Recumbent bicycle frame jigs - HPV and bike frame jig
Recumbent Bike Frame Jigs

By Warren Beauchamp
Created 1/13/04, Updated 6/6/05

When building a bike, it's very tempting to cut the pieces and weld them together by eyeball. I have done this before and it does work and the bike feels fine, but the bike usually dog-tracks a little due to slight mis-alignments, and people riding behind you will give you a hard time because your wheels are not lined up with each other. This may cause both performance and ego to suffer to some degree. What's the answer? You need a jig. Everyone needs a jig. A jig holds all the frame parts and the wheels dropouts in alignment while you weld them together. This not only assures you that the bike is actually straight when you are done, it also holds all the frame tubes together which makes it easier to weld up.

In it's most simple form, a jig needs to hold the rear dropouts and front dropouts in alignment. If it can do that you can build the craziest frame in the world between them and it will still go straight down the road. It's better though, to also hold the major frame components in place. Jigs can be made out of metal or wood. Metal is better because you can make it more precise, but it is also more difficult to build. Here's a jig for an upright bike to give you an idea of what one a professional one looks like.  

Building a Recumbent Bike Frame Jig
I'll discuss two methods for building two bike frame jigs, first one made from wood, then one made from metal, and finally one that I built. A wood jig is easy to build with a minimal number of tools, the metal jig is harder but lasts longer, is more precise, and won't catch on fire if you get carried away with the torch...

Wood Jig Materials

  • 1 - 4x8 sheet of 3/4" MDF (flat!)
  • 1 - 2x4 (straight!).
  • Phillips head wood screws
  • Recommended tools include circular saw, jigsaw, drill press, large straight edge, large square.
  • 8 - 3/8" x 3" bolts and nuts

Wood Jig Platform
To build your wood jig you will first need a completely flat wood base. I suggest starting with a 4x8 sheet of 3/4" MDF (medium density fiberboard). This is better than plywood because the surface is really flat, and it doesn't warp like plywood. All parts for this jig should be made as accurately as possible as any inaccuracies here will be multiplied by the inaccuracies made when building the bike parts!

  • Cut a 2 feet wide by 8 ft long strip. This is the base for your jig.
  • Cut 2 - 6" wide strips and screw them into the bottom 1.5 feet apart to reinforce the structure and make sure it stays flat. Pre-drill and counter sink your holes to prevent splintering.
  • Cut another 6" strip into 1.5 foot strips to go between the reinforcement strips. One at each end and 3 in the middle should be plenty.
  • Mark a centerline down the middle of your new jig platform in something permanent like magic marker.
  • Drill a series of holes 3/8" holes, 2" apart exactly down the centerline. These holes will allow you to vary your wheelbase length in increments of 2 inches.


Jig platform bottom view showing reinforcement

Dropout Standoff Jig
Now you have a really heavy but flat and straight platform that you can put it on some saw horses when using it or lean up in the corner when you're not. The next step is making the standoffs for the dropouts. These will be made with sides of MDF and a core of 2x4. Before building these you will need to figure out whether you are using MTB or road hubs, and what size wheels and tires you will be using. MTB hubs are 135mm spacing for rear wheels, road hubs are 130mm for rear wheels and front wheels are usually 100mm. Cut a precise 2 1/4" strip from the 2x4. Draw center lines on the center of the 2 1/4" width, both sides. This will be the core of the standoff.


Dropout Standoff Jig 

Cut out the sides of the dropout standoff jig as shown in the drawing. Make sure the bottom of the standoff is flat and square by putting it on the jig platform and using a square to make sure it is standing up straight. Fasten the sandwich together with wood screws. You will need to use either the axles from old hubs (quick release axles work best) or some 3/8 threaded rod to make your standoff axles. Measure the radius of your wheel and drill an axle hole through the standoff at that diameter. Use a drill press to make sure the hole is perpendicular to the side of the standoff. Drill 3/8" holes through the centerline the base of the standoff to mount it to the holes in the jig platform (See picture). Mount the axle in the axle hole using the thin nuts and washers to space it to the correct width. Verify that the axle is centered properly on the standoff. Use the 3/8" x 3" bolts to fasten the standoff to the holes in the jig platform. Check that it's square to the base. Check that the axle is the same distance to the base on both sides. Check that the distance between the front and back dropout axles is the same on both sides.

Frame Jig
Ok, now you have the base and a way to mount your fork and rear dropouts in a solid way and make sure they line up properly. The next step is making brackets to hold the frame together while you are welding it up. For the sake of expediency we will be assuming you are building a traditional monotube recumbent. 

The frame jigs are constructed in a similar manner to the Dropout standoff Jigs, except that the 2x4 does not need to be cut down. There are two ways of securing the tubes. Type 1 involves using a hole saw of the same diameter of your frame tube. Cut the hole in half and use wood screws to clamp the tube. Type 2 can be used for a range of tubing sizes and involves cutting a precision V in the 2x4, then using a metal strap to hold the tube in place. Draw a line down the center of the 2x4 on both sides of the wide face to help center the frame tube hole or V cut. By using a half circle for the side plate it is possible to adjust the frame clamp standoff to a wide range of angles. You may need two frame jigs per tube to support it securely. Side plates can be screwed to the frame support 2x4, or clamped with C-clamps to provide easy adjustability.

Examples:
Here is a  not-to-scale example showing how the jigs are used to hold frame tubes together for welding.

This next drawing shows how the dropout standoff jigs are used to hold the bike in alignment while the bikes rear suspended suspension geometry is welded into place.

The wood frame jig in this document is not meant to be the ultimate tool for frame construction, but it's an easy way to make sure your bike turns out straight. If you are planning on making more than a couple bikes, a custom bike jig made from metal is a good idea. 


Metal Frame Jig
As with any good jig, you need to start off with a straight and flat plane of reference. In this case we will be using 2x4" rectangular steel tubing. This is a fairly common item that should be available at any metal supply retailer. I suggest making your frame jig 8ft long. The cuts should be precise so use a chop saw or have your local machine shop make the cuts for you. You cab build the jig from rectangular steel tubing as in the example below, or if weight is an issue (and money isn't!) you can build it from 2x4 aluminum tubing and angle material.

Metal Jig Materials

  • 30 ft of 2x4" 1/8" wall steel tubing.
  • 2 ft of 1.5" wide angle iron
  • 8 - "C" clamps with at least a 6.5" throat.
  • Steel chop saw, Welder or Brazing torch, drill press, square, tape rule, big hammer, etc.
Steel Jig Platform
The parallel rails should be spaced 2" apart, just wide enough that a metal 2x4" tube fits snugly at all points along the frame. Clamp the parallel tubes with a flat board on the top and the bottom to make sure it stays square and parallel. Weld a 6" chunk of 2x4" tubing to each end (or longer for more stability). The jig platform can be supported with sawhorses to allow the frame and dropout jigs to extend below the jig platform.
Steel Dropout Jig
The metal dropout standoff jig is made in a manner similar to the wood one above. 

Steel Frame Jigs
Due to the time involved in making metal jigs, it's recommended to make the frame jigs adjustable. This is accomplished by cutting a 90 degree V long-ways in the end of each frame support jig, and then brazing in a 5" long piece of 1.5" angle iron. Cut up a 4" C-clamp and weld it to the frame support jig to clamp the frame tube in place. This should allow frame tubes between about 1" and 2" to be clamped. If you are using aluminum you'll need to weld the cut up C-clamp to a steel flange and bolt it to the side of the frame jig.
Here's Larry Lem's frame jig, built from these plans. Here, he's using it to shorten a fork from 20" to 16".

Larry says this 12 foot long steel jig weighs 64 lbs. 

Bottom Bracket Jig
The final jig to be created is the bottom bracket jig. While a jig using cones to properly center the BB would be preferable, making them is probably outside most of our range of skill and budget, so we'll just cheat a little. 

Find yourself a junker 10 speed bike, and remove the bottom bracket. Throw the bike away and save the BB's threaded bearing cups. Make two 1/8" thick disks the same diameter as the outside of the cups. Use a compass to make sure they are round. Drill an 1/8" hole in the center to mark the exact center. Braise the disks onto the outside of the cups. Take two more 4" C-clamps and mark the exact center of the moveable end of the clamp. Cut the clamps in half and discard the non-adjustable side. Drill a shallow 1/8" hole in the center of the moveable end of the clamp. Mount the C-clamp to the bearing cup and use the shaft of an 1/8" drill to verify alignment. 


Bottom Bracket Jig
Braise the C-clamp to the bearing cup. The bearing cup should be able to flop around on the end of the C-clamp. Go find the bike you discarded and surgically remove the entire BB. Screw the new C-clamps with BB cups into the BB. mark the center of the BB and align it with the center of the jig standoff. Mark the cut ends of the C clamps so they can be braised to the sides of the standoff. Verify that the BB and clamps are aligned level and straight before brazing them to the standoff. The BB alignment jig will be a bit hard to put on and take off of a BB shell with the threads, also there is a chance that that heating the BB shell will cause the BB cup threads to fuse to the BB shell. To prevent these issues you can carefully file off the threads on the BB cups until they slide into the BB shell without having to screw them in. It should be a tight fit but not so tight that it could damage the threads.  
 

Completed Jig
Here's Larry Lem's completed jig, holding his latest creation, a dual 700C Bacchetta clone. 


Pictured below is the metal jig base, with dropout and frame jigs. The frame and dropout jigs can be clamped into place between the rails with C-clamps, allowing maximum adjustability. Alternatively, a series of holes can be drilled through both sides of the rails to allow the jigs to be clamped using long bolts.

 


Metal frame jig

Frame jigs can be inserted and clamped at whatever angle is needed to build the components of your frame. Steel construction insures alignment won't burn when you are brazing on your rear dropouts.

Jason Erickson built a frame jig from these plans


Warren's Jig

Over a year I decided that I needed a jig and wrote this article. I finally built one. As with many of my projects, what gets built is not exactly the same as the original design. I came across some old 7 foot tall computer racks (free!) this past winter which looked exactly like what I needed to make a jig out of. I cut up the bottom mounting plate for the end plates and "L" brackets, and used the bolts that come with it to bolt it all back together a bit differently. I built the jigs as in the metal frame jig  above, and had to pay $50 for the 8 foot chunk of 1-1/4" x 2" steel tubing (arg!). 

The jig rails are a heavy duty "U" shaped hunk of steel. I use those clamps to hold the jig in place. I'm using hose clamps to hold the tube to the jig for now, I may get ambitious later and cut up some C-clamps later, but the hose clamps work fine for now.

I used more old rack part to make some legs so I could actually braise standing up (what a concept!). In the jig is the front sub-frame to the Cuda-W speedbike I'm working on. 

As shown in this article, a wide variety of materials can be used to make a frame jig. The important thing to remember with each of them, is that your bike will only be as straight as the jigs your build, so measure carefully!

11/11/09
Steve Delaire sent this fork jig:
  • adjustable offset 0 to 150mm
  • axle holder is step threaded to accommodate different axle diameters
  • set screw tabs at axle to precision align perpendicularity
  • default width is 100mm ~ spacers added for drive widths
  • pic should explain the rest

 

 

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