Best Thread for Collar

[Pattnmaker]

I am designing a new fixture for my shop that may become a product. I will have a collar that has to thread onto a flange. The threads will be threaded on and off hundreds or even thousands of times. I would like to make the fixture out of aluminum, I am thinking 6061 hard anodized? I would like the thread to start easily as the collar will be in an awkward position to tighten and the thread will often be started with a wrench. Gravity will hold things together while the threads are tightened so they don't need a lot of pull. I am thinking a multi start thread might be a good way to go as I won't need as much of a turn to start the thread, I don't want a lot of turns to tighten the collar.

What sort of thread would be good for this application?

 

[WizardOfBoz]

wrenching threads on and off several thousand times, using aluminum, is (for me at least) a non-starter. If you are threading aluminum into aluminum, IT IS ABSOLUTELY SURE TO GALL.

Dissimilar metals, or hardened non-stainless tool steel. That hard anodizing will be worn through the first over-enthusiastic wrench tightening. IMHO.

 

[DDoug]

Hmmm

The oil well people have many tapered threads that almost fall
all the way on, 1 or 2 turns to full lock up.

 

[Pattnmaker]

Forgot the to attach the drawing

wrenching threads on and off several thousand times, using aluminum, is (for me at least) a non-starter. If you are threading aluminum into aluminum, IT IS ABSOLUTELY SURE TO GALL.

Dissimilar metals, or hardened non-stainless tool steel. That hard anodizing will be worn through the first over-enthusiastic wrench tightening. IMHO.

I am not dead set on aluminum for all the parts. But I would like the top piece to be aluminum and would prefer the collar be something somewhat softer than steel. The collar could be bronze or possibly steel. I am thinking more a couple thousand times not several thousand.

 

[DDoug]

The fire company here in Erie Pa, have their own thread designation
(and all the surrounding volunteer fire companies carry adapters)

Higbee'd et all for fast spin on

"Erie eight" is the designation.

 

[4GSR]

The oilfield also uses lots of Acme and Stub Acme threads with 2G fits. For make up and break out repeated times over and over you can't beat them!

 

[johnoder]

The important feature

Higbee'd et all for fast spin on

Note in thumbnail Lodge & Shipley even higbeed their spindle noses 108 years back

 

[Bondo]

You say several thousand times. Is that over the course of a year or 30 years? Is this an item that experienced techs will work on or a job to be done by the newest person?

In adjusters I like using acme threads as they hold up very well and last. I have built an easy thousand adjusters and never had 1 fail. I use 5/8 x 8 mostly and it is impossible to cross thread.

As said, alum whatever coating will fail and gall.



Sent from my 2PS64 using Tapatalk

 

[plastikdreams]

7075 is going to stand up much better than 6061

 

[tnmgcarbide]

how do you intend to machine these mating threads? . i assume in a cnc lathe?

or thread milled in a vmc? i looks to be a small assembly, so not much room
for honkin' acme threads or whatever . are the threads doing the alignment, or is
there a boss of some kind to keep things square ? finer than coarser threads
might be best, but i don't know.

as been said here - if it has to be soft - mild steel will last more on/off
cycles than aluminum/aluminum, which wants to share atoms with whatever it touches.

 

[MrWhoopee]

Be nice, make the part that is easily replaced (the nut?) softer than the shaft. Bronze nut on steel shaft, for instance. Coarse threads are harder to cross-thread. Acme is a good choice for something like this. A short pilot on the end of the shaft just under the minor diameter of the thread will ease awkward assembly.

 

[EPAIII]

Definitely not all aluminum. I think aluminum and steel would be good. Perhaps a leaded alloy for the steel as that would be easier to machine.

I think you need a coarse thread, as in a thread with a large cross section. A fine thread would easily become buggered up, especially on the aluminum part. This would dictate against a multi start thread as the cross section of the thread will be divided by the number of starts. That is, a two start thread will have only half the the thread height of a one start one and more so for three or four starts.

As to what that cross section is, I think perhaps that an acme form may be the most durable. The small crest of a Vee thread will more easily get buggered up on the aluminum part. Other forms will be harder to cut and you say that a lot of strength is not needed. Try to find a way to ramp/taper the start of the thread on both the internal and external threads to make it easier to start.

 

[DDoug]

And Higbee the start of the thread.....

 

[Bill D]

Bayonet fitting of some type. Why threads?
Bil lD

 

[Pattnmaker]

Thanks for all the responses. I am open to other fastening methods but the the idea is actually to hold the 2 parts together while allowing for some misalignment. This is why it is a collar around a smaller pad sitting on a larger threaded pad. I was not aware of Higbeeing threads but it makes sense for avoiding cross threading. The usage would be threading on once per day to 3-4 times per day tops. If they wear out after a couple of thousand times they will hopefully paid for themselves.

I don't have a CNC lathe and while I have done a fair bit of 3D milling in aluminum on my CNC router, I think subbing this out makes the most sense at this point.

 

[NAST555]

I do loads of work for the drilling industry... They use a square thread with loads of clearance between them so that if it gets dirty you can still fasten it up. It locks on the face of the parts once all the way in, sometimes on a bit of a taper chamfer and sometimes just on the flat face.

The ID thread is under cut the first thread and the OD thread is cut back the same so that they virtually fall into each other and then you turn to engage the threads. Pitch varies but the most common is 8TPI and roughly 2mm depth per side on the OD thread. It is not actually a "true" square thread.

I agree with the others though, rather don't go aluminium on both.

 

[M.B. Naegle]

My 2 cents: Don't try to make it indestructible. You'll end up with a lot of disappointed users. Make it easy to service and it will "last" much longer.

 

[Mtndew]

Another vote for an acme thread.

 

[Illinoyance]

Why no make it from 1144, It is easy to machine. It can be hardened, if necessary. I am another advocate of Acme threads. A Hibbee start is desirable but not essential. Coarse threads will assemble & disassemble faster than fine. Coarse threads are more likely to vibrate loose.

 

[dgfoster]

OK, one more thread style to throw into the breech so to speak. An interrupted thread like that used on artillery pieces to close the barrel fulfills your criteria for easy fool-proof assembly, excellent strength, durability when expected to be opened and closed a large number of times, and has a proven track record.

Interrupted screw - Wikipedia

Depending on the end use of the fixture, the collar could be cinched up with a pin spanned, stout ears to be hammered, or two, four,or six flats.

Obviously aluminum of whatever alloy or surface treatment would not be a good choice. I'd be thinking along the lines of 4140 PH due to its ease of machining, durability, low cost, and again proven track record.

Denis