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Arc milling using a DRO

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  • Arc milling using a DRO

    I have a Dro Pros 3M 3 axis Dro on my milling machine. I have a job coming up where I will need to mill an arc on some 1' Aluminum plate.
    I have been trying the smooth arc function to get a handle on the procedure. In the manual it shows the procedure using a flat end mill. Because the end mill is always cutting on one edge the input for tool diameter is 0 in this case. This works fine but I was not happy with the finish.
    I tried it again using a ball end mill, so in that case you would have to input the actual diameter of the mill, which in my case was .375". I was using the YZ plane and had the mill centered on the start point. Once you finish all the input and select the final key to start the process in this case the Y axis should be showing 0.000 but on the left side of the display and the Z axis display should be showing 0. Instead I get a Y display on the left of -.3594, the Z display is 0 and the function display only shows Auto R where it should be showing Au. R - YZ.

    I talked to Todd at Dro Pros yesterday and he suggested I try the input in metric values as these Dros are made in China where they only use metric so it was probably originally programed using metric and they use the inch / millimeter conversion function built into it to work in inches. I tried it this morning using millimeters but got the same kind of result. So basically as soon as you put any other value other than 0 for the tool diameter it comes up with this error.

    Does anyone have any experience with this? Todd says they get very few calls on this function because most people don't bother with it so he honestly said he had very little experience with it.
    Larry - west coast of Canada

  • #2
    I found a method that works. The Simple Arc machining method shown in the manual will actually work if you work in millimeters. I tried it in inches but it could not compute. I was working in the YZ plane on the backside of aluminum bar. I found it a little difficult figuring out which preset R type to use. It originally looked like I should be using type 3 but it turned out the type 2 was the correct one for that cut. Once you get all the entries in it can be a little confusing to start with. In my case the Y display showed 0.000 and the Z showed a minus value that doesn't seem to fit anything. When you lower the cutter the Z minus value will decrease and the Y value will start to change. I lowered the cutter until I got approx. .4 mm showing on Y. Then you move the Y axis to zero out that value again and make the cut. You keep going like this until the Z value goes all the way to zero. I got a pretty decent looking arc with the ball nose mill doing this. You have to stay awake because every time you lower the cutter you have to remember to zero out the other axis otherwise you will mill out a gouge in your work. It is probably a good ides to try it out on a piece of scrap before doing the good one.
    Larry - west coast of Canada

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    • #3
      I’ve done this on my DRO in XY using simple arc, and setting the step size to .005 I believe. Been a while since having done this, would have to relearn it.

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      • #4
        I like the fly cutter method better and the finish is superb.

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        • #5
          I have used the simple arc function on mine in the XY plane with good success, and none of the issues or caveats Cuttings described. Mine is just one of the cheap DRO units from Amazon. It seemed fairly simple, at each step just moving the X and Y axes to 0,0 then pushing a button to go to the next step. One could choose to either plunge or side cut with this method, although plunging seems like it'll give better endmill life because it's hard to maintain a decent chip with side cutting in this process.

          Obviously I get a better finish by using the rotary table, but sometimes that takes too long to set up or just isn't appropriate for various reasons.

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          • #6
            Do those DRO's support parabolic arc or just circular arc?

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            • #7
              I believe what complicates the process here is cutting the arc with a ball end mill in either the XZ or YZ axis. The mill starts with it's center on the start point and ends with it's full diameter at the top of the ball on the end point. The programing has to account for this change of cutting position to maintain a good arc. If you were cutting an XZ arc you would be milling passes along the Y axis and if you were cutting a YZ arc you would be milling along the X axis. The smaller the cuts you make the smoother the arc will be.
              I agree with Yondering that the rotary table method gives the best finish. I have used it many times but the setup can be tricky and very time consuming. In this case I will be rounding the edge of 1' Aluminum plate along straight edges. Cutting an arc along the XY axis is a much simpler process although the finish is not as good unless you use a large mill and make a large number of passes to eliminate the ripple affect between passes as much as possible.
              Larry - west coast of Canada

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              • #8
                Oh boy, actual machining content from me for once!
                Using simple radius thingy on the DRO to make equalizer bars for my locomotive project.




                Sent from my iPhone using Tapatalk Pro

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                • #9
                  So how do you mill a arc or radius manually??? increment the X & Y by .001 going back and forth?? That could take for ever.
                  My Acu Rite readouts do bolt hole patterns but don't remember seeing anything about arc milling in the manual.

                  JL..............

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                  • #10
                    Originally posted by JoeLee View Post
                    So how do you mill a arc or radius manually??? increment the X & Y by .001 going back and forth?? That could take for ever.
                    My Acu Rite readouts do bolt hole patterns but don't remember seeing anything about arc milling in the manual.

                    JL..............
                    The cheap Chinese glass scale DRO’s that everyone sells seem to use the same firmware, therefore have the same features. It’s a function built in, and yes, every .001, or I believe I set mine to .005 in those pictures.
                    The DRO head on my Bridgeport I ordered directly from Alibaba. The lathe’s DRO has Precision Mathews name on it, but the same exact manual. They are all the same.


                    Sent from my iPhone using Tapatalk Pro

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                    • #11
                      OK, I get it. I don't believe my Acu Rite has that feature.
                      But alternating back and forth between the X & Y by even .005 to cut an arc can be quite time consuming and I imagine it would produce a segmented cut.

                      JL................

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                      • #12
                        You can easily mill a circular arc with a rotary table. My first bridgeport had an old DRO and I had to use a rotary table for any arc like milling operations unless I could just free hand it but that never gave me good results. If you don't already have a rotary table for your milling machine, you should look into getting one.

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                        • #13
                          Yes, you can machine a simple circular corner quit nicely with a rotary table but you cannot do an arc in the XZ or YZ direction along an edge. That is where the process gets a little complicated.
                          And Yes, it is a time consuming process so you don't want to be using it if you have a great number of corners or edges to round. As my manual says " it is an extremely useful feature to have" providing you can figure out how to get it to work. It took me a lot of trial and error experimenting to get the hang of it.
                          Larry - west coast of Canada

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                          • #14
                            Originally posted by Cuttings View Post
                            Yes, you can machine a simple circular corner quit nicely with a rotary table but you cannot do an arc in the XZ or YZ direction along an edge. That is where the process gets a little complicated.
                            And Yes, it is a time consuming process so you don't want to be using it if you have a great number of corners or edges to round. As my manual says " it is an extremely useful feature to have" providing you can figure out how to get it to work. It took me a lot of trial and error experimenting to get the hang of it.
                            What about mounting a rotary table vertically, or at any angle you're able to mount one?

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                            • #15
                              Originally posted by 3 Phase Lightbulb View Post
                              What about mounting a rotary table vertically, or at any angle you're able to mount one?
                              It is a couple of 1" thick aluminum plates approx. 12" long by 4 - 5" deep. One end is square and the other end it cut at an angle. I will need to cut an arc along the ends.
                              I plan on mounting the plate on the mill table with the ends parallel with the X axis so I can use the power feed to make the cuts. Using a ball nose mill and taking no more than .005" cuts it leaves a pretty decent finish. I will have to convert all my input numbers to metric because that is the only way it seems to work properly.
                              Larry - west coast of Canada

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