Harden hand cut threads in mild steel?

[Grant Gunderson]

I have a few hikes that I’ve drilled and tapped in 2in square steel tube with ¼ walls. Problem is the fasteners overtime keep pulling the threads out. Any ideas on how to harden the threads. Due to the location it’s not possible to weld a nut on.

 

[doublearon98]

Would it be possible to replace that section of square tube with a better material?

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[justanengineer]

Mild steel generally doesn’t harden worth a ****, so your best bet is probably going to be either a rivnut or drilling and welding in a threaded insert.


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[mcj115]

I have a few hikes that I’ve drilled and tapped in 2in square steel tube with ¼ walls. Problem is the fasteners overtime keep pulling the threads out. Any ideas on how to harden the threads. Due to the location it’s not possible to weld a nut on.

Could you install a rivnut?

 

[Grant Gunderson]

Can’t replace that section with another material unfortunately. The rivnut. Idea is great. Only problem is that I’ve been unable to source any larger than 1/2inch. Humm… maybe I just add a Heli oil with retaining compound.

 

[LXCam]

Another vote for rivnuts. Oops just noticed your comment about being larger then 1/2”. What size you trying to do?

 

[Gunfixr]

You cannot harden mild steel, it lacks enough carbon.
However, you can case harden mild steel, since you will supply the carbon.
They won't be hard all the way through, but the hard surface will decrease wear.

 

[matt_i]

There are a couple of possibilities.

You can roll-form the threads with a zero-flute tap, it requires a different tap drill size, essentially its a blend of cutting and then smashing the material into place aka work hardening it. Along the lines of how a modern fastener does not have cut-threads as if you made them with a die.

The other possibility is to case-harden the material locally with something like kasenit - kind of a pain though if you have large parts because of the torch action and trying to get the red hot material embedded in the powder.

You could reduce the torque on the fastener, use more fasteners, use smaller diameter fasteners to get more threads in the material (1 diameter deep is preferable in steels with coarse threads). I'm not trying to bash anyone but have worked with people who didn't have enough "feel" to determine how tight fasteners should be torqued without a click wrench, I spent a lot of time behind one particular person repairing pulled out threads.

You could create a tapping plate of some other material - that slides into the tube and is fastened with 2flat head fasteners that straddle the original location. 4140, A2 come to mind.

 

[Doozer75]

You have a design problem.
Not a thread problem or a steel problem.
Find a way to spread out the forces to lower them.

-Doozer

 

[PCustoms]

What thread are you using?

I suspect with something larger then 1/2” and 1/4" wall you are just not getting enough thread engagement for whatever load you are putting on this.

 

[tool_scrounge]

I have a few hikes that I’ve drilled and tapped in 2in square steel tube with ¼ walls. Problem is the fasteners overtime keep pulling the threads out. Any ideas on how to harden the threads. Due to the location it’s not possible to weld a nut on.

What are "hikes"? A photo would help. In similar situations I have used a block of steel (~1.5" cube) that was just slightly smaller than the tube and thread the hole in the correct location in the cube. This gives increased thread engagement. Then the tube just has a thru hole and the block acts as a nut on the inside of the tube. Of course the cube needs to be made from strong enough steel for the application. You can also make the "nut" longer (i.e. rectangular) if needed. But without knowing your use case I cannot say if this will work in your application

 

[Kenstone1]

I have gotten longer thread length in square tubing by using T-nuts.
I cut the prongs off the T-nut, drill a big enough hole in the tubing to insert the T-nut(upside down?), and then tack weld the flange covering the hole.
That way the extra thread length is inside the tube.
*Knowing the thread size you need would be helpful in offering different fixes. (not just "larger than 1/2")

Here's some 1/2x13 SS T-nuts, pricey though, you might find others that are cheaper:

Amazon.com

Are you able to slide a threaded plate into the tube to position the threads?
If so, you could drill a smaller hole (2) either side of the hole where you need the threads, slide the threaded plate into position/inside the tube, and button weld thru the smaller holes to the threaded plate to anchor it in place/position.
.

 

[doublearon98]

We really need to know applications for this. I'd agree you do have a design problem

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[Walkers]

Maybe drill the hole big enough to weld in a piece of heavy wall DOM that could be tapped. You would have threads all the way through.

 

[BillK]

I am also going t ask what in the heck is a "hike" ????? I tried to search for it but could not find anything.

 

[BillK]

Humm… maybe I just add a Heli oil with retaining compound.

Helicoil does not need any type of retaining compound. Depending on what thread size you are looking for a Timesert might work but they might not be available in that short of a length.

 

[PCustoms]

I am also going t ask what in the heck is a "hike" ????? I tried to search for it but could not find anything.

Seems like a typo for "hole"

 

[bwringer]

Flowdrill, then tap.


I get the distinct feeling this ain't cheap. But threaded holes in thin wall tubing are one of the things flowdrills can do.

 

[nadogail]

How about welding in an insert of steel strong enough to thread with the strength you need to solve the problems you have with your hike.
A picture of the hike will help.

 

[claymont]

I have a few hikes that I’ve drilled and tapped in 2in square steel tube with ¼ walls. Problem is the fasteners overtime keep pulling the threads out. Any ideas on how to harden the threads. Due to the location it’s not possible to weld a nut on.

Drill thru and use longer bolts to go to the other side and external nut.

 

[Kenstone1]

Drill thru and use longer bolts to go to the other side and external nut.

Sadly:
The OP has not been back here to answer all the questions about this application, so don't expect him to respond to your post.
It's hard to help someone like this...
just sayin'

 

[nadogail]

If this question is not important enough to the OP to answer the questions asked of the OP, it isn't important to me either.

 

[theoldwizard1]

Flowdrill, then tap.


I get the distinct feeling this ain't cheap. But threaded holes in thin wall tubing are one of the things flowdrills can do.

WOW !

 

[RPH]

These guys are leaders in friction welds. Did some piston welding machines with them.

MTI Friction Welding Solutions & Manufacturing Services

From planning and development to producing parts and building machines, MTI is a Global leader in friction welding dedicated to finding the right solution for you.

www.mtiwelding.com

 

[Innovate1]

Flowdrill, then tap.


I get the distinct feeling this ain't cheap. But threaded holes in thin wall tubing are one of the things flowdrills can do.

If you have a piece of carbide you might be able to make your own. Here's someone who made one and drilled a hole in a file.