Jan. 26 - Update 1 - Grinding the Limbs
I didn't expect to get a lot done today as my "student", Jesse, was coming over to work on the bow he's building for his dad. However, I made excellent progress in the morning, then Jesse left at 3:00 and I got a lot more done.
We left off last night with the bow shape drafted on the blank. This morning I ground the limb shapes in and tested it for draw...
Here I'm grinding the edge of a limb, working to get down to the outside edge of the pencil line. I'm pushing the work toward the rotation of the belt, not pressing terribly hard, but letting the belt do the work.
As I work, the belt is pushing the tape up. To the right, where I've ground a fair amount away, you can see that the pushed up tape is starting to obscure the line.
At this point, I cannot safely try to work closer to the line, so I stop and use the 120 sandpaper to sand off the tape edge, just as I did when I put the tape on the blank.
Here is the same edge with the pushed up tape sanded off. Now I can work closer, and more carefully, to the outside of the pencil line. I'll go slower and be more careful not to have irregularities such as show here.
Once I've done all four limbs to the outside of the line it's time to smooth out the sides, which, no matter how much care is used will still have some irregularity due to the fact that I'm sanding a long essentially flat surface with the round sander edge. However, that round edge sands off the mass much faster than the flat side would. Now I can go to the flat side and sand with long smooth motions, carefully sanding off the pencil line.
Too far back to show well, but here is the rough finished bow shape, except for the riser, which is still untouched.
At this point I need to see what weight I ended up with. I don't want to cut nocks in yet because if my weight is too light and I have to shorten the limbs by cutting off below the nocks I'm likely to end up having to shorten it too much and end up way over weight.
You're looking at two neat tricks here that enable me to string and weigh test a bow with no nocks. The first thing you need is a tillering string with two really heavy, large leather pockets. These are connected by a heavy tillering string permanently fastened to one end and tied at the other with a bowyers knot. With the bowyer's knot you can make the string any length you need. However, the knot pulls tight with bracing and is a bear to get out afterwards!
The second thing is a way to brace the bow so that you can get the end of the limb into the pocket. If you study the pic you will see that the end of the far limb is braced against a peg inserted into one of the dog holes in my workbench. The riser is counter braced against another peg. I stand in front of the near limb and push it forward until I can slip the pocket on. Voila! A strung bow than can be tested before I decide where to put nocks.
The first test is just to see if it's going to hang together. I don my heavy gloves and a bicycle helmet and go out in the driveway and start flexing it until I reach well beyond my normal full draw. If all feels good, I can then proceed to actually weight test it on a scale. Up to this point, everything about this bow has turned out well. However, Mr. Murphy is always with us. I came in light.
The initial test draw showed the minimum weight Herkimer wanted. Since the bow is till rough, I know that I will lose at least five pounds in the finishing. If a bow comes in heavy, I know I can knock weight off by further narrowing the shoulders on the drum sander, doing more edge grinding on the limbs, or even trapping the lower 2/3 of the limbs. ("Trapping" means to grind the limb side in at about 20 degree angle toward the belly. It's a touchy operation but effective.) However, as neat as all these tricks are, they don't help if you're light! You're going to have to shorten the bow. The question is, by how much?
Herkimer gave me a narrow range to work in, and wanted a full length bow. This is the beauty of my special tillering string. I use a 1 1/4
tip on the upper limb and a 1" tip on the lower. This gives tips long enough to effectively and easily engage a stringer. The bow blank was just over 70" long. If I had cut nocks in to make full length 68" bow and then needed to shorten it, I would have had to cut off a total of 2 1/4". This could raise the weight by a bit more than ten pounds, plus leaving you with at best a 65" or 66" bow. Not having nocks to contend with, I cut 1/2" off the upper and 3/4" off the lower. The difference was a gesture toward insuring that the lower limb would be a bit stiffer than the upper. I then went ahead and put the nocks in... Nothing like confidence!
Here I'm cutting in the nocks, using this nifty little nock cutting jig. They don't necessarily come out perfectly matched, but close enough that a tiny bit of free hand filing makes them so.
With this done, I strung the bow with a real 65" string and weight tested it again. I ended up with a gain of seven pounds, which put me two pounds over Herkimer's range. I could have used a bit more, but I still had a full length bow. By being careful and doing a minimum of heavy mouse and hand sanding, I could stay within the usual five pound loss for finishing, which would put me solidly in the middle of Herk's desired range.
The disadvantage is that to do this, I would be removing a minimum of material and also minimizing the curved limb edges I like to do. This will make the bow lean a bit more toward "American Flatbow" rather than pure Hill style. Ah, well... This is why I'm not a professional bowyer!
Topic: Dick's Bow Swap Build - Part 2 - Final Pix Added - Page 4 (Read 2049 times)
