Sine Bar

**jgedde** · Oct 16, 2012, 07:41 PM

I'd heard that a sine bar is an "exam" for an apprentice toolmaker.

All in all, it took about 3 hours to make (things wen't way too smoothly).

Here it is all done. Almost...

As you can see I didn't go crazy with the grinding on the bottom. Just enough to be flat. The wheel really needed dressing, and I traversed and fed quickly. For the top, I used a carefully dressed wheel, plenty of Crisco for lube and followed it up with about 2 minutes of lapping on 400 grit.

John

**duckman903** · Oct 20, 2012, 04:53 PM

I know how I'd do it but how did you measure the distance of the rounds

**jgedde** · Oct 20, 2012, 06:48 PM

I did it a couple if ways... One was using a height gauge and a DTI to find the high points. This wasn't even close to an accurate method. I came in at 5.003.

I then measured the exact diameter of the rounds, then measured the distance between them and added half the diameter of each round back in. I measured 5.0008 using that method.

Our inspection lab at work confirmed that using the CMM. They got 5.000772 (average). The rounds are square to the long axis within 0.0001.

While I'm content with 5.0008, the imports are twice as good (at a claimed +/- 0.0004)... But, 5.0008 is an error of only 0.016%...

Here's how the v-grooves were located when final grinding for the rounds, I used a dial indicator (2 inch range) and "leap frogged" the surface grinder to the right location. I guess that's why I'm 0.0008 off!

One round is about 0.0002 smaller than the other, but the top surface was ground with the rounds installed to compensate.

How would you have performed the measurment?

John