Will sanding glass lessen cast?

[R H Clark]

I'm not a bowyer yet,just trying to learn.From what I hear some slight sanding may be necessary to get to tiller.After that, does sanding glass down to a specific weight for a customer lessen cast? I'm talking 4-5 lbs to get to weight.

I've heard some bowyers say sanding so much would lessen cast but with other bowyers it seems a regular practice to get to weight.

Have any of you actually tested any bows before and after sanding or if you don't like to sand a lot is it more of a safety issue?

[Apex Predator]

One of my mild R/Ds was shooting 170 fps at 62@28.  After I reduced the weight to 56@28, which included sanding the glass on back and belly, it clocked at 175.  I was shooting 10 grains per pound at each weight.  I learned that this design would certainly perform better with .040 glass, instead of the .050 that I started with.

[Hud]

You did not mention whether it is a recurve or longbow? It has been my feeling, that removing material from the sides is easier to achieve results if you are talking a few pounds. Reducing width can reduce weight, and lessen air deflection. Flight bows have light limbs, and relatively narrow. The older design Bear limbs were faster than the modern version. I think glass to wood ratio is important and would like to see more info. on what bowyers are using.  

My questions is how can material be removed from the back and/or belly and do it uniformly?

[R H Clark]

Hud
I was thinking R/D longbow.

[Hud]

In a typical R/D with length of 62" to 64", 4-lams (tapered), 54 - 64 lbs, the thickness on mine is .430 - .450 at the fadeout, and the glass is .004 (.008). You can see with the  right taper to the nock end, it would take very little off the upper limb to get to a tiller of 1/8 - 1/4". I am assuming the mid-point of the bow is 1.5" below the arrow rest, and both limbs are approximately 1.130 wide at the fade-out, and taper to same roughly the measurement at the nocks (3/8" to 7/16") the riser makes the lower limb shorter, hence stiffer and the tiller is built-in as a result of the design. Once you have the limb shaped and nocks cut, you can put a string on to see where the tiller is and make adjustments to limbs for arch as it is pulled back to 12" on a tiller board and mark on the limbs if there is any flat spot and repeat, gradually increasing the pull on the tiller board. In reality, a bowyer may have slightly different limb profiles on two identical weight bows because of the differences in the wood laminations. I still think it is easierr for me, to remove material from the sides. I don't feel comfortable removing material on a glass bow from the back and belly at the same time. I have made bows with thinner glass on the belly, but all my adjustments have been to the sides. One word of caution, the string alignment needs to be spot-on, or you will end up with a twist. You might think about investing in a DVD, or book on building glass bows.

[R H Clark]

Hud
Some books and DVD's I have advocate sanding to weight while some do not.I've bought or read just about everything on the market.

I am more interested in how sanding effects performance because some bowyers seem to sand just to get to weight.Some bowyers are much more cautious about sanding glass and claim it lessens cast.

Apex,
That is exactly the type info I was looking for.Would you have been comfortable sanding as much with the thinner glass?

I do appreciate the input,guys.
Randy

[TradBowyer]

my thoughts are that cast is just one part of the equation when it comes to bow performance but performance is linked a lot to your glass to wood (core) ratio. When you sand glass to make tiller, weight, ect you are changing that ratio of glass to core thickness which will change your performance output..sometimes it helps (Apex for instance), sometimes it hurts.

i picture limb construction as an upside down U. with the very peak being optimum limb construction (or glass to core ratio) which gives the best performance numbers. the two low points on either side of the high point are solid fiberglass limbs...and the other is no glass at all (self bows, all wood limbs, ect). The ticket is finding that ratio of glass to core thickness that keeps you as near that peak as possible. In a longbow, i would say you would be best with 040 glass for draw weights 55# and under. If you try to use 040 glass for higher weight bows, you ahve to increase your core thickness to the extent that you will start to drift down the other side of the peak to the "no fiberglass" and your performance will start to suffer. where that point or draw weight is depends on your bow design. At that point, decrease your core 20-30% and go with 050 glass.

just my thoughts

TIM

[Apex Predator]

I would not have sanded much, if any, of the glass if I had started with thinner glass.  This was just a design revelation for me, is all.  This bow should have been built with thinner glass, and the next one will be.

[TNstickn]

If your design is perfect and for some reason your tiller is off and it causes you to sand the surface of the glass, the cast of that bow wont be as good as a bow that is the exact same not requiring the sanding. Thats what Jack Harrison says in his book. What do you guys think? Im sure he means after all experimenting and testing has been done to a particular design, to eek out maximum performance.

[R H Clark]

Yes,I have Jack's book and he is one of the bowyers I was thinking of.

[Hud]

I agree, sanding could change the way the bow shoots, and that means cast.  Why risk screwing up a bow, if it is not necessary? You can spend a lot of time trying to reinvent the wheel; same goes for the bow. The arrow goes is more important than the extra speed. There is only so much you can expect from a bow design, and from the materials you use. If you have read Harrison, or Dan Bertalan's book, you will see that different bowyer's will get a range of speed or if you look at their own designs one is usually faster than another. There are slow R/D and there are fast, that doesn't mean the slow is less accurate, smooth, or quiet. Speed is not the most important thing for me and probably rates nearer the bottom than the top. Keep in mind what Hill, Schulz and others have said. Very few shot any better than they did in the field. Durability, stability, vs speed. If you like what you've got, sanding the glass probably won't make it any better. Otherwise, give or sell it to someone and build or buy another.