reinforce tap hole

I just drill and tapped four 5/16 x 18 into some 0.200 wall AL tubing. I can
see this won't hold long term, the threads will strip. What can I do for
strong tap theads in this situation? Some sort of insert???
Karl
Reply to
Karl Townsend
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Yes.
The best option depends on the details of the connection. If the tubing is large dia so the curvature isn't too bad, "riv-nuts" should work. If it's smaller dia tubing with too much curvature for a riv-nut, a larger insert inside the tubing with the threads would work if you can get it into place. If you can drill oversized and do a through bolt with a sleeve that would work as well.
Reply to
Pete C.
Can you form or flow drill the hole next time to create more "wall" to tap?
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Right now, with the current hole... Not sure.
Regards, Joe Agro, Jr. (800) 871-5022 01.908.542.0244 Automatic / Pneumatic Drills:
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Spindle Drills:
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Tapping:
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Site:
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V8013-R
Reply to
Joe AutoDrill
Insert a block in the bore and tap into it, threaded inserts, sleeve the outside, or a combination of all of them. Just depends on what you intend the load to be and what direction it occurs. Also what alloy you're using, extruded hardware store gum isn't the same as 7075- T6.
Stan
Reply to
stans4
5/16 - 32 will give you 6 threads & should be strong enough. 'Course then you'd need 5/16 - 32 bolts, which could be a problem. And, can you relocate for 4 new holes?
Probably not a good idea, Bob
Reply to
Bob Engelhardt
If it's threading the inside of a small tube... Maybe use a pipe-thread (tapered) tap? It would leave near full thickness at the narrow end, but engage fully at the mouth of the tube,
Or, is this drilled/threaded perpendicular to the axis of the tube? For that, an aluminum-soldered (or welded) boss might be stronger; it's how backpacks are assembled with thinner tubing.
Reply to
whit3rd
Thanks for helping think outside the box. If I can find a way to reach down inside the tube and start a bolt from the inside, then twist it tight and form a stud. reaching two feet inside a 4x4 tube and starting a bolt should be fun.
Karl
Reply to
Karl Townsend
If studs will work the easy solution is a rivet stud.
Something on here should do the trick.
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I use the pull up studs and riv-nuts all the time on fire apparatus.
Reply to
Steve W.
I've never heard of anyone trying to do this with a hand drill... Hmm... I'm guessing you might not be able to make enough thrust, etc...
Maybe give them or "form Drill" a call and see what their thoughts are.
I've had discussions with both and found one to be much more helpful than the other... But I don't remember which. Figures, eh?
Reply to
Joe AutoDrill
The poor man's version of that is to drill a hole much smaller than the tap drill, use a long and very tapered punch to extrude metal into the hole. Drill and tap normally. For the 4"x4" tube you might have to have a heavy backer block with a suitable hole and work upside down. :)
Joe AutoDrill wrote:
Reply to
RoyJ
It will be easier if you cut a screwdriver slot across the end, and use a split screw-holding screwdriver to pull it into the threads. Even better is turning 1 - 2 threads off so it will drop into the hole. You could position it with smaller tubing with a vee in the end, and a loop of string through the tube to hold the bolt in place but let it turn.
jsw
Reply to
Jim Wilkins
Is this a square or rectangular tubing, or round/curved? If the former, I would consider a Rivnut for the task. It slides in, and is drawn up to grip on the inside of the mounting surface. The threads already exist, and are used for the drawing. There are speed tools (for smaller sizes), wrench tools (at least to 1/4" and maybe larger), and pneumatic or hydraulic tools.
They were invented by B.F. Goodrich, and now seem to be made by "Böllhoff-Rivnut® Inc" according to a Google search.
Check Out:
They have downloadable PDF documents describing the products, and a certain amount of tooling as well. Or, you might want to make your own tool. The wrench style tools have a thrust ball bearing with the outer nut being turned around a bolt which is held still by a large Allen key which produces the pull necessary to set the Rivnut. This is probably what I would try to make to set 5/16" Rivnuts if I did not already have the Hydraulic tool.
Note that Rivnuts can be obtained with through holes or blind holes, as well as with flat head or countersink design, and those without the knurled sleeve have available a key which will fit in a notch cut by a tool made for the purpose so the Rivnut will not spin in the hole even if you do not set it fully tight.
Here are a couple in the 5/16-18 size, but not quite right for you:
320393707983 Steel, but grip range from 0.027" to 0.150", not your 0.200".
370230283081 Aluminum, with a grip range of 0.040" to 0.200"
The more serious ones (larger, wide flange) take a more serious tool than the vendor is offering. I've got a hand-pumped hydraulic tool of the sort, as well as the speed tools for lighter weight things.
370185982532 This one looks nice too, but too short a grip range.
I don't see any of the hydraulic tools in my old saved searches right now. But I do like Rivnuts for the type of job you are describing.
Good Luck, DoN.
Reply to
DoN. Nichols

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