1. #1
    marbles's Avatar
    Lives in glasgow, United Kingdom. Last Activity: 23 Hours Ago Has been a member for 5-6 years. Has a total post count of 94. Received thanks 8 times, giving thanks to others 32 times. Referred 1 members to the community.
    I'm going to make a 4th axis for carving large blocks of foam and maybe blocks of wood. Doing a quick calculation I see that using a 200mm ballnose end mill I should be able to carve a 800mm x 1200mm cylinder right down to its centre, which is plenty big enough.

    I'm going to have to fabricate most of this from scratch or adapt existing parts and want some advice about ways to do this. Attached an outline drawing of how it might look in relation to the new build gantry router. I know I need to be able to raise and lower the central axial line ie the head and tail stock centre line for different sizes of material. The head stock could be fixed and the tail stock brought in out out to meet the material. I also want to be able to unbolt the both stocks when not using them as they will restrict use of the router bed.

    Head and tail stocks:
    I thought it might be a good idea to repurpose or adapt existing stocks from a metal or wood working lathe. Or perhaps there is something better to use, harmonic drive. I'm all ears as I know very little about lathes etc. We also have a machine shop across the corridor at work and can get parts made up if need be. I suppose it would be good to have interchangeble heads that fit into the head stock to take different types of chuck and rotary plates.

    Motor size and gearing:
    I was planning on using an 8.5nm nema 34 and 100vdc digital driver but not sure what sort of gearing to use. HTD belt and pulley is a tech I know well and 4:1 ratio seems common but may not be appropriate for this particular purpose.

    Chuck and rotary plate:
    wondering about what type is best to hold materials. If its a block of polystyrene best if that glues onto ply ply screwed to plates, plate attached to chuck or on its own morse taper spindle or whatever would be best to take as many different fitting as possible.

    Any pointers, links or questions welcome

    Click image for larger version. 

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    Click image for larger version. 

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    Last edited by marbles; 2 Weeks Ago at 08:55 PM.

  2. #2
    You can get ER collet chucks on straight shanks which are very easy to mount in suitable bearings, that might open the door for you to have simple adaptors which screw to your mounting boards.
    Toothed belt and pulleys should work fine, if you use steel braced belts you can tension the belt with a roller for negligible backlash.
    You think that's too expensive? You're not a Model Engineer are you? :D

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  4. #3
    marbles's Avatar
    Lives in glasgow, United Kingdom. Last Activity: 23 Hours Ago Has been a member for 5-6 years. Has a total post count of 94. Received thanks 8 times, giving thanks to others 32 times. Referred 1 members to the community.
    Quote Originally Posted by magicniner View Post
    You can get ER collet chucks on straight shanks which are very easy to mount in suitable bearings, that might open the door for you to have simple adaptors which screw to your mounting boards.
    Toothed belt and pulleys should work fine, if you use steel braced belts you can tension the belt with a roller for negligible backlash.
    Thanks!
    Good idea about the ER collet shanks. I made a brushless spindle recently from a 100mm ER20 straight shank. I guess i could get a really beefy ones like ER32. The thing will be getting the tension on the material?

    I used HTD 5M belts on the cnc build so happy to use them again, even have some spare idlers.
    Last edited by marbles; 2 Weeks Ago at 12:30 PM.

  5. #4
    Em .. everything depends.
    I think most users missed the 200 mm D endmill, = 20 cm !!!, == 8 ", and carving wood 800 mm in D. !!!

    You get huge forces from the leverage arm, and rigidity is always everything.

    I suspect you need 4-8x the section sizes you are using and a box section spindle holder.
    For the 200 mm endmills in wood at 800 mm D on blank, indicating about 400+200 == 600 mm free length (++) on the spindle ram/holder.

  6. #5
    Quote Originally Posted by hanermo2 View Post
    Em .. everything depends.
    I think most users missed the 200 mm D endmill, = 20 cm !!!,
    Yeah, You added a "D" and assumed it meant Diameter, I think some users missed how useless a 200mm Diameter Ball Nose End Mill is for machining anything but flat surfaces and cylinders and didn't look at the pictures? :D
    Last edited by magicniner; 2 Weeks Ago at 09:13 PM.
    You think that's too expensive? You're not a Model Engineer are you? :D

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  8. #6
    marbles's Avatar
    Lives in glasgow, United Kingdom. Last Activity: 23 Hours Ago Has been a member for 5-6 years. Has a total post count of 94. Received thanks 8 times, giving thanks to others 32 times. Referred 1 members to the community.
    Quote Originally Posted by hanermo2 View Post
    Em .. everything depends.
    I think most users missed the 200 mm D endmill, = 20 cm !!!, == 8 ", and carving wood 800 mm in D. !!!

    You get huge forces from the leverage arm, and rigidity is always everything.

    I suspect you need 4-8x the section sizes you are using and a box section spindle holder.
    For the 200 mm endmills in wood at 800 mm D on blank, indicating about 400+200 == 600 mm free length (++) on the spindle ram/holder.
    ;D
    Thats a 12mm Diameter, 200mm long from RicoCNC.com
    https://www.ricocnc.com/products/248...-Flat-End.html

    No way am I going to carve 400mm deep in wood, foam blocks only! Either way as your saying the frame size needs to be made out of some serious section.

  9. #7
    marbles's Avatar
    Lives in glasgow, United Kingdom. Last Activity: 23 Hours Ago Has been a member for 5-6 years. Has a total post count of 94. Received thanks 8 times, giving thanks to others 32 times. Referred 1 members to the community.
    The big D for me at the moment is working out what software to go with for 4th axis. Aspire is fine but is limited use for 3d models with voids etc. Rhino inc Rhinocam, Fusion 360 or Deskproto currently comparing all three... blimey

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