Add Resistance to Turning a Threaded Rod 2

[rjoto]

Does anyone have a good way to add resistance to turning to a threaded rod? I’m not sure prevailing torque is the right phrase as I’ve only ever heard it in reference to locknuts but that’s the concept that I’m going for.

Basically I have a 1 1/4-5 threaded rod with a nut on the end that goes through a plate. The purpose of the rod is for clamping (kind of like a c-clamp), but it’s used in a tight space that is also hot (400-500F). We have operators pick up the parts with the clamp, put it in, but then they have to reach in there and undo the threaded rod with their hands. I’d like to use a ratcheting box end wrench to help with the putting hands in hot places and access issues, but the problem I’m running into is that once the clamp is loosened, there’s not enough resistance in the threaded rod to overcome the ratcheting action of the wrench so that the clamp can be loosened enough to clear the part coming out. Usually when I have this problem with other things, I just grab the threads or the socket to hold them in place on the back stroke, but I can’t do that here.

Certainly I’m not the only one who’s ever had a problem like this. I’ve thought about using nylon like the inserts in locknuts, but the stuff I’ve looked at is only rated up to about 250F. I’ve tried wrapping wire around the threaded rod, which adds resistance like I want, but it doesn’t engage until after about a quarter turn – much more than what I have to work with.

Any thoughts?

 

[SnTMan]

Self locking nuts are available in all metal varieties. Upset (deform) the female threads?

http://www.mcmaster.com/#hex-locknuts/=row8by,

for example.

Regards,

Mike

 

[1gibson]

If I understand the problem correctly, these twist on quick threading nuts might help:

http://www.mcmaster.com/#slotted-nuts/=rowi4n

Never used them myself but they look interesting. Don't seem to be available there in your thread size.

It could get messy, and at first glance it seems a little backwards, but putting antiseize on the rod might give you enough resistance to allow the ratcheting action. Worth a shot if you don't mind the mess.


You also need to consider that the max temp for those nylon locknuts is for reliable reusability. Some nylons have melting temps above 500*F. Test it in a small oven first, but if they don't turn to a liquid and drip, and you don't mind replacing them after a few cycles, it might work just fine. Give it a shot while you wait for more responses.

 

[Jboggs]

You could give the guys a pneumatic wrench that continually turns in one direction.

Or replace the wrench handle with a crank handle that has room to rotate 360 degrees.

Or put some sort of external ratcheting pawl on the screw to keep it from back spinning.

 

[racookpe1978]

No.

From your sketch, the threaded rod is "loose" at the point where the rod screws through the vertical plate which on the left side of the load.

The "nut" is actually working as the driver of the rod - it could actually be a bolt with your attachment (the operator) turning the head of the bolt to force the tip of the bolt against the load.

If you very slightly bend the threaded rod into an arc it will bind naturally against the thread tapped into the vertical plate that is acting as your C-clamp.

 

[MintJulep]

Put a coil compression spring over the rod between the head and the clamp.

 

[rjoto]

Thanks everyone for your input.

Part of the problem is that the thread is 1 1/4-5 which is not a UNC thread. It might be Acme because Acme threads come in that size but I don't have an Acme thread gauge to check. Even if it is, I haven't been able to find Acme locknuts anywhere, much less all metal Acme locknuts, probably because most people needing locknuts won't usually be dealing with Acme thread.

I'm trying to avoid deforming the threads or the rod at all because this is something that gets used daily and if it gets screwed up (no pun intended), I'm in trouble.

I like the ratcheting pawl idea, but I can't think of any way to configure it so it locks effectively and so the threaded rod can still move in and out when the pawl is disengaged.

MintJulep, that sounds like exactly what I need: simple, easy, clean, cheap, and if I need to adjust it or try a different spring, the original clamp is easy to go back to. I'll try that out and let you know how it goes.

 

[jte]

Instead of a socket and ratchet, do you have room for a socket - U-joint - speed wrench with the U-joint at not quite 90 deg, maybe 70 deg? If you need the torque a ratchet can provide for initial loosening, you could do that first, then switch to the speed wrench.

 

[tygerdawg]

Perhaps you could use an "in-line ratchet" or "open-end ratchet" as in these pics from

Aimco

http://www.aimco-solutions.com/nutrunner_types.asp

This is from

http://www.titanoftexas.com

and probably not appropriate for your use (hydraulic), but the idea of the tool is the same. With enough searching, you could find what you need I'm sure.

Better yet, describe in more detail what it is you are trying to move. There are all kinds of passive clamping devices attachable to chain lifts out on the market.

TygerDawg
Blue Technik LLC
Virtuoso Robotics Engineering

http://www.bluetechnik.com

 

[tbuelna]

MintJulep's approach seems like the easiest. Putting a compression spring between the nut and clamp face, with some thrust washers at each end of the spring, would provide all the prevailing torque you need at the threads to resist the ratcheting force of the tool.

 

[dhengr]

Take a relatively soft/low strength nut, and cut it in half along the length of the rod, that is across the threads. Put these two halves onto the jaws of a vice gripe wrench, or some such. And, adjustably clamp these nut halves onto the rod, to hold it.