What are the odds of getting two bad arbors?

[WobblyHand]

Technically, they were half price!

Quite true at this point. Which is why I will not seek direct satisfaction from McMaster. I hope they claw back the cost from Sierra American. McMaster has been more than fair to me.

Still, I will contact Sierra American, just to let them know of the quality issue. I don't want money or even parts from them. I want them to know they are shipping subpar material. It's up to them to decide what to do next.

 

[WobblyHand]

Say I fit a pin within 0.001" of the threaded hole diameter. The hole appears to be about 1" deep. Let the pin be 2" long. Then the error (assuming an errorless constant diameter pin) would be less than or equal to 0.002"? I don't know if I can make a pin that is roughly 0.269" diameter that is 2" long with constant diameter on my lathe. The length to diameter ratio is pretty high.

What if I made a shoulder screw like this? The flat part would register against the bottom, like a backplate does to a threaded spindle. What would the error be relative to the bottom of the arbor? 5/16-18 thread, 1/8" long 0.25" OD gutter, 5/8" OD, 2" long. Pretty sure I could make a good clean version of this. The bottom of the interior of the arbor is turned. I used a dial indicator (not a DTI) against the bottom face and measure about 0.0006" TIR. With only a 1" bore, it is hard to get a DTI in there and position the pointer to minimize cosine error.

I'm scratching my head how to measure this without altering the arbor. If I use a boring bar to face the bottom of the hole, then I know it is flat, but I have "altered the evidence" so to speak. Assuming a 0.0006" bottom runout, and I make a near perfect screw, the screw is bottomed against the arbor, the baseline TIR at 2" would be 0.002", assuming the screw hole is on center. To minimize the error, it would be better to measure near the bottom shoulder. I need some of the length just to be able to screw it into the hole. I could machine a hex head on the end for a socket, or make a slot for a screwdriver and make it shorter.

Unless someone has a better idea, I will try this.

 

[WobblyHand]

Made the piece on my lathe, in a collet. Single pointed the threads. Turned the shoulder. Later turned down the diameter to ensure it was round. Measured the TIR of the rod and the shoulder and it was 0.0001". Then set up the dividing head for hexes. Due to a brain fart, I cut two hexes, but fortunately, the wrong hex doesn't interfere with the measurement.

I screwed in the shoulder bolt until it bottomed against the shoulder. I put marker on the shoulder to test for contact.
Everything was chucked up in the mini-lathe and I measured the TIR of the smooth cylindrical surface. Then I pushed the DTI towards the chuck 0.500", checked for interference, and remeasured the TIR. I did this for both arbors.

I will add in the TIR numbers in a little while. They are in my phone, but my phone is not nearby. Think they confirm that the hole is off center, but close to parallel to the center, for both arbors.

Edit: Here are the measured TIRs
#1. 0.0205 at edge (like picture above), 0.022" in 0.500" towards chuck
#2. 0.0144 at edge, 0.01375" in 0.500" towards chuck

Also measured the SHCS heads. 5/16"-18 screws have a 15/32" head according to McMaster. I measured some of my screws that I bought from McMaster and they had heads that were 0.002" under 15/32". These screws will not fit these arbors. If the holes were on center, they would just fit. For the two screws supplied by Sierra American, the head diameters were 0.007" under 15/32", just barely fitting, and in both cases hitting the counterbore by a thousandth or two.

Both of the arbor screw holes were packed with swarf. Removed quite a bit of crap from the holes. Clearly they didn't bother to clean post tapping.

 

[extropic]

@WobblyHand

I think it's foolish not to refer the problem back to your supplier (McMaster).
Why? Because informing them of the second defective unit should elevate the problem and facilitate getting it fixed.
By not reporting it to McMaster, they only know of one bad part (from you) and they may dismiss the issue as random.
If McM becomes aware of repeated failures they should purge their stock and resolve it with their supplier.
McM is a top notch performer, with top notch systems in place to handle problems. However, they are not clairvoyant. You need to report the problem.
Once you modify the item, you own it. If you're short of projects, I can probable find some defective crap to sell you.

Similar story: I bought, from McMaster, an arbor for abrasive drums (3" IIRC). It was labeled "Made in USA" and it had unacceptable runout (.08" IIRC). I reported it and they refunded my cost. I didn't want to bother with another POS. I virtually begged them to give me a return label because I wanted some responsible person to see what junk they were passing on. McM didn't want it back. I presume they handled the problem without actually seeing my defective piece. They must have, otherwise they would be going the way of Sears, instead of growing stronger.

 

[jwmay]

This thread has been going for awhile. But just to say my piece. I think you shouldn't have bothered doing anything except sending it back. Time is money, and you've spent plenty of it doing QC work for someone, that they can't and won't use. If it's me, I fix it and carry on...or I send it back. No interest in figuring out how they failed. I've got plenty of my own failures to think on. Lol

 

[sdelivery]

Check every fifth part

CNCs make parts quickly , both good and bad . Have to wonder how QC didn't pick up the issue .

 

[sdelivery]

@WobblyHand

I think it's foolish not to refer the problem back to your supplier (McMaster).
Why? Because informing them of the second defective unit should elevate the problem and facilitate getting it fixed.
By not reporting it to McMaster, they only know of one bad part (from you) and they may dismiss the issue as random.
If McM becomes aware of repeated failures they should purge their stock and resolve it with their supplier.
McM is a top notch performer, with top notch systems in place to handle problems. However, they are not clairvoyant. You need to report the problem.
Once you modify the item, you own it. If you're short of projects, I can probable find some defective crap to sell you.

Similar story: I bought, from McMaster, an arbor for abrasive drums (3" IIRC). It was labeled "Made in USA" and it had unacceptable runout (.08" IIRC). I reported it and they refunded my cost. I didn't want to bother with another POS. I virtually begged them to give me a return label because I wanted some responsible person to see what junk they were passing on. McM didn't want it back. I presume they handled the problem without actually seeing my defective piece. They must have, otherwise they would be going the way of Sears, instead of growing stronger.

Oh boy oh boy can I buy some of your defective crap?
I ll trade you some of my broken shirt

 

[sdelivery]

All kidding aside definitely start with McMaster they have the weight to bring on change. I am sure they don't want to go through the same situation with a thousand other buyers.
I would also e mail the manufacturer and yes do mention that everyone on the forum is watching.
I am not looking for a freebie I am trying to help American Manufactures succeed.

 

[WobblyHand]

All kidding aside definitely start with McMaster they have the weight to bring on change. I am sure they don't want to go through the same situation with a thousand other buyers.
I would also e mail the manufacturer and yes do mention that everyone on the forum is watching.
I am not looking for a freebie I am trying to help American Manufactures succeed.

I agree with you. I will contact McMaster. They should know they are having a problem with the quality of one of their suppliers.
And yes, I plan to contact Sierra American. I don't want or need a freebie. I would like SA to continue prosper, by offering quality product. I want American manufacturers to succeed.

I tried an experiment. I cut two (different) 5/16"-18 screws to length and turned the heads down by 0.050" in diameter. The heads no longer interfere with the counterbore. There is enough wiggle room in the main hole of the cap. So I do not have to alter the arbors. The arbor caps seat square with the precision face. So I have essentially fixed the problem and have 2 functional arbors, at the expense of some non-standard screws.

 

[WobblyHand]

This thread has been going for awhile. But just to say my piece. I think you shouldn't have bothered doing anything except sending it back. Time is money, and you've spent plenty of it doing QC work for someone, that they can't and won't use. If it's me, I fix it and carry on...or I send it back. No interest in figuring out how they failed. I've got plenty of my own failures to think on. Lol

I received the second arbor two days ago at the close of business. In other words, the start of the weekend. McMaster didn't want the first arbor to be returned. It's likely that they wouldn't want the second one either. I just don't need three of them!

I wanted to know what the issue was, so I could fix one of them. It's unlikely that Sierra American really cares, but I will tell them that they are not delivering quality product, and I am disappointed with the experience. I think they are deliberately using undersized screws because their drilling fixture has an offset and they're playing and losing at the tolerance game.

I will tell McMaster that their vendor has shipped them poor quality product. They can put the pressure on SA a lot more effectively than I can.