How do I indicate a threaded hole?
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  1. #1
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    Default How do I indicate a threaded hole?

    I have some holes that I would like to machine, and they are currently threaded. How do I indicate them to precisely find center on my mill?

    Thanks

    Ray

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    Look up "locating screws". Alternatively, a shoulder screw could get you close if you indicate the ground diameter.

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    It depends upon whether you want to locate the centerline of the pitch diameter or the centerline of the minor diameter. The pitch diameter is more accurate but it requires a plug gage like these. Threaded Hole Centerline Location Gages. If you just want to locate the minor diameter (depending upon how accurate you need to be, this might be good enough) you just need to find the largest plug gage that will slip into the threaded hole, and then indicate that.

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    Screw a go/no go guage in without the handle, clock the stem, works
    Mark

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    I do have some tight fitting studs that I can machine and then screw in and indicate off, but I don't know just how close that would be. I am also looking for pretty close (I don't actually have a tolerance) as this is a bolt hole that will get studs installed.

    Beege: what part of MA are you in - I am very close to Chelmsford...

    Thanks

    Ray

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    SouthEast MA, near Brockton.

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    Run a nut up the threads of a good quality cap screw. Cut the hex head off the screw

    Thread the screw into the hole as far as it will go, but don't bottom it out. Snug the nut down to the surface.

    Indicate off the unthreaded shank of the cap screw.

    Or just use a shoulder screw as mentioned.

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    Quote Originally Posted by just4grins View Post
    It depends upon whether you want to locate the centerline of the pitch diameter or the centerline of the minor diameter. The pitch diameter is more accurate but it requires a plug gage like these. Threaded Hole Centerline Location Gages. If you just want to locate the minor diameter (depending upon how accurate you need to be, this might be good enough) you just need to find the largest plug gage that will slip into the threaded hole, and then indicate that.
    Some just use tight fit gauge pin but this better and costs more so often gauge pin for me.
    There is a difference as one is the drilled hole and the other the threads.

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    You might turn a piece between centers having a going-tight-thread,
    That is thread that goes into an Ok nut but having an increase in size that makes it lock up in the nut.

    Making it leave a straight shank of a size that will be easy to relate to, for the gauging from straight diameter.

    offsetting your tail .003 .005 per inch might be a good taper,

    But this is checking after the fact..not placing them in the right place.

    Putting in a high-quality stud, and adding a locking nut would be good Only if you were assured the locking nut had dead true face to thread geometry.

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    Indicating threads is a crap shoot really. If they are not dead square you will get a false reading. Any wear can get you a false reading. When I pick up threads on a Bridgeport I find a snug gage pin and put it in the spindle and poke till it goes in...nothing fancy there lol.

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    did not see this mentioned above.

    run a tap in, indicate off the round top of the tap. should be a bit better than using a looser fitting bolt.

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    There's a reason most machinists (I say most because there's always retards) don't indicate off threads for something that has to be precise is because the tapped hole isn't precise...and if you attempt to do this, well my friend, you are retarded.

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    A different approach would be to start by precisely measuring the hole locations in the mating part and make a drawing. Apparently, the end result is to have larger tapped holes that line up with drilled holes in the mating part. Keep the desired end result in mind when planning the job.

    If the plan is to replace the threaded holes with larger threaded holes, I am guessing that new studs will be made with the larger thread on the end that goes in the tapped holes and will have the remainder with the original stud size to fit through the holes in the mating part. Or maybe the plan is to use an STI tap and use the original studs.

    Either way, you need to enlarge one threaded hole and then locate the other holes from the first using your measurements of the mating part.

    Larry

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    Thanks guys,

    I do appreciate the help even if some consider trying to better oneself as the mark of a 'retard'!

    Anyway, I know the bolt hole circle, so I could indicate off the center and then move out the radius, but I am trying to install dowels in the existing holes that are a bit larger than the existing studs.

    I will try a few things as I have some spare units that can be written off.

    Ray

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    What thread size are the existing holes and what is the fit gauge number like from the tap that might have made the holes?

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    thread is 14mm x 1.5, fit is not that great. I put in what I thought was a tight fitting stud, and drove it down and was able to move it in the hole by hand +- .005.

    This may just be a problem to throw money at...

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    Quote Originally Posted by rbahr View Post
    thread is 14mm x 1.5, fit is not that great. I put in what I thought was a tight fitting stud, and drove it down and was able to move it in the hole by hand +- .005.

    This may just be a problem to throw money at...
    So long as it is rons' money? We could be OK wit' dat'?

    Kinda like a pre-paid vacation funded by the randomly curious.
    Or was it random curiosity?

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    Quote Originally Posted by beege View Post
    Alternatively, a shoulder screw could get you close if you indicate the ground diameter.
    Best answer. Shoulder bolts / stripper bolts are made on purpose to be square and true to the thread, and they are pretty cheap and readily available.

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    Ok, I will look for some shoulder bolts.

    Thanks for all the suggestions!

    Ray

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    Quote Originally Posted by rbahr View Post
    Ok, I will look for some shoulder bolts.
    Metric, eek, sorry. You just said that part I've only used inch. Hope they are available in metric, too.


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