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Thread: Different machine job

  1. #1
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    Default Different machine job

    I build models of WW 1 artillery; previously I have built a 1/6th scale British 18 PDR. My current project is a British 4.5” howitzer (1908 to 1943) in 1/6 the scale and no they won’t fire.

    It has an unusual recoil system that changes the distance the barrel moves after being fired which uses valves controlled by the piston rotation in the recoil cylinder IE: it recoils the full distance when the barrel is horizontal and less the higher the barrel is elevated, no point slamming the breach into the ground is there. To do this the piston rotates in the cylinder which sets valves that control the flow of oil in the cylinder so that the amount of resistance to barrel movement is controlled. Confused yet, wait for it.

    The cylinder has four grooves in it, similar to rifling in a barrel and I needed to make these. How? I don’t have a rifling machine nor do I wish to build one just for this (like I could get it to work right anyway) and getting someone to rifle it would be difficult here and expensive. Plus if I’m going to all the trouble to make parts that no one will ever see or know about, yes I am living up to my Nom de plume, I want to make them myself if possible.

    Not possible or not completely.

    Since it is just a model and doesn’t really work, the cylinder can be fabricated, as are many other parts that I cannot reproduce using the original construction methods. A piece of ¼” brass pipe has an OD just about right for the bottom of the grooves (difficult to find in these days of big box hardware stores but I actually had a piece) so I decided that if the grooves where milled on the outside of the pipe and then soldered into the barrel of the cylinder after which the ID is drilled/reamed etc. it will leave a cylinder with the four grooves on the inside. It actually worked out OK. I had to drill out the ID about 8” long over all, from both ends and there was a misalignment of a few thou but after lapping it most of it was gone. The ID is supposed to be 0.500” in diam. Before lapping a 0.492 pin was able to be pushed through, after lapping a 0.500” gauge pin can be pushed through with a little resistance but a 0.501” pin will not enter.

    I could have set up a gear train or sprockets and chains, between the mills X axis leadscrew and the rotary table to get the right rate of rotation for the milling operation but it was easier for me to go a friend that has a fourth axis CNC mill and get him to do it. Not easier for him though. Later this week he is going to CNC mill the OD of the piston that has to have lands on it to match the grooves in the cylinder. He has already written the code to do this, which was a fair bit harder than the simple code to mill the grooves but he is a brainiac engineer so it works.

    The grooves are 1 in 30 left hand twist, 0.062" wide and 0.020" deep.



    grooves2 by A.N. O'mouse, on Flickr
    The shortest distance between two points is a circle of infinite diameter.

    Bluewater Model Engineering Society at https://sites.google.com/site/bluewatermes/

  2. #2
    Join Date
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    dang, that is cool. Really interesting mechanism too, I hope you'll show pics of the finished project!

  3. #3
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    OK "loose" … not to difficult. I rifled my first black powder pistol barrel using simply a twisted 1/2 " square bar as the rifling guide. Hold the barrel in the lathe chuck (spindle rotation locked) , Mount a plate with square hole on the tool rest and pull a simple single point cutter through by manually sliding the tail stock back. Shim out the cutter for successive cuts. All told a quick "throw- away" set-up.
    Maybe we will see your work at the NAMES Expo here in Wyandotte.

    Joe B

  4. #4
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    So the damping system is going to be variable with elevation angle in your model as well? That's essentially what you're saying to us since you posted that no one will ever see the grooves. And if you're the only one that would ever know that this is the case why not make it without the grooves and just make it spring over some middle amount of distance?

    OK, OK I know.... I'm no fun at all

    So just what is the function of the grooves? And what is it that changes the damping stroke length? Are the grooves tapered in width and depth and form the variable valving? So the damping gets more firm as it travels the length? And the cylinder shifts or the piston shifts so when aimed high the piston is working in the portion with the smaller flow grooves? Or is there some other valving?

    If they are intended to be tapered then cutting them with a rifling like cutter won't work. And for the amount you're going to push on it at the shows or while showing folks your project would a straight but tapered groove not work just fine? And finally at the small scale you're working at the volume of oil to groove is not the same. You will likely only need one groove that is tapered and of a size you can make and it would be good enough to get a nice manner of damping where you push on the barrel and the pushes back then oozes forward in a pleasing way. Pleasing in this case being "not scale" in the degree of damping of the push then return. Because if it were "scale" then it would act more like just a spring. You want it to "ooze" back over about a half second I'm imagining.

  5. #5
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    Aug 2018
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    Loveland,CO
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    Look at Foxfire books, I believe it's volumn #5, it shows how to make several rifling jig, out of wood, how to make the rifling cutters, all very simple.

  6. #6
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    Quote Originally Posted by JoeCB View Post
    OK "loose" … not to difficult. I rifled my first black powder pistol barrel using simply a twisted 1/2 " square bar as the rifling guide. Hold the barrel in the lathe chuck (spindle rotation locked) , Mount a plate with square hole on the tool rest and pull a simple single point cutter through by manually sliding the tail stock back. Shim out the cutter for successive cuts. All told a quick "throw- away" set-up.
    Maybe we will see your work at the NAMES Expo here in Wyandotte.

    Joe B
    I should be there I have been to all of them since it was held at Domino Farms. I will be bringing my models, I hope.

    Quote Originally Posted by BCRider View Post
    So the damping system is going to be variable with elevation angle in your model as well? That's essentially what you're saying to us since you posted that no one will ever see the grooves. And if you're the only one that would ever know that this is the case why not make it without the grooves and just make it spring over some middle amount of distance?

    OK, OK I know.... I'm no fun at all

    So just what is the function of the grooves? And what is it that changes the damping stroke length? Are the grooves tapered in width and depth and form the variable valving? So the damping gets more firm as it travels the length? And the cylinder shifts or the piston shifts so when aimed high the piston is working in the portion with the smaller flow grooves? Or is there some other valving?

    If they are intended to be tapered then cutting them with a rifling like cutter won't work. And for the amount you're going to push on it at the shows or while showing folks your project would a straight but tapered groove not work just fine? And finally at the small scale you're working at the volume of oil to groove is not the same. You will likely only need one groove that is tapered and of a size you can make and it would be good enough to get a nice manner of damping where you push on the barrel and the pushes back then oozes forward in a pleasing way. Pleasing in this case being "not scale" in the degree of damping of the push then return. Because if it were "scale" then it would act more like just a spring. You want it to "ooze" back over about a half second I'm imagining.
    The piston blocks the oil movement up and down the cylinder and it can only flow through the piston/valve ports.The piston rotates by the action of the grooves on the lands of the piston which has aforementioned ports in it (not in the model, to small and impossible to machine). On either side of the piston are the "valves" which also have said ports. As the piston rotates it opens or closes the valves (yes it is hard to understand without pics) which control the oil flow. There is a cam mounted on the carriage which holds the recoil system and a lever that runs in it. As the system is elevated the lever changes position by the cam which lifts an arm, which rotates a shaft, that rotates a gear, which rotates the piston shaft that rotates the position of the valves in relation to the piston. OK did you get all that. And just to mess things up some more the piston is linearly stationary and the cylinder moves back and forth with the barrel. Now if you understood that then please explain it to me, I'm still trying to get a good grip on it.

    P.S. there won't be any oil in it since it is just a display model and the recoil system dosen't have to work properly. I put this detail in it for my own satisfaction/self abuse.
    The shortest distance between two points is a circle of infinite diameter.

    Bluewater Model Engineering Society at https://sites.google.com/site/bluewatermes/

  7. #7
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    I think I got it. Lots of geegaws in the piston which activates said geegaw valving based on rotation produced by the grooves.

    Seems easy enough to me. No fancy valving and no oil in the cylinder then no need to rotate the piston and no need for any grooves..... which would all be hidden in any case.

    If you want a nice feature to wow the plebes may I suggest that you get a close lapped fit of piston to cylinder then fit a simple one way valve in the piston crown. Lightly oil the cylinder and you have what is basically a pneumatic damper. It pushes down as if fired and the one way lets the air flow easily. Then it closes and the piston and barrel ooze back out to the rest position in around a half second. You may need to drill a small air bleed hole in the piston for this to work or with a nice lapped fit it may not want to come back up anytime shy of an hour depending on the oil used and the fit and the length of the piston skirt. And depending on the relative sizes of the cylinder and the piston's shaft you'll get anything from some to a fairly sizeable compression of the air. In fact a small O ring around the shaft and a nice finish with a touch of compressed air in the recoil cylinder and you would not need a coil spring.

    To show it off you push down then release and your hands can be back at your side before the barrel recovers to rest. THAT should get a few ooooo's and aahhhh's... And even at small sizes this is very much a doable plan

  8. #8
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    But that wouldn't be correct.

    As I said I don't do this for others, just myself and it isn't suppose to actually work correctly, more of a semi functional display and possibly a more politically correct form of self abuse. Maybe in a hundred years someone will take it apart and wonder about it.
    Last edited by loose nut; 12-27-2018 at 10:22 AM.
    The shortest distance between two points is a circle of infinite diameter.

    Bluewater Model Engineering Society at https://sites.google.com/site/bluewatermes/

  9. #9
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    How was rifling done back in the 16th century? Might there be a way to adapt that tech, whatever it was?

  10. #10

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    Gentlemen.....button rifling be the answer for this grooved cylinder job, I trust! If the metal of the cylinder is not a hardened steel then this might be the most realistic option to get the grooves into that tube. The rifling button can be made easily to your specifications regarding size and number of grooves. Medium carbon or high carbon steel in annealed state is machined to size and then hardened. E.g. a round file can be annealed and then used for the purpose. even a grade 5 bolt after water quench might deliver a reasonable result.

    Like thusly:







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