PSA: Harbor Freight Digital Caliper $16

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I'm not sure what you mean by joking. I mean turn the chuck my hand, not turn the machine on. Collet? End mill holder? Whatever. You have to clamp the jig in something.

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Even something as small as a Bridgeport would be damn difficult to position with any precision by hand. Try it on a 100 horse power CNC.

expensive
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On my Bridgeport clone, if I put the speed selector in neutral, I can turn the spindle with one finger and either make it turn one or more revolutions, or turn just the slightest amount. I don't have a 100hp CNC mill yet but I'll figure something out when I get one (well into the future).

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This makes several assumptions (you know what an assumption is). It assumes the spindle locks. Most don't. It assumes the sides of the table are accessible. Not often the case. It assumes that the edges of the table are square and flat. Maybe, maybe not. There are finer details that I could go into but I won't in the interest of keeping this short.

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The mill doesn't have to have a built in spindle lock. You just need some way to keep the spindle from turning as you tighten. You can clamp it yourself with a clamp or magnet.
You don't have to use the sides of the table. You can use the side of a T-slot. The indicator stem doesn't have to parallel with the table because you aren't taking an absolute measurement.

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Again, I will explain a few of the problems. I will leave out the more subtle ones for brevity. Assuming that you can get to the T slots, you now angle your indicators to be able to reach them. By angling them, you have reduced the sensitivity giving you the impression, in use, of being closer to "dialed in" than you actually are. You then say to rig something up to clamp your spindle, increasing complexity (and time to execute) of the operation. Now, here you are with your 3 indicators (though, I can't see the point of the middle one unless it is for impression value) mounted on a 6 inch bar (to cover the distance of a 6 inch machine vise) with a spindle mount in the middle of the bar. You are going to hold this with one hand, adjust it for zero and hold it from rotation within .0038 degrees while you tighten it. Okay, lets assume that you do it the easy way. Clamp it in the spindle, bring the indicators into contact with the T slots (you did previously verify the accuracy of the T slots, didn't you?) and adjust the dials for zero. Now, you lower the table or raise the spindle while retracting the indicator spindles to keep them from snapping to the extremes of their travel. BTW, how many hands do you have? You now bring the vise under the spindle and bring the indicators into contact with the vise jaws. After all this, you can now proceed to align your vise. You did verify that the vise jaw didn't have a bump or dip in it, didn't you? How did you check? How did you check the T slot? Can you guarantee that nothing moved in this whole process? How can you verify that? There seems to be a lot of blind faith going on here.

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I was starting to type out why I needed the middle indicator, but I couldn't think of anything. I'm not sure why I initially said three. Two is enough for what I'm proposing.
I concede that either the T slot or the side/edge of the table needs to be straight and parallel to the direction of travel for this to work. Otherwise it won't.
On my mill, I estimate that the indicators would need to be tilted 2 degrees to access the T slot. Would a factor of cosine(2) or 0.99939 really reduce the sensitivity of the indicator?
I don't see why more than two hands would be required. Mount vise on table. Mount gauge in collet/holder/chuck. Raise knee, lower spindle, move X and Y. Up to this point, you would have to do all of this regardless of whether you are using one indicator, or more than one. When doing this, stop when the indicators touch the T slot or edge of table near the vise. Square the gauge by turning spindle with one finger (see other post). No need to dial for zero. Both gauges just need to read the same. Clamp the spindle. Raise the spindle slightly, and move the X axis slightly so that the indicators touch the vise jaw. Now adjust the vise so that both indicators read the same (they don't have to read zero).
You wouldn't move the vise so that the indicator points fall into (for example), the vise jaw mounting holes. If the vise jaw isn't straight, you'll have problems regardless of how many indicators you're using.

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So, prior to setup, you calibrate the surface you are going to use for calibration. Are you going to use another one of your rigs that needs to be calibrated before you calibrate the calibration surface?

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More like 30 degrees in a 5/8 T slot. In addition to the measurement error that would be introduced, you now have put the indicator bearings in a bind, further reducing sensitivity.

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You are going to rotate that spindle .0001 or so and then expect that it will maintain position while you clamp it... Right.

So, now you are just going to go on blind faith that the vise jaws are true. The time to find this out is before you scrap a part. With your rig, you'd never know. This is kind of like measuring the height of a wall with a 6 inch scale or, something many here will really relate to, using 4 different tape measures on the same job. It might work but chances are it won't and you can't be certain until you have produced scrap.

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You would need to check the T slot or table edge/side one time, not every time. You can also check the vise one time. On my mill, 2 degrees is enough to access the T slot. I'm not trying to access the very bottom of it.

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2 degrees isn't even enough to clear the indicator spindle, let alone the body or the mounting lug. You'll be closer to 30 degrees by time you clear everything. So, you're saying that you are going to have a calibrated gagging surface on each machine. You are also going to have a dedicated setting fixture for each machine. Obviously, you are going to have to have calibration fixtures to calibrate those calibration surfaces and, as you seem to believe the dual indicator set up is the way to go, you are going to need a calibration device to calibrate the calibration device that you are going to use to calibrate your calibration surfaces. Of course, there is no telling if the original calibration device is correct. Might be close enough in home shop where you can be reasonably sure of everything that goes on and the accuracy requirements of the work are not that close but in a commercial shop, forget it. To get back to your original thought. Why would a commercial shop sell you an alignment device that is inherently less accurate, by design, than the one they used when making the device? Ever heard the old saying "anything that can go wrong, will"? Only make things as complicated as they need to be to get the job done. Eliminate variables as much as possible.

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The indicators are hanging below the spindle. At 90 degrees it is already clear of the spindle. At 88 degrees, it is clear of the spindle and can touch the top of the T slot. No dedicated setting fixture or calibrated gauging surface required. Just check (once) if the the T slot or surface table if flat and parallel to the axis of travel.

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I just had another idea. If using an end mill holder, forget the spindle lock, using the neutral lever, and turning the spindle by handle. Leave the spindle in gear so that the weight of the gears, belts and motor keeps it in place. Mount the gauge but leave the setscrew loose. When the gauge is square, tighten the setscrew.

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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 snipped-for-privacy@ts-aligner.com
http://www.ts-aligner.com

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

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Well "AL":
Perhaps you should elaborate even more about your ideas! I'm thinking that you should try them and then make an honest report back to the group on how they worked. Maybe after you have actually tried these things they won't seem like such great ideas.
I guess you got my dander up because you specifically mention my product (TS-Aligner Jr.) and how much it could be "improved" with this idea of yours (multiple indicators). I think that it's enough of a lesson if you are forced to try your own idea and report the results back to the group - honestly. Then maybe you might think twice about trying to fool members of this group into thinking you know anything about machinery alignment or Metrology.
Ed Bennett snipped-for-privacy@ts-aligner.com
http://www.ts-aligner.com

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Ed,
In your two posts, all I see is a personal attack. Fair enough because I insulted your product. However I don't see anything that says why the jointer and table saw gauge that I described won't work.
I fully intend to build them and will report back on how they turned out. Right after I install the DRO on my planer. Unfortunately it will be a few months.
I'll build the jointer gauge pretty much as I described. But I'll be building a few different table saw gauges. One will be as I described. In addition, I want some way to get the two indicators to touch the fixed washer on the arbor, so that I can remove the blade and not worry about it being warped. I'm still thinking about how to do that.

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they will work. they'll just be less accurate and a pain in the ass to use.

simple geometry will tell you why this is a much less accurate approach.

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"AL":
OK, I guess you are asking me to help you get started thinking about the problems with your ideas. I don't mind doing this, as you've pretty much admitted in the request that you haven't tried your ideas (or even given much thought to their feasibility).
Whenever you have one measurement device on one fixture you have a stable reference. All subsequent measurements using this same exact setup will be relative to this same exact reference. All the individual variables which make up that reference will be included identically in every measurement so that their relative effect from measurement to measurement is completely nullified. If you introduce a second measurement device and attempt to make the same measurements in a repeatable manner then you create a second reference. All of the variables making up both references become significant. Each variable must be addressed individually and it's contribution to the results quantified and/or eliminated. If this is not done, then you will never know if the readings accurately represent the objects being measured or the effects of these uncontrolled variables.
To put it another way, it might seem rather inconvenient to use one measurement device and one fixture to do multiple measurements, but it is an effortless method which guarantees that each measurement is done with an identical setup. No external variables will influence the results. If two measurements come out differently, it's because the objects being measured are different. If two measurements come out the same, it's because the two objects being measured are identical.
For example, in your jointer knife alignment idea, a rather elaborate calibration procedure would be necessary to ensure that the two dial indicators were providing the same readings for any given measurement. Just because they read the same for one measurement pair (say, the top of the outfeed table) doesn't mean that they actually provide the same measurements. What if one indicator isn't tilted at the exact same angle as the other? What if one side of the fixture flexes more than another? What if the measurement force of one indicator is more than the other? What if the two stylus points are slightly different sizes or shapes?
Yes, it is possible to create a fixture, choose indicators, and account for all the possible variables which can significantly alter the results so that two identical measurements can be performed at the same time using two indicators. But why would you ever want to go to all this trouble when you could just use one indicator on one fixture to make two measurements?
Also, I just can't imagine trying to manage two indicator styli on a knife edge at the same time. You may decide that it's good enough to just worry about one at a time but then where's the advantage of having two indicators?
All of the above applies to your tablesaw alignment example too. In addition, you have assumed that blade warp is always bi-lateral and symmetrical. Sorry, that's a bad assumption. It's also not valid to assume that the arbor and flange (what you call the "fixed washer on the arbor") have no runout. You can obtain different readings on your two dial indicators and not be able to discern if they are due to misalignment, runout, warp, or one of the variables mentioned above. If you obtain identical readings on your two dial indicators, there is no assurance that proper alignment has been obtained. This is truely a case in which no amount of "factory calibration" will help. It's a setup which voilates all the applicable Metrological rules.
An alignment tool must be able to perform it's task without being adversely affected by these uncontrolled variables. Making two measurements with a single indicator setup using a fixed reference (the dot on the blade) is completely immune to all of the variables mentioned. When the two readings are the same then the saw is definitely aligned beyond any reasonable doubt.
This is just the tip of the iceberg. These are just conceptual level reasons why your idea is impractical. There are lots of other things to consider which you'll discover when you attempt to build your prototypes. I would be more than happy to discuss these things and I'm sure that there are others in the group who would be interested in reading along. But, we must agree not to name specific products and identify them as "inferior" when we really don't understand the the most basic principles of the topic at hand. Agreed?
Thanks,
Ed Bennett snipped-for-privacy@ts-aligner.com http://www.ts-aligner.com

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Regarding the jointer gauge, what I plan to do is get an angle plate of the right size, drill and tap two holes on the sides and then mount two indicators. Both indicators first touch the outfeed table. The dials get zeroed. Then the gauge is moved forward to touch the knife edge. Because the goal is to get the dials to read zero again (ie. I'm not measuring a linear distance. Cosine of the angle multiplied by zero.), I don't see any effect if either indicator were slightly tilted (even thought it will be very easy to be sure they are not). The angle plate is identical on both sides so one side wouldn't flex more than the other. The spring tension on the indicators may not be the same, but won't have enough force to either lift the angle plate, or lower the knife. The stylus points won't matter because the part of the point that initially touched the outfeed table, will be touching the edge of the knife. However, I may use disk-shaped points to make it easier to put the point on the knife.
The table saw gauge is more complicated. I am assuming that a warped blade is cupped such that you can turn it so that the curve is in the vertical direction. I'm not sure how to describe this in words. Imagine looking at the blade from the side and seeing something shaped like a left bracket ( . If the warpage is more like a ripple than a cup, then what I am proposing won't work. I'll have to measure a few of my blades and see just what they look like.
The only reason I mentioned your product by name was that everyone knows what I'm talking about when they hear it. If there was a popular brand of jointer gauge like the one I was talking about (Oneway and Powermatic make one--I've seen several more), I would have used that name. In retrospect, it was a bad idea.

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This is an interesting discussion with good points on both sides. However, I would like to interrupt this presentation for a moment to continue this thread started with the $16 digital caliper. This is an unbelievable price since I paid $50 for a dial caliper from Mitutoyo (sp?) in 1976 and thought it was a good deal.
I bought 2 of these calipers. One went on my drum sander to measure its height and one I am going to use for its intended use. If I did not already have a digital readout I bought for over $100 for my planer, I would have CERTAINLY used one on it. Since the mechanical scale on my Delta planer is nearly unusable, I would think that every owner of one should buy one of these calipers for use on their planer.
By the way, I would recommend clamping the caliper arms somehow to the planer. They are hardened and will ruin drill bits if you try to drill through them for attachment. I was able to drill the holes, but I ruined a couple of bits doing it.
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