JCUT 1325 Cutting Parts Oversize??


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Thread: JCUT 1325 Cutting Parts Oversize??

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    Default JCUT 1325 Cutting Parts Oversize??

    Hi guys,

    Im having an issue while cutting red oak where the parts are coming out too long/too wide on both x and y axes. The parts i am trying to cut are 1.875 inches wide and about 60 inches long. The 60 inch is cut on the y axes and the 1.875 is cut on the x (short) axes.

    I am using a 1/4" compression bit and am running at 15k rpm, 150 ipm. I am climb cutting and leaving .005" per side until the last pass.

    Could I be losing steps? Wouldnt that cause smaller parts instead of bigger parts? I see my leadshine controllers are set to 1/4 microstepping. Should i change it to 1/8?

    As for the calibration, i am using the numbers given to me by JCUT for steps per inch. I did a test this morning on the long axis and cut a shallow slot in my spoil board 94" apart. The distance between measured just a hair over on the tape measure. Perhaps about 1/32 over. I also measured my bit with calipers this morning and found that its actually 0.245 in diameter.

    Should I calibrate my axes against a tape measure? I will try to cut another piece using lighter passes and with the proper bit diameter. Any other ideas? Thanks!

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    Default Re: JCUT 1325 Cutting Parts Oversize??

    I forgot to also mention:

    The rectangular parts I am cutting are measuring about 1.900-1.930 when shooting for 1.875. I checked and made sure the gcode was correct and telling the machine to move the proper amount so its not a programming issue. The program I used to cut these parts still has the cutter set to .250" diameter which is .005" too big.

    I am going to try to cut a part again with the proper bit size and without doing the .005" finish cut on the profile. I will report back!

    Last edited by moparx12; 05-02-2017 at 10:16 AM.


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    Default Re: JCUT 1325 Cutting Parts Oversize??

    You probably need to do two things. First check the steps/unit and get a good scale, linear scale or some other method to determine if you are actually getting the correct distance. You are probably setup putting out too many steps/unit. The second issue is when you use an undersized bit in your case .245" instead of .250" you need to tell you CAM program you are using a unique bit create a new one that is set to .245", that way cutter compensation will be adjusted correctly. If you fix both of these issues you should be able to cut your parts to the correct size.

    Russ



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    Default Re: JCUT 1325 Cutting Parts Oversize??

    Keep in mind the undersized bit alone will make the parts slightly bigger because of cutter compensation will be wrong. When you take the .005" on each side of a part it could grow by .010 just due to that aspect.
    Russ



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    Default Re: JCUT 1325 Cutting Parts Oversize??

    Thanks Russ... Going home now to try this. I have an aluminum yard stick (straight edge) I will use to dial steps per unit in at about 35 inches. I have seen some youtube videos where people use an engraving bit to better see where the spindle is so i will try that too. I will reprogram using the new bit diameter and cut a new test. What had me confused and still does, is that the amount that the parts are off is not consistent (on the x axis). Edges are parallel but too far apart!



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    Default Re: JCUT 1325 Cutting Parts Oversize??

    Yeah you are off by up to .055" which is way more than cutter compensation, take multiple tests and using a very sharp engraving cutter will help you measure this more accurately if you don't have a long digital scale to use in the tests.
    Russ



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    Default Re: JCUT 1325 Cutting Parts Oversize??

    Yep, It looks like I was off. the x axis was a little worse than the y but both appeared to be around .010" overshooting at 34". I made the change in mach and ran a new program. Since i can measure the 1.875 with my calipers i did so and got a part that is still a hair over (1.885). The length is harder to measure since the part was 17 inches long. It is certainly acceptable on the tape but not sure how it would measure with something more accurate.

    I think I am going to turn the program 90 degrees and cut the width using the y axis. I will then use that number to dial in that axis even closer. I will then check the final steps per unit numbers by using the ruler again and jogging the machine the full 34". I hope I wont be able to tell the difference.

    X and Y have the same rack/pinion but for some reason the numbers don't turn out exactly the same for steps per inch. I guess that can be chalked up to my measuring accuracy and the variations in mechanical tolerances of the gearing and placement of the rack relative to the pinion gear etc.



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    Default Re: JCUT 1325 Cutting Parts Oversize??

    Quote Originally Posted by moparx12 View Post
    Thanks Russ... Going home now to try this. I have an aluminum yard stick (straight edge) I will use to dial steps per unit in at about 35 inches. I have seen some youtube videos where people use an engraving bit to better see where the spindle is so i will try that too. I will reprogram using the new bit diameter and cut a new test. What had me confused and still does, is that the amount that the parts are off is not consistent (on the x axis). Edges are parallel but too far apart!
    Unless that is a very accurate yardstick, I would use a Stanley tape measure, starting at the ''1'' rather than ''0''. Last time I checked one, it was better than 0.005 in 30 inches, measured with my optical CMM on my mill.



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    Default Re: JCUT 1325 Cutting Parts Oversize??

    It is a cheap empire brand straight edge you can get at the local box store. I have a 16' fatmax tape I could check against.



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    Default Re: JCUT 1325 Cutting Parts Oversize??

    That 16' Fatmax tape will be amazing accurate, like Jim shared they are marked on precision tooling, so being within .005 will give you some pretty good numbers to work with in your testing.
    Russ



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    Default Re: JCUT 1325 Cutting Parts Oversize??

    Ok so x is calibrated at 44 inches and y at 90 inches using the fatmax. I will run a small test part tomorrow to see how it does! If its still cutting oversized i will report back.



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    Default Re: JCUT 1325 Cutting Parts Oversize??

    Alright guys thanks for the help. I think i found the culprit. The grain pattern in oak appears to vary in hardness by enough to deflect my 1/4 inch compression bit considerably. I ran a test part with grain running along the long axis and made cuts both ways a predefined distance apart. I did these cuts manually and that is how i noticed the problem. Where the bit would plunge, i have a visibly larger hole than the width of the slot. If i slow the feed down to 10 ipm or so, the difference is minimized. I tried another 2 flute bit (non compression) and ran that at the slow speed as well. With the regular 2 flute bit i got values within .004" but i could still see the plunge circle bigger than the slot. I think with oak i will have to use bigger bits or slow down or conventional cut to insure i minimize deflection.

    Cutting across the grain, I was within .005" on distance between two slots, even cutting at normal speed.

    Last edited by moparx12; 05-03-2017 at 01:32 PM.


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    Default

    I'm looking for someone local to St. Louis area to help set up my jcut machine. 314.562.0933
    Any help would be greatly appreciated. I have a 5x10 plasma and router table purchased new.



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JCUT 1325 Cutting Parts Oversize??

JCUT 1325 Cutting Parts Oversize??