cut & weld GSXR steering stem

chickenStripCharlie said:
Yeah, they do, for about $200 and an additional $50 to ship to Canada.
The entire front fork cost me less than that

So cognito is my last resort right now simply due to price. will see what local machinists want to redo the piece.
One already turned me down on account of it having metric threads ?!? ..... wtf kind of machine shop is concerned whether threads are metric or imperial?
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It would depend on the equipment that they have. For example my lathe only has the gear sets to do standard threads. The money that it would cost to buy the gear set to do metric threads may not be justified by one job , especially if that is outside of their wheelhouse. If they have CNC equipment that they are doing it on there isn't much of an excuse though LOL

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Do I understand correctly in all this, that the stem you need longer doesn't fit the lower triple you have, and the stem that's too long is too small diameter for the lower triple after the other one is pressed out? If so, could the smaller diameter stem have a bushing turned and pinned into the lower triple to adjust the stem height correctly and eliminate the need for a new stem/welding/stretching, etc?
 
Grimacorn said:
Do I understand correctly in all this, that the stem you need longer doesn't fit the lower triple you have, and the stem that's too long is too small diameter for the lower triple after the other one is pressed out? If so, could the smaller diameter stem have a bushing turned and pinned into the lower triple to adjust the stem height correctly and eliminate the need for a new stem/welding/stretching, etc?
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Not quite because the stem that fits lengthwise (OEM stem) doesnt work with neither the top nor bottom triple of the new forks.

So if you were to do a bushing on the bottom to get it to fit a new triple it still would not be able to attach the new top triple properly

Not that I can think of at least. It would be easier/cheaper to just make a new stem or buy a cognito one at that point.
 
Hurco550 said:
It would depend on the equipment that they have. For example my lathe only has the gear sets to do standard threads. The money that it would cost to buy the gear set to do metric threads may not be justified by one job , especially if that is outside of their wheelhouse. If they have CNC equipment that they are doing it on there isn't much of an excuse though LOL

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I suppose that is fair. The two local guys I reached out to are gunsmiths so I assume they are all old school manual and probably dont have the metric tooling.
 
Unfortunately for this application, lathes have what I seem to recall is called a lead screw and that's the long bolt like thing that moves the tooling to cut threads. If the lead screw is not designed for metric thread pitch it makes it almost impossible to cut that type of thread. It can be done with the right drive gears I believe but that requires an experienced machinist that knows what they are doing.

There are lots of videos on Youtube that your machinist might like to watch. The guy that does my mchining is a tool and guy guy, so he can machine anything - but Cognito might be cheaper.

That may not be 110% accurate, but close enough for gubmint work.
 
irk miller said:
The shiny piece is TL1000r. The dull piece is BMW. Have you seen an airhead top triple? That shiny piece is pressed 3 inches into the bottom piece. The top bearing is held by the threads on the BMW stem. Please show me the math that suggests this needs a roll pin. Like I posted earlier, this has over 3k miles, and nothing has moved even a thousandths of a mm. The top triple is being held at the top screw AND the forks.
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I didn't say it needs it, I said I would. It's 2 additional minutes of work and peace of mind knowing that regardless of the math involved it's not going to move.
YMMV
 
You're unlikely to find a machinist to do the work (correctly) for less than 200 IMO.
 
Found a local machine shop to take this on and remake the entire stem.

Will update once complete. Rough estimate is 1.5 hrs work. Their rate is $100/hr but he said he'll do better than that as he likes to see guys working on projects like this!

Their shop was insane. Along with 20 manual lathes and many pieces of other equipment they had a $1,000,000 CNC machine.
 
I did this on a bike once. I had to lengthen an aluminum stem so I took 2 stems from the same bike and cut both but used the longer to section of one stem to give me the length. The inner diameter of the stems was just under 14mm so I drilled tapped both sides and used a 14mm treaded bolt to go into each side about 1". then I slightly grooved and welded the seam. The bolt inside gave it the strength and the weld kept it in place. It was all done on a lathe to keep it straight. In the end it was still a process and I think having one made is probably the best for strength, but It worked for my application at the time and I put lots miles on the bike.
 
JAGspeed said:
I did this on a bike once. I had to lengthen an aluminum stem so I took 2 stems from the same bike and cut both but used the longer to section of one stem to give me the length. The inner diameter of the stems was just under 14mm so I drilled tapped both sides and used a 14mm treaded bolt to go into each side about 1". then I slightly grooved and welded the seam. The bolt inside gave it the strength and the weld kept it in place. It was all done on a lathe to keep it straight. In the end it was still a process and I think having one made is probably the best for strength, but It worked for my application at the time and I put lots miles on the bike.
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Interesting approach! Did those welds hold up over time? ... considering everyone says the material wont hold up being welded.

Once everything is installed and tightened what kind of force is the stem subject to? 1. Rotational force due to steering ... that cant be that much force? Or am I underestimating?

2. Inline force road bumps ... this one is pretty major, largely dampened by the shocks?

Is the stem subject to any additional force from a different angle, considering the fork (and stem) sit at whatever the rake angle is?
 
I'm not an engineer, but it would seem to me that if you have the stem tightened to the correct spec, most of the stress would be on the bearings where it belongs. There's be a certain amount of pull between the top and bottom by tightening down against the bearings, but once that is established and set, your up n down, besides the springs, is on the bearings. The rotational (steering) force is taken on by the axle bearings, the triples (especially the bottom) and the stem bearings. So, it seems like if the weld on your stem can handle being tightened and then being kept at that torque spec there shouldn't be issues. If my ride had an arrangement as described above w/ the two pieces threaded together and then properly welded I'd complete my assembly and ride, ride, ride.
 
The problem that keeps getting looked past is that you cannot safely weld 70 series alloy, which is most likely what it is. It was brought up her early on. The weld isn't an option on that grade of aluminum. If you wanna trust it to a piece of threaded rod, that's your prerogative, but if you weld over that, the weld is only decoration, or there for a false sense of security.

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ridesolo said:
I'm not an engineer, but it would seem to me that if you have the stem tightened to the correct spec, most of the stress would be on the bearings where it belongs. There's be a certain amount of pull between the top and bottom by tightening down against the bearings, but once that is established and set, your up n down, besides the springs, is on the bearings. The rotational (steering) force is taken on by the axle bearings, the triples (especially the bottom) and the stem bearings. So, it seems like if the weld on your stem can handle being tightened and then being kept at that torque spec there shouldn't be issues. If my ride had an arrangement as described above w/ the two pieces threaded together and then properly welded I'd complete my assembly and ride, ride, ride.
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The thing about the top bearing is that it's only a slip fit. In fact, on my GSXR stem the 30mm bearing was a fairly loose fit at that!
I told the machine shop to make the new one a little tighter than that.

With a loose fit like that, i can't help but wonder whether all of the stress is on the bottom bearing alone and the top is just to keep everything centered and balanced.
 
Hurco550 said:
The problem that keeps getting looked past is that you cannot safely weld 70 series alloy, which is most likely what it is. It was brought up her early on. The weld isn't an option on that grade of aluminum. If you wanna trust it to a piece of threaded rod, that's your prerogative, but if you weld over that, the weld is only decoration, or there for a false sense of security.

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Click to expand...

Yup, even the guys at the machine shop that took my project on said the same thing .... just not a weldable material. period.
 
You might find this interesting:
newatlas.com

New welding process opens up uses for formerly un-weldable lightweight alloy

Developed in the 1940s, AA7075 is an aluminum alloy that's almost as strong as steel, yet it weighs just one third as much. Unfortunately its use has been limited, due to the fact that pieces of it couldn't be securely welded together. That's recently changed, however, thanks to the use of titanium…
newatlas.com newatlas.com
 
There has been a bit of talking within the welding industry about that process. Its all nerd out talk and of no real consequence, but by alloying in the Titanium Carbide, you are changing the Alloy, and therefore it is no longer actually 7075. It is actually a new alloy of its own.

Plus, still doesn't change the alloy that the op's stem is made of ;)
 
Hurco550 said:
There has been a bit of talking within the welding industry about that process. Its all nerd out talk and of no real consequence, but by alloying in the Titanium Carbide, you are changing the Alloy, and therefore it is no longer actually 7075. It is actually a new alloy of its own.

Plus, still doesn't change the alloy that the op's stem is made of ;)
Click to expand...
Only at the weld ;). You're not welding the entire stem are you? HAHA
 
UPDATE:

the stem has been machined (took over a month to make it into the queue).

They did a great job and charged me $150CAD, or about $110USD.

A far cry from what the Cognito stem would have cost me to buy and ship up here to Canada.
 

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