profile shifting - Githubissues

jnweiger / inkscape-gears-dev

Enhanced version of the well known gears extension, allows spokes, center cross, metric module, best evolute shape ...

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profile shifting #9

Open Neon22 opened 10 years ago

Neon22 commented 10 years ago

I see numerous rules about profile shifting appearing when pressure angles and Teeth get below a certain ratio. E.g. "Gears that are smaller than 32 teeth for a 14.5° Pressure Angle, or 18 teeth for a 20° Pressure Angle, have a Root Circle smaller than the Base Circle, resulting in the teeth being undercut."

This doc shows how to determine if undercut will occur. Pitch shift can be both positive (usual) and negative(rare). Negative looks cool - I expect it weakens the gear tooth so undesireable but does look interesting. pg 604 ( doc starts at 595).

http://www.khkgears.co.jp/en/gear_technology/pdf/gear_guide1.pdf seems simple - basically shifting the addendum and dedendum while leaving base circle in same place.

Should we detect undercut and auto shift or just annotate and ask (and maybe add a page about undercut to the tabs) ?

jnweiger commented 10 years ago

This here http://lcamtuf.coredump.cx/gcnc/ch6/#6.2 confirms that profile shift is all about the addendum. The tricky part, appears to be that two meshing gears should have complementary profile shift: The smaller gear has an enlarged addendum, while the larger gear has a reduced addendum.

Neon22 commented 10 years ago

YEs :( and apparently they won;t mesh unless matching. so can only be applied in cases of a gear-train.

However other solution is to undercut. which will work but is harder. That csg code will do it but its a lot of code :(

Neon22 commented 10 years ago

So do you think the right thing is to:

Allow user to enter profile shift parameter. as a ratio (?) split between two gears.
Report in annotation this shift and that meshing gear is expected to have shift of X.

Then we cover this issue - separately from undercuts (for which this is one strategy). Then in gear-trains - we could utilise this feature.

jnweiger commented 10 years ago

Yes. I'd make profile shift a percentage. Two gears would mesh, if one has -X % and the other has +X % profile shift. -100% should mean that the addendum is 0.

And yes, then it is one strategy against undercut. My undercut warning already mentions this.

On Mon, Apr 7, 2014 at 5:03 AM, Neon22 notifications@github.com wrote:

So do you think the right thing is to:

Allow user to enter profile shift parameter. as a ratio (?) split between two gears.

Report in annotation this shift and that meshing gear is expected to have shift of X.

Then we cover this issue - separately from undercuts (for which this is one strategy). Then in gear-trains - we could utilise this feature.

Reply to this email directly or view it on GitHubhttps://github.com/jnweiger/inkscape-gears-dev/issues/9#issuecomment-39692707 .

jnweiger commented 10 years ago

I believe, this was too simplistic. Real profile shift should shift the entire contour inwards or outwards. Not just the endpoints.