Tag Archives: bike

Bicycle frame jigs (2/4)

The election of a frame fixture is not just a matter of budget. It is obvious that if you are going to produce few amateur frames a flat surface or a beam design jig will suit you. If you circulate large amounts of kind of the same type you should ponder over switching to something that ease the assembly and welding at the expense of less versatility.

Potential frame builders have the mistaken idea that the jig must be extremely accurate, built like a precision timepiece and yet possess immense strength for bending and holding the tubing sections in position for welding but in fact the base structure of the jig, sometimes called the backbone, bed, table, base table, face table or frame face can be almost any relative rigid structure. As long as the backbone is level in all directions the real precision and accuracy will come about through the fabrication of the fixtures that attach to this substructure (backbone) and then will be adjusted and secured to position and hold the tubing and parts in place during the fabrication of the frame.

A modified flat plate is enough for welding a bicycle frame

A modified flat plate is enough for welding a bicycle frame

For around 300$ you can start to think about it. In old Europe, for less than 400€ I’m struggling to find the right materials to accomplish my project. I guess this continent is not that cool anymore, isn´t it?

Don´t forget that choosing a frame jig is closely related to the welding technique. For example, brazed lugged construction requires the most from a jig. Full access to each joint is critical. When using lugs, most builders prefer to braze the complete frame in the jig unlike lugsless construction where jigs are used only to tack at 2 to 4 spots on each joint.

Silver brazing a lugged frame

Silver brazing a lugged frame

Consider most jigs offer limited access to one side of the frame. On top of that, if you are gas welding just forget about tackling the job on a cheap parallel beam jig for example. The heat coming from the torch will deform beam materials affecting our setup.

Nowadays TIG welding has become the superstar for joining the tubes of a frame. Both bicycle factories and custom workshops uses it on a daily basis. SMAW, GMAW, FCAW SAW are others common types of arc welding procedures but useless because of the thin-walled bicycles tubes.

Automated robot welder at Merida - Taiwan tacking a full suspension frame.

Automated TIG robot welder at Merida – Taiwan tacking a full suspension aluminium frame. Hand-welded frames are still far superior.

Besides TIG (that uses electricity), gas welding (oxyacetylene for example) is also possible, been the standard for 70 years. As good as it is, gas welding cannot compete with TIG. Anyway, oxy-fuel is still required for brazing, either fillet brazing (bronze weld) or brazing lugs (silver weld). These realiable and old-fashioned methods are still popular between cycle enthusiasts, that’s why you have to keep them in mind for your future jig plans.


Checking the chain stays

So far: budget, quantity and welding procedures have been taken into account. The quality of a frame depends more on your miters, the time you spend fine tuning the geometry and your welds rather on an expensive jig, that can offer good accuracy of course. Amazing frames can be produced with simple tooling and great skills.

But there are also few considerations about the bicycles you are going to build and how you want to work in order to select the right jig:

  • What are the limitations in the seat tube area? Does the top of the seat tube have to be square cut? If it does, you can’t pre-shape the seat tube top, or use a seat lug with an internal ledge for a cut to length seat tube.

  • Does the seat tube holder arrangement pivot about the center of the BB shell? If so, you can’t build with the seat tube offset from the axis of the shell.

  • Can you easily build interrupted seat tube designs? These are common and unavoidable with rear suspension frames.

  • Are you in the mood of ISP? If you are, size the jig up accordingly or fabricate an extension.

  • How versatile is the rear axle arrangement? Most jigs come with one axle for only one spacing. You have to pay extra for any other spacings. 130mm road frames and 135mm mountain frames eclipse other preferences. How do they do 120 mm track spacing, or 126 mm old road spacing (for restoration, repairs, or using classic parts), or 145 mm if the jig also builds tandems, or the new MTB standard142xM12, or 165-170mm for fat bikes?

  • How do they handle the inevitable pull-in of the rear dropouts?

  • Do you want to build the frame from the BB up?

  • How do you build forks? A fork building feature could be integrated in a design. The rear dropout holder doubles as the front dropout holder in the Henry James Universal frame jig for example. A separate professional fork jig usually costs about $500. You don’t usually build forks? That is all the more reason to have one built in for when you do need one!

  • Can you build the occasional tandem on the jig? An attachment of some sort must be used, and you should not expect the adapted jig to be good for a tandem specialist.

  • How do you mount it? Because of the jig weight and bulk, most jigs require an expensive and complex mounting system that can increase your costs.

  • How portable is it? How much storage space does it need? TIG welding is not a straightforward skill. You might want to set up a frame in the jig, then single-handedly put it in your vehicle and take it to a full-time professional welding shop (an easy way to get perfect welds) for tacking while you wait. Even on a moveable stand, most jigs take up a lot of space.


A case of study: 29er inner tubes

Not long ago bike shops struggled to source specific 29er tubes (700x54mm). A widespread practise was to overinflate the classic 26″ size or 700x35c inners with the risk of sudden blow ups, decreased rolling eficiency and more punctures. Only some beefy tubes behaved well with no surprises for this purpose.

Foto 1 Nikki Gudex tubes

Tubes are within the most iconic bicycle components

Now the market is full of 29 inches tubes. For around £4-5, 6-7€ or 7-8$ you can afford good quality spares. Maxxis (Taiwan) and Schwalbe (Germany) are remarkable brands that produce tubes in many different sizes.

After damaging the original “unlabelled” tubes that came with my bike (probably made by CST, Vee or any other asian bulk manufacturer), I picked the Maxxis Welterweight (4,24€) and Schwalbe Extra Light (6,60€), both in online stores, to give them a go.

A thousand kilometers after testing the tubes with new tyres, the Maxxis tube has result in an amazing and absolute quality product. A bargain for the price (now over 5€).

Maxxis tubes are always true to the word of the company. Since the moment you open the box they meet the announced weight in the worst scenario, and sometimes a lot less.

The Welterweight is not a weight weenie product unlike the intended use of the Schwalbe Extra Light. Officially 205g. versus 140g. Note that the thickness of the butyl wall and tube dimensions will determine its final weight. The valve type, porosity and overall rubber quality have a negligible impact on it.

Foto 2

Maxxis tubes are made in Taiwan while Schwalbe units come from Indonesia

The good thing of the Maxxis is the fact that it is a real 29er inner tube. The Extra Light tube width doesn´t meet the requirements to fit securely a 2.4 tyre despite it is recommended for this size. It is clear when you put them close together that something is wrong in the Extra Light product. It looks like a 700x35c spare.

But what is even more shocking is reading the compatibility printed in the cardbox. It suits also 650b/584mm/27.5 wheels! Wouldn´t have been any wiser to make a compatible 650c/26″/559mm and 584mm tube while producing separately the specific 29er size? The discrepancy of the 29er size (622mm) with the 584mm standard is more than the 559mm measure has instead.

Foto 3

A nonsense of tyre matching specifications that even claims 700b compatibility (635mm)

The result is that the Schwalbe model is not a proper 29er tube and nor a 650b one. You have to slightly overinflate them on 2.2 Continental Mountain King tyres for example. It’s tricky to slide equally the tube inside the tyre bulging it on many ocassions unless you use an air compressor.

What’s more I got quite a few flats. None with the Maxxis. I reckon even the rolling eficiency is compromised with such a tight fitting. A hassle.

The final blow came when checking the weights. The taiwaneses are only 40 grams on average heavier than the germans, instead of the expected 65g.

Average weights

Average weights. Less than 40 grams average discrepancy between models

Cheaper, easier installation, more reliable and keeping the pressure for longer my vote is on the Welterweights. It’s great that Maxxis produces almost each single size of bicycle inner tubes. Meanwhile the design of the Extra Light tube is all messed up.

Brompton inner tubes

As we’ve seen in previous entries nothing in the Brompton universe is straightforward. Inner tubes compatibility are ample proof of this.

If you eventually need to replace them, bear in mind that a regular 16″ children bike tube will not fit. This is the one you are likely to find in a rush in a bike shop and for your surprise too wide. You’ll notice is very tricky when sliding it inside the tyre. These inners will cover ranges between 1.75 to 2.125 inches (45-50mm).

On the other hand, Bromptons are equipped with up to 1.37″ (1 3/8″, 35mm) inches width tyres. Schwalbe makes good quality spares and are the ones I recommend.

Compatible inner tubes suit from 28 to 37 mm width tyres

Compatible inner tubes must suit 28 to 37 mm width tyres

Most of the Brompton compatible tubes fit tyres from 340 to 355 mm bead seat and widths from 28 to 37 mm approximately.

16 inches inner tubes are very light :mrgreen:

16″ inner tubes are small and as a result very light :mrgreen:

Brompton Y trigger

Throughout Brompton three speed models history the bikes have been equipped with Sturmey Archer or SRAM internal gear hubs (IGH). The one to service has a SRAM 3 speed gear hub combined with a Sachs Torpedo shifter that operates the gears.

Sachs Torpedo and Sram Torpedo

Sram owned Sachs at the end of the 90’s. Components were relabelled (right picture)

After years of use there are no signs of shifting smoothness at all. The main reasons are rusty cables and a tatty Torpedo unit that needs replacement.

Fortunately the better functionality of the original Brompton trigger, and the fact that can be either used with Sturmey Archer or SRAM 3 speed hubs, will ease gear shifting for peanuts (£12.75 plus gear cables).


Brand new in package. You can reuse the old clamp to fit the new trigger

Sachs Torpedo vs. Brompton Y trigger

IGH control components installed in the bars are very basic as a rule. In the Torpedo’s design the simplicity is carried to an extreme. It looks like an old downtube gear lever but clamped in the handlebar instead. It works in friction, due to the index mechanism is incorporated in the hub. With Sachs Torpedo thumbshifters you will only notice gear changes in your legs because this Sram internal hub gear is very silent unlike Rohloff hubs, for example, that emit a loud click each time you change between gears.

The Y trigger, besides winding the cable, incorporates a design that simulates the ratcheting system of a SIS shifter thanks to a pawl leant against a stepped inner wall. It is different however, as you can tell some play of the lever when you move it slightly back and forth. It reminds me of the Rohloff twister which must be setup with some slack. Now when you rotate the thumb levers you will listen to a reassuring snap noise that confirms the gear has been engaged.


Brompton control trigger has two operating arms so that it can be reached when is in the farther position.

With regard to how conventional indexed shifters work vs. IGH shifters remember that all internal gear hubs require to fully ease pressure on the pedals when operating the shifters. Geared hubs allow users to change gears if the bicycle is stationary, just ease the pedals slightly backwards and the gear will be selected for when you start off pedaling again.

Sturmey Archer 3 spd. vs. SRAM 3 spd. hubs

Both gear hubs surprisingly look and performance the same.  Let’s see a SRAM unit:

Old fashioned IGH shells always bring to my mind the image of sweet corn cans, don't they?. :mrgreen:

Old fashioned IGH shells always bring to my mind the image of sweet corn cans, don’t they? :mrgreen:

As far as the cable attachment and cable tension are concerned these two hubs have similarities and can receive the same shifter. A new trigger installation will be a straightforward task in both cases. The differences start when the gear cable leaves the specific Brompton cable pulley assembly (CPULA):

Forom the point of view of the user, the pinch bolt and chain rods are the only difference

From the user’s point of view, the pinch bolt and chain rods are the only differences

Sturmey Archer system have a rod that goes screwed in to a barrel (B) with a lockening nut (N) that indicates the final point where rods are connected establishing cable tension. In Sram hubs the threaded rod shown below engages easily by pressing the tab (C) of the plastic adjustor A. SRAM has a more solid system (I’ve seen some snapped Sturmey Archer anchor bolts) but it is missing the tension reference provided by the nut.

The down chain must be completely screwed in before setting connecting the rod and pinching the gear cable to the plastic adjustor

Note that the gear indicator chain must be completely screwed in to the hub before connecting the rod and pinching the gear cable to the plastic adjustor A

Shifter installation

The manual for the Brompton Y trigger can be downloaded here.

I’m not going to explain the entire process. In that case follow the instructions. I want to focus and highlight those features that make Brompton parts universe so particular.

The first surprise (and thankfully the only one) was something as common like a gear cable. I knew 80% of Brompton parts are manufactured solely for its design, but I was not expecting a cable to be a problem. I should have inspected the Torpedo carrier first, the narrow groove hints that the head of the cable is smaller.

Hooked carrier conceals a very small cable end

The double hook conceals a very small cable end

My last hope was looking at the Brompton trigger, but a regular cable did not suit as well.

I stripped the whole trigger unit to show that the goes does not go fully home

I stripped the whole trigger unit to show that the cable does not go fully home

The solution was to grind away the excess of cable end so as to ensure hole fitting:

File the tip squarely or if you prefer finish the cable with just two flat sections.

File the tip squarely or if you prefer finish the cable with just two flat sections.

The original cable for these shifters look like this:

From left to right: conventional gear cable (Jagwire), Campagnolo and small headed Brompton shifter cable

From top to bottom: conventional stainless steel gear cable (Jagwire), Campagnolo and small headed Brompton cable (it’s red!)

You don´t need to disassemble the trigger to proceed with a cable or shifter change. If so it will give you an idea that 10-15 pounds items cannot be complex.

The parts are made of plastic. The splined clamp will allow any angle positioning

Inner parts are made of plastic. The splined clamp will allow any angle positioning

To insert the cable select middle gear and slightly push back the lever as I do with my fingers to make visible the hole.


Remember that you do not need to remove the top cap of the shifter to pass the cable. And do it with the trigger installed on the bars if you wish.

Once the end of the cable seats in the resting position go back to top gear, where the cable is not pulled.

Trim the housing, introduce the inner cable inside and gently remove the slack from the rear frame pulley assembly.

Unfortunalety ferrules are also specific and none were used. I hope bare cables don´t slide inside the shifter.

Unfortunalety ferrules are also specific and none were used. I hope bare cables don´t slide inside the shifter.

Then attach the cable to the adjustor A in SRAM hubs or anchor bolt in SA mechanisms and cut the cable. Fit a cable crimp to prevent fraying.

To close the system connect the down chain until cable slack is almost removed.


Feed the grooved end B of the gear indicator chain into the adjustor A until it is just not loose. Observe you are not pulling the indicator chain out of the axle at all.

Don´t go forcing too far when fitting the chain inside the plastic device. The secret in SRAM hubs is to take up the slack of the cable in top gear by pulling it softly leaving 5mm side-to-side movement at D-D (see black and white cable attachment diagrams). In Sturmey Archer hubs the axle nut has a hole to verify gear alignment. In middle trigger position, the chain end should be leveled with the axle. Adjustment is carried out by turning the barrel B to obtain correct setting. Relock the nut N to remember cable fitting. Next time, when you have to take off and reinstall the rear wheel, no tweaks need to be done in the cable tension.

In my bike the cable is just slack in top gear with the Brompton Y trigger. Otherwise the shifter pawl would find the cable taut and difficult to step back along the stepped trigger cage.

Before, when the Torpedo lever was installed, I adverted a tighter cable in third gear.

RIP :)


It is rewarding when every trigger click corresponds the hub gears. Job done.

Desmontar una rueda

Normalmente, los ciclistas piensan que radiar una rueda o simplemente llevar a cabo las tareas de mantenimiento básicas es cosa de expertos. Los bikers, especialmente, solemos arreglarnos nuestras monturas, pero la labor de bricolaje acaba para la gran mayoría cuando tienen problemas en este apartado. No es tan difícil, sólo hace falta ganas, unas pocas herramientas y tiempo para aprender.

No pretendo hacer una guía sesuda con todos los pormenores pero al menos los interesados os haréis una idea del misterioso mundo del montaje de ruedas.

A continuación tenéis los pasos para desmontar una rueda. Para otra vez dejamos el radiado, que lógicamente es lo complejo. Abstenerse usuarios de Mavic feas de serie, ruedas radiadas pareadas y aquellas en la que la cabecilla va unida al buje.


  • Llave de radios tradicional.

  • Destornillador de cabeza plana. Los profesionales usan uno eléctrico para ahorrar tiempo.

  • * El centrador es opcional ya que puedes desmontar la rueda por separado.


  • Primeramente con la llave de radios aflojamos en sentido antihorario/levógiro las cabecillas. No aflojaremos las cabecillas del todo, daremos varias vueltas a la rueda para ir aflojándolas poco a poco. Después de las primeras pasadas podemos hacer uso del destornillador para ahorrar tiempo. Cuando hayamos sacado las primeras cabecillas y el resto estén muy flojas los radios empezarán a ceder y tendremos la rueda tal que así:

  • Cuando empiecen a salir los primeros radios de los orificios intentaremos por contra, que no salgan de las alas del buje para que no se caiga ninguno y se mezclen los de los distintos lados del buje. ¡Menuda catástrofe sería! Debéis saber que las ruedas para disco de MTB y todas las ruedas traseras con núcleo para piñones no son simétricas a ambos lados ya que para dejar espacio a estos chismes (el cuerpo del buje y la araña del disco) los bujes se construyen asimétricos y por tanto los radios a ambos lados de la rueda son de diferente longitud, siendo más cortos los que están en esas posiciones. Los anglosajones usan drive-side/disc-side para referirse a los radios en estos lados.
  • Cuando el buje y sus radios se separen por completo del aro ve guardando por separado ambos tipos de radios. Clasificarlos después de haberse mezclado es una pesadilla, ya que puede que difieran en un sólo milímetro, que es la longitud con la que se fabrican los radios. Los radios se miden desde los codos hasta el final.

  • Ya sólo queda limpiar y recoger el material. En mi caso 16 radios DT sin conificar y de espesor 2.0mm en longitudes de 260mm (etiquetados como disc-side) y otros tantos en 262mm, 32 cabecillas de latón, un buje XT para sistema internacional y un aro Mavic 717XC muy ligero para frenos de llanta.

Próximamente radiamos una rueda, esperemos que con un buje Hope Pro II :mrgreen:

Fallos Sram XX

Hace unos días estuve pensando en el nuevo grupo de Sram con el que esta firma americana debuta en montaña (como grupo completo).

Aquí algunos errores que le veo a modo de telegrama.

– El casete cuesta más de 300€ :mrgreen: P.V.P.
Las cadenas de 10v ya sabemos cómo son. La anchura del eslabón se ha vuelto a reducir para dar cabida a una marcha más en el mismo espacio. La incógnita es ver cómo se comportan en barro. En CX parece que funcionan sin dramas.
El inédito tiro de 1,3 es una jodienda. Los interesados en montar sólo el cambio con los antiguos mandos X.0 de 9v no podrán.
No existe versión gripshift de momento.
Desajustes más frecuentes que en un cambio de 9v. La calidad de las fundas y el mantenimiento se vuelven claves.
Una sola versión de caja para el cambio. Entre la actual mediana y larga de los cambios Sram X.0.
Sólo dos versiones de cassette, 11-32 y 11-36.
No cubre la misma gama de desarrollos que un grupo de 3×9 aunque nos intenten vender lo contrario. Es un grupo para XC, aunque los fabricantes se hayan interesado en montarlo en bicis tope de gama de enduro obligando a sacar más versiones de bielas con más factor Q, lo que a su vez repercute en el precio.
Nuevos BCD de 120mm y 80mm para los platos. Se podía haber seguido usando el de 104mm, al menos, para el grande. Ahora sólo vas a poder escoger el 39, 42 ó 45 que ofrecen, eso sí, a precio de oro.
– La unificación de la tornillería a T25 me deja indiferente, pero en los platos tal vea sea innecesaria.
– Por si fueran pocos los sistemas de pedalier que han aflorado estos años, te sacan otro de la manga “a presión” (GXP PressFit). El Pressfit no es más que una versión barata y una solución chapucera que no ofrece mejores ventajas que las cazoletas roscadas ya que sus tolerancias son peores que el sistema BB30.
El desviador pesa 120 gramos. Parece el ancla del Titanic. Nos venden la moto de que es 40 gramos más ligero que un XTR pero no dicen que antes los XTR añejos pesaban menos de 130 gramos y tenían muelle, recorrido y caja para 3 platos. Te puedes montar un Sram Red con abrazadera y cambio de tiro por poco más y mucho más ligero.
Los frenos tienen una pinza minúscula, como la maneta.
No es grupo completo al 100% ya que le faltan pedales y bujes como hace Shimano.

En resumen, más basura consumista en el monte. Sólo para bolsillos que tengan el dinero por castigo.