[Gareth52]

Hi,
My machine is working very well for general use, But now I am trying to v-carve pictures in wood and am having limited success. Since the max depth of cut is 0.04", I probably need to set up my z axis more accurately. Obviously I cannot do this with the steel ruler that I have been using.

What type of measuring device do I need to obtain such extreme accuracy?

Thanks,
Gareth

[PaulRowntree]

If you are asking about calibrating the movement of Z (steps per inch) ...

A dial indicator is a std way of measuring movements, easily to 0.001", often 0.0001". It is pretty obvious how you can set it up to measure Z movement, and you can just jog Z a given number of steps then measure the actual displacement.

Do you have a decent vernier?
1) use your approximate calibration on Z to machine a flat surface on a piece of wood, as thick as possible. Call this Z=0.00
2) pocket the wood by a chosen depth according to the approximate calibration. Make the pocket as deep as possible for highest accuracy. Make sure your Z is not going to hit the table before starting the program.
3) measure how deep the pocket really was, and use this to adjust Mach3's calibration factor. If the pocket was deeper than expected, you need to reduce the steps per inch settings.

When carving images (PhotoVCarve?) it is just as important to have the absolute position of the tool properly referenced to the top of the work piece. Are you using a ZeroPlate of some description? IMHO this is a bigger source of error than the calibration, since even an approximate calibration will be within a percent or two. Z=0.00 has to be right to within a few thou.
Cheers!

[Gareth52]

Hi Paul,
Thanks for your reply. My vernier caliper is not digital and not good enough for truly accurate readings. Since I first posted, i have ordered a dial indicator, which will hopefully solve my problems.
Yes I have a homemade zero plate, but for v-carving photos, I have been just using a piece of paper and jogging to zero using .001increments. I think that this is about as accurate a z zero reference as I can get.

Cheers,
Gareth

[adprinter]

If you are talking engravings into WOOD, I can tell you from experience, that this will be the ultimate "test" of the acuracy (and consistency) of your machine.
IF it is acurate, and consistent (repeatable movements to EXACT locations are essentail for engravings). Then the other thing that experience has taught me, is that there is no such thing as a "Flat" piece of wood! For the best results, clamp the wood stock to your table, and run a pocket program to "plane it down flat". Usually about 0.010" should do the trick. Once you have done this, you will have a consistently "Flat" surface in relation to your machine. (Provided that you immediately run your engraving program- don't leave it clamped overnight, and expect it to still be flat the next morning). I have learned, that wood is constantly "Squirming". It swells, twists, and warps with the weather. Temperature and humidity changes throughout the day (or night) and it effects all wood. Even if it has been kiln-dried, it is still an unstable material for very delicate engravings (such as photographs, etc.) I frequently do letter engravings as small as 12 point type, with good results. But it does REQUIRE a precise surface to work with, with a depth of cut of only 0.007" To cut ANY deeper renders the hole in a lower-case letter "e" as simply a hole "drilled" into the wood. As opposed to the outline of the hole in a lower case "e". The acuracy, and repeatability I mentioned become very important, should your first attempt not be deep enough into the stock to achieve the desired results. You can simply change the cutting depth, regenerate the g code, and try again (which will cut slightly deeper into the wood stock at the EXACT locations of the first attempt).