Mech Pimping For Cheapskates

[Hillwalker]

Making a cage from scratch? This WILL be interesting. I've considered building a 'frankenrailleur' myself by cannibalising bits from 2 different mechs (Campag and Suntour as it happens... :shock: ) but building the cage yourself? Sincere good wishes...

HW

 

[torqueless]

Re:

What follows is hopefully largely self-explanatory. Each picture shows the result of an operation along with the tools used to achieve it, with the proviso that the work is held in the vice for photographic purposes, and was probably not held in this orientation while the work was being done.

Basic template and raw material for outer cage plate

Cutting corners. Pulley centres punched.

Punching centres for drilling

Drilling

Filing

More filing with round & half-round files (which were camera-shy)

 

[Woz]

Just curious if you weighed it before hacking parts off it?

 

[torqueless]

Re:

After refining the shape a bit with a pen, I thought I'd better get started on the inner cage plate...

..for which we won't be needing this bit:

At this stage I thought I'd better drill out the pulley-centres with both plates held together:

Drill centres punched, here we go again:

A couple of nails to hold the plates together:

A bit more hacksawing and filing with the plates held together:

 

[torqueless]

Re:

Just curious if you weighed it before hacking parts off it?

Do you mean the whole mech? No, I don't have any scales that are up to the job. I'm pretty sure the weight is listed over at velobase?

I don't consider that I've 'hacked' any parts off this derailleur yet... I thought I'd refined a few clumsy shapes, but I concede that I may be delusional...

 

[torqueless]

Re:

After a bit more pen-doodling, I am steeling myself to deal with the pivot for the pulley cage, which will be a PITA

I'll put it about there, and hope it's high enough up the plate that the cage won't collide with the sprockets:

..and I better spend some time cleaning up the faces of the plates, still scarred as they are from their previous life:

 

[torqueless]

Re:

Time to tackle the tricky bit- the connection between the lower pivot and the pulley-cage.

At the bottom of the photo you can see the lower pivot assembly, of which the narrower part, on the right, is also currently the axle of the top pulley. I am hoping to dispense with the integrated pulley-axle, which means I've got to secure the outer cage-plate to the pivot by that little length of thread just beyond the end of the spring.

I searched in my small collection of bike-related tat for a nut which had the same thread as that little length of thread. I found just one, which also seemed to fit the crank-bolt at the top of the photo.

After sawing a slot across the diameter of the end of the nut, I filed the six angles of the nut until it was round. The result is that little component on the end of the crank-bolt.

I now had to tap the same thread into the hole in the middle of the outer cage-plate, but I couldn't find a tap with a fine enough thread- a 5/16" BSF was the closest I could lay hands on, but it's thread was still too coarse.

Well, it's Sunday, and I'm a cheapskate, No way am I going to buy a tap to cut a thread in one eighth of an inch of aluminium, half of which is going to be counter-bored away anyway, even if I could find one for sale- so I quickly improvised a tap of sorts by taking a hacksaw and files to that crank-bolt.

It succeeded in making a thread in the outer cage plate in the end. I use the word 'making' advisedly, in place of the word 'cutting'.

Here is the outer cage-plate attached to the rest of the mech, which has a few vice-prints on the parallelogram arms..

 

[Martin Rattler]

Re:

This is interesting stuff torqueless; I look forward to seeing the finished derailleur. I considered doing something similar in making a replacement cage plate for a Campag unit but fortunately came across a replacement in a 50p box of bits at a jumble so didn’t need to put my fitting skills to the test.

Re making your own taps and dies. I used to do this on occasion when I was at sea and far away from the nearest Halfords. I did this by cutting groves with a rat-tail file in the steel nut or bolt to clear the swarf and then case hardening it with Kasenit powder. This made it hard enough to thread non-ferrous metals pretty easily and mild steel for a couple of goes although it ‘blunted’ and lost its form pretty quickly. I suspect that aluminium alloy can be threaded quite successfully with an unhardened mild steel bolt.

 

[Ian Raleigh]

This is like home made chips! They are much nicer than chip shop chips but cost a bit more!

Ok I'll get my coat................

 

[torqueless]

Re:

Yeah, I think I need to get to bike jumbles a bit more, and possibly save myself a lot of work, but I like to set myself challenges.

In this case, the silver lining to the cloud of working with a less than optimal tap was that I ended up with a nice tight fit between the components.

Here's a close-up picture of the threaded hole:

Here's one of the 5/16" BSF tap I was hoping to be able to use, next to the hastily improvised crank-bolt version I did use. Some time, I'm going to try the 5/16" in a clean BB axle, and see if it 'binds'. Neither of the threads on the Suntour pivot were exactly 'daisy-fresh', so it was difficult to be sure of their dimensions.

Here's some more doodling of prospective cage shapes