Loft face of involute gear works, loft 2d offset of same face doesn't

Post here for help on using FreeCAD's graphical user interface (GUI).
Forum rules
and Helpful information
IMPORTANT: Please click here and read this first, before asking for help

Also, be nice to others! Read the FreeCAD code of conduct!
geobruce
Posts: 48
Joined: Sat May 19, 2018 9:34 am

Loft face of involute gear works, loft 2d offset of same face doesn't

Post by geobruce »

Somewhere else somebody did post a solution to loft an involute gear. (https://forum.freecadweb.org/viewtopic. ... 06#p101106 ).
This works for just two involute gear faces. When I make a 2D offset of these faces in part WB freeCAD starts hanging.

I tried different options and orders of following functions to create a pair of offset gears and loft them.
Wire to Face (Part WB)
Upgrade (draft WB)
2D offset (Part WB)
Loft (Part WB)
3D offset (Part WB)

So what is different between a face made from an involute gear, and the face made of an offset involute gear?
You can find my file here: https://drive.google.com/open?id=18vdh4 ... b0fmDEA7s9
as I have trouble uploading the file to the forum.

Thanks in advance
User avatar
DeepSOIC
Veteran
Posts: 7896
Joined: Fri Aug 29, 2014 12:45 am
Location: used to be Saint-Petersburg, Russia

Re: Loft face of involute gear works, loft 2d offset of same face doesn't

Post by DeepSOIC »

Lofting between two gears with unequal teeth count is a pretty bad idea, because OCC will slice them up to make their edge counts equal. That will double an already high segment count, and generate a lot of extremely short edges that have a potential to be shorter than their tolerance. I have tried adding a circle in between your gears, and make two lofts. But the loft is self-intersecting, looks like an occ bug to me.


I assume you are making gears for 3d printing. Then, fill up the space between them with a simple revolution, in your example just a cylinder is enough.
geobruce
Posts: 48
Joined: Sat May 19, 2018 9:34 am

Re: Loft face of involute gear works, loft 2d offset of same face doesn't

Post by geobruce »

DeepSOIC wrote: Tue Sep 11, 2018 8:52 am Lofting between two gears with unequal teeth count is a pretty bad idea,
But with just the two gear profiles without the offset it works.
I'm trying to recreate these gears as in the picture:
Image

from this design: https://www.thingiverse.com/thing:2220506

I would like to recreate this gear reduction, but parametric and with more tolerance than the original one because it's not going smooth.
User avatar
DeepSOIC
Veteran
Posts: 7896
Joined: Fri Aug 29, 2014 12:45 am
Location: used to be Saint-Petersburg, Russia

Re: Loft face of involute gear works, loft 2d offset of same face doesn't

Post by DeepSOIC »

Then you'll have to do the transition manually, tooth by tooth. No FreeCAD operation as far as I know will give you a transition like on these thingiverse gears.
geobruce
Posts: 48
Joined: Sat May 19, 2018 9:34 am

Re: Loft face of involute gear works, loft 2d offset of same face doesn't

Post by geobruce »

DeepSOIC wrote: Tue Sep 11, 2018 8:52 am I have tried adding a circle in between your gears, and make two lofts. But the loft is self-intersecting, looks like an occ bug to me.
Ok I tried this and now I have more or less a result I can be happy with. (still not as nice as the loft from one gear to another).

But now the next problem is freeCAD won't let me union or connect the objects. Sometimes it works and sometimes it doesn't, If I change a parameter in the spreadsheet it takes very long to recalculate if it ever finishes.
The file: https://drive.google.com/open?id=1Ws4bc ... iL5FN7XX0D
Attachments
loft.png
loft.png (67.23 KiB) Viewed 925 times
User avatar
looo
Veteran
Posts: 3941
Joined: Mon Nov 11, 2013 5:29 pm

Re: Loft face of involute gear works, loft 2d offset of same face doesn't

Post by looo »

why not put a cylinder in between the two gears? Does the connection-section have any functionality?
geobruce
Posts: 48
Joined: Sat May 19, 2018 9:34 am

Re: Loft face of involute gear works, loft 2d offset of same face doesn't

Post by geobruce »

looo wrote: Tue Sep 11, 2018 12:37 pm Does the connection-section have any functionality?
I just want to avoid straight overhangs for 3d printing
chrisb
Veteran
Posts: 53922
Joined: Tue Mar 17, 2015 9:14 am

Re: Loft face of involute gear works, loft 2d offset of same face doesn't

Post by chrisb »

Is there any mecahnical advantage in this quintuple helical gear over the double or herringbone gear?
A Sketcher Lecture with in-depth information is available in English, auf Deutsch, en français, en español.
geobruce
Posts: 48
Joined: Sat May 19, 2018 9:34 am

Re: Loft face of involute gear works, loft 2d offset of same face doesn't

Post by geobruce »

chrisb wrote: Tue Sep 11, 2018 2:23 pm Is there any mecahnical advantage in this quintuple helical gear over the double or herringbone gear?
These are used for a specific kind of planetary gear where which you can achieve a very high reduction in this case 1379 to 1.
I just would like to get a better understanding of this gear and use it for a custom application if everything goes well.
User avatar
DeepSOIC
Veteran
Posts: 7896
Joined: Fri Aug 29, 2014 12:45 am
Location: used to be Saint-Petersburg, Russia

Re: Loft face of involute gear works, loft 2d offset of same face doesn't

Post by DeepSOIC »

geobruce wrote: Tue Sep 11, 2018 2:47 pm These are used for a specific kind of planetary gear where which you can achieve a very high reduction in this case 1379 to 1.
I just would like to get a better understanding of this gear and use it for a custom application if everything goes well.
Laying a circle between two teeth is not an overhang, it's a bridge. Usually prints very well, with only minor visual artefacts. IMO your transition is much more of an artefact than a bridge would be.
Post Reply