I’m hoping to get a little advice here. From the day I got my pro xl, i’ve had trouble trying to get a perfectly level wasteboard. I use a secondary mdf wasteboard that i screw down to the mdf slats and surface that on a fairly regualr basis. For most of what I do, regular surfacing has been good enough but i’ve started making epoxy coasters and after running one or two surfacing passes to remove the epoxy, i end with a inconsistent surface, typically a difference of .01-.02. Any tips on what i can to do improve this? Would tramming help? I’ve always been scared to attempt that in case i make things worse.
Could you post a photo showing how the secondary MDF wasteboard is attached/mounted?
Ive just attached it by screwing it down to the mdf slats. Ive also attsched a photo of what happens after a couple of surfacing passes. The weird thing is, i can run the hello world test and it looks great yet i have problems like this when cutting.
How do you attach your coaster stock to the upper waste board? Reason I ask is that it may be possible that your waste board is flat, but the coaster stock is not being held down flat against the waste board.
If the coaster stock is being held down to the waste only at the corners, it is possible that you are creating a bow in the coaster stock because the downward force is only at the corners so the middle is higher than the corners (does that make sense?).
If the pictured coaster was originally in the upper left corner (from your waste board I assume you make 4 at a time) then that would explain why the lower right corner of the coaster is thinner than the upper left corner.
The green stuff on your waste board also makes me wonder if you are attaching via two-sided tape. If that is the case the tape may be slowly letting go over time. That assumption is based on the epoxy that you may have this stock on your waste board for several days.
While it’s somewhat tedious, you can measure the Z height at multiple points on your coaster stock and see if there is a variance that you can’t measure on your waste board.
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Thanks for the tips Robert. I’ve been using painters tape a glue as my work holding so my stock should be staying flat. Since the picture posted, I resurfaced my waste board again and tried to surface another coaster and while not as bad as the photo, there is still some inconsistences. You may be on to something however, looking at the new coaster a little more closely, it seems that it’s one corner that’s sloping slightly.
Just out of curiosity, i just surfaced off 1 more coaster on a different spot on the waste board. Both coasters are slightly sloped in the top left and bottom right corners, about a .01 difference on my calipers. Measuring from the 4 sides all read equal. What do think think this tells us?
Sounds like your spoilboard is not level or not tight and moves. It’s really the only thing that would cause this. Especially that much over such a small area
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Thanks for your input. I have my wasteboard screwed down pretty good so i dont think its moving, at least not enough to cause such inconsistencies. Just to be sure though, ill take the wasteboard off, reattach and surface again.
Just from a mechanical perspective, the X and Y are at fixed height to the work surface (Spoilboard). A perfect set up machine will have both axis at the same distance from the spoil board no matter where you are on that board. When one or both of the axis are closer to the spoil board at different locations, this will cause your work to end up with different thicknesses from one side to the other. Because the X and Y are fixed, you have to look at the spoil board for differences. This is why (and I am sure you know this) we surface the spoil board to be parallel to the XY axis.
While its possible that the Z could need adjustments to be square/plumb with the spoil board, it would leave a different signature if that was the issue you were seeing here.
At this point, you might want to surface the spoil board. Go light and you should be able to see the areas that are high or low by where the bit touches or does not. The one thing I see in your coaster pic, is a large change in thickness in a very short distance. This makes me believe it was not clamped completely flat or is was moving. Usually when a spoil board is not flat or needs surfacing, we are talking about a few thousands (.015 to .020" ? ) of an inch over 20 or 30 inches. Not over 3-4" of a coaster. Which is why it leads me to the coaster clamping process.
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One other thing, I would check the V wheels to ensure they are adjusted correctly. If not, certain movements could cause the X or Y axis to rock a little it.
If you are using tape and glue to hold the coasters down, could the glue be thicker in one spot?
That’s a good thought, l’ll keep that in mind when i run my next surfacing job.
Have you tried using a dial indicator or test indicator and running it across the fresh surfaced wasteboard to see if it is actually facing the top flat? You might need to get some cheap screw jacks and mount under the bottom wasteboard and jack it level and then re surface. You might of already tried this but hope this may help
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With a recently surfaced spoilboard, I see very little possibility of anything coming off the machine not being of a consistent thickness. Can you try a different workholding method like double sided tape? And also, I second the dial indicator idea to confirm both the flatness of the MDF, but also your workpiece. Is it possible that the epoxy and finishing has caused the coasters to warp at all?
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Just curious if you ever surfaced the hybrid table MDF slats because if not and you surface an extra wasteboard as you have it would be parallel/flat at first (with the spindle), however if you move or rotate this extra wasteboard the result could be the unsurfaced hybrid table coming back to haunt you. I’m thinking when you screw the mdf board to the hybrid table it’ll bend and take it’s shape and if it’s uneven then your extra wasteboard will not have 2 parallel faces and could cause issues if not installed in the exact same location/way as it was during the last surfacing job.
Also wondering what you do to prep your stock like do you surface the side that is going against your wasteboard? If there is any cupping in your stock you will have a high point and it will result in thinner areas on your coaster. Also wondering if you stock is dry enough (humidity level), if it’s has high humidity it can cup/warp over time so if it’s a few days between the initial carving → epoxy → back on CNC for surfacing maybe there’s enough time to experience movement in your workpiece/coaster. For example recently I was carving a rather large part with the tape/glue workholding method and during a toolpath I noticed toolmarks cutting deeper then expected. At first I thought I had a Z height issue however I then notice a small void beneath my project in the 1 corner. This is when I realized the project was on the CNC for 3 days and starting cupping/warping in the 1 corner and the tape workholding started to release. Therefore I had to clamp down the edges to hold it flat.
Thanks for the suggestion Winston. I haven’t had time to to make any new coasters but when i do I’ll check to see if any warping has occurred after pouring the epoxy. I’ll also try double sided tape. What I’ve been doing is securing my stock with tape and glue, cutting out the coaster, pour the epoxy while coaster is still on the wasteboard then surface the excess epoxy at the end. Maybe something is getting warped somewhere along the line.
I appreciate your insight Patrick. Since I’m pretty new to wood working I’ve been buying pre surfaced, or s4s i think its called, so I haven’t been doing anything other then cutting stock down to size and securing it to my wasteboard. I surface my wasteboard but not the mdf slats. I recall inquiring about that when i first got my machine and most folks said surfacing the slats shouldn’t be necessary. My epoxy process sounds very similar to what you were describing, After the coaster is cut out and still secured to the wasteboard, i pour the epoxy and let it cure before finally surfacing so its on the table for a few days. I noticed the inconsistent surface finish mostly at the corners as you were describing so maybe it is in fact warping on the table. I will keep a close eye on this for my next batch to see if I can get this sorted.
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