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  1. #1
    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

    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

    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

    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

    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

    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?

    Last edited by Boyan Silyavski; 08-09-2013 at 10:05 AM.

  2. #2
    The way I see it is that the straight edge will not vary by more than about .12mm over its length. ..Clive

  3. #3
    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.
    Last edited by EddyCurrent; 08-09-2013 at 12:23 PM.

  4. #4
    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?

  5. #5
    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

  6. #6
    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!

    Quote Originally Posted by silyavski View Post
    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.
    Old router build log here. New router build log here. Lathe build log here.
    Electric motorbike project here.

  7. #7
    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. 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

    Click image for larger version. 

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    Last edited by Boyan Silyavski; 08-09-2013 at 06:12 PM.

  8. #8
    G & M Tools - Moore & Wright 24 inch Hardened Steel Straight Edge
    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
    Last edited by mekanik; 08-09-2013 at 07:28 PM.

  9. #9
    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.

  10. #10
    Thanks for the help, its highly appreciated!

    At the end i bought the two triangles / deviation of 0.000055" per inch/ + 2x 7" Electronic Digital Protractor Goniometer Angle Finder Miter Gauge/ 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?

    Click image for larger version. 

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    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 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

    Quote Originally Posted by EddyCurrent View Post
    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/
    Last edited by Boyan Silyavski; 10-09-2013 at 03:11 PM.

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