Defective Part -- Invoice # 419377

[robertr6]

I just received the subject part, PID 1251 (Aluminum GT2 Timing Pulley - 6mm Belt - 20 Tooth - 5mm Bore).

I attempted to place this pulley on the shaft of my (Invoice # 415184) stepper motor (PID 324), and it will not fit onto the shaft.

You need to check your stock of timing pulleys to assess the size of the bore hole relative to the shaft size on
the stepper motor. Both the motor shaft and the pulley bore are supposed to be 5mm.

Please send me a replacement pulley that will fit properly -- slides on shaft with no forcing but not too big/sloppy.

[adafruit_support_mike]

We test parts before we ever consider selling them, and we test the parts we do sell to make sure they live up to the specs when we get new batches.

There's always some variation in dimensions due to manufacturing tolerances, but a case where the maximum material conditions for both a shaft and a hole cause interference is rare. We'll be happy to get you a replacement if you did get hit by a statistical fluke, but since this kind of thing is rare, we'd like to document it.

If you have a caliper, could you take measurements of the shaft and hole diameters please? A standard sliding fit puts the hole about 0.002" larger than the shaft.

Could you also post a photo of the shaft and the gear? There are other things that can cause interference, like swaging or upset, and those would point to a different kind of problem.

[robertr6]

Good morning Mike,
I do not have a caliper, but will buy one today and make the measurements requested. I took some pics, imported into my computer and attempted to attach them to this reply, but get an error message saying "The image file you tried to attach is invalid.." The files are .JPG. I can attach my images to an email message - no problem. Send me your email address and I will send them to you. Otherwise, tell me how to attach my images to a forum reply. Thanks for your quick reply.

[adafruit_support_mike]

I'm torn between saying "you didn't need to buy a caliper" and not being able to imagine life without one.

Fair warning: calipers come in different grades, at prices ranging from $9.95 to $500. The $9.95 ones usually have two digits of resolution.. they let you measure down to 0.01", which is too coarse to measure a sliding fit but handy for day-to-day measurements. You want the next step up, usually in the $20 range for a 4" caliper. Those measure down to 0.001", and are the go-to tool for 90% of shop measurements. The more expensive ones are great if you have them, but my general rule for precision tools is "don't buy them until you know why you need them".

WRT photos, the forum software has a 1M limit on file size. 800x600 images tend to hit the best balance between "big enough to see detail" and "small enough to fit".

[robertr6]

Mike -- I have the measurements for you which were made with a dial caliper from auto parts store.

Stepper motor shaft -- 0.197 in. pulley hole bore == 0.195 in. 5 mm == 0.19685

And some additional data:
A 3/16 size drill bit fits easily in the pulley bore hole. A 13/64 size drill bit will not fit into the bore hole.
The actual size of the bore hole I estimated to be about half way between 3/16 and 13/64.
Half way between would be 25/128. This converts to decimal 0.19538. which is very close to what was measured
with the caliper.

So this data indicates that the pulley bore hole is too small --- .002 less than 5 mm, when it should be .002
larger than 5mm. It is .004 smaller than it should be. It should be about 0.199, versus 0.195. The shaft
size is about what it is supposed to be, 5 mm.

I am going to send some pictures to your support email address, since you have not responded with one.

[robertr6]

Mike -- here are the first three images.

IMG_0056.JPG (58.42 KiB) Viewed 569 times

IMG_0055.JPG (81.68 KiB) Viewed 569 times

[attachment=2]IMG_0050.JPG

[adafruit_support_mike]

The photos look good.. thanks.

Doing a go/no-go test with drill bits was a great idea, but be sure you measure the shanks with the caliper as well. The grinding process leaves the flutes a bit smaller than the raw stock.

It does sound like the hole is a touch too small.. 0.002" under the shaft diameter is a press-fit rather than a slip-fit. Send a note to [email protected] with a link to this thread and we'll get you a replacement.