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Adding threads to fork?

Old 01-09-22, 05:29 PM
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Mr. Spadoni 
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Adding threads to fork?

In stowing away the decorations from what was not the most epic holiday celebration in the History of the Spadoni’s, due to weather and sick kids, I came across several sets of forks. Where they came from is a mystery, but quick inspection shows they have steerers too long for any of my frames and I do have a couple frames that need forks.
so here’s the question: how hard is it to add threads to a steerer tube? Does cutting new threads as opposed to just chasing threads mean the die will need to be resharpened and so it will be cost prohibitive to have it done at a shop? Yes, I understand I will have to trim the steerer when it’s done, but for that, I have the right tool.
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Old 01-09-22, 05:38 PM
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-----

all that is required is the correct die, die stock with correct guide and some cutting oil

guide fit important so the the threads cut do not "woggle"

work slowly and flood frequently with cutting oil

"robert will be thine uncle"

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Old 01-09-22, 05:43 PM
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Originally Posted by Mr. Spadoni View Post
In stowing away the decorations from what was not the most epic holiday celebration in the History of the Spadoni’s, due to weather and sick kids, I came across several sets of forks. Where they came from is a mystery, but quick inspection shows they have steerers too long for any of my frames and I do have a couple frames that need forks.
so here’s the question: how hard is it to add threads to a steerer tube? Does cutting new threads as opposed to just chasing threads mean the die will need to be resharpened and so it will be cost prohibitive to have it done at a shop? Yes, I understand I will have to trim the steerer when it’s done, but for that, I have the right tool.
I've had threads cut further down on a 1" threaded fork. You'll need to find a shop that has the tool, but it's not hard at all. You may have to call around to find a shop that is equipped to do that.
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Old 01-09-22, 05:56 PM
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I've done it. You don't need the park tool. All you need is a cheap 1" x 24tpi die. I got mine on evilbay, I think it was $13 for the die and another $15 for a die stock (die handle). There was no guide, but I felt it wasn't necessary, as long as you're starting from established pre-existing threads.

Here's one!
https://www.ebay.com/itm/185145040888

Many forks' threads are a little oversized compared to 1-28 UNS. Your die may take off some material from the existing threads. It's OK. If your die is the split kind (nicer) and has an adjustable screw, you can expand it a bit to stop this happening so much. Mine did not, and it was fine. Maybe I will cut a slit in it with my grinder for next time.

Yes, the park tool's better. But you're not doing this every day. So don't worry, be happy! It was worth the $35ish in tools, not to have to bug a bike shop about this. They are more interested in selling rich people ebikes anyway, and that's fine.
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Old 01-09-22, 08:00 PM
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It's worth mentioning the risk though. Sometimes the die will make nice-looking threads all the way down, but then when retracting, it rips the threads out by the root.

I have seen this happen only a few times but it was not easily explained; for instance the chips were cleared out and there was plenty of oil. Hard to make generalizations from such a small sample size, but it seems to be more likely if you're adding a lot of threads, say more than a cm or two. Much safer when adding just a few.

Bottom line is, think hard before doing it on an especially valuable fork. The conservative thing to do is sell the too-long fork to a tall person, and go find yourself a shorter one.

Another mostly-unrelated point: don't cut threads into a chrome-plated steerer, that dulls the tool faster. Better to sand off the chrome. I use "emery cloth" strip, a.k.a. "shop roll" or "utility roll" (names you may find it sold under). Good stuff to have around for a home-handyman. Usually coarse is fine, say 60 or 80 grit, but I also keep 200 and 400 grit around 'cuz I'm fancy. Just make sure to get all abrasive dust off the steerer before oiling it up for thread cutting.

Oh yeah one more: Maybe you don't need more threads, if you'd consider a less-thread headset. Kinda like threadless only you do use the threads, just for the top nut. Use the upper headset race from a threadless headset (well you can use the lower race too but it doesnt matter), then add spacers as needed, and a threaded top nut. You need some way to lock the adjustment; I do that with two thin nuts jammed against each other. Here are a couple of examples, rather extreme in the amount of spacers (these were on indoor trainer bikes). But depending on your fork size, you might not need any spacers at all. These forks both have less than an inch of threads, more like 15-20 mm.




The second one above uses an FSA Orbit headset, which seems pretty great for not too much money. The first one uses a Chris King, great but $$$.

That thin jam nut with the notches for a C-spanner came on low- and medium-grade Japanese headsets in the '70s and '80s. Might be a little hard to find nowadays. But there are other ways, such as removing the top lip from a regular nut (aluminum best so it won't rust where you trimmed it). Here's one done that way:



There are also one-nut solutions that lock in place, such as the Gorilla Headlock, or the Growler Headlock from Wheels Manufacturing.

Advantages of this less-thread idea include safer/stronger, no chance of the quill stem expander tightening in the threaded portion. Steerers breaking in the threaded portion is not exactly a common problem, but the stakes are high — it can definitly cause a crash, and you won't see the crack growing until it's too late. Also it's conservative in the sense that you can still put the fork back on the larger frame it was made for.

Good luck, however you choose to do it. Keep us posted!

Mark B
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Old 01-10-22, 06:02 AM
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Here's a pic of me doing a Guerciotti fork with the Park tool. I had just finished adding about 1 1/2" of threads. It went easier than I thought it would and came out great. But, it took a lot more muscle than I thought it would.
Plenty of cutting oil and going slowly was the trick. I backed the cutter off every half turn or so.


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Old 01-10-22, 07:38 AM
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One thing I'd be leery of on the cheap Ebay dies is die material. Often these will be carbon steel rather than tool or high speed steel, which is fine for chasing threads, but cutting new not so much.
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Old 01-10-22, 10:10 AM
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I picked up a VAR 40B a few years ago....$20.... when a nearby shop was closing. I have used it successfully to add threads. As others have suggested: stay away / remove chrome, go slowly, examine the new threads frequently as you proceed. My LBS calls me from time to time to borrow it.

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Old 01-10-22, 10:17 AM
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Originally Posted by bulgie View Post
It's worth mentioning the risk though. Sometimes the die will make nice-looking threads all the way down, but then when retracting, it rips the threads out by the root.

I have seen this happen only a few times but it was not easily explained; for instance the chips were cleared out and there was plenty of oil. Hard to make generalizations from such a small sample size, but it seems to be more likely if you're adding a lot of threads, say more than a cm or two. Much safer when adding just a few.
I've had this happen as well. In addition, I've threaded a couple that, for some reason was not centered, so the threads on one side were very deep, and barely cutting on the other. I've lost faithin my cheapie thread cutter as a result. I'll be shopping for a one with a guide sometime this year.

I've been mostly successful with it in the past, but ruining a steerer on a fork is catastrophic.

Would love to hear from @Doug Fattic on this as well for a third opinion.
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Old 01-10-22, 10:29 AM
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Ok, I will give cutting threads a try. I have a number of forks so messing up one won’t sideline the project. None are chrome, none are so special that damage will cause gnashing of teeth.

one question for scarlson…..understand the 24tpi, that matches with what Park sells. But what’s the 28 UNS you mention below the evilbay link? Pitch?
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Old 01-10-22, 11:04 AM
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Originally Posted by gugie View Post
I've had this happen as well. In addition, I've threaded a couple that, for some reason was not centered, so the threads on one side were very deep, and barely cutting on the other. I've lost faithin my cheapie thread cutter as a result. I'll be shopping for a one with a guide sometime this year.

I've been mostly successful with it in the past, but ruining a steerer on a fork is catastrophic.

Would love to hear from @Doug Fattic on this as well for a third opinion.
@gugie .....I should have mentioned the guide. My VAR 40B came to me without a guide. A few months ago, my LBS wanted to thread a fork that had no threads to get it started. 'Concerned about getting die started straight....and staying straight....I machined a guide with an ID that barely slid over the 1" steerer. Clearance was on the order of .001" on diameter and it did the job. Absent the guide, it is easy for me to visualize the experience you had where the threads were deeper on one side than the other.

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Old 01-10-22, 11:19 AM
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Here in my city in Brazil I didn't find any bike shop that had the tool to make the thread. I solved the problem the same way you did, using some spacers.
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Old 01-10-22, 11:45 AM
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I'll support what Bulgie said about being cautious. It is easy to mess up threads trying to add some more. Problems start with a die that looks okay but has a chip on it somewhere that can be disastrous on threads. Back when I started framebuilding/painting more than 40 years ago I mangled some threads trying to add new ones and that experience has made me very cautious ever since. Another problem can be that the chip from the steerer as the new tread is being cut, can get stuck in the die and when the tool is reversing to take it off, that chip can take chunks out of the thread.

What I do now (to prevent a repeat of the traumatic experience of my youth) is to fully back off the die every 1/3rd of a turn or so. I turn it far enough that it breaks off the new chip. I use plenty of cutting oil. I clean out the new chips in the die frequently with compressed air. Of course this blows out some of the oil too. I don't mind because I don't want to damage the treads that might involve a lot more work.

I've had a lot of steerer thread cutting dies in my career. English ones, Var, Park, Campy. They can get damaged pretty easily with aggressive handling. What happens is that a little corner on the die can break off making either cutting or backing out more troublesome.
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Old 01-10-22, 02:04 PM
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Exactly right, Doug Fattic! Problems start with a bad die, and sometimes it isn't obvious that the die is bad when you inspect it. To me, that's another reason to go for a new, cheap die instead of a used one or asking a shop to do it - unless you're confident that they know more about what they're doing than you do. Much of this talk about how Chinese metal is bad is not true anymore. It may have been true ten years ago. But since then, I've used all manner of tooling, and I can't make generalizations either way anymore. Go slow, back up to clear your chip, as Doug says. You will be fine. After some work, you'll get a feel for things, like when to back up and clear your chip, when it needs oil, that sort of thing. Sometimes if things feel a certain way, I won't back up at all. Some chip load can be good for a tool when cutting, depending on material and the tool geometry. Sometimes I find myself backing up all the time. If you want to practice, get yourself some 1/4" steel rod (not stainless) and a 1/4-28 die (fine threads will be good practice for a headtube) and try it out.

I guess I forget that people don't have a background in this stuff. I haven't had any formal training, aside from a 40-hour machine shop course that was a bit of a joke. I mostly just copied my dad and other old guys who showed me a lot of this stuff when I was a youngster, so I forget that this stuff is not self-evident.

If you feel like a primer in how to thread with a die would be useful, here's a video about it. In it, he checks squareness, backs up, etc. Some people may have different opinions on how to do it, but it looked fine to me.

There are tons of videos out there, so youtube is your friend if you're interested in learning the finer points. Each video will stress something different, and they'll disagree on some stuff, which is fun. Lots of old guys there like the ones who taught me.
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Old 01-10-22, 02:31 PM
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the best results I ever got was when a guy who used to post here (Frank B. in New York) cut extra threads on a CIOCC fork using his lathe and a thread tool, that turned out perfectly tho I was required to remove all the chrome plating before sending it (used emery cloth).
IMO this is the best way to cut them BUT Frank does not have the set up anymore and the only guy in my area who MIGHT have done the same (using a lathe), namely Bernie Mikkelsen, will not do it either.

It would be an enormous benefit if somebody with machining experience and a lathe would offer this service, the cost of a thread-cutting tool is far less than for a good quality die and in the hands of somebody who can use it the lathe does a much more reliable job with less wear and tear (again, IMO).
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Old 01-10-22, 03:23 PM
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@Doug Fattic, that is pretty much exactly how I was taught to cut threads in my high school machine shop class. Gotta break that fresh bite off.
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Old 01-10-22, 03:24 PM
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Originally Posted by unworthy1 View Post
the best results I ever got was when a guy who used to post here (Frank B. in New York) cut extra threads on a CIOCC fork using his lathe and a thread tool, that turned out perfectly tho I was required to remove all the chrome plating before sending it (used emery cloth).
IMO this is the best way to cut them BUT Frank does not have the set up anymore and the only guy in my area who MIGHT have done the same (using a lathe), namely Bernie Mikkelsen, will not do it either.

It would be an enormous benefit if somebody with machining experience and a lathe would offer this service, the cost of a thread-cutting tool is far less than for a good quality die and in the hands of somebody who can use it the lathe does a much more reliable job with less wear and tear (again, IMO).
Oh for sure! I totally agree. I often prefer cutting threads that with a single point on the lathe, especially large diameter fine threads. You can get mighty fine quality this way, and you do more thinking and less working, which I like. With a good setup I would do it, but fixturing an assembled fork in a lathe is a bit of a pain and the lathe bed needs to be pretty long. A further difficulty is putting a centering cone in the bottom end of the steerer, with the fork blades in there. And then they're spinning around begging to tangle your shirt sleeve or grab your hand or whatever, so it's somewhat dangerous. I can think of a couple ways to do it involving some weird faceplate or a long tailstock extension and turning between centers. Fixturing's a bit of a pain no matter how I think about it, though, so I bought a cheap die. And it was fine quality. As good as any die I've ever used.

A bit nerdy here, but 24tpi is super easy to do on almost any American lathe because it factors into a lot of 2s and one 3, so most lead screws (often 8tpi or some other power of 2) will pick up the thread in multiple spots when doing multiple passes.
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Old 01-10-22, 04:07 PM
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Originally Posted by unworthy1 View Post
the best results I ever got was when a guy who used to post here (Frank B. in New York) cut extra threads on a CIOCC fork using his lathe and a thread tool, that turned out perfectly tho I was required to remove all the chrome plating before sending it (used emery cloth).
IMO this is the best way to cut them BUT Frank does not have the set up anymore and the only guy in my area who MIGHT have done the same (using a lathe), namely Bernie Mikkelsen, will not do it either.

It would be an enormous benefit if somebody with machining experience and a lathe would offer this service, the cost of a thread-cutting tool is far less than for a good quality die and in the hands of somebody who can use it the lathe does a much more reliable job with less wear and tear (again, IMO).
Agreed doing it on a lathe is Best Practice. It's more time consuming and requires a big expensive lathe, so it's bound to be more expensive than hand-threading with a die. Unless you get a bro-buddy deal, like provide a 6-pack to have a hobbyist friend do it. There are probably things that can go wrong, but they always came out top notch for me, the half-dozen times I did it, so I consider it safer than the die method.

unworthy1 , when you say a threading tool, do you mean a die? I'm talking about doing it with a single-point tool. Though there are carbide inserts that actually have more than one thread-form cut into them, I'd still classify those as "single point", as opposed to a die.

Another method I've heard of, but never seen in use, is a three-piece expandable die that's used in a threading machine (can be a lathe or a dedicated threading machine). They cut threads just like a die but then they open up to let the part out, so there's no backing up. Tesch used to have one, and he threaded all his forks, so that he only had to make one size of fork in batches, cutting/threading them to length as needed for different frame sizes. He also claimed (conveniently?) that all race bikes should have the same rake, regardless of head tube angle, a dubious claim IMHO. He used a very short-offset rake and people loved the "track bike" style handling. He was so efficient at steerer threading, including turnaround time, that the shop I was at sent forks to him when they needed more threads. This was a shop that had a lathe and a full Campy toolkit including their excellent die with piloted holder. But after you've ruined one expensive fork with your 0.2 kilodollar Campy tool, you're twice shy. And our clapped-out pre-WWII lathe was not great for the job either. Other than round-trip shipping time, sending them to Tesch was painless. I only bring this up in case someone wants to research those expandable dies and see if there's somone in your city who has one.

My "new" (1982) Taiwanese lathe is still disassembled for cleaning and rejuvenation, but I expect it will make good threads once I get it running. I'm actually working on it today so I hope that'll be soon, then maybe I'll be able to offer steerrer threading service. I also have a Campy die/holder in good shape, but I'd be nervous using it on a customer's fork, for more than a few threads. I think single-point on the lathe will be my go-to method. I've also heard some people recommend single-point cutting the thread to 80 or 90% depth and finishing with a die. A sharp and clean die can easily cut that little bit extra, I think probably very safely (touch wood!), so I might try it. Measuring the thread depth with the fork still in the lathe is tricky, involving a micrometer and three thin wires placed in the threads, and you can't take it out to try it with a headset and then put it back in the lathe if the threads aren't deep enough. Well you can put it back, but you lose precision. Anyway I've said too much, this level of detail is interesting to maybe one person out there (if I'm lucky), so it's time to sign off.

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Old 01-10-22, 04:28 PM
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Originally Posted by bulgie View Post
Anyway I've said too much, this level of detail is interesting to maybe one person out there (if I'm lucky), so it's time to sign off.
Mark B
Naw, Sam and I read it with intense interest!
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Old 01-10-22, 05:21 PM
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Originally Posted by scarlson View Post
Exactly right, Doug Fattic!snip

I guess I forget that people don't have a background in this stuff. I haven't had any formal training, aside from a 40-hour machine shop course that was a bit of a joke. I mostly just copied my dad and other old guys who showed me a lot of this stuff when I was a youngster, so I forget that this stuff is not self-evident.

.
This is so true, a lot of what I know I learned by watching old dudes (which according to my son I am one now) and then just trying it out and just building things. BITD guys at Coast Guard Mechanics A school's had a first assignment of making a nut and bold from steel stock and using hand tools only. they all learned a lot both about metal working and new cuss words (that was not me...was on the same location for A school in marine science) I think this it a ton more difficult for current generation
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Old 01-10-22, 07:45 PM
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Originally Posted by scarlson View Post
Oh for sure! I totally agree. I often prefer cutting threads that with a single point on the lathe, especially large diameter fine threads. You can get mighty fine quality this way, and you do more thinking and less working, which I like. With a good setup I would do it, but fixturing an assembled fork in a lathe is a bit of a pain and the lathe bed needs to be pretty long. A further difficulty is putting a centering cone in the bottom end of the steerer, with the fork blades in there. And then they're spinning around begging to tangle your shirt sleeve or grab your hand or whatever, so it's somewhat dangerous. I can think of a couple ways to do it involving some weird faceplate or a long tailstock extension and turning between centers. Fixturing's a bit of a pain no matter how I think about it, though, so I bought a cheap die. And it was fine quality. As good as any die I've ever used.

A bit nerdy here, but 24tpi is super easy to do on almost any American lathe because it factors into a lot of 2s and one 3, so most lead screws (often 8tpi or some other power of 2) will pick up the thread in multiple spots when doing multiple passes.
Ach I didn't see your post until after I wrote mine (I guess I'm that slow...) Needless to say your post was right up my alley, not too nerdy at all. (Thank you Sir may I have another?)

About the lathe needing to be long: not necessarily. I was able to use a steady-rest to hold the bottom of the steerer (right end of the steerer when laid out horizontally). Or was it a follow rest? So many years ago. I do remember mounting a follow to the right side of the saddle for some odd setup (left side is normal). But I think that was for something else, I think I used a steady for threading steerers. Either way, then you can take the tailstock off completely, if the bed is too short to leave it on.

On a short steerers, the steady could get in the way of the tool post, so then you need a center coming off the tailstock. But with so many crowns having some odd curve at the bottom edge, a cone might not fit and you'd need a semi-custom-sized cylindrical plug to grab the ID of the steerer. Though a slight taper could help, you can't use a normal 60° lathe center, it would only touch in two places on the curve. Adding to the difficulty, on most smaller lathes like mine, the ram on the tailstock isn't long enough to reach the crown while clearing the dropouts, so you need to make a long extension on whatever center you're using. I've done a steerer that way too. I made my extended center with a straight shank to hold in a Jacobs chuck, not as precise as a center with a Morse taper, but good enough — it's far enough away from the cut that it doesn't matter much.

OK NOW we're getting nerdy!

For the top of the steerer (left end horizontally), I used an internally expanding 7/8" collet. Ooh I should make one in 22.0 to do French steerers. My lathe is inch-based but it can make metric threads by taking out some gears and replacing them. By happy coincidence the 1.0 mm thread is made with the same gears as inch threads, I just have to flip one of them over so it runs on the 120t side of the 127/120 combo gear. Those guys were thinking! 24 tpi × 127 ÷ 120 = 25.4 tpi exactly.

Mark B
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Old 01-10-22, 07:56 PM
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I have a fork that I needed another ~1/2" of threading on. I took it to a local frame builder (Dale Saso) to align the fork and add the threads. He did it on his lathe, it turned out great
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Old 01-10-22, 09:52 PM
  #23  
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Originally Posted by bulgie View Post
unworthy1 , when you say a threading tool, do you mean a die? I'm talking about doing it with a single-point tool. Though there are carbide inserts that actually have more than one thread-form cut into them, I'd still classify those as "single point", as opposed to a die.


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I am not a machinist so I mis-use the nomenclature, but I was talking about a "single-point tool", not a die (adjustable or not).
I took a fork years ago to a local shop (it's long gone but used to be on Fillmore St. in SF) and they used their name brand die on my fork to extend threading an inch or so.
It was a disaster: my fork was trashed as was their die (which they blamed me for, but I had never touched it!)
After which I understood that LBS were very reluctant to take on this "commonplace job" ...and I came to have the highest regard for the lathe operators who could cut threads without any "drama"...may they RIP!
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Old 01-11-22, 12:03 AM
  #24  
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Originally Posted by unworthy1 View Post
I am not a machinist so I mis-use the nomenclature, <snip>
No, you used the right words, sorry if I sounded like I was correcting you. You said it right, I was just confirming that we were on the same page, 'cuz some people use words differently.

Today I finished cleaning the grime off the last parts I took off the lathe, which is everything but the main chunk: the bed with the headstock attached. I have to get that down into the basement where the lathe will live before I can reassemble it. I think in this bare-bones config it's about 300 lb, so I will have to winch it down, should be exciting (hopefully not too exciting). Then LOTS of reassembly and adjustment, leveling, dialing in spindle bearing preload etc., but hopefully I'll be able to thread a steerer by next week! I'm excited.

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Old 01-11-22, 12:20 PM
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Originally Posted by bulgie View Post
No, you used the right words, sorry if I sounded like I was correcting you. You said it right, I was just confirming that we were on the same page, 'cuz some people use words differently.

Today I finished cleaning the grime off the last parts I took off the lathe, which is everything but the main chunk: the bed with the headstock attached. I have to get that down into the basement where the lathe will live before I can reassemble it. I think in this bare-bones config it's about 300 lb, so I will have to winch it down, should be exciting (hopefully not too exciting). Then LOTS of reassembly and adjustment, leveling, dialing in spindle bearing preload etc., but hopefully I'll be able to thread a steerer by next week! I'm excited.

Mark B
Thanks for your kind words, and more importantly: going forward with your "lathe project"!
You're not the only one excited: if this works out you'll be filing a major and crucial need for us C&V fans (IMO) and deserve maximum kudos for your effort!
Cheers to a Happy New Year for many who of us have (and WILL have) frame&fork mis-matches.
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