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  1. #1
    Hi guys,

    Well been making a nuisance of myself on here for a week or so and I think it's time to make a thread 1 to get some ideas from you lot and 2 so I can put all my ideas in one place for my own reference :)

    The plan is a 2' x 4' fixed bed made from aluminium extrusion and then a moving gantry style for the movement. I have sourced a trim router from an old router table and am looking at using the skate bearing style linear movement. This will run on a sheet of cold rolled steel bolted onto the outside of the ali extrusion. This should give me smooth rolling and a nice straight edge to run along. It will also allow me to get the gantry rock solid by tensioning the top and bottom runners.

    I am still undecided on my drives at the moment might go with timing belt anchored at each end of the bed and then the stepper mounted on the gantry with a pulley and idler roller. I will be driving both sides of the gantry to avoid racking and hopefully give me enough rigidity to allow me to cut lightweight metals. I have looked into leadscrews and ballscrews and allsorts but I think the cost is prohibitive for a hobby machine.

    Primarily I will be using it to cut Balsa and other sandwich materials as a core for my carbon stuff which will then be vac bagged with epoxy. The length will hopefully allow me to make rc planes and eventually a new kiteboard. I would like to be able to machine aluminium blocks but I doubt I will get it anything like for doing that.

    So that's the overview. I will bulk the thread up with many ideas and pictures. Also need to get cracking in Sketchup and make a plan :)

  2. #2
    I'm thinking of going the 2x4 route as my micro mill is just not big enough.
    I favour the timing belt route over screws but so far not found a source of long lengths.
    I am also being a little constrained as I have run out of workshop space and am also persueing a vertical bed design but not sure what the forces would be?
    So I have plenty of ideas but I'm afraid not much advice to give you.

    Peter

  3. #3
    This will probably be a useful thread then for both of us ptjw as I am now looking at a fair few different ways of driving it I want to stay away from leadscrews really have been looking at rack and pinion but that seems even more expensive than leadscrews. I have a theory of using a timing belt that self meshes and running it through a couple of pulleys and over a stepper. This should then mesh against the fixed side which is attached to the ali so instead of 4' of timing belt to sag and keep tight it is running against itself which in my head means it will be a 3" part of the belt that is free the rest is self supported. I have sketchup and illustrator open so let me draw it then it will make more sense :)

  4. #4
    Hi Monza
    Have a look at this http://www.youtube.com/watch?v=OdJoVh6DRPA
    Does what I had in mind to do.

    peter

  5. #5
    That's scary I just drew up my idea in illustrator.



    My theory is that the meshing of the belts will minimise backlash and should hopefully give a nice fast accurate and stable movement :)

  6. have you considered chain drive rather than timing belts? buildyourcnc has an example for a 4x2 and 8x4 blacktoe design

  7. #7
    The one with the roller chain drive? I saw that he was doing that. I think that might be a bit heavy duty for me also I can see the foam and acrylic dust sticking to it and it becoming a real mess as it has to be lubricated. Also my cellar is not the most stable with regards humidity so rust might be an issue. There are many ways of skinning this cat I just need to decide on one so I can crack on with the build.

  8. #8
    Tom's Avatar
    Location unknown. Last Activity: 30-11-2016 Has been a member for 7-8 years. Has a total post count of 172. Referred 1 members to the community.
    Quote Originally Posted by monza View Post
    .... looking at using the skate bearing style linear movement. This will run on a sheet of cold rolled steel bolted onto the outside of the ali extrusion. This should give me smooth rolling and a nice straight edge to run along. It will also allow me to get the gantry rock solid by tensioning the top and bottom runners.
    Hi Monza,

    You won't regret using skates and CRS rails. That element of my router is absolutely rock solid - it feels very robust indeed. More assembly and tweaking time to get it running right than, say, ball bearing carriages, but also MUCH cheaper.

    The machine you're building sounds alot like my next one!:whistling::naughty:
    Alu section is the way forward....!

    All the best,
    Tom

  9. #9
    I think the cold drawn steel will help a lot with stiffening up the bed as well if it is well thought out. I am hoping to build it once and use it lots so I think over engineering now rather than a catch up job later will serve me well. are you using the 6 runners on a block style or a different version Tom? Have you used them on all of the axis as well?

  10. #10
    If a few people are building the same machine then maybe we should all get our heads together and come up with a good scaleable design which will let us get discount on some things and get other bits imported etc in the same box?

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