Some folks were interested in how to taper cores for backed bows, tri-lams and such... namely full length cores with parallel midsections and tapered limbs. I didn't want to highjack the other thread, so here we are...
There are surely other ways to do it, but here's one way I've found to work straightforward and well.
I use an adjustable lam sled and a thickness sander.
If there are two pieces needing spliced, I do that first, then treat it the same as a single, solid, long piece.
Basically we will be grinding and tapering a long piece, from 60-70+ inches for instance, on a shorter lam sled... mine is 40" long.
The piece is already brought to adequate width, slightly wider than finished bow dimensions.
I run the piece through my thickness sander (no sled) until both faces are flat and parallel, and the piece is a uniform thickness equal to what I want the parallel/untapered midsection to be. This will also even up any thickness inconsistancies due to the splice, remove residual glue, etc. Following this step, the untapered midsection is DONE, and won't be ground further. All that is left to do is to taper the working limb areas.
I then lay out all of the length measurements for the bow, marking their location clearly along an edge... to include bow center, handle center, top and bottom of handle, flare locations, end of dip(fade) locations, and the string nock/groove locations. The dip/fade marks will be used as reference during the grinding process, the others will be used again later during glue-up and construction.
Since I want the piece to be parallel from dip to dip, then taper from each dip to its respective tip, I transfer the marks for the dip locations from the edge to the grinding surface of the slat, drawing these 2 lines across its width, so that I can clearly see where the dips will end and the tapers will begin. I do NOT want to grind these lines away, or further grind any of the wood that resides between them. As I noted previously, this area is done.
I then draw a long freehand pencil line on each limb, on the surfaces to be ground... from the dip location marks, the whole way to the tips... just a freehand squiggly line. This simply offers a visual reference to gauge the progression of the work, and watch the taper walk right up the limb and approach the dip area through succeeding passes and gradual thinning/tapering of the piece... allowing us to stop just shy of the dip area without going past it.
In this picture, the handle area is to the left and limb to the right.
The piece is fed in bow tip end first. This end is set flush with the end of the lam sled, on the sled's 'high side'. The limb that is NOT being ground on the current pass will overhang the trailing 'low' end of the sled, and be angled down and lower and will pass under the sanding drum without touching it. This picture is actually of the sled exiting the sander.
The thickness sander's table is initially set to 'just touch' the wood on the leading end(bow tip end) and after each pass the sander is adjusted to take off a little more. You'll see your pencil reference line on the grinding surface disappearing a little more on each pass, letting you know where the new beginning edge of the taper is located on the limb. Keep going, slowly/slightly adjusting the sander thinner on each pass until the taper is at the dip location... i.e. all of your freehand, squiggly reference line will have been removed. This typically takes several passes, or more. If you try to rush it and take too much at a time, there's a better chance that you'll overshoot the dip on your final pass. Go slow. It won't take long.
The limb is now tapered from dip to tip.
You can do one limb, then open your sander and start over on the other limb, OR, to expedite things, you can alternate... grind a single pass on one limb, flip the core end for end, putting the other limb on the lam sled, grind it... THEN adjust the thickness sander a little thinner and repeat.
It may help to write a #1 next to one dip, and a #2 next to the other to ensure you don't forget which one is next to be fed though... or skip a pass on a limb... which I've done
Grind limb #1.
Swap ends.
Grind limb #2.
Adjust table.
Repeat until you bring the taper to meet the dip/fade.
If you did an edequately accurate job of the initial thicknessing, the limb's tapers should approach their dips simultaneously... and you're done.
It actually doesn't take long at all to do.
I hope this makes sense. If you have any questions, fire at will
Topic: How-to... parallel/tapered cores (Read 529 times)
