> -----Original Message----- > From: N. Christopher Perry [mailto:vwpe...@comcast.net] > Sent: Tuesday, May 16, 2017 5:34 PM > To: Enhanced Machine Controller (EMC) > Subject: Re: [Emc-users] new thread inspired by Christophers question about > 3d printer sliceing SW. > > To answer Ken's question... > > N. Christopher Perry > > > On May 16, 2017, at 2:00 PM, Gene Heskett <ghesk...@shentel.net> wrote: > > > > On Tuesday 16 May 2017 11:56:40 Ken Strauss wrote: > > > >>> -----Original Message----- > >>> From: N. Christopher Perry [mailto:vwpe...@comcast.net] > >>> Sent: Tuesday, May 16, 2017 10:07 AM > >>> To: Enhanced Machine Controller (EMC) > >>> Subject: Re: [Emc-users] new thread inspired by Christophers > >>> question > >> > >> about > >> > >>> 3d printer sliceing SW. > >>> > >>> Gene, > >>> > >>> Turns out that printing with a heavy machine like a mill presents > >>> some problems, as the inertia is orders of magnitude higher than on > >>> 3D > >> > >> printers. > >> > >>> 3D printers are designed to have as low an inertia as possible to > >>> simplify > >> > >> the > >> > >>> filament control dynamics. With a larger/heavier machine those > >>> control dynamics get pretty complex as I understand it. Plus, your > >>> prints would > >> > >> take an > >> > >>> eternity. > >>> > >>> N. Christopher Perry > >> > >> I certainly understand that a heavy mill may not be able to move as > >> fast as a very lightweight 3d printhead and printing may take a long > >> time. However, why would "filament control dynamics" be a problem? > > As I understand it on, at least small hobby scale printers, the extruders don't > exactly behave in linear manor during changes in their extrusion rate (your > basically pushing a 'rope' into the extrusion chamber, and the rope isn't > perfectly consistent in geometry or density). They compensate for this with a > variety of parameter like retraction on stop, etc. When inertia of the system is > small the start/stop transients are short enough that the filament controller > can just about ignore small changes in the differential nozzle speed, reducing it > to a nearly on/off control. With slow accelerations you can't ignore the > nonlinearities in the extruder and need a much broader range of control. > > >> With the mill the table would be moving and the filament stationary > >> which should, if anything, make the problem simpler. What am I not > >> understanding? Or are you concerned about the movement of the object > >> being printed? > >> > >> I have not experience with 3d printing. How fast do the typical > >> inexpensive 3d printers move? > >> > > Pretty fast, Ken, when you can't see it move 4" in a u-tube movie. > > Its there, and in the next frame is a blur, and its there in the 3rd frame. > > > > Even if my G0704 could do the Russian step dance, its still 10x slower > > than that. :( > >> Another poster mention 118 ipm ISTR and said that that was a relatively slow printer. My Tormach rapids at 135ipm so I suspect that would be approaching the upper limits of very slow!
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