Wow, 3 meters! Another way I've seen is to use a cable. There are pulleys at each end and the cable forms a loop. In the simplest design a motor powers on of the pulleys. The cable takes the price of a long timing belt. I've seen kevlar cord used for a cord and some steel cable also. In the better design there is a drum where the cable takes a few turns around and a spring to keep tension on the cable. The drum is powered.
With a 3M long rack, I think keeping it clean will be an issue. Perhaps mount is on the bottom of the track so chips fall down and off of it. or use a continuous airblast With gears you will need to have a backlash budget tnad design for it. Or just use a larger motor that still has torque at the low end On Sat, Apr 20, 2019 at 2:03 PM Leonardo Marsaglia <[email protected]> wrote: > Thanks Andy and Chris for your quick response. > > I'll try to answer both messages into one because I lack the quoting > function here in gmail. > > I plan to reduce the servos of the Y axis about 10 to 1 at least. I would > love to use timing belts and pulleys but I preffer to avoid all the trouble > of making the steps for the reduction. The servos I plan to use are 750 W > and 3000 RPM. > > About using a screw. The main problem is my Y axis is 3.5 meters long and > I'm not sure I can get ballscrews that long so easy from China to Argentina > in a safe and cheap way (I don't even know if the Fedex or DHL would ship > me something that long). In case of using a screw that long I guess is a > must to have a rotating nut and that's not a simple task too (at least not > as simple as the planetary reducer). So that's why I'm not thinking about > ballscrews although I would love to use them on all axis. > > > > > > > > El sáb., 20 abr. 2019 a las 17:50, Chris Albertson (< > [email protected]>) escribió: > > > backlash is a big deal. Maybe not so much with wood routing as maybe you > > don't care about 0.1 mm error. But think about a how a backlash in > > the 10:1 reduction translated to linear motion. Every time the servo > > motor changes direction the cutter stops moving until the backlash in the > > system is taken up. I can not imagine a gear system that backlash. > > > > This is why most machine tools use ball screws. Chinese ball screws are > > now nearly cheap as dirt and have zero backlash and can be directly > driven > > with a motor with no reduction. > > https://www.ebay.com/itm/Ball-Screw-SFU1605 > > < > > > https://www.ebay.com/itm/Ball-Screw-SFU1605-RM1605-End-Machined-BK-BF12-Ballscrew-Nut-Housing-Set/182984379186?hash=item2a9ab80b32:m:m0p8OTgikJ4HQd-zu4XytTg > > > > > > > I have some of these kind and as close as my dial indicator can measure > the > > scre/nut is "perfect". The balls are spring loaded so they bear on both > > sides of the screw so there is zero "play" For mettal working these > > screws are only "hobby grade" as they might have 0.03mm periodic error in > > the pitch but I can't measure 0.03 over a 1/2 meter distance. > > > > They also make some really nice Chinese linear ball bearing track as a > kit > > that makes building one of these things "plug and play" Hard to beat a > > full ball bearing linear motion setup for under $100. Here is one > > example. They come os bigger and smaller sizes > > > > > https://www.ebay.com/itm/SFU1605-Ending-Machined-Ballscrew-Set-SBR16-Linear-Rail-Kit-For-CNC- > > < > > > https://www.ebay.com/itm/SFU1605-Ending-Machined-Ballscrew-Set-SBR16-Linear-Rail-Kit-For-CNC-US-Stock/401566069770?var=&hash=item5d7f33f40a&enc=AQADAAADAFjVrDbVsZ8oH%2F8PNHtt9VX4%2Fw7FZcmMuqsX8uaFEduVZdN2xO9SlmphozVEOH7g7jX%2Bxew6Qceghk4QQfAx5sBCl3mvk4eHWuVUGaj8C5BkivfcPYRvofBQwnqo2D6pzU%2BGUd3CvwVXAM1GCvgT5HKYTTJRaAeIZBdXqfWlMXTaon39bDBa3zC%2F1K9ZLnfOKqX05Hd3sFtOKZehDjsf0jFAfy7bTSEmDVD6AmIj6ajz1SzPHtc%2BnojN8s5utpzO3078Jp6elV34r23RIuEGPXeqA%2By3BsRGYYbRCMxUNK7Td2il%2BzXdMr%2BerE%2FeihOQd97OPlL94nECQyCWjqeVGtoxO232cboR1Wve0LY2A8zPL0z50lT0s9SeLuW3dajRLIHWtpgAzCKGxELJnOVNP9le4Jc%2FcbyRcoiJJv%2BGwcEgBY1vrr1dbjwhxAYnUJG43R4TRLGijViWapLTeb2Awsu1sDe2W5XmsXrIpqZ%2FwqZ%2BaPGBvQ72s1dSDJOAlRYgbqhBH%2F%2Fyr1dDEP47jY7CIzBtBCa%2BLIY3nrG49uIxuVA%2FdIYXzBneALLQgf3qNzOCTcTZJ%2B9mek7VnKpPd64lGwhjrGGem%2F28DybqcMFTeyb%2F9sue%2Bntf14YCADI5p%2FBJlGfEgY2ISNKVHriCM%2Bkm4XDW%2F6L%2FptM%2BOXTnhjf42Rhr%2B1Jkd051YRz59z6A0dps9OkNBtAYq4kVrOR6LYMxMWryqdbtzIrV0RnjPeAheOW10TvnQ0kWiXCV9JrZv1Mw4jKCTVIBt2lwm25r%2BgAFIAErGwpUxwOFdoZ4Dg1v6iDMdbmbqeST70Iy5AG1ccQhl69XQvcHN2GTJ8b3qhCzLkLsglFBXTY7%2Bin2x4io6%2FV4vWLAr6sw9%2BB050TxvCZMd0a67R1ZdV4dCLxgFFdc%2BxyiZwmNYtXWOoY04tjWSJJGG9ptIWM1rCArFJqn2kJc1Y1lKu9HjO6y1z4iz4N4HRY2%2B7rQwzoW%2BnmJoqmh%2Fa1c83xr0XP7XkA5jqL3Lwx3Gg%3D%3D&checksum=401566069770871222cfdded49168823fbf139903396 > > > > > > > If you don't like ball screws then try long timing belts. They also are > > zero-backlash and come in any size you need at lower cost then gears > > > > > > On Sat, Apr 20, 2019 at 1:27 PM Leonardo Marsaglia < > [email protected]> > > wrote: > > > > > Hello to all again! > > > > > > I'm defining my router design after some months of inactivity. I > already > > > defined my steel frame and purchased the iron to start building it. The > > > idea is to use the router mainly for wood and melamine boards. > > Eventually I > > > may use it for aluminum but that's not the main purpose of the machine. > > > > > > Since you guys have lots of experience I would like to ask for advice > to > > > define two main concepts for my design: > > > > > > 1- Should I use helical or straight teeth racks and pinions? > > > > > > I plan to use some chinese rack and pinions (MOD 2 with 30 teeth > pinions > > > rotating at a max speed of 200 RPM) for the obvious reason of the > budget. > > > But I can get hardened and ground rack and pinions so I think that > sounds > > > pretty good. Anyway, I think I should stick with the straight rack and > > > pinion since it's the simpler solution and being hardened and ground I > > > think they will behave pretty well but I would like to hear your > > opinions. > > > > > > 2- For the servo-to-pinion reduction: Planetary servo reducer or worm > and > > > gear reducer with timing belt? > > > > > > I'm thinking about the worm and gear because I can machine that in the > > shop > > > and reduce at least the apparent cost (I say apparent because I still > > will > > > have to make more complex mounting plates for the servos and > > reductions..) > > > but also I'm tempted to buy something like this: > > > > > > > > > > > > https://www.aliexpress.com/store/product/high-Precision-Helical-planetary-gear-reducer-5-arcmin-2-stage-ratio-15-1-to-100-1/1155094_32867566227.html?spm=2114.12010612.8148356.28.1b5476fa9wYyAW > > > > > > > > > Do you think they are worth it? I have no experience with this kind of > > > reducers but the seller has good reputation and sells Delta servo > motors > > > wich I'm familiar with and work great. What do you think? > > > > > > In any case, I plan to mount encoders coupled directly to each pinion > > so I > > > can always track the position of the pinions no matter the backlash I > > have > > > in the reduction stage (but off course I want backlash to be the > minimum > > > possible). > > > > > > Those are my concerns for now. Please tell what you think so I can > make a > > > better choice. > > > > > > Thanks as always to all of you! > > > > > > Leonardo > > > > > > _______________________________________________ > > > Emc-users mailing list > > > [email protected] > > > https://lists.sourceforge.net/lists/listinfo/emc-users > > > > > > > > > -- > > > > Chris Albertson > > Redondo Beach, California > > > > _______________________________________________ > > Emc-users mailing list > > [email protected] > > https://lists.sourceforge.net/lists/listinfo/emc-users > > > > _______________________________________________ > Emc-users mailing list > [email protected] > https://lists.sourceforge.net/lists/listinfo/emc-users > -- Chris Albertson Redondo Beach, California _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
