Plasma Bolt Hole Questions
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    Default Plasma Bolt Hole Questions

    Hello all, I work for a small 10 man fabrication shop and do all of the cutting on our plasma table but am having trouble with bolt holes. Particularly in thicker plate. I know taper is common with the plasma process but I am trying to see if there are any tricks that I am missing. We have a torchmate 4800 with the Flexcut 80. I am not super well versed with the different options on the market but I am sure there are some better and worse. We cut a lot of 1/2" plate which is where the taper problem is most apparent. I ran a test with .500 holes with brand new consumables and got two holes that would fit a 1/2 bolt before developing a the taper that prevents the bolt to fit. I am running the feed rate about 60 percent of that of the outside line and using an over burn of .100-.250. I also adjusted kerf settings to match those seen in a line speed test. Any recommendations would be greatly appreciated.

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    disable torch height controller feedback. Forces the torch to stay low during cut, slow down more, 1/2 on 1/2 is possible, I would think 30 percent feed rate with the 80 amp as slightly wag. Lead in have come in at 70 degrees, straight line. If you come in with an arc the taper will start bad with no time to recover, with a straight the tables accel/deccel will give time for arc to start the hole without a taper.

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    Just to make sure you know. The plasma steam is rotating and the kerf it makes will have a larger taper angle on one side compared to the other. So when burning a hole and you want as vertical sides as possible you have to go around in a particular direction. I read one time that one manufacturer actually makes nozzles that send the stream clockwise or counterclockwise according to the operators choice.

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    Quote Originally Posted by memphisjed View Post
    disable torch height controller feedback. Forces the torch to stay low during cut, slow down more, 1/2 on 1/2 is possible, I would think 30 percent feed rate with the 80 amp as slightly wag. Lead in have come in at 70 degrees, straight line. If you come in with an arc the taper will start bad with no time to recover, with a straight the tables accel/deccel will give time for arc to start the hole without a taper.
    We have also found that when cutting round holes that turning off the torch height control helps. We also set our Pearce time for the thickness of the material we are cutting and then Pearce in the center of the hole before ramping out at angle to the actual hole size we want to cut out. Watch your torch to work distance with the torch height control turned off.

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    Quote Originally Posted by memphisjed View Post
    disable torch height controller feedback. Forces the torch to stay low during cut, slow down more, 1/2 on 1/2 is possible, I would think 30 percent feed rate with the 80 amp as slightly wag. Lead in have come in at 70 degrees, straight line. If you come in with an arc the taper will start bad with no time to recover, with a straight the tables accel/deccel will give time for arc to start the hole without a taper.
    I will give this a try. I already turn the torch height control off when we cut 3/4" plate but did not think to try that with the 1/2". I will give the angle entry a try today and see how it works as I have been using an arc so what you said makes perfect sense. Thank you

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    Quote Originally Posted by hobbyman View Post
    Just to make sure you know. The plasma steam is rotating and the kerf it makes will have a larger taper angle on one side compared to the other. So when burning a hole and you want as vertical sides as possible you have to go around in a particular direction. I read one time that one manufacturer actually makes nozzles that send the stream clockwise or counterclockwise according to the operators choice.
    I actually did not know that so I appreciate the knowledge. I will check into that. I remember the manual or a video saying the table cuts one direction better then the other so I will have to check into that. Overall we are very happy with the quality of the cuts we get even in 3/4" plate. The bolt holes are the only complaint we really have at this point.

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    I have slowed down a cut on 1/2" plate running a powermax 65 (at 65 amps), on a Torchmate 4x4 growth series table, to 25 IPM to get the accuracy.

    I did try slower, but much like oxy fuel cutting, it would loose the cut.

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    The plasma arc typically spins counter clock wise, so for exterior cutting have your torch move clockwise and counter clock wise torch travel for internal hole cutting.


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