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Thread: Maintaining hole true position

  1. #11
    Registered Member chevynut's Avatar
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    Nick, yes that's the right idea, but like Rick said it's a pretty big oversize on the hole. Not sure that really matters though. If that's all it took, I'd just make the holes 3/8" and use a 3/8" bolt in the jig, then use 5/16" bolts for the final assembly. Maybe that's how they do it in the "real world".


    Rick, I want to laser cut the holes in the plates and NOT have to re-drill them. So #1 doesn't really buy me anything. #2 is pretty much what I'm doing now.

    I woke up this morning and had a revelation....funny how that happens during sleep.

    Something like this would work great, if the OD was a little smaller.

    http://www.mcmaster.com/#cadinlnord/90596a025/=lxklpi

    http://www.mcmaster.com/#cadinlnord/90975a036/=lxkq6l

    You would put a bolt in it, slip it into the oversize hole, put the threaded end of the bolt in the jig, and lock it down with a nut. It could also be used to weld nuts on the backside of a plate.

    I could also turn then down on my lathe a little so they' the right OD. I could also have some of these made on a CNC lathe or screw machine. The shoulder wouldn't have to be so large. I have wondered why nobody offers anything like this on the market. Seems like this would be a common problem, unless they really do go one full size larger on holes.
    56 Nomad, Ramjet 502, Viper 6-speed T56, C4 Corvette front and rear suspension


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  2. #12
    Registered Member NickP's Avatar
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    I really wish you would post a picture of your task. A visual aid is an extreemly good thought generator. I have built so many different jigs and fixtures in my past lives that were I to see it, I might be able to assist better than this 20 question barage. The shoulder screws I mentioned also come in 5/16" shoulder BTW. Also, a set of locating pins machined to a size needed inserted in the holes for the purpose of location along with a pair of vertical toggle clamps for retention may suffice to the need.



    Again, a picture is worth a thousand words!
    Last edited by NickP; 03-18-2013 at 08:49 AM.

  3. #13
    Registered Member chevynut's Avatar
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    Nick, I thought I described an example of one of the issues I run across. There are many, and I run into this problem all the time. I weld a lot of flange nuts on the backside of holes, so that's a problem I frequently have. Yes, a machined pin would work, but so would a machined bushing. I was just looking for obvious solutions. I'm sure lots of manufacturers run into this problem. Maybe they just oversize the hole to the next larger size and call it good.

    Here's a pic of the seat mounts similar to what I'm building. I have them finished, but I used a 5/16" bolt in a 5/16" hole to mount them onto my assembly jig. Then after welding I reamed the holes oversize. I think the example of welding nuts to a plate is self-explanatory and there are nuts inside the tube in the pic.
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    56 Nomad, Ramjet 502, Viper 6-speed T56, C4 Corvette front and rear suspension


    Other vehicles:

    56 Chevy 2-door BelAir sedan
    56 Chevy 210 4-door sedan
    57 Chevy 210 4-door sedan
    1962 327/340HP Corvette
    1961 Willys CJ3B Jeep
    2001 Porsche Boxster S
    2003 Chevy Silverado 2500 HD Duramax
    2019 GMC Sierra Denali Duramax

  4. #14
    Registered Member chevynut's Avatar
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    I think I've pretty much concluded that manufacturers simply go to the next size up on their clearance holes. I have noticed that 3/8" washers are WAY too big for a 3/8" bolt, so I use 5/16" washers on them and they still fit. Next time I think I'm going to cut the 5/16" bolt holes to 3/8". But that doesn't solve the problem with the nuts. I guess I'll have to use one of the weld nuts I linked, and just drill 3/8" holes. I'll have to give it a try soon.
    56 Nomad, Ramjet 502, Viper 6-speed T56, C4 Corvette front and rear suspension


    Other vehicles:

    56 Chevy 2-door BelAir sedan
    56 Chevy 210 4-door sedan
    57 Chevy 210 4-door sedan
    1962 327/340HP Corvette
    1961 Willys CJ3B Jeep
    2001 Porsche Boxster S
    2003 Chevy Silverado 2500 HD Duramax
    2019 GMC Sierra Denali Duramax

  5. #15
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    Standard clearance holes for most manufuacturing is based on tolerance of the hole location. It's also usually assumed that the clearance holes are never undersize, they are nominal to slightly oversize (that's what a typical drilled hole is).

    This method works for both 1 dimensional and 2 dimensional hole patterns.

    Holes in parts manufactured on a milling machine are usually spec'd at +/-.010". With that tolerance you need a hole that's .020" oversize. So you pick the next drill size that's a minimum of .020" oversize. Once you get over 1/4", that's usually 1/32" oversize with standard drill bits.

    Punched holes in sheet metal +/-.020". Parts that are drilled by hand depend on the equipment and the layout method. Those are going to need .040" oversize holes. Again, once you get over 1/4", drill sizes are limited, you may end up with 1/16" oversize.

    A big hole in a flat washer is a waste, there it's more about a lack of precision in making the flat washer, and maybe quick assembly. When I buy cheap flat washers, I usually buy the next smaller size if the holes are real big.

  6. #16
    Registered Member Custer55's Avatar
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    The last time I welded nuts to a plate with oversized holes I used making tape wrapped around the bolt to keep the nut centered. I worked ok but you have to rewrap the bolt for each hole.
    Brian

  7. #17
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    Quote Originally Posted by chevynut View Post
    Nick, there's nothing proprietary about this. Let me explain better what the problem is.

    I am assembling my seat mounts that have two plates attached to a tube. The two plates have holes in them that match the holes in the tri5 floor, which are nominally 3 1/8" apart. Each plate has two holes, and they get welded to the tube. I want the holes to line up on any car, which has some tolerances.

    The holes on each plate are accurately located. However, I also need to locate the plates accurately relative to each other. I built a jig that has holes in it located precisely where I want each hole to be. I made the holes in the plates 5/16" in diameter, and the holes in the jig at 5/16" diameter. So if I bolt the plates to the jig, weld them to the tubes, everything is located where it's supposed to be. Once the welding is done, I ream the holes out larger, and they're concentric with the jig holes, and supposedly with the holes in the floor of the car.

    I was trying to think of a way to eliminate the reaming operation, and still have the plates located correctly. If I oversize them first, then use a 5/16" bolt to attach the plates to the jig, they can be off-center. As I mentioned, an oversize bolt with 5/16" threads would be one way to do it. I could make a bushing to fit in the hole to locate the parts.

    As I mentioned, I have a similar issue when welding nuts to the backside of a hole. If I oversize the hole, I can't get the nut centered. So I typically make the hole nominal size, hold the nut in place with a bolt, weld the nut, remove the bolt, and ream the hole oversize. If you've ever tried to do this, you know that welding can pull the nut off-center slightly, enough to bind the bolt.

    Just looking for some ideas, or off-the-shelf solutions.
    Take a look at stripper bolts. Misumi and McMaster Carr (and probably others) sell them. You might have to have them made but they're not too expensive. They might solve your problem.

  8. #18
    Registered Member chevynut's Avatar
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    Geez guys, this thread is 3 years old . I solved the problem with locating the plates by slotting the holes a little. I have to line up the slots so they're centered on my jig, but it works fine for the few parts I make per batch. So far I've just been welding the nuts on the backside then I ream the holes out with a slightly larger drill bit. It takes a little time, but it's not that bad since the nuts are pretty hard and I can tell where to stop. I changed the design so I use fewer parts now and it's a lot easier to weld the nuts on.

    I still run into instances where it would be nice to have a bolt with a slightly oversized shank. The shoulder (stripper) bolts go up one whole size so if I wanted to weld a 1/2" nut the hole would have to be 5/8" which is way too big. If I had a way to grind the shanks down they would work. When I was an aircraft mechanic we used over-sized bolts all the time to replace standard size bolts in holes that had signs of metal fatigue. We'd ream the hole out 1/64" to 1/32" oversize and drive the new bolt in. The threads were still standard size..wish I'd kept some of those.
    56 Nomad, Ramjet 502, Viper 6-speed T56, C4 Corvette front and rear suspension


    Other vehicles:

    56 Chevy 2-door BelAir sedan
    56 Chevy 210 4-door sedan
    57 Chevy 210 4-door sedan
    1962 327/340HP Corvette
    1961 Willys CJ3B Jeep
    2001 Porsche Boxster S
    2003 Chevy Silverado 2500 HD Duramax
    2019 GMC Sierra Denali Duramax

  9. #19
    Registered Member NickP's Avatar
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    Quote Originally Posted by chevynut View Post
    Geez guys, this thread is 3 years old .
    Someone must have been looking for some content.

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