Fly Cutter to Cut a 56 tooth Wheel

[JamesBB]

Hi Everyone

I'm trying to make a new 56 tooth wheel for an old grandfather clock. I have a minilathe and have constructed a holding device that allows me to index the wheel (pics attached). I've been making a fly cutter (out of silver steel), quenching and tempering it. But they keep breaking! So I decided to remove the bulk of the waste using a slitting saw (see photo) which improved things slightly and I began to get to depth and form the teeth but then it broke again.

Do any of you have any wisdom on how to improve performance? I heat treated it by getting it to non-magnetic for a couple of mins and then tempered in the oven for 1hr at 180 centigrade. I've been running it at about 400rpm with the cuttter itself 25-30mm from the centre.

There's a YouTube video of Clickspring doing this and he seems to be able to get it to work but the film must be speeded up for the actual cut I think.

Thanks so much for any help.

James

 

[JamesBB]

By the way, the brass blank was 2mm; I've since reduced that to using 1.2mm brass though I haven't tested this with the fly cutter yet.

 

[JamesBB]

PS The cutter itself is made from 6mm bar and the diameter of the end of the cutter is 1.35mm.

 

[Karl Burghart]

I use W-1 steel to cut wheels of similar thickness without issues and I don't even temper. What is the quality of the silver steel? Some of the stuff from Asia and India is very hit or miss.

 

[Karl Burghart]

I also use leaded (engraving brass). What type brass is your blank?

 

[JamesBB]

Thanks Carl; that's helpful. I can't vouch for the quality of the steel but I bought it from a UK source. What Rpm and feedrate do you use?

 

[JamesBB]

I also use leaded (engraving brass). What type brass is your blank?

I'm not sure; is leaded brass easier to cut?

 

[Dick Feldman]

James,
This showed up on the MB some time ago.
It may be of some help.

http://users.neo.registeredsite.com/1/4/7/17557741/assets/Introduction_to_Horological_Wheel_Cutting.pdf

Jerry Keiffer is the wizard of micro machining in the US.
Best of luck,
Dick

 

[JamesBB]

James,
This showed up on the MB some time ago.
It may be of some help.

http://users.neo.registeredsite.com/1/4/7/17557741/assets/Introduction_to_Horological_Wheel_Cutting.pdf

Jerry Keiffer is the wizard of micro machining in the US.
Best of luck,
Dick

Thanks Dick; that looks very helpful in all sorts of ways. Sadly his fly cutters are made differently (in a way I can't manage!).

 

[John MacArthur]

Try tempering the cutter a bit higher - 450-475 F, or 235-250 C. This should be a dark straw or light brown color. Also, 400 rpm is way slow, it should be something like 10 times that. Good luck
Johnny

 

[Dick Feldman]

Also, could the wheel blank itself be chattering?
I have found that can be stabilized by stacking 2, 3 or 4 blanks to be cut at the same time.
Good luck,
Dick

 

[Willie X]

You need a way higher tool speed, try something around 1500 for starters. A small fly cutter (for delicate work) would run at around 4000 RPM. Your cutter is rather chunky, so the 1500 shouldn't be to much off. And make sure the feed has no play. That's zero lash in the feed screw, or whatever you're using to move the work into the cutter there. Willie

 

[Jim DuBois]

Sandvik Steel has the following to say.....

Hardening is a way of making the tool steel harder. By first heating the steel to between 1050 and 1090°C (1922 and 1994°F) and then quickly cooling (quenching) it, the steel will become much harder, but also more brittle.

To reduce the brittleness, the material is tempered, usually by heating it to 175–350°C (347–662°F) for 2 hours, which results in a hardness of 53–63 HRC and a good balance between sharpness retention, grind ability, and toughness.

Tempering should be carried out within a reasonable time after hardening, preferably within an hour or so. It is of vital importance that the blade should be allowed to cool to room temperature before tempering is started. The transformation to martensite will otherwise be interrupted and the hardening results may be impaired. A higher tempering temperature will yield a somewhat softer material with higher toughness, whereas a lower tempering temperature will produce a harder and somewhat more brittle material

 

[JamesBB]

You need a way higher tool speed, try something around 1500 for starters. A small fly cutter (for delicate work) would run at around 4000 RPM. Your cutter is rather chunky, so the 1500 shouldn't be to much off. And make sure the feed has no play. That's zero lash in the feed screw, or whatever you're using to move the work into the cutter there. Willie

I did wonder this but then thought that would only increase the forces on the cutter and increase the likelihood of getting bent? Slow feed rate to compensate?

Thanks for your help.

 

[Willie X]

The breaking "force" comes about when the tool is stopped between cuts. This is due to your very slow tool speed and/or erratic feed. If the piece you're feeding can jump in and out, even a tiny amount this will grab the cutter too, especially if the cutter is running to slow. Willie X

 

[howtorepairpendulumclocks]

Making a cutter by turning leaves the back of the cutting part of the tool unsupported. It may seem imprecise but try making one by filing. For escape wheel cutters this is great. As above, the cutter needs to run crazy fast. Make sure there are at least two bits of protection between the tool and your eyes. As above, take out any lash in the slide with a spring or similar. It can be done... keep at it. Also, the turning method makes it really difficult to get adequate side relief or clearance. I find the edge of the cutter brasses up after a few teeth and all is lost. Try filing.

 

[Jerry Kieffer]

Hi Everyone

I'm trying to make a new 56 tooth wheel for an old grandfather clock. I have a minilathe and have constructed a holding device that allows me to index the wheel (pics attached). I've been making a fly cutter (out of silver steel), quenching and tempering it. But they keep breaking! So I decided to remove the bulk of the waste using a slitting saw (see photo) which improved things slightly and I began to get to depth and form the teeth but then it broke again.

Do any of you have any wisdom on how to improve performance? I heat treated it by getting it to non-magnetic for a couple of mins and then tempered in the oven for 1hr at 180 centigrade. I've been running it at about 400rpm with the cuttter itself 25-30mm from the centre.

There's a YouTube video of Clickspring doing this and he seems to be able to get it to work but the film must be speeded up for the actual cut I think.

Thanks so much for any help.

James

View attachment 635246 View attachment 635247 View attachment 635248

James
I have used single point cutters for many years without issue.

Hopefully, I can be blunt and get to your issues.

You have a number of obstacles based on your description.

(1) While I have not inspected your setup, having learned this the hard way, attempting to cut wheels, gears or pinions on a Lathe is almost always the least effective method.

(2) The first attached photo is of my current Chinese 7" mini Lathe. While it is of current production with all of the latest bells and whistles, quality has not improved from the last one and if anything even worse. We all have our personal standards and as for myself, I have not found the Lathe practical for Horological work.

(3) I am familiar with cutter construction utilizing round stock and do not consider it practical. First, there is no way to sharpen the cutters without changing tooth profile. In your second photo, Unless you have image distortion, the cutter is no where near sharp enough to effectively cut consistent profile teeth from its appearance.
If constructed of square stock, the cutter can be quickly and easily sharpened razor sharp on a oil stone with no profile change. Second photo.
This can then be done before each cutter use assuring max. efficiency. Cutters for cutting teeth should have no side relief.
The sharpness of a home shop cutter is the life blood of the system with breakage a indication it is not yet sharp enough providing it was properly hardened. Final sharpening cannot take place until hardening is complete, thus the oilstone or of course very fine diamond.

In the Wheel and pinion class at the NAWCC, I have the students machine cutters (Not grind) for consistency and accuracy. They are then hardened and not tempered for time considerations. In the last ten years or so, I can only think of one failure when machining brass making full depth single passes when properly sharpened. Of course when time permits and or utilized for steel, they are tempered.

You are correct.
Under no circumstance run a shop made cutter over 500 RPM when cutting teeth. This will very quickly damage the cutting edge. PP Thornton also suggests under 500 RPM for their commercial cutters unless under flood coolant conditions.

It is as brief as I can make a two day course.

Jerry Kieffer

 

[Jerry Kieffer]

James,
This showed up on the MB some time ago.
It may be of some help.

http://users.neo.registeredsite.com/1/4/7/17557741/assets/Introduction_to_Horological_Wheel_Cutting.pdf

Jerry Keiffer is the wizard of micro machining in the US.
Best of luck,
Dick

Dick
You are just to kind.

Jerry Kieffer

 

[JamesBB]

You are correct.
Under no circumstance run a shop made cutter over 500 RPM when cutting teeth. This will very quickly damage the cutting edge. PP Thornton also suggests under 500 RPM for their commercial cutters unless under flood coolant conditions.

It is as brief as I can make a two day course.

Jerry Kieffer

Thank you Jerry! I so appreciate your expertise on this. Especially interested in your views on rpm given that others in this thread advocate the exact opposite. I will stick to lower speeds. The cutter in the photo was my first attempt. I have since produced much sharper ones (I'm primarily a woodworker so use Japanese waterstones) and these certainly worked much better before breakage.

Interested in your thoughts re cutters produced from round stock. Would you make an accurate cutter from square stock simply by filing?

I suppose another way is simply to hand file all the teeth to the right shape? Is that practical?

Many thanks

James

 

[howtorepairpendulumclocks]

Just saying' but I've made loads of fly cutters from 1/4" Round stock. Yes you cannot resharpen without changing the profile so they are not resharpenable but last ages. Thorntons are multi-tooth cutters and yes, when milling pinions from steel, run them slow with lubricant/coolant. For single point fly cutter machining brass. my experience is the faster the better as long as you have adequate safety measures in place. I'd be interested to see a cutter with no side relief? I've never seen a machine tool cutter with no relief. Why doesnt it just rub and get hot

 

[howtorepairpendulumclocks]

Slitting the teeth with a slitting saw and hand-filing is fiddly but yes, it can be done. Thats how clock wheels used to be made. You occasionally see wheels that are only partly rounded up such as reciprocating racks and wheels in astronomical work. Remember only one side of your wheel teeth does any work. This is why a hand-files fly cutter is ok, slight asymetry isn't a problem. Once you have made your wheel, you can try it in the depthing tool with the mating pinion to find out which side works best. A filing jig might be handy if going down the hand route. People bang on about cycloids but the reality is the ogive or addenda of a wheel tooth is a curve. The main thing is SAME shape rather than right shape. Would be fun to try. Equal division is of course important.

 

[JamesBB]

Slitting the teeth with a slitting saw and hand-filing is fiddly but yes, it can be done. Thats how clock wheels used to be made. You occasionally see wheels that are only partly rounded up such as reciprocating racks and wheels in astronomical work. Remember only one side of your wheel teeth does any work. This is why a hand-files fly cutter is ok, slight asymetry isn't a problem. Once you have made your wheel, you can try it in the depthing tool with the mating pinion to find out which side works best. A filing jig might be handy if going down the hand route. People bang on about cycloids but the reality is the ogive or addenda of a wheel tooth is a curve. The main thing is SAME shape rather than right shape. Would be fun to try. Equal division is of course important.

Thanks! That's very helpful. My indexing system works very well (the disc and pointer at the top) and I suspect it is adequately accurate. What does a filing jig look like/ I had considered a few designs in my head but I guess there is an accepted norm?

Thanks

James

 

[John MacArthur]

Not to argue with Jerry, but I too run my shopmade fly cutters a lot faster than 500 rpm. From an experimental viewpoint why not try both? Obviously, to some degree it would depend on the working diameter of the cutter and if it had been properly hardened and tempered (which is where this started).
Johnny

 

[Jerry Kieffer]

Thank you Jerry! I so appreciate your expertise on this. Especially interested in your views on rpm given that others in this thread advocate the exact opposite. I will stick to lower speeds. The cutter in the photo was my first attempt. I have since produced much sharper ones (I'm primarily a woodworker so use Japanese waterstones) and these certainly worked much better before breakage.

Interested in your thoughts re cutters produced from round stock. Would you make an accurate cutter from square stock simply by filing?

I suppose another way is simply to hand file all the teeth to the right shape? Is that practical?

Many thanks

James

James
The procedures suggested for consideration are those I cover in the class room and demonstrate at various shows through out the year.
Students who pay for a class have the right to expect procedures that give them the chance of professional results on their first attempt, in a timely fashion. That is my goal.

There are three concerns when using single point cutters.

(1) It would be rare for a home shop to be equipped in a manner that would allow cutters, to be Hardened/tempered in a manner similar to the toughness of commercial HSS.

(2) With #1 in mind, a single point has to do the work of several points when compared to a multi leaf commercial cutters.

(3) duplicating the original surface finish on formed teeth or a smooth finish will assure restoration of original function.

All three of these concerns are easily addressed by sharpening the cutter before each use. In fact by doing this, one off wheels or gears often have surface finishes that are superior to multi leaf commercial cutters.
In addition, keeping the RPM under 500 allows the single point cutter to actually cut the metal while maintaining a sharp edge. At high speeds, home shop cutters can easily loose their edge and end up in effect pounding a hole, often producing a poor surface finish.
The first attached photo shows a single point cutter Machined (Not filed) to duplicate several replaced teeth between the black outline. The second photo shows the red arrow at an original tooth and blue at one that was machined under 500 rpm. Surface finish can be compared.

Filing teeth is a difficult question. In the cottage industry days teeth were often filled, but those who did it, did it everyday all day long for life. Duplicate that degree of proficiency and accuracy with less experience is something I have not seen demonstrated. But then theres always a first time.

Accurate cutters from square stock are easily machined on either a Lathe or Milling machine with five cuts but with only two critical. Can explain if required.

Jerry Kieffer

 

[JamesBB]

Accurate cutters from square stock are easily machined on either a Lathe or Milling machine with five cuts but with only two critical. Can explain if required.

Jerry Kieffer

Thank you Jerry; that's very helpful. I would be interested in how to make a cutter with a lathe (I don't have a milling machine).

 

[Jerry Kieffer]

interested to see a cutter with no side relief? I've never seen a machine tool cutter with no relief. Why doesnt it just rub and get hot

If you inspect/measure any commercial gear cutter, they will not have any side relief per attached photo. Blue arrow shows cutting tip and red arrow the tail end.

As long as the cutting tip is very sharp and at a speed it can make a clean cut, no side drag of any consequence will occur as long as the side relief is exactly 90 degrees. This is why I machine cutters for assured consistent accuracy rather than hand file or hand grind them. While the same could be done with a filing fixture for each job that assured consistency through out the procedure, I suspect it would not be considered practical by most.

Jerry Kieffer

 

[JamesBB]

Right, I can see how that would work now and in fact have already ground a bit to make the same curve for my fly cutter. So this doesn't look too difficult. I guess one saws and files away the waste in the gaps between the teeth. What material would you recommend for this Jerry?
Thanks so much
James

 

[howtorepairpendulumclocks]

That cutter does effectively have side relief. In order to make the cutters re-grindable, yes they have constant profile but the profile is not at an even radius with the centre of the cutter. It is relieved. look at it from the side. A cutter with no relief will "brass up" and ruin the work/cutter in no time.

 

[Jerry Kieffer]

Thank you Jerry; that's very helpful. I would be interested in how to make a cutter with a lathe (I don't have a milling machine).

James

A square cutter can be machined on a Lathe as follows.
The setup is for illustration only with non compatible items that were handy.

(1) Square stock is mounted in a single point holder that is interchangeable with its compatible milling machine. first photo

(2) The cutter rotational tip relief is machined using a standard lathe tool. First photo

(3) A two flute ball nose endmill is selected of the required size and one half is used to machine the first radius second photo.

(4) The endmill is then shifted to the opposite side and a duplicate cut is taken by reversing the lathe rotation. third photo
This assures that both sides of the cutter are identical. All dimensions are controlled by having a lathe where all axis are equipped with lead screws for the use of hand wheel settings.

In actual use, I use stub length endmills for greater stability and accuracy

Jerry Kieffer

 

[Jerry Kieffer]

That cutter does effectively have side relief. In order to make the cutters re-grindable, yes they have constant profile but the profile is not at an even radius with the centre of the cutter. It is relieved. look at it from the side. A cutter with no relief will "brass up" and ruin the work/cutter in no time.

The side view of the cutter that is of standard industry construction as requested. The only relief is on the nose or front of the cutter for rotational relief. By its construction, nothing is altered including the nose relief when sharpened.

Jerry Kieffer

 

[howtorepairpendulumclocks]

The originator of the thread was asking how they improve the performance of a cutter. There are as you know many factors; hardening, tempering, cutter speed and so on. One factor that will defeat the cutter every time if it does not have adequate relief. The cutter you show appears at first glance not to have side relief but it does, it has to otherwise it would rub, brass would build up on the side of the cutter and the work and/or cutter would be ruined. Yes, commercial cutters are made to tighter tolerances that most people can do at home but nevertheless, they cannot avoid geometry. Yes this cutter has constant form from a re-grinding perspective but it certainly does not have constant form from a cutting perspective. I've done a sketch which I hope helps. When these multi tooth cutters are made the effective centre of the manufacturing profiles is off-set from that of the operational profile which is at the centre of the cutter. I have approximated the centre of the radius that formed tooth t and called it ct. I have approximated (stuck with italics now, cannot seem to be able to turn it off) the centre of the cutter in operation and called it cc. You can see that this off-set generates both top relief and side relief. When a wheel is cut, to generate a straight sided tooth, due to converging radials of a circle, the cutter flank is tapered. Yes the relief on commercial cutters may be small, but it has to be there. The cutters are called form relieved. For anyone who wants to get into cutter making, I strongly recommend the book Wheel and Pinion Cutting in Horology by Malcolm Wild. If after lock-down, you ever get the chance to visit PP Thornton cutters and see the cutters being made, it is fascinating. More to the point, I think the originator of the thread can make make a cutter by filing alone for this type of clock. As long as the Pitch Circle Diameter is correct and the teeth are of the same profile, "right" or "proper" profile, whatever that is is less important. For me, it is important, wherever possible to encourage techniques that are accessible. Yes, having a nicely equipped shop is something to aspire to maybe, but the reality is, many readers of and contributors to this forum do not have those resources and I am concerned about exclusion. Matthew Read

 

[howtorepairpendulumclocks]

...above should say "unintended perceptions of exclusion".

 

[JamesBB]

The originator of the thread was asking how they improve the performance of a cutter. There are as you know many factors; hardening, tempering, cutter speed and so on. One factor that will defeat the cutter every time if it does not have adequate relief. The cutter you show appears at first glance not to have side relief but it does, it has to otherwise it would rub, brass would build up on the side of the cutter and the work and/or cutter would be ruined.

Many thanks for this. My fly cutter, made from 6mm round stock, has relief built in because the the back of it is circular (the half one didn't file away). It can definitely cut so it is more a question of how to keep it cutting and stop it breaking. I'll post on the thread if/as I make progress. In terms of hand filing a 56 tooth gear, I wondered if one was able to make a small filing template that could be moved round with each cutter. So I'm thinking about something from say some 2mm flat bar with a hole so that you can mount it on a small shaft along with the wheel and then the profile cut in the other end at the right radius and then hardened so you simply file the brass to the bar?

Thanks

 

[Jerry Kieffer]

The originator of the thread was asking how they improve the performance of a cutter. There are as you know many factors; hardening, tempering, cutter speed and so on. One factor that will defeat the cutter every time if it does not have adequate relief. The cutter you show appears at first glance not to have side relief but it does, it has to otherwise it would rub, brass would build up on the side of the cutter and the work and/or cutter would be ruined. Yes, commercial cutters are made to tighter tolerances that most people can do at home but nevertheless, they cannot avoid geometry. Yes this cutter has constant form from a re-grinding perspective but it certainly does not have constant form from a cutting perspective. I've done a sketch which I hope helps. When these multi tooth cutters are made the effective centre of the manufacturing profiles is off-set from that of the operational profile which is at the centre of the cutter. I have approximated the centre of the radius that formed tooth t and called it ct. I have approximated (stuck with italics now, cannot seem to be able to turn it off) the centre of the cutter in operation and called it cc. You can see that this off-set generates both top relief and side relief. When a wheel is cut, to generate a straight sided tooth, due to converging radials of a circle, the cutter flank is tapered. Yes the relief on commercial cutters may be small, but it has to be there. The cutters are called form relieved. For anyone who wants to get into cutter making, I strongly recommend the book Wheel and Pinion Cutting in Horology by Malcolm Wild. If after lock-down, you ever get the chance to visit PP Thornton cutters and see the cutters being made, it is fascinating. More to the point, I think the originator of the thread can make make a cutter by filing alone for this type of clock. As long as the Pitch Circle Diameter is correct and the teeth are of the same profile, "right" or "proper" profile, whatever that is is less important. For me, it is important, wherever possible to encourage techniques that are accessible. Yes, having a nicely equipped shop is something to aspire to maybe, but the reality is, many readers of and contributors to this forum do not have those resources and I am concerned about exclusion. Matthew Read

View attachment 635588

This is one of those topics that is easily demonstrated in person but often difficult to explain.

While not knowing the state of hardening and temper of the OP`s cutter, the construction procedure produces a very weak cutter when compared to the photo example and commercial cutters. In addition, it produces sharpening challenges without expensive controlled grinding equipment. All or one can contribute to his cutter breakage.

If you closely inspect a commercial single point or multi leaf cutter, you will find that each cutter tooth will have identical dimensions over its full length. This is the only way a cutter tooth can be sharpened while retaining tooth form. Since you have mentioned PP Thornton, they offer their customers a cutter sharpening service. Again since they are a very customer friendly company and encourage phone calls, you can call them and they will verify/explain if its of importance. If you do call, please mention that I said "Hi".

In operation a gear cutter, actually has minimal side contact due to the rotational clearance and cutter shape required to function, but it still exists. This is easily observed when machining a gear with a degree of width. When complete, insert the cutter into a tooth cavity and you will find that it has a snug fit in all directions. If the cutter had side relief or generated side relief, you would be able to freely twist the cutter side to side slightly, but you will find that it will remain snug without forcing it. Side galling of a cutter is generally caused by poor finish and or the side of a cutter thats greater than 90 degrees to the cutter surface.

Another very common example of cutters without side relief is Taps and Dies. They are used in high speed machines daily without issues in all materials including the most difficult.

Jerry Kieffer

 

[howtorepairpendulumclocks]

Yes, sorry, I went well off-piste there. Apologies.

In summary, the cutter is likely breaking for one of three reasons covered above...

inspection of the broken tip will direct to the answer.

1. Too soft (not hardened enough). Cutting edges will be blunted. Heat and soak at bright orange. Plunge when orange and immediately agitate in cold water.

2. Too hard (not tempered enough). This might be exacerbated by too low spindle speed in relation to feed rate. Cutting edges remain intact, cutter fractured. Temper very slowly from the butt of the cutter on a bed of brass filings until the tip just reaches pale yellow. The rest of the cutter will be tempered more because of heating direction.

3. Inadequate relief. Broken cutter tip will have brass build-up on edges.


As for the hand-filing experiment, I'd do it in two stages. 1, put an angle of with a barrette file if you have one. 2. Join the flats to form a curve.

Hope this helps

 

[D.th.munroe]

There was jigs for hand filing teeth, and much older and primative than the one Laurie Penman shows on page 26 "wheel topping"
https://www.google.com/url?sa=t&sou...FjADegQIBhAJ&usg=AOvVaw3-VBvt3lFgwZNZ57Tgv9LE
Dan

 

[howtorepairpendulumclocks]

... may not be of use but hopefully encouraging... I've just had a practice hand-filing some teeth addenda with a barrette file. No jig. Surprisingly, although keeping the file perpendicular to the work is tricky, one stroke of the file, and the same on the other side looks ok. Would be fun to try... )

 

[Jim DuBois]

I am a bit confused by some of the discussions in this thread. Using a fly cutter to cut 56 teeth in a brass blank is something that should not be difficult. While the discussion seems centered about the cutter itself perhaps some other possibilities should be at least considered in passing. Firstly, there is no need to saw slots in a brass blank just to cut wheel teeth. Secondly, we should at least consider the rigidity of the setup. It has to be rigid in all 3 directions. The wheel blank needs to be well supported and a backing piece is often useful and assists in smooth cutting. If you have any vibration and or squeaking/chattering you are making scrap. The rate at which the cutter is advanced into the wheel blank needs to be fairly slow and quite precise. As the cutter advances into the workpiece the tip does the majority of the cutting until full depth is approached when the tooth adendum forms are done.

The attached photos are of an escape wheel cutter I made of tool steel, hardened and then tempered. I cut 30 teeth in a 3/16" thick piece of 360 brass, full depth, in one pass. I did use a micro-mist coolant/lubrication with vegetable-based oil on the blank. I cut two escape wheels using this cutter, I did hone it just very slightly between the first and second wheels.

I have made a number of fly cutters, some worked better than others, but they all ultimately produced a wheel, usually in just a few minutes.

One additional thought is the original set up shows the fly cutter extended quite far out from the center of rotation. There are parties who report moving the cutter in very close, as possible, to the center of rotation helps with the cutting process. Something about scooping out the brass versus whacking it more with a flat surface when on a longer length of rotation. I have not checked that claim out further but I notice all my fly cutters have been "short."

 

[JamesBB]

Report back: it worked! Thank you to everyone. The three key pieces of advice that you gave were (1) run the bit at a much higher speed (so I ran it at 1000RPM) (2) Ensure it is as sharp as possible (so I honed before and after heat treating on a 6000 Grit waterstone) and (3) ensure as rigid a setup as possible (so I tightened the gib on the cross slide). Picture below shows three cuts (so two teeth) on my test blank (which has loads of other things happening from previous ideas). I took them to depth but not all the way through so there is a tiny wedge at the bottom of the cut but this was a proof of concept so now I will make the wheel to spec. Much appreciate you guys. Thanks. James