~1.250 - 1.500 screw thread connection with low breakout

[Mattm86]

Hi,

Im designing a system for drilling using ~1.750" OD Drill rods.

Im looking for a connection that is very strong for tension and compression, and also torque, but is relatively easy to make and break.

Has anyone experience using ETA threads, multi start stub acme threads or similar?

Regards

 

[hydtools]

What kind of drilling do you want to do? Metal, hard rock, soil core?
What research have you done in regards to drill rod threads?

Ted

 

[Mattm86]

Drilling through metal.

We have looked a few, such as AMMT etc which we do use on certain parts, but its difficult without testing them all to know what would suit as Im unfamiliar with mining or boring type connections.

Currently Im investigating ETA and also a multi start acme thread connection I have designed, but Im looking for some guidance into weather or not a multi start will reduce the breakout torque required (which I believe it will) and also if there are existing tapered threads that would be also useful as they are stronger for a given wall section (I would like to have a thru bore option)/

 

[pylfrm]

Mattm86,

What are ETA threads? Do they have anything to do with BTA (Boring and Trepanning Association) threads?

The number of starts is not directly relevant, but more starts usually go along with a larger lead angle. The lead angle and various other angles are extremely relevant.


pylfrm

 

[Mattm86]

From what I can see, ETA threads are generally used in the borehole industry, we have used a company called drillwell to supply 2 rods for testing, but Im struggling to find any technical info on them, and drillwell either don't have the technical details, or I think are unwilling to share too much. My go-to machine shop have never heard of it.

With regards to your point about the lead-angle, I was generalising somewhat regarding multi-starts as I thought it was perhaps inferred that the increase in lead-angle was part of this, but I understand your point.

I guess the increased lead angle will reduce the break-out torque once shouldering out. But Im just looking for some other input/advice. e.g. what about a multi-start tapered thread (I actually 3D printed one I designed and it seemed to work reasonably well). what about rope threads, Ive recently come across this:

https://www.youtube.com/watch?v=RFXO9a-XfCE

Thanks

 

[hydtools]

Rope thread depends upon shoulders, square and/or tapered, to carry thrust loads. They are free running when making or breaking a joint. Tolerant of muck in mining or construction conditions.
Have you looked at trapezoidal threads? Strong, tend to centralize the components.

Ted

 

[Mattm86]

Thanks.

I have looked as some trapezoidal threads.but not in depth. I will see what i can find.