iab

Thank you.

For fine work, the vacuum is an absolute necessity. Take a close look at the where the cable comes out of the hood. I did not degas the urethane and there are hundreds of micro-bubbles making a horrible finish. If you do that with the silicone mold, you will get the opposite, a lot voids around the part that will get filled with the urethane.

Anything with a low durometer, 35-85 Shore A, will be highly viscous and does not like to release its trapped air. If you mold a hard urethane, 60 SHore D, that has the viscosity of water and there is no need for a vacuum.

Degassing silicone works pretty well. And when you pour it into the cavity, do it slow with a flat ribbon, you can see air bubbles "pop" in the ribbon. The urethan is a different matter. It really doesn't like giving up it air. But what happens is that the bubbles are so small, they cannot break the viscosity of the liquid. There is a "skin" on the surface, no voids.

I am trying new techniques to remove all bubbles from the urethane so a clear version will actually be clear.

Numbskull

Brilliant.
Thank you for posting this.
Your pictures, instructions, and (in particular) additional hints are outstanding.
I've long been considering doing this to cast lead fishing lures and your clear instructions are a inspiration to proceed.
Once I have the stuff for doing that I might as well make some Campy hoods in the older dark color you can't get from current reproductions.

rootboy 

That's interesting. It was always my impression that the older, darker color came from just from age.
I vaguely remember buying a set of original hoods from a bike shop in Salt Lake, maybe mid to late 80's.
And they were about the same color as the current repops, if I remember correctly. They were pretty scarce
even then and the shop owner would only sell one set per customer. They were 24 bucks.

On Iab's Vittoria hoods, the fact that maybe only 5 or 6 others would be interested in buying these, if that, is missing the point.
It's the voyage that counts, in my view. Really great documentary.

SloButWide 

Thanks for taking the trouble to describe what you've done. You've gone to great detail! There is so much knowledge locked up in folks' heads - it's nice to see posts that are "Here's How". Not that I have anything against the "Look what I did!" posts.

obrentharris 

Oh no! A whole new world of fabrication has been spread out in front of my eyes. I am an inveterate tinkerer and this is difficult to resist.
Thank You iab... I think.
Brent

Darth Lefty 

Nicely done.

If you can cast the compound into the vacuum bell through a valve, the stream falling into the cup will degas as you do it. It's easier for a bubble to make it out of a narrow stream than from the bottom of a cup. You can also put the mold under vacuum once you've cast the part in order to pull any voids out of the part.

What level vacuum, or are you measuring it? I don't think I'd have trusted that pot.

juvela

thanks so much for this fabulous post iab!

a beautiful job with the project and with its documentation.

this model of Vittoria brake lever hood is called the Giro d'Italia.

they did another model which was without the bumps and which was called the Tour de France.

iirc Ambrosiana Gomma also made the hoods for Fratelli Pietra and for Giovanni Galli S.p.A.; do you know if that is correct?

Thank you again.

Kactus

I feel that I'm fairly handy, but seeing projects like this makes me feel very inadequate. Outstanding work iab.

Numbskull

The first campy brakes I owned were back in 1972. The hoods were a darker translucent root beer or light mahogany color. These current reproductions seem sickly in comparison. I've thought about trying to dye them but I suspect it wouldn't work particularly well. Making them, however, seems very possible thanks to iab's guidance.

juvela

same for me with the pietras. always liked the translucent colour and the blue hotstamp. they came that way through about 1976. beginning about 1977 they went to a more milky looking material which was opaque and eliminated the hotstamp.

Pars 

Nice job and great thread!

unworthy1

A fantastic "how-to" and very professional! I have done a little bit of mold-making and casting but my efforts are embarrassing compared to this.

a slight hi-jack: I'm curious about what this means:
"BTW: If anyone is considering a low cost alternative to a vacuum pump, look into an inline vacuum generator + on/off valve that uses a conventional air compressor. The tiny vac. gen is basically a venturi with exhaust port. Handy for small projects like the above or veneer glue downs on wood (along with with bag), etc."

I'll poke around on Google and see if I can find more info but if crank_addict can show us a picture...
I'm hoping that a "conventional air compressor" is something I already own....

iab

A venturi valve, https://en.wikipedia.org/wiki/Venturi_effect , can take a compresser air flow and turn it into a vacuum.

My experience with them is not good. It comes no where close to drawing a vacuum like the pump I pictured.

One example

Venturi Vacuum System-Carbide Router Bits | Router Bit Sets | Shaper Cutters | Saw Blades | Planer Knives | Jointer Knives | Infinity Cutting Tools

Velocivixen

@iab - I echo everyone's sentiment and say Thank You and job well done! Very creative and resourceful. Thank you for the excellent photos and explanations.

Now I'm sitting here wondering if I could do that and what I would recreate!

fleslider 

I second the 600 EX hoods i need a couple pairs!

rccardr 

David, you continue to astound me. Nicely done!

Michael Angelo 

Innovative and informative.....post of the year.

OTS 

Great write up, great job, interesting topic.......A++++ ( 4 out of 4 stars )

ItalianPower

Unbelievable work David! Really impressed with your work and how you have documented the process. Thanks for the lesson!

crank_addict

(unworthy1 quote)
a slight hi-jack: I'm curious about what this means:
"BTW: If anyone is considering a low cost alternative to a vacuum pump, look into an inline vacuum generator + on/off valve that uses a conventional air compressor. The tiny vac. gen is basically a venturi with exhaust port. Handy for small projects like the above or veneer glue downs on wood (along with with bag), etc."

I'll poke around on Google and see if I can find more info but if crank_addict can show us a picture...
I'm hoping that a "conventional air compressor" is something I already own....

Agree to not hi-jCK Daves brilliant project.

(In short, long time user of a Festo made inline vac gen used on a lathe for securing spinning and finish work of 'porous wood' vessel and platters. With an air tank and compressor (even if small cap.), should there be an interuption of electric power, the air reserve in the tank, via the vac chuck provides a safety net in holding the work piece, allowing plenty of time for one to remove the work piece. You're welcome to pm and then exchange e. Having a difficult time with comm. browser and or this site.)

79pmooney

Nice work! Not my bag but I used to build high quality hand laminated sailboats with vacuum bagged balsa cores.  Completely different operations (and scale!) but much of the same attention to preparation.

Ben

RosyRambler

WOW!! DIY Award of the year!

Bikerider007

Had to bring this one back, not sure how it was missed! Phenomenal work @iab. You should make and sell some various types of hoods, at least for the forum ;-) .

Thanks to Juvela for posting this link in the Legnano thread.

iab

Thanks.

I recently tried to cast a mold off of a Galli hood for smontonaro. Did not turn out well. Wherever the silicone touched the hood it did not cure. Maybe 0.5mm of goo. Seen that twice before. First time was a rookie mistake when I used a silicone spray as a release agent. On the Galli hood I used the proper naval jelly spray. Second time is when I used oil-based clay to fill some gaps. I have since found that Sculpy clay does not have an adverse affect.

repechage

I was surprised the example shown did not have issues. I was told long ago to make a hard pattern, then use stripable spray vinyl as the release agent for the mold.
The other acceptable known method was "ID" clay as used in the auto design industry most notably, its biggest ingredient is wax.
I have actual notes, but its been decades!