Z axis inconsistent

I’m pretty sure I already know the answer to my question but just seeking confirmation. I am having problems getting consistent depths at different points of the machine.

  1. It is not intermittent. I don’t believe I’m losing steps or anything. Depth of cuts near home position are accurate but as the machine moves to the right it becomes inaccurate.

  2. I checked the Inventables support (https://inventables.desk.com/customer/en/portal/articles/2090921-depth-is-wrong). Can mark all of those as checked except for wasteboard level/flat and material flat (see later).

At first I thought it was the material because at first I had a had a sheet of 1x12 from Home Depot that was not flat (tried forcing flat as best as possible with clamps during cuts). I finally finished using up that piece and got a new piece that was flat as can be and still had issues.

So I finally had a chance to sit down and really test some things after reading many threads here. I clamped down some MDF and drew a sketch that had 3 circles of different depths (.100 .200 and .300) deep in each corner of the board.

You can kind of see one lone black dot in the bottom left. That was home.

Front Left - .001 too deep
Front Right - .034 too deep
Back Left - .024 too deep
Back Right - .047 too deep.

I took the spindle to the back right corner and zeroed the z onto a washer I had laying around and moved the spindle around the board and tried sliding the washer underneath at various spots and found that the wasteboard is definitely not flat. (Right side higher than left side. Right side is deep in the back, gets shallower, then deep again at the front. )

So the answer to my question I am pretty sure is to skim cut my board, right?

With that in mind, I am planning to do a few mods and in particular a new table (possible torsion box), dust shoe and y axis sitffening (x is done already). Since I am going to be doing those and possibly moving the spindle up and down to get the dust shoe fit just right, and the wasteboard may move or sit different on a new table and with supports securing it and the Y axis… I probably want to either A. Skim cut the board for now and then reskim it after doing those mods or B. Leave it as is until I finish the mods and then skim it?

Once again I am pretty sure I know the answers I will get but just seeking confirmation (I don’t want to skim off the nice Inventables grid lines =( but it seems necessary).

Is your wasteboard level? In relation to the spindle…not to the ground.

Sorry I accidentally posted before I was done typing the post. I edited it and think I addressed your question.

Wasteboard and X axis level to each other.
Wasteboard and bit appear to not be level to each other.

You could attack a sacrificial wasteboard on top of the nice one and level that one…that is what I did.

I found that the middle of my wasteboard was about .030" lower than the left and right sides. I originally had a melamine secondary wasteboard on, but ended up replacing it with a thinner MDF secondary wasteboard and used a 3/4" flat bit to cut a level pocket in it.

I made a video on how to do it, if you want something to think about. I also addressed a couple issues in the video, such as how to read the lines left by the large bit to determine if the spindle was truly square to the wasteboard. X-Carve Maintenance/Troubleshooting Videos - Add Your Own!

Since you’re thinking of a torsion box, here’s what I did with my 1000x1000 xCarve:

  • Build torsion box, used 3/4 plywood for the top, didn’t put a bottom on it, so it’s more of a torsion ladder. I used 1x3 for the vertical parts of the box, and it is dead flat and super strong, so I didn’t need the bottom of the box.
  • Remove the base frame from the xCarve.
  • Remove the middle base frame makeflide member, the one that supports the wasteboard in the middle.
  • Clamped the base frame to the top of the torsion box, squaring it up carefully using a known good square (check it first!)
  • Marked the top of the torsion box where slots were in the ends of the left and right sides of the makerslide.
  • Took the frame off the torsion box, used a known good (I checked) straight edge to connect the marks representing the slots are.
  • Drilled slightly oversize holes through the 3/4 top of the torsion box, cleaned up any blowout, so the surfaces were smooth.
  • Added pre-insertion nuts in the bottom slots of the makerslide frame, I think you can get these in even when the frame is assembled, but I had taken mine completely apart, alternatively, use post-insertion nuts.
  • Using appropriate length bolts, with washers, bolt through the torsion top into the nuts you inserted in the frame, don’t tighten things up.
  • Now, carefully checking square as you go, tighten the bolts until the frame is completely square and secure.
  • At this point, I took 3 pieces of Rockler T-Track, cut them to fit inside the frame, running front to back, with a 1 inch gap at both ends (so I could get the t-bolts in and out when I want to move them), more or less evenly dividing the area into 4 more or less equal parts (hey, I was rushing it by this point!!).
  • I took my old wasteboard (which I had made, I didn’t buy the inventables one), and cut it into the four pieces I needed to fill in between the t-tracks, shortening it so that it would drop into the frame, the left and right ones need extra relief for the corner brackets. You really want this to fit loosely at this point, if it fits snugly, you may have some buckling problems.
  • Now bring the rest of the xCarve assembly over, set it in place, and reattach it to the frame, checking for square and binding, etc, as you go.

This has worked out well for me, even though I haven’t yet had the need to skim the 4 wasteboard pieces yet. If you need to do that, you probably want to screw them down (recess the screws!!) first, then when you’re done, make sure you mark the pieces as to where they go and their orientation.