Geometric Self Opening Die Heads

I've looked at them in the past but haven't had a job where I could justify getting one as mainly doing low volume stuff so just used split dies although I did make a double ended die holder with a die for roughing and the other end set for a finish cut for one job threading stainless tube. On this side of the pond they're called Coventry die heads and the heads and chasers are quite common on ebay. If you have a surface grinder my understanding is the chasers can be resharpened a few times if they become worn.

Geometric Self Opening Die Heads ... I am sure if I look around I can find a used version of this tool for less than a brand new one, but I need to ask. Have you used a tool like this. The self opening die head, not a turret lathe. I am sure lots of you have used a turret lathe. How easy was it to setup for each job? How affordable where the thread jaws? Did you find it worked reliably? Do you have nay other feedback for using one or reasons not to? Bob La Londe

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Great manual. Thanks.

Ah... the cost of the "chasers" is really what I was wondering about. Thanks. I probably wouldn't buy a new die head at this point, but it would be nice to have a couple sets of dies "chasers" if I decide its worth the trouble to integrate into a process.

It looks like they are just referenced by slot size. I wonder how interchangeable they are.

Ah... the cost of the "chasers" is really what I was wondering about. Thanks. I probably wouldn't buy a new die head at this point, but it would be nice to have a couple sets of dies "chasers" if I decide its worth the trouble to integrate into a process.

It looks like they are just referenced by slot size. I wonder how interchangeable they are.

-- Bob La Londe

---------------------------------- "Chasers" were originally hand-held chisels with multiple teeth filed into the end, used to clean up initially filed or hand guided single point threads cut on lathes that had chisel tool rests like a modern wood lathe.

I have an antique die stock that pressure forms male threads between V grooves in a floating row of die blocks with straight thread profiles on the walls, no cutting edges. The thread forms could have been cut into the die blocks by a shaper or planer. The sizes appear to be 18, 16 and 14TPI.

Looking at older ways to form screw threads shows why we had advanced little beyond the Romans until the thread cutting lathe became available around

Looks like I may have been wrong. They appear to be referenced by maximum thread size.

Looks like I may have been wrong. They appear to be referenced by maximum thread size. Bob La Londe

--------------------------------- Turret lathe tooling is beyond my experience. I have enough trouble picking up a thread to extend it, perhaps from the wear and play uncertainty of my old lathe. I have six 3/8" x 5" Grade 8 bolts to modify with another 1/2" of thread, because the store doesn't stock the 4-1/2" long bolts that would fit better. The supplier was there taking inventory when I looked and we discussed which area stores had more room for larger selections, but I had recently checked one of the best and not found 4-1/2" Grade 8 there either. At least threading is indoor work, out of the East Coast "heat bubble" of tropical humidity.

I'm upgrading my hoisting equipment for the 4500 Lb log in queue for the sawmill. Weighing it at both ends (2570+1930) damaged the tripod baseplates and pushed the rest close to its rated limits, so I bought G100 overhead lifting rated chain and fittings to upgrade. Apparently the difference between G80 or G100 alloy and G70 transport chain is better shock overload capacity, carbon steel chain may be more brittle. I've seen (from a safe distance) falling logs break equipment.

The new tripod baseplates are 14 gauge CRS steel remnants hammered into shallow bowls over a depression in wood, with their corners turned down and a flanged hole in the middle that serves as a socket for the ball or acorn lower end caps on the tripod legs. They dig in at the flange rim and corners without seriously damaging the lawn and 14ga was probably the thickest steel I could hammer to shape neatly on the wooden 'stump' and my anvil. The bowl shape stiffens them and causes them to sink straight into soft soil instead of twisting.

Yeah, at a little over 2 bucks a piece for the cheapest ones in the right size I'd modify hardware store bolts too.

Yeah, at a little over 2 bucks a piece for the cheapest ones in the right size I'd modify hardware store bolts too.

-------------------------------- I gave the approximate length for simplicity, actually they are threaded just far enough to keep all shear loading on the full diameter shank with only enough axial clearance to minimize cantilever loading and avoid binding when the locking flange nut is snugged. I may have to leave more shank to fit the stronger chain. The Grade 2 4-1/2" bolts didn't have quite enough shank length and one showed thread damage when removed.

This is more fussing than I would design into a commercial product unless higher performance justified it. I've been the tech doing that custom adjusting, like cutting coax cables to length to match the propagation delays, the timing error tolerance was equivalent to around 1/16". They were for a machine that tested computer memory chips for speed and errors before they were cut from the wafer.

At the start of WW2 when we took on the manufacture of foreign designs, the Merlin engine and Bofors AA gun, we found that hand fitting was still common in Europe.

Another groups take on the subject:

Another groups take on the subject:

-------------------------------- "For that matter, at one time, not so very long ago, in terms of history, NOBODY had made such good threads. But somehow, those poor crawling and ignorant cretins (who would not be allowed by the forum police here to even discuss the matter), managed to make very accurate threads, despite the fact that they had no prior experience making them, and had never even seen such an accurate thread until they made one. And they made good micrometers that had those threads. I will guarantee that none of them used dies or dies heads to make those threads. More precise methods were needed."

Holtzapffel described the early crude and precision threading methods in detail. It turned out that an angled knife blade carving a spiral on a rotating rod was about as good a method as any other. The simple way was to tin a brass rod and wind a clean brass and black iron wire side by side around it, press then together and dip in solder, that wouldn't stick to the black iron which was unwound afterwards, leaving the brass wire spiral.