Woodworking 101 thread. Beginner needs help!

That would help. You could try a 4 x2 laid flat to support the end of the 17 or 18 sheet up and a 4 x 2 vertical to support the end of the 32 to 34 sheets up whichever keeps the plywood flattest but the wedges would give better support.

Having fewer sheets and clamping them as SamSam suggests would be even better.

In view of the above comment, don't even think of doing any more cutting until you have solved the warping problem.

 

If I had to bevel 3 or 4 sides of hundreds of lightweight ply sheets, I would make a 4x8 table of 2x4s and 3/4 ply on some sawhorses. I would drill some holes in the saw plate and attach a skillsaw like troy did, but screw it to the edge of the table in the middle of an 8' side. On both sides of the saw attach some 1x4 or 2x4 to form, along with the saw, an 8' fence. Sand the table smooth, I would wax it also. Wire the trigger on the saw "on", plug and unplug it from an extension cord to turn it on and off.

Rigging up some featherboards or something would flatten out the area being cut and negate any slight warpage you might have. The only problem I can see is that once the cut is made, the cut edge of the 3mm ply might be so fragile as to not be able to ride against the fence too well. I believe that could be remedied. If it is able to guide itself evenly, it will slowly eat a track in the fence, so every once in a while the fence would have to be shifted a little to present a fresh face.

 

Put the guide fence at the far end of the table so it will be against the sound edge, or use a recessed track slide.

 

But what I was talking about was the saw is stationary and the ply moves- like a large tablesaw with the blade on the edge. What do you mean about a recessed track slide?

 

LOL
ten four on the "pecker height"

Catbuilder, a couple of points:
If the waviness gets to be a problem try screwing down a batten or two up and down the hill... grind down one side and then switch over. when I had that issue I just pressed down a little harder on the sander, but you just have to be careful you dont cut "uphill" and booger them up that way.

Try and keep the width of each exposed laminate in each ply even. You will know if your scarf is right when the three plys are all straight, and even thirds. Keep moving! back and forth. Use the belt sander on the final passes to even them up and touch up the work. The belt sander is lighter and therefore more maneuverable. keep it oriented straight up and down, but move it gently from side to side. You can, however, run it back and forth laterally, or even diagonally, especially on the longitudinal scarfs, where the grain of the bottom ply runs with the scarf,and will tend to tear out easier. but keeping it oriented up and down will insure that all your scarf angles are identical. The longer the lenght of the sander, the better.

I agree with those advising you to cut fewer panels at the time. It will also be easier to keep track of which bevels go where... are you ripping the middle panels so that you have two longitudinal scarfs? I found it best to handle the panels as little as possible, because you have noticed by now how fragile the scarfs are. The more you move them, the more they will get boogered up. Space was (is) a big consideration in my project, so I only beveled those panels I would use for one run at a time. While the lamination was curing on the mold, I would prep another batch.

You can do this. But get some help.

 

To answer SamSam, I mean a moveable guide like on a regular table saw which would move with the sheet holding at 90 degrees.

 

I get it. But I don't know how that would work when doing the end's with almost 8' sticking out. Wait, now I get it, like a giant miter gauge, not a fence.?

 

Like a giant miter gauge, but permanently locked at 90 degrees, and very long tracks with support at the far end of the cut so the whole thing doesn't drop away.

 

Most of the valid points have been made here. You need a god solid surface to support the ply evenly. Try fewer sheets at a time. We use screws behind the scarph line to hold everything flat. We start off with the planer or a 9" grinder with 36 grit, when we get close we switch to a belt sander. Again with 36 grit, 50 is too fine, you are cutting not massaging. All of these tools require skill to use. Keep everything as even as possible right from the get go. Always cut going downhill. The glue is very hard and will kill disks,belts plane blades quickly. Dull tools won't do the job. And the good news is that this is an epoxy boat and minor flaws in your scarphs won't matter. The surface splits in your plywood is not a good indicator of quality ply. You can also cut these scarphs easily on a table saw. You lay the saw on its side and make a large fence to guide the ply. This is definitely not a one man method though. Relax its all happening ok and you will start cooling off in about two months.

 

- The plans specify (strongly) a 12:1 scarf (and strongly specify 1.5" here) for this boat. .... This boat is very carefully engineered to be very light and very strong. Shouldn't I stick to the plans?


Are we talking Kurt Hughes here. Very bright guy, default position is to always stick to the plans. But you could ask him. The reality is that longer scarphs are for highly stressed woods that will have fiber quality that justifies it. That is doubtful in this case. This isn't graded wood. Even Lloyds just mean someone says it is good.

Four other things. These are hulls, the loading is just not that extreme, whatever they say; the new cm hulls use longi curvature, maybe these really long scarphs are for that, in which case, forget whatever I said, mine was old style mold; There is ply under the scarph. Obviously the scarph still has to be good, but it isn't like a scarph in a stringer. The inner plies are very unlikely to even be highly loaded, like the foam core in composite glass hulls. So save your best cuts for the outside; Final point, it is way more important for strength to have properly cut scarphs than the right slope (unless new mold or something else). The longer the slope the more forgiving it may be since you are more likely to get contact with a 15 bevel segment of longrain than an 8mm, but that said, it doesn't take much inaccuracy to blow 2 mm on one side and you are out by half the fiber when they come together. So enphasis needs to be on accuracy, then slope, in general. My remark about butts was not to say you could do that, just that everything is fixable.

Not sure 8-1 will be all that easier to cut, but it is much easier to machine since in many cases you can't get machines that will cut such fragile gains.

My scarph jig is like Troys, except one lumber side was hollow core, and the other was plywood. This allowed me to get vac near the edge, and to hold down the edge through a series of holes. This is for saw jig.

I probably wouldn't cut that many scarphs at once, but then I don't know if it is harder.

 

Boston, the weight of the saw just rides on the jig, as the jig slides atop the plywood. Since I had another 2x4 clamped to the plywood as a fence for the jig to ride against, the saw was very much under control--with less danger of a kickback than there is when freehanding plywood with a Skilsaw.

Of course, I used both hands while cutting. For the picture, I let go with one to hold the camera....

 

An inch and a half above the concrete probably isn't much better than being physically in contact, as far as collecting moisture....

By all means, buy or make yourself some sort of a work table. It'll make life easier in a lot of ways, including on your back and knees.

 

One other problem with the setup I described in post # 62 is that the typical skillsaw



tilts towards the larger part of the saw plate. The larger part offers a sturdier surface area for screwing to the side of the table, but then the blade would tilt the wrong way, into the table.

You could either bevel the side of the table so the saw (set at 90 degrees) when attached would have the correct slant to saw the bevel in the ply or the saw could be attached with spacers that would give the correct slant to the blade. Both those ways would give a feed from right to left, which seems correct to me.

Another remedy would be to plunge cut the saw into a piece of 3/4" ply (Widen the slot so the blade has clearance when tilted) and first attach the saw to that and then the piece of ply to the side of the table, so you end up with the motor and blade above the table and the saw is able to tilt the right way to make the bevel. The feed would then be from the left to the right, which to me is backwards and uncomfortable.

 

That's definitely the next step. I need it for countless other parts of the project, so I guess it's time.

 

Troy described the scarfer attachment I mentioned earlier. They definately work well on thicker plywood. However, 3mm is very thin, and you will need a gadget to keep the sheet flat while cutting, at least if you want to keep the saw stationary.
Using the saw (modified) as Troy described, this problem is less important.

3mm scarfs in okoume are probably the indy 500 of woodworking. The wood is going everywhere by definition, and okoume is so brittle...

But again, what will the total thickness of the part be? How many layers of 3mm plywood will you glue together? What glue is described in the plans?.

With resorcinol glue or carpenters glue, I can imagine the scarfs, but with epoxy...
When we built a 14.5 meter sailing yacht, out of 3 layers of 9mm ply, then glassed over, we never bothered about scarfs, not lengthwise, not side to side. This ship is still sailing, the owner stupidly even beached it one day. (no major damage, but could use a new paintjob and a new rudder...)

Otherwise do some destructive tests with scarfed and non-scarfed panels. Where do they break, why do they break.