B17

Just what the title says! I just bought an MTB fork that's 1 1/8", threaded, but far too long for my head tube. The fork is threaded and has a keyway, which I'd like to keep going. Is there anyone out there still doing this work? The fork isn't expensive, but I'd like to try it on a build I have going. My head tube is 100mm and the steerer of the fork I just bought is 175mm with 40mm of thread, so I probably need another 20mm of threads cut and then the steerer cut down to about 145mm.

Thanks in advance!

Dan Burkhart 

We could probably help you better if you indicate what your location is. If you are local to me I have the means to extend the thread and cut the steer tube, but I'm not set up for broaching a keyway.

B17

Thanks so much!

I'm in North Alabama, but I'm willing to mail the fork to where you are, if you know how I'd use the fork without a keyway. It takes cantis (I'd rather not use v-brakes) and so needs a cable hanger under the top nut. I'm sure it's possible, but I don't know how it would keep from spinning or keep the top nut in place. I know just enough about this not to know anything, so whatever you can tell me would be great help.

Dan Burkhart 

I am in Canada, so two way postage would make this prohibitive, not to mention that with the current situation, there are long delays in the cross border postal service.
I would consider myself an absolute last resort for the job, and I'm sure there are others in closer proximity that could help you out.
Good luck.

B17

I understand. Thanks for the info all the same and the offer!

Dan Burkhart 

No worries.
Also, the keyway is not essential, although it does help to hold the bearing adjustment. I have extended threads beyond the keyway and just filed the locking tab off the washer. The jam nut action of the adjusting nut and lock nut will hold it if torqued properly.

2old

My LBS had a tool for that years ago and haven't needed it done recently, but you could check around; also should be an easy job for a machine shop (if they're open in your area now). Some businesses in socal are are operating on "curbside" drop off/pick up".

FastJake

You can use a threadless headset and then use the top cup and locknut from a threaded headset to lock the bearing adjustment instead of a star nut. I've done this a couple times. It works great and doesn't require the fork to be modified.

If the steerer tube is *really* long, just cut off the threaded portion and use it as a 100% threadless system. But then you'll need a threadless stem, of course.

WizardOfBoz

There is some bike shop out there that has something like this:
https://www.parktool.com/product/for...ding-set-fts-1
As well as the accessory die and guide for 1-1/8 inch tubes. Not a common item, google "fork thread cutting" or somesuch.
Using the guide and the die in the dieholder, the threads shouldn't be tough. Cutting the tube shouldn't be tough, either (just make sure that you cut the thing with a nut already ON the fork so that when you take the nut off it effectively chases the threads where you cut).
The keyway is likely milled, as there's a stopping point and most of the stopping points in a keyway that I've seen are round, like an end mill.
That said, you can file a keyway. Or use a Dremel tool and a a burr. Very carefully, and with a guide (like a split piece of pipe, hose-clamped to your steerer tube).
Here's someone that did an internal key, but the same approach might be useful for your external key.
https://www.instructables.com/id/Fil...eyway-by-Hand/

BTW, the old school approach would be to use special chisels called cape chisels to hand-cut those keyways. In the old days, they'd do motor shafts and pulley interiors and such use these chisels, a hammer, machinists layout dye, rulers, and special files called rifllers.

Dan Burkhart 

At 1/16" wall thickness, there is not much room for error with a non precision cutting method. I would forgo the keyway rather than risk compromising the integrity of the tube that the stem quill puts so much outward force on.

Andrew R Stewart 

Cutting new threads on a 4130 steerer (or other steel for that mater) can be more of a deal then most will ever know. The vast majority of threading dies provided by the bike industry are not really meant for cutting fresh threads but to chase/clean existing ones. It's a well known issue that tearing off the thread form when "cutting" is very easy to do. Extending a few threads, where the top race still contacts the OEM ones, can be done with good results but much more and expect poor results. Of course if you have access to a lathe and the skill one can single point the threads but that's well beyond most who post here (including me). I've used quits a few brands' dies, some new and others well used, and found the results are not consistent enough to quote the job any longer. (I was young and eager once and thought my touch was unique...) Given the time and tool costs with today's liability concerns most shops won't consider this job.

BTW a warding file is how many builders hand cut the lock washer tab groove. Or if they are set up with machine tooling, a simple slitting saw of the right width does a nice job. Andy (who long ago gave up on lock washer tabs holding anything still while adjusting preload)

WizardOfBoz

Unless the OP is a dreadnought-level machinist, I'd agree. But are steer tubes all 1/16? I seem to recall that my Paramount tube was thicker - maybe more like 3/32 or so? Anyway, if the OP absotively posilutely had to have a keyway, I'd have said machinist set this up in a milling machine. With a good rigid machine, you'd have no problem splitting 1/16 (0.0625). On Edit: Upon reflection, I suspect that a talented metalwork could do this easily with a mill or more time- and skill-intensively with a cape chisel. But either way, I'd put a sawed-off quill, tightened, to stiffen up the tube wall.

But wait! There's an anecdote! I was reading was reading about this on a professional machinist's site, and one of the old retired dreadnought machinist guys, who worked in Seattle Navy Yard machine shops all his life*, was describing an early experience. This would have been in the 60s probably. He was an apprentice, and he and a buddy were tasked with removing the shafts from about 20 pumps, so that the shafts could have worn pulley keyways re-machined. This also required removing the impellers, bearings, etc. A real hassle.. These were ~4" diameter shafts and the shaft/impeller weight was in the 1000s of pounds. He asked his boss if he could try to hand cut the new keyways in place, without removing the shafts and impellers. His boss said "give it a try, but cut them undersize first, and let me inspect". Apparently, the machinist did a good enough job, because he was asked to cut 20 keyways. Took about a day apiece IIRC, which was about a week less than removing the shaft, the impellers, and so forth. On Edit: Thinking about this, I realized that the expert doing this work was dealing with a very rigid shaft. Hence the suggestion to put a sawed off quill in the tube before doing any milling or hand-chiseling.

He did the job with a ruler, keyway attachments (which allow you to ensure that your ruler is aligned with the shaft axis when you lay the ruler on the shaft), layout dye, scribers, and the aforementioned cape chisel. Back when guys would try stuff like this - and succeed.



*The same guy now teaches surface scraping (a machine tool technique to generate extremely flat metal surfaces - it's done by hand!). So he's definitely in a different league that most people in terms of manual skill and experience.

WizardOfBoz

These are good points. For most sizes of threads, you can buy chasing dies (typically hex shaped) or cutting dies (typically round). Industrially, most threads on bolts are roll-formed, not cut, but as Dan has pointed out, the steer tube wall thickness are thin. This precludes roll-formed threads on steer tubes. The likely industrial process likely involves a geometric die head. This is a big cylinder of steel (for steer tubes, probably about 4 inches in diameter) that has a mechanism to hold 4 thread cutting plates very rigidly. It works like a die. Held in the tailstock of a lathe, with the steer tube held in the the chuck. The die head advances into the rotating steer tube and cuts the threads (with plenty of lubricant an coolant, and with the proper "surface feet per minute" cutting speed. When the thread depth is proper, a lever on the die head is thrown and all of the cutting blades retract outward. The alternative process for cutting threads would be what's called "single pointing" where a single 60 degree cutting bit cuts the grooves as the lathe turns. This requires multiple passes, and the bit must be "clocked" properly with the tube each time. Quite time consuming and expensive.

The main point is that 4130 is easily threaded with the proper tools, machines, coolants, and lubricants. But in an assembled fork, there are difficulties with geometry (The fork blades make the thing hard to chuck in a lathe!), with the steer tube (its being so thin makes it flexible which makes threading a bear), and with available tools (most chasing dies are not of the quality level, nor do the have the right geometry for cutting new threads.

I'm more of the obsessive-compulsive type when dealing with mechanisms. "If the original mfr wanted a keyway there, then there should be a keyway there". Besides having more experience with forks, Andy has a much more reasonable and healthy approach to the problem. A washer without a key should work fine - as is proven by its use in a lot of great bikes.

Dan Burkhart 

You speak the truth, as usual.
I have more success extending the threads if I don't rush the job.
Thin wall material will heat very rapidly during any process of forming or cutting, and even when liberally oiled, that heat can cause the tube to expand and the die to cut deeper than it should, making for a very rough job, and it's murder on the tool.
It could take me all day to extend the threads 20 mm, but I do it in very small increments letting everything cool completely in between.
It does not mean my time is not productive. I will have it all set up in my fork vise while I am working on other tasks, advancing the die maybe one complete rotation whenever I walk by it.1/4 turn advance, half a turn back to clear the chips.
This results in nice clean threads, and preserves the die.

AeroGut

If the only reason you want the key way is for the canti housing stop, one option is to use a fork-mounted housing stop. Fairly common on cyclocross bikes. Many argue that brake performance is even improved.