Hi guys I am looking at doing some moulds for our friend on our machining centre - we mainly do high end 3D production parts and injection moulds. I am interested in making Lrtm moulds but cannot find much info out there on sizing the flanges. Part will be 5mm thick with some fairly complex geometry on the B mould side. Around 1m long and 250mm wide by around 200 deep. It is a remote control boat with pockets inside for the batteries motors etc. Can anyone give me some info on how the flanges are worked out?

So you're making a top and bottom mold for this boat - which will be filled with fiber and infused with resin... are you planning a core kit to fill the spaces between the B-side and the A-side in way of the complex geometry?  Generally the flange will be the thing to provide the clamping pressure in LRTM using a vacuum clamp between two sets of seals - so a big flange!  The resin feed will be an issue to sort out beforehand... feeding from the perimeter may be a good option depending on part geometry but maybe not... Either way you'll need a perimeter manifold for resin or vacuum that overlaps the excess "flash" material onto the flange. So long and short - you'll want big flanges!  300mm is not uncommon. 

There are some really useful videos by JHM Technologies on YouTube: 

https://www.youtube.com/watch?v=7knLFB87ENg

https://www.youtube.com/watch?v=-f4UlpXpaXA

Thanks Chris, things have moved on with this now and it looks like just the basic hull will be moulded now. The pockets and voids for batteries inside will be made by machining a billet aluminium insert so it is much more simplified. I have watched the videos you mention and almost every other I could find and understand the concept. No one really goes into detail about the width required to get enough flow around the channel etc. or whether making the channel thickness different to the part may help etc.
I am using the term lrtm loosely here. We are proving out the design of this thing and trying to learn about the process this way eventually it will be metal tooling. It looks like I may have another toolmaker who is willing to share some knowledge which might help hopefully too.

Cheers