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Framework – 2

Ok, so I don’t have to climb a ladder quite that big to put the finishing touches on this frame. That is a lot of parts to design, fabricate and keep track of. Without computers. At once humbling and further proof, should any be required, that Zeppelins are insane.

Cross bars made from cold-rolled 1080 carbon steel. The small ones are for the top bar and the large ones for the bottom. These are rough-cut to length and squared and ground (sanded really) to just under their nominal finished length. These parts do not play a role in locating the sides of the frame (the laser-cut parts do that job), but they do locate the group and the taps so there can’t be too much play. In practice this translates to a length of within 0.2mm of, but always less than, nominal.

Drilled, countersunk, tapped and deburred.

The uprights are cut from lengths of rectangular tubing and are temporarily tagged and machined in pairs. This means that the left and right halves of each pair is the same length and, where necessary, hole placement is symmetrical. The baby 1″ clamps are made by Kant. The design with the central pivot eliminates twisting so the clamping force always remains axial between the jaws. Consequently, parts don’t slip out of alignment as the clamp distorts when they are tightened. Very clever, very useful.

The tops of the tubes will be filled with a coupon of 1/8th steel which is drilled and tapped for the ball studs that hold the cup warmer in place. This is the first time that all of the parts of this iteration of the design are being assembled so the coupons are left blank in order allow adjustment of the hole position, if necessary. Once I know that everything fits as it is supposed to the holes can be laser-cut the next time this part is ordered.

All of these things meet each other for the first time in the upright frame assembly. <digression> Interesting word thing. At some point in my education I learnt that the English word “thing“, along with its German and Dutch cousin “Ding/ding” and Scandinavian “ting“, original meant assembly, as in an assembly of people. A thing was a gathering of the populace to legislate, adjudicate and elect leaders. In other words, it is a precursor to our courts and parliaments rolled into a single time and place. For the Vikings, “Are you going to that thing on Friday night?” meant finding out how many pounds of salt cod your neighbor Leif owed you because his son Svend borrowed your longship without asking and crashed it. </digression>

The pieces are brought together in the jig along with an extra spacer-bar across the top that will not be welded in place. In this particular jig, the left side and bottom rails are installed permanently perpendicular to each other while the rest of the transverse parts are allowed to move slightly from right to left. This permits clamping and means that the frame can be removed from the jig despite the inevitable slight distortion to the thin walled tubing that occurs during the welding.

After beefing up all of the fragile tack welds, the sections of the frame can now finally be united with the words: with this TIG I thee weld. Though admittedly an actual three-way wedding would be a little weird. Front and upright.

Back, front and upright held in place against carefully aligned stops welded to the table.

Almost complete!

Now that the tubes are in their final place the end fillers can be located and fixed with a delicate weld. The gaps are left purposefully so that welds don’t have to be ground where they would interfere with other parts.

A satisfying row of finished frames cooling with a vintage bicycle…

The next step is to cover them in a skin made of cotton painted with aluminum, put a gas bag made from cow intestines inside, fill them with hydrogen and fly them to New York. Perhaps not. (What were they thinking?)

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Halloween special – framework 1

©iStockphoto.com/GloablIP

Have you noticed that the vast majority of how-to videos about metal work, welding, car repair etc all have heavy metal soundtracks? Not around here. In fact, most of the shops that I go to have a top 40 station on – you know the kind – where it is always time to ‘check on the traffic’. Not that I have anything against heavy metal mind you – it just seems like it sits firmly on the opposite side of the spectrum from what Tom Waits would describe as “easy listening music”. I find that unless the work I’m doing involves deliberately breaking things, heavy metal (unless you have the volume really, really low, and what would be the point of that) is just too deleterious to the concentration.

Meanwhile, the new sheet metal supplier shipped the bulk of the parts for the frame and the bodywork. I started cutting the pallet wrap before I remembered to take a photo. Patience is overrated.

Many good things in this shipment, but the most exciting part (to me, at any rate) is the third generation frame design. Yes, only here can you have a third generation without the first two having being made available for sale :). The new frame base parts are made from 0.120″ HRPO steel (Hot Rolled Pickled and Oiled – do you want fries with that?). Why this material? Well, stainless is three times the price and at least three times more difficult to work and would therefore be prohibitively and needlessly expensive. Galvanneal is theoretically better, but would still have plain old steel exposed at all the cut edges. Most importantly, welding Galvanneal without a full face mask, forced clean-air supply and complete ventilation of off gases leads to an early and unpleasant death. So that is kind of out. I thought about it mind you.

Unlike the previous versions (which in fairness were prototypes) that were cut from flat stock and formed using a somewhat simpler hand-bender, these are CNC laser-cut from sheet stock and CNC folded. The precision is, if you will pardon the pun, mind bending. The width across the two bends, which is a compound error (one bending error added to the next) is getting fairly close to the measurement error of my metrology equipment. Which, if you care about such things, is at least one whole order of magnitude higher than the design specification. This is a nice problem to have.

All of the frame corner brackets plus an extra one for the business end of the electronics box.

Frame spacer. This is an deluxe addition to the new frame design which helps with strength, alignment and precision. Using a laser-cut part means that the fame width, which is critical for a good fit of the bodywork, will have very high repeatability (precision and accuracy for a change!).

So that, apart from a couple of tiny details which we will get to later, is it for the “made-by-others” parts. Now for the in-house bits. The front corner brace doubles as a support for the electronics box. It receives a stainless self-cinching threaded insert – because tapping holes is boring and slow.

Sometimes you could have parts made, but unless you need 1000 pieces the time spent preparing drawings, requesting quotes, tracking packages etc would be more than just making them yourself – even if you don’t have the proper tools. The drip tray retaining detent is a good example. It’s just a piece of stainless wire (aka welding rod) cut to length and bent to 90 degrees. A simple thing, but without it the spring clips that hold the drip tray in place would have to be a friction fit against the frame. Which would wear the paint . Which just wouldn’t be cricket.

Frame preparation. So the right way to do the next bit is to use a robotic capacitive discharge stud welder. But I checked all of the tool drawers in the shop three times and I couldn’t find one. Home Depot didn’t have one either. Guess it has to be done the wrong way for now. All of the little holes in the frames are laser-cut to just under 4mm. This makes them both easy and fast to tap at M4 with a power tool and guide block. Once tapped, the stainless threaded studs can screwed in temporarily and perfectly aligned for welding. Side note: the 12mm M4 threaded studs had to be custom made.

Before welding.

And after.

Then all of the frames get introduced to “Rocky”, the new finishing machine. Rocky is shy, so no picture for the moment, but he does a good job: if you look really closely you can see the dots of different color where the stainless welds have been blended into the mild steel frames.

Two final details to take away for today:

1 – “But why not just use nuts and bolts instead of going to all the trouble of welding (custom made!) stainless studs?” Well, because nuts and bolts would mean in-your-face visible fasteners on the exterior and that, at this particular epicenter of fastidiousness, is just not on.

2 – Even though the frame will be powder-coated, the frame detent and the threaded studs will be exposed as they wear, thus they are made of stainless steel.