I have a friend who hardly ever eats vegetables. He calls veggies “food for food.” I think that’s pretty funny. But it made me realize, it’s no different than my wife snickering at me when she asks “You’re only buying that tool to make more tools, right?” Well, yes…what else?
When I purchased my small single-seat Fun-Kist, it had a particularly funky front axle arrangement. The wheel itself is typical: bolt-together halves with tapered roller bearings. But the axle hardware consisted of a steel tube, with a couple of sleeves to shim the bearings to fit, and a stack of washers for spacing the axle, which was an AN4 bolt (¼-28). Although it worked, it was a challenge every time to reset the hardware stack, fit everything into the wheel, squeeze it all into the nosegear, and thread the axle through the whole shebang.
In the process of coming up with a design that would integrate the hardware into an easy-to-install assembly and increase the axle size to an AN6 bolt (3/8-24), one of the challenges was the very narrow clearance between the fork and the wheel. I settled on a simple thru-axle design common to motorcycles and bicycles.
This style can have a narrow flange-to-flange dimension, but it typically requires two thin-head wrenches—one wrench to adjust and hold the bearing preload and another to tighten the jam nut. Unfortunately, a thin-head wrench is not an everyday item. I checked an industrial supply catalog (McMaster-Carr) and found a wrench close to my needs, but at 13/64 (0.203-inch), it was too thick. I figured I could grind it to size, but the deal-breaker was the price: over $100 each and I need two.
Wrenches are simple. The basic form consists of parallel flats with the appropriate spacing, and a handle long enough to impart the required leverage. There is no need to reinvent anything or over-think it. Keep it simple. While making a wrench is the tutorial focus, the techniques apply to any number of items related to aircraft construction: from metal brackets to gussets and so forth.
Commercially made thin wrenches are laser cut or forged. In the not-so-distant past, they were stamped from plate or sheet, depending on how thin they had to be to fit particular wheel hardware. Unlike a forged wrench, a wrench made from thin plate or sheet must have a comparatively wide section at the saddle to keep from bending. The material also needs to be reasonably tough to resist indenting or twisting.
As you can see from the photo, my axle hardware (bearing cones and locknuts) is really thin: about 0.150-inch. Since I was making the wrench from sheet stock, my only real choice was 0.125 inch. The next question was what material: regular low-carbon steel plate or something fancy like 4130.
I ended up choosing 11-gauge low-carbon steel. A high grade alloy like 4130 would be overkill for this application because the parts I am tightening are aluminum. Any carbon steel would be tough enough, provided the cross section is not too thin. Depending on the local steel supplier, 11-gauge could sometimes be erroneously marked as 1/8-inch. Sheet is made to gauge thickness standards and not to inch or metric values. In the case of 11-gauge, it’s actually 0.119-inch, not 0.125-inch. That’s not a big deal for our project, but if you’re making something that actually requires a thickness of 0.125, you need to be aware of this quirk and either compensate in your design or purchase dimensionally accurate stock. In general, sheet is sold in gauge thickness values up to about ¼-inch (0.231). At ¼-inch and up, you start to see plate sold by the metric or English dimension. Google it, if you’re interested in more information.
Laying it Out
Start by laying out the basic shape. In this case, I borrowed from existing com-mercial designs. There’s no need to be fancy about either the wrench design or the drawing. You could sketch it on a computer, use a pencil and graph paper, or a sheet of plain paper. Once it looks right, double-check the key dimensions and make a full-scale photocopy. This is a project you can make any number of ways. A water jet, laser, or plasma cutter would be fastest. A CNC milling machine would be the most precise. But a bandsaw and grinder or disc sander can, in this case, produce a comparably usable tool.
In fact, a hacksaw and a good set of files would work, too. The only difference is time. In the end, the objective is to produce a wrench that does the job and looks professional. Since this column is called “Home Shop Machinist” I made the demonstration wrench on a machine—in this case a metal-cutting bandsaw.
It is easy to get caught up in the idea that it always takes some sort of machine to make something. In reality, you can do a lot with hand tools. Don’t get me wrong, machines are wonderful. Without them, life would be at least inconvenient, if not downright unbearable. But for some jobs, machines offer mere convenience, or at the most, only one means to a particular end.
We’ll use the photocopy (or copies) as the cutting pattern. Use adhesive spray to glue it directly to the steel plate. You could also use dye marking fluid to mark the plate and scribe the outline, but that can be tricky. Later in the project I will use dye marking fluid to precisely scribe the lines for the wrench flats, but for rough cutting on a bandsaw, paper patterns are fast and easy.
To the Bandsaw!
A series of bandsaw cuts are necessary. The bandsaw is not a precision machine, so the idea is to cut just outside the marking lines and then use grinding, filing or sanding to refine it to the desired dimension or shape.
There are a number of tricks to using a bandsaw. One is have a fresh blade. Another is to be patient and don’t force the cut. Don’t cut into anything other than what you intend, including fingers. It is OK to back out of any cut that starts to get too close to the outline. If the radius of the pattern is too tight for the scrolling (cornering) capabilities of your particular bandsaw blade, back out of the cut and come in from a different angle. The blade on this saw was ½-inch wide with a variable-tooth (14-18) configuration. This width is not suitable for making tight curves, so the order this day was to make cuts as close to the lines as possible and then back out and start over at whatever angle allowed me to intersect the previous cut.
Bandsaws are notorious for drifting off the intended cut line. The more worn-out the blade, the more drift becomes a problem. This is not due to the teeth dulling; it’s due to the way the blade is designed to manage the stress from the constant cycling around the band wheels under high tension. Every blade has what’s called benching tension that was introduced into the blade at manufacture. Since the manufacturer of the blade cannot know the exact configuration of every saw, such as the tension setting, the crown of the wheels and so forth, it’s impossible to perfectly tune one blade for every saw. Even with a new blade and a well-tuned saw, it’s not unusual to have to adjust for the drift one way or the other as you feed the material into the blade.
To cut the opening for the wrench, saw close to the line and make a series of kerf cuts (kerf is just a fancy name for the slot left by a saw blade) to the inside curve of the wrench.
Continue to saw a series of diagonal slots, more or less as shown. Once you can no longer remove any significant material by sawing, start filing or grinding (or both) to remove material up to the guide line. Creep up to the line and check the fit frequently against the nut you’re planning to use. Stop sawing when you’re within 1/16-inch or so of the final size. You do not want the final fit to be established on the bandsaw.
Use a grinder, disk sander or hand files to complete the outside shape. Deburr all the edges. Once the handle and open end are shaped to satisfaction, it’s time to make the final fit of the wrench flats.
Finding the Line
This is where layout marking fluid comes in handy. A thin coating allows you to make very crisp scribe lines that won’t wear away. Make sure the lines are parallel and, assuming you drew it that way, perpendicular to the handle. Slowly file or grind until you just kiss the layout lines. Check the fit as you start to get close. Keep in mind that patience is probably the toolmaker’s greatest skill. You can measure your progress with a caliper, but it’s easier and faster to test the fit against the actual nut or bolt on which you intend to use the wrench. The exactness of the fit depends on the application. For my particular use, the flats on the hardware are all exactly the same size; this allows a snug fit with almost no play. A close fit is desirable because it means the wrench is less likely to slip and damage the aluminum parts. Production bolts and nuts could have so much variation that it might fit some, or be loose or not fit at all on others.
To finish the wrench, you can use anything that’s convenient from paint, black oxide dip, nickel or chrome plating. (If you plate, be sure to account for the plating thickness, however minimal, when fitting the flats). If you want to add a comfort touch, you could apply Plasti Dip to the handle.
The sequence to completion: (1) Rough pattern (2) Shaped and ready for fitting (3) Precision marked (4) Sandblasted (5) Painted. Not counting the sketch time, it took an hour and 30 minutes to the pre-paint stage.
When asked “Where’d you get that tool?,” there is obviously some pride in being able to answer “I made it.” But more important, such skills can get you closer to the ultimate goal, which is to get your project airborne.
Got a question for or job that needs assistance from the Home Shop Machinist? Send us a description of the part and where it’s used. We’ll consider it for a potential topic for a future HSM column. If we pick your request, be prepared to supply the raw material and, if it’s part of a published plan, access to the original design drawings. Send inquiries via e-mail to: [email protected] and put HMS in the subject line. Due to liability, certain items may be limited to the construction of a demonstration part for instructional use and display only.
Bob Hadley is the R&D manager for a California-based consumer products company. He holds a Sport Pilot certificate and owns the VW-powered Victory Stanley Fun-Kist.