fork crown seat cutting

[NBC]

hi all

what's the best crown cutting tool currently available ?

i've heard stories of some cutting under size seats, don't know if this was a bad cutter or improper usage

is it best to have them cut on a lathe ? even if this means going to an outside company to do this ?

thanks for your advice

nathan

[Rody]

The best tool is the one that you possess, are intimately familiar with, and provides consistent results.

For me, that tool is a lathe.

r

[Kumo Cycles]

The best tool is the one that you possess, are intimately familiar with, and provides consistent results.

For me, that tool is a lathe.

r

Wise words.

Would like to add that procuring a lathe was an event that changed my framebuilding practice.

Opens up a lot of options for facing tubes and lugs, making small fittings quickly and easily and I always use it for cutting crown races.

Especially after my Campy crown race cutter started eating steerer tubes...

[afwalker]

I bought the Cyclus crown race cutter 1" and 1 1/8", very nice tool. But, if it starts off center, it finishes off center. If there is any play between the steerer and the tool, it won't line up perfectly. I've cut some races off center until I learned to wrap tool wrap around the steerer. So now I just use a lathe to get close before I braze the blades, then use my Cyclus for final fit.
cheers
andy walker

[NBC]

thanks guys,

i don't really have the money to purchase a lathe, at least not one that is of sufficient capacity

i was thinking about a myford super 7, but tbh they're tiny, i'm not sure how it would be best to mount a steerer & crown, as i believe the spindle bore is significantly too small.

the one i'd been looking at would be a colchester student 1800, approx 8" swing over the cross slide, and a 40mm spindle bore, though the decent ones really start somewhere around £4000, and i'd need to have 3 phase wired too, at roughly £2000, just is a pill a little large to swallow !

i get the idea that the facer handle plays most of the part of getting a concentric and parallel face of the crown, so might it be feasible to have a handle manufactured that could use a currently manufactured cutter, but have tightly fitting bushes both top and bottom, to stay tightly centred on the steerer ?

just an idea, please tell me if i'm mistaken, or have different suggestions

all help is appreciated

thanks

nathan

[Andrew R Stewart]

My experiences of under cutting crown race seats have all been related to the amount I was trying to cut with the tool. Now I cut with a 27.0 cutter first then finish with a 26.4 cutter (of course for a 1" steerer). Since this stepped cutting process i have not had a problem. Andy.

[Doug Fattic]

My preference for a crown race cutter is the Park because it has a collet that tightens around the steerer so the cutter has to be perfectly centered around it. A big top nut takes up the slack so it can still move and not have any play. Like Andy, I start out with the JIS 27.0 (the old cheap size headset) and turn the cutter around and finish with the 26.4 (originally Campy size until it became the de-facto standard). I've never had any problems doing it this way and cut to the perfect size every time. I also have a Campy and Var and something else in my inventory somewhere. The Park would be my 1st choice again because of the collet feature. What I don't like about the Park is that it does not come with a spring and nut to keep the cutter moving forward while it is being turned. I use my Campy parts for that. If it is a threadless steerer, I hold the spring down with the Park cut-off tool that can tighten around the steerer.

What tooling and equipment one buys is very personal and will obviously change for each individual. A lathe would be way down my list of needed equipment. To start with doing fork crown races requires a big through hole that the more economical lathes do not have. So it is going to take some decent money and space to have a big enough lathe that in actuality preforms a very small percentage of framebuilding procedures. It is a luxury item that is never really needed. I'm glad I have my South Bend (which were made near where I live) and there are projects I do on it, but think many others things would take priority if I were to start again. For example, I use my vertical mill much more often (for like drilling and countersinking my fork brake hole). Of course, YMMV.

[Clockwork]

My preference for a crown race cutter is the Park because it has a collet that tightens around the steerer so the cutter has to be perfectly centered around it. A big top nut takes up the slack so it can still move and not have any play.

I have the same Park Tool cutter and am not as happy with it. As tight as I make the collet, the cutter can still rock back and forth.

-Joel

[bencooper]

I also found the trick was to do it on a lathe roughly, then finish off with the Park tool. So I braze steerer to crown, roughly cut in the lathe, braze in the blades and finish the forks, then do the final cutting with the Park.

Myfords are lovely, but you don't need that kind of thing - my roughing lathe is a Rollo Elf which I got for £300. Have a look at Lathes for some good second-hand old lathes.

[Jonathan]

I'd like to have a lathe big enough to do the job but since I don't I use a file to take off some material and then a campy crown race cutter. A beginner tip is to run a few layers of masking tape adjacent to the crown to keep the file from kissing the steerer. I've never had an issue doing it this way.

[Tristan]

i was thinking about a myford super 7, but tbh they're tiny, i'm not sure how it would be best to mount a steerer & crown, as i believe the spindle bore is significantly too small.

I've cut crown seats on my ML7 (not Super 7) and to be honest it's a real pain. The spindle bore is too small so you need to use a steady which leaves the work cantilevered out a long way.

I have seen a mount which clamps to the dropouts and is held by a live center - if I was doing a lot of forks on a small lathe I'd investigate this further.

[bencooper]

I use a bullnose live centre in the tailstock.

[Alistair]

thanks guys,

i don't really have the money to purchase a lathe, at least not one that is of sufficient capacity

i was thinking about a myford super 7, but tbh they're tiny, i'm not sure how it would be best to mount a steerer & crown, as i believe the spindle bore is significantly too small.

As some others have mentioned doing, I braze up a steerer/crown sub assembly and then turn the crown race close to size on the lathe. After brazing in the legs I use the VAR crown race cutter to get the crown race to final size.

I have a small 9" South Bend lathe (3/4" spindle bore) so I turn the steerer/crown sub assembly between centers using a drive dog and catch plate at the headstock end with a dead center in the spindle, and a bull nose live center in the tailstock.

I ground up a dedicated left hand HSS cutting tool with a slight radius on the nose (somewhere between 1/32" an 1/64") and get it nice and sharp by honing it on a diamond bench stone.

This gives a nice judder free cut with a good finish so that when it's time to do the final ream with the VAR tool everything goes nicely.

Alistair.

[Tristan]

I have a small 9" South Bend lathe (3/4" spindle bore) so I turn the steerer/crown sub assembly between centers using a drive dog and catch plate at the headstock end with a dead center in the spindle, and a bull nose live center in the tailstock.
.

Have you got a photo of your catch plate Alistair?

[Alistair]

Have you got a photo of your catch plate Alistair?

This pic shows it ok, not great though. It's just a plate with a slot in it for the tail of the lathe dog. It threads on in place of the chuck of course,




Hope this is helpful,

Alistair.

[Tristan]

Hope this is helpful,

Alistair.

Thanks. The setup I had seen previously and tried to describe was holding a complete fork. A special plate had been made up which was adjustable for the fork's rake and clamped the dropouts. This could be mounted at either end of the lathe I suppose - the setup I remember seeing was mounted in the tailstock with a live center. The steerer was then clamped in the chuck.

[Alistair]

Thanks. The setup I had seen previously and tried to describe was holding a complete fork. A special plate had been made up which was adjustable for the fork's rake and clamped the dropouts.

I've seen a similar setup, for single point threading of steerer tubes. The plate with the adjustable offset dummy axle for the front dropouts was at the headstock end (presumably held by the chuck?). The steerer was held in a steady rest, leaving enough of it sticking out to give access to the portion being threaded.

Never done this myself, I think I saw it on someones Flickr site some years ago.

Alistair.

[EnginCycles]

It was Brett Fleming from Efficient Velo Tool.

Also not to be a jerk but can people please refer to this as the correct term. The CROWN RACE is a part of the headset. The crown race SEAT is the shoulder on the fork that has the press fit and the base which the crown race sits on.

Single point turning a fork is a rather simple task. If your lathe is small the steady is how you would go about setting it up. This is not very efficient time wise but will be accurate.

-Drew

[steve garro]

File it close with a warding, finish it off with my Bringheli = "nuts on"
- Garro.

[Alistair]

Also not to be a jerk but can people please refer to this as the correct term. The CROWN RACE is a part of the headset. The crown race SEAT is the shoulder on the fork that has the press fit and the base which the crown race sits on.

Drew,

you're not being a jerk at all. It's important to get this stuff right. What can I say, despite my efforts, sometimes I get sloppy when describing this kind of thing, even though I know better.

Alistair.