Decreasing machining time in 3D carving

[phil_o]

On the Vectric forum there is a thread discussing a method for decreasing machining time when carving in 3D. The poster uses Mach 3 and he increases the Z and X axis acceleration but not the Y. I don't really understand this very well. The link to the thread is below.
I'm wondering if this is workable in SB software.

http://www.vectric.com/forum/viewtopic.php?f=28&t=4220

[stevem]

Here's the short version: If you increase feed rate by 100%, you reduce machining time by 50%. If you increase acceleration, you also reduce machining time. This assumes that your machine will function reliably with the increase in speed and acceleration.

[dubliner]

and in particular, concentrating most of the movement to the Y & Z in our case. I've tried to do that a few times based on having seen a Carvewright cut 3D at probably somewhere from 8 to 12 ips with surprising accuracy, Mind you it did break a lot more than my 'Bot :-)

[harryball]

I read though that... sounds like you just set your acceleration to the maximum your machine can handle per axis and let her rip... err cut.

/RB

[jhicks]

Well I think the most significant change from my experience is the change in Z acceleration and plunge rate. Given that one has pretty much optimized the X&Y acel rate for your machines max effectiveness, the limiter will be the plunge rate and Z acceleration since it will restrict the X or Y to keep pace with a slow Z.
Therefore one may often see the machine actually moving slower than the planned move speed because the slow Z has "the brakes on" regulating X&Y to pace the slowest of 3 axis moves.

Since 3D is generally both shallow and small stepover an increase in Z really is not a problem like it might be plunging deep into hard maple for example.
This is particularly true in foam and the like.
The key is to really understand where those Deep Z plunges are going to show up. Like the outside edges of a steep straight edge for example.
So if one starts the cut file at the highest elevation (usually the inside moves) and progressively moves in an ofset manner, each pass is only a slight increase in depth generally but if you have a slow plunge and Z accelleration you are driving with the one foot on the gas and one on the brakes.
(Raster covers all depths every pass but can still be used. Its the 1st pass Max depth one has to watch out for)
So test the same file with one Z plunge at 35 and one at 65 to see the impact on your run time.
Too much of an increase in the X&Y acel rate can make the direction changes a bit abrupt and create some gantry flex or bit flex as well so its all about dialing in the best for your machine and desired results.
We have a standard plunge at 35 IPM on the Z for most cutting but when on a 3D we increase it to between 45 and 65 depending on the relief and stock being cut.