You'll see I'm right if you run your test like this: put in the shortest probe you can use to measure "runout" on an inside diameter - a bored hole is perfect. Note TIR. Now, raise the Z-axis and do it again with a longer probe. You'll see that TIR will be reduced by roughly the ratiometric increase in probe length. I say roughly because the angle of the prpbe with respect to the Z-axis centerline will have some effect on your readings...
A coaxial indicator is accurate with only ONE probe length.
Since you're measuring a tilted plate, you need to measure the SAME points with both probes - not easy to do. The longer the probe, the less the needle will move for any given displacement. Since you're measuring points further away from the "pivot point" your setup compensates for the increase in probe length because the displacement of the plate has increased..
You don't understand what you are seeing. I show plainly that the probe length doesn't matter in this configuration, the needle deflection remains the same. The coax indicator is behaving exactly like a protractor and measuring angle, not distance. The angle is independent of the probe length. It is explained at my metal working at home website.
@spudzwon Ahhh now that's a horse of a different color. It is indeed measuring angle in a sense. The angle could be calculated from the TIR and the diameter being described by the probe tip. I need to try this with my coax on a known angle and verify the math...
I enjoyed the other video on tramming too, with the brake rotor. What are you using for a surface plate in this video? It looks like a piece of granite. Makes me wonder about using a polished granite floor tile. Though the bottom is not polished. I would think it is very flat judging from the way light reflects off the surface. I am going out in the shop to tram mine now.
That is a granite tile from the local Home Depot. It isn't adequate for tramming as there's no assurance the surfaces are parallel, but for this demonstration I was tipping the tile at a slight angle, so it didn't matter. The polished surface is fine for checking dimensions and simple layouts, but not flat enough for scraping.
The purpose of this test was to show that a coaxial indicator does not lose sensitivity if the probe length changes. This is a common misunderstanding.
You'll see I'm right if you run your test like this: put in the shortest probe you can use to measure "runout" on an inside diameter - a bored hole is perfect. Note TIR. Now, raise the Z-axis and do it again with a longer probe. You'll see that TIR will be reduced by roughly the ratiometric increase in probe length. I say roughly because the angle of the prpbe with respect to the Z-axis centerline will have some effect on your readings...
Ziknazoo 10 months ago
A coaxial indicator is accurate with only ONE probe length.
Since you're measuring a tilted plate, you need to measure the SAME points with both probes - not easy to do. The longer the probe, the less the needle will move for any given displacement. Since you're measuring points further away from the "pivot point" your setup compensates for the increase in probe length because the displacement of the plate has increased..
Ziknazoo 10 months ago
@Ziknazoo
You don't understand what you are seeing. I show plainly that the probe length doesn't matter in this configuration, the needle deflection remains the same. The coax indicator is behaving exactly like a protractor and measuring angle, not distance. The angle is independent of the probe length. It is explained at my metal working at home website.
spudzwon 10 months ago
@spudzwon Ahhh now that's a horse of a different color. It is indeed measuring angle in a sense. The angle could be calculated from the TIR and the diameter being described by the probe tip. I need to try this with my coax on a known angle and verify the math...
Ziknazoo 10 months ago
I enjoyed the other video on tramming too, with the brake rotor. What are you using for a surface plate in this video? It looks like a piece of granite. Makes me wonder about using a polished granite floor tile. Though the bottom is not polished. I would think it is very flat judging from the way light reflects off the surface. I am going out in the shop to tram mine now.
CncObsession 1 year ago
That is a granite tile from the local Home Depot. It isn't adequate for tramming as there's no assurance the surfaces are parallel, but for this demonstration I was tipping the tile at a slight angle, so it didn't matter. The polished surface is fine for checking dimensions and simple layouts, but not flat enough for scraping.
The purpose of this test was to show that a coaxial indicator does not lose sensitivity if the probe length changes. This is a common misunderstanding.
spudzwon 1 year ago