Ok so I should have re-read the first message in this thread before sending that. I now see the OP is looking for a way to handle the overtravel from decel on the Z axis after the probe has touched. I'm guessing that just probing slow enough to be able to stop quickly is less than desirable because of the amount of time it will take for probing before every cut.
How far will the head overshoot at probing speed once the probe event occurs? Is the machine too rigid to just handle the flexing while the axis decelerates? Do people regularly use automated probing on a mill to set tool length to work surface, or is it only done on a special pad to absorb any overshoot? When I worked running Haas and Fadal machines we just jogged by hand while sliding a gauge block back and forth until it hit snug to set length offsets, and the Hitachi-Seiki had a special "tool setter" that was set on the table and the machine probed down to it's surface. I would guess there was some give to the surface on that device. Jim On Mon, Nov 12, 2012 at 11:00 AM, Jim Coleman <drunkenwhip...@gmail.com>wrote: > Is the reason behind the floating head so there won't be damage if the > head hits an object while cutting, like a warped part sticking up? I'm > having trouble grasping why it's needed. Again, I have very little > experience with plasma tables, being limited to the one machine my former > employer had. That machine had a "rigid" Z axis with the plasma torch > coupled with a device that used air pressure to hold the assembly in > place. If the head crashed into a raised part, it would knock the 2 parts > off from each other and the torch side would fall loose within the > constraints of the other side of the housing and trigger an error on the > control. To reset the head you had to pull it outward and lift slightly to > reform the seal and the head would stick back in place. It took some tries > before getting it to seal and stick, before you developed "the touch". The > mechanism was maybe 4 inches square, with the joining interface itself > appearing to be round. A very similar machine can be seen at > http://www.plasma-automation.com/mod_fabricatorHD.html and the page has a > link to a slightly better image of their "collision protection" but they > don't seem to provide many details. When the machine touched off, it > appeared to use some form of conductivity to probe the surface. Holding a > piece of steel off of the surface of the table and letting the head touch > it wouldn't trigger the probe, until it pushed the steel down to the > surface of the table. If it was strictly capacitance based, it seems it > would trigger as soon as it touched, unless a human body holding onto a > piece of scrap doesn't have enough capacitance to set it off. > > I'm sorry if I'm completely missing the point of wanting the floating > head, I'm trying to comprehend the need. At first I thought the intention > was for the head to just ride the surface of the workpiece and not use THC, > but now I see that THC is to be implemented for cut height so I'm a little > lost. Unless the float will replace the need for an electronic probing. I > hope someone can clear up my confusion, and sorry if all of this is > irrelevant. > > Jim > > On Mon, Nov 12, 2012 at 7:17 AM, andy pugh <bodge...@gmail.com> wrote: > >> On 12 November 2012 11:32, Les Newell <les.new...@fastmail.co.uk> wrote: >> >> > I have been thinking about this for some time and a while back I came up >> > with a very different design to all of the others I have seen. First of >> > all, you don't need or want a ball screw on Z. Z doesn't need to be >> > hugely accurate. It needs reasonable resolution and it needs to be dirt >> > resistant. >> >> Are double-helical racks available? It seems to me that those would >> give good location in a number of degrees of freedom, and allow direct >> stepper control. >> (Google) I can't find any. It would be reasonably expensive to make as >> an injection moulding, though relatively expensive to hob. >> >> -- >> atp >> If you can't fix it, you don't own it. >> http://www.ifixit.com/Manifesto >> >> >> ------------------------------------------------------------------------------ >> Everyone hates slow websites. So do we. >> Make your web apps faster with AppDynamics >> Download AppDynamics Lite for free today: >> http://p.sf.net/sfu/appdyn_d2d_nov >> _______________________________________________ >> Emc-users mailing list >> Emc-users@lists.sourceforge.net >> https://lists.sourceforge.net/lists/listinfo/emc-users >> > > ------------------------------------------------------------------------------ Everyone hates slow websites. So do we. Make your web apps faster with AppDynamics Download AppDynamics Lite for free today: http://p.sf.net/sfu/appdyn_d2d_nov _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
