Hydraulic cylinder gland thread oval from weld on fitting
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  1. #1
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    Default Hydraulic cylinder gland thread oval from weld on fitting

    I'm wondering what is your technique for reducing the heat for when using weld on fittings on to hydraulic tubing. The tubing has a internal thread of 3.250" UN-12 thread. There is one tube that is about 0.030" out of round.
    To add to the problem, what are the different techniques to pull it back to round for thread chasing.



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    Obvious
    First weld on the fittings then cut the thread

    Peter

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    If you have to stick a threaded boss on a ram or whatever first insert a threaded male plug into the nipple then weld, if you weld without ( aka like the other thread ( pun) free state then the bugger will distort, if you must the 12, 6, 3, 9 o clock tack to hold it round, even then without support it can go out of whack, we had copper plugs in work but Ali and some white heat transfer grease works ok, or as correctly pointed out by Peter thread after weld, I know that’s a bugger as chips and scarf go down the hole, magnet in the fitting to catch sometimes helps
    Mark

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    Did the copper insert screw into the glad thread?

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    Make a very close fitting plug and install it in the barrel with lithium grease before welding. Don't drill the through hole for the fitting until afterwards so that you don't have grease coming out into the fitting while welding.

    You will need to be able to pull the plug out either with a bolt and a plate, or knock it out with a bar from the opposite end of the cylinder barrel. It will likely still spring back a little bit. A slight bit of ovality can be corrected by pressing the barrel back into a more round condition. Typically, I would then skim the bore of the cylinder again, just to take off the high spot beneath the weld of the fitting. Do this carefully with very sharp tools, and you may have to feather the cut slightly as the tool gets to the far side of the hump so as not to leave any sort of a ridge that will grab the seal.

    Cutting the thread should be done last, but if you have to skim cut the thread, then press the barrel as round as you can and chase the threads.

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    What welding technique were you using? Tack around and allow to cool. Use small wire and move fast. Small bosses are difficult to weld around continuous, allow to cool when you have to reposition.

    If you screwed up the welding and the thread is out of round, so is the cylinder barrel. Pressing it back round is the only solution.

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    Dirty method would be to find a plate and tack it at 3,6,9, and 12 so the barrel won't distort. Weld fitting on, then cut off plate. If you're welding on a fitting I would assume repaint of the cylinder so a little extra weld wouldn't matter.

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    Quote Originally Posted by HuFlungDung View Post
    Cutting the thread should be done last, but if you have to skim cut the thread, then press the barrel as round as you can and chase the threads.
    Great idea, I tried pressing it with a 90 degree vee block underneath and one on top, I was starting to get it then a flat spot formed on the pipe. Hopefully this problem won't happen again. If I had to press a similar job in the future I would use a swallow vee block.

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    Hi Lanza:
    I was trained to weld bushings and threaded plugs by stitch welding them to keep distortion to a minimum.
    So tacks all round as gbent advocates in post #7.
    Then weld from 11 o'clock to 1 o'clock
    Then from 7 o'clock to 5 o'clock
    Then 10 o'clock to 8 o'clock
    Then 2 o'clock to 4 o'clock
    etc etc etc.

    I used to weld new bushings for earthmoving equipment that way during my one and only stint as a welder 40 years ago.
    We'd put in a hardened dummy shaft first to align everything and keep it perfectly round, weld it up and press out the shaft.

    Sometimes we'd need to kiss it with an expanding reamer afterward, but rarely.

    We always put acetylene soot on the shaft first...I have no idea if it did any good or not.
    Supposedly it prevented the shaft from galling the bushing on the way out.

    Cheers

    Marcus
    Implant Mechanix • Design & Innovation > HOME
    Vancouver Wire EDM -- Wire EDM Machining

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    I can tell you what to do if you are making a new barrel out of unhoned tubing. You drill your port holes in the tube, prepare the base end for welding on your baseplate/fitting, cut a steady rest spot on the thread end of the tube, weld on your port bosses, then skive/hone the barrel after you are done with the welding. Chuck the barrel on the base end and use your steady rest on the thread end and cut your gland thread and lead in chamfers. Then weld on your baseplate/fitting.

    It gets a little more complicated if you are using honed tubing. Weld your port bosses sparingly and spot hone the tube where the welds are on the tube.

    On the base end, there is usually a little space due to a locknut under the port weld so that port boss is not usually a problem. For the same reason the baseplate/fitting weld will also be far enough away from your piston seals. On the gland end make sure you do your gland thread and spot honing after you weld your port boss.


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