How to do a surface skim, for this project

[nlalston]

This is a project that I designed up as a gift to my mother-in-law.  It was carved from a 20" square piece of 1/2" MDF, with a .125 DOC.  My initial intent was to Oramask the surface, but wound up having a fight with that masking material.  As such, I moved away from that, and just did a bare carving in the MDF.  I spray painted in the surface, after sealing the piece.  Now, I need to do a surface skim the board, so as to have just the carved areas with color.  My question is this: What's the absolute minimum setting that I should have my surfacing bit starting at?

Advanced thanks.

[eagle55]

My feeling is that if you sealed the MDF before painting it hopefully didn't penetrate the surface. I think I would just use a random orbital disk sander with something like 180 or 220 sandpaper. And sand the paint layer off. I have virtually no experience with MDF (by choice) but do this with real wood (sealing before painting) and Corian (no sealing needed) and it turns out great. My feeling after doing on epoxy reasin inlays is that you begin to loose shallow parts of the engraving if you take off too much, which can happen easily if you remove the piece to paint and them put it back on the bed. Sometimes you don’t get it mounted perfectly flat on the table. If you still maintain that you want to surface it, I would create a surfacing tool path of .001 or .002 and if the first one doesn’t get it all, re-zero the Z axis and runn it again until it comes clean. I guess it depends on how find the small details are. I did a 4” diameter coaster that if I tried to surface .002” and I had a error of .003 not getting it perfectly level when I put it back on the bed, I would loosbig areas of fin detail.

[eagle55]

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[nlalston]

Dec 22, 2023 9:48:58 GMT -5 eagle55 said:

My feeling is that if you sealed the MDF before painting it hopefully didn't penetrate the surface. I think I would just use a random orbital disk sander with something like 180 or 220 sandpaper. And sand the paint layer off. I have virtually no experience with MDF (by choice) but do this with real wood (sealing before painting) and Corian (no sealing needed) and it turns out great. My feeling after doing on epoxy reasin inlays is that you begin to loose shallow parts of the engraving if you take off too much, which can happen easily if you remove the piece to paint and them put it back on the bed. Sometimes you don’t get it mounted perfectly flat on the table. If you still maintain that you want to surface it, I would create a surfacing tool path of .001 or .002 and if the first one doesn’t get it all, re-zero the Z axis and runn it again until it comes clean. I guess it depends on how find the small details are. I did a 4” diameter coaster that if I tried to surface .002” and I had a error of .003 not getting it perfectly level when I put it back on the bed, I would loosbig areas of fin detail.

Thanks, Roger.
 
It turned pout that I did opt for the surfacing manner, for the project.  I do have an old, Random Orbital Disk Sander, but didn't have the proper connecting elements for the smaller dust port of that tool.  As such, I went the route of (as mentioned) surfacing the MDF, due to the feelings that my dust collector would mitigate at least SOME of the concerns over the properties of MDF.  I LOVE the way that it carves, but don't care at all for the dangers that it emits (and I won't use it again).  I DID follow your DOC settings suggestions, and things did go well - regarding that.  Being impressed with the outcome, I took it off the CNC's bed, to do a little something else.  Then, I thought about something.  My mother-in-law lives in another state, meaning that the project will have to be shipped to her.  To minimize shipping costs (even to a small degree) I settled on drawing up a circular profile cut, to separate the body of the project from the four corner areas.  During this cutout, my EM ran off the cut line, and wrecked the work.  The bit biased about .75 to the right, (also as just mentioned) ruination resulted. I brought that up due to your having spoke about what could happen, negatively, if a project piece is removed from the CNC - for whatever reason, and placed back on the bed to continue with a carving procedure.  I really THOUGHT that I was lined up being exactly where it was before. But, apparently not  .

Another experience - another thing learned  .

MERRY CHRISTMAS.