Monday, October 27, 2008

CNC Routers, Vacuum Bag Test and a Surf Canoe

This past week was a hodgepodge of work. The F22 building process is somewhat on hold because I'm waiting for materials to be shipped from the mainland. Hawai'i is a wonderful place unless you need to find unusual materials. Biaxial fibergass is one of these. I'm currently waiting for a large shipment of fiberglass, fillers, vacuum bagging material and laminating tools from Fiberglass Supply in Washington state. It will probably be another two weeks before it arrives. Bummer.

Until then, I have been keeping busy with several mini-projects. The first one is a test of pulling a vacuum bag on the foam surface. When I was laying the foam strips down for the core of this boat, I extended the strips proud of the keel join line and further forward and aft of the ama's overall lines. On these extensions, I covered the foam with a putty mixture of epoxy, microspheres and colloidal silica. To test the vacuum that could be achieved, I re-used a piece of bagging material from another project, recycled breather material and a single vacuum port.

The picture below illustrates this better than I can in words, but the net effect is that I was able to obtain a vacuum pressure of 12 in Hg (roughly 6psi). This is not ideal (I'd prefer around 15-20 in Hg), but it will do. I think the leaks are due to the fact that 1) air is being drawn from the deck flange, especially at the bow and 2) I am reusing bagging material with holes that have been patched with masking tape (the blue tape). I'm hoping that the actual bag will be a bit better.

Also, the Marine Education Training Center now has a CNC router, which takes CAD drawings and converts them into computer code (G-code) to cut out patterns. We have a three-axis router and I hope to use it to cut out bulkheads, form frames, the deck and foils (daggerboard + rudder). It is so cool to watch the router process, so I have attached a video below. The sharp pitched squeaking noise is from the spindle RPM being too low. We increased the RPMs from 12,000 to 18,000 during the cut to eliminate them.


Finally, I spent a large part of the week filling and fairing a 4-man outrigger surf canoe, which I built from April to August and now just needs to be painted. I built this boat because it has a similar construction to the F22, foam core and knitted double bias (+-45/45) fiberglass with epoxy resin. It is reinforced with carbon fiber stringers for the hull and around the waes in case the canoe will be sailed (to anchor traveler, etc).


Tor Rabe said...

I think also 3) It is not possible to get a tight seal between foam and tape, you have to either lay down a strip of putty or a strip of peel ply as an attachment point for the vacuum tape.

I also think the deck flange area will cause you trouble. I ended up hand laminating the reinforcement layer, then using that as a mould for the vacuum lamination.

I wish you luck with your project!

Mike Paulding said...


You and I are on the same wavelength for this task. I ended up coming to the conclusion that I needed a layer of the deck flange as a surface for the sealant tape and also hand laminated the reinforcement layer.

I mixed a slurry putty of epoxy and microspheres to form the bagging surface on top of the keel foam, which was 1-2" proud of the keel batten. I was able to attain a pressure of 22 in Hg using this approach.

Perhaps I should read the blog comments before I "reinvent the wheel".

Thanks for your insightful feedback.


VW-Whispher said...

Hi Mike,
I am looking for a CNC Foam Cuter in the Honolulu area. Can you point me in the right direction.

soajay at hot m a i l .c O m

Frank Hylewicz Fräsmaschinen said...

Hi Mike,

what type of router motor do you use for that, how many watt etc ?


Frank Hylewicz Fräsmaschinen said...

Hi Mike,

what type of router motor do you use for that, how many watt etc ?