Lathe Question

[Jake Rosenfeld]

Mike what an awesome and complete reply. Thanks for taking the time to do that.
I feel like we were just coming at it from completely opposite ends of the issue. Your concern was that someone with little to no knowledge of machine safety let alone lathe operation would see photos and go after that task like it was a matter of course and what the lathe manufacturer had in mind all along.
My stance was that with proper care, caution and cognizance that it was an ok project for an experienced hand to accomplish.
I have my own opinion of the task but still completely agree with your POV 100%. Really I do.


Question for Jonathan;

Of the machinists you talked to about turning forks, did you actually put one in their hands to hold?
I say give them two forks, one to heft and try to tear apart with their hands so they can judge the structure and one to turn.
I'll bet you'd get a different answer.......

Not picking at you but often times guys that work in the physical world aren't the most solid of theorists.

food for thought (literally);

[Jonathan]

Question for Jonathan;

Of the machinists you talked to about turning forks, did you actually put one in their hands to hold?
I say give them two forks, one to heft and try to tear apart with their hands so they can judge the structure and one to turn.
I'll bet you'd get a different answer.......

Not picking at you but often times guys that work in the physical world aren't the most solid of theorists.

Both are cyclists and both have built frames in the long ago past. I think it has to do more with a formal education maybe?

Theorists vs practice? They machine stuff for our space and power industry and they own this little business.

http://www.victorybicycles.com/

[Jake Rosenfeld]

Both are cyclists and both have built frames in the long ago past. I think it has to do more with a formal education maybe?

Theorists vs practice? They machine stuff for our space and power industry and they own this little business.

Victory Bicycles

thanks Jonathan, I wasn't knocking anyone or their abilities. Just wondering how you asked that's all. Wondering if it was a case of them telling you 'no, because we don't think you are qualified to do it and we dont want you to try' or 'no because I can't imagine a bicycle fork would hold up to that'

You've cleared that up for me.

[Mike Mcdermid]

Ah yes. That's not how I do it so it didn't come to mind.

Are there pro machinists who would have no problem turning a complete fork/unbalance object like Mike refers to it? The two I've talked to have said no way and they had big lathes.

Jonathan you said it yourself they have big lathes

[Mike Mcdermid]

Mike what an awesome and complete reply. Thanks for taking the time to do that.
I feel like we were just coming at it from completely opposite ends of the issue. Your concern was that someone with little to no knowledge of machine safety let alone lathe operation would see photos and go after that task like it was a matter of course and what the lathe manufacturer had in mind all along.
My stance was that with proper care, caution and cognizance that it was an ok project for an experienced hand to accomplish.
I have my own opinion of the task but still completely agree with your POV 100%. Really I do.


Question for Jonathan;

Of the machinists you talked to about turning forks, did you actually put one in their hands to hold?
I say give them two forks, one to heft and try to tear apart with their hands so they can judge the structure and one to turn.
I'll bet you'd get a different answer.......

Not picking at you but often times guys that work in the physical world aren't the most solid of theorists.

food for thought (literally);

I'm not. Without sin I have done some stupid in hindsight things with rubber heat and pressure which I would put into the R&D research and dumbest catagory

[Jonathan]

thanks Jonathan, I wasn't knocking anyone or their abilities. Just wondering how you asked that's all. Wondering if it was a case of them telling you 'no, because we don't think you are qualified to do it and we dont want you to try' or 'no because I can't imagine a bicycle fork would hold up to that'

You've cleared that up for me.

No worries,
I asked them 3-4 years ago in the context of "this is what I want to do, what do you think?" They misunderstood me thinking I wanted to turn a complete fork. I don't braze forks like that so I was really just asking about steerer and fork crown turning and they seemed ok with that. Fwiw, I still don't own a lathe with the capacity I'm looking for. When I told my machinist friend about the scheme I had cooked up for reaming head tubes on my mill she shook her head too. I responded that it was just a vertical set up like used on a lathe horizontally not unlike the fixture Marchetti sells. She couldn't believe people would ream a headtube on a lathe either. Holding the frame while the cutter advanced was just not something she would admit was acceptable in a professional machine shop even though 10s of thousands of frames have been reamed that way. They ream things with machines for accuracy and not having the part clamped down is a major problem in their minds for accuracy and safety. The attitude of "this is just a bicycle" didn't fly. That was my original point in all of this that i took interest in. Some of the things we do and get away with are frowned upon by folks at the pointy end of the machine world and we scoff when told about it like noobs do when given advice they don't want to hear.

[Mike Mcdermid]

No worries,
I asked them 3-4 years ago in the context of "this is what I want to do, what do you think?" They misunderstood me thinking I wanted to turn a complete fork. I don't braze forks like that so I was really just asking about steerer and fork crown turning and they seemed ok with that. Fwiw, I still don't own a lathe with the capacity I'm looking for. When I told my machinist friend about the scheme I had cooked up for reaming head tubes on my mill she shook her head too. I responded that it was just a vertical set up like used on a lathe horizontally not unlike the fixture Marchetti sells. She couldn't believe people would ream a headtube on a lathe either. Holding the frame while the cutter advanced was just not something she would admit was acceptable in a professional machine shop even though 10s of thousands of frames have been reamed that way. They ream things with machines for accuracy and not having the part clamped down is a major problem in their minds for accuracy and a precision safety. The attitude of "this is just a bicycle" didn't fly. That was my original point in all of this that i took interest in. Some of the things we do and get away with are frowned upon by folks at the pointy end of the machine world and we scoff when told about it like noobs do when given advice they don't want to hear.

A precision machinist is a temperamental beast if it's outside what they learned, fwiw I was also taught a reamer should float or you are running the risk of it becoming a single point boring tool

Ben cooper was right when he kind of pointed out just because someone says it's wrong doesn't mean it is especially when you do it. And prove it

[Jonathan]

Ben cooper was right when he kind of pointed out just because someone says it's wrong doesn't mean it is especially when you do it. And prove it

I can appreciate that.

[Jake Rosenfeld]

Vsalon; more happy endings per gigabyte than anywhere else on the web.

[bencooper]

Many years ago, I was at a bike show in York, standing around with a bunch of other exhibitors watching a wheelbuilding instruction video. Everyone agreed that the way the man in the video was doing it wasn't right, but no two people agreed on the right way...

[Jacques]

I think this is a good and valid point. We can probably all use a little reminder of such things now and then, and not everyone has the experience to know how to do something safely, even if it might seem obvious to others. I think, though, that its often how something is said, that raises a bit of ire, as opposed to the content of the message (*).

Dave

* NOTE: This is not in reference to any particular post or poster, its just an observation, and something that, unfortunately, seems to be common to many forums.....perhaps contributed to by the use of anonymous user names?

Hey Dave, since it was my comment which first lit things up here, I think I should respond. Though I realize my use of profanity might have contributed in arousing the ire of some, it really wasn't intended to antagonize, just an expression of alarm on my part. That said, I can't believe how sour some of the replies were simply for bringing up a safety concern, if only for those who'd come across such an image lest they give it a try.

For the record, I'm also a professional machinist which I didn't mention since I hoped to appeal to logic, rather than to whatever authority that title confers to me. (But if it means anything, Jonathan's unscientific survey is 3/3)

-Jacques

[Jonathan]

Vsalon; more happy endings per gigabyte than anywhere else on the web.

This thread is a winner. I've learned some stuff.

[Jacques]

Back of an envelope (literally) calculations - assuming 160rpm, an offset of 30mm (a bit more than half average fork rake), offset mass of 500g (a couple of fork blades), I get a force of 4N.

That's not very much at all.

That's true if you're simply spinning the fork in the air, but it becomes a lot more complicated when you apply a cutting tool to the workpiece. A dull cutting point, set too high, too low, wrong feed per rev or sloppy feed disengagement at the shoulder could all mean tens or hundreds of pounds applied radialy to the work, not to mention the cutting speed in this scenario is 10% of what it should be for carbide tooling.

The danger hides in the variables we're unaware of.

[bencooper]

True, but that would apply to any work, not just a fork.

[Alistair]

the cutting speed in this scenario is 10% of what it should be for carbide tooling.

Good point. For this job I ground up a left hand HSS cutting tool. I make it keener than I normally would for a regular turning tool, and I lap it in with a diamond bench stone. It wears faster than a regular turning tool, but it lets me run a low speed and take very light cuts.

I'm reminded of some threads on this subject from the old Bikelist.org message board, when someone would ask about what crown race seat cutter they should buy. The reply would often involve a well known pro builder saying that their crown race seat cutter was their Monarch/Hendy/Hardinge (etc.) lathe, and that they sold their VAR/Campy/Park cutting tool years ago, because they weren't using it anymore.

Off the top of my head, I can think of a half dozen pro's who turn whole forks in their lathe (I think some of them read here? Not sure of that though). I'm kind of surprised that they haven't chimed in on this subject.

Then again, maybe I'm not..

Alistair.

[Mike Mcdermid]

True, but that would apply to any work, not just a fork.

do you know what ive edited this just to read i cant be arsed any more

[Mike Mcdermid]

Good point. For this job I ground up a left hand HSS cutting tool. I make it keener than I normally would for a regular turning tool, and I lap it in with a diamond bench stone. It wears faster than a regular turning tool, but it lets me run a low speed and take very light cuts.

I'm reminded of some threads on this subject from the old Bikelist.org message board, when someone would ask about what crown race seat cutter they should buy. The reply would often involve a well known pro builder saying that their crown race seat cutter was their Monarch/Hendy/Hardinge (etc.) lathe, and that they sold their VAR/Campy/Park cutting tool years ago, because they weren't using it anymore.

Off the top of my head, I can think of a half dozen pro's who turn whole forks in their lathe (I think some of them read here? Not sure of that though). I'm kind of surprised that they haven't chimed in on this subject.

Then again, maybe I'm not..

Alistair.

your confusing a machinist with someone who has learned to machine stuff and build bikes? and with that i think its just better to leave this alone now an argument with condescending tone you just get dragged down to their level

[Mike Mcdermid]

double post....

[bencooper]

do you know what ive edited this just to read i cant be arsed any more

tl;dr: Machine tools are dangerous, don't be an idiot.

[Mike Mcdermid]

tl;dr: Machine tools are dangerous, don't be an idiot.

I werent having a dig at you Ben but seriously a lot of these high brow pro builders will dissapear up their own arse before they have an accident anyway. its no skin of my nose either way