Woodworking 101 thread. Beginner needs help!

I agree that scarphing 3mm plywood is a level (or more) above scarphing 3/8" plywood. But if you stack multiple layers and hold them firmly, you can saw them in a single pass. That doesn't really give the 3mm much time or room to get squirrely on you, and start doing things like warping into waves....

I would suggest setting a 2 x4 as a fence for the jig to ride against--and screwing it down solidly with bugle-headed deck screws, right through the stack of 3mm. You can reuse the same screw holes in the 2 x 4, for each stack of plywood you do.

By the way, I didn't invent that jig for the Skilsaw; I found it on a blog. I'll try to find the blog again, so I can give proper credit to the boat designer the blogger says he learned it from.

 

But with a scarf of 1-1/2", the depth of the skillsaw cut limits it to 1 sheet at a time.

 

Without actually doing the math, I think you could do about three sheets at a time. Don't take my word for it; I just worked 12 hours, drove 168 miles home, and slammed a few beers....

But to begin with, I question the necessity or practicality of cutting a 1 1/2" scarph on a piece of plywood less than 1/8th of an inch thick. In my experience, trying too hard to put a feather edge on scarphs is an invitation to grief to begin with--and those proportions basically turn the entire scarph into a feather edge.

I'm an experienced general woodworker but not a professional boatbuilder, so maybe I'm completely off-base here (I'm sure someone will let me know if I am...). But even trying to glue up such a thin scarph sounds like a nightmare.

 

Here is the way another guy tackled the problem. I haven't tried this, but it looks promising

http://www.dorydesign.com/images/scarf1.jpg


check out his building site

http://www.dorydesign.com/boat.html

I should have explained, that is a router, with a wedge attachment across the base- and a 1/12 inch flat bit.

 

The router jig looks very good.

 

You really want to stay away from butts if you are vac bagging with a shopvac, a la Kurt. The shopvac method works fabulously well. I have three pumps, and use the shopvac for this kind of work. However, the edge of panels is normally not glued, there is an inch or so where it won't get pressed down hard enough. The 2 pounds of pressure depends on flat panels, and triming away edges. but with a joint in the middle of a panel there won't be the ability to trim it away. Scarphs are essential to getting the edges down. The example I gave of making a panel without scarphs was for a tortured hull.

 

I think you are probably right. A 12 to 1 scarf seems a bit much. If the depth of cut was 2", two sheets at a time would be an 8 to 1 scarf, 3 sheets would be somewhere between 5 or 6 to 1. I bet that would work. I don't think 12 to 1 would be all that difficult to do, but I think it comes down to how 'mechanically inclined' a person is, and how many odd things they've done over a lifetime that add little bits of obscure knowledge that can amount to something useful.

As far as using a shop vac for vacuum. A shop vac is a large volume-low suction apparatus. Vacuum bagging is a no volume operation, once the few cubic inches or feet of air is sucked out it's a matter of ability to suck that matters. Much better are refrigerator or air conditioner compressors. The suction side offers much more suck than a shop vac and they are free.

 

In general that is true about vacs, and Kurt has modified his process over the years so I don't know where it currently stands, though he did send me the lattest manual. When I did it shop vac was recomended, and gave very reliable results. It isn't for most uses, but it handled plywood well. There was some bogus concern that higher pressure vacs should not be used. Shopvacs do have high volume which does make simple vac systems pretty easy. You actually want some air movement to stop them burning out and it makes dealing with slight leaks, and cheap bags and accessories a breeze, another case of sticking with the plans whatever they currently say.

 

You're right on the scarphs, of course. Using a 12:1 angle, the saw wouldn't touch the second piece until it had cut 1 1/2" back, no matter how you stacked them. And a 7 1/4" Skilsaw blade won't cut three inches (although I think an 8" blade will).

I should know better than to operate a keyboard when I've been drinking....

 

http://www.multihulldesigns.com/pdf/cm/CYLINDER MOLD MULTIHULL CONSTRUCTION.htm

if i read it correctly, this says 8.1 scarf

 

L

Those are not the boat plans.

 

It still is a total mystery for me why to risk a $250 shopvac for some vacuming, something for which it is definately not made, while a $150 vacuumpump can do the same and more...

A shopvac usually draws a 20% vacuum, while I would love to have a 50% vacuum, to get it all compressed very well.

 

no, i realise that, but why did you post that, if it is not relevant, it appears that an 8.1 scarf might be easier for you

 

if 1/4" can be sacrificed from the length of the plywood then a 1.5 mm deep by 1" groove can be cut in the plywood, then the quarter inch cut off and the lap joints joined

 

Shopvacs are $60 here. Because they are high volume, you can use plastic for a bagging material instead of expensive, purpose built bagging. It is fantastic at tolerating leaks, due to high volume air flow. Same bagging pressure as putting full 5 gallon jugs of epoxy over every square inch of the panel to be bagged.


Works well since the 1980's