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Cutting straight 90deg edges to make sheets

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Old 06-10-2012, 10:16 AM
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ChinookRC
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Default Cutting straight 90deg edges to make sheets

I'm looking for a way to trim plank sheets so they match up well when glueing them edge to edge to make wing or fuse sheets.

If I use a straight edge to trim each edge the blade will often tilt and I don't get a 90deg edge. Depending on the grain, the blade sometimes rips the wood away from the straight edge. If I stack two sheets this problem is even worse. A balsa stripper will give me a 90deg edge but the edge needs to be straight, and I want the two edges to match.

I'm sure there's a clever way to do this, but I'm not clever enough to think of it.


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Old 06-10-2012, 11:50 AM
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Default RE: Cutting straight 90deg edges to make sheets

Using a long steel rule and a sharp hand held hobby knife has always worked quite well for me. Just like you I use masking tape to hold both joint edges tight together along the length of the joint, then turn the sheets over and open the joint into a V shape and run a bead of carpenter's glue along it and then close the joint and lay the sheets on a flat surface with adequate weights applied to keep them flat, wiping off all excess glue with a damp cloth.

Karol
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Old 06-10-2012, 11:51 AM
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Default RE: Cutting straight 90deg edges to make sheets

How do you get a good straight edge on a sheet of balsa? The same way you get to Carnegie Hall, practice man, practice!

Of course you need a good straightedge. One problem with making the cut is having the straightedge move during the cut. What I do is stick a few short pieces of Scotch double stick tape on the back of the straightedge, this will help keep it from sliding around while you hold the straightedge down. By the way, get the tape off when youre done. If you leave it on it's nearly impossible to get off later.

The next issue is keeping the blade vertical. Here's where lots of practice helps. I find that I tend to tip to the same side so I always go a little the other way and it comes out very close. If your blade is wandering, guided by the grain of the wood, you need to make lighter cuts. The sheeting should be cut with several light cuts, this will make a truer cut with less wander.

By the way, before you make the cut, check the position of your left fingers and make sure they're not over the line of the cut. I've been making cuts this way for almost 50 years and just a few weeks ago I wound up cutting the tip off of my left index finger while cutting poster board. The moral here is watch your fingers while you cut, not ...

After the pieces are cut you should get a fairly good fit. I use a long sanding bar to touch them up if needed, again watching carefully to keep the bar square to the sheet. Or you can make an edge sanding guide that will ensure a straight, square edge. http://www.airfieldmodels.com/inform...ture/index.htm

Dave
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Old 06-10-2012, 11:56 AM
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Default RE: Cutting straight 90deg edges to make sheets

The only way I found how to do it is with a homemade sanding jig I made from 2 1/2" angle iron (or aluminum if lucky) that I drilled & bolted a 3" strap on to one side that I covered with Great planes sandpaper rolls . Laid the wood against the sandpaper & just slid it back & forth a few times . Mine is 4' long & VERY heavy but does the job Ok . Max H.
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Old 06-10-2012, 04:55 PM
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Default RE: Cutting straight 90deg edges to make sheets


Quote:
ORIGINAL: dbacque
After the pieces are cut you should get a fairly good fit. I use a long sanding bar to touch them up if needed, again watching carefully to keep the bar square to the sheet. Or you can make an edge sanding guide that will ensure a straight, square edge. http://www.airfieldmodels.com/inform...ture/index.htm

Dave
I have used a set-up similar to this with good results and the same taping method that you are using with good success. Just needs patience and a little practice.

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Old 06-10-2012, 08:17 PM
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Default RE: Cutting straight 90deg edges to make sheets

Thanks a lot for the help guys. This is one of those topics that I could google all day and not find an answer to. After an excessive balsa dust in the home fiasco this weekend (sigh) I was hoping for a solution that didn't involve sandpaper but I picked up a 4-foot 1-inch square aluminum tube, spray tacked some 150 grit paper on one side, clamped it to my bench and used some smooth foam board to raise the balsa a bit and make it easier to slide back and forth. Works perfect and stores away nicely. The only improvement would be to build a grip to hold the balsa down firmly as documented in the airfieldmodels link above.

Gap-free sheeting finally. Thanks again!
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Old 06-21-2012, 06:51 PM
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Default RE: Cutting straight 90deg edges to make sheets

Just need to pay attention to grain and which your slicing. YOu want the grain to pull the blade into the straight edge now away from it. I find just holding the blade verical works best.

I use a 1/2" square hollow alluminum 36" long. Blade rests against the side so I know its square and wth proper wood grain orientation (and a sharp blade) it's a snap.
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Old 06-26-2012, 08:07 PM
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Default RE: Cutting straight 90deg edges to make sheets

I like this method of match cutting balsa sheets. No need to have a perfectly straight cut or at a perfect 90 degree angle. Slight wavyness or angle changes in the cut doesn't matter. Try it!

skeeter

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Old 06-27-2012, 04:14 AM
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Default RE: Cutting straight 90deg edges to make sheets

That's the method I was trying to remember skeeter - no sandpaper! The #11 carbon steel Swann-Morton scalpel blades and handle I got yesterday should cut like butter through two sheets at once. And now I can go ahead and cut the 1" sq tubing into 2" and 3" lengths to be filled with molten lead to serve as weights on my new 4'x7' 5/8" tempered glass bench top.
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Old 07-06-2012, 07:22 AM
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Default RE: Cutting straight 90deg edges to make sheets



After I make a long cut with the sheet I usually just take my long T bar sander, make a few passes making sure I'm holding that at 90 degrees and it gets rid of that little curve from the blade. Works for me every time.


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