Mach 1 Instructions

Sheets 1-10 are the Mach 1 Drawings. Use the sidebar to navigate back and forth.

SHEET 1 - Donor bikes – If you have choices you can make about what bikes to use, focus on three things.

One – Steel tube bikes, or chromolloy. Avoid (unless you have the welding skills) Aluminum frames, and oversized tubings. With rare exception the lugged 10-speed frames common to a lot of old road bikes serve our purposes well.

Two – hardware. I look at the crank – you want a three piece cottered or cotterless crank bike – at least for the one you use as the front end of the bike. The cotterless crank with the narrower (roughly 1 5/8” Dia) bottom bracket, offers you the most choices later for upgrading hardware – different cranks, sealed cartridge bearings, and so on. This is called the English Bottom bracket - a pretty broad industry standard.

Three – weight. Steel bikes come in an endless variety of tubing thicknesses, all of which contribute to the overall weight of the bike. If it’s a boat anchor, move on. If it’s a featherweight racer – the odds are that a first time metalworker will have a hard time with such thin tubing.

Reference for new mechanics. Brad Graham's book, "ATOMIC ZOMBIE'S BICYCLE BUILDER'S BONANZA", has a superb section early on about how to strip a bike down to it's bare frame. The Atomic Zombie website is now about ordering the book and a variety of bike plans - who can blame him, but your library might have it by now - if not, ask them to get it. ATOMIC ZOMBIE is worth a read for the new mechanic (and for alternate building inspiration!). If you read that and are following along here, DON'T chop the frames up the way Brad does - it ain't wrong, but it is not the method detailed here.

2005 added note --- Also note that the dimensions given for cutting in my drawings are rough guidelines. See the rough layout I show in the third shot on Picture Page 1? This rough layout, for Assembly #1, is the key to a great bike. When you decide on the final cuts for the front end, make this front triangle as small as practical. Use a stray crank in the test layout, and a fork inserted in the head tube. Keys to the layout - the crank and the front wheel shouldn't cross, and the 'up' tube in the triangle needs enough room for a front deraileur to mount later.

Where possible I like to re-use the fork and head cups/bearings from this first bike on the finished recumbent. Matched parts and all.

SHEET 2 - Same notes on donor bikes, except you don’t need to worry about the crank from this bike. It helps if donor bike #2 is a really tall frame, we use all the length of the old seat tube here.

I strip the paint off of all bike frame parts I salvage - after I make the critical cuts. You don’t want to weld/braze over paint jobs, and you’ll burn existing paint beyond recovery anyway. I use a torch in a well ventilated area to toast the old paint on bike parts, then I wire brush them clean. Please be careful, and do not breathe toxins. Sandblasting is safer, and nicer if you have access to it. Eventually, you can safely sand or wire brush all the paint off.

SHEET 3 - The first assembly is the easiest – no alignment to do. Do that rough layout before making the final cuts and the fishmouth cut, etc. The most difficult cut is the fit for the old seat tube under the top tube. Pre-assemble the sleeve joint with the top tube offset slightly over the old seat tube, and mark the angle of the intersection. Cut carefully at this angle, but ¼” to 3/8” longer than you need it (there is a picture reference for this cut on Picture Page 1). Then file a ‘fishmouth” onto this end, removing material towards and away from the head tube in a curve to meet the underside of the top tube as closely as possible. File and fit, file and fit, until you get it right. The down tube is a spliced sleeve joint. Usually a small piece of salvaged top-tube, smaller in diameter than the down tube, makes a perfect inside sleeve for the joint. Braze or weld these two joints. Be sure to flux and heat the sleeve joint thoroughly so that braze material penetrates deep into the joint.

The second assembly is easier to fit, and harder to align. For most common donor bikes, the top tube of the front donor bike will sleeve nicely into the old seat tube of the ‘rear’ donor bike.

Length factor? – you. I am an average 6’-0” person, and about 38” long for a top tube is generous for me. A frame for a truly 5’-0” and slightly smaller person might have a total top tube length of 30” - this is probably a minimum. A tall person – 6’-4”, say, might want a 40” top bar. Trim the old seat tube from bike #2 to adjust length and overlap.

Before welding/brazing, lay the unbrazed assembly flat on a table where you can weld. Make sure the head tube and bottom bracket aren’t on the table interfering with the tubes lying flat, and use washers to shim the front (narrower) portion of the top tube and the (Bike #2) cross bar so that everything is parallel on the table. This really is your first critical alignment - take the time to jig and shim this into shape. I take a long walk to the back of the table, and get my eye down at table level to sight parallel to and just below the top tube. In this foreshortened view of your frame, are the down tube at the bottom bracket and the downtube here at the back end in line and in plane with each other. Even just a little bit off? Fix it. Take the walk again, eyeball it. Over correct. Bring it back. Fiddle with it and get this alignment right!

SHEET 4 - Try bending the rear triangles salvaged from both bikes. I guarantee you will like one of them more than the other one after bending (do this before stripping the paint off the chosen part). I use the torch to heat both top stays at the same point (on the inside of the stays), and then I press the bend in by hand down to the height shown. One correspondent uses a conduit bender to do this bend cold - I haven't mastered this yet.

New Jan. 30, 2005 - There is a picture series of a jig I made to help on this bend. See the Rear Triangle Jig page on the sidebar for this. You don't have to make a jig. Scrap one donor rear wheel - cut out all the spokes and use the hub to bolt the two drop-outs together. If you can find a bit of 4" steel pipe, use that to wrap the bend around....

The top ends of the top stays are sometimes heat-bent as well. Test how they might fit at the attachment point (where the old saddle clamp was) first - you may or may not need this extra bend. I hold the part in a vice with both ends sticking up. (See Picture Page 2 for pictures of this.) Heat the stay about 2” down on the outside, and then bend it out about 10 degrees (I use a 18” piece of conduit as a bending lever). Do the same on the other stay. Then heat the inside of the first stay at a point about 3” down from the end, and reverse the bend 10 degrees back. This brings the original bend back parallel to the center axis. Do the same with the other stay –this should align both stays parallel to the top tube you are about to attach them to, and just at the right width to press tightly to either side of what was a seat lug. Have the cut-off seat tube end from bike #1 in hand (from your trash pile) to test this as you heat and bend. You may have to come back and fiddle with this bend again - as you mechanically assemble the rear triangle to your bike and make a judgement about alignment, you will want to fiddle with this bend.

The THIRD assembly, adding the rear triangle to the bike, is the trickiest to align and the most telling on the finished bike. This can be jigged and measured for your assurance – there are very fancy alignment tables and micrometers for just this purpose. Fortunately, the Mach 1 geometry is a very forgiving geometry for rear triangle alignment – a thorough set-up and visual inspection will do for alignment. I set the existing partial frame perpendicular to my work table and upside down. Then I set-up the rear triangle on the table, shimmed up (on 3/8” spacers) and already in place with the top stays pressed onto the bike’s top tube. I put a hub in the rear dropouts for proper spacing - this is jussst off the end of the table. This is pictured on Picture Page 2. I stand off 6-8 feet and eyeball the resulting alignment from front and back. That extreme foreshortened view from the front - is the rear end properly centered relative to the plane of the bike? Your eye defines the plane - the long top bar, the downtubes fore and aft - these define a visual center line. Look at the rear triangle as 'bisected' by this center line. See a steep triangle, left and right of center? Are the two 'triangles' the same size? Again, fiddle with it. Develop the fine tuning eye - it is worth it. Over correct, go look again. Move the jig a fingernail, go look again. We will have one more chance to correct alignment before we close the frame, but get as happy with this visual alignment as you can.

Now go to the back of the bike, stand off 6 feet, and eyeball it again. Yes? No? Often I find the front view and the back view are different in perception, and I will go back and forth from one to the other until I get an alignment I like from both ends. This process is not perfect.

Now stand off to the side of the bike – hold the drawing upside down and nearby – does it look like that? Top tube and top stays parallel and aligned? Check the other side.

It’s worth the trouble.

Weld/braze the top tube and the stay in this position on both sides, along the wide point of contact between the two parts. Both sides, then flip the bike over and weld/braze on top of the joints. BE generous with braze metal, fill the gaps - this is where the weight of the rider bears most.

NEW THOUGHT 8/18/03 - After this assembly I have taken to putting the unfinished bike in the stand and mounting a wheel in the rear drop outs. See Picture Page 3 Check your alignment now - is the wheel in plane with the frame? Tilted up to down? Hand bend the stays a little - you can do this cold with the handle of a hammer for a lever. Out of plane front to back? Leave the wheel in the frame, put it on the floor on it's tilt-to side, and gently step on the newly brazed joint to adjust. It sounds weird and crude, but it works. Get satisfied with alignment now, before we lock it in by adding the bottom rails in the next step.

SHEET 5 - Bottom Rails. You can use something finer and lighter than EMT tubing if you want to. I don’t mind. Before doing the final assembly, check out SHEET 6 about bell-forming the ends to join over the donor bike stubs. Those stubs are often oblong and strangely shaped (often crimped) depending on the stays from the donor bikes used, and the bell shaping idea allows you to cope with all those variations. Test assemble one bottom rail. When you like that, repeat it for the other one. A well formed 'bell' joint IS, in fact, just like the lugged construction of your donor bike - heap big strong for braze welding!

The (nominal) '5 degree bend' is useful for spreading the rear triangle slightly. As you assemble the frame with the ‘open’ bells, rotate the bend out slightly and evenly to align the bottom rail with the bottom stay on the rear triangle. When you have what you like, clamp the two tubes tight against the downtube. You may even vary the '5 degrees' - I do not measure that by any means - just bend one until I 'like' what it does, then bend the second rail to match.

With both rails loosely in place, stand off to the side. Like it? Look like the picture? Adjust while you can. Stand to the rear. Leave that wheel in the drop outs - is alignment still OK? Fix it. Like it? I leave an old wheel (no tire) on the frame throughout the process of adding these bottom rails. Right up until the point where I braze the final joints, I continue to stand off and check visual alignment.

Happy with your assembly?

Braze weld both rails to the downtube right where you are now, without closing the bells. This locks the rails in position. Now heat and bend/form the bell ends over the bike frame’s stubs. Do this thoroughly and carefully on all four joints – leave no gaps where the edges of the bells lap over the stubs of the donor bike.

Now with the bells closed, last time, last chance - check the alignment and adjust. Long walk to the rear, be honest. Fix it if you need to.

Clean, wire brush, and flux everything. Braze all joints thoroughly, from top and bottom.

YOU FINISHED THE HARD PART – THIS IS (almost) THE FINISHED FRAME!!!!!!!!!

A note on EMT. You are burning noxious chemicals off of the EMT as you heat it - zinc galvanizing to say the least. Ventilate thoroughly – do not work in an enclosed space. Do not do this for a living – not a good idea at all!

See notes above on when and how to close the bell ‘flaps’ onto the bike frame stubs. This process may take a few practice tries before you do the actual work on the bike, eh?

Cut off the extended stub of the 'back' downtube flush below the bottom rails.

SHEET 7. Time to admire. Does your frame look good to you? Still like that rear end alignment? What is right? What is wrong? What can be adjusted? Like it enough to finish it? Once in a long while, I still find one that gets away at this point. Sometimes an alignment boner I can fix with cold bending, sometimes not. Sometimes an error in proportion. Is it fixable or not? Sometimes a gap in a brazed joint – those you can fix. Now is a good time to decide whether this frame is worth taking through the rest of the process of becoming a great bike.

Depending on the donor bike and the bend in the rear triangle, usually a 26” wheel is the easiest fit with the existing brake bridge on the top stay of the rear triangle. Sometimes a 27” wheel will fit. If you really want a 27" – cut this brake bridge loose now and add your own. Or add direct pull studs, etc.

C. The chain idler is not really necessary. It helps carry the weight of the extra chain which is otherwise pulling on a deraileur spring that wasn't designed to hold it, and it keeps the chain (potentially) out of the dirt. I drill a piece of ¼” threaded rod through both bottom rails of the bike in the position shown, and mount an idler wheel salvaged from a rear derailleur on it between a couple of 2 ½” plastic washers.

NOT SHOWN - I usually run the very long rear deraileur cable along the bottom, right hand rail, much the way it is run on the typical 10 speed road bike. I add one extra (usually salvaged) cable stop braze-on, just behind the rear down tube and ahead of the 5 degree bend on the right rail. This acts as a slight mule block for the rear deraileur cable and keeps it from fouling the chain.

SHEET 7A. This is just pretty. To me, anyway. Gives some idea of how a human fits on the bike.

SHEETS 8-10. Parts. This is the sling seat I use. I can and have put a Rans seat on this bike. And you can make a plywood seat and get by just fine. I like this one a lot – rode 150 miles on it with a broken tailbone, no less! But that's another story. The secret of bending that really odd shape is to mount a conduit bender in a table height bench vice. Then bring the ½” EMT tubing, thoroughly marked, TO the bender. ½” EMT bends pretty easily by hand, yet is rigid enough to stand up to this 270 lb. rider (I once was) without deforming. Bend the 45 degree end first, then bend the 90 degree "bucket" for the seat. Take care in the bender to visually align each bend on the same axis at the first bend. There is a full picture/essay on how to make the seat frame here - Seat frame construction .

Buy extra conduit, make extra tries at bending it just right. Conduit is cheap (well, it used to be) – make four (4) side rails and choose the best two for your seat. A full sized pattern is a help and I have some PDF files on the website that you can paste together into a pattern!

Seat covers. I use a vinyl mesh fabric – Power On Cycling sells a very good mesh for seats in small quantities. I hear there is a great rip-stop nylon fabric for sale at REI that works too. I stitch my covers on around the seat rails with nylon monofilament. Looks great. It is possible to stitch and grommet a separate cover and lace it onto the frame. Or to do what Rans and others do in the way of a cover that wraps around the the back of the frame and then is cinched with zipties. My method for stitching a seat cover on this frame is covered on yet another sidebar page - Seat Covering

SHEET 9. Seat stays. This item, bolted onto the extra holes in a rear drop-out, is a fairly good, lightweight way to hold up a seat back. There are other ways.

A typical seat brace, made per the drawing, installs like this.