On Thu, Oct 4, 2018 at 5:49 AM Leonardo Marsaglia <ldmarsag...@gmail.com> wrote:
> > > About the last question. Is there any disadvantage other than may be a > little more mechanical complexity with the one motor and shaft approach? > Because I've seen lots of routers driven with two motors that I almost > think it's mandatory for some reason. > What are the guide rails made of? precision stainless steel or chromed? They will need to be very high quality and very expensing if you use a bronze bushing. I think most people are going with HDPE. The friction is lower and you never need to use lube. that last part mean the rails are never coat "dust magnets" You can buy HDPE bearing for not much money. Typically there bearing are not very thick and are pressed into aluminum housing Also they make rails that lay on the table like rail road tracks the seem like a good way to go and then use round rails in the second axis. or use these for both. They are inexpensive and you can mount them to aluminum extrusions of any size. these would be absolutely rigid and you'd not have to make anything. Like save money too as they don't cost a lot. Here is a smaller set, they make them bigger needed .ebay.com/itm/2-X-SBR12-1000mm-For-CNC-12MM-Supported-Linear-Rail <https://www.ebay.com/itm/2-X-SBR12-1000mm-For-CNC-12MM-Supported-Linear-Rail-Shaft-4-Pcs-SBR12UU-Blocks/202160641942?_trkparms=aid%3D555018%26algo%3DPL.SIM%26ao%3D1%26asc%3D52885%26meid%3Db5963b764d384f598e468b383f921b1c%26pid%3D100005%26rk%3D4%26rkt%3D12%26sd%3D401470856046%26itm%3D202160641942&_trksid=p2047675.c100005.m1851> I know someone who built a large router and, all I can say is the quality of the rails REALY matters. That is where all the budget needs to go. The supported ones are nice because you can place shim shock under them and use a laser to get perfect alignment. About rack and pinion. You will need way-expensive rack and pinion set to reduce backlash. Butter to use a timing belt (with curves tooth profile) as these have zero backlash and cost less. The other option is ball screws. Ball screws will out perform racks and cost a lot less and again bell screws are zero backlash User direct drive or timing belt reduction as gear reductions on the motors have backlash. It is assign how much the cost of zero backlash ball drives have fallen. They are now the lowest cost option for precision linear drive. These are made mostly for the Chinese domestic market but some are sold on eBay The Chinese domestic market is HUGE compared to Europe or USA and we can take advantage of their economy of scale. For usr use a 12mm diameter screw would work well. Use them at least of the shorter axis (certainly the axis) here is an example. I have a set of these. The bearing are hold in compression so there is zero backlash and they measure "perfect" at least according to a dial indictor. With these ball screws nd a pair of the rial mounted guedes you can mill mild steel and certainly aluminum and have resolution at better them 0.001 inch. Use normal stepper motor as the systems nearly frictionless. Cost is very low. Maybe $200 per axis plus the motor for a one meter square router. It is almost disappointing to use this as there is"nothing to build" Just some mounting brackets and you are done. ebay.com/itm/CNC-Ball-Screw-12mm-SFU1204-w-Ballnut- <https://www.ebay.com/itm/CNC-Ball-Screw-12mm-SFU1204-w-Ballnut-BF-BK10-End-Support-L-250mm-1500mm/173060231282?hash=item284b319072:m:mg4uq51qVvrK8RmcksDoOUg> > > Thanks again! > > Leonardo > > > > > > > > > El jue., 4 oct. 2018 a las 0:03, Gregg Eshelman via Emc-users (< > emc-users@lists.sourceforge.net>) escribió: > > > The easiest method is mechanically connect the two sides with a shaft > > along the gantry and use one motor. Then it *cannot rack* or have any of > > the other issues that can happen with driving both sides of a constrained > > axis with two motors. > > If you need more Z height, you can elevate the racks on the sides. Or run > > chains or belts from the cross shaft ends down to stub shafts with the > > pinion gears. > > > > On Wednesday, October 3, 2018, 4:03:48 AM MDT, Leonardo Marsaglia < > > ldmarsag...@gmail.com> wrote: > > > > Hello to all! > > <clip> > > > > About how to drive both Y joints as one axis: I've read that there's a > way > > of simply adding two Y joints for the Y axis in the 2.8 master branch > but I > > don't know if there's documentation available already. > > _______________________________________________ > > Emc-users mailing list > > Emc-users@lists.sourceforge.net > > https://lists.sourceforge.net/lists/listinfo/emc-users > > > _______________________________________________ > Emc-users mailing list > Emc-users@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/emc-users > -- Chris Albertson Redondo Beach, California _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
