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chrisspen / gears

OpenSCAD gear generator.
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rack has incorrect pitch due to use of 'clearance' #9

Open mark1010 opened 3 years ago

mark1010 commented 3 years ago

The 'clearance', which didn't appear in the original library, causes the rack to mismatch a spur gear with the same module / modul. Removing the 'clearance' fixes this issues. Animating the example rack and pinion will show this.

module rack(modul, length, height, width, pressure_angle = 20, helix_angle = 0) {

    // Dimension Calculations
    modul=modul*(1-clearance);

...

fix: //modul=modul*(1-clearance);

...

Image showing rack with modul=modul*(1-clearance) and black marks at correct pitch, rack mismatching pitch. Rack exactly matches spur gear pitch radius and should have the same number of teeth, it doesn't.

with-clearance

Image showing rack without clearance, black marks at correct pitch, in line with rack.

without-clearance
AcstomScientific commented 3 years ago

Good

wosym commented 2 years ago

Can confirm that this issue exists. However, I can not confirm that removing clearance solves it. At least not for herringbone racks. Also: the clearance parameter did exist in the original lib. It is not newly introduced.

alastaira commented 1 year ago

Just came across this same problem myself (though it took an embrassingly long time to discover: when my rack became unaligned I first began to doubt whether my maths was correct that it should move π gear reference diameter with each revolultion - it should!). I can't see any reason why that line exists to adjust the value of "module" in the rack() module - it's inevitably not going to pair correctly with the spur gear if you do (unless the spur gear is also meant to have `modul=modul(1-clearance);` ? But then neither one is the size specified!)