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Old 05-11-08, 10:34 AM   #1
Banzai
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Cutting a threaded steerer

Does anyone here know how to cut and re-thread a 1" threaded steerer? Is this feasible or advisable?

I'm having some fork issues and I may be forced to get a new one, but I'm having trouble finding one where all the measurements match correctly. The closest so far doesn't have a steerer short enough.

Thoughts?
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Old 05-11-08, 10:39 AM   #2
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Have the shop extend the existing thread (if it needs it), then cut the steerer to desired length....in that order. You might have a hard time finding a shop willing do the threading job.

Last edited by roadfix; 05-11-08 at 12:26 PM.
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Old 05-11-08, 10:50 AM   #3
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Originally Posted by Banzai View Post
Does anyone here know how to cut and re-thread a 1" threaded steerer? Is this feasible or advisable?

I'm having some fork issues and I may be forced to get a new one, but I'm having trouble finding one where all the measurements match correctly. The closest so far doesn't have a steerer short enough.

Thoughts?
You should be able to cut a fork at home.

Find a steel topnut to fit the fork, thread it on and use it as a cutting guide. Once you've filed the cut smooth, give the threads a slight bevel on the edge. Removing the nut should clean up the threads.

Just be sure to check if the fork has enough threads for your headtube length and headset stack height. Pre-assembling it is a good idea before committing to cutting.
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Old 05-11-08, 11:09 AM   #4
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Look for an old timey bike shop, they should have the die to cut the threads. Then, follow word's advice on cutting. Measure twice, cut once.
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Old 05-11-08, 11:30 AM   #5
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How far off is it?

I've got dies for extensing steerer threads, but I wouldn't want to have to add too many - it's pretty hard work. I've got a thread-on saw guide for cutting the fork too.

If your fork is just a few millimeters long it's common to add a spacer between the upper race and the locknut.
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Old 05-11-08, 12:16 PM   #6
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You should be able to cut a fork at home.

Find a steel topnut to fit the fork, thread it on and use it as a cutting guide. Once you've filed the cut smooth, give the threads a slight bevel on the edge. Removing the nut should clean up the threads.

Just be sure to check if the fork has enough threads for your headtube length and headset stack height. Pre-assembling it is a good idea before committing to cutting.
+1 Good instructions, Wordbiker!
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Old 05-11-08, 12:58 PM   #7
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With the fork I'm looking at I'd need to saw off 4cm. Which would leave me with 1cm of threads. So...I would need to cut new threads down the steerer tube.

This all started with an old bike I'd been restoring. At the time I didn't have calipers, so when I took the frame to have the new headset installed I asked them to make certain it wasn't JIS. The shop installed an ISO headset, and said it was fine.

When I took the bike out for the first ride, the steering didn't feel right. And there was a bit of play to the steering column. So I take it home and drop the fork out.

No crown race.

Apparently the shop wrench pressed the cups in, then tried to install the crown race to find that it (obviously) wasn't close to fitting. His solution for that problem was to simply not install a crown race and hope I wouldn't notice.

Now I'm trying to find a place that can mill the fork crown down to 26.4 mm, but if it gets screwed up I'm going to need a new fork. The forks I've found that match most of the dimensions don't have short enough steerer tubes. (I need 120mm.)

I can't find a bike shop yet that has the tool for milling the fork crown. I was wondering then if it's easier to buy a fork, cut the steerer to size, and cut new threads.

This is turning into a huge headache. I'm reasonably certain I can't extract the headset and install a JIS one, since it's very likely the headtube has stretched and will no longer fit JIS cups.

I'm concerned as well that stretching the headtube may have weakened the brazing under the lugs.
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Old 05-12-08, 10:47 AM   #8
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Milling a JIS crown race to ISO diameter is quite straight forward and should be an easy job for any competent LBS.

Apparently your (former, I hope) LBS doesn't deserve the title "competent". Leave off the crown race and hope the customer doesn't notice??????
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Old 05-12-08, 10:50 AM   #9
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Look for an old timey bike shop, they should have the die to cut the threads. Then, follow word's advice on cutting. Measure twice, cut once.
Amen! The only problem that one may have is trying to extend the threads on a chromed fork. If you are looking for a fork to buy and modify make sure that the steerer tube is not chromed in the area you need the threads otherwise you will ruin the cutting tools...been there done that!

BTW: what is the material of construction for the bike. I am confused by the comments in the post above regarding "Stretching the headtube" and no crown race...the bike mechanic who did your work owes you an explaination and possibly some compensation for the work done improperly. San Rensho is right a good old time bike shop could do the job of cutting the fork down and extending the threads very easily. Good Luck.

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Old 05-12-08, 08:24 PM   #10
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It's a steel frame. Squeezing the ISO cups in there would have, I'm certain, stretched the headtube ever so slightly...likely making fitting JIS cups impossible.

What's important is that both of my possibilities are, well, possible. Step one is to get the fork crown milled. However, I've only found one shop that says they even have the tools, and they sound doubtful about their ability. If the fork gets screwed up in the process I will have to buy another one. I've found two with the measurements I need, save for the too long steerer.

What a disaster this is shaping up into.

I like the owner of that bike shop, and if he had done the work I don't believe this would have happened. It was one of his young wrenches...the owner was very upset. He's offered to mill the crown, but he doesn't have the actual tool to do so, and I don't think something like this can be trusted to a Dremel or something similar...not if I still want a good interference fit.

The owner basically sells me everything at 5% over cost, because we get along so well. It's a pity this incident had to happen.
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Old 05-12-08, 08:50 PM   #11
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Amen! The only problem that one may have is trying to extend the threads on a chromed fork. If you are looking for a fork to buy and modify make sure that the steerer tube is not chromed in the area you need the threads otherwise you will ruin the cutting tools...been there done that!
True, sort of. Chrome is much, much harder than steel and so it will destroy a threader very quickly. But, if the tube is chrome plated, it is not hard to remove it first. A brass-wire wheel will work very quickly for this.

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Old 05-12-08, 09:06 PM   #12
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Does anyone here know how to cut and re-thread a 1" threaded steerer? Is this feasible or advisable?
Although there are other ways of getting jobs done, I am a big proponent of using the tools that are specifically made for the job. In this case, this is what you want (a 1" threaded saw guide):

http://www.parktool.com/products/det...49&item=SG%2D1

and, this page tells you exactly how to do the job:

http://www.parktool.com/repair/readhowto.asp?id=115

-- just make sure and scroll down to the section for "Threaded Type Forks".
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