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
