Yet another welding/machining/misalignment problem on Saturn 2. Sigh. - Page 7


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Thread: Yet another welding/machining/misalignment problem on Saturn 2. Sigh.

  1. #73
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    Default Re: Yet another welding/machining/misalignment problem on Saturn 2. Sigh.

    Peter, I guess my assumption was based on stress relieving as they used to do with cast iron by putting it out in the "bone yard". I didn't know that steel did not behave in the same manner.

    So that brings up another question - would repeated movement of the machine back and forth in the same area tend to relieve residual stress in that area if there were any, similar effect as vibratory stress relieving?

    Saturn 2 4848
    CRP Plug & Play NEMA 34, 2.2kw Spindle, Mach3


  2. #74
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    Default Re: Yet another welding/machining/misalignment problem on Saturn 2. Sigh.

    Hi Mick - There are various metals that "age" like cast iron and heat treatable aluminiums. These have internal metallurgical mechanisms that change over time. This allows various internal strains to redistribute as the grain structure changes. This does not happen in MS. Movement from the machine is unlikely to be big enough to go anywhere near the yield stress of the material so unfortunately this won't relieve stress. Stress relief (SR) is carried out around 600C 1000F at this temp the hot strength of structural steel is about 40% its ambient strength. So a 250MPa steel would only be 100Mpa strength. So any area over 100Mpa would relieve to 100Mpa. There is debate over whether a static structure like a bench needs stress relief at all. If its a dynamically loaded structure like a truck chassis the internal stress contributes to fatigue failure. Since a bench sees very little stress then the internal stress state does not matter and since the metal does not change over time it again does not matter. What does matter is if you plan to machine the bench after fabrication then it will move when you remove metal due to geometric changes. So SR helps in stabilising the bench for that purpose ie it will move minimally when you post machine it. One strategy in benches is to not fully weld the connections. A 100% welded connection is not needed for a bench. So perhaps only 2 sides of a square section perhaps and weld the side that contributes less to distortion. Benches tend to be constructed in a rectangular format to allow storage underneath but this shape tends to warp. If they were triangulated the movement would be less but they would be less user friendly. Another strategy is to braze weld the bench (TIG or torch) so you do not melt the tubes so you do not strain the joints due to the parent shrinkage. This will result in a bench with very low internal stress. Cheers Peter S

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    Default Re: Yet another welding/machining/misalignment problem on Saturn 2. Sigh.

    Thanks for the detail, Peter. I guess I'm never too old to learn!

    Saturn 2 4848
    CRP Plug & Play NEMA 34, 2.2kw Spindle, Mach3


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    Default Re: Yet another welding/machining/misalignment problem on Saturn 2. Sigh.

    Quote Originally Posted by micknm View Post
    Thanks for the detail, Peter. I guess I'm never too old to learn!
    There are many ways that you can stress relieve a steel frame, Heat treatment it just one way they have ultrasonic /Vibratory which in some cases is better then Heat, if the area is small it can be done with a Torch by hand and induction Heating works very well also, shot peening has been used for a long time as well, but each has it's own place and where it is best used

    Vibratory has been as successful as Heat treating fabricated steel parts like these machine tables, and does not need blasting after heat treating for paint prep

    A way to check your machine to see if it has had any type of heat treatment, is if there is any paint missing and you see shiny places where a disc- grinder has been used then you will know it has never been near any heat, I doubt that any of these machines have ever been stress relieved

    Mactec54


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Yet another welding/machining/misalignment problem on Saturn 2. Sigh.

Yet another welding/machining/misalignment problem on Saturn 2. Sigh.