How Would I Machine this CAD designed Ratchet

[SillyOldDufferModerator @sillyoldduffer]

Thinking about an odometer-like mechanism recently I came up with a ratchet drive in which a pawl pushed a wheel one click by pressing on a flat face like ‘C’ whilst riding up a curved opposite slope ‘A’ until it dropped down into the next notch.  (The pawl moves left to to right on a hinge and is spring loaded)   Something like this:

 

Though surface ‘B’ is rounded, wouldn’t matter if a cutter spoilt that.

Even so, how could those curved ratchet notches be machined?  I can’t imagine either a straight or form cutter doing it however tilted.  Have I smacked into a design that’s easy to CAD but hard to make for real?  Or am I missing the obvious?

Ratchets like this exist, so there must be a way.

Help!

Ta,

Dave

 

 

 

[JasonBModerator @jasonb]

A form cutter a bit like a 1 sided involute gear cutter would probably do it if the centre section could be soldered into a ring so that the cutter could have run out room or have the centre recessed to just below the valley of the teeth

You would also have to watch that the cutter’s diameter was not too large otherwise it would hit the opposite side

We did have  asimilar thread about hole saws which need a similar sort of cut

If you could have a small radius in the internal corners then that opens up more possibilities

[JasonBModerator @jasonb]

Something like this would cut the tooth profile, just index it round.

[Paul LousickParticipant @paullousick59116]

Is the boss in the centre of the ratchet necessary?  Because it is very difficult to machine into a blind hole that has a sharp corner.

I made a ratchet wheel for the lubricator on my engine by cutting teeth on a long piece of rod with a chamfer tool, then cutting a slice off the end for the ratchet. (lots of spare material for future projects).

[Julie AnnParticipant @julieann]

As drawn the size of the gap seems to get smaller towards the centre. So a form cutter will not work. Even if the blank is tilted slightly a form cutter will probably not generate an accurate profile. It will be a compromise, like cutting a bevel gear on a manual mill.

If the item must be as drawn then get it 3D printed.

Otherwise back to the computer!

Julie

[SillyOldDufferModerator @sillyoldduffer]

Feels like back to the computer.

This is the shape of the removed metal, which I hoped might suggest a form cutter profile, nope!

Jason’s ‘D’ cutter does what Julie feared, I think.  Could be cut but the teeth won’t ratchet, the yellow lines aren’t parallel:

Thanks for the suggestions, seems tricky!  I’m off to sleep on it.

Dave

[Phil PParticipant @philp]

I made a radial toothed clutch for my little barring engine which was a similar problem. The only way I came up with was using a slotting head and a dividing head linked to the X axis of the mill.

 

 

[Michael GilliganParticipant @michaelgilligan61133]

Not sure [and I am certainly making no claim to fame] but I wonder if Jason was recalling the question I asked years ago about cutting a verge crown-wheel for a clock.

If so, it was never fully solved.

I will have a look for the old thread next time I wake-up in the middle of the night.

🙁

MichaelG.

.

Edit: __ ‘twas much easier to find than I anticipated:

https://www.model-engineer.co.uk/forums/topic/how-do-i-cut-a-verge-crown-escape-wheel/#post-212482

… still sipping a Glenmorangie

Edit: __ some of the content in that 2015 thread has gone awol so, for completeness I am quoting an observation I made in a related eMail:

Although JasonB and Mark C both provided very useful sketches … on close examination, both of them actually ‘demonstrate the problem’ rather than answering the question.

Mark was particularly helpful, and provided me with some more-detailed drawings; but the big ‘niggling’ question remained. [Zoom-in on a tooth in his SolidWorks rendering, and you will see that the tooth-tips are inappropriately shaped.]

[John HaineParticipant @johnhaine32865]

Change the shape of the pawl to fit a space you can cut?

[Nigel Graham 2Participant @nigelgraham2]

The crown-wheel form would be the easiest, as the cutter runs right through the gullet and into the fresh air in the middle.

Alternatively, can the wheel be of more conventional form with the teeth cut across the disc thickness? (Shaped like a circular saw.)

Your original form is not an example of something being easy to generate in CAD but not make physically. You can do that in manual drawing too; and it seems quite a common mistake.

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