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  • #31
    Originally posted by Toolguy View Post
    When looking at CNC machines, I much prefer a bed mill to a knee mill. I used manual Bridgeports for over 25 years as a tool & die maker. I now have 2 CNC bed mills. On the knee mill, either the knee is cranking up and down like crazy or you just have the quill doing the Z axis. This is very limiting when you have tools of different lengths. On a bed mill, the table is a stationary height and the head goes up and down. This gives a spindle that is always rigid and short plus much more Z travel. My small mill has 20" of Z and the next size larger one has 24" of Z. The head is also always the same (lighter) weight than the knee with different projects on the table. The bed mill has much fewer limitations and problems to work around in the Z axis than a knee mill. Many people don't learn about all the problems until they have bought the machine and try to use it. A knee mill can be a viable CNC machine, but if you're starting from zero, a bed mill is a better choice.

    That's a tough one. I have both. My knee mill does have a Kwik (not a misspelling) change (sorta) tooling system. It does only have 6 inches of quill travel, and at first I kind of begrudged the effort to crank up and down the table, but in some ways its easier when it comes to setup. I just crank the table up until my tool setter reads zero, remove the setter, and press start. I always leave the home z offset set at the height of the tool setter. I never fiddle with it or accidentally crash into the tool setter. One might argue that I should also tighten up the knee every time which would make it more tedious, but I've never had any issue with it so I just leave knee locks loose and go. If I used the tool tables it would not work out to be so convenient. Tool lengths would be an issue when say changing from a stubby mill in a screw lock tool holder to a half inch jobber drill in a drill chuck. Just like you say. I actually tried to use and setup tool tables on the machine at one time, and if I used it for a specific range set of jobs it might be possible. Since its really a more general purpose machine that didn't work out. Of course for me the big deal about the mill was the price for a heavy weight (middle weight by today's standards.) I bought it at auction for $500 and put about 2 grand into retrofitting it to a modern control system. Do I wish I had a bed mill the same weight and the same power? Sure I do, but this machine is very utilitarian for me too.

    The advantage to a bed mill seems obvious, but its about size - and quality. On my little high speed machines I only have about 6 inches above the vise. Of course they would never drive a 1/2" jobber drill LOL. If I need a 1/2 hole I do it with spiral interpolation and a 3/8 or 1/4 end mill. I have crashed the tool into a tool setter before and damaged the setter or broken the tool. A couple of them over the years. I had a bigger bed mill at one time, but head nod and quality played a huge part in why its no longer in service in my shop. Gack!

    If all things were equal I might prefer a bed mill over a knee mill, but all things are almost never equal.

    Originally posted by MaxHeadRoom View Post
    This was one nice feature of the XLO's I had, they had a motorized Ball jack system with a brake to position the knee bed height quite rapidly to pre-position if a longer tool or material height changed.
    Max.

    P.S. I have considered putting a power feed on the knee of my KMB1, but I've gotten used to it now.
    *** I always wanted a welding stinger that looked like the north end of a south bound chicken. Often my welds look like somebody pointed the wrong end of a chicken at the joint and squeezed until something came out. Might as well look the part.

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    • #32
      I'd have given up milling years ago if i didn't have my knee power feed

      My mill is 3 axis cnc. Power feed on the knee makes it all come together and can get used many times in a job. A tool changer would really make a difference, but my Kurt power draw-bar will have to do for now..

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      • #33
        I've just added the knee axis to my Bridgeport conversion - with a bit of coding it now takes all the tool length compensation so i keep full quill travel - works really well and i wish i had done it ages ago.
        If it does'nt fit, hit it.
        https://ddmetalproducts.co.uk
        http://www.davekearley.co.uk

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        • #34
          Thank You MaxHeadRoom for this. I am going to do this first to my 602. it has sat for a long time. Currently figuring how to disassemble; has ball screws. I have looked at manual PDF and am reading old posts.
          Sincerely Dave b.
          Last edited by boringdave; 04-17-2018, 09:55 AM. Reason: Give Credit

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          • #35
            Originally posted by Black Forest View Post
            That is a Centroid conversion. He used the Centroid Allin1 DC board. It has three drives mounted on the board to control DC brushed servos. The Acorn board utilizes an updated software package called CNC12 with Intercon. Later in the year Centroid is going to update the software for the Allin1 DC and their Oak board to the CNC12. As it stands now if you want all the features that gets included with the Acorn and the Ultimate software package for the Allin1 DC and the Oak board it will cost an extra 2 or 3 thousand dollars! It is somewhat confusing to figure out what will cost what from their website. For right now the Acorn is a great deal if you don't need more than 4 axis. It is not expandable axis wise as are the other boards.

            Don't take what I say as Gospel as it is just my understanding of what is what.
            Hmmmmmm.........I have a 6 year old M400 Centroid control using the All-in-One board with a 4th axis add on. As far as I can figure my software is the same as the Acorn's optional ($139) software. Mine had Intercon as standard included with the board. I also have the Centroid probe which included the optional ($399) Acorn probe package. I may have had to buy the optional G50,51, scaling and mirroring (it may have come with the probe system though, not sure). I've found scaling is a nice option.

            Real soon I'm planning on buying an Acorn to convert a DynaMectronics mill. I'm hoping, but not totally sure the Acorn ($139) software is as advanced as the included M400 software. For instance, does it have the macro programming?

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            • #36
              Originally posted by DR View Post
              Real soon I'm planning on buying an Acorn to convert a DynaMectronics mill. I'm hoping, but not totally sure the Acorn ($139) software is as advanced as the included M400 software. For instance, does it have the macro programming?
              I'm pretty sure it's the same DR plus touchscreen capability if wanted. You can ask about specific functions on the forum & get an answer pretty quickly.

              As far as macros go, there are a LOT of macro-related posts on the forum. AFAIK all custom macro questions users dream up are answered by helpful forum experts that know this stuff or by Centroid support. Me? Not so much.

              The one time I needed help (I wanted Aux keys 8 & 9 on the VCP to manually home the X or Z axis on demand on my lathe) I received a link to the tech bulletin that explains how to do it. After struggling with it, one of the Centroid support guys straightened it out for me in a flash.
              Milton

              "Accuracy is the sum total of your compensating mistakes."

              "The thing I hate about an argument is that it always interrupts a discussion." G. K. Chesterton

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