Repeating a drilling scheme

Discussion in 'Off-Topic' started by atferrari, Dec 23, 2010.

  1. atferrari

    atferrari Thread Starter AAC Fanatic!

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    I am looking for a practical solution:

    Given two, three (or more) holes on a small plate, in order to repeat the drilling on another one, I would like:

    1) Measure the diameter of each one.

    2) Measure the distance between each pair of holes.

    3) What if the holes are not drilled on a flat plate?

    Just for you to have an idea, imagine I want to mount a stepper on a frame and that the mounting holes of the stepper are NOT symetrical to each other.

    My need is by NO means limited to the stepper case, so please consider a generic situation where two, three or more holes drilled in a plate and that the plate is NOT available as a "template".

    I have no access to any equipment.

    Could you also add some idea of how much precision I could obtain with whatever method is suggested?

    Gracias for any help on this.
  2. jpanhalt

    jpanhalt E-book Developer

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    There are several ways to line up holes for drilling. Measuring the C/C distances and using standard layout techniques is one way. If I am forced to do that, I will typically draw the pattern using a 2D CAD program, print it out, and use the printout as a template.

    If the holes are threaded, you might consider making pointed ends on matching screws, putting them into the holes, then tapping your plate on top to get centering punches. That method also works well, if the holes aren't threaded. Sets of pre-sharpened rods are available to match all common drill and hole sizes.

    If you have a plate and need to copy the holes to another, you can just clamp them together. If they are relatively thin, a special clamp, called a Cleco, can be used. Imagine drilling matching holes in aircraft sheet aluminum. The Cleco goes into one hole, then expands to hold the sheets together and in alignment.

    Finally, another technique use with aircraft is called a strap duplicator. It can be used when you cannot access the sheet with the holes to drill matching holes. That would occur, if you had overlapping sheets and the bottom sheet was the one with the holes, but you couldn't get to its backside.

    [​IMG]

    You can make a strap duplicator from almost any material. The pin can be a screw, pop rivet, etc.

    John
  3. beenthere

    beenthere Retired Moderator

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    There is always an optical device, basically a lens with an engraved scale. This is not a plug, but the first hit on "linen tester" - http://www.linentester.com/
  4. thatoneguy

    thatoneguy AAC Fanatic!

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    I have a few of those, and unless the measuring reticle is illuminated, they aren't too helpful.

    For the prices shown, using one for an experiment may work well. Try to put an LED in the side of the reticle pane so it will light them up if the markings are engraved.
  5. Kermit2

    Kermit2 Well-Known Member

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    Ruling out a template as you did in the original post is just self defeating. You want a simple way to accomplish drilling something in the same way time after time? You WANT a template.

    If you want to make this difficult please continue trying to find a SIMPLE way to do this without a template.

    I'm not trying to be mean, just practical.

    Perhaps a different kind of template is what you really need
  6. someonesdad

    someonesdad Senior Member

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    You give no dimensions nor tolerance needs, so the answers you'll get are going to be general. You also say you have no access to equipment, so it is presumptive of us to suggest methods without knowing what exactly you do have.

    Measuring the Cartesian coordinate hole positions with a rule is probably the most fundamental method. You'd then lay out the same hole pattern on the plate to be drilled, center-punch the holes, and proceed to drill them. The accuracy of the method is dependent on the skill of the person doing it. You can make an estimate of the positioning accuracy by knowing the uncertainty of the measurement and doing some simple uncertainty calculations. Unless you're skilled in shop work, this will definitely be a lower bound estimate to the actual uncertainty. In addition, there are additional tolerances with drilled holes and they depend on how the hole is made.

    Machinists have a variety of tools to improve on this basic method. For example, using a vernier height gauge, surface plate, and an angle plate, you could improve the location of the hole layout by an order of magnitude or better. Using toolmaker buttons, perhaps two orders of magnitude (these are old techniques that have been around for a century or more). Modern electronic equipment can do even better, but few have access to that stuff.

    One of the most practical methods for duplicating some drilled holes is to use transfer punches. These can be made or bought. For threaded holes, transfer screws are used, but you'll be surprised at what they cost if you want to buy some.

    If you have to make more than one copy, it can help to make a drilling fixture. If you're going to make a bunch, then you'll want to look into some fixture plate and drill bushings. For a few in a home shop, you can make a suitable fixture from a chunk of wood.

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