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Thread: Gantry mill for precise milling of aluminium

  1. #37
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    Default Re: Gantry mill for precise milling of aluminium

    Video of machining part for rotating ballnut for bigger machine:


    I also tried milling stainless steel 304, and it went fine. I will post video soon.



  2. #38
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    Default Re: Gantry mill for precise milling of aluminium

    That's fantastic work! Really awesome!

    What kind of acceleration settings did you use in the video?

    For my own build I still haven't made a final decision between gas struts or a pneumatic cylinder. Please tell me more about your pneumatic cylinder setup. What kinds of pressures are you running in your cylinder, what is the inner diameter of the cylinder, and how big of a reservoir are you using? Have you experienced any leaking anywhere so that you would periodically need to top up the pressure? I'm thinking of using a cheap pneumatic cylinder from ebay, but I'm not sure if it will leak.

    Once again, what you've done is fantastic!



  3. #39
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    Default Re: Gantry mill for precise milling of aluminium

    Thank you.
    Acceleration is 1500mm/s*s Can go almost as high as you want with those mitsu servo motors, but it hurts even watching gantry at some high acc rates
    About cylinder.. I made research as well. I called company which produces gas struts, and they advised me not to chose it for my application. They said it wont handle fast travel so many times.
    There are pneumatic cylinders specially for this kind of applications, but I choosed ordinary one and had no problem till now.
    I was also thinking about reservoir etc.. And decided that best option is, to buy one of those cheap 100USD 25L compressors. It already has pressure valve on it, you only need air preperation unit.
    There is no chance you wont have even slightes leak.. And compressor handles this great. It will power on maybe once per week, so it will last very long, and you dont have to worry about pressure in sistem.
    Problem with gas struts is also that when it travels down, it will provide much higher force than on top, while air cilinder doesnt make any practical pressure change in sistem when travels down, due to very small displacement compared to air reservoir.
    I needed cylinder fast, so I bought festo here in my conutry, which was a bit expensive, if I had time, Id also buy cheap Chinese one. I just ordered whole bunch of different dimensions, and price for piston diameter 40mm, travell 250mm is about 5USD.
    So if those will last more than year, it is already good
    Another bennefit using air cylinder is, you can adjust force with pressure regulator.
    Inner piston diameter for my cilinder is 60mm. But I am using it in opposite direction - it lifts when it travels up. So you have to calculate surface of piston - piston rod. Then you can calculate pressure nedded. In my case it is 300kPa.
    You can go with bigger cylinder, assemble Z axis, and unscrew ballscrew nut, and then just apply pressure so long, that it lifts Z axis. Then you lower it a bit, to have a bit of weight pushing down, to eliminate any ballscrew backlash,



  4. #40
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    Default Re: Gantry mill for precise milling of aluminium

    Thanks for the info!

    I'm thinking about using two small Inner Diameter air cylinders at a max pressure of 80 - 90 PSI. That way I would only need a very small reservoir. I was thinking about a small fire extinguisher bottle or small propane tank mounted to the back of my Z plate. Something very small. The higher the working pressure, the smaller it can be. I don't really care if the top of the stroke force is off by 25lbs from the bottom of the stroke force.

    I just don't know if the cheap EBay pneumatic cylinders will leak at those pressures. They say they will take the pressure, but will they leak, I don't know.

    Gas struts would be the easiest, but they all have damping . Hard to even see a damping spec on an inexpensive gas strut, they usually don't mention it.

    Really awesome machine you have made!



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Gantry mill for precise milling of aluminium
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