Yeah, I made a new cross slide nut and screw for my lathe a few months ago and still have some Acme threaded stock from that on hand. It’s not a match.
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Is This an Acme Thread or Something Else?
- Thread starter David2011
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After a lot of texts back and forth between the Battleship Texas guy that asked me to make this I learned a lot. He said that a standard 1” x 8 tpi bolt fits the coupling that this shaft screws into. He also said that he can’t see why it needs to be 0.948” instead of 1”. It’s a connection shaft that operates the elevation computer (a mechanical gearbox computer) on a 5”/51 caliber gun. The computers were added in the 1925 refit. They tie into the main fire control system and show the operators the elevation and training (azimuth) with pointers on dials. The gunners move the gun to make a second set of pointers match those from the fire control computer.
One thing that has stood out in working on the deck guns is how standardized the dimensions are. The engineers back in 1910 when the plans were drawn used regular numbers that you find on a ruler, in 1/16” increments. This is the first part I’ve worked with that wasn’t an off-the-shelf dimension. It makes me wonder if it’s a replacement that was made from larger stock on the ship. Another similar shaft has an OD of 0.951”. That came to light in the last few minutes.
Bottom line is that the shaft will be made from 1” stock, threaded to standard Imperial threads and left at 1”.
One thing that has stood out in working on the deck guns is how standardized the dimensions are. The engineers back in 1910 when the plans were drawn used regular numbers that you find on a ruler, in 1/16” increments. This is the first part I’ve worked with that wasn’t an off-the-shelf dimension. It makes me wonder if it’s a replacement that was made from larger stock on the ship. Another similar shaft has an OD of 0.951”. That came to light in the last few minutes.
Bottom line is that the shaft will be made from 1” stock, threaded to standard Imperial threads and left at 1”.
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There are standard stub Acme and stub V threads. Check them out.
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You are making parts for the defense department?
Man, that's cool. I always thought you were a bad dude!!
Bad in a good way
Thanks but the Battleship Texas is a museum ship now, owned by the State of Texas. She became a museum ship in 1948. I'm one of many volunteers helping the staff that's restoring the deck guns and other pieces of the ship while she's in the shipyard for the major repairs. She is the official flagship of the Texas Navy. Yes, there really is a Texas Navy. All appointments are by the Governor at the rank of Admiral.You are making parts for the defense department?
Man, that's cool. I always thought you were a bad dude!!
Bad in a good way
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Somewhere in my files i have a detailed picture of all the treads. It is not a Buttress. Buttress is somewhat one sided thread. approximately 45 degrees on one side and approximately straight on the other side. Take my word for it you don't want to price a tool or a die for a Buttress thread.. If my memory serves me right Buttress threads were used for clamping. I have an old Atlas Clausing power hack saw that has a Buttress thread for the vice. The nut was originally in 2 pieces, and I only have the bottom piece so I may just make a new screw and nut for the vice when I get around to restoring it.
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I think it’s supposed to be that way, makes it a cheap quick release!
I think you should match that thread up with a standard fish tail gauge.
I've seen "similar" on threadded assemblies where there is a "normal" thread (usually a large one), where the "top" of the threads are missing, like a very, very heavily truncated thread. Forcing screws, or connections on parts (not fasteners) were meant to be repeatedly assembled and disassembled. The "missing" top of the thread makes them very robust as far as not getting damaged or sticky with frequent use and abuse.
I've never heard of it (and never looked for it), but it would not surprise me even a little bit if there was a standard for such a thread as Illinoyance mentioned.
What is the diameter of the part "above" the threaded area?
If you put a fish tail gauge (or a threading tool) into the thread, if you were to approximate just how much of the top of a standard thread might be missing, does that equate with the 0.050" (or slightly less) that's missing from a standard 1 inch thread?
Do you have a way to quantify the "light gap" in the thread gauge? I find that on stuff that old, it's NOT uncommon to find some "slight" thread pitch discrepancies. "Hard" steel wasn't so much a thing, soft threads have a lot more give, so the precision we're used to today just wasn't necessary to get "full strength" out of screw threads.
I'm clearly speculating a bit based on what I've seen (not spec's), but I'm very curious now, as I've seen (I believe I've seen anyhow) similar threads, but never gave it another thought, since that's how they came.
I've seen "similar" on threadded assemblies where there is a "normal" thread (usually a large one), where the "top" of the threads are missing, like a very, very heavily truncated thread. Forcing screws, or connections on parts (not fasteners) were meant to be repeatedly assembled and disassembled. The "missing" top of the thread makes them very robust as far as not getting damaged or sticky with frequent use and abuse.
I've never heard of it (and never looked for it), but it would not surprise me even a little bit if there was a standard for such a thread as Illinoyance mentioned.
What is the diameter of the part "above" the threaded area?
If you put a fish tail gauge (or a threading tool) into the thread, if you were to approximate just how much of the top of a standard thread might be missing, does that equate with the 0.050" (or slightly less) that's missing from a standard 1 inch thread?
Do you have a way to quantify the "light gap" in the thread gauge? I find that on stuff that old, it's NOT uncommon to find some "slight" thread pitch discrepancies. "Hard" steel wasn't so much a thing, soft threads have a lot more give, so the precision we're used to today just wasn't necessary to get "full strength" out of screw threads.
I'm clearly speculating a bit based on what I've seen (not spec's), but I'm very curious now, as I've seen (I believe I've seen anyhow) similar threads, but never gave it another thought, since that's how they came.
The shaft and the major diameter of the threads is .948" on this one; another example measures .951. This is not a piece that would be disassembled frequently. Details are above in the first paragraph of post #12.
As with many things on a battleship, these shafts do not need to be ~1" in diameter to do their job. The computers that they operate would function on less than 10 ounce inches of torque. The shafts have to be durable against outside forces like something being slammed into them in rough seas and the turning resistance imposed by watertight seals.
You may be underestimating the precision of machining from the early 1900s. After working on the Battleship Texas for almost 3 years I have been very impressed at the fit and finish of the parts. The insides of the gearboxes and the mechanical computers on the guns look and fit line anything made with modern CNC machinery. Manual production lathes have not changed significantly since the late 1800s in function or precision. The computers look like fine clockworks inside.
The missing thread is indeed what would be missing from a normal 1" thread. I don't have an accurate way to measure the light gap but the eyeball says it's .001"-.002". On my 27" monitor the shaft is almost 6" wide. I think the most significant feedback I got back from the Battleship Texas employee is that an off-the-shelf 1" x 8 TPI UNC bolt will screw into the coupling "perfectly."
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