Another thing to watch out for is that while this tester does help you adjust your bit to perpendicular, it doesn’t really help with getting the z axis travel perpendicular…
Yes, I’ve been trying to figure out how to adjust this but have not been able to come up with an “easy” way. As you can see in the photo, the shim is not that thick and is placed between the spindle holder and the Z-gantry tube.
Tweak your leg heights, right?
Adjusting the z rails and z motion relative to the plane of x/y motion would not be affected by leg height. I think it can be fine tuned to some degree by the tension bolts ABC but I have not paid attention to the details of which bolts move which way.
I was assuming if the z isn’t perpendicular to the bed the xy plane is probably off.
When you level the spoilboard, XY will be parallel; however, if the Z is not perpendicular, you will see lines along the tool path caused by one side of the bit being slightly deeper than the other.
Alright, this will take some modeling (and trial and error) but I think I know what to do to adjust the Z-rails. I’m going to modify the top and/or bottom parts of the gantry (in my case, I only need to modify the bottom part) to add set screws that will allow the bearings on the top and bottom parts to be moved front and back (by no more than 1-2 mm) - specifically, the set screw will allow the bearing to be moved to the front. The Z-rail can be kept snug by loosening/tightening the screws on the front bearings.
I’d like to hear Ryan’s take on this, if he has any issues before I spend the time.
Don’t know if this will make more sense as to what I’m thinking, but the photo shows the top (XYZ_J_burlly - modified) partway printed to show where the two set screws will go plus the widened (by 2mm) screw hole.
Keeping an eye on what you’re doing - interested to see if it has any affect…
Did you increase the diameter of the hole for the bolt (to allow the set-screws to push it forward)?
Not the entire diameter, just widened it perpendicular to the set screws.
This shouldn’t be needed. Tightening that screw should pull the other two bearings closer to pull that part of the Z back and tighten the grip. Are you trying to adjust the Z separate from the tension?
Yes. I originally adjusted the spindle perpendicularity using the dial arm from my first post and used shims to adjust such that the bit/spindle is perpendicular but the rail movement is still not perpendicular to the XY plane. The modification will (should) allow me to adjust the z movement while maintaining proper tension on the bearings.
While I’m confident the modification will work (the mechanics are straight forward and I did a test fit with loose parts), I’ve decided against installing it on my machine. I did a test cut a 80 mm (L) x 80 mm (W) x 40 mm (H) cube with facing operation on the top.
This tells me that, for what I need, my MPCNC is dialed in to tolerances well beyond what I could use it for and I should just “let sleeping dogs lie.”
If anyone is interested in the part, let me know and I’ll post the obj. file - I only modified the top part, which allows the Z rails to be moved from the original position towards the negative X and Y (i.e., spindle movement in the positive X and Y direction).
Do you have the dual endstops setup on your machine? I ask because I didn’t have them on my machine at first and my original test of XY perpendicularity seemed really well dialed in. Later when I did some real parts (this was in metal, so less forgiving than just wood carving) I noticed some very real out-of-square issues (not horrible, but measurable and noticeable). The worst part, for me, was that the skewed-ness wasn’t consistent from run to run. I’ve recently bitten the bullet and installed the dual endstops and auto-squaring. I’ve not yet run any parts with that configuration, but I’m hoping it will hold tolerances better than I was seeing before.
Just my experience…
The machine can easily rack when the motors are off, or if you ever skip steps. The key to square cuts is having a consistent starting procedure that includes having the gantry in a specific location when you start the motors. After that, it will move in lockstep, until you skip a step. It is the same principle as the dual endstops, just less automatic.
I do have the dual endstops setup and I spent quite a bit of time adjusting X-Y movement with no issues since dialing them in, very consistent.
Alright, the verdict is in - figured why not install it, I already printed the parts! So I did… and it works like a charm! Here are some photos showing the dial reading after adjusting the set screws. I ended up installing top and bottom parts. The set screws have a teflon lock-nut on the inside and a nut on the outside to lock the screw once adjusted. Basically the set screws push the main screw/bearing against the Z-body conduit pushing it in the negative direction or releasing it, to the positive direction. I used 2 set screws to have one on either side of the bearing for better adjustment.
Looks nice but isn’t that a too long lever that will minimally bend anyway?
I was wondering the very same thing. Even when I use a metal rod to attach these kind of gauges, the reading vary a tiny bit, so I’m pretty sure plastic will be even less accurate…
isn’t the bend going to be the same in all directions though?
It’s only 15cm long and the profile has a spine to minimize bending. That’s not to say it won’t bend, but if it does, it’s negligible, e.g., a few thousands of an inch…
