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Projects Frame Thick Enough to Tap?

Discussion in 'Traditional Hot Rods' started by pa2000xxxx, Sep 18, 2019.

  1. pa2000xxxx
    Joined: Mar 16, 2014
    Posts: 1

    from Destin, FL

    I have a 57 Chevy Bel Air frame I want to drill and tap in a few places. I’ve seen people do this for smaller screws that go in fuel rail brackets but I’m not sure the frame is thick enough for slightly larger bolts...I want to tap for bolts to hold trans cooler. Frame is boxed so I can’t get a nut inside and it’s powder coated so I don’t want to weld at this point.

    Anyone drilled and tapped frame with bigger bolts? Any can’t find any online guidance on minimum metal thickness for bolt size. Thanks.
  2. el Scotto
    Joined: Mar 3, 2004
    Posts: 4,183

    el Scotto
    from Tracy, CA

    Self tapping garage door fasteners!
  3. alchemy
    Joined: Sep 27, 2002
    Posts: 14,690


    The garage door screws don't even stick in my garage door, I sure wouldn't use them on a car.

    I'd think a lightweight cooler would be just fine held by bolts tapped into the frame. If there is a heavier bracket that holds it, I'd use a rivnut instead of tapping the frame. Just be aware you can't really torque hard on a rivnut.
  4. Too bad no welding. A piece of cut to fit, DOM tubing, would be nice ... running thru frame and boxing. Sure as heck, wouldn't go anywhere.

    Don't they sell, push thru riv nuts ?
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  5. squirrel
    Joined: Sep 23, 2004
    Posts: 44,249


    Any metal is thick enough to tap, but how much load the screw will support, will depend on how thick the metal is.

    If you use 10-32 screws it will have a couple threads engaged, and should be able to support a transmission cooler. Use more than two screws to hold it on, because spreading the load among more screws reduces the load on each screw. And support the hoses with clamps near the cooler, so they are not tugging on the cooler,

    But seriously, the transmission cooler should go in the front of the car, not on the frame rail :)
  6. Happydaze
    Joined: Aug 21, 2009
    Posts: 886


    x2 rivnut

    And those self drilling, self tapping bolty screw things are a pita to remove even when fully unscrewed!!! I know this as previous owner of one of my cars used them quite extensively :(. They seem to hang up on the cutting area somehow - unwind until you know the threads are cleared and then grab and pull with pliers! I waged war on them replacing with rivnuts, or tapping the holes.

  7. Rule of thumb for machine screws, the full thread engagement should be one diameter of the screw/bolt minimum. So, 1/4 inch diameter bolt, 1/4 deep tapped hole.
  8. nochop
    Joined: Nov 13, 2005
    Posts: 1,307

    from norcal

  9. el Scotto
    Joined: Mar 3, 2004
    Posts: 4,183

    el Scotto
    from Tracy, CA

    My buddy installs garage doors for a living so I’ve gotten boxes of fasteners from him. They work out great for me, 1/4” shank, have held parts of my shitty old cars together for thousands of miles and the garage doors are still holding together fine. :)

    I guess it might be one of those “your mileage may vary” kinda things... :D
  10. 3/16" steel pop rivets… Put a washer under the rivet head, if you ever need to remove the brackets off the frame, just grind the heads off.

    That's what I used to replace those 'garage door' screws when they started falling out shortly after installing the new doors...
    Last edited: Sep 18, 2019
  11. krylon32
    Joined: Jan 29, 2006
    Posts: 5,997

    Alliance Vendor
    from Nebraska

    I've held the B&M trans coolers off many 32 Ford boxed chassis with 10 Gauge metal and 1/4 inch bolts. Never had one fall off yet. You could also use a good quality nutsert of your worried about strength. I've also done that many times.
    mcsfabrication and Hnstray like this.
  12. Rice n Beans Garage
    Joined: Dec 17, 2006
    Posts: 1,449

    Rice n Beans Garage

    Nutserts will work fine
    mohead1 likes this.
  13. Nutserts x 5
    jimmy six, indianbullet and mohead1 like this.
  14. Blues4U
    Joined: Oct 1, 2015
    Posts: 4,253

    from So Cal

    How are these installed? Drill a hole slightly smaller than the nutzert and hammer it in, then when tightened it expands? Or does it take a tool to install them?
  15. Squablow
    Joined: Apr 26, 2005
    Posts: 14,042


    Just got done bolting a front bumper on my '57 and I think the frame is too thin to drill and tap unless you're using some very small diameter, fine threaded bolts. They're not real thick. I like the idea of rivets or nutserts much better. I'm sure self-tappers would work for something light weight but it sounds like this is a pretty nice car, being the frame is fully powdercoated, so I feel like it'd probably be worth the extra effort/expense.
    kidcampbell71 likes this.
  16. error404
    Joined: Dec 11, 2012
    Posts: 229

    from CA

    Yes, you can buy/make a tool to install them, essentially a nut, bolt, and a few washers. The nutserts squish sort of like a pop rivet. Drill a hole just large enough to fit the nutsert in there, but not large enough for the lip of the nutsert to go through. Sometimes you have to tap them every so slightly, but it doesn't have to be a press fit, it can be slightly loose. Tthen you install them by tightening up the nut on the installer, while holding the bolt with another wrench, "drawing" the nutsert and squishing it like a pop rivet.

    If you go the nutsert route, definitely 'sacrifice' a few nutserts on some scrap metal to get a feel for how they install. And you'll be able to see the back side on those tests pieces, to see exactly what's going on.

    They work very well, but definitely practice on a few of them first. And make sure to get ones designed for the thickness of metal you are working on. The ones I use have ribs/serrations on them that I think help them bite into the metal better. I've never had one spin on me, after I learned how to install them.

    The only thing to note, is that the lip of the nutsert will sit slightly proud of the surface you're installing them to. Usually doesn't make a difference, but just FYI.
    Last edited: Sep 18, 2019
    dan31 and Blues4U like this.
  17. Buckster
    Joined: May 3, 2010
    Posts: 222


    The nut-serts I used went into a hole the size of the nut-sert's body. I screwed a Allen head fastener into the sert with a washer & a little oil on the fastener's threads. Tightening the fastener pulls the body up against the inside of the wall. Just like a molly anchor used on drywalls.
    Link to what I used: Aluminum body
    Steel body-
    kidcampbell71 likes this.
  18. ekimneirbo
    Joined: Apr 29, 2017
    Posts: 639

    from Brooks Ky

    Look for a "kit" that has the installation tool and a nutsert assortment. They aren't very expensive and they work really can use them for sheetmetal too. They look nice in your toolbox when not in use.
    Automotive Stud likes this.
  19. Hnstray
    Joined: Aug 23, 2009
    Posts: 10,962

    from Quincy, IL

    Consider using anti-seize compound on the bolts/screws when installing the accessory. While I like nutserts, they will not hold tight when removing the fastener if any rust or corrosion develops in the nutsert and it will just turn in the hole. "an ounce of prevention is worth a pound of cure"

    squirrel likes this.
  20. Beanscoot
    Joined: May 14, 2008
    Posts: 1,202


    For installing Nut-serts or even for tapping into thin metal I drill a bit under-size and use a reamer to finish the hole.
    Or is it only me who can't get a nice, clean round hole with just a drill?
  21. That's the reason I don't like these. Worse yet, when trying to drill the screw/bolt to get the part off the damn insert spins....
    Hnstray likes this.
  22. squirrel
    Joined: Sep 23, 2004
    Posts: 44,249


    yup, that's a problem with nut-serts.

    The last one I built got 3/16" aluminum rivets to hold the cable/tube clamps to the frame. The trans cooler was mounted to tabs welded to the radiator support (note that it's not on the underside of the car, it's up front where the cool air is)

    Usually I use sheet metal screws. I might use self drilling screws to drill the hole, but I like to go back and install a screw with a better looking head on it. (and those self drilling screws are expensive)
    Hnstray likes this.
  23. Marty Strode
    Joined: Apr 28, 2011
    Posts: 4,256

    Marty Strode

    Use a step drill, the HF ones are bulletproof.
    Texas57, bct, MAD 034 and 1 other person like this.
  24. phat rat
    Joined: Mar 18, 2001
    Posts: 4,307

    phat rat

    I've got over 75K on the cpe with the trans cooler mounted back by the rear-end. Haven't had any problem yet. It does a fine job out on the road even as low as the cpe sits. If needed, such as a lot of stop and go traffic, it does have a fan that I can turn on
  25. 2OLD2FAST
    Joined: Feb 3, 2010
    Posts: 1,826

    from illinois

    Garage door screws work just fine IF you don't overtighten ( strip) them , all the factory directions state specifically to NOT use an impact driver....
    Hnstray and kidcampbell71 like this.
  26. error404
    Joined: Dec 11, 2012
    Posts: 229

    from CA

    Yep, step drills work much better on sheet metal than a regular twist drill. I usually do start the hole with a regular 1/8" drill bit though.
  27. I used exact length through bolts, with shoulders to prevent collapse, on my boxed frame for anything other than cosmetic attachments.
  28. RJP
    Joined: Oct 5, 2005
    Posts: 1,263

    from PNW

    socket head stainless shoulder bolts the appropriate size. since you're doing it, might as well do it right.
  29. 4wd1936
    Joined: Mar 16, 2009
    Posts: 798

    from NY

    I use Loctite on the outside of the rivnut and Neverseize on the inside threads, seems to work quite well. Buy good quality rivnuts or nutserts, the cheap ones are well, cheap.
    kaspar likes this.

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