Precision Straight Edge - How to make one
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- Опубликовано: 10 сен 2013
- The accuracy of so many marking out operations, joint and component preparation, and tool tuning, rely on the use of straight edges. As a tool, the precision straight edge is a valuable piece of kit.
In this video I'll show you how you can prepare three precision straight edges, using three steel rulers or three lengths of flat bar, etc. and some abrasives.
This is a beautiful video. It's a shame that more people don't realize the value of this concept and how fundamental this process is to the advancement of humanity's technology. This method described is also known as the "automatic generation of gauges" it was the key knowledge that allowed for the industrial revolution's technology to advance and lead to the machine age. The creation of the screw cutting lathe that could refine itself is created using an very similar concept. Something this simple and seemingly useless is what allowed humanity to make that leap from that early iron-age level technology to the truly modern era of precision manufacturing and measurement with computers and CNC machines that are well calibrated.
Thank you. Maybe RUclips is too quick a format to get this over to some people.
Who made the very first straight edge and what was his reference?
I don't know who, but you don't need a reference. Start with three edges and gradually adjust them all so that they each fit with each other. When that process is complete all three will be straight.
Hey dont sweat all of these negative comments on how you did not actually build a straight edge step by step. You explaind it all and thats good enough for most tool wise guys!
Cheers. I think I'd get more negative comments if I just demonstrated it. Can you imagine how boring that would be 😂
@@mitchwoodwork Well yes it might be boring to some. But if you were to wear flipflops and cargo shorts in your shop while grinding the nastiest scrap of steel that you can, it might help... Joke!
Very informative, thank you.
Ray Oakley Thanks Ray. Hope you give it a go.
Thorough video going through all the points (no pun intended). It's rare to see videos where everything is covered.
If you need a 'rough' straight-edge and you have nothing but a new MDF-sheet, the edges of the MDF sheet should be straight. Maybe not extremely precise, but fairly good as a ruler for a plunge-saw or a router.
If you need most of the MDF, mark the factory-edge, cut a thin strip (say 10cm thick) from one edge and use that as your ruler; you do not need to cut it precisely (you maybe have only one MDF and no other 'straight-edge'), a hand-saw - even at an angle - will get the job done; because you already marked which edge is the factory edge.
You can now use this slice to make straight cuts on the large MDF piece and you can also use the large MDF-piece to make the other side of the 'straight-edge' straight.
I hope that wasn't too confusing, it's a way to get a 'free' straight-edge if you have the MDF already.
Other types of board are not recommended, as their edges are much more rough.
Remember that a string can also be used as a straight-edge, but it's not as sturdy, so it might be cumbersome to work with, depending on the type. -Even single core wire can easily get imprecise if they have a bend or 'curl'.
Thanks, and nice tip for the MDF
This is the method used to scrape machine ways, and babbit bearings to square. I don't usually bother with scraping the sole of a plane to make sure it is perfectly square but if I were to do so I would use your method. First verify the straight edge with this method. Next check the plane with the proven straight edge and scrape down the high spots.
As an aid to finding the high spots Prussian Blue is rubbed on one of the rules and the other set against it. Any points of contact on the second straight edge are daubed with Prussian Blue and can be stoned until the whole blade edge is consistently covered with Prussian Blue after touching.
P.S. Prussian Blue is a fun thing to put on the bottom of drawer pulls on your buddy's tool chest. Before you know it every bit of the shop is covered with blue fingerprints.
Thanks Dave. Great tip about the Prussian blue, but you're right about the fingerprints, I remember them from metal shop class!
I had the pleasure of managing a couple of tool rooms and a machine shop at different times. Skilled trades tend to be a bunch of pranksters. Prussian blue and Dykem were their two favorites. At one shop the big joke was for one of the guys to paint your fingernails while you were unaware. You learned to stand with your hands in your pockets.
Great Video
Cheers
An excellent demonstration of the standard 3 plate test check for flatness invented a long time ago. But even Moore & Wright, Starrett, or Mitutoyo dial calipers are at BEST only reliable to + or - one count on the dial. So there manufacturers will only say there accurate to within + or - .001" in imperial. A lot better test would be if you have a quality table saw with a ground cast iron top you can trust and at least a .001" reading dial indicator is to position the indicator beside the saws fence and use that as a guide to pass your 24" straight edge under the indicators tip. Even better would be a .0001" reading dial test indicator, but few wood workers would have that or a precision surface plate. I don't blindly trust even Starrett or Mitutoyo equipment without a check first. So far there equipment has always fell within the factory specifications, but if you don't check you simply can't know that for sure. Even the best can and do make the odd mistake at times.
Thanks. The method breaks down once the gap is too thin for light to pass through. I'll give that a try and compare results. Although I very much doubt my table saw's ground cast iron table is flat to within +/- 0.001"! Cheers, Mitch
I've started hunting for straight references as theyt are needed for fixing my handplanes. Two pieces of glass. One is off so I don't trust neither. Some cutoffs from local stone mason. Inconsistent, so I don't trust such cutoffs. Then I started thinking that not having a reference to begin with I can only check such surfaces in a way you would go about in actually making a straight edge from scratch. So, what a peasant can use to establish actual physical straightness? Bingo! Steel strings! And so I got myself some unkinked high-grade violin strings. Now I need cylindrical strainers. Printer guide rod pieces should do.
Good idea!
Remember to keep in mind that some things might sag; rods and strings included.
-But I second the violin strings; good choice.
The edge of a MDF-board is fairly straight, but it's not perfect.
A rod may bend.
However, if you "glue" the rod onto the edge of the MDF-board, you have a rod that does not bend (unless it's already damaged). =)
Try a granite surface plate...
Thanks
Cheers Robert
would this work for checking cylinder head?
I rebuilt a few engines in my youth, using potentially less accurate straight edges, and had no issues! However modern engines are built to tighter tolerances so best to check with a mechanic to be sure.
right on
couldn't you also use string attached to a bow as a method
Good question, and for many practical purposes, a taught line (wire, string, etc.) will be close enough. But due to external forces such as gravity, it won't be dead straight.
What grit of wet and dry paper would you use?
I'd finish with probably 180, but work up to that through the grits. Do the main grunt work with the coarsest paper you have, to save time.
That was lovely to watch. Only problem I have is you are using bits of tree. Precision and bits of tree?😸 Exactly same technique for all disciplines though.
Making a flat surface would be a good video..Three more bits.
I know I have taken accuracy, straightness and squareness for granted in some of my tools. It is incredibly hard to find (or should I say hard to know and trust that you will get when you pay your hard earned cash) basic rules, squares and so on with fine accuracy these days.
That's so true. Even well regarded brands sometimes fall far short.
Presumably there is another part coming which tells you how to make a straight edge as the title suggests?
This one just tells you how to check it!
Hi,
One of my very early videos! I just watched it to check what you said. The instructions on how to make one from a steel rule are there, but I agree it should be clearer and go further. Thanks for the observation, I'll try and get a replacement sorted.
Happy woodworking, Mitch
At 5:10 - It wouldn't work if the distortion was rotationaly symmetrical, like an "S" shape.
Good spot! I didn't consider that. Don't think it's a problem though, since the edges would only match in one precise linear location (could be more if both had identical fixed frequency and amplitude waveforms), and so they wouldn't slide against each other without a gap appearing.
Thanks for pointing it out, I shall try and remember for next time. Cheers, Mitch
@@mitchwoodwork Also if you think about it all 'straight' edges will have some degree of that error even if its down to the atomic level. So we deal with it the same way by rotating parts, testing, and so on.
Just move the rulers slightly. Unless all of them have very fine waves all the way, you should be able to see if light shines through.
"that shape"
If a piece of PAPER is sufficient to straighten my edge, it was straight enough in the first place.
Haha, did I abbreviate aluminium oxide paper to paper - I really ought to take more care. Thanks for watching
@@mitchwoodwork To me, you made it clear that it was aluminium oxide paper.
However, an A4 sheet often has a pretty straight edge; unfortunately it's not easy to 'work with' and gets dirty and damaged too quickly.
I don't get all the sloping-brow comments asking why Mitch Peacock did not make a "precision" straightedge because that is "precisely" what he demonstrated.
Thanks, it's refreshing to hear from someone who understands. I am tempted to repeat the idea in a new video 😉
Sorry but this took way too long to explain a very simple concept, it's like watching James May explaining about straight edges
Atul Lall Agree - one of my very early videos. I really should replace it soon
Yeah that was painful to watch .
This is a demonstration of how to discern a straight edge, not how to make one.
+john connors I don't recall it all, but if you can discern it then surely that's all you need to know. A little filing and sanding of high spots will do the trick. I do have plans to revisit this topic soon, so maybe I'll do a better job of it:)
Hi there, I hope I did not offend, I fully understand the value of accuracy in one measurement. Do have a good day, I look forward too seeing you're video on making a true straight edge.
Not at all John. Critical comments help me weed out the poor videos, and as in this case determine which subjects I should cover again 👍
Great.
Dont touch that paper bare handed !!!
Nice video but why put "how to make one" when it is more of an observation video, no attempt to make one at all. Frustrating and unhelpfull.
This is a topic I plan to revisit, and I shall be starting with three edges that are far from straight. That said, I do think all you need to know is in this video, but I agree that I could have demonstrated better. Thanks for taking the time to comment
+Mitch Peacock - WOmadeOD Thanks for the reply Mitch, I look forward to the new video, I love to learn new skills. On a personal note I am learning to hand scrape at the moment so a good strait edge will come in very handy.
+Robert Scratchet I'd like to give hand scraping a real go. It sure is a more refined method than sanding!
Great stuff, but by Einstein's Theory there is NO straight line!!!!
i fell a sleep
+Nixy Gill Feel free to watch it whenever you're struggling to sleep. Or if you're really struggling, try my restoration of a Stanley #4.
Nixy Gill it's funny because with his voice I did get really sleepy within a few minutes.
Nixy Gill it's funny because with his voice I did get really sleepy within a few minutes
.
"Precision Straight Edge - How to make one" Well that's a misleading title; if not an outright fib. Apparently you're understanding of the meaning of the word "MAKE" differs from the rest of the world's understanding of what that word means. At NO point did you show how to "make" ANYTHING. However, great video on the subject of checking to see if an edge is in fact straight, but not very helpful to most of us who clicked on your video based on the title.
tru.. I con cure
Why did you take so long to say it all? Did I miss you making a straight edge? Frustrating and unhelpful.
All the information is there to make a straight edge, but I agree I took too long to present it
@@mitchwoodwork Maybe it took long to present it, but personally, I think you did a great job. Though I'm not a fan of videos with many pauses in them, this is an exception, because you gave time for the information to "sink in".
I'd also like to say that I'm happy that your videos aren't "contant speech without any pause between the words" - it's an annoying habit people got on RUclips, to remove all "spaces" between words; like their videos are one long word of constant babbling.. ;)
too slow, huge pauses, good points but re-edit
Agreed
Whoa so much talk and nothing said.
Holy shit its not rocket science you only need one rule to check itself for straightness. pull your head out then take a peace of plain white paper place it on a piece of glass in front of you on a table (glass is the flattest thing most people will be able to find and it is important to use a flat surface when checking your strait edge) , now put the rule /strait edge on the paper with one of the two short ends facing you, we'll refer to this as the bottom edge of the rule then using a mechanical pencil with fine lead while holding the rule down tightly with one hand draw a line all the way down the right side of the rule in one swift controlled motion with your other hand. make sure to run the metal tip of the pencil down the edge of the rule not the pencil lead itself, this is easily achieved by only having a tiny amount of lead sticking out of the metal pencil tip and by angling the eraser end (the dumb end) of the pencil towards you at a 15 to 30 angle as you draw this first line. Then slide the entire rule to the right slightly more than the width of the rule so the left edge of the rule is now next to the line you just drew. Retract pencil lead into metal pencil tip or break it off just make it gone. Now space the top and bottom left edge of the metal rule the same distance apart from the top and bottom edge of the first line you drew using the metal pencil tip as your spacer, then hold down the metal rule and draw a second line just as you did the first but down the left edge of the rule this time. when done correctly you should be left with two very strait uniform pencil lines extremely close to each other with a very small uniform gap in between them. If there is any waviness or uneven gap in-between these two perpendicular pencil lines or planes, your shits fucked up and its not a straight edge anymore dummy throw that shit in the bin directly. by using more than one beat to shit rule to check the other ones your just adding endless variables and more wasted time doing useless nonsensical testing. P.s. way to take the longest way around humanly possible while accidently, simultaneously allowing endless room for as many variables and mistakes as someone possible could make all while effortlessly reversing the very evolution of mankind thus far, Thank you now everyone listening or watching this is dumber.