Thursday, December 25, 2008

Obtaining and keeping perfect sixty degree triangles

Making a bamboo fly rod can be an exercise in frustration. In 1998, five issues of “The Bamboo Fly Rod” magazine were published. Many of the articles were excellent. Some of my favorites were those by Stuart Kirkfield which described the magic of fishing with classic bamboo rods. One of the articles which puzzled me most concerned the difficulty in correctly measuring the height of sixty degree strips with dial calipers. The article implied that the inconsistency inherent in measuring tiny triangles with sharp apexes was due to crushing those apexes with the measuring tools. Highly recommended was a V-block tool which affixes to one jaw of the dial calipers. Relief is provided for the exact corners so that measurements are made from the sides of each strip, making it much less likely your tools will crush the delicate apexes. Immediately I bought one of the V-blocks, and began using it.

Soon thereafter, my rod blanks began exhibiting glue lines which resulted in several trashed blanks.

To eliminate the glue line problem, I began to re-think everything about the way I made rod blanks. I thoroughly examined, then resurfaced my planing forms. The glue lines persisted. Two new sets of planing forms were purchased. Still, there were those ugly glue lines. I re-ground the sharpened edges of all my plane irons. Glue lines, still. I examined my planing techniques, using a mirror to be sure the plane was held level. I measured strips over and over, and it seemed no matter what I did, though the strips seemed to measure out correctly, I still had glue lines. I changed glue. I changed binders. I did everything I could dream up, and the glue lines were still there.

Finally I removed the V-blocks from my dial calipers and started measuring strips. It seems that if my angles on each strip were not perfectly equilateral, the V-blocks hid that fact. With the V-block a strip might measure .150", .149". .151". That’s a very good strip. But if I removed the V-block, that same strip could measure .147", .138", .159", and that’s no good. After all that searching I finally determined that my glue lines were due to measuring errors. So I figured out a way to measure consistently and plane out strips that were as close to equilateral as possible.

It’s important to get your angles correct as soon as possible. But that isn't always easy. I have probably sent more strips to the bonepile for bad angles than any other reason. I'm nearly to 200 rods, and still find myself chasing good angles.

I rough the strips out on a beveller. My beveller puts an initial taper in the strips, but I leave them about .050" oversized. I then move to the final planing form. I always set the taper in the shallowest part of the forms which will accommodate the desired final dimensions; and extend the dimensions out larger and larger all the way to the deepest end of the form. I initially set the taper .003" oversized at every station.

To obtain and keep good sixty degree angles when planing bamboo strips, you must first learn to set your plane iron correctly. It seems simple – insert the iron and move it laterally until it protrudes from the sole of the plane evenly. But because the bedding surfaces on hand planes are rarely perfect, that doesn’t always work. Instead, insert the iron until it barely protrudes. Next, gently take some metal shavings off your planing forms. Remember, the blade in your plane irons is made from harder metal than your planing forms. When sharp your irons will gently take a few microns of steel off the top of the forms. You know the forms are flat, and you want the plane to work down to that surface.

What you’ll notice is that the plane iron will likely shave more on one side of the forms than the other. Adjust the blade laterally until it cuts right at the groove on the forms. Ideally it should cut on both sides of the groove and all the way across. But as long as it cuts at the groove, we’re okay.

Next you’ll need to remove the enamel from your strips of bamboo. I use a combination of scraping and sanding until I get at least the center of each strip all the way down to the outermost power fibers. After the enamel has been removed, mark each strip in pencil on the enamel side at each 5" station.

When I begin planing, I have only the tip-most 15" or so of the strip in the forms. I make three passes on one side, then three passes on the second side. Those six passes take out any roughness from the beveller. Then I grab the calipers and start measuring. I hold the tip end of the strip up. I measure side A (one pith side), then side B (the other pith side), then side C (the enamel side to the pith apex). I always measure in the same order. Every single time. And I remember the three measurements. I correct the measurements --- one station at a time.

Change to a a very, very sharp blade in your plane; as sharp as you can possibly get it. On a test piece of bamboo set the plane for a cut of .005", with the normal amount of pressure you use when planing.
Place the strip in the form at its final destination. Make a very, very light pass over the entire strip from one end to the other. Put absolutely zero downward pressure on the plane. One hundred percent of your effort should be focused on keeping the sole of the plane level to the forms and keeping it moving from one end to the other. You'll find that with zero downward pressure on the plane, it will not remove the .005" per pass.... more like .001"
Chances are good the plane will not cut all the way down the strip. It'll skip and jump. That's okay. Where it does cut, chances are good that it will cut a shaving smaller than the width of the strip. That too is okay.
Now, flip the strip to the other side, and repeat... very light, very level pass.
Back to the original side, and repeat. I will cut and flip several times. Perhaps as many as five passes on each strip.

In a few passes, you'll find the very sharp plane beginning to cut all the way down the piece of bamboo, and cutting a shaving the same width as the strip. Now quit.

I'll usually do this in batches... Remove enamel and flatten all the strips. Mark all strips. Make the light passes over all the strips. Measure and correct angles on all strips. Finally plane all strips to metal as described below.

Now, go back to your calipers and measure each strip at each mark. I think you will find that the very light passes with a super sharp blade have, to a large degree, corrected your angles. You may have a few that still need some correction.

Here’s how I correct the angles. When measured the way I do it, if side A is the largest number, I know I need to lean the plane away from me. If side B is the largest, I need to lean the plane towards me. If side C is the largest, the apex needs to be reduced by leaning the plane that way one pass per side.

Here’s a .pdf file that may help you visualize the way I measure strips then correct the angles. with my thanks to Stephen Dugmore.

Let's say my three measurements are .145, .140, .140. I'll lean the plane away from me and place the strip in the form in such a way that as I'm cutting I reduce the width of the enamel side. With my plane set to make shavings of .005", I'll usually make two passes. Then measure again. Chances are I'll be close to equilateral. If not within .001" on all three sides, I cut again, repositioning the strip, the plane, or both as needed to bring the triangles back to equilateral.

When the tip-most station is correct, I move to the next station and repeat the process. Often each station in each inter-nodal area is off in the same direction. Stations at nodes can get really screwy.

When all the stations I have planed (remember I have only planed the tip-most 3-4 stations at all) are correct, I move the strip forward 5". Then I make three passes on each side and repeat the process. Usually those stations corrected the first time are still correct. If not, I work them over again. The butt-most stations I just planed usually require some correction. Repeat the process above.

Move the strip forward another five inches and repeat. And repeat, and repeat.

Once the entire strip is equilateral (THIS IS IMPORTANT) I pull the strip back towards the large end of the form till the tip-most 15" or so is all that protrudes above the form. Now I'll change planes. I go to a plane that cuts only .004" shavings. I plane with the strip in that position till I 'm taking metal. Then I move the strip forward, closer towards its final destination by 5 inches

As soon as the entire strip is in the form, I change to a plane that cuts only .003" per pass. And I re-check everything. If any stations are out of whack, I correct them again. I plane down to metal, turning after each pass. When I can take no more bamboo off, I move the strips up another 5 inches. Switch to a plane taking .002" shavings. Plane to metal again. By this point the strip is usually about 3-4 inches downstream (towards its final place) of the forms. I measure again, and make any minor corrections necessary. Then I switch to a plane which makes the tiniest shavings imaginable and move the strip forward about 1" per pass. Once the strip is in its final position I shave down to the metal again.
Now measure each station, and write the measurements on the form with a Sharpie. It should be EXACTLY .003" oversized. Remember that I set the forms .003" large? Chances are very good that some stations need to be closed by .003", but others may need .002" or .004". Re-set the forms as necessary. Then while taking whisper-thin shavings, plane again to metal. Re-measure. If any stations need a little more off, you can re-adjust the forms. Obviously, this process of re-setting the forms is only done on the first strip.

A couple more things worth mentioning if you've stuck with me this far.

A. Straight strips are much, much more fun to plane. Spend whatever time is needed to get them straight before planing and the time saved will be worthwhile in the long run.

A+ Get the angles correct early, then keep them correct. The method I've described will help with that. So will training wheels on your plane as described first by John Bokstrom in The Planing Form. You can purchase a set for your Stanley plane from Jerry Wall at JW Flyrods.

B. Almost ZERO downward pressure should be placed on the plane. I hold the plane with my fingers on each side. No index finger on the brass nut which hold the mouth in place. Putting the index finger there tempts one to push down on the plane. As close to 100% of your energies as possible should be moving the plane forward. Let the weight of the plane work for you.

C. Dare I say it? Sharpen your blades. If your blade isn't sharp, you simply must press downward to get any shaving at all. If you're having to press down, your blades need sharpening.
Hope these ideas prove helpful. I'm sure there are other ways of doing this just as effective. But this is what works for me.

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