GearHeads Corner

Hi,
Big newbie here...
I made my first XL pulley today.  If has 90 teeth and around 5.7" in diameter.  It is made in MDF as a test.
When  I put a belt around the belt starts meshing and by the time it gets around 1/4 of the way around it starts to loose mesh.  However, if I pull on the belt (stretch it) it starts to fit., but to get it to engage fully I have to pull quite hard.  Of course I do not have the matching smaller pulley yet and I'm doing it all by hand so I am not sure if there is something wrong or if this is normal?
Any suggestions are appreciated.
Thanks

Hi Tomb:

Sounds off. It should fit fairly easily.. but it doesnt have to be off by much to create what your describe. In fact the
fact you can pull it to get it on means your  pretty close. When you place the belt on the pulley you should be able
to hold that pulley with the belt pinched between two fingers on the other side to my mind. I usually can, not that Ive
done a lot of pulleys but a few..
  If you can put the belt on by pulling it tight, I think Id tell your controller to use a tool diameter a bit smaller than the
actual tool. Your tool being just a touch smaller than entered ( or many other issues ) can make the pulley cut a bit larger
than it should be, and it doesnt take much at all. The larger the pulley the easier it is to be off, however much your off
adds up by the number of teeth.. the more teeth , the more accurate you need to be. Thats what Ive found at any rate.
Id cut a second one cutting just a hair off the declared tool diam, and see the difference.. gauge it from there.
 
  In 3d printing of pulleys Ive learned to scale to 99%, but I suspect all 3d printers will be a bit different..

Art




 

Hi,
Thanks.  You are right.  I am using a new CNC Mill (Shapeoko-3) and I don't yet have it dialed in well enough.  The diameter of the gear is more than it should be so that's the source of the error.
So, I'll tune this up a bit better and then if I still have issues I will take your hint of 99%.
Thank you, Tom

Hi,
Setting the tool size to .99 the real size made a big difference.  The belt meshes pretty well perfectly.
Thanks.

Tomb:

Thx, and thanks for letting me know, nice to hear your results are now good.

Art