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PostPosted: Wed Sep 30, 2009 3:19 pm 
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nice. i think also you should try and bend some of the flange over the dropout where the seat stay ends for maximum contact. i think it will be hard to profile it just right. hope you have lots of files to hand!


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PostPosted: Wed Sep 30, 2009 3:47 pm 
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Yep plenty of files here! I was thinking of just cutting off the flange flush to the 'face' (outside) of the mount. That would leave quite a narrow contact with the frame so probably would need welding rather than brazing which would be stronger. With welding its good to have a v-channel for the weld anyway and there would be that on the inside of the mount due to the round profile where its been folded over to form the flange (see front end view). I think it will be plenty strong enough with a fairly thick weld, something like the same thickness as the other frame welds. The back end of the mount is about 12mm from the end of the seatsay where it meets the dropout.

I could leave a little bit of the flange there when I trim it down so it sticks out from the face about 3mm giving slightly more contact area. Any more than 3mm would make it look odd because of the mounting holes. I think I'll try that first. 'You can always take material off but you cant put it back!' (quoting my old college lecturer) :lol:

Ive got some 6mm ally plate so I'm going to make a universal jig that can be used on other frames. Just need to order some 10 & 5mm threaded bar and a few bolts and washers.


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PostPosted: Wed Sep 30, 2009 3:53 pm 
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sounds good. also be careful it doesnt warp sideways if your welding it. that could be problematic. just make sure you clamp it tight


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PostPosted: Wed Sep 30, 2009 4:02 pm 
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just found this. its sort of relevant :lol:

Image

i found it at
http://images.google.co.uk/imgres?imgur ... N%26um%3D1

somebody has modded a lobo to take discs with a weird arm!


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PostPosted: Wed Sep 30, 2009 7:02 pm 
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A little update...

I remembered I had an old style 143mm Hope wavy rotor so I put that on the wheel and mounted the caliper. I used some electrical tape to tie the brake lever to the bar so the caliper would naturally stay in place. I then tweaked the position of the caliper to match the IS standard for the location of the bolt holes. (oddly the inside face of the dropout isnt in line with the mounting face on the caliper. Per the IS these two areas shouldbe in line. I checked the caliper and the pads are nicely centralised. Perhaps the Hope caliper is designed to run quite thick wahsers on the mount? I don't know.)

Having positioned the caliper I then set about modding the A2Z mount. Its a very tricky process and involved taking small amounts of material off at a time and constancy checking the fit every 5 mins or so. I had to file the area in 3 stages, each with a slightly shallower angle to match the taper of the satstay (the angle of the seatstay necessitates this). A really worrying process that involved several cig brakes to calm the nerves! :lol: Once I got into it I developed a technique for getting a good shape to the contact area. Its not perfect but its pretty good I think for a hand tool job.

A member over on the MTBR frame building forum is sending me some scraps of tubing for the brace. Having said that some on the frame building forum have told me its no really needed. Part of me wants to leave it to save weight but the other part of wants to hae it there for peace of mind. I'll probably have the brace but I'll make it as small as possible. Still not 100% decided though.

Image

Next up is to make a jig to hold the mount in place for welding. Then I'll buy a big packet of biscuits and find a friendly local welder! :lol:


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PostPosted: Thu Oct 01, 2009 10:43 am 
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[quote="mikesnowdon"](oddly the inside face of the dropout isnt in line with the mounting face on the caliper. Per the IS these two areas shouldbe in line. I checked the caliper and the pads are nicely centralised. Perhaps the Hope caliper is designed to run quite thick wahsers on the mount? I don't know.)[quote]

i think im right in saying not many of my mounts totally match :? im might be wrong though


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PostPosted: Thu Oct 01, 2009 2:42 pm 
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Im assuming hope design their caliper to allow a few washers on the inside face of the mount for tweaking the caliper alignment. The offset is about 3mm here.


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PostPosted: Thu Oct 01, 2009 7:13 pm 
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Been working on the brace and Ive got a couple of options to choose from so far:

Option 1: (unfortunately I broke this one but it can be joined back together with the brazing)
Image

Option 2:
Image

Option 3:
Image

I like the first one as it doesn't have the bolt hole. It looks better, but they all look quite good I think so its a case of judging which will be most effective at strengthening the area. One option spreads the load to the dropout and chainstay, the other would seen to spread the load to one area about an inch from the dropout. From what I remember from school the forces are greater at the narrowest part so maybe the first 2 options are the strongest? I don't know. Aesthetically I prefer option 3.

Hoping for some feedback here to help me decide, even if its just to say which you like the look of best.

Cheers in advance.

- Mike :)

PS: Prizes for guessing what the brace is made from :D


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PostPosted: Thu Oct 01, 2009 9:58 pm 
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I did a bit more work on the mount today and I've got it really good now I think. any gaps are under 0.5mm now :) I've trimmed off the last remaining bit of the mounting flange and faced* the mount front and back. (*lots of hard rubbing with a piece of sandpaper placed flat on the bench top)

Ive decided on the brace too.....

Image

Where the brace meets the chainstay I'll have the braze built up quite thick so as to fill the small hole and build up the front edge. I'll then file it down to shape it in niceley.

Like this:

Image

Now Im all ready for the brazing! :)


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PostPosted: Fri Oct 02, 2009 1:52 pm 
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i think you need to go for option one or two. not 3. as you say the force is most at the narrowest point. the braces in one and two would dissipate the force into two forces that arent as strong as the original and they would also spread the forces out from the single point at the seatstay into two points at the chainstay


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