Tom Porter's Recumbent Bike Plans - SWB versions
Tom Porter's Recumbent Bike Plans 2005

Dual 700C Z-Frame Build 2005       Tubes    Frame    Dropouts    Stays    Final
Cutting the tubes
Layout Table/Workbench
Top is ¾” x 24” x 72” Smooth sanded softwood plywood backed with 1” x 8” x 72” dimension pine. This gives a total thickness of 1.5” for mounting frame blocks.
The black layout lines are for positioning frame blocks. These are done with a Sharpie marker, if one doesn’t want something as permanent and hard to remove, use a soft lead pencil.
Main Frame Tube
The main frame is built from a 1.75” x .035” x 60” 4130 cromo steel tube from Dillsburg Aeroplane (no website). A lower cost alternative would be the 1.75” x .049” tube from Wicks Aircraft as the weight difference will only be about ½ lb for the main tube.
All steel comes with a protective coating that I use lacquer thinner to remove although after this is done you will now accelerate rusting.

If you look carefully at the tube after remove the coating you will see the mil spec and the dimensions of the tube

This shows the marker pen ink drawn on part of the part where it has been sanded and also where the natural oxide remains. I sanded the tube for clarity on photos, its not really necessary.
Layout And Cutting BB (Boom) Tube
Note: The length of the BB tube varies between designs because of the wheel OD and the crank arm clearance.

Boom tube is marked at 17.5 for the bottom.
Next the boom tube is rotated 180 degrees and the top measurement is done.

The top of the boom tube for 700c is 18.5”

Making The First Cut
My cutoff wheel is a 10” Norton that I got at Home Depot. The cutting guide is set at 65 degrees as this will yield the 130 degree compound angle when rotated 180 degrees to the other side of the miter cut. 
The adjustable triangle is a drafting tool. Be sure the cutoff wheel is set high enough to cut through tube, say 2". If you want to hand saw this you will have to use a miter box and hacksaw.

Now take the main tube and cut fairly precisely, there has been an extra .250 (1/4)” added fudge factor. Better a little too long than . . .

After each cut there will be burrs to remove on both the inside and outside of any tube. I use my belt sander for this but a file can also be used, just a little more work. The table for the sander is set at a perpendicular with a square and the miter guide is set a 65 degrees. The clamp is only to show how the tube is to be held against the guide. 

Patience is a virtue, take your time, measure twice cut once, yadda ,yadda , yadda.
Frame Blocks
Six frame block sets (upper and lower) will be needed
These are made from a 1” x 4” x 48” piece of hardwood. 
The frame blocks will be 6" wide, so cut six 6" long frame blocks. Next, locate the centers of the frame holes by drawing a line exactly halfway across 4” wide side of the block horizontally, then another line of at 3” vertically. Now you can use a drill press or handheld drill with either a hole saw or forstner bit for round hole. Alternatively can also make vee cuts with a hand, jig, band or table saw after cutting the blocks in half lengthwise. If cutting round holes, cut lengthwise after drilling the holes.
 IMPORTANT: Try to make all the blocks as similar as possible, this will save you from having to shim them.

Use a drill/countersink for the first set of holes on the lower blocks, using a 3” center. Drill/countersink holes in top block at 5” center.

Use a square to position lower frame blocks on plywood layout table, this is one of those crucial things.
I notch the frame blocks at the centerline to aid alignment. Best thing to use is a utility knife while carefully scribing against edge of square.

Number the blocks to ensure you keep matching blocks together.
Layout And Cut Downtube
The length of the down tube remains the same for all frame designs

Top is marked at 12.75 inches

Again the tube is rotated 180 degrees and the other measurement is done.
Bottom of tube marked at 12.875 inches

These measurements include a .125 (1/8)” fudge factor.
Making the 2nd cut for the down tube on the table saw.
Take your best educated guess lining up tube for perpendicular, don’t worry you’ll be able to come close.
Layout And Cut Seat (Bottom) Tube
Top of seat tube is marked for cutting with the usual .125” fudge. You know the drill, rotate the tube . . .

This tube has parallel ends so the same measurement applies. Just cut and dress.
As an alternative to using a cutoff wheel your best bet to make some 65 degree templates and go at it carefully with a handsaw. Use a bench grinder (you could use a file if desperate) to fine-tune the angle. It’s not impossible just a lot of work.
Locate the Bottom Bracket Cut
Mount lower frame blocks 1 & 2. Align and square them about 9” apart. 

I like to use an electric drill to drive in the bugle head woodscrews with either a square or torx drive head, the Philips drive heads tend to slip too easily. These are 2.5”, #7 screws.
Use a square at the junction of layout lines to ensure the tubing cut is aligned properly. When both sides of the mitered end touch the square, its ready.
Clamp the matching numbered frame blocks on tube. I like to use a screwdriver that has the corresponding head for the screws. You have to apply pressure gradually to maintain square so an electric tool is not the best here.
Locate the high spot on the front of the mitered tube using a square. This way is close enough
Forming 1.75” To Accept 1.5” BB Shell
The 1.75" boom tube is formed into an oval shape to fit the 1.5" BB shell with these soft wood blocks mounted in a bench vise. Use soft wood because hardwood will leave dimples in the tube
The round tube is placed in the vise blocks and checked for level and square. I wouldn’t trust my eye for this.
Now the vise is tightened slowly until the oval end is 1.5”. Go slowly and check often, once the deformation of the tube starts it’ll be easier to maintain square.
Cutting Tube For BB Shell
This is a manufactured professional quality tube/miter jig. These really are indispensable. This one is probably too expensive for someone cutting a small amount of tubing, But Grizzly has one for 60 USD and Harbor Freight has one for 40 USD which would be adequate for limited building. Yes, you can get by without one; it’ll be a lot more work.
The jig is adjusted for a 90 degree cut (they are all degree marked). JD Squared says you can mount these in a drill press, they all come with a bracket that will allow this, but they recommend you just clamp it in a vise and use a ½” capacity electric drill for ease of cutting.
This shows the 1.5” bi-metal hole saw mounted on the threaded shaft. The tube is clamped TIGHTLY and a light cut is taken. You’ll be able to see when you hit the marked centerline properly, if you’re a little bit off just rotate tube a tetch.
Be sure to use a cutting oil on the saw when cutting steel, otherwise you’ll dull the saw very quickly. See how easy and quickly you can make cuts with a jig.
Fitting BB Shell
Check the fit of BB shell after cleaning burrs off tubing. This bb Shell is from Power On and you can see the Mil Spec so you can tell its 4130.
Clamp bb tube vertically in vise and check for plumb.
Now the bb shell is placed in the miter cut and checked for level, if you have taken care it should be level like this.

Click here to go to page 2 - Fitting and Welding

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