RE: [CAD_CAM_EDM_DRO] Skipping steps, avoiding resonance

Just to eliminate the software try it on something like TurboCNC. You
can get a full featured, unregistered copy at www.DakEng.com and it will
run from a DOS boot disk.

Tim
[Denver CO]
Sherline Products at Deep Discount
Mach1 & DeskCNC with Credit Card ordering
Contact me for discounts on DeskCNC & Sherline bundles
www.KTMarketing.com/Sherline

> -----Original Message-----
> From: Randy Gordon-Gilmore [mailto:zephyrus@...]
> Sent: Sunday, December 01, 2002 11:35 PM
> To: cad_cam_edm_dro@yahoogroups.com
> Subject: [CAD_CAM_EDM_DRO] Skipping steps, avoiding resonance
>
>
> I have a perplexing problem. Recently I've put together a
> gantry milling machine from mostly surplus components--a
> Techno-Isel stepper-driven gantry table (500x500x100mm
> theoretical travel, with zero-backlash leadscrews), three
> General Controls "Dragon Driver" 2.5A bipolar chopping drives
> (fed by a 28V transformer) and a Sherline headstock, for
> which I made an adapter plate to bolt it onto the Z-axis carriage.
>
> I finally got the thing running this weekend, and it is not
> running reliably. I have the drivers in half-step mode,
> which with the 4mm-pitch leadscrews gives 2540 steps per
> inch. I can jog the X and Y axes at insanely fast speeds
> (200 ipm,) but I have fast jog set at 60 ipm. I'm using
> CNCPro running under DR-DOS 7.03.
>
> Running 3-axis Gcode generated by Visual Mill Free, all 3
> axes "drift" during machining. I'm cutting acrylic with a
> .50 roughing endmill, with cutting speed set at 10ipm. The
> motion is actually more like 2.5D--it goes to a depth and
> then pockets that level before going to another depth and
> repeating. It spirals down into the material.
>
> Cuts at each depth should line up, but I end up with a
> "terraced" effect because the X and Y will shift by .005-.050
> inches between depths. I have also measured the depths (each
> "level" is set at .050") and they are not consistent either.
>
> I'm baffled, but suspecting that the spiraling between levels
> is what is throwing things off, along with maybe arcs in XY.
> When I got the drives, they were set for full stepping, and
> the table lost steps very easily. I think that the coarse
> leadscrews contribute to that, because the motors are
> stepping fairly slowly. Now that I have the drives set for
> half stepping, and have a decent acceleration programmed into
> CNCPro to get to running speed quickly, and keep all my
> motions to 5 ipm or more, I seem to be avoiding the low-speed
> resonances OK for straight moves.
>
> But what can I do about arcs? By their nature they will be
> moving the axes slowly through the suspected resonance range,
> and spiral leadins will do that for all 3 axes. How do I avoid that?
>
> I truthfully don't know for sure that the arcs are the
> problem. But straight-line motion with handwritten Gcode
> works fine. I have the stepper motor cables away from AC
> cords as much as possible. CNCPro works pretty reliably on
> my Sherline mill, so I don't think that is the problem. I
> have run the Gcode through editNC to backplot it, and it
> looks fine so I don't suspect that. So that pretty much
> leaves arcs and spirals, doesn't it?
>
> Newbie again,
>
> Randy
>
> Randy Gordon-Gilmore ,----.___________ ______________
> _________________
> ProtoTrains // = = === == || == == == = || ==
> == == = == =|
> Rio Vista, CA, USA
> /-O==O------------o==o------------o==o-----------o==o-'
> zephyrus@...
> http://www.prototrains.com
>
> Addresses:
> FAQ:
> http://www.ktmarketing.com/faq.html
> FILES: http://groups.yahoo.com/group/CAD_CAM_EDM_DRO/files/
> Post Messages: CAD_CAM_EDM_DRO@yahoogroups.com
>
> Subscribe: CAD_CAM_EDM_DRO-subscribe@yahoogroups.com
> Unsubscribe: CAD_CAM_EDM_DRO-unsubscribe@yahoogroups.com
> List owner: CAD_CAM_EDM_DRO-owner@yahoogroups.com, wanliker@...
> Moderator: jmelson@... timg@...
> [Moderator]
> URL to this group: http://groups.yahoo.com/group/CAD_CAM_EDM_DRO
>
> OFF Topic POSTS: General Machining
> If you wish to post on unlimited OT subjects goto:
> aol://5863:126/rec.crafts.metalworking or go thru Google.com
> to reach it if you have trouble.
> http://www.metalworking.com/news_servers.html
>

http://groups.yahoo.com/group/jobshophomeshop I consider this to be a
sister site to the CCED group, as many of the same members are there,
for OT subjects, that are not allowed on the CCED list.

NOTICE: ALL POSTINGS TO THIS GROUP BECOME PUBLIC DOMAIN BY POSTING THEM.
DON'T POST IF YOU CAN NOT ACCEPT THIS.....NO EXCEPTIONS........ bill
List Mom List Owner



Your use of Yahoo! Groups is subject to
http://docs.yahoo.com/info/terms/