PSA: Harbor Freight Digital Caliper $16

[Ed Bennett]

Sorry Al. Yes, about a year ago there was a guy who came along with his own tablesaw alignment procedure. He claimed that this procedure enabled him to achieve repeatable 0.0001" accuracy on his tablesaw. No, that's not mistake, one ten-thousandth of an inch accuracy - IN WOOD! Of course, it took a monumental effort to get him to submit samples of such claimed accuracy. And, of course, his own samples (tested by an unbiased third party) proved him wrong. Turns out he was using a 0.001"/div indicator to "guestimate" 0.0001" accuracy. His "comparator stand" consisted of a China import dial indicator mounted to a China import magnetic base. His "surface plate" was a piece of 1/4" plywood on top of a contractor's style tablesaw. The whole thing was liberally sprinkled with sawdust. I can probably dig up the photo - send me email if you are interested.

One of the central themes in his alignment procedure was finding something he called the "null axis of the warp". Basically, he was convinced that blade warp was always bi-laterally symmetrical. In his case, he believed that a line could be drawn across the surface of any blade which was perfectly perpendicular to the arbor's axis of rotation. Finding this line (the "null axis of the warp") was the key to his (flawed) procedure.

Trust me Al, you're lucky you missed it. And, you wouldn't be in good company to hang on to such flawed reasoning.

Ed Bennett [e-mail]

[Ed Bennett]

Sorry Al. Yes, about a year ago there was a guy who came along with his own tablesaw alignment procedure. He claimed that this procedure enabled him to achieve repeatable 0.0001" accuracy on his tablesaw. No, that's not mistake, one ten-thousandth of an inch accuracy - IN WOOD! Of course, it took a monumental effort to get him to submit samples of such claimed accuracy. And, of course, his own samples (tested by an unbiased third party) proved him wrong. Turns out he was using a 0.001"/div indicator to "guestimate" 0.0001" accuracy. His "comparator stand" consisted of a China import dial indicator mounted to a China import magnetic base. His "surface plate" was a piece of 1/4" plywood on top of a contractor's style tablesaw. The whole thing was liberally sprinkled with sawdust. I can probably dig up the photo - send me email if you are interested.

One of the central themes in his alignment procedure was finding something he called the "null axis of the warp". Basically, he was convinced that blade warp was always bi-laterally symmetrical. In his case, he believed that a line could be drawn across the surface of any blade which was perfectly perpendicular to the arbor's axis of rotation. Finding this line (the "null axis of the warp") was the key to his (flawed) procedure.

Trust me Al, you're lucky you missed it. And, you wouldn't be in good company to hang on to such flawed reasoning.

Ed Bennett [e-mail]

[Ed Bennett]

Like I said, it's a common mistake. You'll see the same thing in books, magazines and other products. It's unfortunate to see such prominent examples. Knowledge and expertise are not pre-requesites for selling something in this marketplace. Crap is super-abundant! I suspect that some gages are outsourced by a Marketing department with virtually no engineering input. There are also a plethera of hacks selling very ill conceived products based on no formal (or even informal) education whatsoever. It makes it very difficult for me to differentiate my products.

Don't be ignorant just because you see examples of other people being ignorant. The "rules" are based on science.

It's a great book to have. It's even better to read and understand what it says. You'll find yourself in good company!

Thanks, Ed Bennett [e-mail]

[Ed Bennett]

So, this is where this discussion got off to!

I read through all the messages. Al, I have to say, you could benefit from a lot more knowledge and experience. I applaud your ingenuity and desire to invent new ways of doing things. But, if you're honest, you'll have to admit that all of this is just conjecture. You really haven't done any of this. How do I know this? Because your method seems to evolve as objections are raised. You're talking to people who have been doing it for a long time. It's not a matter of being closed-minded to new ideas. It's a matter of knowing without a shread of doubt that the multi-indicator idea is chock full of pitfalls. And, you are stepping into most of these pitfalls without even knowing it.

The single indicator method is very elegant, functional, efficient, and most of all RELIABLY ACCURATE. I can't turn or clamp a spindle by hand, any spindle on any machine, to 0.0001". But, I can very quickly use a 0.0001"/div test indicator to align a vise in less time than it takes for you to get your rig installed. I don't have to trust that the table slots are aligned to the table motion. Honestly, I don't even care! And, your rig would be useless on any machine where they weren't (which is all the machines I've ever used!). Yes, they are usually close, but not good enough to beat the single indicator method.

Read, learn, practice, and understand how and why things are done. If you don't, then your ideas won't benefit from the thousands upon thousands of minds which have already pondered these things and evaluated the alternatives. Without this benefit, you are likely to stumble into all kinds of embarrassing pitfalls.

WRT the topic of the other thread:

"The sine angle caused by misalignment with a flat contact is a much more serious cause for error than the cosine error" "Fundamentals of Dimensional Metrology" Second Edition (c) 1989 Delmar Publishers Inc. p. 264

The example given shows how a one degree tilt on your indicator can cause more than 0.002" error in reading. That's with just one indicator. You've proposed using two. The error multiplies! While you're busy trying to align your indicators with less than one degree of tilt, I've already aligned the knives on the jointer using just one indicator and a round stylus point.

Read, learn, practice, understand, and then innovate. Your ideas will gain much more respect and your life will be a lot easier.

Ed Bennett [e-mail]

[AL]

Absolutely! I never once said I already built the gauges I was describing.