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  1. #1
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    Default Dowel pin question

    Would drill rod be accurate enough for use as dowel pins?
    Also will a 1/4" reamer be accurate enough, and how tight a fit should there be?

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    "No" on both counts if you want to use it as intended. 1/4" dowel pins are 0.250 +0.0002". You need a reamer that is 0.2498 for a driving fit. Also dowel pins are hard and soft drill rod would just gall up.

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    Default Dowel Pins

    Dowel Pins are very hard, and ground to size, you should use dowel size reamers, which depending on size will be a -.0005 for the tight side, and +.0005 for the slip side, pins depending on size are +.0000 -.0002. The reamers are often sold in sets of a tight and a slip reamer. Check out the MSC catalog, they are better than most with information.

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    Toms - pins are +.0000 to +.0002

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    A box of dowel pins from McM is damn near free. If you need dowel pins, buy dowel pins. There are some things you fudge, and then there are things that are just so cheap that there is no point in trying to fudge them.

    Though endmill shanks make really good dowel pins also. +.0000 -.0002, I'm OK with that. Nice and hard, HSS or carbide.

    If you're looking at an oddball size for your fixture, gage pins. I consider gage pins as a consumable. In the 1/4" range, they are a few dollars a pop. You can't make a .226 pin cheaper, I guarantee that.

    I guess it depends on what you need to do with the dowel pin. I'm not making molds, but I do make multiple piece fixtures and I dowel them together. .2505 reamer, and I used to use a .2495 reamer on the press side, but I decided I was lazy, so now I just use the bigger reamer and run a 1/4" form tap down the hole I want to be a press. Much better than the "ball bearing" method.

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  8. #6
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    I use my 1/4 with a little slower speed than usual for a good slip fit...

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    I don't use a press fit on blind holes. I ream them on size and use loctite. Otherwise air gets trapped behind the pin.

    For odd sizes, get fixture pins with a necked area between diameters (Carr Lane has them) and have your local tool grinder grind one diameter to whatever you need. That way you can use a standard reamer on one side. I do it all the time and it's not expensive.

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    For fixtures that need necked odd sizes you can put standard 1/4" or 1/8" dowel pins on the 4th axis facing up and put a wheel on the spindle. 10 lines of gcode will grind them to whatever size you need. I keep an old diamond wheel just for that. 1/4" pins can be turned down to size, but 1/8" needs to be ground.

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    Default reamer sizes

    reamers come in all different sizes for 1/4"
    .
    0.2495" for light press fit with long pins
    0.2490" for medium press fit for medium long pins and can be used with a portable drill
    0.2480" for tight fit in thin materials.
    .
    using soft drill rod for pins is only if you want soft steel pins. most use hardened steel pins which are available in 2 main sizes
    0.2502"
    0.2510" oversize pins sometimes work with regular 0.2500" reamers. i usually have both types around. if for some reason 0.2502" pin is loose then i try the bigger 0.2510" pins

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    Another source for inexpensive precision ground stock for odd size dowel pins is punch pins, as are used in punch press dies. These are typically available in 2.5" and 4" lengths, hardness is typically 58-63 Rc, and they are available in decimal diameters of .001" increments, although sizes to the .0001" can be special ordered. Tolerance is +.0003/-000. Cost is around a buck an inch.

    I've made dowel pins from punch pin stock when I've needed odd size pins because either the existing holes were wallowed out or were mis-placed and wouldn't clean up when jig ground; also where I needed odd size pins to prevent incorrect assembly of interchangeable mold inserts.

    Dennis

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    Quote Originally Posted by ewlsey View Post
    I don't use a press fit on blind holes. I ream them on size and use loctite. Otherwise air gets trapped behind the pin.
    use a vented dowel, flat or spiral, or just grind a flat on a standard one.

  14. #12
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    It depends on what your trying to locate and other variables.Drill rod and .250 reamer can work for some apps.I ream holes daily and I can tell you that even if a reamer is a certain size and marked a certain size it does not mean the hole it cuts will be that size nor will it cut the same size in different materials.


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