Monday, October 10, 2011

Double-Sided Milling with MeshCAM

For those interested in my discoveries in how to do two-sided milling with MeshCAM, here are my notes:

Secure material to spoiler board with either double-side carpet tape or masking tape on all sides.  Remember, if you put double-side tape under the model to start with, you'll need to be sure to use it on both sides so that that Z height doesn't change (or re-zero the Z axis after flip if you don't use it on the second side)

Zero x0y0z0 at lower left, top(z0) of model, but leaving room to drill registration holes in -XY areas

Determine best distance from center of material for registration holes.  Best locations are equidistant from the Y centerline, outside the millable area.
Example: Millable Area=1.75" square and 0.75" tall:  First Pin=x-0.25y-0.25 Second Pin= x-0.25y2 (z-1 = 0.25 into spoiler board)

Optionally, add two extra pins at x2y2 and x-0.25y2 to further secure the model so it will not move.

Manually drill registration holes by jogging the machine to the proper coordinates and drilling down through the material and into the spoiler board in one operation.

Install registration pins through holes in top of material, taking care to be sure they sink all they way into the spoiler board holes you just drilled.

Mill Top or Bottom

Flip in Y axis, line-up holes in material with pins to registration holes in spoiler board, secure material.  So, the edge that was on the bottom is now at the top after being flipped.

Mill other side

*Milling notes: 

1) I used registration pins that were shorter than my model (just 0.125" round brass stock, cut into short pieces).  Since they sink into the spoiler board about 0.25", they are below the stock surface.  With the vibrations generated via the actually milling a couple of them started rising up in their hole and sticking out above the material surface.  Obviously, if they have come up more than 0.25", they are no longer helping to keep our material centered.  I ended up stuffing some wadded up masking tape balls into the holes to keep them in place. 

2) Before you start, test the bit/end mill you plan to use to make the registration holes on the drill press.  Even though I tried four different 0.125" bits (end mills and drill bits), only two of them produced a nice, tight registration hole.  The others produced holes that were too large and would allow too much play, causing side-to-side registration issues.  The winners for me were both end mills measuring about 0.124" in diameter (one two-flute ball-nose and the other a four-flute flat-nose).  The surprising last place choice with too much wiggle room was an actual 0.125" drill bit.

1 comment:

  1. Hi John- I'll just reinforce the what I think are a couple of the most important things for two sided milling:

    1) Accurate measurement of the stock. Because MeshCAM does all of the math internally to flip the model, any miscalculation will absolutely show up in the finished part.

    2) If you can, use the center of the part in the Y dimension as the program zero. Since this is the point that the stock is flipped around, using it as the program zero tends to eliminate some of the measurement problems in the Y direction.

    3) When combined with #2 above, two alignment pins will really help out a lot. I prefer to use precision shoulder screws that I get at McMaster Carr so that I can combine clamping and alignment in one part.

    If there is anything I can do to help out, let me know.

    -Robert (MeshCAM Developer)