Crooked Spar

[sarpysam]

Just opened a box of spars for a Hatz CB-1 project. The four fronts are fine but two of the rear spars have a belly in them. One is 3/16" and the other is 1/8" both being in the vertical. That'll be enough to be detectable in the finished product, will it not? Being a first time builder, I'm wondering if I should be squawking to the provider or is this the norm. 43-13 doesn't address straightness that I have found. Any input would surely be appreciated.

Sarpy Sam

[WLIU]

Wood is interesting stuff. Not as stable as plastics or metals.

Two points.

First, how different would the humidity at Wicks warehouse be from where you are? If you are in the desert vs their upper midwest location, the stock may move again as it acclimates to the moisture content of your environment. This takes a little time.

Second, is the stock oversize? If it is, it likely can be planed to take out the curve. If not, then you will likely want replacements shipped.

Best of luck,

Wes

[Mike Switzer]

First, how different would the humidity at Wicks warehouse be from where you are?

The East St Louis area is normally pretty humid, but this year has been very bad in central & southern Illinois. To quote Forrest Gump "One day it started raining, and it didn't quit for 4 months". Yes, it has been that bad.

[sarpysam]

Thanks for the feed back. I needed a 3 11/16" spar out of 3 3/4" stock so there's not enough to take it out and Wes, how did you know it came from Wicks? The humidity deal could be an issue but I have six that are very nice and perfectly straight and two with the belly in them. Eastern Mt is drier I'm sure but we're at 60% today which is the exception. 10-20% is more normal.
Sarpy Sam

[planecrazzzy]

First... Can't understand "Belly"

It could have a "Crown" or "Sweep"

Belly sounds like some Bulge...

A "Sweep" is a Non issue... Ribs and Cross braces will handle this easy...

A "Crown" is a little Stiffer... In Steel Beams... They put the crown "UP"...

You CAN put weights on your wood... Set them in place for a while to straighten them...

Or maybe put the crown "Down" to support static load while it sits...?
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Gotta Fly...
JAM
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[Kyle Boatright]

Thanks for the feed back. I needed a 3 11/16" spar out of 3 3/4" stock so there's not enough to take it out and Wes, how did you know it came from Wicks? The humidity deal could be an issue but I have six that are very nice and perfectly straight and two with the belly in them. Eastern Mt is drier I'm sure but we're at 60% today which is the exception. 10-20% is more normal.
Sarpy Sam

You can take all of the 1/8" belly out on one and 1/8" of the 3/16" belly out in the other one. That'll be good enough for an Oshkosh grand champion...

What you do is this:

Get yourself a nice long fence - preferably the length of the spars. I've used a piece of steel angle before.

Get a router with a straight cut bit. Figure out what the offset will need to be so the bit only trims 1/16" when the router base is against the fence.

Let's pretend the spar is 12' and the "belly" is at the midpoint of the spar.

Using the convention where the spar has a "U" shape (a really flat U shape), with the inboard and outboard ends high and a sag (or belly) in the middle, here's what you would do:

Set your fence so you trim the top of each the spar. The trim will be 1/16" at each end of the spar, tapering to 0" at a point in the middle of the spar, and back to 1/16" at the other end. You need to make sure your fence is VERY straight. Check it with a laser, a string, whatever, after you've clamped it in place. Check it again, then tighten the clamps, check again, and make the cut. Do this on both spars.

Once you do that, you have one board with a 1/16" "belly" and another with a 1/8" belly.

Now, you set up to cut 1/16" out of the belly:

In our hypothetical case, you clamp the fence so you will cut 1/16" out of the bottom (belly) of the spar at its midpoint (where the belly is largest). That cut will taper to 0" at each end. Make the cut on each spar and now you have one that is perfectly straight and one that has a 1/16" bow. Since you never cut more than 1/16" from any point on the spar, your spars are in spec.

Clear as mud? If it makes sense, just say so. If not, please ask follow-up questions.

I figured this out making some Champ spars fit once upon a time...

[sarpysam]

Kyle: Your suggestion is right on and would work however I cut a 3 11/16" spar out of 3 3/4" stock so I just didn't have enough to work with but everyone needs to know that Wicks have replaced the two spars in question. There was no negotiating. They just simply are shipping new ones! Everyone needs to know.

Sarpy Sam