4 and 5 Axis Setup - Minimill
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  1. #1
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    Default 4 and 5 Axis Setup - Minimill

    Hi there,

    I'm pretty new to the CNC and even machining arena. I'm a university student on an internship and I'm having a bit of trouble with our mini CNC mill here. It's a Minitech GX mill (Mini-Mill/GX - MINITECH MACHINERY CORPORATION), with 4 and 5 axis stages(5th Axis - MINITECH MACHINERY CORPORATION). I understand the basics of G-code, and I know how a dial test indicator works, but I'm struggling to understand how to set up the 4th axis, the trunnion table. I've looked online a ton, but haven't found anything that really helps with my issue. Here it is:

    So I have the trunnion table on the mill, but it isn't straight on the roll, pitch, or yaw axes. I understand how to run the dial test indicator along the table in the x-axis and y-axis for roll and pitch and how to shim it up, but yaw confuses me. I had the table accurate to under half a thou over a couple inches (we're only making small parts) in the x- and y-directions, but when I ran the DTI along the table at +90 and -90, the runouts are different. So I believe that the base plate on the trunnion table isn't level with the axis of rotation, but I don't know how to accurately level the axis of rotation if I can't count on it being level with the table. I attached a picture of my setup, if that helps: 20200626_140746.jpg20200626_140746.jpg

    Any help is appreciated! I've been reading lots of these forums, and thanks to all of you for answering other folks' questions too,

    S

  2. #2
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    I would recommend a bolt in the center of the 1,2,3 block. Not pinching it under a portion of the side of the head like you show it.

    If your artifact is moving, you are chasing your tail.

    That giant spongy stack of shim screams of slobbery, chewed on tail.

  3. #3
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    Quote Originally Posted by SpencerFTO View Post
    Hi there,

    I'm pretty new to the CNC and even machining arena. I'm a university student on an internship and I'm having a bit of trouble with our mini CNC mill here. It's a Minitech GX mill (Mini-Mill/GX - MINITECH MACHINERY CORPORATION), with 4 and 5 axis stages(5th Axis - MINITECH MACHINERY CORPORATION). I understand the basics of G-code, and I know how a dial test indicator works, but I'm struggling to understand how to set up the 4th axis, the trunnion table. I've looked online a ton, but haven't found anything that really helps with my issue. Here it is:

    So I have the trunnion table on the mill, but it isn't straight on the roll, pitch, or yaw axes. I understand how to run the dial test indicator along the table in the x-axis and y-axis for roll and pitch and how to shim it up, but yaw confuses me. I had the table accurate to under half a thou over a couple inches (we're only making small parts) in the x- and y-directions, but when I ran the DTI along the table at +90 and -90, the runouts are different. So I believe that the base plate on the trunnion table isn't level with the axis of rotation, but I don't know how to accurately level the axis of rotation if I can't count on it being level with the table. I attached a picture of my setup, if that helps: 20200626_140746.jpg20200626_140746.jpg

    Any help is appreciated! I've been reading lots of these forums, and thanks to all of you for answering other folks' questions too,

    S
    Someone stop the madness please!

    heres a few tips.
    your indicator looks to be too far back and looks to be rubbing on the shaft rather than hitting the ball ( couldnt see a ball on your indicator tip either in blowing up the picture, so maybe you dont have one )
    your part Flat out sucks for location and clamping. has a chip under it in upper right corner, doesnt look flat against the fixture and in all honest your locating fixture flat out sucks, chewing gum would be a better improvement.
    you need to add more shims under the main fixture as I dont think you have enough.

    Just for shits and giggles have you tried indication just the fixture in 1st? thats the best way, once that is done then place your part in but not like you have.

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    get rid of that shit under the 4th axis, indicat the X axis (long axi) should be zero or close, if not check your indexer mounting and remedy. Checking the y axis ( short one) is a matter of small incremental jogs of the indexer untill you get the reading you're lookin for. G92 the A axis ( your indexer) when you get Y to indicate near zero. I don't see any 5th axis on there.

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    If it was me... those shims under the 4th would be scaring me.

    I start by popping the trunnion off the table and verifying basic machine alignment:
    1. Clamp a precision square to the table, put an indicator in the spindle, align the square so movement in X does not deflect the indicator. Indicate the Y axis. This should be square. (Checking Y motion is square to X motion)
    2. With the indicator in the spindle, traverse the length of the table in both axes. (Checking that the table is aligned in the XY plane)
    3. Put a gage rod in the spindle and check spindle runout.
    4. Put your square on the table, aligned in XZ. Indicate along the long side. Repeat this with the square aligned in YZ. (Checking that Z motion is perpendicular to the table)

    OK, now you should be reasonably convinced that things are square in 3 dimensions. If something here is messed up, stop and fix it before moving on. Now you can drop the trunnion on and move forward. Otherwise you're just chasing your tail....

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    Thanks everyone for the tips!

    I guess that step 1 would be to take off the trunnion again and indicate on the main table of the machine. I did this before, but didn't worry too much, thought I would just fix it as I aligned the trunnion. This was likely the first mistake.
    Step 2 would be to mount the trunnion back again, and indicate it in, first in x, then in y.

    My main concern is what to use on the trunnion as reference. That ground block on top is just so I have a good surface to indicate on. I don't think that the main base of the trunnion is level/parallel with its axis of rotation. I have a mounting block, a breadboard (black plate on picture), on top of the trunnion, which I think I will have to shim independently of the trunnion in order to truly have a level surface that is parallel with axis of rotation. This could have been a beginner mistake, I will try again today.

    GENERALDISARRAY, delw, greggv: my shims are just too loose and floppy? What exactly should I fix?
    greggv: you suggest that I get my x perfectly straight, then use the program to align y? Thank you, I was using shims, this will work much better.
    delw: I tried to indicate the trunnion in first without the block, but once I got x and y aligned, I would indicate along the table at +90 and -90 and would get different results. I thought that this meant that the table had a weird shape to it, so I tried with the block. Also, I made sure that the indicator ball was contacting don't worry What would be a better part for referencing?
    trochoidalpath: thanks for the good overview of alignment. I'll go back and double check this.

    Thanks for your quick replies! This definitely gives me something to go off of today! If anyone has anything else, especially in terms of aligning the trunnion, I'd really appreciate it!
    S
    Last edited by SpencerFTO; 06-30-2020 at 01:44 PM.

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    Just so you know, the threads in the mill are 1/4"-20. This is why my fixtures are a bit weird, I can't just bolt an ordinary 1-2-3 block in, and I work at small facility that isn't a machine shop. Not tons of good options, but can purchase.

    Thanks again!
    S
    Last edited by SpencerFTO; 06-30-2020 at 09:41 AM.

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    So I have an update: I took off the trunnion and levelled out the base table. When I put the trunnion table back on, 0.005" difference left to right (x-axis). This is pretty much the same problem as before. My concern is that the axis of the table's rotation isn't parallel with the plane of the table top, so leveling the x-axis here actually isn't aligning anything. Only problem is that I'm not sure how to measure the axis...

    Thanks for any help!
    S

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    From the link, the mill only weighs 200lbs ?. Not sure how accurate your going to get, and will it stay put once machining starts.

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    Yeah, it's really small, but we also only manufacture really small parts (8mm or less) and not too much material removal. The goal is just to get as accurate as possible now and go from there.
    Thanks Wsurfer,
    S


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