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Thread: Drill Jigs

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    Default Drill Jigs

    If you were faced with a simple bolt pattern with +/-.005 tolerances on a large, awkward or hard to fixture part, would you use a drill jig to put those holes in?

    Example, 4x 1/4-20 threaded holes on a large 2" thick steel plate cut in a funny shape making it difficult to put on a machine.

    Other options would be mag base drill or mag base drill and a drill jig. Would you really need a jig for the tap or would it follow the hole well enough. I guess a couple assumptions are that the drilling tapping is done with new tools and the operator is pretty careful and experienced. Just wondering what tolerances you could hold with a good jig.

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    If I recall correctly drill jigs can achieve about 0.008" with sharp drills and a careful operator. With less than ideal conditions probably triple that.

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    Quote Originally Posted by vmipacman View Post
    If you were faced with a simple bolt pattern with +/-.005 tolerances on a large, awkward or hard to fixture part, would you use a drill jig to put those holes in?

    Example, 4x 1/4-20 threaded holes on a large 2" thick steel plate cut in a funny shape making it difficult to put on a machine.

    Other options would be mag base drill or mag base drill and a drill jig. Would you really need a jig for the tap or would it follow the hole well enough. I guess a couple assumptions are that the drilling tapping is done with new tools and the operator is pretty careful and experienced. Just wondering what tolerances you could hold with a good jig.
    I'm afraid that I don't follow.
    Please forgive me as I have only been in the business for >30 years...

    ...but when you say that it is an awkward part to fixture, then you ask about a "jig".
    What exactly is this "jig"?


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    Quote Originally Posted by vmipacman View Post
    If you were faced with a simple bolt pattern with +/-.005 tolerances on a large, awkward or hard to fixture part, would you use a drill jig to put those holes in?

    Example, 4x 1/4-20 threaded holes on a large 2" thick steel plate cut in a funny shape making it difficult to put on a machine.

    Other options would be mag base drill or mag base drill and a drill jig. Would you really need a jig for the tap or would it follow the hole well enough. I guess a couple assumptions are that the drilling tapping is done with new tools and the operator is pretty careful and experienced. Just wondering what tolerances you could hold with a good jig.
    .
    i have hand layed out 1000's of drilled and tapped holes to .010 and .015" tolerances and if part needs to be pinned to limit movement that was never a problem
    .
    usually a clearance hole is .015 to .060 bigger than the screws. if needed i would make 2 holes bolt part on and align and the rest of the bolt holes would act as the drill jig. sometimes a part was clamped on and the holes are centered punched with a transfer punch that fits tight in the screw holes
    .
    many parts you clamp on a shelf for a part to rest on to aid in located it. obviously if part is heavy it helps to prevent it from falling

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    Positional accuracy of the work depends on (1) the positional accuracy of the drill bushings, (2) the running clearance of the drill in the bushings, and (3) the parallelism of the bushings to the spindle.

    Get those three things right and you can easily repeat within tenths, e.g. a pattern of 4 drilled holes will go onto a matching pattern of 4 bullet-nose pins with <.0005 diameter clearance. Get any one of them wrong and you wasted your time...

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    Quote Originally Posted by Ox View Post
    I'm afraid that I don't follow.
    Please forgive me as I have only been in the business for >30 years...

    ...but when you say that it is an awkward part to fixture, then you ask about a "jig".
    What exactly is this "jig"?


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    Ox
    I think what he is asking about is a device that will fit on an oddly shaped work piece(or workpiece inside device) that will allow you to copy a set of hole patterns to multiples of the oddly shaped work piece. What do you think the hardened drill bushings that all the industrial supply houses sell are for? For making drill jigs, of course.

    Early on, long before I was introduced to CNCs, I made hundreds of drill jigs for drilling and reaming holes in Aluminum plates. Put the part in the jig, and walk down the line of 50 drill presses, drilling and reaming as you went. Some part had upwards of 200 holes of 40 or more sizes. I wish I had been able to take pictures or saved some of them for your perusal.

    Sorry, Ox. I don't speak Oxese well enough to tell it that way.

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    Drill jig. Like a 1" thick plate with 4x #7 thru holes so you can clamp in place, follow pretty accurate with a drill then hand tap. Maybe one short one also for threading. I've used all the other methods when you have a mating part but this question more pertained to stand alone hole patterns.

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    Quote Originally Posted by alphonso View Post
    I think what he is asking about is a device that will fit on an oddly shaped work piece(or workpiece inside device) that will allow you to copy a set of hole patterns to multiples of the oddly shaped work piece. What do you think the hardened drill bushings that all the industrial supply houses sell are for? For making drill jigs, of course.

    Early on, long before I was introduced to CNCs, I made hundreds of drill jigs for drilling and reaming holes in Aluminum plates. Put the part in the jig, and walk down the line of 50 drill presses, drilling and reaming as you went. Some part had upwards of 200 holes of 40 or more sizes. I wish I had been able to take pictures or saved some of them for your perusal.

    Sorry, Ox. I don't speak Oxese well enough to tell it that way.

    I understand "drill bushing"

    But how does a bushing'ed "jig" work on an "odd shaped" piece that can't be (or hasn't been) "fixtured"?
    How is that s'posed to work?
    What good is a bushing setting out in space doo for you?


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    Quote Originally Posted by vmipacman View Post
    Drill jig. Like a 1" thick plate with 4x #7 thru holes so you can clamp in place, follow pretty accurate with a drill then hand tap. Maybe one short one also for threading. I've used all the other methods when you have a mating part but this question more pertained to stand alone hole patterns.
    Is there a callout on hole to hole spacing tolerance? If your part really can't be clamped into a cnc or on a drill press table, then hand drilling is probably your only option.
    What about a Bridgeport? You can rotate the head into all sorts of directions then use that to drill thru the jig that you described above.
    If you have to resort to a porta-mag drill, then be aware of how much head flex you get, when they get whopped out they push away pretty good.

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    As mentioned they can hold pretty good tolerance if well made & cared for. They also steady the drill so center drilling or spotting aren’t needed.

    Up until the ‘80’s they were used everywhere, mostly with table type drill presses & radial drills. With something like wheels to closely fit hubs, the jig is bored close to the hub pilot size for locating. With odd crap you’d usually have 3 locators (often pins) 2 would reference a plane & the other would reference and end (or step) of the part (triangle, still 3 pins).

    We were holding location, concentric & angles of rotation (abs) inside of .002” on coal truck hubs & rims a large as 8’dia back then. If someone mishandled one it was a real pain to get them back in shape (oval a ring that size with .002” clearance for a hub you get a real appreciation for assemblers try to fit out of round parts, LOL).

    Good luck,
    Matt

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    Thank you all for the first hand knowledge. As for the drill bushing versus Jig nomenclature, I think a bushing would go in to make up a jig. BUT I think for just a few uses, a non bushed steel jig with tight fitting holes would suffice. As mentioned you need to locate the jig on the part, but that's a whole different issue outside of the possible feature to feature accuracy of the jig itself. Plus you can easily mill features in the jig itself to locate the pattern like pins and square corners...

    I am glad to hear first hand experience that a tight drill jig can get +/-5. That was really the drive of the question.

    Question for those who used jigs heavily in the past. What was the process for tapped holes? was there another jig with threads so that a tap could follow something accurate into the hole?

    Thanks

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    Quote Originally Posted by Ox View Post
    But how does a bushing'ed "jig" work on an "odd shaped" piece that can't be (or hasn't been) "fixtured"?
    How is that s'posed to work?
    What good is a bushing setting out in space doo for you?
    Obviously anything you're going to drill through a bushing requires some kind of structure to locate and hold the work relative to the bushing. The OP would be better off to buy a book on jigs and fixtures than asking us to explain chapter and verse in a thread. Some drill jigs can be pretty clever, with removable liners to allow a larger tool like a countersink or tap to follow the drill. We used to make some where the whole bushing plate would swing out of the way to permit a whole series of piloted tools like step reamers and port cutters to follow the drill. Alphonso's manual transfer line of 50 spindles is an example of the accurately repeatable and productive setups factories used to manufacture complex parts before there was CNC (and for some years after that—for stubborn workaholics).

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    Quote Originally Posted by Oldwrench View Post
    Obviously anything you're going to drill through a bushing requires some kind of structure to locate and hold the work relative to the bushing. The OP would be better off to buy a book on jigs and fixtures than asking us to explain chapter and verse in a thread. Some drill jigs can be pretty clever, with removable liners to allow a larger tool like a countersink or tap to follow the drill. We used to make some where the whole bushing plate would swing out of the way to permit a whole series of piloted tools like step reamers and port cutters to follow the drill. Alphonso's manual transfer line of 50 spindles is an example of the accurately repeatable and productive setups factories used to manufacture complex parts before there was CNC (and for some years after that—for stubborn workaholics).
    I completely understand that.
    I have used them on transfer lines and smaller projects as well.
    I'm old enough to have used drill bushings and such....

    But what I don't understand was the fact that if the part is too funky for a fixt .....


    aw heck, forget it ...


    Suffice to say that for a drill bushing to be of any use, not only does the bushing need fixtured, but so does the part.
    One fixture in a CNC with use of a center drill is half of the fixturing that needs done to a part that is

    Quote Originally Posted by vmipacman View Post
    too large, awkward or hard to fixture


    AFAIK "jig" is synonymous with "fixture".
    If this is not so - please edumacate me!



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    Quote Originally Posted by vmipacman View Post

    Question for those who used jigs heavily in the past. What was the process for tapped holes? was there another jig with threads so that a tap could follow something accurate into the hole?

    Thanks
    My experience with this setup would be a larger, permanent bushing that has a smaller drill bushing. This bushing has a slip fit and is placed in the larger bushing, rotated 90 degrees under a screw that keeps it from spinning. This would be a .201 bushing for the tap drill. Then, that bushing is removed and a .250 bushing is placed in the larger bushing for a 1/4" tap. This was common on low to mid production setups back in my day making and using drill jigs.

    here is an example.

    GRAINGER APPROVED Slip Fixed Renewable Combination Drill Bushing, 5'/'16", I.D. 1'/'2", O.D., 5'/'16"':' Drill Size - 11V133'|'SF328IM - Grainger

    Paul

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    [QUOTE=Ox;3204300


    AFAIK "jig" is synonymous with "fixture".
    If this is not so - please edumacate me!



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    Ox[/QUOTE]

    Pretty much so.

    The drill jigs/fixtures I made and used were portable; just slide them along the table until you get to the drill you want.

    As far as drill bushings go they were pressed into the jig/fixture material. Most of the jigs we made were of aluminum. Mostly "suitcase" design, bottom plate with pocket for part to set in and a hinged lid that had al the drill bushings in it. One of fanciest ones we made was to drill five sides of a traffic light controller box.

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    Quote Originally Posted by Ox View Post
    But how does a bushing'ed "jig" work on an "odd shaped" piece that can't be (or hasn't been) "fixtured"?
    I think he's talking about plate jigs, which can have locating tabs to fix the position relative to perimeter features of the odd-shaped part.

    And I think the OP asked if you need a jig for tapping. I'd say "no" for locating. If you are tapping by machine, you don't have to worry about squareness, either. If you are tapping by hand, it would be nice but not essential to supply the operator with a simple "hold it square" jig/tool to get the tap started right.

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    Quote Originally Posted by sfriedberg View Post
    ...If you are tapping by hand, it would be nice but not essential to supply the operator with a simple "hold it square" jig/tool to get the tap started right.
    And that can be as simple as a piece of scrap aluminum with a hole drilled in it. I do that every time I hand tap a hole.

    Set the block on the part, start the tap through the block, get a few turns so you know it going in straight, then remove the tap handle and slide the block off and finish tapping to depth.

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    Then, that bushing is removed and a .250 bushing is placed in the larger bushing for a 1/4" tap.
    You better measure your 1/4" taps...


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    Ox

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    So, would it be safe to say that the diff between jig and fixt (at least in this h'yah case) is that a fixt would hold the part, while the jig is to hold a bushing(S)?

    Like maybe the jig may have 3 dowel pins to use to locate onto the edges of the part, with one or more bush's in it. And then this jig could be C-cramped to the part?


    On a side note, they ust'a make drills for use this way. They were called "double margine", and also "subland". Either of them are tough to find these days. Subland's was Mohawk Tool's big runner back in the day - next town over, but they closed up shop about 25 years ago.



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    Quote Originally Posted by vmipacman View Post

    Question for those who used jigs heavily in the past. What was the process for tapped holes? was there another jig with threads so that a tap could follow something accurate into the hole?

    Thanks
    That's a good question. I have used drill jigs a lot and put all the accuracy into the drill jig i.e. made on milling machine (Hint: Jig Borers). The tapping was then done with a Tapmatic, without any guides, with "good results" (no figures available ). Not sure about tap guides, but I doubt they would be threaded!

    However - you are talking about heavy plate which presumably can't be moved around easily. So to use a drill jig and tapping head you would ideally have a radial arm drill or perhaps a drill table which can rotate and swing? Or were you thinking of hand drill and tap....I have done that to machinery "on-site" where precise hole patterns were required - made up a drill jig before hand, usually using dowels to locate off existing edges or existing holes or perhaps measuring to the edge of the jig. All location edges, dowel holes, drill bush holes, made on the mill at the same time.

    Edit - just noticed this thread is in CNC Machining forum...sorry I am in the wrong room.


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