Hand built bespoke bicycle frames in the heart of the Wiltshire countryside - dmoframeworks@gmail.com.
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Saturday, 15 February 2014

A bit of a random one...Formula RX caliper rebuild...

Making bikes is ace, but riding them is even better. I realised last weekend that I had certainly let my maintenance slip on the element when I found a seized piston in the rear brake calliper and couldn't go for a ride.

As such I decided to give them a good strip down, release the seized piston and replace all the seals.

The only issue here was that I really struggled to find any literature on removing the pistons and replacing the seals on the formula RX brake callipers - so where better to put my rebuild procedure (to hopefully help out someone else trying to do the same bit of maintenance) than on my blog!

To start with I removed the callipers from my bike to wash all the crud off them - if there is one thing I've learnt about hydraulics its that cleanliness is of paramount importance.

This turned out to be fail number 1!! In hindsight I think removing the pistons would have been easier using the hydraulic force from the brakes themselves while on the bike but hey ho.

On inspection of the callipers the first thing that struck me was the large anodised red cap on the left hand side - see pic below.

I figured that you must have to remove this to service the callipers. Here began my search for the tool to remove the aluminium blanking plug. Unfortunately I couldn't find one, so in true DMO style - I just made one.

4 Pin plug extraction tool
As it turns out, and having done some more reading, you don't actually have to remove this plug to service the callipers - the hole which the plug blanks is simply there to enable the caliper to be machined - cashback!

Anywho, seeing as I had made the tool I thought I might as well use it, and as it goes it worked a treat.

Tool in position ready to remove blanking plug

Blanking plug removed - job done!
My top tip here is that, in order to undo the blanking plug, you obviously need to hold the calliper firmly. To do this I simply bolted it back onto the bike. The caps were both tight but they did undo (right hand thread) without any excessive force.

So next up was to remove the pistons - this is when I realised that the easiest way to remove the pistons is to remove the one on the opposite side of the calliper to the blanking plug first!! So back in went the blanking plug.

To remove the right hand piston simply tie a tie-wrap around the left hand piston (this stops this one coming out first) and then remove the small bleed grub screw. You need to make sure that you now blank off the "pressure in" hole on the left hand side of the calliper (where the brake hose connects to) before applying some pressure to the bleed hole.

The way I did this was to just use one of the formula bleeding syringes. The piston will just pop out. If it doesn't pop out then you will require more pressure, a compressor or even a track pump may be required depending on how corroded the pistons are in the seals. It turns out that the hose off the formula bleeding syringe is a perfect fit on my air gun - see below:

If compressed air doesn't work then the track pump should do it. In order to hook my track pump upto the formula bleed hose I found one of the removable valve inserts from an inner tube was a perfect adapter. Even with the full pressure my track pump could provide it took a fair bit of back and forth and GT85 to get the stuck piston out - but out it did come!

Next snip the tie-wrap on the left hand piston and remove the blanking plug (for the second time in my case). I then just used a 5/8's socket and my vice to press out the left hand piston, see below:

Once the pistons have been removed you can simply pick out the two piston seals and the o-ring (I used a scalpel to do this).

Next up is to thoroughly clean the calliper. I just used regular brake cleaner (Halfords, about a fiver). Once de-greased and clean I would highly recommend blowing out each small oil hole with compressed air. I was very surprised at the amount of crud that came out when I did this.

Now all the old bits have been removed and everything is clean you need to put in the right hand piston seal. Before inserting this in the calliper grease it all over with a silicon grease. 

Once the right hand piston seal is seated in its groove you need to insert the right hand piston - I used the 5/8's socket again and just pressed it into place.

Now you can grease and insert the left hand piston seal and the blanking cap o-ring.

Before inserting the left hand piston I replaced the blanking plug (just putting a touch of 243 thread lock on the thread beforehand).

To insert the left hand piston I did this by hand from the inside of the calliper body (where the brake disc runs). To seat the piston in the housing I just just used the handle of my scalpel (blade removed).

And thats about it, all that remained was to put the calipers back on the bike and bleed.

So, not much frame building here, but at least I can go out and blow off some steam on my bike!

Saturday, 8 February 2014

Internal Cable Routings - Technique Sorted!!!

One of the many things on the list for today was to finish Taylor's internal cable routing's. I had already formed the internal tubes (using my new "mini" bender) so all I needed to do was to braze them in place, fettle them back and then braze on the strengthening surrounds.

I learnt quite a bit about brazing internal routings whilst on my honeymoon a couple of weeks ago - the major lesson being to use silver solder to fit them in place and not regular brass brazing rod like I had in the past.

The reason for using silver is that its melting point is considerably low compared to brass (630-660 deg C compared to 870-809 for Sif 101 brass).

Perhaps unsurprisingly in hindsight, when I did the internal routings on my first frame I had a complete nightmare - the brass internal tube kept melting away! The reason for this is that I was using brass filler rod which melted at the same temperature as the brass internal guide tubing - fail!!

Using silver filler rod was like cheating - it made what had previously been quite a daunting process into one which I now can;t wait to do on a future frame!!

So, to summarise, I used Sif solder number 43 and the Cycle Design Stainless Light Flux paste - don't forget this flux simply dissolves in hot water.

I will be leaving the internal routings on my next bike like this - super clean.

And here is the brazed on strengthening surround piece - nice!

The last lesson I learnt today was to make sure the oxygen valve is open on your oxygen tank before you start to braze - I had just enough oxygen in the lines to get going and then this happened - messy!!

On the cards for tomorrow is finishing off the brazing of Taylors front triangle and then I need to get on and shape the seat and chainstays for both bikes.

Sunday, 2 February 2014

Bespoked frames taking shape....

I will be bringing 3 bikes with me to the Bespoked show in April. I am building two new frames, one is going to be very similar to the original Element and one is going to be a 29er+.

These new frames will be accompanied by the now rather bedraggled looking original Element frame - which by now has done over 1000 off-road miles.

A 29er+ is a "FAT" 29er which is able to fit 3.0" tires. The main design challenges with any 29er frame is fitting everything into the rear triangle, a 29er+ just exacerbates this issue whilst tyring to keep the wheelbase sensible.

The image below shows a 29er+ tire on a carbon Niner fork - there is just about an 1/8th of an inch clearance - definitely time for some helitape here!

In order to minimise the wheelbase you need to tuck the rear wheel in as close as possible to the seat-tube. However you also need to have sufficient clearance to the front sprocket. To help with this I have designed a custom steel chainstay yoke - see below:

Custom yoke, waterjet cut by Blade Engineering in Chippenham
Here's hoping the finished frame looks something like this!             

 The version of the Element 3 I'll be taking to the show will be TiG welded, however the new Element frame I'm building will be fillet brazed - here is the BB shell to seat-tube braze.

Here is the Element Number 2 frame - the first for a real customer!!
 So that's where we are up to at the moment, there has been some significant brazing learning over the last couple of weeks but I'll up-date you on this in the next post.

Until then, thanks for reading!!

Benders big and small.....and new website is launched!!

Its been a while since I have posted on the blog - what with Christmas, Honeymoon and spending a lot of time finishing the designs for the bikes I'm going to be taking to the Bespoked show in April - its been a hectic couple of months!!

I have also been working on my new website, this is all up and running now (big thanks to Neil Warwick consulting - http://nwarwick.co.uk/wp/index.php/web-design/), please check out:

Moving on from the Element mk1 my main aim was to make it easier to build accurate frames in the future - the way in which I was hoping to achieve this was by making a new jig and some custom tube forming tooling.

Here we have my new internal cable routing's tube bender. I machined this from aluminium and it is designed to bend the standard 7mm brass tubes used for guiding internal cable routing's.

The 7mm tube bender in all its glory - we like to call it "mini bender"
Simply slide the straight tube through the support hole
Align the end of the tube to the end of the support hole
And hey presto, perfectly bent tubing with no crimping or squashing - ace!

I found that it was still necessary to heat the brass tube prior to bending, this made it much more malleable and less likely to collapse or crimp during bending.

Next up is my new seat and chain stay bending tooling. This was a little more difficult to machine due mainly to its size and the very large radii I wanted in the tooling.

My intention was to machine a deep circumferential 16.0mm groove into a block of aluminium, into which you would align your tube and then simply pull it around the groove to the desired position. The reason for such a deep grove is to support the tube during bending, hopefully stopping it from collapsing or crimping.

Here you can see the large tooling block and the removable 'capture pin'
Simply insert the capture pin, and slide in the tube to be bent.
Then give it some beans and bend your tube around to the desired position.
And there you go - job done!!

I was really pleased with how well this worked, the bend was nice and smooth with no squashing and most importantly no ripples.

So here's hoping this works as well on the 4130 tubing I will be using for the seat and chain stays on the next two frames.

In the next post I'll be bringing you guys up to speed with the developments I have made on the bikes for the Bespoked show in April.