Z-Axis not aligning properly

LowRider CNC Troubleshooting
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Ok guys, I’m at a loss, again… l0l. Anyway, my Z-axis isn’t behaving properly. I first noticed it in my latest Crown test (after learning more about G Code). The “left” side of the crown was lighter then the “right”.[attachment file=“80448”]

I then did some more testing to see if I could figure out where things were going wrong. For reference, here is a pic of my LR [attachment file=“80449”]

My first test was to lower Z to Zero and see if I could see anything. I noticed that on both side of the machine, the Y Negative side of the gantry is resting on the wheel support but the Y Positive side is up about 2mm. This is a pic of what I am talking about. [attachment file=“80450”]

I then did some measurements to see if what I could find out. I left the Z Axis at Zero, and moved the X Axis all the way to the “near” side (LCD side) and measured the height of the X Plate to my table. It was 21.24mm. I then moved the X Axis all the way across the table and measured again, this time it was 19.25mm. Essentially, 2mm across the width of the table which is 1290mm (4’ usable surface). I know that’s not a lot of error, especially for a 3D printed machine but I’m wondering if that error will start to show up when I’m routing out 3/4" thick plywood. I’m thinking it will show up as a tilt to the routing.

Some additional info. When I raise my Z-axis and then power off the machine, the LCD side of the machine won’t go down on its own, but the far side does. To get the LCD side to go down, I have to “pull” the bottom of the Y Plate out a bit while leaving the top in position (basically rotating it around its onw Y Axis. If I do this, then the gantry will drop. I need to pull it out - 2mm. (that number keeps showing up). This side of the gantry is also easy to raise up without the power on, I can just pull on the XZ Main and the gantry raises up. Strangely, the other side of the gantry goes down just fine when I power it off, but I can’t pull on the XZ Main to get it to go up - that just stretches out the coupler. In order to manually raise this side, I have to turn the leadscrew (which turns easily by hand).

In reading other posts, I have loosed up the screws holding the XZ Main to the XZ and XZ Side Belt pieces as much as possible (just tight enough so the Z rails won’t fall out). I have also backed out the M3 screws on the leadnut about 1 full turn.

One other piece of info, my 3D printed parts are off by about 1.5 degrees in the Z axis. My friend who printed them didn’t realize his machine was off that much. He reprinted both of the XZ Main for me, but I haven’t asked him to do any other parts. Should I? I also am not sure which are the vital ones for the Z Axis. The X and Y axis look good from the Crown Test, if just seems to be the Z that is off.

I know this is a long post but I’m crunched for time - I need to get it running in order to make a Christmas present for my mom. Lol! I could also be way over-analyzing this and the machine is fine as it is.

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Both of those pieces should be sitting perfectly flat on the pieces below, not just touching at an angle.

1-There is a notch inside the XZ part, make sure your Z rails are below in not on it.

2-Lossen the 4 clamping screws on each part. If you tighten them incorrectly you can angle the Z rails incorrectly. Are the tops and bottoms of your Z rails equal distances apart?

3-Your coupler looks like it might not be long in this world. Make sure your leadscrew and stepper shafts are touching.

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The long pipes might also be tightened in place, but with tension and not flat. I’m not the expert in this, but I think Ryan has said those pipes should rotate by hand with a moderate grip. If they are tighter than that, one kight be tightened down, and twisted, which is lifting the other end of the part.

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Wow! That was fast!! Thanks Ryan!

1 - Yeah, I have the Z Rails butted up against the notch in the XZ and XZ Side Belt parts.

2 - It looks like the Tops and Bottoms of the Z rails are off a bit (hard to measure quickly without taking it apart). I will loosen the screws as much as possible. I had them loose enough at one point that the Z Rails where falling out. I’ll go to that point again and then tighten them just enough so that the Z Rails don’t fall.

3 - My couplers on both sides are a little messed up. At first I didn’t have them installed properly and they got stretched during some badf testing. I need to order new ones from you (I have them in my cart already with stuff to make a MP3DP, lol).

I’m guessing I should have ordered the 3D printed parts from you for this and not have it done on a machine with a 1.5 degree Z axis (I think it was Z) deviation. I’m thinking that’s part of my problem. Another possible problem is I cut out the Flat parts by hand using a printed template. I’m guessing if the holes for the 3D printed parts aren’t exact that will throw things off as well. I think the first thing I use my LR for is to make it’s own flat parts. Do you think it is “accurate” enough at this point to do that or should I keep troubleshooting??

Again, thanks for your help and this amazing machine!!

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I’ll check that as well Jeff, I’m open to checking everything at this point! Lol.

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Well, I figured out the 2mm difference across the width of my table, my Unistrut rail on the far side of the table is 2mm lower then the one on the near side. I put a 2mm spacer under the wheels to temporarily block it up and not my measurement across the width of the table is accurate to 1/100th of a mm! I’d say that’s pretty damn good!

Edit: after running it up and down a bit and testing at different Z heights (Zero, +30 and +50) it looks like I’m off about 0.6mm across the width of the table now. Good enough I think until I build my own MP3DP and reprint the parts myself.

Now I just have to get a 2mm spacer to put between the XZ Main and the Y Plate on the far side so at least my Z zero will be closer.

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I still have the same issue. Never could get the top piece to lay flat. the front rail has a gap like the problem listed above.

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@Jeff, what’s the Project for you mom? If you can just start the motors reasonably square and the project isn’t large, the middle of the work area should be just fine.

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Jeff, I think I’ve got it close enough now. I’m making her a “Christmas Tree” display stand to hold her Department 56 Dickens Village. She has over 50 houses for it and really no good place to display them in her new house (she just moved in). The tree I am making is about 7’ tall and 48" wide at the base. I’m routing out the “limbs” and the circular platforms. Here is what I have done in Fusion 360.[attachment file=“Tree (2).jpg”]

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Wow. That is a nice big project. Luckily, it’s all through cuts so the Z shouldn’t be a problem. I know you’re short on time, but take it slow. I would definitely cut out a test piece and check the dimensions on it. I would also try to mimic the joints in a small test piece with the same material, to make sure you’re dialed in. Then cut it one piece at a time, making sure to test and measure everything along the way. Remember that sand paper and glue and paint can forgive a lot of problems and don’t point out your mistakes, you’re the only one that will notice them. And please take a lot of photos :).

It’s going to be a lot of cutting too, but don’t leave you’re machine alone. They are more prone to fires than 3D printers.

Looks awesome. Have fun!

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Thanks for the tips Jeff! This is my first CNC project (and my first Fusion 360 design) so it’s a steep learning curve!

Ive been doing a lot of reading on these forums to pickup tips.

Delivering it late will be better than having things go sideways (or burn down)!

I am doing the final project out of 1/2” and 3/4” cabinet grade Maple plywood. I have 3/4” thick pine boards that I will be testing with.

I will definitely take lots of pics and some video as well. Thanks again for all your advice!!

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This makes me ?. First test in styrofoam. I did the Crown test but forgot to tell it how thick my material was. Anyway, it seemed to work like a champ! I even had it doing tabs and I used G92 to set X0 Y0 Z0 to my manually centered starting point. I think I’m actually figuring this all out now!! (Thanks to the help on this forum)

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Yes, it looks pretty good. Makes me smile as much as it does you I am sure about that!

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Everything seems to be working well now - except, the far side Z axis won’t stay “up” if I leave the machine turned on and walk away from it for a few minutes, it must slowly just fall back to zero. Any ideas?

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That is correct, unless your steppers are energized, then they should hold. If unplugged on not moved (energized) the Z should NOT hold itself up.

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Depending on your firmware version they will only stay energized for 6 or 15 minutes, then they will automatically power down if not moving.

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That explains it! I am walking away for at least that long (with the machine plugged in). The far Z will fall on its own, I still don’t know why the near one will not go down (except if it is told to go down in the G Code or by the LCD). When unplugged, the near Z axis will stay up and won’t go down. I still have to “pull” the bottom of the Y Plate out a bit to get it to go down. I’m thinking it’s due to the inaccuracy of the 3D printed parts and my manual cut out of the Y plate. Any other thoughts?

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Usually just the weight of the router, or the side it is nearest. If not tension is just greater on one side than the other, not typically an indication of anything wrong with the build.

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Thanks again Ryan!!! I think I’m just being overly paranoid. Lol. It definitely seems to be running properly.