Front fork braze-on bolts

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oneten
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Front fork braze-on bolts

Postby oneten » 27 Jun 2020, 7:09pm

Hi, just a quick question about front fork braze-ons. I assume that the 5mm hex bolts should be in place when no front rack is fitted, to prevent water finding its way inside the forks. But I've noticed that the hole seems to go right through the fork. 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 ?
I don't want to risk leaving the inner hole open nor risk chipping the paintwork around the hole in experimenting. Perhaps I am missing something obvious here ? Thanks to anyone who can put me right on this. :?

tenbikes
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Joined: 11 Jan 2009, 6:41pm

Re: Front fork braze-on bolts

Postby tenbikes » 27 Jun 2020, 10:08pm

On my forks a short stainless steel bolt from both sides work but of course yours may be different........

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horizon
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Re: Front fork braze-on bolts

Postby horizon » 27 Jun 2020, 11:49pm

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.
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

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gaz
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Re: Front fork braze-on bolts

Postby gaz » 27 Jun 2020, 11:57pm

oneten wrote:... I've noticed that the hole seems to go right through the fork. ...

It may be a simple sleeve through the fork, as used to be supplied with Blackburn CL-1 low-rider for brazing-on (brazing-in?).

I've had those on a couple of forks, happily left them empty when not using a low-rider.
2020 : To redundancy ... and beyond!

AndyA
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Re: Front fork braze-on bolts

Postby AndyA » 28 Jun 2020, 12:09am

Fork rack mounts are either two water bottle bosses or one long boss that goes through a hole on either side. British frames are usually the former, Surlys and other Taiwanese frames the latter

AndyA
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Re: Front fork braze-on bolts

Postby AndyA » 28 Jun 2020, 12:10am

Either way, fill that hole with a screw to prevent it filling up with water and corrosion

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Redvee
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Re: Front fork braze-on bolts

Postby Redvee » 28 Jun 2020, 12:41am

I use disc rotor bolts and a dab of copper grease to fill all the unused braze ons on my Tripster AT frame.

gregoryoftours
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Re: Front fork braze-on bolts

Postby gregoryoftours » 28 Jun 2020, 12:52am

Yep it can vary, my Surley fork has a continuous right hand thread from outside to inside. I bought some plastic Phillips M5 bolts to fill unused mount points, although it's also a good place to store spare steel bolts and washers.

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531colin
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Re: Front fork braze-on bolts

Postby 531colin » 28 Jun 2020, 8:52am

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?

oneten
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Re: Front fork braze-on bolts

Postby oneten » 28 Jun 2020, 1:43pm

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?


Thanks for the answers and suggestions. In 531colin's reply, it's definitely a case of less is more and I was indeed missing the bloomin' obvious!

Even though I could bolt right through with a long 'un, I'm going to use two little stubby 5mm bolts per fork blade so they don't bottom out. And, if fitting something such as a rack in future, I imagine it would be better anyway to fix either side of the fork blade with separate bolts rather than risk crushing the hollow steel blade by possibly overtightening a longer through bolt.

Thanks also 531colin for the useful bike fitting document - downloaded and saved for reference.
Now, at least half-a-dozen volunteers needed to turn the bike while I hold the Allen key....any offers?

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531colin
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Re: Front fork braze-on bolts

Postby 531colin » 28 Jun 2020, 3:38pm

oneten wrote:
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: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?


Thanks for the answers and suggestions. In 531colin's reply, it's definitely a case of less is more and I was indeed missing the bloomin' obvious!

Even though I could bolt right through with a long 'un, I'm going to use two little stubby 5mm bolts per fork blade so they don't bottom out. And, if fitting something such as a rack in future, I imagine it would be better anyway to fix either side of the fork blade with separate bolts rather than risk crushing the hollow steel blade by possibly overtightening a longer through bolt.

Thanks also 531colin for the useful bike fitting document - downloaded and saved for reference.
Now, at least half-a-dozen volunteers needed to turn the bike while I hold the Allen key....any offers?

One long bolt will go through 2 separate fittings either side of the tube, provided that the holes are accurately in line, and the thread is "in phase"....unless somebody knows an accepted term, "in phase" will have to do; general screwthreads have only one "start" and it will have to line up on the bolt and the (second) fitting.
At the risk of being super-pedantic, you can't crush the tube if the bolt is threaded into both sides.

Brucey
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Re: Front fork braze-on bolts

Postby Brucey » 28 Jun 2020, 4:21pm

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
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fastpedaller
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Re: Front fork braze-on bolts

Postby fastpedaller » 28 Jun 2020, 4:51pm

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.


cheers


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

Brucey
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Re: Front fork braze-on bolts

Postby Brucey » 28 Jun 2020, 5:02pm

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
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531colin
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Re: Front fork braze-on bolts

Postby 531colin » 28 Jun 2020, 5:05pm

Brucey wrote:….. using a length of M5 studding (coated in a suitable stop-off material) to fixture them during brazing....

Damn! does that mean that when I'm using a bolt to jig up something I'm brazing, I can coat the bolt so it doesn't get brazed up?
….wish I'd known that a couple of weeks ago!
Cross-posted! Tipp-ex it is then!