should a protractor head read like this?

[Craig Behnke]

just got a protractor head, when i look at the degree scale with the locking nut facing up, everything lines up properly. seen here:
100_5131.jpg

When i rotate the locking nut to facing down, the marks DO NOT line up properly, they look like they are off 1 or 1.5 degrees. seen here:
100_5130.jpg

Why is that, why does rotating it seem to make it read differently?

[Mike Henderson]

Looks like a defective unit to me.

Mike

[Myk Rian]

Ditto on defective. How close is it at 90º?

[Craig Behnke]

it's spot on at 90. given that the protractor body is closed on one end you can only measure 90 on one side/scale, but not the other.

[Craig Behnke]

Looks like a defective unit to me.

Mike

Mike, the crazy thing is that I thought that also, so I picked up another of the same brand (Starrett) and it has the SAME EXACT issue.

[glenn bradley]

I don't see how that can be right. How would you know which side to trust; the tick on the left or the tick on the right?

[Bill Orbine]

Nope, it ain't looking right.... I'm beginning to like all the older Starrett tools much more than what's made today. But that's me being picky!

[John Coloccia]

I think the simple solution is that the markings do not take up exactly half the circle...they take up slightly more. That would sort of imply that it's not designed to be turned more than 90 degrees. Functionally, that's probably fine, but it seems like a strange way to design it. I've used them from time to time, but I've never owned one. Seems very odd to me, but as flaky as some of Starrett's offerings have become, I don't think that they've gotten THIS bad yet, so there's a probably a good reason for it.

edit:
even at 0 degrees, it appears to be almost a half degree off on the left marking when the right marking is lined up dead nuts. Hmmmm.

[Rick Gibson]

From the picture it looks as if your locking nut is not tight. That would allow some play. Tighten the nut and see if you get the same thing. If you do a letter or email to Starret would be in order. Possibly a bad batch got out.

[Ken Fitzgerald]

If it doesn't read the same when positioned in both positions, you'd think the scale and the two reference marks are something less than 180º apart in one position and greater in the other position OR

the opening the rotating portion rides in is elliptical versus being absolutely circular.

[Craig Behnke]

From the picture it looks as if your locking nut is not tight. That would allow some play. Tighten the nut and see if you get the same thing. If you do a letter or email to Starret would be in order. Possibly a bad batch got out.

tightened the nuts, checked both protractor heads that i have (same exact model, both brand new) both show the error, one shows 1 degree , the other shows 1.5 degrees off.

[Ronald Blue]

I don't think it was ever intended to be used that way. I can't think of any reason why you would need to. I am not home so I can't check my Starrett but it is easily 75 years old as it came from my uncle who died in the early 70's and I bought all of his machinist tools. I am confident it won't be a "faulty" batch. The scale is designed to work in the range that is up to 90 degrees off zero in conjunction with the ground surface on head. I am probably not stating this well but I am certain that this will be true of any brand of protractor head. Just my .02 worth.

[Mike Henderson]

I just went into the shop to check. I have a Mitutoyo head and a Starrett head. Both can be rotated 180 degrees and they are aligned. The Starrett is somewhat old, but probably not more than 25 years. The Mitutoyo is probably of equal age. I'm just guessing on the age of both.

Mike

[Dan Hintz]

Looks like a failed stamping... maybe their die was slowly shifting out of alignment.

[John Coloccia]

The fact that even in the first picture, you can see that it's already off by almost 1/2 a degree indicates something is very wrong. You know, Starrett quality has been going into the toilet for a good number of years now. Brown and Sharpe seems to have gone to hell too. Mitutoyo is still solid as ever.