Friday, 18 September 2009

Brake hanger, part 2.

Do you remember the abomination of a brake hanger that I showed you a while ago? Well, the time has come to make a proper one. This is how I go about it. There are of course a lot of ways that you could do it, but this is an easy one, especially if you are familiar with Adobe's wonderful vector-drawing application "Illustrator".

The prototype made from scrap pieces of steel (top part of image) is fundamentally correct, but has an awkward shape that I want to improve on. I also want to add some "meat" to certain parts of the hanger now that we're switching from steel to aluminium. So I put the prototype on a flat-bed scanner and place the resulting JPEG-file as a background image in a new Illustrator drawing.

Using vernier calipers, I take some really exact measurements of the real thing (length, width, size of the hole for the steel spacer) and make sure that the scanned image of the hanger gets the exact right size in Illustrator. Now that I have the scanned image as a background/template in the right size, I can draw a nicer looking hanger "on top of it" and still get the measurements correct and the needed holes in the right place (lower part of image). Once satisfied, I do a printout of my new hanger in 100% and check against my prototype.

Finally, I export the Illustrator file as an "AutoCAD Drawing"/dwg file and send it off to the laser/water cutters. If all goes according to plan I will receive a 15 mm thick alu part cut to my specification next week. This part will need a little bit of milling to get the right thicknesses (its thicker at the back) but it's still easier than doing the whole thing in the mill.

The reason why the hanger is a little bit longer than normal is that I want to be able to secure the "tuning fork" part of the hanger to the little stud inside the swingarm that keeps the hanger from rotating, using a screw. And in order for me to get to that stud it needs to be welded a little further forward on the swingarm – to clear the brake disc. The hanger will be black and most of it will be hidden by the black swingarm anyway so that's no problem.


  1. Marcus_of_MarcusMotoDesign20 September 2009 at 08:35

    Cool way of doing it!
    What laser/water cutter firm do you use? Decent prices? How fine is the cutted surface?

    /Marcus Kick-CAD

  2. Illustrator works well for simple items composed of lines and arcs but the converted files can get very messy when you start to use curves (b-splines and part ellipses for example). Its mainly to do with the file conversion to DXF/DWG, sometimes these items get turned into lines... lots and lots of lines!!! This poses a problem for the CNC machine as the cutting head momentarily pauses at each new co-ordinate point. On a Laser, this means a lot of part cleanup due to burning.

    Later versions of illustrator may be better but if you are going to generate an AutoCAD file, it's really best to do it in AutoCAD or a similar CAD program (Solid Edge 2D Drafting is a free download from Seimens and it has excellent DXF/DWG output). The process of generating the item will still be the same.

    Laser Cutters and Abrasive Water-Jet cutters prefer not to have sharp corners (for the reasons described above) it's best to put a small radius instead so the cutting head changes direction gradually.

    One last thing, be aware that the cut sides will not be parallel, they wil have a slight taper due to the taper of the beam/jet. This is not normally noticable on thin material but on 15mm plate it will be a bit more obvious, check with the shop doing the work. Some places also have an issue with laser-cutting Aluminium... I have never been given a good reason for this.

    Keep up the good work, I eagerly await each new installment!

  3. I promise to an honest follow up on the pros/cons of cutting rather than milling once I get the part back.