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Modifying multi-tooth HSS wheel cutter
- Thread starter rgmt79
- Start date
- Replies 22
- Views 2,868
You can grind the teeth in the as-is, hard condition without problem, that's what a tool grinder does. I wouldn't recommend anneal, machine, and reharden, as the required features may move.
Though why you would want to reduce the depth of cut is beyond me.... Why can't you use it as-is?
Though why you would want to reduce the depth of cut is beyond me.... Why can't you use it as-is?
Illinoyance
Stainless
- Joined
- Aug 24, 2015
How do you intend to maintain the relief angle? It looks like these cutters are form relieved.
"Though why you would want to reduce the depth of cut is beyond me.... Why can't you use it as-is?"
Two reasons: 1) This is a restoration project on an 18c qtr striking clock where the depth of cut on the great wheels are shallow to match the o/d of the spring barrels. 2) To avoid having to remake the whole wheel including the inner click spring mechanism, I have turned down the old broken teeth as far as possible to o/d of the click spring, which leaves me producing a ring with new teeth and attaching to the original hub. I did this with the standard cutter, but the teeth were only supported by a thin base which buckled under the high torque imposed by the main spring when fully wound. The short form cutter would give me an extra 0,5 mm thickness to base of the new toothed ring
Richard
Two reasons: 1) This is a restoration project on an 18c qtr striking clock where the depth of cut on the great wheels are shallow to match the o/d of the spring barrels. 2) To avoid having to remake the whole wheel including the inner click spring mechanism, I have turned down the old broken teeth as far as possible to o/d of the click spring, which leaves me producing a ring with new teeth and attaching to the original hub. I did this with the standard cutter, but the teeth were only supported by a thin base which buckled under the high torque imposed by the main spring when fully wound. The short form cutter would give me an extra 0,5 mm thickness to base of the new toothed ring
Richard
I intend grinding 0,5 mm from the top of each tooth while maintaining the existing angle of relief.
Richard
Limy Sami
Diamond
- Joined
- Jan 7, 2007
- Location
- Norfolk, UK
Check very carefully as to whether the relief angle is a straight line or radius.
Maybe I'm being naive but why is this important?
Limy Sami
Diamond
- Joined
- Jan 7, 2007
- Location
- Norfolk, UK
Because if you get it wrong, when the cutter is re-sharpened ** the profile will not be correct.
** As a form relieved cutter re-sharpening is done on the cutting face and not periphery.
Thank you, now I understand. This is just for one project and is unlikely to need resharpening, but I take your point. On close examination I can see that the relief has a slight radius so I will need to follow that when grinding.
michiganbuck
Diamond
- Joined
- Jun 28, 2012
- Location
- Mt Clemens, Michigan 48035
Radial form relief cutters can be sharpened on many tool and cutter grinders as described in the free down-load of the Cincinnati #2 or #1 TC grinder manual. but altering the form is another problem.
Cincinnati Milling Machine Co. - Publication Reprints - Cincinnati #2 Cutter and Tool Grinder Manual | VintageMachinery.org
Anybody using machine cutting tools should have this book.
QT [I want to modify it to a short form (reduce depth of cut).] pretty tricky to modify such..because the form needs stay the same going down down as the dull area is removed if the cutter need be resharpened..one may need dress the form into a wheel and then roll the cutter in a radial relief fixture.
Cincinnati Milling Machine Co. - Publication Reprints - Cincinnati #2 Cutter and Tool Grinder Manual | VintageMachinery.org
Anybody using machine cutting tools should have this book.
QT [I want to modify it to a short form (reduce depth of cut).] pretty tricky to modify such..because the form needs stay the same going down down as the dull area is removed if the cutter need be resharpened..one may need dress the form into a wheel and then roll the cutter in a radial relief fixture.
Last edited:
implmex
Diamond
- Joined
- Jun 23, 2002
- Location
- Vancouver BC Canada
Hi rgmt79:
Are you certain you can make this work and get an acceptable gear out of it when you're done?
Reducing the clearance at the root of each gear tooth which is what you do when you grind your cutter means of course that your mating gear blanks all need their OD's cut down to correspond.
That means you need to recalculate the tooth depth in order to preserve the pitch diameter, and if you casually violate that, the involute form of the teeth will be wrong and the gears won't roll together properly.
Did you take all that into account with your proposal?
Is there a compelling reason to make this change?
Are you content to ignore the root fillets you'll lose when you knock off the tips of your cutter?
Having said all that, the proper way to proceed if you don't have a form relieving attachment, is to grind primary relief first, then add secondary relief to be sure that the modified cutter will not rub on the heels of each flute as you engage it with the stock.
You should make a CAD drawing of the side view of the tooth shape to know what the primary and secondary relief angles and the primary land widths need to be in order to preserve your front clearance to avoid this "heeling" problem.
Smaller cutters are more sensitive to this than bigger ones are, so for Thornton sized cutters you need to be able to grind within a thou or so of what you intend, and of course each tooth must be exactly the same as all the others within very close limits (tenths) or you'll end up with effectively a single tooth cutter which then has to do all the work and won't last very long.
Be aware your cutter is now well and truly fucked for sharpening as others have pointed out.
However, as is obvious, the cutter is well and truly fucked for making normal gears anyway, so if you intend to throw it away after this special project; it's not like you didn't know beforehand.
So you must do as you believe is the best way forward, and this is how you can do what you wish and still have a cutter that will cut and survive.
Cheers
Marcus
Implant Mechanix • Design & Innovation > HOME
Vancouver Wire EDM -- Wire EDM Machining
Are you certain you can make this work and get an acceptable gear out of it when you're done?
Reducing the clearance at the root of each gear tooth which is what you do when you grind your cutter means of course that your mating gear blanks all need their OD's cut down to correspond.
That means you need to recalculate the tooth depth in order to preserve the pitch diameter, and if you casually violate that, the involute form of the teeth will be wrong and the gears won't roll together properly.
Did you take all that into account with your proposal?
Is there a compelling reason to make this change?
Are you content to ignore the root fillets you'll lose when you knock off the tips of your cutter?
Having said all that, the proper way to proceed if you don't have a form relieving attachment, is to grind primary relief first, then add secondary relief to be sure that the modified cutter will not rub on the heels of each flute as you engage it with the stock.
You should make a CAD drawing of the side view of the tooth shape to know what the primary and secondary relief angles and the primary land widths need to be in order to preserve your front clearance to avoid this "heeling" problem.
Smaller cutters are more sensitive to this than bigger ones are, so for Thornton sized cutters you need to be able to grind within a thou or so of what you intend, and of course each tooth must be exactly the same as all the others within very close limits (tenths) or you'll end up with effectively a single tooth cutter which then has to do all the work and won't last very long.
Be aware your cutter is now well and truly fucked for sharpening as others have pointed out.
However, as is obvious, the cutter is well and truly fucked for making normal gears anyway, so if you intend to throw it away after this special project; it's not like you didn't know beforehand.
So you must do as you believe is the best way forward, and this is how you can do what you wish and still have a cutter that will cut and survive.
Cheers
Marcus
Implant Mechanix • Design & Innovation > HOME
Vancouver Wire EDM -- Wire EDM Machining
michiganbuck
Diamond
- Joined
- Jun 28, 2012
- Location
- Mt Clemens, Michigan 48035
You can grind down the teeth OD and give the new form some faceted (normal) clearance and it will cut just fine...but then you loose the future ability to resharpen it in the way that keeps the original form for a number of sharpenings. by taking stock from the face only....
QT: [ do I need to soften first and then re-harden?] no a normal grinding wheel will grind HHS
QT:[I intend grinding 0,5 mm from the top of each tooth while maintaining the existing angle of relief.]
I think you mean from the diameter or OD ...
The common way to do that is to spin circle the OD to the size you wish like a cylindrical grind..
Then go to grind the tooth clearance to just come up to the sharp edge. Yes likely need a primary and a secondary clearance so the heal does not rub.
The circle OD grinding eliminates the chance if teeth being high and low due to grinding wheel breakdown of flex in the toth rest finger.
Your cutter seems to have no helix so the top of teeth don't have an angle one way or the other.
If it did have a helix or top angle , or if it was a stagger tooth mill the circle-grinding first would make accuracy so all the teeth would be correct.. When coming in to clearance such teeth the land where the clearance comes to the edge would need adjustment as a straight-to-the-edge would make the cutter correct and all teeth to the same diameter and the same height.
QT: [ do I need to soften first and then re-harden?] no a normal grinding wheel will grind HHS
QT:[I intend grinding 0,5 mm from the top of each tooth while maintaining the existing angle of relief.]
I think you mean from the diameter or OD ...
The common way to do that is to spin circle the OD to the size you wish like a cylindrical grind..
Then go to grind the tooth clearance to just come up to the sharp edge. Yes likely need a primary and a secondary clearance so the heal does not rub.
The circle OD grinding eliminates the chance if teeth being high and low due to grinding wheel breakdown of flex in the toth rest finger.
Your cutter seems to have no helix so the top of teeth don't have an angle one way or the other.
If it did have a helix or top angle , or if it was a stagger tooth mill the circle-grinding first would make accuracy so all the teeth would be correct.. When coming in to clearance such teeth the land where the clearance comes to the edge would need adjustment as a straight-to-the-edge would make the cutter correct and all teeth to the same diameter and the same height.
michiganbuck
Diamond
- Joined
- Jun 28, 2012
- Location
- Mt Clemens, Michigan 48035
I might add the quick trick for making OD clearance drop edge below center to get a needed clearance angle.
Cutter diameter x clearance desired x 87 ..Say a 5" cutter and you seek 5* clearance..5 x 5 x 87 = 2,175 The drop is .217
On the floor one would just use 9 so to do it in your head 5 x 5 x 9 = 225 (.225") plenty close enough with a half degree allow on most any cutter.
Yes you set the tooth edge at center line then drop your tooth rest finger to the correct number.
For a steel cutting cutter perhaps looking for 5* primary and 8* secondary. Sec= 5 x 8 x 9 = .360" drop
Cutter diameter x clearance desired x 87 ..Say a 5" cutter and you seek 5* clearance..5 x 5 x 87 = 2,175 The drop is .217
On the floor one would just use 9 so to do it in your head 5 x 5 x 9 = 225 (.225") plenty close enough with a half degree allow on most any cutter.
Yes you set the tooth edge at center line then drop your tooth rest finger to the correct number.
For a steel cutting cutter perhaps looking for 5* primary and 8* secondary. Sec= 5 x 8 x 9 = .360" drop
Screwmachine
Titanium
- Joined
- Mar 8, 2001
- Location
- Switzerland
Guys this is a cycloidal gear, common on clocks. Only the addendum of the gear is in use, the dedendum is to clear the mating pinion addendum. As long as the root depth clears the pinion addendum it should be fine.
If this was on my bench I'd make a flycutter and not mess up a nice commercial cutter.
If this was on my bench I'd make a flycutter and not mess up a nice commercial cutter.
Limy Sami
Diamond
- Joined
- Jan 7, 2007
- Location
- Norfolk, UK
Ah, that makes things a bit clearer, …….and I'd make the flycutter as well.
Limy Sami
Diamond
- Joined
- Jan 7, 2007
- Location
- Norfolk, UK
With your hamfisted ways?
michiganbuck
Diamond
- Joined
- Jun 28, 2012
- Location
- Mt Clemens, Michigan 48035
My post 13 begins with "I might add." it is to go along with post 12 that tells how to circle grind the cutter , Yes certainly the form is changed, and begins a new life as a faceted ground cutter not anymore a radial relies cutter.
The simple formula is how to get your desired clearance angle to a circle ground, or any cutter with setting the cutting edge above or below center.
To sharpen with retaining the original form, taking from the face only, it is best to down load the Cincinnati book and read the section..I have sharpened such cutters many times on hob grinding machines and TC grinders.
Grinding a radial relief cutter is a bit tricky and that is why I say read the book..You roll the cutter into th e wheel, not feed the wheel into the cutter.
So the cutter face is ground on a radial plane, not ground parallel to the radius. This way the grind/take is more off the top face front , rather than taking the same amount off the face top front as is taken from the top face neared the rear of the top face...
michiganbuck
Diamond
- Joined
- Jun 28, 2012
- Location
- Mt Clemens, Michigan 48035
You really need to look at the Cincinnati hand book to understand that because it does/may seem odd. But I have checked radial relief cutters and by taking (grinding away)the same from the front of the face and the rear of the face changes the form making it more narrow at the rear or less narrow at towards the OD.
Say you have a .015 wear land at the cutting edge and you touch to make your wheel touch/grind flat to the tooth face. Then you in-feed going flat into the face so taking .015 near the cutter edge, and also .015 from the tooth face back toward the gullet, That may seem correct but is wrong and changes the form (shape) the cutter will make.
Doing so you are also changing the tooth rake angle because the new tooth face is more below center line.
I think around page 40 - 41 or about.
Cincinnati Milling Machine Co. - Publication Reprints - Cincinnati #2 Cutter and Tool Grinder Manual | VintageMachinery.org
Say you have a .015 wear land at the cutting edge and you touch to make your wheel touch/grind flat to the tooth face. Then you in-feed going flat into the face so taking .015 near the cutter edge, and also .015 from the tooth face back toward the gullet, That may seem correct but is wrong and changes the form (shape) the cutter will make.
Doing so you are also changing the tooth rake angle because the new tooth face is more below center line.
I think around page 40 - 41 or about.
Cincinnati Milling Machine Co. - Publication Reprints - Cincinnati #2 Cutter and Tool Grinder Manual | VintageMachinery.org
