Depth Adjustment

[redandbon]

Hello CNC'ers:

I am having nightmares trying to carve text to the proper depth in 1/4" lucite. See photos. I have set the depth using a V-carve toolpath and a 60 degree v-bit. As you can see, the top line of text is fine, while the bottom line is not. In particular, you cannot read the year 2018. I'm really scratching my head on this one. Any help would be appreciated. Thanks.

Red Mulvanny
Murrieta, CA

[gkas]

Your spoilboard is not level. You need to plane it.

[adze_cnc]

Your spoilboard is not level.

Perhaps level is not quite the right word? It could be dead level and this still could happen---if the Z-axis of the machine is not perpendicular to the centre of the Earth.

Technically, I suppose, one could say the XY plane is not perpendicular to the travel of the Z axis at a set Z height. To sum it in a word I'd use: "true".

For the original poster: you probably should make sure, as gkas mentioned, that the spoilboard is surfaced true. But...

Notice that "Red" is almost OK but the letters around are less successful? This to me questions whether it really is an uneven spoilboard---why would it be that uneven is such a small area?

Was there a build up of Lucite on the bit? "Red" and "Merry Christmas" all look "smooshy" as if they were abraded/melted by "skudge" stuck to the bit. Perhaps they should actually look like 2018 and the other names?

Is the Lucite of a consistent thickness? Why are the faint letters still of an almost acceptable width but have no apparent depth?

[SteveNelson46]

It looks to me like everything is too deep. Instead of a v-carve toolpath try using a profile toolpath on the line.

[FixitMike]

A diamond drag bit works well for engraving acrylic, and the spring loaded diamond compensates for varying thickness of the material. I use the engraving toolpath with the depth set to half of the total compression available on the drag bit. (If it compresses 3/8" maximum, set the Depth/Pressure to 3/16").

The preview that I get isn't very good, but the results are nice. (Better than the photos.)

[LittleGreyMan]

V-carving and carving on the line will be very sensitive to height variations: spoil board, machine not square, acrylic not strictly flat, not correctly hold on the board, …
Cast acrylic is better than extruded for carving, but less constant in height.

That's why using a spring loaded diamond drag bit as Mike suggested is often the best solution. Vectric products have a specific toolpapth for thi: the quick engraving toolpath.

[redandbon]

Thanks to all of you for suggestions. I'll take them and make this work.

Red

[martin54]

Machining acrylic well is a lot more difficult than machining wood, things like speed & feed settings are far more critical, so is good chip evacuation
Re-welding of chips is a common problem people have when they don't have a good way to remove dust & chips.
Easiest solution as Mike has pointed out is a diamond drag bit but you can get good results with a bit of experimenting. Sharp bits & good dust removal are key, if you don't have a good extraction system using an airline to blow chips from the cut works well & helps cool the bit