 10 times with no problems. Better to shake it properly though, and I have not forgotten since!!! Silicone seems to be quite forgiving.

The urethane is less forgiving - if you don't make a perfect mix you can get some tyres that don't set properly and ooze out of the mould

This is why I am switching to urethane mould making rubber (rather than urethane casting rubber - it seems to be what most of the professionals/semi-professionals use for tyre making.

By the way - apparently urethane rubber contains alcohol and water and finished tyres can sometimes appear to become "wet" some time after casting - this is normal weeping from the urethane and is not an indication of a problem.

If you use softer urethane - store the tyres side down flat and not in a pile - I shoved about 12 NASCAR tyres into a tub after they were a few days old (fully cured so I thought) and a few weeks later some of them had taken on a distinctly kinked oval shape!

Have fun Pete - and let us know how you get on (preferably with photos) - the urethanes will transform your escorts, zeds and minis on Sport Track. No magnets required.

 

[petestrike]

QUOTE (Mr Modifier @ 9 Apr 2012, 16:37) <{POST_SNAPBACK}>Have fun Pete - and let us know how you get on (preferably with photos) - the urethanes will transform your escorts, zeds and minis on Sport Track. No magnets required.

with the help of your idiot-proof help i dont think i can go wrong! it may be a while before i get to it (lots of irons in fires & all that) but i will most cetainly keep any progress updated , with pics. magnets are just plain wrong wrong wrong on the old classics....i enjoy "@rse-out" action too much. besides my eyes cant keep up with the modern sidewinder stuff with mags....i get too dizzy!!! wheres the fun in that?

i also had another thought...like you do. do you reckon that it would be possible to cast a "custom" tyre by clamping the chosen rim onto a flat base (ie; g clamp on the end of an axle) centralised in a plastic tube with the i/d appropriate to the desired o/d of the tyre? cast a little "proud" , then trimmed back and trued up? thinking out loud , i believe its called!

 

[Mr Modifier]

Hmmm - interesting idea.

Initial thoughts in response......

Getting the wheel perfectly central and parallel to the tube will be tricky - the less central - the more truing will be required.

Depending on the wheel (some hubs/spinners stick out further than the rim so you couldn't do this) you might try this;

Get a sheet of glass.
Cut down the plastic tube to the desired tyres width. Cut the tube as square as possible and sand the edges as smooth as you can.
Spread PVA glue (white wood glue) thinly on the glass.
Stick the wheel, outer rim down, onto the glass.
Stick the plastic tube down around the wheel with the wheel as central as possible.
Wait a couple of days for the PVA to fully dry.
Mix your Urethane and pour into the mould around the edge of the wheel. Use a syringe if you have one and make sure you dribble the urethane in so the air can get out.

Once the urethane has set remove the tube and pull up the wheel/tyre combo.

Wait a couple of days for the urethane to cure properly.

True the tyre and sand the edges to your desired radius.

Now use the tyre as a master to make a silicone mould so you can make more.

Extra thoughts;
If you want the tyre outer edge to be slightly proud of the rim (sticking out wider than the rim) simply make your tube a bit deeper and add a shim on the inner rim to build it up a bit, then turn the tyre around on the rim (inner edge becomes outer edge) and sand it back when truing. Of course I am assuming your wheel has an inner hub that stops you laying it inside edge down - if you can lay it inside edge down then you don't have to turn the tyre around. Just be careful not to damage the rim when sanding the tyre.

 

[dangermouse]

Here is a link to a guide on doing just what you were thinking

http://www.oldweirdherald.com/scalestuff/o.../silicones.html

I haven't used this method but have thought about it - I use silicone to make the mould of the tyre and Smooth On Reoflex 40 urethane

cheers
DM

 

[petestrike]

QUOTE (Mr Modifier @ 10 Apr 2012, 08:16) <{POST_SNAPBACK}>Hmmm - interesting idea.

Initial thoughts in response......

Getting the wheel perfectly central and parallel to the tube will be tricky - the less central - the more truing will be required.

Depending on the wheel (some hubs/spinners stick out further than the rim so you couldn't do this) you might try this;

Get a sheet of glass.
Cut down the plastic tube to the desired tyres width. Cut the tube as square as possible and sand the edges as smooth as you can.
Spread PVA glue (white wood glue) thinly on the glass.
Stick the wheel, outer rim down, onto the glass.
Stick the plastic tube down around the wheel with the wheel as central as possible.
Wait a couple of days for the PVA to fully dry.
Mix your Urethane and pour into the mould around the edge of the wheel. Use a syringe if you have one and make sure you dribble the urethane in so the air can get out.

Once the urethane has set remove the tube and pull up the wheel/tyre combo.

Wait a couple of days for the urethane to cure properly.

True the tyre and sand the edges to your desired radius.

Now use the tyre as a master to make a silicone mould so you can make more.

Extra thoughts;
If you want the tyre outer edge to be slightly proud of the rim (sticking out wider than the rim) simply make your tube a bit deeper and add a shim on the inner rim to build it up a bit, then turn the tyre around on the rim (inner edge becomes outer edge) and sand it back when truing. Of course I am assuming your wheel has an inner hub that stops you laying it inside edge down - if you can lay it inside edge down then you don't have to turn the tyre around. Just be careful not to damage the rim when sanding the tyre.

mr modifier....can you please get out of my head now please?

thats pretty much on the button to what i had in mind! i dont think any of the rims that i may possibly try this with would have proud centres but as another thought...if a sacrificial wheel was available then it could be drilled through and bolted/screwed to a smooth base (good old fashioned formica) etc rather than glass. i have , in years gone by , made moulds for grp jobs using it to good effect. all these ideas and ive never even had a go.....yet!!

 

[Mr Modifier]

exiting head ... now!

 

[petestrike]

QUOTE (Mr Modifier @ 10 Apr 2012, 21:16) <{POST_SNAPBACK}>

exiting head ... now!

phew...thank gaawd for that.... you , me .... and all these ideas buzzing round ...... it was getting a bit crowded in there!!