posted for cougar.
http://www.modelbouwforum.nl/phpBB2/viewtopic.php?t=33186&postdays=0&postorder=asc&&start=0
I am curious as I saw one photo of sanding in progress…
I am almost to a point where I must construct a “long board” for fairing a hull… and see in the photos the use of a very short (to me) block being used. I had planned on using a thin 3mm (1/8 inch) plywood, 3 inches wide. Adding a handle on each end and epoxy bonding a “Bull Dog” paper clip to the top side at each end to grip sandpaper. Then purchase some beltsander belts, cut and attach via the clips at each end. It was the idea of allowing the plywood backer to bend somewhat to take on a hull conformity is used diagonally, yet at the same time, spread the bend over a longer (21 inch) length of the board to (hopefully) factor out any low/high spots that might happen with a shorter backer block.
With my big boat, I used as long a piece that I could handle as a backer - but acknowledge that on a big hull some very minor lower spots might not have the impact as if they were on a 1-2 meter long hull.
Dan (and others) - what length of backer board are you using for sanding down strip or foam hulls? If you are using a short block, please provide your reasoning. Thanks in advance.
thanks dan
i found this guy making over in euprope. this guy is an artist. i cant read dutch . but check out the pictures. the planking job he does is excellent. the only thing that throws me . is he is putting on a paste, after he does a coat of resin. NOW i would normaly assume you would put a filler on the wood . To fill up a low area. and maybe make for a smoother finish. but he seemed to do it backwards. but look at what he did. this is art folks. i wished i had half of his talent. the finish on the plug is nuts. i think i can see clouds in the hull.
just way too good
cougar
Dick,
If an area of the hull is really ruff, I use a regular sanding block (about the size of an index card) wrapped with some 200 grit paper. Once I have knocked down any really bad high spots, I switch to a new never used sponge (It muse be new, so that it is soft and flexible). Just as before I use 200 grit paper. The final step is plain old hand sanding with 200 or 300 grit paper, depending on how much material still needs to be removed.
I feel that hand sanding gives me more control of the paper. If you have a high end after market paint shop in town, watch them, or for that matter any of the hotrod shows on the discovery channel, sand a car before paint. They start out with the power tools, but always finish by hand.
At a recent car show, I talked to a guy with a 69 boss 302 that won for best paint. He said the paint job took roughly 2000 man hours, and 75% of that was hand sanding.
It will take longer, but hand sanding is the way to go in my opinion.
Jeroen is one of our member…he is also the guy who made my rig for my MicoMagic.
He also made one of Graham’s boat…also very nice!
I much prefer a good low angle block plane for fairing planked or carved wood hulls. Block planes were designed to cut cross-grain, so you can fair using proper diagonal strokes to avoid flat spots.
You need one with three adjustments (depth, angle, and throat). My favorite is a Millers Falls 16C, long out of production but examples show up on eBay all the time. (Stanleys are also available, but you pay a premimum because of all the Stanley collectors out there) You need to lap the sole (flatten the bottom) by grinding in a figure 8 pattern on a flat surface, and sharpen the blade using the Scary Sharp technique (google for it). Once you fair with a plane you’ll never go back to sandpaper again.
We ran an article in the USVMYG newsletter called “Make Shavings not Sawdust” that covers the use of planes in hull building. PM me with your email if you’d like a PDF copy.
Cheers,
Earl
Hi there,
Thanx for te comments. I haven’t done all the work on te plug. I’m building this boat with 2 other people.
There is a reason why i’m putting on filler after I have put epoxy with glasfibers on it. The epoxy resin and the glasfibers do hold the planks together so they can’t move any more.
And the resin makes the balsa a lot harder so you won’t sand throug the balsa planks. The filler will attach better to epoxy than to balsa.
The sanding block I’ve used was a bit to small but it did work fine for me.
Regards
Jeroen
To expand a bit on the method for fairing a hull (plug).
I gave a try to a method discussed with a local auto body shop. Normally I use Microlite filler mixed with epoxy to add a slurry/paste to a hull plug in order to fair and remove low spots.
This time I tired “Bondo” - but went the way the body shop suggested. I had asked about ways to “thin” Bondo, since it is a fairly heavy “paste” and I wanted something more creamy. The following is what I “did” - but not necessarily a recommendation. Try it at your own risk…
To thin Bondo, you can mix in polyester resin to get the consistency desired - then add MEK or similar as your hardener agent. This will leave you with whatever thickness/thiness desired for floating onto a hull.
If you only have small amounts of Bondo but want very thin, you can also use laquer thinner. This will not “flash off” as fast as acetone, and will also allow thinning to some extent. I used this method as a trial, and it worked OK, except I mixed very light hardener to provide a slow cure. Added with the laquer thinner and it took about 6 hours to get to a sandable stage.
Here is the one I have yet to try - but with one of my old pressure paint spray guns. The guys at the shop add the polyester resin and stir /add until the Bondo becomes consistency of heavy cream. They then add hardener - AND laquer thinner until it can be sprayed. A quick clean up of gun is required, but they indicate it is a great “quick-build” primer, has fewer pin holes, and they can mix to be thick or thin, depending on where they are working. As noted I haven’t tried this, nor can I (yet) recommend it - but it was an idea. If any does give it a try, please post on how well it worked. In the meantime I am sticking with laquer thinned Bondo simply for cost reasons compared to epoxy fillers - plus it seems to sand easier as well compared to epoxy based fillers.
I would still use epoxy filler for anything exposed to water. For a plug for mould, Bondo is fine.
A little bit off course but check out this for building a mould for a 12 footer yacht in NZ. It goes thru the whole process of mould building thru to sailing.
Dick, I think what you need is Evercoat? FeatherFill, A High-Build, High-Solids Premium Polyester Primer Surfacer, $18 a quart.
john
The yard that built this is also the builder of EC12’s in NZ - Davie Norris - turns out brilliantly finished products in any size boat 