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My MeshCAM Notes for machining brass

PostPosted: Fri Apr 03, 2015 1:14 am
by monolith
Your mileage may differ, but the following discoveries and lessons learned (many from this forum, and Randy's tireless help), have made MeshCAM work for me in machining brass parts. If I had known these things three months ago, I would have saved many hours and many scrap parts:

1) Parallel finishing advances the Z-Axis at the Feedrate (it is not restricted by the Plunge Rate setting, the Plunge Rate setting only affects the initial entry of the end mill into the block). Set the Feed Rate to your maximum desired plunge rate.
2) Maximum plunge rates for brass: 0.25" end mill: 2 ipm (1.5 preferred)
3) Feed Rates (X-Y) for brass: 0.25" end mill: 5 ipm
4) Stepover must be 50% or less of cutter diameter or islands might be left for several passes (up to 7 in my experience). The islands might suddenly be mowed down in a single pass in Roughing (or in a subsequent operation).
5) Capped holes become permanent if the job is Saved (up through V6.25)
6) Area to exclude does not work in V5.45, but does work in V6.25
7) In V6.25 if tool paths are not generated for Top Setup and/or Bottom Setup, try reducing the tolerance (from 0.003 mm to 0.03 mm worked for me)
8) Save toolpath button is missing for Bottom Set in V6.25. Clicking Bottom Set again restores the buttons.
9) The center line of the end mill will not venture outside the confines of the block's X and Y dimensions. If this causes undesirable cutting patterns (leaving material where none belongs), the size of the block can be adjusted to a larger phantom size. However you must remember to account for the missing material when finding the X edge.
10) Two-sided machining assumes two different XZ-datum planes on the squared block. While this is very convenient for quick set ups of the Bottom-side (simply flip block about the X-Axis), it introduces some "pencil width error" in aligning the X-Axes of the top and bottom setups (depends upon accurate measurement of block's Y-Dimension). If precise alignment is important, the same XZ-Datum plane can be used by adjusting the Y component of the origin on the bottom-side of the setup. Aligning the top-side and bottom-side X-Axes is easy if the block is the actual size, and the part geometry is centered in the block. If however, the block is not the actual size (i.e. defined as a larger phantom size as mentioned above), and the part is not centered Front/Back, it will be helpful to know how the XZ-datum planes behave: Front XY position is relative to the Part Zero, but the Back XY position is rotated about the Block Zero
11) My semblance of a "Floor Cutting" pass (to avoid jagged side walls in 2.5D part machining):
a) Define an end mill 0.015" larger in diameter than the actual end mill (this assures me there will be no jagged walls)
b) Run Parallel cuts with a ridiculously low feedrate... equal to the set Plunge Rate (this assures me the Z component of the feedrate will not rocket the end mill into a horizontal surface)
c) Rely on Pencil Cleanup to pick up all of the scallops left on the floors by the Parallel pass

Hopefully some of these concepts will be helpful to someone. None of these points are meant to criticize MeshCAM in any way. This is a remarkably capable and easy system to use! Room for improvement, of course! But thrilled with the functionality I get with such a small investment of time and money!


Re: My MeshCAM Notes for machining brass

PostPosted: Sun Apr 05, 2015 3:14 am
by tgdavies
Thanks Scott, it's great to have real world experience documented like this.

Can you also mention:

1. RPM of spindle
2. Number of flutes on the end mill
3. Depth of cut
4. Lubricant if any



Re: My MeshCAM Notes for machining brass

PostPosted: Sun Apr 05, 2015 12:10 pm
by monolith
Hi Tom

Sure, I'd be happy to share my "non-MeshCAM" notes as well...

End mill selection
- 4 flute (for higher rigidity)
- Material: Cobalt*
* I've tried HSS, and carbine (both coated and noncoated), but have found cobalt to outlast them all. While carbide holds its edge well, the corners chip off during the occasional unforeseen chatter session. The price of cobalt end mills is also very reasonable.

- 1/8" dia. end mill: 10,000 RPM (maximum for Sherline with high speed pulleys)
- 1/4: dia. end mill: 5,000 RPM (approx.)

Depth of cut
Roughing: 0.020" (1/8" dia. or 1/4" dia. end mills)
Waterline (vertical walls):
- 1/8" dia. end mill: 0.020
- 1/4" dia. end mill: 0.050
Waterline (contoured surfaces, ball end mill):
- Fine - 0.005" with step over 5% of cutter dia.
- Normal - 10% of cutter dia for both depth and step over

- None, just a constant stream of air to clear chips

These choices work well for; my mill (Sherline 5400), small brass parts (under 3"), and the types of parts I machine. There are likely other choices which work as good or better than mine for different situations. For example, a more ridged machine and flood coolant would probably allow faster feed rates and greater depths of cut. In any case, my choices are probably conservative, and provide a safe place for anyone to begin machining brass parts.


Re: My MeshCAM Notes for machining brass

PostPosted: Thu May 21, 2015 10:51 pm
by monolith
Here is another nugget that will hopefully help someone...
The feature indicated below was getting machined off in MeshCAM (fortunately caught it in Cutviewer before committing to metal):
feature_monolith.png (40.95 KiB) Viewed 5896 times

I discovered that tightening up the tolerances when generating the STL file in my 3D CAD system (NX 9), completely solved the problem. Following are the settings I used (metric).

Before (part gouged):
Triangle Tol: 0.08
Adjacency Tol: 0.08

After (part not gouged):
Triangle Tol: 0.005
Adjacency Tol: 0.005

Of course the names of these settings will differ depending upon the CAD system, but this will provide the basic idea, and an order of magnitude of what worked and didn't work for me (on a 90 mm wide part).

PS. I checked the Before and After quality of the STL in Meshlab, but it revealed no problems in either file.


Re: My MeshCAM Notes for machining brass

PostPosted: Fri May 22, 2015 3:49 am
by joseph
That's a good set of notes, more like the basis for a complete study guide.

A set to cut out and keep ...

Thanks for that-


Wow, I must be too quick, forum says - You cannot make another post so soon after your last.