# Fork building input - Bontrager Switchblade style



## AndrewTO (Mar 30, 2005)

I have two fork projects I wish to pursue. I want to make a fork very similar in style to the old Bontrager Switchblade rigid fork from the '90s, with the billet aluminum crown, and I also want to make a dual crown version (aesthetics - I just like how DC forks look).

I would appreciate on hearing from experienced fork makers on my build process .....

The crown would be machined on a wire EDM. All 3 holes would be 1 1/8" ID. I plan on using straight gauge aluminum tubing for the steerer tube and legs (might use titanium tubing later). I realize the crown race on conventional 1 1/8" steerer forks is larger than this and I plan on having an adaptor made to take up this gap. The dropouts will be machined on a mill and will be a bolt-on affair while I dial in my desired a2c and offset. (i'm actually making a few different crowns and drop outs for this)

*My biggest dilemma is what wall thickness to use. I could really use some input here, please.*

The fork is going on a 29er, piloted by a 170-ish pound tall scrawny bastard. Bike is a "do it all" unit, mostly on road, with some trail/single track riding. Disc brake.

I realize the tubing for the legs isn't going to be expensive, nor hard for me to obtain. Making the mistake of choosing tubing with too thin a wall, however, is a mistake that could cost me far more than time/money can replace (if you get my drift).

Any help is appreciated.

PATIA!


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## pvd (Jan 4, 2006)

Wire EDM. Are you kidding?

Also, I figure those forks just used steel pista blades. Nothing special.


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## AndrewTO (Mar 30, 2005)

pvd said:


> Wire EDM. Are you kidding?


No.

{QUOTE=pvd]Also, I figure those forks just used steel pista blades. Nothing special.[/QUOTE]

Still doesn't tell me anything, though. I don't plan on using steel. I would prefer to use straight gauge aluminum, to start with, to help keep the weight and cost down.


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## Walt (Jan 23, 2004)

*Most of us can't help you*

I have built hundreds of forks, but I would never use aluminum for one - it's a great material for a lot of things, but not for forks. That said, you've made your choice. Off the top of my head, you probably want about 2.5x the wall thickness of a standard steel fork blade of the same diameter. So 2.5x1.2mm would be about 3mm walls. That's if you're using 70-series. 60 series would probably need to be thicker, I imagine, but I don't know for sure.

BTW, this is not a lightweight design in general, nor a particularly good one. If you're after the look, that's great, but PVD's advice (just use steel blades) is good, IMO.

-Walt



AndrewTO said:


> No.
> 
> {QUOTE=pvd]Also, I figure those forks just used steel pista blades. Nothing special.


Still doesn't tell me anything, though. I don't plan on using steel. I would prefer to use straight gauge aluminum, to start with, to help keep the weight and cost down.[/QUOTE]


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## pvd (Jan 4, 2006)

AndrewTO said:


> I don't plan on using steel. I would prefer to use straight gauge aluminum, to start with, to help keep the weight and cost down.


Why did you refer to the switchblade then? That is a very specific type of fork that has only been done on a few occations. It uses an upper machined crown and lower pista type round tapered steel blades. It sounds like you are making something more traditional, something more like what we've seen hundreds of times in many ways, like what most are doing in carbon now.

https://www.whitebrotherscycling.com/rock.shtml


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## themanmonkey (Nov 1, 2005)

The blades on the Bontrager and Tange Switchblade folks were not standard track blades, maybe some of the early ones were. They were much thicker wall, and at least the Tange were custom drawn blades. A dual-crown version isn't going to work that well unless you want to fork to be really tall. Even the Bontrager and Tange fork blades would occasionally slip in the crown. So you'll need to add, not subtract, material to the crown to make it a dual-crown.


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## dr.welby (Jan 6, 2004)

For starters, just find an old Manitou crown. It takes a 28.6 tube for the leg. i suppose you could also look at the aluminum stantions to get some idea on their wall thickness.

I should probably make the obligatory note that if you don't have the engineering knowledge to determine the appropriate material and dimensions for your project, do you really want to be experimenting on a fork? And unless you're referring to yourself in the scrawny third person, do you really want to be testing with someone else's teeth?


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## AndrewTO (Mar 30, 2005)

pvd said:


> Why did you refer to the switchblade then? That is a very specific type of fork that has only been done on a few occations. It uses an upper machined crown and lower pista type round tapered steel blades. It sounds like you are making something more traditional, something more like what we've seen hundreds of times in many ways, like what most are doing in carbon now.


I referenced to the ORIGINAL '90s design, not the newest version. It's in the second sentence of my opening post.


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## AndrewTO (Mar 30, 2005)

Walt said:


> I have built hundreds of forks, but I would never use aluminum for one - it's a great material for a lot of things, but not for forks. That said, you've made your choice. Off the top of my head, you probably want about 2.5x the wall thickness of a standard steel fork blade of the same diameter. So 2.5x1.2mm would be about 3mm walls. That's if you're using 70-series. 60 series would probably need to be thicker, I imagine, but I don't know for sure.
> 
> BTW, this is not a lightweight design in general, nor a particularly good one. If you're after the look, that's great, but PVD's advice (just use steel blades) is good, IMO.
> 
> -Walt


Could you further explain why you feel aluminum isn't a good choice for forks please?

As you said, i've made my choice, but i'm still curious to know your reasoning. Thanks.


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## AndrewTO (Mar 30, 2005)

themanmonkey said:


> The blades on the Bontrager and Tange Switchblade folks were not standard track blades, maybe some of the early ones were. They were much thicker wall, and at least the Tange were custom drawn blades. A dual-crown version isn't going to work that well unless you want to fork to be really tall. Even the Bontrager and Tange fork blades would occasionally slip in the crown. So you'll need to add, not subtract, material to the crown to make it a dual-crown.


I've read about the slippage and i'm hoping that my decision to use a wire EDM to make these crowns will help with this, what tiny little bit it may be. The finish left on the surface is comparable to a bead/sand blast finish, as opposed to a smooth, machine bored finish. Again, what tiny bit of help it may be.

Not sure I understand the concern about the DC design needing to be taller. Do you mean each crown needs to be thicker? I'm inclined to believe that with two crowns one could afford to make each one thinner than if using a single crown (not necessarily half the thickness, but thinner nonetheless).


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## AndrewTO (Mar 30, 2005)

dr.welby said:


> For starters, just find an old Manitou crown. It takes a 28.6 tube for the leg. i suppose you could also look at the aluminum stantions to get some idea on their wall thickness.
> 
> I should probably make the obligatory note that if you don't have the engineering knowledge to determine the appropriate material and dimensions for your project, do you really want to be experimenting on a fork? And unless you're referring to yourself in the scrawny third person, do you really want to be testing with someone else's teeth?


This is being made for three people - me, myself and I. 

Yes, apologies for not being more clear about that. I have NO intentions of making any forks for anyone else. The whole teeth thing is the perfect way to put it. I've actually started a small business in the past making stuff I was going to market, but the liability concerns stopped me. 

Regardless ..... i'm going with something bigger in diameter simply for strength. Correct in the observation that I don't have any degrees to help me out here, but I at least know bigger tubing is stronger tubing, so it's a first step in help to protect my molars.  We all have to start somewhere, and apart from spending hundreds on one of these old forks - which i'm not interested in doing - and then having to chop it up to find out - which i'm certainly NOT doing - then this is my start. The idea of comparing suspension fork IDs has already been performed, but thank you very much for suggesting it.


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## dr.welby (Jan 6, 2004)

AndrewTO said:


> Regardless ..... i'm going with something bigger in diameter simply for strength.


Bigger than what? 28.6mm is 1 1/8".


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## bobbotron (Nov 28, 2007)

How are you planning on joining it together?


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## Feldybikes (Feb 17, 2004)

I wouldn't use Al, either. IMO, 28.6 is barely big enough for a steel fork (speaking as someone who is relatively tall but not particularly lanky for a cyclist -- 6', 175ish). I would think Al would flex too much. Even XC suspension forks now have 32mm stanchions. Since we're talking about ~3' of tubing, don't see why cost matters all that much between steel and Al. Also, I would guess with your OD constraint, Al *might* actually end up heavier by the time you increase the wall thickness enough vs. steel.


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## AndrewTO (Mar 30, 2005)

dr.welby said:


> Bigger than what? 28.6mm is 1 1/8".


Sorry! My bad. Working on something and I have a whole bunch of numbers running around in my head at the moment. Apologies.


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## AndrewTO (Mar 30, 2005)

bobbotron said:


> How are you planning on joining it together?


Same way Bontrager did - bolts.

I had always thought they re-enforced it with some epoxy or something, but apparently they didn't.


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## pvd (Jan 4, 2006)

AndrewTO said:


> I referenced to the ORIGINAL '90s design, not the newest version. It's in the second sentence of my opening post.


That's what we have all been talking about. That was made very clear.




























https://www.equusbicycle.com/bike/tange/tangebrochureforktube/pdf/tangebrochure01.pdf


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## AndrewTO (Mar 30, 2005)

Feldybikes said:


> I wouldn't use Al, either. IMO, 28.6 is barely big enough for a steel fork (speaking as someone who is relatively tall but not particularly lanky for a cyclist -- 6', 175ish). I would think Al would flex too much. Even XC suspension forks now have 32mm stanchions. Since we're talking about ~3' of tubing, don't see why cost matters all that much between steel and Al. Also, I would guess with your OD constraint, Al *might* actually end up heavier by the time you increase the wall thickness enough vs. steel.


Excellent point and i've thought of the same. I might have to try it. I'll see how things go with the 1 1/8" stuff first. Thanks.


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## pvd (Jan 4, 2006)

AndrewTO said:


> Correct in the observation that I don't have any degrees to help me out here, but I at least know bigger tubing is stronger tubing, so it's a first step in help to protect my molars.


Please god stop now.


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## AndrewTO (Mar 30, 2005)

pvd said:


> That's what we have all been talking about. That was made very clear.


I was using that fork as an example mostly for it's crown. Apologies for not being more clear.


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## AndrewTO (Mar 30, 2005)

Walt - since you don't take P.M.s ..... can you please delete this thread? Thanks. I'd do it myself, but apparently MTBR doesn't allow it. 

If not then please forward the request to someone that can. This is not going anywhere positive and I really can't deal with it.


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## AndrewTO (Mar 30, 2005)

pvd said:


> Please god stop now.


Sorry i'm not an engineer!  Sue me for asking for HELP.


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## jgerhardt (Aug 31, 2009)

AndrewTO said:


> Walt - since you don't take P.M.s ..... can you please delete this thread? Thanks. I'd do it myself, but apparently MTBR doesn't allow it.
> 
> If not then please forward the request to someone that can. This is not going anywhere positive and I really can't deal with it.


Actually Walt, please do NOT delete this thread.

While maybe not the intent of the OP there is a lot of good information from several builders here regarding forks.


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## dr.welby (Jan 6, 2004)

AndrewTO said:


> If not then please forward the request to someone that can. This is not going anywhere positive and I really can't deal with it.


Before you give up, why don't you explain some more about why you want to build this fork this way? Aesthetics? Adjustability? What is the end goal?


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## Feldybikes (Feb 17, 2004)

Andrew, don't sweat the comments from PVD.

Walt, please don't delete and instead post a pic of La Cuchara Muerte (which I now realize should really be El Tenedor Muerte, but really that error really is fitting with the rest of the project)


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## jay_ntwr (Feb 15, 2008)

pvd said:


> That's what we have all been talking about. That was made very clear.


Very cool, *Standard or 1 1/8" Steerers*. That's kind of funny 20 years later.


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## pvd (Jan 4, 2006)

1 1/8" is the DH version!


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## vulture (Jan 13, 2004)

I liked the HD bontrager version with aluminum dropouts. A couple of my friends had the extra tall cutouts for wtb wide flange hubs. RAD.
I have a switchblade fork in my shop right now that I picked up at a yardsale last summer for $5. Made me laugh so I bought it.


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## edoz (Jan 16, 2004)

You might want to reconsider the wire EDM part for cost reasons. It will probably cost a lot more than having a crown machined, (unless you have a hookup) and if what you're interested in is a bead blasted like finish, then any machine shop is going to have a blast cabinet. Mill, blast, save $ 

Also, I'm gonna say +1 for steel legs. At 1 1/8" aluminum isn't going to be stiff enough at pretty much any wall thickness south of ridiculous, and when aluminum fails it gives less warning then steel. The cost difference is virtually nil, but steel is better for the application. You will get a better ride out of a steel fork anyway, imo. For a 29'er, you might look into True Tempers unicrown fork legs, they'd give you that nice tapered look of the originals, plus you would have a nice range of dropouts to fit. They are available from Henry James. 

Don't give up on the project, those are badass forks. Just realize that most of these guys ARE trying to help, they just may not seem overly polite about it. Such is the internet.


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## byknuts (Aug 9, 2008)

hey andrew! 
I've got an old JrT fork with bolt-on triples that you can take measurements off of if you want.
(FYI the trips have seen a good beating so I wouldn't let anyone ride them, but for location measurements, they're fine) 
I think the 28.6 (or 30mm) legs would work fine for xc type work, (looking at your stable I'm pretty sure that's your aim anyways  )

mikesee has (or had) a snowbike that had a rigid fork with double triples, i think 40mm legs. looked to me like the triples were 888 items. if you search for snoots you should find it. 

suggest for quickest mock-up, take your measurements off something on hand for the trips and work from there.

pm me if you need help with anything else.
a friend with EDM access is a friend indeed!  

FWIW I understand why everyone's saying "go cromo" but noone ever gets somewhere new if all they try is the established path. so I say go for it. 
(remember the days of "aluminium can't make a good mountain bike, steel forgives, aluminium never forgets"?)


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## dr.welby (Jan 6, 2004)

edoz said:


> At 1 1/8" aluminum isn't going to be stiff enough at pretty much any wall thickness south of ridiculous, and when aluminum fails it gives less warning then steel.


I quickly scribbled out some numbers and I think you could make it work without having to get ridiculous with the wall thickness - Walt's guess of around 3 seems to jive with what I'm getting (my calculations were super rough so I won't bother posting actual numbers). It changes a bit depending on whether you're designing for ultimate strength, stiffness or fatigue life. With aluminum you also have more material choices to puzzle over as a newb, and then there's also surface finish (you'd be smart to get them shot-peened). I didn't bother to look at weight - it's probably a wash.

I think the consensus, which I agree with, is it would be so much easier to go with a chromoly leg, picking a wall thickness that matches with a similarly sized fork leg from a bicycle tubing supplier.

But in the interest of experimentation I think it could be an interesting experience to try aluminum legs, with the already exhausted caveat that you could make a poor choice and hurt yourself.


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## pvd (Jan 4, 2006)

Aluminum has been done ad nausium. Everyone is doing carbon these days for a reason. Why not carbon? Al is pretty much old news.


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## coconinocycles (Sep 23, 2006)

I wasn't going to say anything but it seems that i have more experence then everyone else here {not a cheap shot - it looks like i do} as i actually tested stuff indirectly for awhile that was new from B-trager. I destroyed every part they made  So, i the beginning, there was the tapered blade model. it came in vertical D-out model, touring with eyelets & the "dinosaur head" model with a Horiz, slot to adjust rake. they were heavy, and chromed, curved blades {rare} and straight legs. all steel. the canti spigots were welded on. next in I think, 90'? they came out with the "comp", which had thinner wall legs of a bigger diameter {1.125"}, Al. dropouts, *and* a bonded in Al. sleeve inside the legs which extended beyond the bottom of the crown. the canti posts were a bonded sleeve with removable spigots & they had a rivit to hold it in place as it was bonded. the Al dropouts could creak & come loose but i never saw that part actually fail, but sent a few back much to the distress of the R&D guys. they had allot of trail flex, but rode really well. if you really hit things the legs were bomber, the crown would twist. the Steer had a c-clip for backup, a slip fit Al. crown race, and the four bolts were 1/4". on big drops you could shove the legs up in the crown, but it had to be drastic. *the article you show says the frames were Al., but they were not* - **except** for a model i saw one of, which had an Al. front triangle & the rear was assembled just like one of the forks. i was told they all busted. I did have a machinist make me some Al. legs for touring that were THICK & rode sucky unloaded. LASTLY - IRD made a fork very similar to the B-trager, but with Al. & Ti. legs, but Vulture would know more about those then I. hope this helps a bit - Garro. PS - the Tange forks were pure crap, they all bent forwards just below the canti bosses.......


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## Evil4bc (Apr 13, 2004)

themanmonkey said:


> The blades on the Bontrager and Tange Switchblade folks were not standard track blades, maybe some of the early ones were. They were much thicker wall, and at least the Tange were custom drawn blades. A dual-crown version isn't going to work that well unless you want to fork to be really tall. Even the Bontrager and Tange fork blades would occasionally slip in the crown. So you'll need to add, not subtract, material to the crown to make it a dual-crown.


Well I'm glad to see a thread like this , first off I LOVE MY SWITCHBLADES !!!

Way back in 1988 i was a young kid stil in middle school and saved a whole year to buy a new MTB my luck was that the shop that had the bike has scratched the stock fork and needed soemthing to put on my bike before I picked it up , my luck was that they only had a switchblade fork in stock and I scored !!
Ever since that day i have een in love with the 3 pc. composite fork design , i have a few differnt Switchbade forks in my collection as well as some bontrager forks as well .

Now regarding your question about legs - they were NOT standard Pista legs in fact these were custom double butted taped legs that had a press fit aluminum ship / BERT pressed into the upper section of the leg under plastic leg top cap to help reduce the "clamping " on the fork legs so the crown stayed tight .

To make one of these forks today you will need soome custom legs , internally reinforced and a upper CNC or forged crown - EDM ??? way too much tech for this little part


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## Evil4bc (Apr 13, 2004)

coconinocycles said:


> I wasn't going to say anything but it seems that i have more experence then everyone else here {not a cheap shot - it looks like i do} as i actually tested stuff indirectly for awhile that was new from B-trager. I destroyed every part they made  So, i the beginning, there was the tapered blade model. it came in vertical D-out model, touring with eyelets & the "dinosaur head" model with a Horiz, slot to adjust rake. they were heavy, and chromed, curved blades {rare} and straight legs. all steel. the canti spigots were welded on. next in I think, 90'? they came out with the "comp", which had thinner wall legs of a bigger diameter {1.125"}, Al. dropouts, *and* a bonded in Al. sleeve inside the legs which extended beyond the bottom of the crown. the canti posts were a bonded sleeve with removable spigots & they had a rivit to hold it in place as it was bonded. the Al dropouts could creak & come loose but i never saw that part actually fail, but sent a few back much to the distress of the R&D guys. they had allot of trail flex, but rode really well. if you really hit things the legs were bomber, the crown would twist. the Steer had a c-clip for backup, a slip fit Al. crown race, and the four bolts were 1/4". on big drops you could shove the legs up in the crown, but it had to be drastic. *the article you show says the frames were Al., but they were not* - **except** for a model i saw one of, which had an Al. front triangle & the rear was assembled just like one of the forks. i was told they all busted. I did have a machinist make me some Al. legs for touring that were THICK & rode sucky unloaded. LASTLY - IRD made a fork very similar to the B-trager, but with Al. & Ti. legs, but Vulture would know more about those then I. hope this helps a bit - Garro. PS - the Tange forks were pure crap, they all bent forwards just below the canti bosses.......


WOW seems like Steve has some first hand knolange on these a bit more than I do , or a least he was older at the time of riding these .

I never bent any of the Tange forks but saw 3 IRD models fail in front of me on the trail and one on the bike lane in front of apple WHQ was a guy front Canada flipped over his bars from his forks breaking at the canti bosses from a hard stop at a light :skep:


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## AndrewTO (Mar 30, 2005)

pvd said:


> Aluminum has been done ad nausium. Everyone is doing carbon these days for a reason. Why not carbon? Al is pretty much old news.


Peter, if you need to ask questions like this please don't bother. Just stay out of the thread if you are going to continue the way you are. Thank you.


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## Evil4bc (Apr 13, 2004)

AndrewTO said:


> Peter, if you need to ask questions like this please don't bother. Just stay out of the thread if you are going to continue the way you are. Thank you.


andrew 
If you post a question to the open fourm then don't be miffed when people reply with their thughts .

BTW- Aluminum for fork blads is crazy talk , Carbon or steel if you want to live past your 3rd ride on this fork.


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## AndrewTO (Mar 30, 2005)

Always the same crap around here. 


1. wire EDM - I work in a machine shop and have this machine at my disposal. It's far easier and quicker to have this wired. 

2. goal - to make it, I like the way they look and because I can't weld anything right now. I can also make any a2c and any offset I want. I'd like to produce something that can actually be used to ride with on a bicycle. I'd prefer not to make a "for show only" piece. 

3. (@ Steve G) - THANK YOU! I've read about the flex, even seen why personally with a fork I modded for a fellow member a short while back (he's the only person I know that has a 1 1/8" threadless aluminum steerer tube in his  ). Do you feel anything would have helped make the crowns resist flex at all? (besides a material change) Perhaps I should not bother with a SC version and just stick with the DC? I'm thinking narrow-mindedly here - my solution for "fixing" the tubes is to go with a thicker wall. My solution to "fix" the crown is ..... Idunno. (if I need to)

4. (@Evil4bc) - what's a BERT? I find way too many unrelated hits with a Google search. Would you mind narrowing it down for me, please? Thanks. 



Material is prepped. Waiting for programs to be made for the crowns. Would you believe it?!??!?!? I can find more options in wall thickness in titanium than aluminum with my local go-to sources! :madman: Almost tempted to use it, too. :skep: 



Thank you to all those that have provided something(s) constructive. There's a lot of crap that goes on unregulated around here and I find it VERY frustrating. I need help, i'm asking for it - getting crap and criticism in return is counter productive. This is THE forum in all of MTBR where i'd like to think that maturity can prevail, along with understanding. For those that don't understand that simple concept - FORK OFF!   

Thanks.


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## dr.welby (Jan 6, 2004)

BERT = BAR END REINFORCEMENT THINGS a.k.a. aluminum inserts sold for the Titec 118 titanium handlebar to keep bar ends from tearing off their thin ends.


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## AndrewTO (Mar 30, 2005)

dr.welby said:


> BERT = BAR END REINFORCEMENT THINGS a.k.a. aluminum inserts sold for the Titec 118 titanium handlebar to keep bar ends from tearing off their thin ends.


Oooooooh, damn, forgot about those things. Damn, I feel old now.


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## pvd (Jan 4, 2006)

AndrewTO said:


> ...and because I can't weld anything right now.


But you said you worked in a machine shop. A shop with a wire EDM and no tig welder?


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## AndrewTO (Mar 30, 2005)

pvd said:


> But you said you worked in a machine shop. A shop with a wire EDM and no tig welder?


Is the Bontrager fork welded? No. 

Fork off, Peter.


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## AndrewTO (Mar 30, 2005)

Evil4bc said:


> andrew
> If you post a question to the open fourm then don't be miffed when people reply with their thughts .
> 
> BTW- Aluminum for fork blads is crazy talk , Carbon or steel if you want to live past your 3rd ride on this fork.


Are you saying this because of the shape of the tubing or ..... ? I have a lot more than 3 rides on my Misfit Psycles fork, but it's a different beast. Same goes with my Noleen/Girvin linkage fork _which I tried running rigid by replacing the shock with a solid piece of aluminum_, but again, different animal.

Is the tubing shape the concern or ..... ? Don't tell me "because it's aluminum". It's just not a valid response. It's like saying "you can make ANYTHING in the world out of aluminum ..... except rigid mountain bike forks". It doesn't make sense. Please, explain.


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## ElkCycles (May 31, 2010)

Andrew,

A DC option would limit your low speed steering and add complexity to your design. Your material choice of aluminum already seems set in stone, although again, in the road community the options are really only CF or steel as aluminum was abandoned long ago for its ride characteristics. I'd be hard pressed to find a road bike under $600 that doesn't use some form of carbon fork. I have personally used all three extensively, and much prefer the ride quality of a segmented steel fork to carbon fiber. 

The only benefit I can see to your choice of aluminum is that it won't have to be painted and can simply be polished or clear coated/plated for aesthetic purposes. 

If you have access to an EDM, and the programming skill to use one properly, then you can likely make an impressive crown for your fork. Good luck and be careful.


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## pvd (Jan 4, 2006)

AndrewTO said:


> Is the Bontrager fork welded?


Brazed at least.


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## themanmonkey (Nov 1, 2005)

Evil4bc said:


> Well I'm glad to see a thread like this , first off I LOVE MY SWITCHBLADES !!!


But you had the Brodie Gatorblade up there which I thought was a much better fork than the 'trager. YMMV


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## bobbotron (Nov 28, 2007)

pvd said:


> Brazed at least.


I think if I read descriptions of it above, that isn't the case? It was just held in there the same way a stem holds handlebars?


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## satanas (Feb 12, 2005)

FWIW, I worked for the Australian importer of ALAN frames from the late 1970s until the late 1980s. Most ALANs used a bonded aluminium fork with a 1" threaded alu steerer; the steerer was machined and had a very thick wall at the bottom of the crown. (The exception was the Competition which used a steel steerer.) The fork crowns were forged alu, blades were tapered, raked, round alu, and had alu dropouts bonded and threaded in. IIRC, the dropout slots were machined after the fork was bonded together, so alignment was perfect; the ALANs I owned or rode were always exceptionally stable descenders. I'm not sure if the blades and/or steerer were screwed into the crown as well as glued, and never cut up a fork to see or to check out wall thicknesses, but the forks were noticeably light compared with Reynold 531 or Columbus SL.

I *never* saw one of these forks fail, including those on bikes which had suffered severe enough frontal impacts to damage the main tubes and/or joints. The worst fork damage I ever saw was a very slight rearward bend near the crown. The fork blades flexed quite noticeably under heavy braking or on large bumps - as did the steel forks of the time. The forks were super comfortable over bumps, unlike some later alu forks like those which came on the Specialized Allez Epic.

One of our customers used to commute on his bike every day in all weathers and never did any maintenance. The frame and fork were still intact and looked as new 10+ years later, so the idea that alu has to fail, and cannot be allowed to flex is not necessarily correct, at least for bonded/mechanically joined frames.

ALAN weren't perfect, and some models of frames had issues (especially the Tourist and early carbon frames), but the Competition, Super and Sprint were very reliable, if not abused or crashed frequently. Their CX frames were popular for many years in Europe, however I can't comment as we don't have CX in Oz.

Bottom line is that I wouldn't necessarily write off alu as a fork material, but I would agree that it does need to be handled perfectly.


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## coconinocycles (Sep 23, 2006)

Evil4bc said:


> WOW seems like Steve has some first hand knolange on these a bit more than I do , or a least he was older at the time of riding these .


I had the pleasure of wrenching in a shop that carried B-trager, Mtn Goat, Moots, Fat City, Mantis, Brodie, WTB, Mc Mahon, Mtn.Cycle, Etc. at the time. I got to see & test all that cool old stuff circa 85' on. The Gatorblade the Monkey talks about was pretty interesting, but all the ones i dealt with creaked......as per age, yeah, I'm a crusty old 42yrs..... - Steve Garro, Coconino Cycles.


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## coconinocycles (Sep 23, 2006)

AndrewTO said:


> I have two fork projects I wish to pursue. I want to make a fork very similar in style to the old Bontrager Switchblade rigid fork from the '90s


my junk box just kicked you guy's junk boxes asses. - not for sale! - Steve Garro, Coconino Cycles.


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## hollister (Sep 16, 2005)

coconinocycles said:


> I wasn't going to say anything but it seems that i have more experence then everyone else here {not a cheap shot - it looks like i do} as i actually tested stuff indirectly for awhile that was new from B-trager. I destroyed every part they made  So, i the beginning, there was the tapered blade model. it came in vertical D-out model, touring with eyelets & the "dinosaur head" model with a Horiz, slot to adjust rake. they were heavy, and chromed, curved blades {rare} and straight legs. all steel. the canti spigots were welded on. next in I think, 90'? they came out with the "comp", which had thinner wall legs of a bigger diameter {1.125"}, Al. dropouts, *and* a bonded in Al. sleeve inside the legs which extended beyond the bottom of the crown. the canti posts were a bonded sleeve with removable spigots & they had a rivit to hold it in place as it was bonded. the Al dropouts could creak & come loose but i never saw that part actually fail, but sent a few back much to the distress of the R&D guys. they had allot of trail flex, but rode really well. if you really hit things the legs were bomber, the crown would twist. the Steer had a c-clip for backup, a slip fit Al. crown race, and the four bolts were 1/4". on big drops you could shove the legs up in the crown, but it had to be drastic. *the article you show says the frames were Al., but they were not* - **except** for a model i saw one of, which had an Al. front triangle & the rear was assembled just like one of the forks. i was told they all busted. I did have a machinist make me some Al. legs for touring that were THICK & rode sucky unloaded. LASTLY - IRD made a fork very similar to the B-trager, but with Al. & Ti. legs, but Vulture would know more about those then I. hope this helps a bit - Garro. PS - the Tange forks were pure crap, they all bent forwards just below the canti bosses.......


bonded comp legs was '88ish


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## pvd (Jan 4, 2006)

Awesome!


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## Evil4bc (Apr 13, 2004)

hollister said:


> bonded comp legs was '88ish


Yea now that totally kicks Cocchino's fork with one useable leg.

I too have a few different versions of Bontrager and Tange forks here in my box of parts .
Hollister is the 3 forks over from the left a Road or cyclocross version ??


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## hollister (Sep 16, 2005)

Evil4bc said:


> .
> Hollister is the 3 forks over from the left a Road or cyclocross version ??


thats a rollercam/U brake fork

the funky cx fork looks a little different


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## dr.welby (Jan 6, 2004)

hollister said:


> the funky cx fork looks a little different


Oh man, you're bringing me back to Surf City at the Armory and Swan(pt)on Hill.


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## [email protected] (Jan 3, 2009)

*Fork Building*

I made a set of mtb forks back in the late 80's using a block of 6016 ali machined up on a lath. The fork legs were fabricated from reynolds 531 pg tube with a wall thickness of .5 mm. The tips were made from 6mm mild steel and braised to the front of the fork leg(to give the propper ofset). three sets of the forks were built with me still having two of them still on two of the custom built mtb's that I have built.(I have a Reynolds 753 ticket). The reason for having the forks bolting together was to stop the heat effected area at the top of the forks from cracking and bending. I will dig them out of the shed and take a photo of them and post a pic of them.


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## coconinocycles (Sep 23, 2006)

hollister said:


> bonded comp legs was '88ish


been thinking about it, and i am pretty sure {but a little fuzzy} and I think I picked up my Dinosaur head chromed from from Johnny Thess @ B-trager's booth at interbike in Anaheim in 89' {while dropping John Parker a bag of bent Yetis - i think he must still hate me, but he was beeing a dick about it} . before 90' wasn't there only one B-trager MTB model, then it split into the race & race lite? I had a 90' race lite & a 91' Salsa ala carte, both with comp blades........ - getting old, yo. - Garro.


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## Blaster1200 (Feb 20, 2004)

[email protected] said:


> I made a set of mtb forks back in the late 80's using a block of 6016 ali machined up on a lath. The fork legs were fabricated from reynolds 531 pg tube *with a wall thickness of .5 mm*.


Sounds scary at most any usable diameter. :eekster:


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## xy9ine (Feb 2, 2005)

satanas said:


> Bottom line is that I wouldn't necessarily write off alu as a fork material, but I would agree that it does need to be handled perfectly.


i've got an alan cx fork (w/ 1" legs). i've not heard any horror stories, so it doesn't seem an unreasonable application - done right as you say.


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## Linnaeus (May 17, 2009)

There's thousands of Kenesis 6061 Al road forks running around without issues (Al steerer, crown, and blades). I crashed one pretty hard, about ~35mph direct impact. Taco'd the front wheel, snapped my steel frame into 3 pieces, and bent the fork up -- but the fork didn't fail catastrophically. It actually fared better than the steel frame. Long story short -- Al is fine when done properly, just like any other material.


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## JunkMail (May 5, 2010)

Has anyone ever managed to find a supplier for replacement blades? I don't even need them to be original or authentic (though that would be pretty cool). But has any builder out there stepped up fill the void? 

Any leads would be greatly appreciated! Thanks.


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## dbohemian (Mar 25, 2007)

Seems like Andrew TO posts a lot and wants some hand-holding....but....we can't give you any better advice than has been given.

Why? We all know about Aluminums fatigue limit. Certainly one can design around this issue as has been shown on various examples. Problem is, none of us can tell you exactly what it should be. Without proper engineering and subsequent mechanical testing one cannot know if it will be safe or not. You only option is to massively overbuild it (I think 3mm minimum was mentioned). Steel and carbon blades are known entities. Just copy your favorite fork or use great information (i.e. walt and his forks) that has been disseminated here. Since I don't know a single small framebuilder who has ever made an aluminum fork you are pretty much treading new ground.

Personally, I don't think your idea is smart at all. I like the EDM'd crown but any of the other materials would be preferable IMHO. If only because it has been done before and we have good examples.


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## TimT (Jan 1, 2004)

Andrew
I don't think EDM will do what you want. I run 3 Charmilles wires at work. (mold and die) A 310, 440 and 440c. So if your worried about the fork blade slipping I'd machine a groove at the top of the crown for a C clip. You can still bolt the blade in and the clip will keep it from slipping in the crown.

Tim


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## Jak0zilla (May 16, 2010)

So ... um ... I thought I'd stick my head in here and ask a question which is vaguely on-topic. Kind of hot in here isn't it?  (Still, it seemed like the place to ask.)

I've had the (bad?) idea floating around my head for a very long time that it would be nice to have some STEEL blades built to fit into the crown on my old Judy. I know it wouldn't be the lightest option, or the strongest, or any of that. It would let me salvage the rest of my vintage ride in it's entirety. No new stem, headset, etc. 

Has anyone seen this sort of thing done? Done it themself? 

I'm picturing a set of legs built out of medium weight CrMo, dropouts, canti posts, or perhaps even holes to bolt the original brake arch back on. (Not that it is anything special.) I'd imagine that the hardest part would be finding tubing of appropriate OD and wall thickness ..? Is this madness?


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## dr.welby (Jan 6, 2004)

Jak0zilla said:


> I've had the (bad?) idea floating around my head for a very long time that it would be nice to have some STEEL blades built to fit into the crown on my old Judy.


Judy legs had a weird OD if I remember correctly - something like 30.0 mm?

Manitou crowns, however, used 28.6 legs which makes conversion easy. Here's one I made  by sleeving 25.4 track blades in 28.6 x .058" uppers.

If you just *have* to use your Judy crown, I'd probably try to adapt 28.6 tubing up to the Judy size to make life easier.


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## Jak0zilla (May 16, 2010)

dr.welby said:


> Judy legs had a weird OD if I remember correctly - something like 30.0 mm?


That sounds correct to me.

I like what you did there! That is more or less what I'm thinking of.



dr.welby said:


> If you just *have* to use your Judy crown, I'd probably try to adapt 28.6 tubing up to the Judy size to make life easier.


I just thought it would be the easiest route (once it was a fabricated item that is). It's a decent crown, again not exceptional, just sturdy enough and it's already installed.

I know the real solution is to just cough up the $$$ for a fork. (and stem while I'm at it.) Anyone who would build such a thing for me would probably charge 2/3 - 4/5 of the price of a fork. If not more for the hassle of designing it. I imagine it's the sort of thing that one could build a half dozen of, and find homes for, but that's not going to make that much money as compared to just popping out a frame or two.

If I were handy with a torch I'd probably have a stab at it myself. Actually ... who am I kidding? I'd just build a fork! 

I just keep looking at the thing, and thinking "fork blades ... "


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## JunkMail (May 5, 2010)

Jak0zilla, it was that kind of thinking that made me buy this crown. I figured, very naively, that blades would be easy to come by. In my head, it would be so easy to make them up.

But apparently it's much harder than I thought, or all the blades are in a secret society. I dunno. Seems like such a shame to let a nice crown go to waste.


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## jeff (Jan 13, 2004)

dr.welby said:


> Judy legs had a weird OD if I remember correctly - something like 30.0 mm?
> 
> Manitou crowns, however, used 28.6 legs which makes conversion easy. Here's one I made  by sleeving 25.4 track blades in 28.6 x .058" uppers.
> 
> If you just *have* to use your Judy crown, I'd probably try to adapt 28.6 tubing up to the Judy size to make life easier.


How does that fork ride? Any brake twist?


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## dr.welby (Jan 6, 2004)

jeff said:


> How does that fork ride? Any brake twist?


Nope, it's actually really stiff, since it's .085 at the top and uses the heavy duty True Temper track legs.


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