1/4 Scale Cosworth DFV Engine

[Vixen]

Mike,
...............Also there's less likelihood of scrapping a print because one area failed.
Maybe your cheap Chinese printer might still be able to produce a decent model?

Jon

No chance, I gave up on the 'cheap as chips' Chinese printer and gave it to my grandson to play with.

Mike

[JonC]

Hello Jon,

That looks to be a very practical solution to the staggered cylinders and belts. 

I assume the crankshaft pulley has the two belts running side by side.

I am impressed with your idea of building a plastic mock-up to tease out all the tolerance and clearance issues before you commit to the castings. You cannot afford to find problems, once the die is cast, as they say.

Mike


Hi Mike,

Yes, both belts run off the crankshaft

Jon

[ddmckee54]

Jon:

That printed tire master that you showed back in Post #45 was outstanding!  What material did you use to print it, and what printer did you print it on?

Don

[JonC]

Hi Don, thank for the comments. It's all PLA printed on a cheap Labists FDM printer with Simplify3D slicer.

Jon

[ddmckee54]

Jon:

What was the layer height?  I've gone down to 0.1mm and I can still see the layers.  I couldn't see any layers in that picture and I thought maybe you used a resin printer.

Don

[JonC]

Hi Don,

I think I used 0.2mm layer height and then did a lot of post process filling and sanding. I also printed it in three sections, the first was half the tyre including a side wall but because this needed a load of support I did the other half of the tyre by printing just the outer diameter and then the side wall separately and then glued it all together. This is a master for a mould I'm making so they can be produced in rubber so only the outer detail was important.
BTW, the AVON lettering is also printed separately and the very small lettering I bought and again glued them both on.

Hope this helps

Jon

[crueby]

Very impressive results - looking forward to see how you mould them!

[tvoght]

Very impressive results - looking forward to see how you mould them!

Agreed. What was used for glue on the PLA, and what as a filler?
--Tim

[ddmckee54]

Jon:

When you showed the inside of the tire I can see that you did indeed do a lot of post-processing - excellent work!

When you say you printed the AVON separately and glued it on, do you mean that printed the letters flat and then glued them on the curved tire, or did you print the letters on a section of the tire?

Like Tim, I'd like to know what you used for a glue.  I've used Weldon 4 as a PLA solvent cement before and had fairly good luck.  I used it on a red filament and for some reason it bleached the red out of the filament, the bond was excellent though.  Apparently I didn't have the cap screwed on tight enough to the can, because when I wanted to use it several weeks/months later it had completely evaporated.  I've read that Weldon 3 doesn't evaporate as fast as Weldon 4 so maybe that would be a better choice.  Or maybe even Weldon 16, since it is thicker still and comes in a tube.

Don

[JonC]

Hi Don,

I just use super glue. The AVON was printed flat with just a couple of 0.1mm layers and connectors to all the letters and other areas where they are free, ie the centre of the A etc. I then curved the whole set over a similar radius prior to gluing onto the tyre. The connectors were then cut off.
We have some really good aggressive Emery we use at work that makes the sanding really easy. I’ve used commercial body filler before for major filling and Humbrol fine filler for more detailed work.
Ive already moulded rubber spark plug bungs and CV boots for the DFV and FG400 so I’m hoping the tyre works as well, although I’m now told that they ran Goodyear’s in the 70’s

Jon

[ddmckee54]

Jon:

From the quality of your master I think your tires will be just fine.  How thin of a tire cross-section are you planning on molding?  Getting the mold for the tire interior out of the completed tire will be the big challenge.  How many parts do you think the completed tire mold will be made of?

Don

[JonC]

Hi Don,

I've taken a guess at the cross sections. The walls are squared off internally to try and ensure some strength when supporting the car and are 4mm at the thickest part. The diameter is only 2mm thick but I'll add some support in the way of a foam ring if it's not sufficient.

I've thought about various ways of making the internal mold so it can be extracted and come up with a 12 piece segmented 3D print that will hopefully work.

The finished tyre will be ultimately be from a two part mold with the split line around the corner step of the tyre.

Jon

[crueby]

Love the sliding dovetails on the inner mould pieces.   

[ddmckee54]

Jon:

Will the tire compound be soft enough with a 4mm wall thickness to give you a realistic tire contact patch?

Also are you planning on using anything to seal the gaps between the mold segments?  When I molded the silicon boot for the hot block on my 3D printer I also used a 3D printed mold.  I didn't seal the gaps between the mold sections and I got flash in every joint. (I allowed 0.25mm between parts, and there were 7 parts to that mold.)  Any flash between your sliding segments might make it hard to remove the segment after the tire is cured.

Don

[Vixen]

Fill the gaps between the mold segments with a good dollop of petroleum jelly (Vaseline). If you use a paintbrush, you will get an even coating of the jelly on all surfaces and it will act as an excellent release agent

Mike