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IndustryArena Forum > MetalWorking Machines > CNC "do-it-yourself" > Milli a new composite mill kit
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  1. #1381

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    Aug 2021
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    Re: Milli a new composite mill kit

    Hi Peter,
    Milli seems to be evolving through multiple personalities since it’s inception way back at the beginning of this thread. A robot is so cool. I’ll be following this thread with great interest.

    Jayne

  2. #1382

    Re: Milli a new composite mill kit

    Could use hydraulic (oil) bearings instead, that would be plenty stiff and air bearings are mostly useful for high surface speeds and/or to avoid transmission of vibration which are two features that won't really be an issue for you. In the same vein you could use a magnetic bearing, stiffness is higher than an air bearing and also a programmable feature, but the most involved type in terms of design.

    Allowable size tolerances on the oil bearing would be looser to.

    Still, given your application it would seem a bushing would suffice and a rolling bearing would excel. In our robots that we build at work we are using a lot of cheap plastic bearings actually, but we have a complex pick and place situation of light objects, 99% of the bearing load is just the robot dynamics and not the material being moved. Plus we design iterate and rebuild all of the robots every year since we don't sell the equipment to the clients and we're still in startup mode.

    Our investors, which includes two major SCARA and industrial robotics suppliers, favor large rolling element bearings. They withstand the abuse of customers very well and for some reason no engineers ever want to admit they crashed the $65k 6-axis robot into something when they were dicking around...

  3. #1383
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    Jul 2018
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    3488

    Re: Milli a new composite mill kit

    Hi Strawb - Oil recovery on hydraulic bearings would be a pain. I admit I have crashed robots, CNC mills and manual laths, probably every piece of equipment I have used I've crashed at some point I think I'll stay with the HUB bearings for now just have to find a good supplier. Peter

  4. #1384
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    Re: Milli a new composite mill kit

    Hi All - dropped into a truck parts place today and looked at hub spiders for the base bearing. They are big! plus two bearing companies are looking for a suitable HUB3 type for me. So once those are sorted I can commence designing the Milli-IRB. The rest is fairly straight forward... Peter

  5. #1385
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    Nov 2020
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    227

    Re: Milli a new composite mill kit

    Hey Peter,

    Ever used food grade oil for tapping? I'm thinking colza oil(rapeseed oil), really popular here instead of sunflower oil but since its used in machinery too, I got curious if I could use it for tapping. I have a 1.4404 stainless steel plates and need to tap M4 threads. It's a part of a custom humidifier and since I'll be breathing in whatever is on the surface I'd love to avoid anything that's not biocompatible. The tap is a 3 piece.

  6. #1386
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    Re: Milli a new composite mill kit

    Hi Ard - Nope always used tapping fluids for stainless. We call 1.4404 S316 here. Only one way to find out - try it. Peter

  7. #1387
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    Nov 2020
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    227

    Re: Milli a new composite mill kit

    Quote Originally Posted by peteeng View Post
    Hi Ard - Nope always used tapping fluids for stainless. We call 1.4404 S316 here. Only one way to find out - try it. Peter
    I'm thinking I should have made an extra hole in the plate just to try things out. Anyway looking forward to the robot. Have you decided on what servo's to use on the axes? A harmonic+servo combo or a dedicated bldc drive? I've been looking to add 4th and 5th axis and found this https://www.aliexpress.com/item/1005...63996440%22%7D

    It's about $200 cheaper than a harmonic+80st servo I was considering before.

  8. #1388
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    Re: Milli a new composite mill kit

    Hi Ard - re lub. I used to run a draw bench for making aluminium tubes and it used a combo of peanut oil and pigs fat. Horrible stuff when it went rancid the tank had about 600kg of the stuff... The bench was 22m long and the motor gearbox was the size of a small SUV... I have no idea about motors yet. I have to sort the bearings. I usually think through the design and try to solve the hard issues first. Motors are easy so way down the list. Looking at these for the arm bearings. But they are heavy. The first version will use as many stock easy to get parts as possible.

    https://www.youtube.com/watch?v=6YiPrytt_Ss

  9. #1389
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    Re: Milli a new composite mill kit


  10. #1390
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    Re: Milli a new composite mill kit

    Evening All - I have spoken to my resin supplier and they are happy to do a tensile modulus test on the CF sample. Excellent. Waiting on a drawing of the coupon size so I can get into it. Peter

  11. #1391
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    Re: Milli a new composite mill kit

    Morning all - I have the drawing and finish specs for the test coupons. They are a bit different to usual for composites. I asked them some questions and they usually test neat resins so I shall prep a coupon how its usually done for composites. They wanted it polished to G6000 and I said nope and why? I can see that small defects in neat resin coupons would be an issue but not on a CF coupon... So many things to get done. This will come to the top of the list soon. On a commercial project for a welding robot installation I have been speaking to the people at Octopuz very good off line programming software....Peter

  12. #1392
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    Nov 2020
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    Re: Milli a new composite mill kit

    Hey Peter, I finally found a vendor that sells all three types of slewing rings I mentioned. https://lyyjindustry.en.alibaba.com/

    For reference the stiffest YRT series eg.YRT80 costs $160, YRT200 $560.

  13. #1393
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    Re: Milli a new composite mill kit

    Thanks Ard - I want to cast the CF test coupon next. Now I have a suitable cutter for composites... Peter

  14. #1394
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    Re: Milli a new composite mill kit

    Hey Peter,

    Will you be using direct drives for each joint or regular servo's with belts?

  15. #1395
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    Re: Milli a new composite mill kit

    Hi Ard - Been offline for a while. My elderly mother passed away and I've been supporting the family and making arrangements etc. Shes in a better place now. Milli-IRB will use ballscrews for the main axis and I hope to use tendons like in our arms for the outer axes (biomimicry) Servos will be used with axis position sensors.. I have a nephew who is a mechatronic eng and he's keen to be involved so two heads are better then one, plus the forum input should be good.... But Frankie is the next machine. I have been doodling in down times and have resolved a few things for Frankenrouter so will be concentrating on that first...when I get back next week some time... not sure when the dust will settle...Just figured out my passwords to forums and emails and catching up at the moment...Peter

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