Need advice from a machinist for drilling holes
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  1. #1
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    Need advice from a machinist for drilling holes

    I've got a small welding job to do that requires I accurately drill 3/16" holes every 1/2" along the centerline on one side of a 30" piece of 1" square steel tubing. I have a drill press, but no other machinery remotely applicable to this task. The holes have to be on the center line and equally spaced because a U shaped gadget will straddle this tube and use a hole to locate the gadget.

    Can anyone suggest a technique or home made tool that could do this job? Scribing lines and center punching them is too tedious and inaccurate. I'm looking for a way to drill the first hole and then use it as a stop to drill the neighboring hole, etc, etc, where the technique or tool guarantees spacing and centering.

    BTW - I don't own a mill or lathe or any other motorized tool that has fine adjustment potential.

  2. #2
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    Re: Need advice from a machinist for drilling holes

    If it were me I'd make a simple jig to align the drill. Start by making a saddle that will fit snugly on the tubing. In the center of the saddle mount a drill guide bushing such as 8491A142 from McMaster. https://www.mcmaster.com/#drill-bushings/=1byeke8

    Come off of the side of the saddle with a short strap with an alignment pin.

    You can optionally make the strap a few inches long and install several guide bushings in it so that you can drill several holes before you have to realign the saddle.
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  3. #3
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    Re: Need advice from a machinist for drilling holes

    Quote Originally Posted by RoatanBill View Post
    I've got a small welding job to do that requires I accurately drill 3/16" holes every 1/2" along the centerline on one side of a 30" piece of 1" square steel tubing.
    I'd probably use masking tape and carefully mark out the holes, center punch them and drill away...

    It's only 30" long... shouldn't be that time consuming.
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  4. #4
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    Re: Need advice from a machinist for drilling holes

    You know if you've only got the one (or even two) 30" piece to do I can hardly see it being worth the time to make up some kind of drill locating jig/fixture. Now if you had a whole bunch of them it would be a different story. What kind of accuracy tolerance do you think you need to keep on these hole locations? If it's just in the neighborhood of + or - .030" I'd just lay them out, center punch and drill them and be done with it. Doesn't seem to me to be something that should take any more than a half hour or so to do.

  5. #5
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    Re: Need advice from a machinist for drilling holes

    I mentioned that I wanted a home made tool because of where I live. There are no appropriate stores to visit here and ordering on line takes 3 weeks minimum to get the delivery from Miami.

    I've done this by hand numerous times before and ended up mating pieces where the holes should have lined up but didn't due to inaccuracy. For example, I built 24"x48" angle iron frames of 1-1/2 angle iron with 1/4" ply tops for shelving. These mated with 11' tall angle iron legs. The holes on the frames were supposed to mate up with the holes in the legs so the frames and legs could be considered interchangeable parts. I built 8 sets of legs (32) and 64 frames for 8 units.

    I drilled the leg holes every 4 inches on both webs (I believe that's the term) so I could move the shelves around and add shelves as needed. Since it takes 4 legs per unit, the holes needed to be in the same horizontal plane when the unit was assembled. Trouble was that not every frame fit every leg hole and in frustration, I just took a drill to any stubborn situation. I'd like to avoid this in future, so I'd be willing to build a tool to better position holes.

    If you're asking why I didn't just purchase shelving, I did. It was expensive to get it to Miami due to the weight, then added expense to get it from Miami to me, along with customs paperwork, import duty, customs broker fees, and lawyer for paperwork. That's why I build stuff.

    I've invented a tool in my head to do this but it's pretty elaborate since I want it to work for all the steel I normally use - 3/4" to 3" angle iron, flat stock and square tubing. I was hoping someone had already invented a gadget simpler in design than my imagination, or there was a machinist's technique that I could employ.

    In short, this tiny project of needing only 2 of these 30" pieces, has spurred me to ask the question here because I'm determined to find a solution to this positioning problem as I'm likely to need it again and again and again.

  6. #6
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    Re: Need advice from a machinist for drilling holes

    Do you have a drill press vice? Once you have that bolted down in the proper position, that will take care of the centering problem. Then come up with something that would drop a peg into the previously drilled hole to space out the next hole.
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  7. #7
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    Re: Need advice from a machinist for drilling holes

    Yes, I have a vice and a home made fence to clamp things to.

    The problem is that peg thing.

  8. #8
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    Re: Need advice from a machinist for drilling holes

    Is the 0.5” spacing important or is it also important that after, e.g., 30 holes, you cover 15”? If you only care about the spacing and that the two parts match, then a last-hole spacer seems like a fine approach. If you care also about absolute distance, any error in the spacer will multiply by the number of holes.

  9. #9
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    Re: Need advice from a machinist for drilling holes

    This is fairly simple :

    But for your application where the drill is stationary and the piece is moved along to the next hole, you would want the spacer block fixed to the vise or drill press table. Then drop your pin (bolt) into the previously drilled hole as you move the work piece.
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  10. #10
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    Re: Need advice from a machinist for drilling holes

    You need to do all your layout from the end, if you try to go hole to hole and there is any inaccuracy it can multiply as you go. The most accurate way to drill would be to start your holes with a #1 center drill, because center drills have almost no lead they have much less tendency to "walk".
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  11. #11
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    Re: Need advice from a machinist for drilling holes

    jwmelvin: The hole spacing for this application is actually arbitrary, but once decided upon, it needs to stay consistent. I fully realize that errors add up and in this case, any small error in the initial spacing of holes wouldn't matter. If I'm short a hole or have an extra hole, that's OK.

    The important thing is that both 30" pieces end up with the same hole spacing when both pieces are held vertically so that a hole on one is in the same horizontal plane as the hole on the other. I intend to drill a nominal 60" piece and then cut it in half.

    BTW - 30 holes covers 29.5", center to center with exact 1/2" spacing.

  12. #12
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    Re: Need advice from a machinist for drilling holes

    bead-boy: I'm aware of that technique and used a variation of it in the shelf build I previously mentioned. I built a steel jig with a 1/16" hole in it that slid along the angle iron web and the other end of the jig had another 1/16" hole in it that I shoved the rear end of a 1/16" drill bit into. This was all hand drilled, which was another mistake.

    The lead hole was my positioning hole to drill a 1/16" pilot in my target material. The trailing hole was my "peg" hole. It worked OK except that the angle iron is never 90 degrees between webs (always greater and the 2-' length curved like a banana) and the critical distance was from the interior of the angle out and I was going from the edge of the web in. The web wasn't exactly 1-1/2 everywhere, so I ended up with these 1/16" pilot holes slightly off sometimes. The other issue was that my lead jig hole got enlarged by just a tiny bit with every hole I drilled in the target material and I told myself it wouldn't matter as that hole got more and more sloppy. Well, it did matter. I was also leaning my peg drill bit differently every time before I clamped the jig to the target so that it also produced an imperceptible error that added up over the 11' distance. The final 1/4" holes looked great but they were ever so slightly off sometimes so that I couldn't put a 1/4" bolt through them and the ones on the shelves.

    What I learned was to care for where the critical distance is knowing that the steel I get is all hot rolled and not uniform in dimension. I also learned to use a peg smaller than the hole and hold it absolutely rigid use to use and touch the peg to either one side of a drilled hole or the other consistently before clamping in place to drill.

    BTW - I tried duplicating the jig as the hole got sloppy, but that wasn't working either, so I stuck with the original jig to the bitter end.

    CAVEMANN : I'm doing this on a drill press to get its benefits and intend to use the tip of a center drill that won't wander. The material is .065 thin wall.

  13. #13
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    Re: Need advice from a machinist for drilling holes

    Depending on the quality of your drill press, a cross slide table, good vise, edgefinder, and an indicator might be worthwhile investments.

    There's just not a cheap, accurate way to accomplish the task you're got with a drill press. About the best I can come up with would use a travel indicator and a mag base, but you would also need a vise.

  14. #14
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    Re: Need advice from a machinist for drilling holes

    Simple tool to make. HF sell transfer punches and a center drill might help you start the hole since your drill press chuck might wobble.. I did a few hundred for a job using this method. Then tapped them.

    Years ago somebody on this forum had a locating/indexing fixture that attached to the drill shaft. As the chuck lowered the indexing point lowered into the previous hole. Thus the spacing was consistent.
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  15. #15
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    Re: Need advice from a machinist for drilling holes

    machinisttx, tapwelder: My drill press is 20 yeas old. It stands 6' tall and weighs enough so when I move it on its cast iron base I have to be REAL careful not to lean it too far so I can handle the cast iron top heavy load. It drills a nice hole, but it does vibrate a bit. A step drill greater than 7/8's causes the belts to slip no matter how hard I attempt to tighten them on the slowest setting. I wish there were a way to replace the belts (original equipment) and pyramids of pulleys with a chain and sprocket set up.

    I'm going to look up what an edge finder and indicator are and what they do. Thanks for the suggestion. As far as transfer punches are concerned, I already looked that up and what a great idea. I've been staring down holes and trying to mark a spot with a Sharpie for years. I never knew that they existed. I have some centering hinge drill gadgets (Harbor Freight) that are nearly worn out because they're cheap junk, but they do manage to start a hole accurately inside an existing hole. If anyone knows of where I can get quality ones meant for metal work, please let me know.

    These gadgets, however, would cause me a 3 week delay to get delivery.

  16. #16
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    Re: Need advice from a machinist for drilling holes

    I dunno Bill...I use this thing daily with transfer punches, regular pencils, red pencils. I also use these all the time(vid)

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    Last edited by Bonzoo; 03-14-2018 at 03:24 AM.

  17. #17
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    Re: Need advice from a machinist for drilling holes

    Bonzoo: I was aware of the center finder in concept, not that particular device. I usually eyeball where the center might be, say on square stock, and use a square as a depth gauge to get close to that spot and make a mark. Then I rotate the square 180 and make another mark. Center is between the marks. If the marks are too far apart, i'll nudge the setting on the square to get tighter tolerance. Using a center finder with my newly discovered transfer punch makes a lot of sense. Admittedly the center finder is a much better tool for the purpose. I'll put one in my shopping cart on my next Amazon order along with a set of transfer punches.

    I can't buy anything from Harbor Freight any longer since they banned shipping to freight forwarders as company policy. I never gave them any trouble and got numerous (computer generated) emails from Eric Smidt, the owner, over the years but I got jettisoned as a matter of policy.

    I do all my tapping on a drill press to keep it square to the work. I just spin the chuck by hand. I tried those drill taps and the 1/4" worked well on 1/8" at drill press speed, but broke on 1/4" so I'm back to drilling the hole and then tapping it the old slow way. The drill taps smaller than 1/4" broke too easily at 300 rpm even on 1/8" material. I can see the value in the tap and drill guides for field work or when the work won't conveniently fit on the drill press table. I didn't know either of those existed even in concept. I drilled holes in scrap lumber to act as a guide when needed. That worked well for one or two holes.

  18. #18
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    Re: Need advice from a machinist for drilling holes

    Take two pieces of flat.

    Draw a center line on one piece, then mark where you want the holes to be. Drill the two holes with the same size bit you'll be using to drill your shelving supports.

    Tack, or screw, a fence to that piece. This will ride along the workpiece, and keep a true center as you go along.

    Insert a piece of round stock the size of the hole you'll be drilling in one of the holes you drilled in the flat. Tack it. Or use a sacrificial drill bit same size as holes you'll be drilling (most accurate method)

    Drill the first hole with the pin off the workpiece, and just the open hole on the workpiece. Once you have the first hole, then just move the gadget along while dropping your guide pin in the previous hole you drilled. Only use your guide hole to dimple the material with the drill, DON'T USE IT AS A GUIDE BUSHING WHILE DRILLING, OR YOU'LL WALLOW OUT YOUR GUIDE HOLE.......JUST USE IT TO CENTER YOUR DRILL.

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    You can leave the locating pin as a tight fit without tacking, if you need to start the first hole further along the piece, and the pin would interfere.
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    Re: Need advice from a machinist for drilling holes

    Take about 10 minutes to make. And all's ya need is your drill press to make it.
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  20. #20
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    Re: Need advice from a machinist for drilling holes

    With something like this, you have to make sure you run the edge along the same surface on all pieces you'll be drilling. This will insure lineup when multiple workpieces are mated. Mark which side you used to run the fence on, and mate the pieces so's they match when done, and ready to assemble.
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  21. #21
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    Re: Need advice from a machinist for drilling holes

    farmersamm: You're describing essentially what I did on my shelving project as I previously posted in this thread. It worked OK, but has its flaws that I enumerated.

    I understand, and understood at that time, that dimpling the target as opposed to drilling it with the jig in place would have been a better idea to help avoid enlarging the jig hole, but without drilling the hole there is no hole to act as the peg location. Dimpling with the jig and then removing the jig to drill the hole is a possibility, but doing that in a drill press has it's own issues especially with a small bit. Trying to center the dimple below the bit so the bit won't bend while drilling to produce a slanted hole that becomes the peg hole for the next iteration comes to mind. If the bit is rigid enough not to bend (center drill) then it's also rigid enough to land on the slope of the dimple instead of the bottom producing a hole where it shouldn't be. Admittedly, these are tiny errors, but they add up when repeated multiple times.

    It really gets down to how good the tolerance has to be for a given project. I'm an engineer and by nature I want things to fit so you can't see daylight between them as a goal. I take primer and paint thickness into consideration on some projects when I draw them up in CAD.

  22. #22
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    Re: Need advice from a machinist for drilling holes

    Quote Originally Posted by RoatanBill View Post
    farmersamm: You're describing essentially what I did on my shelving project as I previously posted in this thread. It worked OK, but has its flaws that I enumerated.

    I understand, and understood at that time, that dimpling the target as opposed to drilling it with the jig in place would have been a better idea to help avoid enlarging the jig hole, but without drilling the hole there is no hole to act as the peg location. Dimpling with the jig and then removing the jig to drill the hole is a possibility, but doing that in a drill press has it's own issues especially with a small bit. Trying to center the dimple below the bit so the bit won't bend while drilling to produce a slanted hole that becomes the peg hole for the next iteration comes to mind. If the bit is rigid enough not to bend (center drill) then it's also rigid enough to land on the slope of the dimple instead of the bottom producing a hole where it shouldn't be. Admittedly, these are tiny errors, but they add up when repeated multiple times.

    It really gets down to how good the tolerance has to be for a given project. I'm an engineer and by nature I want things to fit so you can't see daylight between them as a goal. I take primer and paint thickness into consideration on some projects when I draw them up in CAD.
    Ya mean you don't even have a drill press vise? Drill off the vise so you can remove the jig while keeping the material locked up in the vise. Geeeeeeez. Make the jig so's the fence contacts the material off the vise. Jayzus F'n Cheeeerist.

    If the hole is too large, requiring lotta down pressure on the stock, shim the free end of the stock to take the force.

    Or buy a dam mill

    And then put a DRO on the dam mill, cause the leadscrew has built in error that multiplies over distance.

    Engineers
    Last edited by farmersamm; 03-14-2018 at 10:30 AM.
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  23. #23
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    Re: Need advice from a machinist for drilling holes

    Or make a dam stop that will contact the jig on top of the workpiece, and keep the dam workpiece in the dam vise on center.

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  24. #24
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    Re: Need advice from a machinist for drilling holes

    By God, go to Africa, Cuba, Hell......even Russia, and they figure out how to make stuff work with bare bones minimum.
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  25. #25
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    Re: Need advice from a machinist for drilling holes

    snicker

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