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  1. #11
    Quote Originally Posted by m_c View Post
    Yes and no, would be the answer to that.
    The big benefit of using a closed loop stepper in this application, would be they do tend to self correct to a certain amount so would move the stock back into position, and they would let you run things far closer the motors limit, however any movement could still scrap the part.
    It's a case of balancing up your needs, and what compromises you can make.

    I have just thought of one option if you don't need much speed, how about mounting a stepper onto a cheap rotary table?
    They should be adjustable for backlash, and they'll give you lots of gearing in a compact format

    I was in the workshop today trying to learn how to program simultaneously 4th axis and had a bit of wood on the 4th. When I put some pressure on the edge of the wood I can see a small amount of movement at the motor. Iíve got a digital driver on that 4th and wonder if it might also Ďhave a go atí self correcting, not as good as a closed loop thought iím sure.

    From the movement I could see it looks like the wee pulley on the motor needs some mechanical advantage help so I think your idea of the rotary table might be better. I see people using 30:1, 100:1 gearing, what kind of gearing is on a rotary table. At this point I wish I knew more about mechanical engineering. ..

    All things considered was pretty surprised my attempts without using specific kinematic actually worked to program some simultaneously 4th axis action just using a basic mach3 post processor?!

  2. #12
    m_c's Avatar
    Lives in East Lothian, United Kingdom. Last Activity: 5 Hours Ago Forum Superstar, has done so much to help others, they deserve a medal. Has been a member for 9-10 years. Has a total post count of 2,437. Received thanks 279 times, giving thanks to others 7 times.
    Quote Originally Posted by Boyan Silyavski View Post
    On the best diy heavy duty mill/lathe 4rth axis as far as i remember relation was 1:7 and there was possible via second belt change to raise that. And i remember talking to the guy and he was using 120?mm mountain bike hydraulic brakes and discs. Check ebay the standard size of brakes nowadays, could be around 200mm. Hydraulic brakes is the way to go i believe, fix the discs on the shaft somewhere.
    I'm guessing you mean the InTurn thread on MachSupport?
    IIRC you could swap the belt to get a double reduction for more torque.

    You can get bicycle disk brakes from 120 to 220mm, however I wouldn't use one for a brake as they're too flexy. I think the InTurn used a motorbike/scooter disk, as some of those use pretty small disks, but the disks are also pretty substantial and won't flex like a bicycle disk. He also built his own caliper setup. All you need is a lever, and a suitable taper.
    Avoiding the rubbish customer service from AluminiumWarehouse since July '13.

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  4. #13
    Just checked my MTB and yes, if you push them from side, discs could bend but not easily, they are steel. But if mounted properly there will not be a problem. If a disk holds 100kg guy racing downhill with 60km/h, it will hold the machining too.
    project 1 , 2, Dust Shoe ...

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  6. #14
    Thanks for the ideas and support, much appreciated.

    I’m frequently asked if I can do two types of statue milling. 1: where a client wants a copy of a sculpture, If I can do these as a continuous 360 helical mill I will do but often that strategy can’t get all the detail so that why i’mcurrently learning 2: index milling to get better 4 sided definition and detail. Or to put it another way have more control over the access to difficult areas. So yes I as I don’t need speed I just need holding torque I could do with a reduction to help the motor pulley side but also a brake so yes the bicycle or moped hydraulic brake might be fine.

    Thinking extra laterally here for a moment as a short term solution what I could do is mill a few 300mm wooden disks with degree marking added or included as holes for pegs and just use separate files to orientate the stock to the angle I want and lock it off with a g-clamp. I know I know not very high tech but if all I have to do is remember to remove and reclamp the g-clamp to hold it steady i’d go for that.

  7. #15
    I just remembered I bought a few of these a few years ago. Very high quality wormscrew mechanisms. Might be worth a tryout
    Rino Ondrives Worm Gear Reducer 30:1 Vexta Nema23

    Click image for larger version. 

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  8. #16
    They look like a top bit of kit - accurate to about 0.1 degree if I've read the Ondrives data correctly.

  9. #17
    m_c's Avatar
    Lives in East Lothian, United Kingdom. Last Activity: 5 Hours Ago Forum Superstar, has done so much to help others, they deserve a medal. Has been a member for 9-10 years. Has a total post count of 2,437. Received thanks 279 times, giving thanks to others 7 times.
    Quote Originally Posted by marbles View Post
    I just remembered I bought a few of these a few years ago. Very high quality wormscrew mechanisms. Might be worth a tryout
    Rino Ondrives Worm Gear Reducer 30:1 Vexta Nema23
    They're certainly worth trying.

    Quote Originally Posted by Voicecoil View Post
    They look like a top bit of kit - accurate to about 0.1 degree if I've read the Ondrives data correctly.
    Looking at the OnDrive website for Nema mount version, it looks like you can get either an 8 arc minute, and a 30 arc minute version, which is 0.1333, or 0.5 degrees.
    It all depends what kind of accuracy is needed. 0.5 deg works out about 1.3mm of movement at a 300mm diameter. Off course the 0.5deg figure is the worst case scenario.
    Avoiding the rubbish customer service from AluminiumWarehouse since July '13.

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  11. #18
    Just out of interest i've knocked up this manual trunnion positioner to allow me to 5 faces foamboard up to 750x400x200mm. Ideally yes this would all be automated one day with the OnDrive Rino units I have but in these COVid times i'm doing a temp improvisation with what i've got in the workshop to test the proof of concept. Hopefully one day this will be a fully automated unit with amazing holding torque and a brake but for now just got to test it works. Watch this space for an update.

    I should point out the top plate is attached to the foamboard with jumbo helical insulation screws and that plate is mounted to a 360 deg turntable, which should allow for quick changeover of stock. I have afterall got 144, 5-sided parts to mill!!

    Click image for larger version. 

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    Last edited by marbles; 1 Week Ago at 09:40 AM.

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