Hey all!
I am making a mold for motorcycle fairings and have a question.
What I have is a recess that is approx 30mm diameter and 30mm deep. Traditionally I would get tremendous bridging if I tried to do this in a conventional method. Any suggestions on how I could make a mold while maintaining these recesses?
Thanks!
It will give you little trouble if you can create a slight draft angle into the wall when making your plug. Think slight conical close to the hardware,But leaving tolerance.
Thank you for the response. I can use some filling material to make it slightly conical.
My main concern is how to get the molding material to properly fill this recess? Typically I would use epoxy and fiberglass but I seem to get very bad bridging no matter how good my vacuum is. I was wondering specifically if I should use some other material? Fill it with chopped fiberglass?
I have tried this several times without positive results, I always get voids.
Mixing up some resin and chopped glass or strands VERY fine should make a decent putty to build that zone on top of your tooling gelcoat as you make your mold. Just be detailed in the shape you make and think of how the next layer of mat/cloth will drape.
Depending on the size of the fairing you could use epoxy mould making putty altogether… with a good tooling gelcoat it should be no problem. The conical tip is good too.
Yet I take it its quite a large part, are you worried the gelcoat will lock when you pull the plug? Shouldnt be a problem with a quality gelcoat and good release agent.
The mould making putty, you will need a lot for a side fairing, but you could use it on all the fasteners in conjunction with fiberglass.
cheers
On a detail like that, if I suppose to make many parts out of that mould, I prefer to shape on a lathe an aluminium plug that fits the cavity, letting the mould to surround it.
This sounds like it has possibilities. Would you be able to recommend a mold making putty? Having never used something like this, I am assuming the following steps:
Tooling gelcoat
Putty the recesses
lay epoxy/fiberglass until mold is complete
Obviously overly simplified but is that the general idea?
Thanks Roberto but sadly I do not have access to CNC equipment or a lathe.
High PainfullySlo,
sorry for the late reply, I have made several moulds from the putty alone, and it works as follows:
The site has more detailed instructions and a video, but just to get the idea.
In your case, since you are doing a motorcycle fairing i presume, you will need quite a lot of putty, here is how I would do it.
Build a mould frame from timber, tall enough to accomodate the depth of the part, pva release and wax to the plug (i think with chemical release agent the gelcoat will tend to run off). attach a sheet of release film to the frame and lay it on a flat surface, make sure its nice and stretched, this will be your flange surface, you can work inside the frame.
cover the plug and surface of flanges with a coat of tooling gel, if it seems a little thin, allow it to reach tacky stage and apply another coat.
When the gelcoat is tacky, mix up your putty and with a rolling pin roll it out to approx 1/2 to 3/4 inch depending on how much you have, place the putty over the part and and press it down all over the part making sure its in good contact with the gelcoat everywhere.
Depending on how thick your putty is, you can use additional glass fiber and laminating epoxy, in cloth form or light CSM to reinforce the the putty right to the sides of your frame.
When all has cured after 24hrs or so, flip your mould over, demould and thats it. 
the putty can be found here:
http://easycomposites.co.uk/products/starter-kits/epoxy-mould-making-starter-kit-large.aspx
there are of course many ways to do it, but i reckon it will create a solid mould for indefinate uses.
cheers
1: Do it right, no bridging. 
2: extend the bolt, and add a spacer, while keeping the bolt location flat. I don’t see how a bolt head would be less aerodynamic than a hole like that anyway. SPacer can be nylon, delrin, chunk of carbon, etc.
I followed those instructions as per the supplier and had the tooling gel breakaway from the putty, I tried a couple of times to verify that I had not done something stupid.
When I spoke to the suppliers about my problems they told me that I should wet the tooling gelcoat with epoxy resin, once it had become tacky, prior to placing the putty, even though they themselves omitted this stage from their instructional video.
I have not bothered using the putty since but have seen on this site people have used the putty successfully over the tooling gel but between glass cloth. I am going to try this method next time as the idea of bulking a mould with putty over glass cloth saves both money and time.
This is exactly how I do it. I’ve never had inteface problems. All the tooling doughs/compounds that I have used have always recommended doing this.
As an aside, you may consider filling the female sharp edges with a piece of tow (can be pulled out of a woven) in order to reinforcce that feature. That seems to work ok with wet lay-up, and can work very well with an infusion. Best of luck.