$16.41 2.7:1 speed reducer

[DonInReno]

I don’t know why I find it so interesting to order parts from multiple suppliers just to see the variation in what is being sold, but I do!  I usually encourage people to buy twice as many as they need since odds are something won’t be quite right.  

The two “40mm” servo drive pulleys showed up.   Both are advertised as 40mm - a little smaller than I’ve seen advertised before. 

One measures 42.5mm - they wouldn’t be the first to round down or up to make the product sell better.  The other is nothing more than a 45mm pulley being sold as a 40mm.   It’s not even 44mm - measures a full 45mm.

These are clearly not made in the same plant.  The mold marks and design of the part are slightly different.   The aluminum alloy is different and the darker of the two has a much better finish and fewer little voids from how the metal flowed into the mold.  

The one that appears nicer also has an entire extra operation performed to the bore - a reamer has taken down about 25% of the surface to exactly .591” (15mm).   If someone was designing an injection molded part to not be reamed at all they’re cast it slightly larger - out of curiosity a quick check with gauge pins showed exactly that.   The one that cut corners in not only material quality, but bore size was 001” oversized and was $3 more expensive.

Once again I’d suggest that not all Chinese sewing machine pulleys (or machines, or anything else) are made in the same plant just because they look similar!  Lol

 

[dikman]

Keep up the good work, Don, you're finding out all sorts of things and saving us the trouble.