Broken Brompton hinge

[lkingscott]

I've finally got the repair bored to take the new hinge pin tube. I didn't quite open it out on the line I had intended, so I rebored 6.5mm with the correct alignment. In the pictures below, the gap at the hinge end looks slightly bigger than it should because of the oversize bore. I still need to bore the ends to 8mm, to take the bushes and I can adjust the also alignment then.

You will also notice that the hinge pivot joint gaps are big. These will be filled with the brims of the top hat bushes. As the mating faces on the unrepaired front part are rather rough, if there is still space, I may add some shim washers.

The cylindrical head bolts are temporary. I have some flat head bolts and also some countersink bolts. The countersink bolts would make the most sense and look nicer, but I'll try the flat head bolts with lock washers to start with, as no change to the original front part is required.

Anyway, it's looking good. It will soon be ready for powder coating.

[lkingscott]

Well it doesn't look like I have done much, but I've broken 4 drill bits since my last post, drilling the hole out!

I realised the alignment wasn't as good as it could have been (sometimes I can be a perfectionist), so as I needed to open the ends up to fit the bushes, I was drilling / reaming in effect off centre / with a different alignment.

Well I've fixed the alignment at one end perfectly and the other end is now correct in one plane, but it's slightly high above the plane of the closed hinge line, producing a gap. I pondered adding a blob of braze at the clamp end, but as there an inclusion in the hole, giving a weak point, I have decided to try and get it right as the inclusion is exactly where I need to add material to move the hole over a bit. My plan is to use braze. I tried with a blow torch, but it doesn't get hot enough. I will use the TIG to heat the outside of the hinge and hopefully I can melt some braze inside the hole from the heat

I forgot to photo it while assembled, but the bushes have taken up all the endfloat and it's rock solid. The bolt with flange in the pictures is not great. It's a Torx type, but the size isn't very accurate. I'm tending towards using the countersunk bolts and they will look neater.

Anyway, here's a couple of pics of the latest instalment! The bushes are great, I put a few extra loose ones on the board. The new hinge metal looks a bit dirty due to the flux I used when I tried to braze with the blow torch.

[lkingscott]

Braze added. It looks like a mega retrograde step, but I needed to move that hole on one end.

It looks a bit grey. I think I overheated it a bit, so some of the steel melted, but when filed, it's definitely silicon bronze. I read somewhere that you shouldn't melt the steel when TIG brazing as it makes the joint more brittle, however copper iron alloys are often used for screws and wire to improve tensile strength of copper. In fact iron-copper alloys with 5 - 10% copper have the highest strength. Maybe the concern is that incorporating substrate weakens the substrate.

I tried using the TIG from outside to heat the metal and melt braze on the inside of the hole, but it wouldn't melt, even when bright red.

I put the TIG electrode into the hole and hopefully I've got the inclusion filled. If not I'll get some silver solder or similar.

[lkingscott]

The new blob is gone! Nice and shiny bronze now. 

It looks great after an initial grind and file, but my perfectionism might braze a couple of imperfections.

However... although I managed to move the hole down so that the hinge line fits nicely on the end, I managed to move it back as well, so the alignment is now skewed. Hey ho!

I also managed to break another drill bit...!!! Off to buy some grinding bits for my mini tool (cheapo Chinese Dremel style thing). I only realised today instead of drilling, grinding would be much more controllable. I.e. when I add material to the hole, the drill self aligns on the line of least resistance - hence the broken bits. Whereas the grinder will allow me to grind wherever needed.

[Tim Hall]

Three spare holes, just in case...

Seriously though, good work. Watching this with great interest.

[lkingscott]

Three spare holes, just in case...

Seriously though, good work. Watching this with great interest.

 

Many thanks!

The minitool (cheapo Dremel copy) has been brilliant. I have adjusted both ends really easily, but that meant the bushes were too loose, so I've put a bit more braze on. I'm just about to grind that down to see how it looks and works.

[lkingscott]

Strange, I just noticed that my last but one post appeared 3 times! Extras now removed.

[lkingscott]

Finally, everything lines up and the hinge is ready for coating!

However the rest of the frame needs a sand down before coating.

There's a few pinhole inclusions, but I can fill them before coating.

[rogerzilla]

Very neat!

[lkingscott]

Very neat!

 

Many thanks!

[lkingscott]

I started the powder coating today, with less success than I'd have liked.

I tried various liquid solutions, probably the best of which was acetone. However, although it seemed like the acetone had evaporated and I could heat the metal/paint, the remaining acetone would immediately boil.

A test piece of metal, which I simply painted with the acetone / powder mix, but didn't heat, actually ended up better.

So in the end I used the hot metal approach, using a heat gun to heat the metal. Unfortunately I didn't sprinkle the powder very evenly, so I ended up with something looking a bit wrinkly!

Anyway it's amazingly hard, so not a problem, just needs a bit more time to flat it all down with wet and dry.

Here's some pics, only just started flatting.

[lkingscott]

The powder coat is amazingly tough, needing a metal file to flat it down. After a bit of work, I offered the parts up and found I'd put way too much paint on the hinge pivot end mating surfaces.

After filing the parts fit perfectly.

The paint needs another coat, but I think I'll get a proper powder coat gun to do it as there's some other areas which also need work.

The bolt is still not final, but I came across some cylinder bolts which I think will be perfect, in place of the stainless tube which took so much effort to make! I was looking for inline skate wheels as they are supposed to be better than the mini wheels on the luggage rack, and the cylinder nuts for them look a perfect size, 6mm diameter. Furthermore they have a serrations to stop them moving, which is perfect.

Anyway, here are the pics!

[lkingscott]

I know this thread looks as though it's stopped, but stuff has been going on behind the scenes...!!!

I've invested in a proper powder coat gun, which took time... Should I buy one or build (3D print) one and what sort, tribo or high voltage, etc... I went for a tribo gun, which happens to be 3D printed. It saved a lot of time printing it myself, getting all the additional bits and finding it didn't work properly!

I'm also building a powder coating chamber / oven. I couldn't get the fibreglass panels locally, for a really simple oven, so I decided to make an aluminium box, with open front, which can also double as a powder coating cupboard, although I haven't added a fan so far. I bought a couple of damaged stock infrared patio heaters.

Everything takes longer than I expect!!!

[lkingscott]

I finally completed the 'oven'.

It's just an aluminium box, which I can use to powder coat and also to bake the coating with a couple of high power infrared lamps.

I think I went a bit OTT with the size, it's 1m x 6ocm x 50cm!!!

The Brompton should fit, just about!!!

[drossall]

You're going to have a whole alternative Brompton factory soon. This is a great thread!

[lkingscott]

You're going to have a whole alternative Brompton factory soon. This is a great thread!

 

[lkingscott]

As the powder coating box is done, I've got on to brazing a crack in the seat post tube.

I filed a V in the crack before brazing, but to reduce the likelihood of the crack reopening, I'll leave a the braze slightly raised.

[lkingscott]

Next job, remove the bottom bracket bearing, as the powder coat curing will not do any good to it, but also it's knackered anyway!

I hate the splined bearings. There is so little depth for the tool to mate and the socket tools have such an offset, that there is a high chance if it slipping, if the bearing cups are siezed.

And guess, what? They were rusted on solid. I had to check the direction I was turning them as there was no movement and Bromptons are notorious for being weird! All the YouTube videos stated the same, i.e. standard BSA, except one, which claimed BSA threads are the opposite of reality! In the end I took a magnifier to the tiny amount of exposed thread on the non drive side. Sure enough, it's standard BSA thread.

As it just wouldn't move without risk of the tool jumping out, I worked out a nice technigue in the end. I used a big G clamp between the tool on one side and the end of the crank shaft on the other. I could put as much force as I wanted on it and it took me jumping on the spanner on one side and the other, I had to use a 1m tube over the spanner.

I must admit that I completely wrecked the drive side by attempting to undo it with the vice. I didn't realise that it pressed the splines inwards, so the tool didn't fit and slipped anyway. I got the spline tool to fit using a big old vice instead of the G clamp.

I was so relieved that the G clamp method worked. I saw another nice technique for one of the flat tools from people like Park Tools, using a cup bolted onto the crank shaft, which pushes the tool against the splines. Something like an old blunt hole saw could do for that.

Once off, the old BB looks horrible. It's pretty obvious that the aluminium against steel has corroded the steel, presumably helped by salt water penetration in the Winter. Luckily I have a BB thread tool. I will clean everything up, but won't rethread until I've powder coated. I might used the old BB shells to stop powder ingress, but I need to be carefull they don't get too coated too, as the coating could chip off when I remove them.

I'll check with the owner, but Hollowtech bearings and crank would be a nice upgrade.

Now all I need to do is grind, sand or file off any more loose paint, flatten the rest, then clean it all down ready for powder coating at last!

[lkingscott]

Just realised, the old Brommie label needs to come off too.

I've seen a technique to use a laser router to cure powder coat patterns. I might try that, but I'll need to do a lot of testing first!

[rogerzilla]

Older ones have FAG bearings with plastic cups.  These are renowned for stripping their lobes as soon as you apply the (metal) removal tool.

[Kim]

I was so relieved that the G clamp method worked. I saw another nice technique for one of the flat tools from people like Park Tools, using a cup bolted onto the crank shaft, which pushes the tool against the splines. Something like an old blunt hole saw could do for that.

Nice idea with the clamp.  I once solved this on a recumbent using the bolt-the-tool-in-place method.  After much heaving and bashing it occurred to me to return the seat to the fully upright position, attach a spanner at my usual 'starting off' crank angle, then climb on the bike and simply pedal it off.  You can generate an awful lot of force with your leg muscles when you've got something to push your back against.

[Asterix, the former Gaul.]

Bromptons are notorious for being weird

I say, old chap, do you mind?  They are British, how can that be?

Seriously, your achievement is amazing!  I used to work in a ship repair workshop, on the admin side. It was fascinating to see the skills of the various departments - no repair they wouldn't have a go at (officially or unofficially). Swept away years ago.

[Tim Hall]

There's a recent thread somewhere where I asked questions about powder coating (getting powder coating done by a specialist rather than a Ninja powder coater who builds their own oven).  Anyway, someone there suggested masking threads off with the relevant cup/bolt/whatever then screwing said blanking part in slightly. to break the bond before removing, rather than unscrewing directly.

[drossall]

I hate the splined bearings. There is so little depth for the tool to mate and the socket tools have such an offset, that there is a high chance if it slipping, if the bearing cups are siezed.

I'm a big fan of Pedro's socket holder. Mine's the simpler, older version, but it works well.

[lkingscott]

There's a recent thread somewhere where I asked questions about powder coating (getting powder coating done by a specialist rather than a Ninja powder coater who builds their own oven).  Anyway, someone there suggested masking threads off with the relevant cup/bolt/whatever then screwing said blanking part in slightly. to break the bond before removing, rather than unscrewing directly.

Nice idea!

I thought about removing them while the frame is still hot, but finding somewhere to hold without screwing up the paint would be difficult.