Building an Archery Shooting Machine
Everyone likes to compare bow speed. I’m not sure why… human nature, I guess. My basic questions are: “Did the arrow get from here to there?”, and “Did it hit where I wanted it to?” I’m pretty happy if I get two yeses. However, now that I’ve started building bows, I suppose I need some benchmarks to tell me how I’m doing
I don’t really see myself getting into envelope pushing bow design, though it could happen. I really, really like longbows, especially old fashioned straight longbows. I like Hills and I like wide limbed flatbows. In building, I’m much more inclined to play with flatbows, because so many people build Hill styles. With the flatbows, I’m more developing my own thing as I go, and there’s a lot of satisfaction and fun in that.
Flatbows and Hills, in my hands, are slow bows. I have a slight physical abnormality in my upper arms that limits my draw length to 24 to 25 inches. I usually say I have a 25 inch draw, but that’s like saying I’m 5’ 8”. I’m really 5’ 7”… if I stand really, really straight. (But I used to be 5’ 8” when I was young :^) Anyway, on top of this, I have lost a lot of strength at age 70, and can now draw a realistic maximum of about 38#, less is far more comfortable. My first bow effort, “Slowpoke”, came out at 28# and I’m loving it.
Some of the guys have kind of wondered about where I’m coming from. It’s just a different place. There are people who really insist on having a Weatherby, so they can try shots at 600 yards at antelope on the plains. I’ve always been more inclined to wander through the woods with an old 32-20 Winchester, shooting trash. I also like pizza. At the end of a day, I don’t have to clean an antelope or drag it 600 yards back to where I shot it from. I just put the trash I shot into a barrel and go home and have a pizza. My approach to field shooting with a bow is much the same. Consequently, I haven’t really minded dropping bow weight that much, other than the difficulty of getting bows I liked that were tillered as I wanted them. Now that I’m building my own, I want to do a good job of it, even if the bows I’m building are not cutting edge design. Good looking, effective and easy to shoot will do for me. However, to achieve that, I need to learn a lot, and I’ve really appreciated all the help from the boards.
If you build, you have to have a concrete basis for telling if you're improving from one bow to the next, and to evaluate what worked and what didn't...
So… a shooting machine… A shooting machine is just a framework to hold a wooden or metal arm, on which is rigged some way to clamp a bow, and which provides a way for the bow to be mechanically drawn, released and shot through a chronograph to get an accurate reading of speed without the variations caused by hand release.
The first requirement is an adequate, sturdy base. I had that covered from the get-go. I have a Triton Super Jaw floor vice. These are, or were, made in Australia and did not show up commonly here in the US, but I stumbled on one and bought it immediately. Very heavy, incredibly steady, and folds up to put away behind the workbench. I learned just this week that Rockwell is now importing them, or perhaps making them under license, and Rockler Woodworking is selling them. These are a fantastic tool for a bowyer, if a bit pricey at $180. Anyway, that will be my base. I went downstairs today to start this project, only to find that Ann had invaded my work space! This was very aggravating. This is my space… my shop… my sacred male cave. I mean, do I invade her upholstery shop and use her layout tables and measuring equipment, and glue, and foam? Do I sometimes start a huge project like making a new Baker tent and keep her from working for a week? Well, actually…
So, instead of starting, I set up the vice and gathered parts, most of which were on hand. Here’s how that went:
Vice for base - check
Board for arm - check
Heavy wood block to mount arm on - check
Scrap wood to fit different risers on arm - check
Archer‘s trigger release - check
Marine jam cleat - check
Stout line - check
Special clamp for risers - need to get
If I get the special clamp, I appear to be ready to go. I’ll try to get that this afternoon, and, hopefully, reclaim my shop tomorrow and continue…
Here are a some pix of my floor vise:
Here it is folded up, though not quite correctly. That leg to the right actually fits into the square hole just behind it and locks, making the leg a carrying handle.
I got the clamp yesterday afternoon, so I’m ready to go today. It was kind of a make-shifty day… put some pieces together… will that work?… Hmmm, maybe not… Would this be better?… Maybe so. I ended up with the basic structure, i.e. the beginnings of a bow bracing system and a release system in place, but was snagged on a good way to keep the setup adaptable to different riser shapes and to both left handed and right handed bows. For one paragraph, it was actually kind of a long day, but I quit confidant that approaching the problem with a fresh mind tomorrow would do the trick.
I'm taking a break, having hit an obvious stopping point. This is an interesting project! I did come up with a nice system for holding the bow in, and one which I can adapt to any bow. It's not elegant, but it will work well. Right now, I have a working block for straight grip longbows. I also have a box of varied sizes of 3/4" plywood rectangles from which I can quickly select one for a sliding/locking base and one to saw a pattern in to fit the grip of a recurve or RD riser. I figure I'll make one each time I have a bow I can’t fit, and once I have half a dozen, that will cover almost anything that comes through the door.
I also learned that shooting from a machine is FAR different from shooting by hand. First, at this stage, I'm shooting the machine horizontally. Ultimately, I will shoot it on about the same angle as you would normally cant the bow. However, as now rigged, the machine is not accommodating a typical sight picture, nor is the arrow on the normal plane of paradox. Hence, when I let off the first shot, it went high! How high did it go? There is a model railroad bench that runs about a foot above my indoor target. If I had had a train on it, the Silver Streak would never have made it to San Francisco!
I also learned that even at my weights, we are playing with a lot more force than we might think. The test bow I'm using is a little 20# York longbow... a real kid's bow from the 50's. I was really shocked at what it felt like to pull that bow back in a static setup like this. If someone had asked me, I 'd have said it felt like 40 pounds or more.
Anyway, progress is being made. After a refueling stop at Starbucks, I'll continue.
Oh, yeah... the UPS man came and delivered a very nice little present..... Actually, a very big present…
Two large planks of Pacific Yew. This stuff is hard to find in board form and I'll be able to resaw awful lot of lams out these. They average 8" wide by 2". One is 4 1/2' and the other a bit over 5'.
Third Day – Second Installment
Whew! I’m tired. I’ve spent the whole afternoon really hustling about, with some good results but clear indications that improvements are needed.
I did not get my bow cant block installed, and that is needed. When shot horizontally, the bows want to shoot the arrows way high… lots of corrective positioning of the base is needed.
I also still need to find a better way to hold the bows in. What I’m doing works, but I know it can be better. I’ll work on that some more tomorrow.
My biggest single problem is the Prochrono chronograph… I need to understand its use and lighting requirements much more than I do. I tried indoor and outdoor, natural light and their indoor lighting kit. At times I had it working well, at other times I couldn’t make sense out of the readings. It would be as if it had dropped the first digit. However, fun withal.
Pause… Please, someone tell me that indoor lighting kit was issued as a practical joke. I can’t conceive of any engineer ok’ing it for continued use or any marketing manager allowing it to leave a factory. I’ve worked for carnivals assembling kiddie prizes that were better made. I have to try to come up with something better.
Also… is this machine calibratable? I can’t find anything in the manual about that, so I assume that if you get consistent reading, it’s OK.
Because I wasn’t happy with the bow clamping system, I didn’t check as many bows as I wanted to. I just checked a few key ones I’m interested in right now… Some real surprises here for me… The figures seem high, but as best I can tell I set things up kosher… 26 1/2” from the deepest spot on the riser. I tested two straight grip longbows and two RD’s… (Note: I later found out that it should be 26 1/4". Actually, I found out I was doing several things wrong, but by the time I finished I had it all sorted out...)
I tested two R/D bows… a J.D. Berry Viper and a Sapphire Hawk from Ernie at Saphire Archery. . Both bows are rated 38# @ 28”. The Barry came out at 201 fps and the Sapphire at 196. These were three shot averages. Given the somewhat jury rig nature of my work, that’s essentially identical. I expected them both to be fast, but that still seems quite high. I assume I have some significant difference in my setup that may cause high readings… but in any event all bows were at least treated the same. The bow I just finished, named Slowpoke ain’t quite as slow as I thought. It picks up a little speed when machine released. It came in at 145 fps.. (For the story of Slowpoke and my first laminating effort (how not to do things!) see:
"Beginning Bowyer Log"
(Note: That's a very long page... not quite a build along, more of an agonize and worry along, as I make mistake after mistake and correct them.)
I did test a third bow, and it was quite a surprise. I couldn’t resist. I tested Howard Hill’s bow. (Yes, you read that righ!) It is 50# @ 28”. It’s an old bow, early 1950’s at the latest, with glass roving rather than the sort of glass we use today. However, from the machine, it shot 186, 187,186. It's doing better in its old age than I am!
Now, unless my machine is just totally out of whack, these figures represent a fair comparison of the bows. Except for Slowpoke, they all seem higher than I would expect. This may be the machine or my procedure… or they can be good readings. Time and more practice will tell.
OK… here come some pictures with comments. Remember, this machine isn't done yet…
Here's the primary clamp, after I first installed it.
Next I made this sliding board that clamped with the two inset knob/screws. As you'll see later, this wasn't fully satisfactory, but it was a start.
Here's the heart of the mechanism.. a stripped down trigger hand release mechanism and a rope that runs through a marine jam cleat. As you pull the rope it's automatically clamped at the length you stop at.
Early effort... That's Slowpoke in the clamp. You'll note that I chickened out and decided I would be a belt and suspenders man in this instance. You can see than I have tied the bow down with several wraps of nylon line in addition to the clamp.
Actually, a couple of days later... life and neglected chores caught up with me...
At this point I had a working machine, but I didn't like the horizontal shooting. It was too hard to get lined up on the backstop target and get the arrow flying through the chronograph. I had also had problems using the chrono. I phoned the company and got some information that straightened me out. The chrono is based on available light, and is much more sensitive and fussy than I thought. Once I started operating with the advice of the experts at the company that made it, things went much better. (I was also told that they are coming out with a new improved indoor light setup, which I will grab as soon as it is offered.) My further efforts were all outdoors and properly set up for the cloudy days we were having.
I was also not happy with the adaptability of my clamping system. When I approached that again I decided that I was simply overworking the problem and trying to make it too complex. I shortened the sliding board and moved it forward so that intstead of trying to clamp the bow ahead of it and then put a shaped piece behind the bow to accomodate the riser shape, I just braced the bow against the rigid board and inserted a filler piece in front of it. This proved much easier and more solid. The clamp still functions to hold the bow down, supplemented by the nylon lashing, which I will replace with bungee cord.
I also found that the bow didn't work well flat agains the main board. This put the string too low for a clean release. I tried putting a piece under the bow, then the bow, clamped down, with a filler piece in front of the riser, between it and the clamp support board. This worked very well, being solid and raising the string.
Finally, I installed a block with an angled bottom so that the bow shoots from a canted position, just as it would if you were holding it. In the process of doing this, I really learned what a great tool that vise is. At times I was clamping the board at one end, and I found the vise so solid that the board's leverage didn't bother it at all.
Here's the vise as I install the block...
The machine clamped in on shooting angle.
From the business side...
Ready... aim... fire..
This was Slowpoke, with what turned out to be a very light arrow, just under 8 gr. per pound of draw. Not a valid reading by "official" standards, but exciting when it happened :^)
Machine ready to be put away..
This shows the block with angled side. Tipping it two sides in the clamp sets it up for a left handed bow.
There you have my basic speed testing machine. It works! A couple of days after these pictues my foster son came over and we ran some more tests, which bore out the earlier results. I set the machine up ready to go in about 5 minutes. Slowpoke again tested out at 146 fps with a proper 9 gpp arrow. The loaner Sapphire Hawk at 186 with a 9.3 gpp arrow. The Hawk tested at 196 with my regular 1616 arrow that weighed in at 8.2 gpp. It actually shoots that arrow, which is my favorite and which I use in a number of bows. It shoots that arrow dead straight and would make a great set up for me to use in 3D. I called Ernie and told him I didn't want to return it... it's now mine! Fantastic bow...
My early efforts suffered from a lot of confusion over just how poundage and draw were measured. I wanted to do my testing to the same standard that is used in the Walk the Talk competitions. I finally got that sorted out. WTT measurements are taken at 26 1/4" from the deepest part of the belly side of the riser. Normally, bows are marked for draw at 28". This is measured to the back of the bow. Apparently there is an assumption or accepted standard that riser depth averages about 1 3/4" from belly to back of bow. So, just to keep everything on an even keel, for WTT measurement, draw weight is verified at 26 1/4" from the deepest point of the riser, and draw length on the machine is set for 26 1/4". That way, all bows are as close to equal as possible. This is the way I'm set up and will do it from now on.
It's been a fun project, and one I'm sure I will get a lot of use out of. I hope you have enjoyed "doing it" with me.