Accurate angles are *really* hard. A right angle is the easy case. Integral fractions of 360 aren't too bad, but non-integral fractions are *very* difficult.
Accurate angles are *really* hard. A right angle is the easy case. Integral fractions of 360 aren't too bad, but non-integral fractions are *very* difficult.What tolerances do you get with a good sine bar and gauge blocks?
A good variant is to use a 10 second or better level to scrape two faces parallel, then rotate 90 and scrape the other faces level using a leveled surface plate. I'd surely want an old piece of cast iron if I were going to do all that work.
Accurate angles are *really* hard. A right angle is the easy case. Integral fractions of 360 aren't too bad, but non-integral fractions are *very* difficult.What tolerances do you get with a good sine bar and gauge blocks?
Depends upon the sine bar, gauge blocks and skill of the user. For a standard set of blocks in 0.0001" increments and a 5" sine bar the resolution is about 4 arc seconds. So with a cheap set of blocks and sine bar, 15 seconds is probably the best one can hope for. And that's being optimistic. A more realistic expectation would be double that and one minute if you did not have good temperature control and were in a hurry.
Just wringing the blocks is a bit of an art form to get consistent results. And then you have to wait for them to cool off from handling.
Accurate angles are *really* hard. A right angle is the easy case. Integral fractions of 360 aren't too bad, but non-integral fractions are *very* difficult.What tolerances do you get with a good sine bar and gauge blocks?
Depends upon the sine bar, gauge blocks and skill of the user. For a standard set of blocks in 0.0001" increments and a 5" sine bar the resolution is about 4 arc seconds. So with a cheap set of blocks and sine bar, 15 seconds is probably the best one can hope for. And that's being optimistic. A more realistic expectation would be double that and one minute if you did not have good temperature control and were in a hurry.
Just wringing the blocks is a bit of an art form to get consistent results. And then you have to wait for them to cool off from handling.
No offense, but it seems unnecessary to degrade the resolution from 4 arc seconds to 1 minute. Gage block accuracy, temperature, and errors due to wringing aren't serious issues at that level. And impatience ... that is certainly not a legitimate limiting effect.
A cheap set of gauge blocks is only good to 50 millionths. A cheap sine bar to 100 millionths.
Just handling the stuff is a serious temperature problem.
Obviously you have not sat waiting for the temperatures to normalize if you think patience doesn't matter.
Lacoste & Romberg developed the airborne gravimeter. Everyone else said it could not be done. I saw a scrap damper at a geophysical convention and was chatting with the guy at the booth. One of their interview questions for machinists was, "How long do you think it would take to make this part?" Typical answer was a week or so. Actual company experience over many years was it took a month.
In the late 40's John Strong built a ruling engine at Johns Hopkins. The machine was submersed in a temperature controlled oil bath in a room inside a room. Staff could only remain in the outer room to inspect the operation for very brief periods of time because their body heat would distort the ruling engine and ruin the diffraction gratings. There is a great set of articles about this in Scientific American circa 1948.
What tolerances do you get with a good sine bar and gauge blocks?
My response was based on what I thought I could reasonably expect to achieve with the $500 or so of Chinese tooling I have for doing such a setup. I might well do better, but I'd have to have another way of making the same measurement to have any confidence.
How accurately spaced are the rolls on the sine bar? I don't know.
How accurately round are the rolls? I don't know.
How straight and flat is the sine bar? I don't know
How parallel are the rolls? I don't know
How flat is that part of my surface plate? I don't know.
How accurate are these particular gauge blocks? I don't know.
Most of the tolerances for the factors i mentioned are 0.0001".
Most of the tolerances for the factors i mentioned are 0.0001".
So, do you know the tolerances or not?
As you disagree with my estimate of accuracy, you can then provide a tutorial for the OP on how to calculate the tolerance band for a sine bar setup using your tooling.
What tolerances do you get with a good sine bar and gauge blocks?A person who asks this question is not familiar with either the tools or the work practices required to get the best performance. I see no benefit to suggesting that the tolerances achievable by a master toolmaker using the best tooling made are relevant to such a question.
[...]
For ordinary workshop tooling the typical specs are:
5" Sine bar:
roll diameters 0.0001" x 2 = 8 arc seconds
roundness 0.0001" x 2 = 8 arc seconds
parallelism 0.0001" = 4 arc seconds
Gauge blocks
2 B grade blocks 2*0.00005 = 0.0001" = 4 arc seconds
B grade surface plate 0.0002" = 8 arc seconds
The total assuming all tooling is in calibration is 32 arc seconds tolerance range.