Thursday, 27 February 2014


Have I mentioned the importance of alignment already . . . If you missed it the first few times then here it is again.

There are several important aspects to alignment, as distinct from frame geometry:

  1. The tubes of the front triangle must be in a single plane.
  2. The axis of the bottom bracket must be perpendicular to this plane.
  3. The two halves of the rear triangle (i.e. the left and right seat and chain stays) must be equidistant either side of this plane so that the rear wheel lies in the same plane as the front triangle. In addition, the dropouts must also be aligned so that the wheel is held in this plane.
  4. The front fork stays must be equidistant either side of this plane, and their dropouts aligned to facilitate this.
The simplest method to align the front triangle is to use a straight edge and construct the frame joint by joint, starting with the HT-DT, then ST-BB, DT-BB, and finally installing the TT. Or you can use a flat piece of wood with shims under the smaller diameter tubes, then clamped so that they all lie in the same plane. In the old days pinning was used to hold the tubes in place while they were brazed in a brazing hearth. This generally required cold setting of the joints afterwards - basically, bending them back into aligment if they had moved. Steel is very forgiving of this type of treatment and it was commonplace to cold set before the advent of 'precision' framebuilding.

By far the simplest method is to use a jig in which the whole frame can be assembled in the correct alignment. The frame can then be either brazed in situ or tacked and removed for brazing. Some people say that brazing in situ causes unwanted stresses to build up because the metal is not allowed to move naturally under the heat of the torch, and indeed, if the frame is tacked and brazed out of the jig brazing must be performed in a definite sequence to minimise movement. What this sequence is I have yet to entirely figure out - suggestions on a postcard please.

In the end I decided to make a jig, tack, then take the frame out for brazing. As you will see in a later post there was some movement, about 1 mm out of plane. But let's face it, the only person who will notice this is me, and I think it's not too bad for a first timer.


Tuesday, 11 February 2014

Preparing the Tubes

Let's have a recap before I proceed. So far I've decided on the type of bike I want, measured myself up and designed a frame to fit these measurements. I've also skipped ahead a bit and described the frame jig which I've built, so I need to back-track a little, to the point just after where I designed the frame with the spreadsheet.

The drawing

The frame design spreadsheet enabled me to do two things: input my design choices, such as HT and ST angle, then compute the remaining tube lengths and angles; and play around with the HT and fork length so that some of these complementary angles were as close as possible to the lugs and BB that are available. The advantage of this was that I didn't have to modify the components and risk sloppy fit between tubes and lugs.

So, now I've got all the measurements I need to make a drawing. This is important because the spreadsheet only gives me centre-centre tube lengths, which is not enough information when you start cutting tubes and mitering the ends so they fit together. The drawing, however, will be a scale drawing of the front triangle with tubes and their intersections, so I can then measure from the drawing the actual tube lenghts where they butt up against each other. The other great thing about a scale drawing is that you can compare the evolving frame to it as you go and check that it's coming out OK . . . a useful thing, believe me! I showed you the drawing in the last post, but here it is again:

Tube mitres

I'll assume that you've bought the tubeset and other bits and pieces that you need to make the frame. I got mine from Ceeway (, who supply a beginners kit containing everything you need, though I did substitue some components because I wanted my build to have different angles than the standard 73/73 geometry supplied, but that's just me being fussy. I'm not going to give you a blow by blow account of the process because it could easily be wrong and every build is different, however, there are some useful tips that you need to know:

  • You can cut the tubes with a junior hacksaw.
  • You will need a vice.
  • Tube holders can be made out of two pieces of 2.5" x 3" pine. Clamp them together with a bit of card between, then drilled through with a flathead bit. You will probably only be able to find metric bits, so the relevant sizes are 25 mm ( 1"), 27 mm (1 1/8") and 32 mm (1 1/4").
  • Sort out the tubes, label them and and mark up which end goes where (you WILL mix them up otherwise) with a felt tip pen. You can also mark a central axial line down each tube using a length of angled aluminium, which is essential for lining up the miters at each end of the tubes.
  • Grind out the inside of the lugs with a rotary tool, fitted with a sanding wheel, so that the relevent tubes fit into them without the need to force them, but so that they stay located withou falling out.
  • Take measurements of the tubes from the drawing then line up a miter template and tape it in place. You can print out the template using the tubemiter programme by Giles Puckett ( This essential to produce decent miters without years of daily practise - a least it was for me!
  • You can rough in the miter with a hacksaw and then prettty much get away with an 8" bastard half-round file to do all the miter work as shown below.
  • The miters for the ST and DT which fit into the BB shell can be traced on with a felt tip pen around the edges as they protrude into the BB.
  • Miter the TT-ST end LAST. Before you do this fit the whole thing together and compare with the drawing to check angles and tube lengths. Mark up the ST where the TT will fit then miter the TT-ST end bit by bit until it JUST drops neatly into place at the mark. You can only really do this if you clamp the other tubes in position on a flat surface such as a piece of MDF, or use a jig such as the one shown here.
  • Only when you are happy that the miters are a good fit and at the correct angles should you fit everything together with the lugs.