Front fork braze-on bolts

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fastpedaller
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Joined: 10 Jul 2014, 1:12pm
Location: Norfolk

Re: Front fork braze-on bolts

Postby fastpedaller » 28 Jun 2020, 6:38pm

Brucey wrote:
fastpedaller wrote:Hmm - that's an interesting concept, what can be used as a 'stopping material'?


simplest and easiest is 'TippEx' or similar. Most braze alloys won't wet onto it, regardless of the flux used.

cheers

Well that's weird - I wouldn't have thought of that, and surprised it can take the heat without disappearing.
Reminds me of an incident many years ago...... had painted some steel with simple red oxide spray paint, and subsequently needed to heat the steel up to red hot. The paint survived fully intact. One day I ought to try this with with 'high temp exhaust paint' to see if it lives up to the marketing hype!

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horizon
Posts: 10173
Joined: 9 Jan 2007, 11:24am
Location: Cornwall

Re: Front fork braze-on bolts

Postby horizon » 2 Jul 2020, 9:59am

531colin wrote:
oneten wrote:….. Now here's my question. Is the hole on each side of the fork blade tapped with a right hand thread (requiring a short standard bolt to wind in from each side) or is it threaded to receive one long bolt all the way through and out the other side?...….

horizon wrote:
oneten wrote: Perhaps I am missing something obvious here ?

Possibly in that since the inner arm of the rack must be held in place, there has to be a screw thread on each side. AIUI, they are both right hand threads so I suppose that that is your answer - one long screw won't do it.


Here is a little experiment. Find a nut and bolt. Remove the nut and turn it over; will it screw onto the bolt?


What threw me :oops: was discounting using a nut (strange, given that that is exactly what I've done on my rear rack) but then trying to visualise two opposing threads (which of course are or can be actually part of the same thread). :oops: And no, I don't work in Halfords.

The good news is that on a Spa Tourer the threads are indeed in line and in phase (but then you knew that perhaps? :wink:).

Any views on whether a long bolt is better or worse than two short bolts?
When the pestilence strikes from the East, go far and breathe the cold air deeply. Ignore the sage, stay not indoors. Ho Ri Zon 12th Century Chinese philosopher

Brucey
Posts: 39500
Joined: 4 Jan 2012, 6:25pm

Re: Front fork braze-on bolts

Postby Brucey » 2 Jul 2020, 4:19pm

fastpedaller wrote:
Brucey wrote:
fastpedaller wrote:Hmm - that's an interesting concept, what can be used as a 'stopping material'?


simplest and easiest is 'TippEx' or similar. Most braze alloys won't wet onto it, regardless of the flux used.

cheers

Well that's weird - I wouldn't have thought of that, and surprised it can take the heat without disappearing.
Reminds me of an incident many years ago...... had painted some steel with simple red oxide spray paint, and subsequently needed to heat the steel up to red hot. The paint survived fully intact. One day I ought to try this with with 'high temp exhaust paint' to see if it lives up to the marketing hype!


IIRC tipp-ex is white because of its Ti Oxide content. Ti Oxide is pretty inert/unwettable and there is precious little binder in the mix (which burns/volatalises); the result is that tipp-ex makes a pretty good stop-off material.

cheers
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~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~

Jdsk
Posts: 884
Joined: 5 Mar 2019, 5:42pm

Re: Front fork braze-on bolts

Postby Jdsk » 2 Jul 2020, 6:19pm

Thanks, I was wondering why it worked.

Composition:
http://www.staples.co.uk/Content/Static/pdf/2017/10/297781020.pdf

Jonathan

Brucey
Posts: 39500
Joined: 4 Jan 2012, 6:25pm

Re: Front fork braze-on bolts

Postby Brucey » 2 Jul 2020, 7:21pm

thanks for posting the link to the data sheet. Reading down the list

Ti Dioxide -that's the white stuff which is inert at high temperatures and doesn't wet easily with braze metal
Napthas- solvents that evaporate (they used to use Trich for this)
Acetate- binder to hold it all together, less than 1%
Carbon Black- Dunno what that is doing there! A thought; maybe the product is otherwise 'too white' and a bad match for most paper (which has tiny black flecks in it when examined under a microscope)…?

cheers
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531colin
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Joined: 4 Dec 2009, 6:56pm
Location: North Yorkshire

Re: Front fork braze-on bolts

Postby 531colin » 3 Jul 2020, 12:47pm

horizon wrote:….The good news is that on a Spa Tourer the threads are indeed in line and in phase (but then you knew that perhaps? :wink:).

Any views on whether a long bolt is better or worse than two short bolts?

No, I didn't know that!
For the fitting, I would go with Brucey's recommendation here.....basically a long stud all the way through fixed with threadlock so the (nylock) nuts each side work independently, but with the best possible support/fixing for the stud.
Brucey wrote:FWIW I have fitted mid-blade low-rider braze-ons in exactly the way Colin describes, i.e. 'in phase' with one another (no central spacer tube) using a length of M5 studding (coated in a suitable stop-off material) to fixture them during brazing.

A similar result can be achieved by brazing one threaded and one unthreaded fitting into the fork; after brazing an M5 tap is run through the threaded fitting and provided the tap is long enough to engage with both sides at once, the new thread in the previously untapped fitting must be in phase too.

A long bolt or studding can be used to secure the rack. A low-strength threadlock can be used to hold the studding in position, making the use of nylocks easier on the racks.

cheers