Is This Thread Possible ?

I again fall back to my oilfield experience. There is an adjustable bent housing used in directional drilling that relies on the different effective pitches presented by a single lead on one end of the assembly and a double start thread on the other. IIRC, it was either Sperry-Sun or Dresser Downhole that ran that style of housing. That is the subject is for another thread though. There are a number of approaches to solve the problem unique to locking an adjustable bent housing at precise angle.
 
Just so happens I'm working on a threaded assembly design that is what we refer to as a two step thread like the hydril thread above. The larger thread is a 8"OD 4-pitch Stub Acme thread and the smaller thread is a 4" OD 4-pitch thread. Both threads are in timed with each other. And yes, it goes on a down hole oil tool. There are many two step threads used in the oilfield industry. And yes, you can cut them.
 
Ok for the folks in the know. We now know that such a thread does exist, but what are it's advantages? I honestly can't see any apart from making a part that will only mate to another the same.

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atunguyd said:
Ok for the folks in the know. We now know that such a thread does exist, but what are it's advantages? I honestly can't see any apart from making a part that will only mate to another the same.

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As for the Hydril thread, CS, PH-4, and PH-6, they incorporate a three point gas tight metal to metal seal for tubular members used down hole. A two step thread is also a quicker make up when assembled, too.
 
To 'atunguyd" ---- The initial post asked only if it could be done. There was never any mention of using it. All the other threads only stated that yes it could or had been done. This is a case for my third quote below. It reads, "There are those that see things that are and ask - Why? There are others that see things that have not been and ask - Why not?"

"Billy G"
 
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There are many reasons for this type thread, most of which wouldn't be of interest to the hobby machinist. Let's just say that the simplest of them involve OD/ID relationships and strength of the joint. Others involve flow rate and makeup torque.

If you're really bored, there are some white papers on tool joints that you might enjoy.
 
Wreck™Wreck said:
A more useful actual product and an excellent challenge would be making a multiple start thread, how is it done?
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Carefully...
The method needing least tooling is to "walk the spindle", cut the first start to full depth as normal, then mark the spindle, leadscrew and idler gears (chalk or soapstone's traditional), disengage the idler so you can rotate the spindle to the next lead (e.g. 12 teeth round a 48-tooth spindle gear will give the next of a 4-start threading op), reengage the idler (with marks matching on the leadscrew gear) and cut to depth, rinse and repeat.

Otherwise, an indexing plate between chuck and spindle. etc. - more tooling cost, not actually that much faster once you're used to the procedure!
 
Dad used to make tool holders that would hold two inserts that were used to single point both threads at the same time on the Hydril two step threads.
 
You can do multi start threads using the compound. Turn it so it is at zero (parallel) to the X axis. Cut the first thread, then divide the pitch by the number of threads and advance the compound and cut the next. Could also cut between centers, and use the dog on the jaws to do a 3 or 4 start that way.
 
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