On Thursday 04 October 2018 15:28:52 Ken Strauss wrote: > I haven't been following this thread so I apologize if this was > previously noted. > > One possible solution to the ball screw whip issue is to spin the > ballnut rather than the ballscrew. In this scheme the ballscrew does > not rotate and if you tension the screw you should be able to use a > much smaller diameter screw. > This is what I did for the Z drive on the toy HF mill. Rotated the head housing 90 degrees to allow access to the front of the post part of the slider casting, and made a nut carrier extension on the post, putting the motor above the top of the post with a timing belt drive to the nut. Carrying 2 bronze nuts on a 1/2" acme bolt fixed into the slider, so the backlash can be adjusted, backlash has stayed below 3 thou for several years now. And with the same driver as the xy axis uses to drive those ball screws directly, Z is still about 3x faster than xy.
> > -----Original Message----- > > From: Leonardo Marsaglia [mailto:ldmarsag...@gmail.com] > > Sent: Thursday, October 04, 2018 2:42 PM > > To: Enhanced Machine Controller (EMC) > > Subject: Re: [Emc-users] Yet another topic about gantry homing > > > > Hello Chris, > > > > I would love to have ballscrews but I thought I would need to large > > of a diameter to avoid them to whip. Remember that I have a 3.8 > > meters in lenght for the longest joint. I've reading about using > > anti whip guides that move with the gantry and also aply tension in > > the screw with a nut to improve the work speed and reduce whip but I > > don't know wich option is better. Also there's the solution of > > rotating the nut. > > > > Anyway, for such long ways and screws, I need to see if I don't have > > too much trouble importing them to my country, because of the size > > of the package. I'll just have to make a call to DHL here in > > Argentina! > > > > Thank you! > > > > El jue., 4 oct. 2018 a las 14:58, Chris Albertson (< > > > > albertson.ch...@gmail.com>) escribi�: > > > 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%26 > > pid%3D100005%26rk%3D4%26rkt%3D12%26sd%3D401470856046%26itm%3D > > 202160641942&_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:mg4uq51qVvrK8RmcksDo > > OUg > > > > > > Thanks again! > > > > > > > > Leonardo > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > El jue., 4 oct. 2018 a las 0:03, Gregg Eshelman via Emc-users (< > > > > > > > > emc-users@lists.sourceforge.net>) escribi�: > > > > > 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 > > > > _______________________________________________ > > Emc-users mailing list > > Emc-users@lists.sourceforge.net > > https://lists.sourceforge.net/lists/listinfo/emc-users -- Cheers, Gene Heskett -- "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author) Genes Web page <http://geneslinuxbox.net:6309/gene>
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