Well I've been reading the 2.8 Master branch manual about homing and how to configure two joints for one axis and I think I understand but since I don't have a Linux PC here to try it out I would like to clarify something.
In the two motors for one axis gantry configuration, does LinuxCNC export home switch pins for each joint? Or does it export the pins for each axis? Because the best solution I came out with to have a precise homing without rocking (and I think is doable) is to have one homeswitch per joint with a robust mechanism to manually adjust them as precise as possible. And then use absolute encoders on the pinions to achieve the maximum accuracy level. This way I can guarantee that if there is some difference from time to time when hitting the home switches, that won't be a problem since the absolute enconders keep the exact angular position of the pinion. Am I right on this? Or is this just a redundancy? Sorry for the long questions but I've never really worked with this kind of setup, and I'm used to have both the switch and some encoder reference to make the homing. Thank you! El jue., 4 oct. 2018 a las 12:39, Leonardo Marsaglia (<ldmarsag...@gmail.com>) escribió: > Hello Les, > > No, I plan to support 50 mm bars every 600 mm more or less. I'm attaching > some pictures of the design I'm working on. (The adjustable stands for > levelling are not in the assembly because I'm saving resources on this > laptop) > > I like the idea of using the rectangular ways but unfortunately they are > quite expensive for this project and also there's the aligning problem. > With the setup I'm trying to do I can adjust the parallelism on every > corner of the machine and also individually adjust every suport to level > the guides perfectly. I'm sending pictures of everything to clarify what > I'm intending to do. Please note this is under development and some things > are going to change a little bit. > > The idea of welding the frame is out of discussion because I plan to move > and set up this thing in place. Also, I don't have the means to guarantee a > clean and squared welding for the frame. Instead I decided to do what you > can see in the pictures, having an enormous amount of bolts to keep the > parts rigid and firm. > > No problem about using tubing to lower the inertia. I also thought about > reducing the 3000 max RPM with the worm and gear to 100 RPM on the shaft > and then increase the size of the pinions to have the linear speed I want. > This way the long shaft doesn't have to withstand the high RPMs. > > I uploaded the pictures because the list doesn't allow me to attach them. > Here's the link: > > https://imgur.com/a/7kLUWsq > > > > El jue., 4 oct. 2018 a las 12:13, Leonardo Marsaglia (< > ldmarsag...@gmail.com>) escribió: > >> Hello Dave, >> >> Well, to avoid the backlash is that or may be using timing belts and >> pulleys to drive the shaft too. The gearbox is a good idea but I think that >> can raise the cost too much. Anyway I'll give it a look because I don't >> want to discard any option. >> >> In any case I'm still not sure about wheter use two motors or one motor >> with a shaft. The latter option makes me feel more secure because it can't >> go out of squaress easily, unless you have loose belt or something breaks. >> >> By the way I just re send another message that was rejected by the list >> because of the size of the pictures, I don't know if now you can see it. >> >> >> >> El jue., 4 oct. 2018 a las 12:04, Leonardo Marsaglia (< >> ldmarsag...@gmail.com>) escribió: >> >>> Hello Les, >>> >>> No, I plan to support 50 mm bars every 600 mm more or less. I'm >>> attaching some pictures of the design I'm working on. (The adjustable >>> stands for levelling are not in the assembly because I'm saving resources >>> on this laptop) >>> >>> I like the idea of using the rectangular ways but unfortunately they are >>> quite expensive for this project and also there's the aligning problem. >>> With the setup I'm trying to do I can adjust the parallelism on every >>> corner of the machine and also individually adjust every suport to level >>> the guides perfectly. I'm sending pictures of everything to clarify what >>> I'm intending to do. Please note this is under development and some things >>> are going to change a little bit. >>> >>> The idea of welding the frame is out of discussion because I plan to >>> move and set up this thing in place. Also, I don't have the means to >>> guarantee a clean and squared welding for the frame. Instead I decided to >>> do what you can see in the pictures, having an enormous amount of bolts to >>> keep the parts rigid and firm. >>> >>> No problem about using tubing to lower the inertia. I also thought about >>> reducing the 3000 max RPM with the worm and gear to 100 RPM on the shaft >>> and then increase the size of the pinions to have the linear speed I want. >>> This way the long shaft doesn't have to withstand the high RPMs. >>> >>> (Second attempt to attach the pictures) >>> >>> El jue., 4 oct. 2018 a las 12:00, Dave Cole (<linuxcncro...@gmail.com>) >>> escribió: >>> >>>> I'd avoid a worm gear drive. They are prone to wear and backlash. >>>> I'd look for a good deal on a servo grade planetary 10:1 gearbox that >>>> fits your Chinese motor. >>>> Probably the easiest and most rigid drive solution is to use two motors >>>> each with a planetary gear box and direct drive a pinion on a rack. >>>> If you want to mill aluminum and need rigidity, that's the way I would >>>> go. >>>> You might want to weld the frame in sections and then bolt it together. >>>> If you don't have a platen to weld it on, you might want to contract >>>> out >>>> part of the frame welding. >>>> >>>> Dave >>>> >>>> On 10/4/2018 10:41 AM, Leonardo Marsaglia wrote: >>>> > By the way, on the pictures there are missing details I didn't draw >>>> yet, >>>> > like setscrews for parallel regulation and things like that. Also, I >>>> have >>>> > yet to modify the design for the one motor and shaft approach and see >>>> wich >>>> > is better. >>>> > >>>> > El jue., 4 oct. 2018 a las 11:37, Leonardo Marsaglia (< >>>> ldmarsag...@gmail.com>) >>>> > escribió: >>>> > >>>> >> Hello Les, >>>> >> >>>> >> No, I plan to support 50 mm bars every 600 mm more or less. I'm >>>> attaching >>>> >> some pictures of the design I'm working on. (The adjustable stands >>>> for >>>> >> levelling are not in the assembly because I'm saving resources on >>>> this >>>> >> laptop) >>>> >> >>>> >> I like the idea of using the rectangular ways but unfortunately they >>>> are >>>> >> quite expensive for this project and also there's the aligning >>>> problem. >>>> >> With the setup I'm trying to do I can adjust the parallelism on every >>>> >> corner of the machine and also individually adjust every suport to >>>> level >>>> >> the guides perfectly. I'm sending pictures of everything to clarify >>>> what >>>> >> I'm intending to do. Please note this is under development and some >>>> things >>>> >> are going to change a little bit. >>>> >> >>>> >> The idea of welding the frame is out of discussion because I plan to >>>> move >>>> >> and set up this thing in place. Also, I don't have the means to >>>> guarantee a >>>> >> clean and squared welding for the frame. Instead I decided to do >>>> what you >>>> >> can see in the pictures, having an enormous amount of bolts to keep >>>> the >>>> >> parts rigid and firm. >>>> >> >>>> >> No problem about using tubing to lower the inertia. I also thought >>>> about >>>> >> reducing the 3000 max RPM with the worm and gear to 100 RPM on the >>>> shaft >>>> >> and then increase the size of the pinions to have the linear speed I >>>> want. >>>> >> This way the long shaft doesn't have to withstand the high RPMs. >>>> >> >>>> >> Let me know if you can see the pictures. >>>> >> >>>> >> >>>> >> >>>> >> El jue., 4 oct. 2018 a las 10:52, Les Newell (< >>>> les.new...@fastmail.co.uk>) >>>> >> escribió: >>>> >> >>>> >>> Using two motors is mechanically simpler and has lower rotational >>>> >>> inertia but I am not a fan of this setup. If you use a tube rather >>>> than >>>> >>> a solid shaft, you won't add a lot of inertia. I'm thinking of >>>> building >>>> >>> another plasma cutter and it will probably use a shaft rather than 2 >>>> >>> motors. >>>> >>> >>>> >>>> But the thing is, I'm planning to use round guides >>>> >>>> with bronze adjustable bearings. >>>> >>> Do you mean guides that are only supported at the ends? This is a >>>> very >>>> >>> bad idea. They'll flex and bounce all over the place. You are also >>>> >>> likely to get a lot of wear unless you pressure feed lubricant. If >>>> you >>>> >>> do that oil will go everywhere. My router uses box ways on the Y >>>> and Z >>>> >>> axes with oil feed. It gets pretty messy at times. >>>> >>> >>>> >>> Most modern commercial routers and many machining centres use >>>> >>> rectangular linear ways, such as this >>>> >>> < >>>> >>> >>>> https://www.qualitybearingsonline.com/lwl25r240bhs2-iko-maintenance-free-linear-guide-rail/ >>>> >. >>>> >>> >>>> >>> They are very rigid and lasts a long time with very little wear. The >>>> >>> only disadvantage is that you need to be careful to make sure >>>> everything >>>> >>> is perfectly aligned. These have very little give in them. Another >>>> >>> option is supported round rail such as this >>>> >>> < >>>> >>> >>>> https://www.amazon.co.uk/TEN-HIGH-Supported-SBR40UU-BlockBearing-Bearing/dp/B01N10JF5N >>>> >. >>>> >>> >>>> >>> For the sort of size machine you are talking about you'll need at >>>> least >>>> >>> 40mm round rail. Round rails wear faster than rectangular but are a >>>> lot >>>> >>> less fussy about alignment. >>>> >>> >>>> >>>> So, to sum up, with these kind of bearings I expect more >>>> resistance on >>>> >>> the >>>> >>>> joints, and also the router is 2 meters x 3,8 meters long so to >>>> have >>>> >>> enough >>>> >>>> rigidity I'm planning to use steel and cast iron, so that's why I'm >>>> >>>> oversizing the motors. >>>> >>> To give you an idea about motor sizing the motors on my router (1 >>>> per >>>> >>> axis) are about 1.8kw and it's scary. My tool changer is mounted >>>> on a >>>> >>> bracket made from 50mmx50mm box section. I messed up the tool change >>>> >>> sequencing a while back and it pushed the tool changer out of the >>>> way >>>> >>> without breaking a sweat. It tool a lot of effort with big levers to >>>> >>> twist it straight again. Here is a link to a similar machine to >>>> mine but >>>> >>> without a tool changer >>>> >>> < >>>> >>> >>>> https://www.bidspotter.co.uk/en-gb/auction-catalogues/cjm-asset/catalogue-id-cjm10389/lot-47df49af-bf1a-4676-ab88-a75a00f5f92b >>>> >. >>>> >>> >>>> >>> Lots of heavy steel and cast iron. Mine originally had 4 drill >>>> heads and >>>> >>> 2 spindles. If it was easy to dial back the power I would. If >>>> something >>>> >>> goes wrong the machine will keep pushing until something breaks. >>>> >>> >>>> >>> I do maintenance work on a router with 750W motors. A while back the >>>> >>> spindle stalled while it was cutting. It bent the 1/2" cutter >>>> nearly 90 >>>> >>> degrees and carried on. >>>> >>> >>>> >>> Les >>>> >>> >>>> >>> On 04/10/2018 13:47, Leonardo Marsaglia wrote: >>>> >>>> First of all, thank you guys for your advices as always! >>>> >>>> >>>> >>>> I'm gonna try an asnwer this on one message because sadly gmail >>>> doesn't >>>> >>>> have the quote selected text feature anymore. >>>> >>>> >>>> >>>> About the oversized motors. Yes, I also think that for a normal >>>> router >>>> >>> 1 kw >>>> >>>> per side is too much. But the thing is, I'm planning to use round >>>> guides >>>> >>>> with bronze adjustable bearings. I decided this because I want more >>>> >>>> rigidity for an eventual need of machining aluminum, and also >>>> because I >>>> >>>> think this kind of guides with whipers are much more reliable than >>>> the >>>> >>>> recirculating ball ones. Also, I don't think I can have the >>>> adjustable >>>> >>>> feature with the slotted ball bearings. I'm attaching a picture of >>>> the >>>> >>>> bearing I plan to make, there are no lube channels on the model >>>> but they >>>> >>>> will be on the final part. >>>> >>>> >>>> >>>> So, to sum up, with these kind of bearings I expect more >>>> resistance on >>>> >>> the >>>> >>>> joints, and also the router is 2 meters x 3,8 meters long so to >>>> have >>>> >>> enough >>>> >>>> rigidity I'm planning to use steel and cast iron, so that's why I'm >>>> >>>> oversizing the motors. Besides, there's no much difference between >>>> a >>>> >>> 400W >>>> >>>> and a 1Kw chinese servo motor and drive on ebay. >>>> >>>> >>>> >>>> About how to drive and home the gantry. From what we've been >>>> talking and >>>> >>>> thinking it through a little more, I'm thinking that the best >>>> solution >>>> >>> is >>>> >>>> the one Gregg suggested. To have a transversal shaft on the gantry >>>> >>> driven >>>> >>>> by the servo motor by a worm and gear reduction with the timing >>>> pulleys >>>> >>> on >>>> >>>> each end of the shaft driving the pinions. This way I can adjust >>>> and >>>> >>> square >>>> >>>> the two columns and it should stay squared at any time. This is >>>> really >>>> >>>> important because this is going to be used by a regular operator, >>>> so >>>> >>> this >>>> >>>> has to be as reliable and fail proof as possible. >>>> >>>> >>>> >>>> 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. >>>> >>>> >>>> >>>> Thanks again! >>>> >>>> >>>> >>>> Leonardo >>>> >>>> >>>> >>>> >>>> >>> >>>> >>> >>>> >>> _______________________________________________ >>>> >>> 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 >>>> >>>> >>>> _______________________________________________ >>>> 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
