Source: 2025 Q4 Beartracks, George Huntington
MAKING BENDING DIES TO BEND A RADIUS TO FIT AROUND A TUBE: This trick is great for matching a bend radius to a tube, such as aluminum panels that might be installed under the cabin doors and wrapping around the longerons. First, find a thick tube whose inside diameter matches the outside radius you want.
-use the procedure from the this tip to get a straight line on each side off the tube, then cut the tube in half lengthwise. Clean up the edges and cover them with masking tape, so as not to mark the aluminum sheet when bending.
-now using a tube that fits into the half tube with some clearance for the sheet aluminum you are using, place it into a vise or use “C” clamps to form the sheet aluminum into a nice radius. This works good for the elevator cable attach access at the tail, and the kick panel at the entrance. It also makes a nice large radius like I used for my gear fairings.
Duplicating Fitted Tube Ends with Paper Templates
Source: 2025 Q4 Beartracks, George Huntington
DUPLICATING FITTED TUBE ENDS: For example, if you have fit a tube for one side of the fuselage, and want to make a second tube for the other side:
-Stick a small piece of 2-sided tape place between the two tubes at each end, then wrap masking tape around both tubes near the ends (leave a space for marking). This helps to hold the 2 pieces of tubing secure without either one turning.
-Next take a new box cutter blade and using the back side, draw it across the sides of the tube. This makes a perfect straight line down the tubes, as you just remove the manufacturing scale. Be careful not to press too hard, as you only want a nice fine line. A small fine file works good for this step also.
-While the two tubes are taped together, the other side can be marked also, giving you a nice center line on both sides. This can be useful in drilling a straight hole, by drilling from each side.
-Take a piece of paper and wrap it around both ends of the fitted tube, slightly overhanging the coped ends. Tape the paper to itself, but not too tight as you’ll want to slide it off of one tube and onto the new one. You can also use a rubber band to hold the paper in place while still being able to move it around.
– Use a half round file on each end of the tube to remove the excess paper from the fitted ends. The file is cutting the paper where it is rubbing the paper between the tube end and the file. When done, the paper will have the exact shape of the fitted tube.
-Next take a sharp pencil and mark the other end of the paper, corresponding to the center line that you scribed on the tube. Measure and record the distance between the 2 pieces of paper, or the total length of the tube.
–Slide each paper off of that first tube, and onto the next tube you want to cut to fit. Set the length and align the pencil marks with the scribe mark along the length of the tube. Using a felt marker, trace the paper’s outline on the ends of the tube. Now the tube can be trimmed to make a duplicate tube.
If you want to make the same tube but mirror it for the opposite side of the fuselage, untape the paper templates and roll them up opposite way around the tube, making sure you can still see the pencil marks for the centerline. Install them as above, mark and cut the tube. Now you have made a left and right tube.
Making Spar Cap Strips from Sheets Using a Table Saw
Source: 2023Q4 Beartracks, Todd Stock
In early September 2023, I was contacted by Carlo Cillier, a serial plans-builder that had seen a Patrol at Oshkosh, purchased a plans set, and found me just 20 miles away on the Bearhawk Builder Map (brilliant site…simple and it works!). With wing rib production under control by mid-October, and our spars freshly bent at a local sheet metal fabricator, Carlo started looking for spar cap stock, finding that it had not only tripled in price since I had sourced mine in 2022, but both the 1/8” x 1” bar stock for the main spar and 1/16” x 1” angle stock for the aft were out of stock at multiple vendors. A quick check on 4’ x 12’ 1/8” and 1/16” 2024-T3 sheet showed in stock and could be had for just over $1700 (!!!) delivered… which was still less than the cost of a single set of cap strip bar stock and angle aluminum delivered. We elected to mill up three full main spar sets and six aft spar sets and offer the excess sets to other builders in similar straits at cost plus shipping.
If contemplating a similar course of action (group buy or reverse group buy), here’s what we learned about milling spar caps from sheet stock.
Setup
A 10” cabinet saw or well-tuned contractor saw will do the job with a dedicated aluminum blade such as the Freud Diablo D1084L (available at big box stores for about $77). The Diablo has a 0.100” kerf in aluminum, making the math simple on the width lost per pass to the cut. A clear space of 14’ in front of and behind the saw is needed for infeed and outfeed, and enough space to the left side of the blade to make the initial cuts to reduce the 4’ wide sheet to three ~16” wide sections. Trying to move a 4’ wide sheet through the saw is difficult, and the waste generated by ripping the stock into three narrower, easier-to-manage pieces did not reduce overall yield.
An ideal setup would be long infeed and outfeed tables for stock handling, but we made do with four portable flip-top saw stands and three pairs of hands. We did not run the cyclone dust collector because past experience had shown that the chips generated stayed in the bottom of the saw, while the aluminum dust was difficult to clean out of the cyclone filter.
Also worth mentioning that any milling process is going to scuff the stock, so paying for the plastic protective sheet on both faces is a work-saver. Our quality standard was no scuff or scratch in the primary section of a cap (the portion to be used after cutting to length) which could not be cleared with maroon Scotchbrite. The extra cap strip generated per section (13 needed for the main spar; 14 caps out of each piece) on the 1/8” and 2 per section on the 1/16” gave us some opportunity to cull for excessive bow, deeper scratches, or narrower-than spec width.
Milling the Stock
As mentioned, we reduced the 4’ wide sheets to 15.590” nominal, leaving a straight-edged center section of 15.9” width. This was the most difficult part of the job, followed by milling out the 1/16″ strips, then finally the 1/8″ strips. We milled the strips 0.010” oversized (1/8” caps to 1.010” and 1/16” caps to 0.760”, assuming we would lose about half that to edge cleanup. In retrospect, we could have gone
0.020” oversized and still gotten out the 14 caps per 1/8” piece and the 18 caps per 1/16” piece. The critical dimension for the cap strips is distance between upper and lower and then nominal width, so slightly oversized caps are easily managed by either bringing them down to nominal measurement with an aluminum file or just living with the extra weight.
We measured every other strip when milling the first ~16” wide piece of both 1/8” and 1/16” stock, then every 5th strip as we milled the remaining pieces. This helped us in recognizing any problems such as a slipping fence setting or blade damage before it resulted in waste of the entire piece. Division of duties was an infeed person that managed the position of the stock prior to the cut, my job, which was to maintain pressure against the fence when the stock was being cut, and our outfeed person that carefully pulled the nearly-cut strip through the last bit of the cut, as well as stacked the strips. We wore A5 rated high-grip cut-proof gloves, eye, and ear protection, with a flip down face shield for the person managing the saw cut.
Our goal was no scuff or scratch deeper than could be easily dressed with maroon Scotchbrite and no more than 1/2″ of end-to-end bow on the 1/16″ material and 1/4″ of bow on the 1/8″. Both the 1/8” and 1/16” inch sheets were covered on one side with plastic to avoid the need to do individual strip wrapping to prevent fretting in shipment.
With that 200% Russian aluminum duty in place and other global sources tapped out (aluminum is like oil… last few percent of supply determines market pricing), our final cost for material plus shipping from vendor to Carlo was $308 per set of 1/8” cap strips and $102 per
set of the aft spar 1/16” sets.
We were fortunate to be able to use a corporate account for less-than-truckload shipping, with the first order – one set of main spar caps and two sets of aft spar caps costing just $71 to ship from Frederick, MD to Indiana. For those contemplating a group buy and then shipment
onward to participants, a set of caps fits nicely between two spruce 2×4’s milled to 2-5/8” width, with 3/8” ply sides to close the crate. The first shot was taken as I started clean-up- lots of sweeping and time spent cleaning out the bottom of the saw (filled to within a few inches of the motor). The second shot is as we packaged the deburred stock in plastic and prepped the crate. Finally, our caps did sustain some light scratches and scuffs, but those were easily cleaned up. Compared to my set of cap strips sourced from a major supplier, our milled strips are much, much cleaner and will require far less prep to address surface condition.
Bob adds: He has done it this way but has found he prefers to keep the aluminum stationary, and cut the strips with a handheld circular saw with a fence. He also uses a non-ferrous metal cutting blade.
Handling Aluminum
The Bearhawk is constructed from various alloys of Aluminum and Steel. Because you will be constructing an aircraft and you want it to be as safe as possible, there are some basic guidelines for the handling and working of these metals. Airplanes tend to have more vibration than something firmly attached to the ground and they are made to be as light-weight as possible, so their structures require more care to prevent fatigue cracking. Builders can best mitigate these concerns by following the designer’s material specifications exactly, and by preventing stress risers during fabrication.
Bend Radius
Whenever bending a piece of aluminum or steel, it is extremely important that you do not form a sharp inside corner. Sharp bends create a small-condensed point of stress that can crack, causing the part to fail. All corners must have a radius, and the minimum is specified in AC43.13. For most all of the aluminum that you will use on the Bearhawk, 3 times the material’s thickness is a sufficient radius. So for .025 2024T3, the minimum radius would be .075, which is just a little bit more than 1/16”. 1/8” gives even more margin. After bending, check for cracks (preferably with a 10X magnifying glass) and discard any items found with cracks.
Tooling Marks and Burrs
The processes of cutting and drilling of materials leaves tooling marks and burrs. Any scratches, marks, or burrs on metal that has been cut or drilled must be removed. These imperfections can cause stress risers, which will eventually lead to cracks and possible structural failure. General rule – if you can feel a scratch with your finger nail – it must be polished out. All edges must have a smooth finish. One of the best ways to smooth the edge of aluminum sheet is to run it across a medium grit Scotchbrite wheel mounted on a bench grinder. These are available from Brown Tools in Oklahoma and other tool places.
If your aluminum comes with a plastic sheeting covering it, you’ll want to find compromise with leaving the sheeting in place. It can protect from scratches, but it can also be very hard to remove if it stays in place too long. Always remove the plastic before deburring.
All drilled holes must be de-burred, and for small holes, a dogleg deburring tool with a countersink bit works well (see photo to the right). Be careful to only remove the burr and not countersink or enlarge the hole.
Cross Contamination
Different metals coming in to contact with each other can often create a situation which will increase corrosion. For instance, steel coming into direct contact with aluminum may cause corrosion to accelerate.
For this reason, it is wise to have some sort of protective barrier between differing types of metal. In your Bearhawk, you will mostly use (as did the factory) paint or sacrificial cadmium plating. When selecting hardware, avoid stainless steel when a cad-plated steel is available. The cad-plated part will rust eventually, but which would you rather have corrode, the hardware, or the airframe? By using cad-plated hardware, you can direct the inevitable corrosion to the most replaceable part. Do not bolt different metals to each other for any long duration without a protective barrier.
Do not use graphite pencils to mark aluminum, as they will scratch the surface. Felt-tip “Sharpie” markers are great, though the purists recommend avoiding the black variety due to a tiny corrosion concern in the black ink. Get the bulk pack of the extra fine tip variety, you’ll likely use dozens.
Do not use the same Scotchbrite wheels to smooth steel and then aluminum. Do not use steel wool or any kind of wire brush on aluminum. Scotchbrite pads and disks are a good substitute. Do not use carbon-based sandpaper on aluminum- use aluminum oxide.
Making Custom-Length Band Saw Blades with Silver Solder
Source: 2016 Q1 Beartracks, Stan Timmerman
Building a tube and fabric airplane requires simple tools. In a production setting, speed is more important than the price of the tool. I prefer inexpensive and readily available tools, even if they are slower. This article deals with my first attempt at cutting 4130 steel. I purchased an old Sears woodworking band saw off craigslist for $50. Wood-working equipment is common there. I did not find it to be useful for cutting aluminum ribs or mdf form blocks. I decided to repurpose it for cutting metal. There are several problems with using wood equipment for metal.
The first problem is wood band saws typically have a blade speed in the area of 3000 ft/min. A metal band saw needs to have a blade speed lower than 300 ft/min. The second problem was finding a blade for cutting metal. Metal blades are called bi-metal. Wood blades are just carbon steel. Bi-metal blades are tool steel welded onto a flexible carbon steel backing. An 80-inch bi-metal fine tooth blade to fit my woodworking saw is not easy to come by. There was a local solution. The big box stores sell portable metal band saws. The saws are expensive, but the replacement blades are not. I was able to buy a box of two replacement blades, each 44 7/8 long, for $15. The next problem was welding the two blades together.
From my days of running around a junk yard, I had salvaged a large chunk of aluminum. I had intended to be buried with it. After much thought, I decided this project was worthy of using it instead. There are many ways to make a jig. YouTube can be an excellent resource. I cut a ledge to hold the blade and added a couple of toggle clamps. The area in the center is where the weld will be made.
Before I took the band saw apart, I cut a slot in a piece of mdf (left). I tried to get about a twenty degree angle. I then used a sanding disk mounted on my table saw to “scarf” the end of the blade. Holding a blade in the slot the same way produces the correct scarf. It requires a little thought to join two unrelated blades since the final product has to have all teeth going in the same direction.
I find Dremel tools to be invaluable. Here I used a brush attachment to clean up the edge near the scarf. Soldering requires everything to be clean. The silver solder is also cleaned. The picture on the next page shows a scarfed blade. There is also a tiny fleck of silver solder laying near the future joint. After carefully overlapping the two opposite scarfs, I apply a flux made for silver solder. I then sneak the fleck of silver solder between the two blades at the scarf.
Then with a small flame I warm the area up. I am trying to drive off all liquid. The area will first bubble like caramelized sugar. Then when it is completely covered in crystal, the flame is brought close to reach silver solder melting temperature. People that do silver solder call it flashing. The crystal material turns into a glass-like material as the temperature goes up. Then very suddenly the silver flashes and flows.
I try to move the flame away slowly, to help anneal the area of the weld. I then release one of the toggles as quickly as possible. I do not want the thermal contraction felt at the weld site. In truth when I first laid the scarf together, I did not completely overlay them. My thinking is that when I heat them they will expand and close the gap. If that is so, when I solder them and let them cool, I have to let go of one side so they can contract.
One last step: I use a Dremel to clean up the glass like flux and make sure that no bumps from silver remain. To the right is a photo of my lifetime supply of hard silver solder. Hard silver solder melts at a higher temperature than medium silver solder. Medium silver solder melts at a higher temperature then easy silver solder. I first polish it with Scotch Brite and then cut out tiny slivers of silver. Keep it clean: no oxides, no finger prints. Solder is item number 101702 from riogrande.com, and the flux (Handy Flux Paste Soldering and Annealing) is 504086.
After a few years my flux dries up. I use a child’s rock tumbler to turn some of it back into a paste. Replacement belts for rock tumblers can be purchased from Harbor Freight. Tumblers are often found at GoodWill. I also use my tumbler for quart size paint. I like tools that you can turn on and walk away.
