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lazlo
12-28-2008, 05:12 PM
From Forrest:

The gadget you see in the photos is the base I made to check squares following the calibration method I described above.. The device's base is mounted on adjustable legs to clear the square's stock. The mast is offset so the DTI gets a straight shot at the square's beam. The little lip at the bottom contacts the square's beam near the stock. Naturally you can take DTI readings at any height and compare them to the parallelism of the beam thus by interpreting the readings determine the straightness of the beam to the accuracy limit posed by the limitations of the DTI. If the DTI was changed out for an LVDT and gage amp you could work to millionths.

http://i164.photobucket.com/albums/u15/rtgeorge_album/ComparatorbasePuba.jpg
http://i164.photobucket.com/albums/u15/rtgeorge_album/ComparatorbasePubb.jpg

If one needed to know the flatness and straightness of the stock in contact with the flatness reference on which this procedure is staged, one only has to apply a haze of skin oil on the surface of the stock, rub it on the plate, and examine the haze for removal much as though taking a blue reading. In grazing light the haze removal will be apparent. If the removal is uniform the stock surface can be taken as straight within a few millionths. A spin test will eliminate the possibility of convexity confusing the rub reading.

If care with temperature, nulling of the indicator reading, and repeat zero is employed and sufficiently accurate indicating equipment is used, a hard square may be calibrated in a large number of increments along the beam in the home shop as accurately and reliably as a fully equipped calibration lab. Thus for the home and small commercial shops this apparatus and technique is definitive for determining squareness and straightness of the beam of a hard square.

http://i164.photobucket.com/albums/u15/rtgeorge_album/WorkingSquarePuba.jpg
http://i164.photobucket.com/albums/u15/rtgeorge_album/WorkingSquarePubb.jpg

Forrest

BadDog
12-28-2008, 05:23 PM
Thanks for posting this Robert! However, you might want to edit and place the images on separate lines vertically. :D

Teenage_Machinist
12-28-2008, 05:31 PM
This is... much easier to understand.


Thank you.

Mcgyver
12-28-2008, 06:11 PM
wow. now that's a square!

J Tiers
12-28-2008, 06:55 PM
The first order errors in this would be then

1) the finish on the "bumper strip" in case the absolutely exact same spot is not hit each time.

2) the precision with which the blade of the square is known to be parallel as far as its front and back surfaces.

lane
12-28-2008, 08:36 PM
A few other method`s to check for square . first you check a master to set indicator then check part.
http://i178.photobucket.com/albums/w277/lane5263/Files/Checking%20Squarness/filesandsquarechecking004.jpg

http://i178.photobucket.com/albums/w277/lane5263/Files/Checking%20Squarness/filesandsquarechecking006.jpg

http://i178.photobucket.com/albums/w277/lane5263/Files/Checking%20Squarness/filesandsquarechecking007.jpg

With the surface gage you set a ball in the v notch at the bottom of the gage.

http://i178.photobucket.com/albums/w277/lane5263/Files/Checking%20Squarness/filesandsquarechecking008.jpg

The top gage has a ball made in the bottom of the very front The second one is ground with a radius at the bottom front . With all you set indicator against a master square are angle plate then check the part.

aboard_epsilon
12-28-2008, 09:19 PM
hmmm i check my squares with other squares .......if three line up without letting any light through when interchanged with each other there is a very good chance they are spot on ....well as near enough spot on for the use i put them to.

my thoughts

Squares are only used for checking the work before you use another method..........so i cant see any point of using any other method than that Ive just described ......or i could be wrong please say.

of course a large square like forests could be used as a master for all smaller ..then it would need checking .........perhaps with a couple of friends large squares..

all the best.mark

Forrest Addy
12-29-2008, 12:14 AM
epsilon. That old square is about a zillion years old, home made by some olt toolmaker named Tucker when he emerged from his apprenticeship and I got it at a garage sale after he passed on. It was pretty rusty but I got it cleaned up. I'd never checked it before I took those photos. It's accurate as hell, within a tenth if I get to pick the right spot on the granite flat. Come to think of it if a man wanted to noodle out a good system...

oldtiffie
12-29-2008, 01:25 AM
All very well and good.

I have no real problems with the principles - I have a few - but I'd like to see the amounts quantified in terms of parts of an inch/mm per inch/mm or in parts per million (PPM) by quoting or citing the appropriate "Standards" etc.

This is an extract of/from a post I made on a separate current thread.

Answers and amounts please.




............................................

I think that as many here seem to either be pulling numbers and/or "standards" "out of the air" that it would be instructive and add to the credibility if the standards and quantities and acceptable limits of or within those "standards" were posted.

This is particularly so given that these "Standards" specify different "classes" of items such as surface plates and squares - to mention just a few.

The US and ISO standards are pretty well the same as one is usually a "hard" and/or suitably "rounded" copy of the other - the UK (British - aka BS) Standards are similar.

So how about all you knowledgeable gents who are "calling up" or "quoting" or "citing" those "Standards" posting them for the edification of any who either haven't seen them or don't have access to them?

Forrest Addy
12-29-2008, 01:50 AM
I'm all for a thorough survey of the particulars of the square under calibration ie visiual inspecting check lineariity, flatness, and parallelism of the square's elemets etc. I'm also for providing stickers and certificates, where the error is listed as a slope, and the direction of error is referred to the interior or exterior angle of the square reference, etc as I mentions on the other thread.

Sometime i wonder if people read all the way through these posts. I know I often don't.

oldtiffie
12-29-2008, 05:47 AM
Well,
once again, no one either knew or chose (not?) to rise to the challenge.

I suppose I will have to make my all-be-it feeble "best shot" and "give it a go" myself then.

So here is the ISO standard for "squares" - ISO DIN875

http://www.stormspa.it/cms/index.php?option=com_content&task=view&id=129&Itemid=47&lang=en

http://www.google.com.au/search?hl=en&q=din+875&meta=


Surface plates:
http://en.wikipedia.org/wiki/Surface_plate

http://www.starrett.com/pages/860_granite_surface_plates.cfm

http://www.tru-stone.com/pages/faq.asp

http://www.tru-stone.com/pdf/Fed%20Spec%20GGG-P-463c.pdf

http://dspace.dsto.defence.gov.au/dspace/handle/1947/9371

http://dspace.dsto.defence.gov.au/dspace/bitstream/1947/9371/1/AEL-0286-TM%20PR.pdf

http://www.google.com.au/search?hl=en&q=surface+plate&btnG=Search&meta=

I suppose that while I am at it and apparently "on a roll" I thought I'd "have a go" at "slip guages" (aka "Joe blocks"):

http://en.wikipedia.org/wiki/Gauge_block

http://www.google.com.au/search?hl=en&sa=X&oi=spell&resnum=0&ct=result&cd=1&q=slip+gauge&spell=1

Now, that doesn't seem to be too hard to get - or does it?

If some old, decrepit, senile old "dick" like "tiffie" can do it, why didn't or couldn't??? anyone/someone else do it too/instead?

Now if my fading memory is correct:

a.
Grade 2 is "shop" grade;
Grade 1 is "Inspection" grade;
Grade 0 is precision grade.

b.
checking/calibration should be carried out by/against a standard at least two grades higher/"finer" under specified controlled conditions.

I have a set of "Grade 2" ("shop") slip guages as well as two "Grade 1" and two "Grade 2" try-squares - all to the required DIN standards (we are "Metric" in OZ - in case anyone either "didn't know" or "(just??) forgot".

OK.

Now that this decrepit , senile old "dick" (like??) "tiffie" - who is in his dotage - can do it, why didn't or couldn't??? anyone/someone else do it too/instead?

Now.

How about a reality check and re-stating all the test requirements and results in terms of the standards above.

But, a caveat.

They should not be in esoteric terms, but in terms that EVERYBODY can understand and relate to - if you can stand dealing with or at the level of the lowest common denominator.

Careful there - that's me at the bottom of the heap.

No?

Go on - I'm sure you can.

The Brits, being the good-hearted chaps that they are will lend you their "stiff upper lip" and all that. Jolly fine chaps.

Norm (aka "Aviemoron") - are you listening??

Any other comments?

J Tiers
12-29-2008, 09:40 AM
b.
checking/calibration should be carried out by/against a standard at least two grades higher/"finer" under specified controlled conditions.

I have a set of "Grade 2" ("shop") slip guages as well as two "Grade 1" and two "Grade 2" try-squares - all to the required DIN standards (we are "Metric" in OZ - in case anyone either "didn't know" or "(just??) forgot".



How about a reality check and re-stating all the test requirements and results in terms of the standards above.


I'm not quite sure where the demand for academic citations came from..... this IS a HOME SHOP forum, and advanced metrology is highly amusing, and even nominally "on topic", but quite out of the realm of reality.....

Since I get regularly bashed for getting anywhere past the 0.1mm/0.005 general area of precision, its a bit rich for us to be getting into millionths now.

However, let me ask you, Tiffie...................

If the standard of precision must be 2 orders greater than the object measured.......

Everything is jake until we need to GENERATE or CHECK those advanced standards.

NOW we have a problem. This problem can only be solved with measurements using "natural constants" (light), and by manufacturing methods which "automatically" generate the desired result.

Lapping three stones together can generate a plane as perfect as your grit can produce. It is "inherently so" through geometric truth.

The measurements only verify that the generating method did indeed work, and that no errors crept in. They don't "make" the part.

However, the generating methods can, independently of the measurements, "make" the part *perfectly*. You can't prove it without measurements, but it could in reality be the most perfect plane surface ever generated.

Note that the measurements are verifying that it worked, not necessarily showing where to do more work. Of course the measurements also can show a correction table, either for actual correction of the piece, or for use in correcting measurements taken with it.

And, of course, you can use a different method and at least theoretically make a plane surface using only measurements to correct it and show where to remove high spots. Scraping is one such method.

So.... eventually the self-referential academic methods employing means 2 orders better than the item measured must fall back on outside input to provide a reality check.

And, eventually one MUST take something on trust..... By definition, you can NEVER "check the checking means", because your methods are many times more imperfect than the reference.

Your argument is merely with the point at which things are taken on trust.

Which brings it back to the HSM, who has likely got no gage blocks, let alone a wavelength-based measuring reference.

The best measurement possible to the HSM is therefore 0.001 (0.25 mm). What price your millionths?

jkilroy
12-29-2008, 12:04 PM
I'm with JT on this, all of those standards, while having a place in industry, mostly for protection from liability, are close to meaningless to a hobby home shop guy.

"I have no real problems with the principles - I have a few - but I'd like to see the amounts quantified in terms of parts of an inch/mm per inch/mm or in parts per million (PPM) by quoting or citing the appropriate "Standards" etc."

Here we have people spending there own good time to demonstrate techniques usable by others that frequent this board and all that can be pointed out is that these techniques are not supported by some "standard".

My question to you is WHY? Please explain how some project you are currently working on will be compromised without "...amounts quantified in terms of parts of an inch/mm per inch/mm or in parts per million (PPM) by quoting or citing the appropriate "Standards" etc."

Do you bring this up only to cast dispersion on the offered (freely no less) techniques while not offering any usable counter technique even in verbiage, much less pictures of the actual implementation?

oldtiffie, if I didn't know better I'd label you a poser or noob so you might consider how others might react that haven't read your posts for so long.

lazlo
12-29-2008, 12:27 PM
All very well and good.

I'd like to see the amounts quantified in terms of parts of an inch/mm per inch/mm or in parts per million (PPM) by quoting or citing the appropriate "Standards" etc.

Answers and amounts please.

I don't understand this comment. Forrest is showing a jig with which you can test your machinist square by the method that Lane shows for a flat object.

You can measure the square with a plastic ruler, a DTI, or with gauge head, depending on how much accuracy you want/need.

tiptop
12-29-2008, 12:35 PM
This is a little off topic for the origanal post, but I myself find this very interesting. In that most of the work I do at this time can be machined to a "by eye" method and I don't need these tolerances most of the time. But I have contemplated the idea of creating more accurate work in the near future. I have also gone down the path of trying to create a square that is accurate. I have taken / hosted one of Forrests scraping classes and enjoyed it immensely. I do believe that upon occasion any machinist would question how square, square is, just because of the inquiring mind that most of us have. Most of these tecniques are based upon the experiences of our fellow members and I for one am always looking for ways to make machining easier and more fun. Knowing that a setup is accurate at the start is part of this experience.
Please carry on, and remeber learning is good even if it means change.

Jay

lazlo
12-29-2008, 12:42 PM
Forrest: I have an 18" Mitutoyo machinist square that I bought NIB on Ebay. Unfortunately, like many precision metrology devices that show up on Ebay, it's way out of tolerance -- I'm guessing it was a quality-control drop-out.

Can I just make a jig to hold a diamond lap perpendicular to the blade, and carefully lap it back to square? Or is there a better way to do this?

rockrat
12-29-2008, 12:46 PM
Personally, I have had a few metrology classes and I learned just enough to know that its never simple when it comes down to measurements being perfect. In the big shop where Rockwell would hang us out to dry for a gear blank being wrong, I would trace the CMM, laser mic and ceramic joe blocks back by using an outside calibration company. Outside of that, everything in the shop could be traced back to those three things. For us, this worked, i.e.-its all relative.

Which brings up 2 good points. (Or maybe I'll just make 2)
1) Most here are home shop machinist and .001" to .0005(maybe) is good enough. For those here that find it is not good enough, they know what they need to get to where they are going, if not, they study and find a way.

2) Even thought we (in general) are HSM's, the discussion is good for the brain. It is good to know a bit more than you need because it helps you do the normal things better, faster, quicker, etc. Learning is always good.

In the end it is all relative to what you are doing. As long as the discussion stays civilized, why not read, think and learn?

As for Forrest's post, I'm still studying it and thinking about it. I have learned quite a bit from his writings. But I always strive for an example to make sense to me before I do it.

My only opinion so far would be that this might have been better as a new post with a link to Forrest's original post. Minor issue.

rock~

lazlo
12-29-2008, 01:21 PM
My only opinion so far would be that this might have been better as a new post with a link to Forrest's original post.

There's no original post -- this is it :) Forrest asked me to post this, because he was having trouble with the embedded images.

mochinist
12-29-2008, 01:24 PM
I don't understand this comment. Forrest is showing a jig with which you can test your machinist square by the method that Lane shows for a flat object.

You can measure the square with a plastic ruler, a DTI, or with gauge head, depending on how much accuracy you want/need.I think tiffie is just bored and likes to type sometimes

Teenage_Machinist
12-29-2008, 02:33 PM
:mad: :confused: :rolleyes: :eek:



I normally work pretty loose, but some things do need to stay tight. I would probably be using the tenths mike, the half-thousandths indicator, the Grade B surface plate. It is important to make a distinction in metrology between "dimensions" and "precison" things like straightness, roundness, paralelism, and flatness.

Gage blocks give me no interest. Space blocks are for sine bars. Mikes are mainly for precision fits and anti-taper measurements, not for "how big is this." But the indicator stand and surface plate is good for things that need to be flat and need to be straight and paralell or perpendicular.


For my specific purposes I would have things be parallel to, oh , say 0.0003 or closer, perpendicular maybe more like 0.0005, but the more the better.

oldtiffie
12-29-2008, 08:29 PM
Originally Posted by lazlo
I don't understand this comment. Forrest is showing a jig with which you can test your machinist square by the method that Lane shows for a flat object.

You can measure the square with a plastic ruler, a DTI, or with guage head, depending on how much accuracy you want/need.

All I want to know is what "Standard" is being used that I can relate to. If the scraped surface plate is "at least to the NIST standard of "Grade 2" which is at "Workshop" and "Tool-Room" standard as regards flatness etc. ......... " I would be satisfied.

As I should be.

Anything less can be seen as an arrogant "because I say so - end of discussion" or a more polite "Trust me - I know and I say so". I don't like pontification or illusions of or delusions of grandeur or omnipotence. That seems to me to be the preserve of clerics, Politicians and "Wankers".

"Grade 2" and its equivalents for micrometers, squares, slip guages etc. are more than acceptable in my shop - as they should be. If it is certified or proved to be to the required standards - I'm happy. I can neither detect nor measure to anywhere near those standards in my shop. I don't have to either.

The traditional "3-plates" method of scraping etc. is well proved and it works. But to say that if it has a "coverage" of "contact" of say 80% or a specific number of "dots" in a specified area while physically demonstrating the accuracy is not measuring it. But I accept that for "shop" purposes, it doesn't have to be. But I do get concerned if someone says that it is - for example - "............. within a tenth ......" without saying over what area and how it was measured etc.

For me, an item at a NIST standard is more than good enough for me to use as a base or reference even though there are tolerances and limits within that acceptable standard.

To take that to an acceptable standard and reference in most shops - "Grade 2" IS the "shop" standard.


I think tiffie is just bored and likes to type sometimes

Thanks mochinist - I really had a wry smile at that. I am retired and like many retirees, I really don't have time to get bored. I don't necessarily like to type but like many things, when I think it necessary, I do it - whether I'm bored and like it - or not.



I normally work pretty loose, but some things do need to stay tight. I would probably be using the tenths mike, the half-thousandths indicator, the Grade B surface plate. It is important to make a distinction in metrology between "dimensions" and "precision" things like straightness, roundness, paralelism, and flatness.

Gage blocks give me no interest. Space blocks are for sine bars. Mikes are mainly for precision fits and anti-taper measurements, not for "how big is this." But the indicator stand and surface plate is good for things that need to be flat and need to be straight and paralell or perpendicular.

For my specific purposes I would have things be parallel to, oh , say 0.0003 or closer, perpendicular maybe more like 0.0005, but the more the better.

Well, well, T-M,
that is one of the most informative and insightful and practical posts I've seen on this (sort of) topic. You seem to have really "put your finger on it" - the "reality" aspects of satisfactorily working in a shop - in most cases.

I suspect that you speak for many others.

The degree of accuracy you "want" is not always the degree of accuracy you "need" - and vice-versa.

Many of the "standards" are quoted in terms of "micro-inches" which are also (known as) "millionths of an inch".

So lets put that into perspective in practical terms and use in the shop.

The "thou" (0.001") is one thousandth of an inch. So 0.001"/1,000,000 = 1,000 "millionths/micro-inches". A helluva lot of bloody small stuff there - ain't there? Too bloody right says I.

Now for the "tenths" that so many quote as "super accurate". Well that "tenth" = 0.0001" = 1/10,000" = 10,000/1,000,000 = 100 "millionths/micro-inches". So, if a "tenth" if hard to get or measure then those millionths are even harder.

Now as regards "slip guages" or "Jo-blocks". My Class 2 set has 83 pieces in it and all are within millionths of an inch. Just to put that into perspective, if each of those 81 pieces were 10 "millionths" over-size (which they damn sure are not) the total error would be ((81 x 10)/(1,000,000)) = (810/1,000,000) = 0.0008" - yup only "8 tenths". Not bad huh? So given that all are very accurate and that there will be some "over" as well as "under" so there will be a lot of "canceling-out" which makes it even better. Given that I use the least number possible (rarely more than three or four) its gets even better.

My slip guages are to DIN 861 Grade 2 ("Shop") and are individually numbered as part of a numbered set calibrated at 20 degree Celsius.
http://business.vsnl.com/toolcentre/slipgauges.htm

So its pretty good and more than good enough as a base or reference in the shop. I use it to check a micrometer etc. or use as a comparator if accurate work - say, better than "half a thou" or "a couple of tenths" is really needed. Otherwise I rely on the micrometer and the height guage etc.

I have four "sine bars" but all are incorporated in "other stuff" - one is a "Tool-makers" vice, another is a tilting magnetic chuck, another is a tilting plate and the last is for setting angles for dressing required angles on my grinders.

I don't have and so far in this shop have never needed a "stand alone" sine bar as they are a PITA to use in many ways. So I use "work-arounds".

On ANY "sine bar" I would tend to make and use a piece of "stuff" to within "a thou" - or better - as that is plenty good enough most times with a "sine bar".

For example, in the horizontal plane or on a table a difference of 0.001" over 10" ("10 inch sine-bar") the "error" is arctan/arcsine 0.001/10.000 = 0.0001 = 0.0057 arc degree x 60 = 0.3438 arc minutes x 60 = 20.6265 arc seconds. Now surprise, surprise, that is as near as dammit to the 20 arc second calibration on the hand-wheel of a standard rotary table. It is quite easy to extrapolate ("read") to 10 arc seconds.

Now the common old garden variety of rotary table becomes a precision angular "setter" or "measurer" with an accuracy of at least 1/10,000 = 0.0001" per inch!!

The rotab is very handy as it can be used in the vertical or horizontal or better yet, used on a tilting table as well. And stuff can be clamped to it. I use it to make "angle setters" for the top-slide on the lathe which is a lot more accurate and a lot less trouble than any other method.

As an aside, the "0.001 error per 10.000" that I quoted earlier is the "worst case per 0.001" as the error in angles set on a sine bar gets worse (ie less "angle per 0.001" error) as the angle increases and is virtually useless at or above 45 degree.

Proof? Sure.

If the "guage" is 10.0000" for a 10" sine bar the angle will be precisely 45 degree. If the "guage" is actually 10.0010" (a "thou" "over") the angle is the arctan or arcsin of 10.001/10.000 = arctan 1.0001 = 45.0029 arc degree = 45 deg 0.17105 min = 45 deg 0 min 10.3127 sec. So, at "zero" angle the difference for an "error" of 0.001" (20 sec) is twice that for 45 degree (10 sec) and it gets worse faster as you "go up" to 90 degree.

This doesn't surprise me, and I hope and think it won't surprise "JT" (Jerry Tiers) but we agree a lot more often that we disagree as regards standards in "machining". He almost always goes back to fundamentals and/or "reference" for which he/I can use as "base-points" or "references". I find him be very "down to earth" and concerned about the "basics" as well as degrees of accuracy. I know that it doesn't seem that way but I think it is. We may not always agree but we can "agree to differ". Its just that I think we can't resist "prodding" or "having a go" at each other.

lane
12-29-2008, 08:52 PM
Will I do not thank any of us are building a space ship. For the HSM I think +- .0005 is fine and may be to close for many. I have worked to fifty millions but I do not plan on doing it at home are never again. Most tolerance around here is +- .005 might as well be a mile.In this part of the world If a shop has JO blocks they are what they are and are used for inspection. Same with a granite plate are angle plate they are the master.
Now I know things can get real sticky here and people can get carried away with precision are how accurate something is. But we aint building rocket ships and we are not going to the moon. In another post some one asked about a piece of granite counter top. I say if it all you got use it its flatter than the floor in your shop. Depending on what you are building you can get carried away with precision.As far as I am concerned+-.0005 is close enough and you better have a good grinder to hold that day in and day out. For flat i have a 12x18 granite plate I bought years ago that was sold new to me as a grade A+ plate and I have a 6x5x5 harden and ground angle plate that is good to .0000025 in 6 inches how i know is it was calibrated against a 12x12x12 master granite plate we bought new at a company I worked many years far and the owner only bought the best. Money was no object when we bought tools.
As far as certs on stuff it is only a matter of how far you want to carry it.
If a guy in his back yard is building something and using the tools he has to measure with I guarantee it will fit and work. Now not to say his 1 inch may be a 1 thousand bigger than yours which is no good in industry but fine for the back yard.

Just a show of hand here to prove my point how many here hold every dimension to the exact on every thing they build. None I bet not even me.
I think as far as triffie is concerned the standard is what each of us have to use as a master. His granite plate plate may be a grade B work shop grade and forrest may have a laboratory grade. I have a A= are inspection grade . what you got is what you use one shop I worked in years ago had a bunch of tomb stomes they used turned over writing down. that was precision flat as far as they were concerned.

oldtiffie
12-29-2008, 09:24 PM
I am in the same room as Lane.

I like a bit of a challenge at times, but I ALWAYS start off at what some may regard as the "roughest" end of the scale on any job and only "move up peg" if it really is necessary. But that is where I stop - full stop.

My slip guages are getting their first "airing" in over a year. The digital height guage has not seen the light of day in over a year - probably more. My grinders - surface, T&C and "Universal" might not get used for months as a time - and then its "School and manual" time again!!.

The band-saw, oxy-acet/MIG welders get a bit of use. The plasma cutter is sulking because it thinks its unloved. The pedestal grinder and the angle grinder get a lot of use. The mills and the lathe get occasional use. The pedestal drill, hack-saw and filing get more use than just about anything else.

I mark all of my lines and holes out with a surface guage (aka "scribing block") and a square. I always centre-punch by hand. This is fine for "spot-drilling" as I get no "wander" and I quite often just use a hack-saw to "rough-out" and the pedestal grinder or hand-filing or the belt-sander to "finish off". I am not in the business of "rush" or "time" or doing everything by machine. But I'd beat many who insist on doing stuff by machine if its not too "heavy" or precise. I can "mark-out" and "centre-punch" quite accurately. If I have to use the mill for that standard of work, I will often just use the "pointy" "wiggler" in the chuck and "centre" it with my thumb-nail and then "eye it in" (surprisingly accurate), "spot drill" and then "follow-up" wit larger drills. I don't even need a DRO or precise hand-wheel settings. When accuracy is really needed, I use it, but not otherwise.

But sometimes I don't use the shop for weeks - or more - at times.

But its there as and when - and if - I need it.

I quite often just want to "try something out". After I've finished, I just scrap or junk it to the scrap pile or the dump. I seem to make a lot of "tools for making tools" and not doing much - if anything - that anyone else might regard as "nice" and/or "useful".

J Tiers
12-29-2008, 10:28 PM
Ok.....

It just seemed odd to get right out there about references and standards all of a sudden.

Particularly since the only two items in question are 1) a granite flat, and 2) a DTI.

Both can be "reality checked" by the very same process of reversal that was used for the square..

Simply turn the "DTI holder" around, so it checks the front of the blade with the square remaining in the same position it was to check the back.

Get the same reading? You are golden within your measuring capability.

Get a DIFFERENT reading? Now you don't know much except that either you made a mistake, or the flat is NOT flat.

Go check the back again to verify the prior reading, and show that the DTI setup did not move. If that is OK, the flat is the suspect in case of a difference when reversed.

If there was no difference when reversed, and it repeated the backside reading, you can be reasonably sure that the setup didn't change either, so you really are good on the square.

Note that this is NOT a question of errors repeating..... because you have moved the same measuring tool to a different spot on the flat, and all you care about is any difference. If you find one, it pretty much proves that the flat has issues, particularly if you can repeat the prior measurement from the backside again.

rockrat
12-29-2008, 10:37 PM
There's no original post -- this is it :) Forrest asked me to post this, because he was having trouble with the embedded images.

I could have typed that better. I meant that the continuing conversation on the benefits of tracing something back through NIST or the such could have been in another post. The thread has good material but I (opinion) think that we have wandered from the original topic.

Still reading the responses. Been out in the shop working on moving a Van Norman from one garage to another. Need to catch up.

rock~

Forrest Addy
11-01-2010, 04:11 AM
Yeah, well, It's been years. As I recall some people wanted to know how to check a new to them hard square. Using the method I outlined supported with some preliminary checks for stock and beam parallelism and straightness the DTI reversal method conforms to the NIST method for self-checking precision squares. I can't cite the exact reference but I know this assertion is true.

What inspired the hair-splitting and scholarhip comes from I don't know but it's to be encouraged as acedemic rigor applied to settling nettlesome quetions.

The people protesting "this does not apply to me" can take satifacton that others do. Mix and match square checking sure works but if there is an error how much is it and does it make the interior acute or obtuse? Sometimes you need to know so you can compensate.

Reducing raw error readings is a matter of bonehead shop math once you quantify the error, its fetch, the sign, and append the units

If your work doesn't need exaulted equipment certifiable back to the ores from which its materials is smelted; that's also fine. But when somebody in a bind asks you to check something like an aircraft part and those readings have to be documented you have to pass. You are legally obligated to pass if you can't certify your equipment complies with the relevent standards. It's not snobbery, it's facing facts - it's business. These things happen even tiny home shops. People hear about you and may regard you as a technical reource. They come to you hat in hand: can you help me? It can be a heady experience to pronounce on the merits of things only you can fully understand. It's a tug few vanities can withstand.