Repeatability, Accuracy or Resolution

[dusty]

I started this thread as a result of having read the thread on the Miterset; however, the Miterset is NOT the intended target of this discussion. The target is basically "technique".

I would suggest that before you comment you take a few measurements of your own using whatever tools you feel are your most dependable for this sort of task.

First, zero your miter gauge. Use whatever method you feel will give you the most accurate results. I used my Miterset.

Now clamp your miter gauge somewhere that allows you to use something like the Wixey (a digital angle gauge) to make a series of measurements. I suggest ten (10) to start with.

I clamp the bar of my miter gauge in a bench mounted vise. Clamp it so that the miter bar is as close to vertical as you can get it without the use of measuring devices other than your calibrated eyeball.

Now zero the angle indicator against the miter bar which is mounted vertically. This should put the face of your miter gauge near horizontal. Measure it. If perfect, it should read 90 °.

Record that pair of readings. Hopefully they will be 0.00° and 90.0°. Hopefully, they are all 0.00° and 90.0°.

Keep in mind, nothing moved. The miter bar was forever vertical and the face of the miter gauge was horizontal. Were all of your readings as expected? That is 0.00° and 90.0. I doubt it. Why? Because there are factors other than the relative position of the two reference surfaces that come into play.

Repeatability of the measuring device being one of them. However, not necessarily the most likely culprit.

Technique. Understanding your tools.

To make my point, set your digital measuring device on a smooth relatively flat surface and zero it. Now without doing anything else, carefully change its position by pushing on one corner of the gauge so as to slightly rotate it. The reading will change.

The face of the miter gauge remains at 90° with respect to the miter bar but the angle indicator does not agree.

Why? The technical characteristics of your angle indicator is why. Technique must take those characteristics into consideration. Often we do not.

There are other ways to make this point but this one should do for now.

Repeatability, Accuracy or Resolution

Incidently, I have cut probably thousands of 90° cross cuts without the use of digital measuring devices. In years gone by I used to set my miter gauge to 90° by loosening the locking device, turning the gauge upside down in the miter track and pushing the face of the miter gauge up against front rail of the main table. Lock the miter gauge there and go for it. Close enough for segments? Probably not. Close enough for most of what I do? Absolutely!

[rjent]

Incidently, I have cut probably thousands of 90° cross cuts without the use of digital measuring devices. In years gone by I used to set my miter gauge to 90° by loosening the locking device, turning the gauge upside down in the miter track and pushing the face of the miter gauge up against front rail of the main table. Lock the miter gauge there and go for it. Close enough for segments? Probably not. Close enough for most of what I do? Absolutely!

What an outstanding idea! Thanks for that tip!

Thanks Dusty!

[algale]

It would be neat if the main table were drilled with the miterset holes from the factory!

[dusty]

It would be neat if the main table were drilled with the miterset holes from the factory!

I don't know how I feel about that. For me, the first thing I would have to worry about is "how to keep track of the pins". As it is now, after I use the miterset, I pack it all back in the box it came in and store it.

I am also not sure that I would like all of those holes in my table top.

[Gene Howe]

I've definitely seen the Wixey variables in setting the table for bevel cuts.

[jsburger]

I started this thread as a result of having read the thread on the Miterset; however, the Miterset is NOT the intended target of this discussion. The target is basically "technique".

I would suggest that before you comment you take a few measurements of your own using whatever tools you feel are your most dependable for this sort of task.

First, zero your miter gauge. Use whatever method you feel will give you the most accurate results. I used my Miterset.

Now clamp your miter gauge somewhere that allows you to use something like the Wixey (a digital angle gauge) to make a series of measurements. I suggest ten (10) to start with.

I clamp the bar of my miter gauge in a bench mounted vise. Clamp it so that the miter bar is as close to vertical as you can get it without the use of measuring devices other than your calibrated eyeball.

Now zero the angle indicator against the miter bar which is mounted vertically. This should put the face of your miter gauge near horizontal. Measure it. If perfect, it should read 90 °.

Record that pair of readings. Hopefully they will be 0.00° and 90.0°. Hopefully, they are all 0.00° and 90.0°.

Keep in mind, nothing moved. The miter bar was forever vertical and the face of the miter gauge was horizontal. Were all of your readings as expected? That is 0.00° and 90.0. I doubt it. Why? Because there are factors other than the relative position of the two reference surfaces that come into play.

Repeatability of the measuring device being one of them. However, not necessarily the most likely culprit.

Technique. Understanding your tools.

To make my point, set your digital measuring device on a smooth relatively flat surface and zero it. Now without doing anything else, carefully change its position by pushing on one corner of the gauge so as to slightly rotate it. The reading will change.

The face of the miter gauge remains at 90° with respect to the miter bar but the angle indicator does not agree.

Why? The technical characteristics of your angle indicator is why. Technique must take those characteristics into consideration. Often we do not.

There are other ways to make this point but this one should do for now.

Repeatability, Accuracy or Resolution

Incidently, I have cut probably thousands of 90° cross cuts without the use of digital measuring devices. In years gone by I used to set my miter gauge to 90° by loosening the locking device, turning the gauge upside down in the miter track and pushing the face of the miter gauge up against front rail of the main table. Lock the miter gauge there and go for it. Close enough for segments? Probably not. Close enough for most of what I do? Absolutely!

I absolutely agree with you that technique is a very important component to making accurate measurements.

I did your experiment with the miter gauge set with the Miterset. I got 0* and 90* +- 0.1* every time I made a measurement with my Wixey. The stated accuracy and repeatability of the Wixey are both 0.1*. So I would say the results are what I would expect.

As for as your second point, if the surface is only "reasonably flat" and not level in all directions (a true reference surface) the reading will change as the Wixey is rotated. This has nothing to do with technique. It has to do with the fact that the surface used is not a reference surface. Am I missing something?

The advent of cheap and reasonably accurate digital measuring devices have made us question the accuracy of our alignment settings using other methods. As you said in your last paragraph, that method worked perfectly well for years and I doubt it was as accurate as the stated 0.1* accuracy of the Wixey.

[dusty]

I started this thread as a result of having read the thread on the Miterset; however, the Miterset is NOT the intended target of this discussion. The target is basically "technique".

I would suggest that before you comment you take a few measurements of your own using whatever tools you feel are your most dependable for this sort of task.

First, zero your miter gauge. Use whatever method you feel will give you the most accurate results. I used my Miterset.

Now clamp your miter gauge somewhere that allows you to use something like the Wixey (a digital angle gauge) to make a series of measurements. I suggest ten (10) to start with.

I clamp the bar of my miter gauge in a bench mounted vise. Clamp it so that the miter bar is as close to vertical as you can get it without the use of measuring devices other than your calibrated eyeball.

Now zero the angle indicator against the miter bar which is mounted vertically. This should put the face of your miter gauge near horizontal. Measure it. If perfect, it should read 90 °.

Record that pair of readings. Hopefully they will be 0.00° and 90.0°. Hopefully, they are all 0.00° and 90.0°.

Keep in mind, nothing moved. The miter bar was forever vertical and the face of the miter gauge was horizontal. Were all of your readings as expected? That is 0.00° and 90.0. I doubt it. Why? Because there are factors other than the relative position of the two reference surfaces that come into play.

Repeatability of the measuring device being one of them. However, not necessarily the most likely culprit.

Technique. Understanding your tools.

To make my point, set your digital measuring device on a smooth relatively flat surface and zero it. Now without doing anything else, carefully change its position by pushing on one corner of the gauge so as to slightly rotate it. The reading will change.

The face of the miter gauge remains at 90° with respect to the miter bar but the angle indicator does not agree.

Why? The technical characteristics of your angle indicator is why. Technique must take those characteristics into consideration. Often we do not.

There are other ways to make this point but this one should do for now.

Repeatability, Accuracy or Resolution

Incidently, I have cut probably thousands of 90° cross cuts without the use of digital measuring devices. In years gone by I used to set my miter gauge to 90° by loosening the locking device, turning the gauge upside down in the miter track and pushing the face of the miter gauge up against front rail of the main table. Lock the miter gauge there and go for it. Close enough for segments? Probably not. Close enough for most of what I do? Absolutely!

I absolutely agree with you that technique is a very important component to making accurate measurements.

I did your experiment with the miter gauge set with the Miterset. I got 0* and 90* +- 0.1* every time I made a measurement with my Wixey. The stated accuracy and repeatability of the Wixey are both 0.1*. So I would say the results are what I would expect.

As for as your second point, if the surface is only "reasonably flat" and not level in all directions (a true reference surface) the reading will change as the Wixey is rotated. This has nothing to do with technique. It has to do with the fact that the surface used is not a reference surface. Am I missing something?

The advent of cheap and reasonably accurate digital measuring devices have made us question the accuracy of our alignment settings using other methods. As you said in your last paragraph, that method worked perfectly well for years and I doubt it was as accurate as the stated 0.1* accuracy of the Wixey.

You can look at it that way but if one does not understand that the digital angle indicator can/will report differently depending on its orientation or if one tends to disregard that fact, the readings that are provided are less reliable. I consider it technique. I used to blame it on the Wixey but once I learned of the limitations of the digital angle indicator, I realize that the errors were/are attributable to "my poor technique".

[jsburger]

I started this thread as a result of having read the thread on the Miterset; however, the Miterset is NOT the intended target of this discussion. The target is basically "technique".

I would suggest that before you comment you take a few measurements of your own using whatever tools you feel are your most dependable for this sort of task.

First, zero your miter gauge. Use whatever method you feel will give you the most accurate results. I used my Miterset.

Now clamp your miter gauge somewhere that allows you to use something like the Wixey (a digital angle gauge) to make a series of measurements. I suggest ten (10) to start with.

I clamp the bar of my miter gauge in a bench mounted vise. Clamp it so that the miter bar is as close to vertical as you can get it without the use of measuring devices other than your calibrated eyeball.

Now zero the angle indicator against the miter bar which is mounted vertically. This should put the face of your miter gauge near horizontal. Measure it. If perfect, it should read 90 °.

Record that pair of readings. Hopefully they will be 0.00° and 90.0°. Hopefully, they are all 0.00° and 90.0°.

Keep in mind, nothing moved. The miter bar was forever vertical and the face of the miter gauge was horizontal. Were all of your readings as expected? That is 0.00° and 90.0. I doubt it. Why? Because there are factors other than the relative position of the two reference surfaces that come into play.

Repeatability of the measuring device being one of them. However, not necessarily the most likely culprit.

Technique. Understanding your tools.

To make my point, set your digital measuring device on a smooth relatively flat surface and zero it. Now without doing anything else, carefully change its position by pushing on one corner of the gauge so as to slightly rotate it. The reading will change.

The face of the miter gauge remains at 90° with respect to the miter bar but the angle indicator does not agree.

Why? The technical characteristics of your angle indicator is why. Technique must take those characteristics into consideration. Often we do not.

There are other ways to make this point but this one should do for now.

Repeatability, Accuracy or Resolution

Incidently, I have cut probably thousands of 90° cross cuts without the use of digital measuring devices. In years gone by I used to set my miter gauge to 90° by loosening the locking device, turning the gauge upside down in the miter track and pushing the face of the miter gauge up against front rail of the main table. Lock the miter gauge there and go for it. Close enough for segments? Probably not. Close enough for most of what I do? Absolutely!

I absolutely agree with you that technique is a very important component to making accurate measurements.

I did your experiment with the miter gauge set with the Miterset. I got 0* and 90* +- 0.1* every time I made a measurement with my Wixey. The stated accuracy and repeatability of the Wixey are both 0.1*. So I would say the results are what I would expect.

As for as your second point, if the surface is only "reasonably flat" and not level in all directions (a true reference surface) the reading will change as the Wixey is rotated. This has nothing to do with technique. It has to do with the fact that the surface used is not a reference surface. Am I missing something?

The advent of cheap and reasonably accurate digital measuring devices have made us question the accuracy of our alignment settings using other methods. As you said in your last paragraph, that method worked perfectly well for years and I doubt it was as accurate as the stated 0.1* accuracy of the Wixey.

You can look at it that way but if one does not understand that the digital angle indicator can/will report differently depending on its orientation or if one tends to disregard that fact, the readings that are provided are less reliable. I consider it technique. I used to blame it on the Wixey but once I learned of the limitations of the digital angle indicator, I realize that the errors were/are attributable to "my poor technique".

I don't know how to look at it any other way. If I zero my Wixey on the 8" thick granite table of the Zeiss CMM machine I used at work that is perfectly level and in a climate controlled room and rotated it as you describe I would expect it to be within the stated accuracy of the Wixey. 0.1* accuracy and 0.1* repeatability. If you have never done something similar how do you know the device is wrong or inaccurate. Do those tolerances add? I don't know. If so then the variance would be +- 0.2* on a dead flat level surface.

So you are saying due to your poor technique (your words) a better technique would render your "relatively flat" surface of unknown levelness to be perfect within the tolerances of your measuring device.

The reason for having measuring devices is to check things in the field relative to a standard. That standard is the measuring devices calibration from the manufacturer to what ever accuracy is stated. I used to use Starrett bore gauges that were calibrated to 4 1/2 digits (0.00005). Most of us do not have laboratory standards in our shop to check calibration.

So I guess if you don't trust the gauge don't use it or get one that you do trust.

[JPG]

Moving a measurement device about an irregular surface and getting differing readings has nothing to do with accuracy or repeatability. More than likely the irregularities will exceed the influences of technique.

When using the wixey(or similar), stiction has to be allowed for and is likely the determining factor of all it's accuracy deviations.

[jsburger]

Moving a measurement device about an irregular surface and getting differing readings has nothing to do with accuracy or repeatability. More than likely the irregularities will exceed the influences of technique.

When using the wixey(or similar), stiction has to be allowed for and is likely the determining factor of all it's accuracy deviations.

I think that is what I have been trying to say. Dusty seems to disagree for some reason.

I don't know why stiction is a factor. Stiction is the FORCE required to to overcome static cohesion and slide two stationary objects in contact with each other on a parallel surface. How does that translate to reading differences?