Strongback leveling tips?

[Grumple]

Hey Guys,

I finally got my stem laminations glued, and so I'm ready to finish setting up my strong back/molds.

I've built my strong back as per CanoeCraft, except I added a middle leg for peace of mind. As of right now it is all together except the top, and I've done an initial pass of leveling it.

What I've found is that while everything is generally pretty good, my two sides of the box beam aren't perfectly aligned. When I run along my 'leveled' strongback checking for level side-to-side, everything looks good in most places, but a few spots I can tell one side is slightly lower or higher than the other. I think it is probably less than 1/16" (not more), but everywhere I read seems to indicate that the strongback should be as good as possible horizontally.

Having thought back through my steps for sources of error, I think my mistake was that when I cut the plywood sheets on the table saw I must have slightly rotated the sheet in some places while pushing it through.

Any tips on correcting this cleanly? My first thought was to just use a block plane to lower the higher side in these places, but I'm not even 100% sure which side is actually 'wrong' (i.e. high side might actually represent the truer straight line lengthwise along the beam). I could also try gluing some very thin shim material into the low spots if I can decide which needs correcting..

Maybe I'm worrying too much and I can just compensate with the molds, or will I end up with a spiral shaped canoe if I proceed as-is? =)

Just looking for some advice before I do something I regret and/or fasten everything in place.

[Jim Dodd]

Grumple

I don't worry too much about leveling the strongback, left to right, as I can compensate for that, when I set my forms. Most of my strongbacks are a little warped.
I do try and level aft to stern, as much as possible. Not that it will make a big difference, it's just a little anal blood in me.

Draw your centerline on the stronback.

I make sure my two end forms are plumb with each other,then stretch a line from the top of the first form to the top of the last form. If I'm building a straight rockered hull, all forms must be very close to touching it.

If your forms are in line with both of these planes, you should be real close ! I always finish check my form setting with a good eye balling.

Hope that helps !

Jim

PS. make sure your forms are set 90* to the centerline on your strongback. Left and right, up and down.

[Grumple]

Ok, thanks for the info, Jim.

Normally I wouldn't get stuck on small errors, either. but one thing that has really stuck with me from Canoe Craft was just how often he underscores the importance of accuracy, especially regarding the strong back.

Being my first time through all this, I just don't know how much error I can actually tolerate and still end up with a finished product that I can be happy with.

[Denis]

The more accurate you are from the beginning, the fewer errors you will have to fix along the way.

Denis

[alick burt]

I agree with jim that it is of most importance to get the strongback straight along a centre line.(I use a string line for this.Then I put a spirit level at 90 degrees across the top of it at different points and if it is slightly twisted I can shim up my supports under the relevant foot.I have three and they are screwed to the floor.shimmed where needed).
Then when I set up the stations (screwed to blocks) I also check they are upright with a level on their centre lines and finally I run a string line along the top of them as per canoecraft.
I realise that all this checking can be tedious but it works for me!
Cheers
Alick

[Grumple]

Ok, that makes sense to me. I think I'll make one solid attempt at eliminating any high/low points along the box beam top, then hopefully correct any remaining/niggly issues when setting up the molds themselves.

Thanks guys