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View Full Version : Help needed with understanding accuracy in measuring tools. I want to go straight :-)



Boyan Silyavski
08-09-2013, 12:03 PM
Hi, i need some help there.

I am on my way to purchase some precision instruments needed for my build and hopefully for next builds. On the cheap:monkey:

Basically i need instruments for precision squaring of the CNC.

1. I just bought from ebay Super accurate pair 3" and 3.5" machinist square accurate to +/- 20 sec of arc (http://www.ebay.es/itm/130974439282?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1497.l2649)

Sellers description:

This is a pair of solid machinist squares. One square is 3" x 3" with a 90 and dual 45 degree angles and the other is 3 1/5" x 2" with 90, 60 and 30 degrees angles. Angular accuracy is insanely accurate to 20 seconds of arc. So just what is a "second of arc?" A full circle consists of 360 degrees. One degree can be divided into 60 minutes of arc. Each minute of arc contains 60 seconds of arc, so a second of arc is an angle that is 1/3,600 of a degree. 20 seconds of arc would be 1/180 of a degree, or a deviation of 0.000055" per inch. These squares are made from hardened carbon tool steel and are ground and lapped for straightness and parallism. These are the most accurate squares you will find for this price anywhere.

2. Now i am contemplating of buying from aliexpress 2 pieces of Universal Bevel Protractor Angular Dial Length 150mm 320 Degree (http://www.aliexpress.com/item/Universal-Bevel-Protractor-Angular-Dial-Length-150mm-320-Degree/1294724601.html)

The first buy will be used to adjust the 2 universal protractors squarish.

3. Now i need a straight edge. It will be used to check rails mounting surfaces and so on. Aslo i intend to use it for connecting it to the 2 squarish protractors and check and adjust rails parallelism. Here comes the question.

I will like this to be as large as possible without breaking the bank. I saw on ebay 2 options:
a/Igaging 36" straight edge beveled precision ruler hardened steel (http://www.ebay.es/itm/Igaging-36-straight-edge-beveled-precision-ruler-hardened-steel-/141006432462?pt=LH_DefaultDomain_0&hash=item20d4a368ce&_uhb=1)

Sellers description:
These straight edges have hardened, satin chrome finished blades that are ground and lapped for straightness and pallalelism and have true right angle on all edges with one long beveled edge. Beveled edge is graduated in 64ths and is precision photo etched and then black filled for easy readability. Rules are 36 3/16" long, 1 9/16" wide and 3/16th thick and weigh in at almost 4 pounds. These are substantial rules. Accuracy is guaranteed to be +/- 0.0015" (one and a half thousandths of and inch) over the length of the 36" rule. Rules come in an imitation leather pouch.These straight edges are perfect for setting up machines, checking work for straightness and scribing straight lines. These rules are US engineered and manufactured to strict tolerances in factories overseas. These are well made and precise and I am convinced they offer a reasonable alternative for anybody unwilling to spend the money required for the more premium line of US made precision tools.

b/ Maun Carbon Steel Straight Edge 48in (http://www.ebay.es/itm/Maun-Carbon-Steel-Straight-Edge-48in-1701-048-/390545761926?pt=UK_Measuring_Tools_Levels&hash=item5aee576686&_uhb=1)

sellers description:
Accuracy is 0.01% of the length of the straight edge.

Size.48 inch.
Width 2in.


Hence the questions:

- am i on the right way?
- obviously the maun straight edge is longer 42 inch versus 36 inch, but what does the stated accuracy mean? I can not understand it, percentages, etc? can somebody translate?
-any other options, better or cheaper? And preferably from Europe.
-other ideas?

Thanks!:kiwi-fruit:

Clive S
08-09-2013, 12:20 PM
The way I see it is that the straight edge will not vary by more than about .12mm over its length. ..Clive

EddyCurrent
08-09-2013, 02:21 PM
There's nothing wrong with getting more gear but do you need it ? what's wrong with measuring diagonals with a strip of wood having a chisel point at each end to get into the corners ? I'm thinking those squares are quite small so that over a distance of say 1000mm any error would be magnified. There again I've just rechecked the prices and you might as well get them.
There's a 'law' that goes something like this, in your workshop you need 3 things, tools, materials, yourself, but there's always just enough room for 2 of those.

Boyan Silyavski
08-09-2013, 06:38 PM
I was interested in the straight edge, for checking the gantry profile after welding. And as i have nowhere to machine it and havent found around where to do it, i was contemplating checking and filing until is flat. i believe its called " elbow grease " in English.

My idea also was to do the same with Bosch profile i have, as its quite straight. The small triangles i bought as i needed sth really straight as a starting point for all projects.
maybe i am wrong, but how to make a precision machine if i don't have a straight ruler to draw straight line?

Apart from parallel i would like the Y rails / the long ones/ to be straight, not just following each other curvature. Any other way to do this with simple tools like a Bosch profile?


So you say the price is ok?

EddyCurrent
08-09-2013, 07:22 PM
I think they look very nice for the price and I agree a straight edge is essential but I'm not sure you really need the other items though I'm sure they will be useful for some jobs.

As Clive said 0.01% of length = (0.01/100)x1200mm = 0.12mm

Jonathan
08-09-2013, 07:24 PM
It all depends on how accurate you want to be. I'm sure a lot of people make a machine which worsk, without using this equipment, but they wont make a really accurate machine without it. For the machine I recently made I used a 24x12" surface plate to measure and correct the rail straightness. Fortunately I won it for about 20 at an auction!


Apart from parallel i would like the Y rails / the long ones/ to be straight, not just following each other curvature. Any other way to do this with simple tools like a Bosch profile?

Not cheaply. People have experimented on CNCzone with using a tensioned wire to make a straight(ish) line for reference, but it's not going to be as good as the proper device.

Boyan Silyavski
08-09-2013, 07:54 PM
Thanks guys,
so it seems clear to me that i will pull the trigger at the straight edge. A sort of investment.

The 2 angle finders from aliexpress will wait for the moment. My idea was to use them like this:

Look at the gantry picture bellow. Using the straight edge or epoxy , like for the long rails, i could flatten the upper side/1/
But then how to flatten the opposite side? I don't have a fixed gravity epoxy formed horizontal surface at home. If it was my proper house, i would have done it long ago. So just flipping sides and pouring epoxy would be simple. So i thought of connecting the 2 angle finders un U like shape so i can measure distance and parallelism bots sides. So using the epoxy leveled top or bottom as a reference i could file , sand and so on, the other side. if they were on one plane , it would be easier, but damned overhang...i don't like it.

Anyways, i bought 2 packs of 1kg west system epoxy kit 105/209. After pouring some where necessary, the rest i will use to form a flat table surface and fix some short adjusting legs. As i have a very precise inclinometer / ~0.5mm per 3m, or so i calculated it when i bought it, don't remember but was the most precise on ebay/ i can fix me a portable level base precision surface for similar projects. I need a bigger garage:-)

Another thing is that just now i found how to make precision straight edge at home (http://home.comcast.net/~jaswensen/machines/straight_edge/straight_edge.html). 3 edges in fact. very interesting read. Now i am contemplating how to make it in reality. will need some polishing paste. maybe vibrate the edge for quicker removal. or slowly, like making a katana, while watching movies at night at home...

PS. i want to be as most as precise as possible, cause i know that even if you try, you are not. So if you don't try, its even worse


10048

mekanik
08-09-2013, 09:11 PM
G & M Tools - Moore & Wright 24 inch Hardened Steel Straight Edge (http://www.gandmtools.co.uk/cat_leaf.php?id=9648)

Grizzly.com (http://www.grizzly.com/products/36-Bevel-Edge-Straight-Edge-with-Scale/T21580)
grizzly is US but this is the sort of kit you need, a basic rule will be to flexible sideways(that's what i have)

Just found this on e-bay looks like the grizzly
http://www.ebay.co.uk/itm/New-36-iGaging-Premium-Precision-Hardened-Steel-Straight-Edge-Beveled-Edge-/130928183063?pt=LH_DefaultDomain_0&hash=item1e7bed8717

EddyCurrent
08-09-2013, 10:08 PM
That Moore & Wright seems cheap for the brand. Also silyavski you do want a straight edge with a beveled edge because you can see the light shining through gaps under it very accurately.

Boyan Silyavski
10-09-2013, 05:05 PM
Thanks for the help, its highly appreciated!

At the end i bought the two triangles (http://www.ebay.com/itm/Super-accurate-pair-3-and-3-5-machinist-square-accurate-to-20-sec-of-arc-/130974439282?ssPageName=ADME:L:CORT:US:1123)/ deviation of 0.000055" per inch/ + 2x 7" Electronic Digital Protractor Goniometer Angle Finder Miter Gauge (http://www.ebay.com/itm/7-Electronic-Digital-Protractor-Goniometer-Angle-Finder-Miter-Gauge-/140775658827?ssPageName=ADME:L:OC:ES:3160)/ Resolution: 0.05 degree /

I bought last month the protractor as a present and i liked it very much, very substantial feel, precise enough, quite handy, unbeatable for the money, so it was on my purchase list.

Now for the straightedge. Let me share. It will be great if somebody finds it helpful. After 2 days and tons of research, here is what i have found:

Which straight edge?

1. the Igaging straight edges even if advertised as top precision are shot in the dark. Many people received a bad ones, so as i don't like Russian roulette when spending hard earned money i dismissed them. Source:Amazon reviews and forums

2. Axminster straight edge- same as above. Could be perfect or a total crap. Source: Axminster reviews and forums.

3. Starret straightedges: good but expensive. People complain about spending insane cash for a long straight edges and receiving them without a box , wrapped in oiled paper only. No hook hole. Heavy.

4. Moore & Wright- dismissed- brand new, insanely expensive.

5. Second hand straight edges- dismissed. Jump in the dark if you dont buy from an respected machinist, even better fellow forum member

6. Maun straight edges- not precise enough, at least for me, i found more precision rulers for the price. If it was a ruler, i would buy it for the thickness

7. On the cheap: people use Stanley and Stabila ground beam levels with great result +- 0.5mm/per meter, which is quite good for the price and

8. Other rebranded mostly black in color sold " for cylinder rectification" , no specs or whatsoever.

9. Other brands in USA mostly, normally priced but expensive to ship from abroad + eventual tax.


Now come the good ones/ for the buck/

9. Veritas : people love them. At Axminster they sell aluminium ones with 0.075mm precision over the entire length and steel ones. Citation: " These Canadian-made precision steel straight edges are ground flat over the entire length on both edges, the 610(24") length to within 0.025mm and the 915mm(36") length to within 0.038mm. All have been stress relieved to remain true under temperature variation. Useful for checking whether surfaces are flat or straight, they are 38mm wide and easily stand on edge unsupported, leaving both hands free for precise measurement or tool adjustment. All have hang holes, allowing storage on a nail or hook"


Good choice for the money, either steel or aluminum. Couldn't find a bad word for them.



10. It seems the magic word that i needed to find is din 874

But what DIN 874 /00 874/1 874/2 mean?

10049

10050

So now knowing the magic word./ for EU i mean/ it seems DIN 874/00 on ebay made in Germany can be found at short lengths quite cheap. Longer than 500 become prohibitively expensive.

But hey, i am happy with Din 874/2 . 33 micrometers = 0.033 millimeters / on the entire length.

So now i am contemplating which length exactly, 1200mm or 1500mm, which would be easier to handle. Or maybe even 1 meter. Made in Germany-I like that. Cheap, i like that also.
Example/ from very nice page (http://www.praezisionstools.com/mwgpt/lineale/flachlineal/stahl874_2/wg1pt.html) with all kinds of stuff :
Straight Edges Steel DIN 874/2 Z032021000
lenght 1000 mm, height 40 mm, width 8 mm, Accuracy in accordance with DIN 874/2 lenght 1000 mm, hei...
Price without Tax: 63,65 EUR Price incl. Tax: 75,74 EUR





That Moore & Wright seems cheap for the brand. Also silyavski you do want a straight edge with a beveled edge because you can see the light shining through gaps under it very accurately.

You almost got me there :-) . But isn't it that a square straight edge has 4 edges that could be used for that against the ones that have only 1 sharp edge?
I believe their purpose is a bit different and definitely i believe i need the square- to compare between rails in all directions / the twist i mean/ .


That is all folks. If you have some info i missed just say it for the future generations who read this:-)

Conclusion: Maybe i am crazy, but i don't see how i can make a precise machine without precise instrument, so i need one/ at least, i am a kind of instrument junkie/

mekanik
10-09-2013, 05:22 PM
Top marks M8 i have bookmarked that supplier just in case i need one @ some stage, love a guy that does the research PPPPPP
Mike

Boyan Silyavski
10-09-2013, 05:26 PM
PS.
Just discovered on the page of the DIN 874 straight edges, that there is another page. Its called: Straight Edges made from Steel, no DIN, Testing Accuracy in Item Description, Faces grounded, Length from 500 mm to 6000 mm. Here are the even cheaper " scrap like" :-) edges. Scrap for them, treasure to me.
Example:

enght 2000 mm, height 40 mm, width 8 mm


Straight Edges Steel
finely ground,
Tolerance flatness: 112 m,
Net- weigth: 4,8 kg

Made in Germany

Price without Tax: 114,50 EUR
Price incl. Tax: 136,26 EUR

So 112 micrometers =0.112 millimeters, and thats for 2 meters. Not bad for 136 euro. If i make a big build i will definitely buy one similar

Greeny
10-09-2013, 08:10 PM
This one looks ok.
MeasureShop.biz: Flat straightedge, steel (http://www.measureshop.biz/en/measuring-instruments/straightedges-rules-and-small-gauges/straightedges/flat-straightedge-steel-3.html)

Part no: 1689 104
2000 x 60 x 12mm
din 874/2. 58 micro meters
111.80 + vat

EddyCurrent
10-09-2013, 08:34 PM
You almost got me there :-) . But isn't it that a square straight edge has 4 edges that could be used for that against the ones that have only 1 sharp edge?
I believe their purpose is a bit different and definitely i believe i need the square- to compare between rails in all directions / the twist i mean/ .


If I'm reading you correctly you mean this;

10053

But if you angle the straight edge on the left it will bend and not be straight any more.

Boyan Silyavski
10-09-2013, 09:19 PM
If I'm reading you correctly you mean this;

10053

But if you angle the straight edge on the left it will bend and not be straight any more.

Hi,
maybe you misunderstood me because of my English. I meant there are 2 types, beveled/like a knife/ and ones that look like bar. So as far i understood, you said that the beveled is better, cause you can see easier the light, when touching some surface to be measured.
So what i believe, the square could be more useful for me, constructing a cnc, because it has 4 edges versus one of the beveled.

10055

First it can serve as a master guide to straighten the first square shaft supported rail when mounting on the red axis, fig 1 , so its true straight

Then check the straightness on blue axis, fig2 /hence proper tightening on hopefully straight surface or if not-if properly shimmed.

Then check twist/ green axis/ fig 3 and 4.

With a beveled edge i don't see how you can perform and alight twist, as many of the beveled edges i saw are straight only at the knife beveled blade. fig 2 is where the beveled edge shines, but if i simply flip and use one corner, its the same.

10057

PS: edited, axis not showing

JAZZCNC
10-09-2013, 11:54 PM
I've got both and the bevelled edge is far more versatile and the one used most.

You cannot angle the straight edge like you show because your straight reference edge is lost because it's bending and will just follow the curvature of the surface. The reference edge is only meant to be used in one direction and must be 90deg to surface your checking any tilt/bend and error is introduced.

Boyan Silyavski
12-09-2013, 02:35 PM
I've got both and the bevelled edge is far more versatile and the one used most.

You cannot angle the straight edge like you show because your straight reference edge is lost because it's bending and will just follow the curvature of the surface. The reference edge is only meant to be used in one direction and must be 90deg to surface your checking any tilt/bend and error is introduced.

Thanks, i get it now. Ok, i will look for a beveled one.

Now recapitulating everything it seems that the Maun even if not ultra accurate is made from carbon steel opposed to all other mentioned. And at theit web site i saw it was beveled.

So i send a couple of emails.

-To Maun, to ask them if its hardened carbon steel, cause at their web they don't say so, say steel. No carbon at any place. All sellers say carbon. We will see.
-To Measuresop which Greeny suggested, cause here (http://www.measureshop.biz/en/measuring-instruments/straightedges-rules-and-small-gauges/straightedges/straightedges-with-bevel-edge.html) they have some beveled straight edges which look quite cheap , so i asked about the accuracy.
-To Precison tools to see if they will ship to Spain this (http://www.praezisionstools.com/mwgpt/lineale/fasen/Fasenlineal_Z035111000.html) and if this (http://www.praezisionstools.com/mwgpt/lineale/massstab/din866a/Massstab_Z041011000.html) can serve as a straight edge, cause it states tolerance 40micrometers
- to ebay member who is selling the Igaging 36 inch to ask if he could check straightness before sending. yes, back here, as the brand ones a very expensive.

Will see what happens.

mekanik
12-09-2013, 06:43 PM
Hi M8
This is only my opinion and i am sure others may disagree but i would forget about the Maun straight edge, i couldn't see any thickness quoted so it's more than likely a bendy one,the other bevel edge rule is quoted as steel and galvanised and i didn't see any tolerance/flatness quoted, i would stick with the magic numbers DIN 874/2 a parallel straight edge of reasonable thickness should be fine you can see the smallest of gap by placing a light behind the straight edge.
Take no notice of e-bay sellers the DIN 874/2 rules will be checked under controlled temperature conditions in a tool room using some rather expensive gear. a box for your precision straight edge is a must buy.
Hope that helps, i am now awaiting the flack.
Mike

JAZZCNC
12-09-2013, 08:32 PM
Hope that helps, i am now awaiting the flack.
Mike

No flack from me I'm 100% in agreement. My bevelled edge is 5/8" thick came from Vickers tank factory and would cost more than a small car today and weighs nearly has much. It also has stamped on it working temperature range it's accurate at and it's quite narrow, it will also be fair way from calibrated by now so I treat it with kid gloves and it's away in it's wooden case ASAP.

You get what you pay for.!!

Boyan Silyavski
13-09-2013, 10:55 PM
Thanks a lot for the info!

The Maun edge if happens to be from hardened steel/ still no info/ , could be good for drawing straight lines
Here is the drawing from their web:
10110


I will stay with the magic number.
Will fiddle until the end of the week and if nothing more interesting jumps, will buy from Germany. They answered me and told me that the scale also is a straight edge. Yes, i wanted beveled, scale and hardened and inox :monkey: but ...$$$.

Boyan Silyavski
18-09-2013, 04:18 PM
2 more questions before i push the button:

-Wood box i will do. But how you keep it in the wood box? Horizontal? And if horizontal, laying on its thin side or its flat side? Cause i will make the wood box if it comes without any

-I live near the seaside so everything rusts. The product i use is called Barricade rust protection for firearms. I treat all machines with it. Its oily and dries quickly in ultra thin film.
Is it ok? Stainless beveled edges are out of my league/1m i mean/

mekanik
18-09-2013, 04:38 PM
Hi M8
All our straight edges in the stores where i used to work (VSEL)were laid horizontal on dexion shelving, so not flat by any means. so yes lay it on its flat side. The only problem i can see is in the shipping of your precision gauge if it is not already in a substantial box.
Mike

Boyan Silyavski
19-09-2013, 05:02 PM
Thanks for the info. They would ship it together with flat wood piece for protection, i believe.

You were right. I get what i pay for :-)

The Igaging digital protractors came. Hughghghgh. Checked against my new supersquares and even against my ordinary squares, when zeroed on flatish surface and then measured 90 degrees, they show 89.75 or 90.25, depends if you take the measures from inside or outside. Ha ha ha. for 11 euros each, that's all folks. However i played around with them and noticed that the electronics and the dro discs are extremely accurate. The problem comes because they did not drill the axle hole on the right place.:hysterical:

I thought of throwing them to the bin. Then decided to think deeper. Measured the plates, each is perfect. Then what? Opened them to 180 degrees so both corners touch a flat plane. Zeroed. Closed so again both corners touch a flat plane. Spot on 180 degrees.

So, i invented a cure. Open them flat to 180 degrees until they are dead flat. Zero. Close them untill shows 180. One edge is not at the same plane compared to the other. Scrape it and repeat until they are spot on. In other words file untill the bolt is where it should be- at the center.


PS. I couldn't do it. At least for educational purpose opened it to see whats making it tick. Now i get it. Wasnt the problem in the steel axle hole placement. Encoder disc attached to the axle which enters a cavity, like a bearing entering its place. So , plastic in plastic. That means the screws and the plastic construction of the device is the problem. The encoder disc not being in perfect center makes the problem. And as its not a tight fit, it could never be centered.
Bottom line: You get what you pay for

Boyan Silyavski
25-09-2013, 12:49 AM
So after spending so much time contemplating, FYI here are the best 3 choices I found in Europe,
considering price, type of metal, thickness and height and first of all certified precision and usefulness. Forget the list from before!

Ignored are all shady no brand, rebranded Chinese and similar of unknown origin and non answering for specifications, in other words- trappy ones. Ignored are the mild steel ones which are beveled and the expensive ones

1. Veritas square aluminum straight edge 36" and 48"

Probably the best combination of price, precision and weight. Read a review on the net with precision test, it stands better accuracy than stated

2. Helios-Preisser / made in Germany/ square straight edge DIN 874/2 1000mm / 66 euro with shipping

The one i bought for now. Best price for what it is. Catalog (http://www.helios-preisser.de/scripts/relocateFile.php?ContentID=142&NodeID=920&FileID=92&ContentDataID=155&save=1)with prices in English
Can be bought from here (http://www.fixx-werkzeug.de/navi.php?a=15050&lang=eng)
I guess i have to live for now with 33microns inaccuracy :beer:

3. Messwelt / Made in Germany beveled knife straight edge. Din 874/0 1000mm 197 euro

This one rocks!

In the catalog (http://www.messwelt.com/pdf/messwelt2013.pdf)the price is 340 euro but on their web (http://www.messwelt.com/Haarlineale/Haarlineale-bruniert/) the price is 197euro which is great, in fact unbeatable by any other, for a darkened, hardened, ground and lapped made from tool steel knife beveled edge.
Note on their web in the english version is a mistake stating 700mm, when change to German is 1000mm, its at the bottom of the page .

That would be my next edge. I did not went for the other beveled edges as they were mild steel and the cheapest cost 150 euro with shipping. And that one comes with a box.


I hope that will help some body who needs one.

Boyan Silyavski
01-10-2013, 03:51 PM
Update:
Just received the 2. Helios-Preisser / made in Germany/ square straight edge DIN 874/2 1000mm / 66 euro with shipping. I am impressed. Perfectly ground and polished with no marks, katana -like. Great deal. Came just with cardboard case but well protected in big cardboard box. I could not be more happy, especially for the money i spend and the quality i received. Made in Germany + Din 874= good choice. I am quite happy i spend so much time making a choice and did not rush to the shady ones. thats all for now. Hope that all this experience will convince DIY guys that its worth spending some money on precise instruments that don't cost arm and leg.

mekanik
01-10-2013, 06:17 PM
Thanks for the update, glad you got a good one
Mike