Need help with TX200 piston latch rod thread size.

Need help with TX200 piston latch rod thread size.

Joined: July 24th, 2010, 1:44 am

March 27th, 2012, 10:16 pm #1

The latch rod of a TX200 piston unscrewed from the piston with a bit of applied heat to soften the thread locker and I'm in the process of creating a long TX piston rod so UK spec velocities can be achieved without a "weak spring" or clipping coils.

I am a bit puzzled by the latch rod thread size. The latch rod diameter measures 9.92mm (I'm assuming 10mm nominal), and the thread pitch is 1.5mm.

Now the puzzling part, the latch rod will freely thread into the piston after cleaning off the thread locker, however my 10x1.5mm tap won't freely screw into the piston and the latch rod won't freely screw into a 10x1.5mm die.

What am I missing, will I have to single point cut the thread on my lathe?

Any advice to this North Carolina "wanna be" springer butcher is greatly appreciated.
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Joined: August 20th, 2006, 5:36 am

March 28th, 2012, 4:04 am #2

But are you SURE it's a metric thread, Ed? A metric 10x1.5 is really close to a 3/8"-16. Just a thought. Later.

Dave
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Joined: July 24th, 2010, 1:44 am

March 28th, 2012, 6:50 am #3

fits the latch rod thread perfectly and not a 3/8"-16 thread. A 3/8"-16 bolt will screw into the piston but binds before getting 1/2" deep.

Actually, I think that the thread AA uses for the latch rod is a "close class fit" which is why it won't thread into my 10x1.5mm die.

A fellow on one of the UK forums suggested that I split one side of my 10mm die so it will cut a slightly larger diameter thread.

Oh well, perhaps it's time to learn single point threading! Hummm....I'm wondering how hard is it to grind a bit to cut a thread?
Last edited by nced1 on March 28th, 2012, 6:50 am, edited 1 time in total.
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Joined: July 24th, 2010, 1:44 am

March 28th, 2012, 8:28 am #4

But are you SURE it's a metric thread, Ed? A metric 10x1.5 is really close to a 3/8"-16. Just a thought. Later.

Dave
A UK forum post confirmed that the thread is indeed 10x1.5mm nt
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Joined: August 20th, 2006, 5:36 am

March 28th, 2012, 3:56 pm #5

fits the latch rod thread perfectly and not a 3/8"-16 thread. A 3/8"-16 bolt will screw into the piston but binds before getting 1/2" deep.

Actually, I think that the thread AA uses for the latch rod is a "close class fit" which is why it won't thread into my 10x1.5mm die.

A fellow on one of the UK forums suggested that I split one side of my 10mm die so it will cut a slightly larger diameter thread.

Oh well, perhaps it's time to learn single point threading! Hummm....I'm wondering how hard is it to grind a bit to cut a thread?
I have some extra threading tools, maybe I have something you can use. Later.

Dave
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Joined: July 24th, 2010, 1:44 am

March 28th, 2012, 5:19 pm #6

if you have a good used American (or equivalent) split die that you could sell cheap, I would be interested.

I learned last year that the new cheap Chinese stuff I have isn't nearly as good as the better quality American stuff. I'm supplementing my Social IN-Security income with whatever odd jobs I can get and last year I got a machining project that included drilling and tapping both ends of 6 stainless Steel rods with a 1/2"-20 fine thread.

Well......I got out my "trusty" new TIN tap that I bought at Lowes and immediately learned that the tap wouldn't cut the SST, it simply "work hardened" the drilled hole, even though I was only cutting 60% thread. I ended up going to an AllMetal outlet and buying a GOOD tap that cost a LOT more than the Lowes tap. Since the industrial taps were pretty pricey I only bought the cheaper plain HHS tap.

Long story short......the 1/2"-20 tap from AllMetal tapped the SST like butter (well, almost LOL) and I could even use my LatheMaster bench top lathe to tap the holes with the tap in the tail stock. I did check online for a good split 10x1.5mm die and learned that they were priced from $40 to $60 plus shipping, so I opted to "make do" with my existing Chinese die.
Last edited by nced1 on March 28th, 2012, 5:57 pm, edited 1 time in total.
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Joined: July 24th, 2010, 1:44 am

March 28th, 2012, 5:43 pm #7

The latch rod of a TX200 piston unscrewed from the piston with a bit of applied heat to soften the thread locker and I'm in the process of creating a long TX piston rod so UK spec velocities can be achieved without a "weak spring" or clipping coils.

I am a bit puzzled by the latch rod thread size. The latch rod diameter measures 9.92mm (I'm assuming 10mm nominal), and the thread pitch is 1.5mm.

Now the puzzling part, the latch rod will freely thread into the piston after cleaning off the thread locker, however my 10x1.5mm tap won't freely screw into the piston and the latch rod won't freely screw into a 10x1.5mm die.

What am I missing, will I have to single point cut the thread on my lathe?

Any advice to this North Carolina "wanna be" springer butcher is greatly appreciated.
First, a pic...........

Obviously, the top rod is the factory latch rod thread and the bottom is the thread that I cut using my 10x1.5mm die. As expected the thread class of my thread wasn't as close fitting as the factory TX thread, however it screwed into the piston just fine. I did an extra step that isn't on the TX piston....I cut a thread relief in the rod to create a square edge for the latch rod to "bottom out" on in the piston head. The TX piston has a closer thread fit, however there isn't and thread relief cut for run-out.

Well, I screwed my homemade latch rod blank (just a "dry run" mock up) into the piston, then spun the piston in my lathe to get a handle on the run-out. Yep, there was a bit of run-out as expected with the looser thread, but certainly within the realm of "tweaking straight". Next I screwed the factory TX latch rod into the piston and did the same "spin test". LOL.....even with the closer thread fit the TX latch rod run-out was double what I got with the die cut thread. Actually, that was kinda surprising!!

Well......on to working the uncompleted "catchey end" and currently grinding a couple bits to match the corner radius of the "catch".
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Joined: August 20th, 2006, 5:36 am

March 28th, 2012, 6:17 pm #8

But I still think you should have single pointed it, just for the practice, of course . Are you going to heat treat the O1, or just leave it as machined? And if so, what's your process? I have some O1 on hand I'm using for various parts, it machines pretty nicely. But I haven't tried hardening/heat treating any of it yet.

Re: split dies, sorry, no such luck. I have a Sears Craftsman tap and die set I bought about 30 years ago, I've only lost/broken a couple of taps over the years. Not the best, but it's done what I've needed it to do for a very long time, and it's standard and metric through 1/2"/12mm, so it covers a lot of ground. Later.

Dave
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Joined: July 24th, 2010, 1:44 am

March 28th, 2012, 6:51 pm #9

I used to make and found it to work well. Matter of fact, to test if the hardening/tempering were "up to snuff" I used to tin the rod end that got POUNDED into the "press fit" hole in the steel head with silver bearing solder, and I used a steel hammer to pound directly on the hardened "latch end" (I only hardened the "latch end"). If the pounded "latch" didn't break of get marked by the steel hammer I considered it good. After the latch rod was pounded in place I heated the piston head/latch rod with a propane torch to fuse the tinned rod end and tinned piston head press fit.

Anywhoo......right or wrong here is what I always do.......heat the latch rod catch to a cherry red color, then immediately quench it by swirling it around in oil (don't just let it sit in one spot) holding it with pliers or a ViceGrip. Then I would spin the hardened latch rod end in my lathe and polish it with fine emery cloth (cover the lathe bed so it doesn't get "gritty"). Then temper the hardened end by reheating till the metal it turns a dark" straw" color, however I'm guessing that any color from "dark straw" to "purple" would work. As soon as the rod turns "dark straw" I quench it by swirling in water.

Here is a link that shows the proper way to harden and temper O1 tool steel...........
http://threeplanes.net/toolsteel.html

In the beginning I used W1 tool steel (water hardening), however I would get stress cracking at the "corner" of the catch when making R9 pistons after quenching (I probably did it wrong), however I haven't had any problems with any of my R9 pistons. Here's a pic of one of my home made R9 pistons when I was playing with oring sealed molly filled piston caps............



LOL.....the last NEW R9 piston I bought only cost about $45 and came with a brand new piston seal and piston liner so it didn't make sense for me to "roll my own" any more. I bought the piston here..........http://www.specialtyshootingsportsoutdo ... t_554.html
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Joined: July 24th, 2010, 1:44 am

March 28th, 2012, 7:06 pm #10

But I still think you should have single pointed it, just for the practice, of course . Are you going to heat treat the O1, or just leave it as machined? And if so, what's your process? I have some O1 on hand I'm using for various parts, it machines pretty nicely. But I haven't tried hardening/heat treating any of it yet.

Re: split dies, sorry, no such luck. I have a Sears Craftsman tap and die set I bought about 30 years ago, I've only lost/broken a couple of taps over the years. Not the best, but it's done what I've needed it to do for a very long time, and it's standard and metric through 1/2"/12mm, so it covers a lot of ground. Later.

Dave
showed that a Chinese die with a thread relief would give me less runout than the factory latch rod.

The issue for me and my belt driven/gear changin' bench top lathe was to first determine what change gears to install, installing the gears, then grinding the 60 degree bit, then etc. Then after I did all that I'd have to reinstall the original gears to return the lead screw to "normal" rotation to turn the "catchey end". LOL
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