As the title says, after running some cuts and finding inconsistent depths in different parts of the cutting area, I decided to run a small experiment. I used Octoprint to probe the height of my spoilboard along a 5x9 grid (roughly 4’x8’ total cutting area) and the results are as follows:
As you can see, the first half is quite lower than some of the spots in the second half. Maximum difference is of about 3.1mm. This is enough to cause (I think, correct me if I’m wrong) a significant difference in the load that the bit feels when cutting. Imagine you want to cut with 1mm DOC, you have pretty much two options:
Start the job with the bit close to the material, in which case some of the passes will have 1mm DOC while others will have up to 4mm DOC. Seems a bit ridiculous.
Start all jobs with enough clearence=max difference. The thing is that if you do 1mm passes and only a slight portion of the spoilboard is elevated (as is my case), you end up with unnecessarily long jobs with the router cutting air. Seems ridiculous as well.
Of course any intermediate option will balance both pros and cons, but they seem ridiculous as well, I want consistent DOC and as short as possible runtimes
So I figured the solution is to surface the board. The main question I have right now is: how do you surface over the screws holding the spoilboard to the actual table? I built the parametric torsion box and have a spoilboard attached to it with screws. Should I drill a hole and have the heads sink deeper than the pass will be? Or how would I deal with this?
Also if anything I said is wrong, happy to learn why. And happy to take whatever advice you have for me at this stage. It’s my first build and would be my first usable CNC.
Exactly, unless you’re going to glue the spoil board down and I wouldn’t recommend that.
Something you might want to check before you start - is your router absolutely 90 degrees to your table, in all directions? Many of us have to shim it in the mount by a small amount to make it sure it’s true. There are various prints on printable to mount in the collet to help accentuate snh tilt to help correct it.
If you don’t what you might see when you surface is steps or tram lines.
Yes surfacing the spoil board. It is usually done with larger bits designed for taking a wide swath of material. Searching for “surfacing router bit” will usually bring lots of results.
It’s advisable to do it in shallow passes. Deep passes can tax a router or even burn it up.
It can be helpful to first apply some type of coloring, or pencil markings, or some type of marked or painted grid, so you can tell when you finally got it all done. As long as any islands of your pre-marked coloring remain, you know you have not gone deep enough.
It produces a ton of MDF dust, which is not good for human lungs. Nasty, nasty stuff if you breathe it. Be sure you have solid dust collection place, that you wear a respiration mask, and that you keep tabs on your collection bin, as it will fill up quickly.
Once you get your table flat, consider adding a new secondary spoil board on top, so that when you later have too many digs/gouges in it and need to replace it, you won’t have to repeat the whole process.
Yes, I was planning on tramming the router before. I was aware of the print by Ryan to check for alignment but I’m not aware of any prints to help tilt it. Is there any “default one”?
Also, now that I think about it. there might be sort of a “chicken and egg” problem with tramming and surfacing since an uneven board might not indicate tilt correctly. Granted this is surely small and one can first tram, then surface and iterate if needed.
is it necessarily going to produce dust? I read somewhere that surfacing with the appropriate chipload produces chips instead of dust, but I might be wrong.
wouldn’t I need to surface the upper board as well? I suspect my board is uneven due to the base material not being the same exact width at all places
I use 1mm passes with my 1" surfacing bit. Try to find your highest spot to do the touch off though. I forgot about that part and my 1mm pass turned into a 3mm pass real quick.
Maybe you can get larger chunks than I got. Remember that MDF is basically dust that has been glued together with chemicals and you’re going to be disturbing/ freeing the chemicals no matter what chip load.
You flatten the existing top. Then you put a flat piece on the flat top. MDF is flexible. It conforms to whatever shape you put it on. If you put a flat piece of it on a flat table top, then the new piece is also gonna be flat. You should not have to resurface a new piece, if put onto a surfaced, flat table.
I think so, but remember what @barry99705 mentioned about doing your Z probe/ touch off from the highest point on the table. I made the very mistake he’s talking about. I started off with a 1 mm depth of cut, but as it climbed into higher parts of the table, it turned into a much deeper cut. I did not realize it and I literally burned up a router.
I think that in one of my videos that displayed/ mentioned my feed rate and other details for a spoil board surfacing. But I’m not positive. I may try to check here in a few minutes.
Sorry for the late reply, I got tied up with life and other things and could not focus on the LR3 for a while. If it helps: to do this, I decided on NxM points to measure my table at and set up a grid accordingly (that is, give each point x,y coordinates in actual mm). Then, start by homing all axis and, for each point,
go to its x, y position
G28 Z0 to home Z axis
do G38.2 Z0 to probe the min z with a touch probe (you can do it a few times per point and get the average if you want, but I think it’s overkill)
M114 to print coordinates (note them down)
I created a script in python that does this if you input a few variables like N and M, but it’s pretty pointless without this other OctoPrint plugin I created that reads M114 prints and writes them to a log. I can look for it, but it’s pretty barebones and you do have to be running OctoPrint in the first place.
Then, with all the measurements, take the average and subtract it to every number. You’ll end up with a grid that tells you how far off it is from the average height of the bed. I plotted it using matplotlib.
