[TDonald]

Hi Everyone!

I'm new here, and have spent a day or so scouring the forums looking for some rather specific information....and didn't find it. So, I'll toss out my questions and hope that someone has some good input for me.

I'm a disabled retiree who has always been a big archery fan. A few years ago I started playing with making my own bows, but always liked the feel of a compound bow vs. a long or recurve bow. Well, I've decided I'm going to make a compound bow from scratch after watching a couple of knuckleheads on Youtube.com make theirs out of PVC pipe and pulleys. I'm not going to redneck the project that much, but had originally considered modifying their approaches. Since I used to work in machine maintenance (mostly in plastic factories), I'm somewhat familiar with plastics and machining.

Ok, enough history, on to the project. I want to create limbs for a home-designed, horizontal limb, compound bow. The riser will be 24" and I expect AtA (Axle to Axle) length to be about 26". The cams will be of my own design and the riser out of laminated maple (think high quality maple plywood, multiple sheets glued together and then carved/cut/sanded to shape). I had originally playing with the idea of using PVC sheeting (or heating/flattening PVC piping as in the Youtube videos), laminated with fiberglass and/or other materials to create a highly stiffened limb without much deflection which would increase the final poundage of the bow. While looking for PVC sheeting, I came across a couple of websites that discussed acetal plastics (Delrin) and UHMW (polyethelene), and started to wonder if I should up the quality of the plastics I was going to use. Originally the idea was to only use materials available at the local hardware or big box stores, but I think I've changed my mind on that one.

Here are my questions: With limbs roughly 20-24" long, would it be better to simply use a solid block of material with some slight forming, or laminate different plastics together to increase stiffness, energy storage and durability?
If so, what plastics, and what method of bonding? (Please remember this will be done in a hobbyist's shed with limited access to machinery)
Should other materials be included, such as fiberglass, wood, metal?

I know with wooden bows I can dial up or dial down the tensile strength of the limbs depending on which woods I use, what taper and so on. I also know that to use wooden limbs on a compound bow, I'm looking at making them upwards of 4" thick to withstand the stress. On your typical compound bow, the actual force applied to the limbs themselves is quite a bit more than the poundage (energy required to pull the bow) by a typical factor of at least 5 (60 lbs. pull = 300 lbs. force - or more - on limbs).

Any thoughts or ideas would be greatly appreciated

[TDonald]

Well, I'd like to thank everyone who replied......

....oh, and a quick note to all 56 views: thanks for your silence.

[ger21]

Well, I've never seen a discussion of bows here, so perhaps nobody here can really answer your questions?

One thing top be aware of, is that it's very difficult to bond anything to PVC and other plastics. Epoxy and fiberglass will not stick to it, so it won't last long.
Carbon fiber laminates or phenolics would be a better choice, and are easily bonded with epoxy.

[jfong]

Making a compound bow is not a everyday common occurrence and I used to shoot FITA with a Olympic class recurve. All I know is the limbs I used were carbon fiber over a wood/syntactic foam core. Couldn't tell you what a compound would use these days. Archery tech has changed much since I was shooting in the 90's.

[TDonald]

I've built long bows, recurves and take-down recurves that shoot with quite a bit of accuracy and max draws of about 75#+/- 5#. I was hoping to avoid "hard to get" materials and was just searching around when I came across a discussion on acetals v. UHMW, which sort of sparked the whole idea. The deflection (or lack thereof) is quite nice, but I'm not sure they would be strong enough on their own to handle the stress.

[TDonald]

One thing top be aware of, is that it's very difficult to bond anything to PVC and other plastics. Epoxy and fiberglass will not stick to it, so it won't last long.
Carbon fiber laminates or phenolics would be a better choice, and are easily bonded with epoxy.

That's what I was afraid of. I know that a standard bow (carbon/fiberglass over wood) won't stand up to the stresses. If I went with straight PVC, I could use standard PVC cement, but I doubt I'd get the sort of draw weight I want...at least not and have anything that looked halfway decent.