Hello,

I am trying to brainstorm a way to make a mold for a 3" diameter sphere. I want the final part to be a bare carbon fiber sphere for a shift knob in a vehicle. Will make 3 of these knobs, one for me and one for each of my two roommates. Thinking of a mold that splits the sphere in half as I don't really care about a split line in the carbon on the actual part.

The only real challenge is how to join the actual part during the layup. Thinking a joggle gasket type setup? Anyone have any recommendations or other ideas for how I can accomplish this?

Thanks for any help!

You can use foam as the mold then dissolve or scrap away the foam. However it probably would be a good idea to make it solid. So you can mold it over a block of wood, or whatever suitable material you can find.

Lay up two half spheres in female molds, let them cure. Trim down to mold edge. Then lay solid beads of thickened epoxy around the edges, and clamp together. My favorite glue for carbon, is 3M DP490.

Lars.

Will gluing the top and bottom part together with epoxy thickened with graphite powder be strong enough? Seems to me this part will have a small surface area to be joined together. Might have to build up a ledge on both parts for more surface area?

Is there going to be a place you need a threaded insert or something to attach it?. Use that to your advantage. Make the mold. You can inflate a balloon through there. Layup one side flush with parting plane, the other 1/4" above. Before joining, wrap this side with fishing line to lay the fabric down. Join the two halves with balloon in place. Cut and remove the string. This will give a nice seam. Clamp and inflate.

Or, why not buy a cheap one and add carbon fiber to the outside. After, wet sand and polish it if needed.

Cf is not a good material for any kind of handle. Any small splinters of carbon coming loose can get embedded in your skin and the travel around inside of you. At best they can be an irritant.

Im not worried about splinters at all. The final part will be clear coated with a 2k paint. The fishing line sounds like the best idea. I think ill give that a shot and see how it turns out

All tog
Hi nighthawk

It might be worth concideing making PU foam core first and just do a wet lay up and compress it all together.
Around the join line just run a wrap of twill carbon or double bias carbon around it , making sure you have 5 to 10mm overlap passed the seam. Very simple and effective.

Or
another option would be get your hands onto some polystyrene balls.... these can be brought in many many different sizes from craft stores etc and use this as your core. Using polystyrene this won’t get effected buy epoxy so your safe there.

Also....... If you going to make a mould of a 3inch sphere , it probably easier to find the right size plastic ball or solid rubber or silicon ball to use as your plug for the moulds. Just make life easier and quicker for you.

Cheers

Tim

You only want 3off so forget the mould.
Gear knob so weight is not a issue.
Find a ball the correct size, apply layers of glass.
Sand the steps from the layers of glass back to smooth.
Then do your carbon layer being carefull to get lay of clothe correct for looks.
A few layers of clear epoxy then sand and polish.

Might want to glue some dowel on to form shank for thread..

If you have made a mould, bog core would be easy and create a large surface to glue halves together.

Aren't there already countless bling bling carbon gearshift knobs on the market? None are suitable?
3" would be a pretty gigantic shifter knob, no?

Perhaps use a pool cue ball or such, make a typical parting board type mold, with bladder through the hole for threads.

I've made custom shifters for a long time with all kinds of stuff in them.

I just use a half spherical mold from the local fiberglass shop. Works great.

Bonus, the more the shifter is used, the more transparent it gets.

Aluminium bath bomb mould eBay

You could always fake it with hydrographics.

As mentioned 3" is way to big, I definitely over estimated the diameter the sphere needs to be.

The idea behind using a mold is to get a hollow part. With a shift knob you really want the thing to be as heavy as possible. I plan to make the hollow part and fill it with casting resin with copper bbs to add weight. Then add a insert for the threads.

I like the look of real carbon fiber and really enjoy hand made parts. Yes I could just buy a shift knob but the satisfaction just would not be there for me. This is all for fun!

Originally Posted by NighthawkF-117

As mentioned 3" is way to big, I definitely over estimated the diameter the sphere needs to be.

The idea behind using a mold is to get a hollow part. With a shift knob you really want the thing to be as heavy as possible. I plan to make the hollow part and fill it with casting resin with copper bbs to add weight. Then add a insert for the threads.

I like the look of real carbon fiber and really enjoy hand made parts. Yes I could just buy a shift knob but the satisfaction just would not be there for me. This is all for fun!

Work is shutting down for Chrissy, I'll be going in to machine some wing moulds.
I'll have spare time so could machine a mould for you. Price labour $100, material steel is free or maybe have some alloy. Postage allow $100 for steel to the USA.

Will need to know size of ball and thread.