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  • away from home: need a simple way to file a square on a shaft

    Discussion in 'The main mechanical design forum' started by thorq, Oct 29, 2015.

    1. thorq

      thorq Active Member

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      Hi guys, I am for some time away from home so I don't have access to my tools. I need to file a square on a shaft and just realized this is harder than it seems. Because I am on a business trip I stay in a temporary rent so I don't want to buy expensive/much equipment for this task. Also going to a shop around here is out of questions, prices in northern europe are out of this world. I am trying to narrow it down to as few tools as possible, I have a file and a vise, cordless drill and some other useful tools for a rent. I was thinking at a sort of jig where I put the shaft at a certain depth so that the portion that will be filed out remains above it. Then I file it until I touch the jig. Then I do it again for the other 3 sides. But I have no idea how I can build that jig or what common parts I can use. Thanks.
       
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    3. thorq

      thorq Active Member

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      Forgot to mention that I only need to square a small length, about 10mm. My only requirement is that it be square. Also the shaft is 8mm in diameter.
       
    4. tonycro

      tonycro Well-Known Member

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      just to be clear, you need to put a square hole into something or you need to make an external profile square and what is the material ?

      assuming something ferrous - you are going to struggle !

      if its external, then the file and measure. A square blind hole in anything is always difficult - does it have to be square ? if so then the best your going to be able to do it drill out the hole, starting in the middle and work out to the perimeter and then file as best you can ?

      tony
       
    5. thorq

      thorq Active Member

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      It is an external square profile in a ferrous rod. The challenge is that I can't really file a 90deg square by hand without using some props. I was thinking of somehow placing the rod in the vise with the portion to be filed out left above the jaws anf file until I touch the jaws. But if I look from the side I can see that whe jaws aren't perfectly aligned and when I tighten an object between them, the play in the moving part of the vise is causing the jaw to go wherever the play allows it to.

      But with so many limiting factors I guess I'll have to settle with less than perfect :(
       
    6. K.I.S.S.

      K.I.S.S. Well-Known Member

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      thorq,
      You haven't mentioned what sort of required accuracy you need, and what sort of load will be exerted on either the shaft or the part it mates with, so if you're just looking to get a good press fit with relatively low torque or either compressive or tensional load, you can do that easily with a vise and two files - see here:
      http://i1248.photobucket.com/albums/hh497/KISS54321/Knurlingassembly_zpscbd5b2ac.jpg

      It's a very easy way to make a cross knurl with the most basic of tools.
      Hope this helps.
       
    7. thorq

      thorq Active Member

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      Hi KISS, very ingenious solution out there.

      I need a good press-fit so that the rod will not be deviated from the motor's shaft. I know I can do a single flat and add a set screw to prevent rotational backlash but I want to have a square coupler for a better grip at higher torques. I don't know if it will help much but this is what I have got at the moment.

      My rod is quite long and It will be difficult to have it in a vertical position in the vise (guessing). The forces shouldn't be too high, this will be used to transmit the rotation from stepper motor to the XY axis of a cutting plotter (vinyl, cardboard and such).

      Thank you.
       
    8. thorq

      thorq Active Member

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      This is what I am trying to achieve: https://www.dropbox.com/s/v833mtbr3y2u079/PlasticCoupler-5mmShaft-to-8mmRod.jpg?dl=0

      The coupler is pretty small and I am trying to achieve as much square surface contact as possible while still maintaining concentricity of the two cylindrical parts (motor shaft and rod). Because I can't guarantee that I file just the same amount of metal from all 4 sides I kept enough of the original rod inside the coupler to guarantee the concentricity while the square length has been reduced and pushed to the end of the rod. One side is filed on the whole length where it sits in the coupler. This filed plane also receives the set screw.

      The rod goes another ~200 mm below the coupler, vertically (motor is up).
       
      Last edited: Nov 3, 2015
    9. s.weinberg

      s.weinberg Well-Known Member

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      It will probably be painful whatever you do, but, since you're ok doing this visually, maybe try the following:
      (I came up with this in a couple minutes, so very possibly there are mistakes)

      1. Get a compass (the kind used for drawing circles), and center it on your shaft (just set to your radius, and make sure that its tracing your circle, or try something like http://www.instructables.com/id/How-to-find-the-center-of-a-circle/?ALLSTEPS).

      2. Set your compass radius so that the circle will inscribe your intended square.

      3. Draw the circle.

      4. Get a ruler, and draw a line tangent to the circle (can use a set-square using the circle center and vertical) to both sides of the outside of your shaft.

      5. Repeat for all 4 sides.

      6. File to your line on all sides.

      Hope that helps.
       

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