GTA
All Springer/NP/PCP Air Gun Discussion General => "Bob and Lloyds Workshop" => Topic started by: BigBird on July 26, 2021, 02:34:31 AM
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I've been thinking about threading a tube for a fill plug using a tap and die for a while now and I found a way that I can do it straight. I cant fit the tube on my lathe due to length and girth. I have a tube that I am using for practice. It is 1" x .083 DOM and the tap is a 7/8 x 24. The 1018 plug I made (on the lathe using a properly alligned die) works well and I am testing the oring with liquid (gravity) now. I don't have a valve pinned yet to do a hydraulic test but that is next. I will measure length, width, girth, evaluaate theads and fitment, etc.
With the assumptions that everything is straight, and there is proper thread engagement (say 70%) I have a couple questions. I have about 17 threads. I don't have a thread calculator (or a subscription to one). I wanted to have enough threads so I dont rely on the end of the tube as about 1/8" was gouged a little in starting the tap.
How many threads are needed for an inboard oring? I calculated the outboard oring and think that is feasible as long as everything is threaded properly but will go with an inboard o ring. I know there is additional tube prep for outboard rings too.
Should the oring groove be far away from the threads or can I relocate it nearer? The crosman fill ends have the oring further away and also just a few threads.
Other info, I do have other materials but this 1018 was 7/8 and quick to mock up. The tube ID is about .830-.832 and taping creates threads that extend down more. Some reaming with the plug had to be done to fold thread tips. There may be a better way to do this. Obviously If I had a bigger lathe it would help. I only say this because I do know this.
I am not sure I want to use this method on an airgun but I will use it on this "dummy" tube. It seems to be working.. Threads on 1018 usually come out rough. So pleased with that.
Thanks!
(https://www.gatewaytoairguns.org/GTA/MGalleryItem.php?id=8032)
End
(https://www.gatewaytoairguns.org/GTA/MGalleryItem.php?id=8033)
Tube
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Looks like plenty of thread, to be safe the id of the tube can be used as the length of the thread engagement.
You can put the O ring right after the threads, as close you can get it to seal without leaking.
I have used 15mm of thread on 24mm id tube and it held 850bar no problem. Pitch was 1.25mm
Marko
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Thanks Marko.
Dang. Thats some pressure. I always get bubbles in my hand ram and struggle for 7500 psi. Urethate orings?
Well I'm going to be doing some more testing. There were no leaks on the paper under the tube but its not as straight as I thought. The long plug helped indicate that. I've got more tweaks to implement to get the tap straight and more tube that I can practice with. No "fuzzy feeling" and I will pin the tube. I can always thread the rear end of the tube. ++
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Pump uses some bespoke seals, and all the o rings are viton.
You need to make some sort of tap guide that slides over the tube and other end that guides the tap true from the shank.
Should not be too difficult to make since I recall you have a lathe?
Marko
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Ok. I do have a lathe but not a big enough spindle bore. So I am trying to tap a tube without that important function. Basically getting a tube with the proper ID=minor diameter is key cause I can't bore out a tube to that diameter on the lathe.
I messed around with this tap trying to get it to thread backwards and sharpening it and it didnt work.
I lost all hope and threw some things around in my little shop and ordered another tap on ebay. Then I decided to go for broke and reprofile the whole tap so into an extended plug tap that has the proper diameter "guide" on front. Seems to be cutting now. I made 3 threads and had to do something else. I have to test this to see if it really guides it straight. I have the breech end of this "test tube" that I am working on now.
Had to make a makshift tool post grinder to hold my $25 chinese dremel to reprofile the front end to ID. Once I figured out the proper angle I used a $10 HF angle grinder/holder and custom tap positioner to cut the "spiral" tap.
(https://www.gatewaytoairguns.org/GTA/MGalleryItem.php?id=8045)
Yeah it looks rough but I was cutting teeth here (literally and figuratively).
(https://www.gatewaytoairguns.org/GTA/MGalleryItem.php?id=8046)
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makes perfect sense. I cut almost all external threads with dies.. No time for manual threading .. I use a 4 inch chuck in the tailstock to act as a die holder.. Just machined a knub for the backplate , so my keyless chuck can hold it . you know if you annealed the front of the tap , threw it in the lathe and made your guide recess with a carbide bit , you could reharden the backend for tapping.. I saw a brillaint video for running a die straight on a tube in a vice ( no lathe ) He basically had a collar that fit the tube size o.d in front of the die.. SO it literally couldnt go on crooked. the key is the collar being in front of the die , so its self guided.
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A little ugly. The base of the threads about where the tube ID is so I just spun both tools, ground and checked and kept doing that. Haven't read much up on tool grinding but I thought (now actually think) it will work. Tap/die was cheap but $15 (iirc) is still money I dont want to spend from my project funds right now (Id like a compressor some day). However I did get a replacement tap for $7.
I didn't anneal since my grinding tools were taking down the metal. Went through a few stones. When cutting across the first threads with the angle grinder it did change some colors. I used some cutting oil on the next which splattered but better than nothing. I dont have a way to flood it.
I did clean up my lathe really well after grinding. Took off the chuck and disassembled.
(https://www.gatewaytoairguns.org/GTA/MGalleryItem.php?id=8048)
New one came in today ($7).
(https://www.gatewaytoairguns.org/GTA/MGalleryItem.php?id=8047)
Quick n dirty Threading.
I havent perfected this yet. I probably need to incorporate lazers.
(https://www.gatewaytoairguns.org/GTA/MGalleryItem.php?id=8049)
Camera went to mini-model-mode
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that setup in the lathe is about as accurate as you need to get.. i assume this tube isnt for NASA
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I have an actual rocket scientist friend. You can't even show them this stuff or they puke.
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I think your doing fine!
Is this a good time to reveal that I'm an engineer? ;D
A good man can get the job done with poor tools, but lousy man can't do it no matter what tools are in use.
That's how you differentiate good workers from bad ones.
The rocket scientists they are just that, scientists and they don't see past their own box.
Marko
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I agree, you are doing fine. I know your tap looks like poopoo but it works like it should. To be honest, I think I have about three taps in my box I have profiled the same way.
Good job finding a way to do a job correctly with what you have. It’s what keeps forward progress going.
Dave
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Marco, hope you didn't puke or take offense :D. My aerospace friend got very upset when he was trying to find a wrench on my workbench.
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Messy workspace - case/point: I had this sliding door hinge on my workshop desk for at least 2 years until I figured out it would make a great makshift "tool holder". Reason why it stayed: there is no play in the hinge and is heavy-duty. Put a long screw through it so it is adjustable (enough).
(https://www.gatewaytoairguns.org/GTA/MGalleryItem.php?id=8051)
Dave. Thanks for the encouragement. It felt like I was doing something forboden! However if it doesnt work it WILL BE socially unacceptable! A risk in showing any work.
My goal in airgun modification is really not to blow anything up or cause injury ....ironically so that I can make a (small) pneumatic explosion to shoot some animals and kill them.
A "hypocrites" oath. :D
I definitely welcome any information to make sure I don't hurt myself or others!
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Dan thats awesome work using what you got, nothing wrong at that!
My shop is a mess, but its my mess and I know where stuff are. I have all sorts of tools and equipment around just waiting for the right use.
Marko
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Yes. My mess. Thats what I tell my wife when she happens by. :D
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i forgot to ask , what are you making ?
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i forgot to ask , what are you making ?
Rob,
This is just a so I can test a screw fill end on a 1 x .083 tube. I have another tube with a single pinned valve, an untested balanced end. I was about ready to add a fill end but figured if I can add a screw on it would be much easier to do some other things with it. I hope to add my "shotgun" "upper" at least for testing porpoises. It would be a one or 2 shot. I think a screw in fill end would lend itself to a double tube setup that I have been thinking about. Not sure it will all work. Some implied ifs there. So really testing a bunch of stuff that I've wanted to do for a while.
(https://www.gatewaytoairguns.org/GTA/MGalleryItem.php?id=7874)
(https://www.gatewaytoairguns.org/GTA/MGalleryItem.php?id=8053)
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makes sense , i do all sorts of testing . i hope it works
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I hope it works for you as well, keep us posted. I, like Rob, am constantly tinkering and trying out ideas. Building is half the fun for me.
Dave