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  1. #1

    Cast Bench Top CNC Build

    Kia ora,

    Thought id share some concepts of a new build im currently doing. This is my first build so please feel free to steer me in the right direction if you see my going the wrong way.

    As all the work i currently do is aluminium and plastic and the build volume is too big for a mini mill conversion.

    Goals:

    -Eat aluminium for breakfast.(Possibly Steel with light cuts)
    -Cast in SG iron
    -Working area of 700mm x 550mm x 160mm
    -Fully enclosed with flood coolant.
    -Easily replaceable fixture plate.
    -Base to be machined in 1 operation and gantry to be machined in 2 operations.
    -Cut out in bed to allow for larger parts.
    -Gecko Drive G540
    -UCCNC
    -Double nut ball screws with angular bearings and low backlash motor coupling
    -Hiwin linear guides.
    -4 pole 800hz spindle
    -Landrover engine mounts

    Things i need some help with.

    1. I was planning to put 25mm linear guides with double blocks on both X and Y axis with a 2005 ball screw. 20mm linear guide with 1605 ball screw for Z axis. I know that this is slightly over kill but is there a disadvantage to going overkill with these bearings? Assuming i can machine my tolerances high enough to mount them correctly.

    2. What have people found to be the best homing switches? I was planning to use some inductive switches. As i plan to try mount some fixtures and possibly a 4th axis in future.

    3. What have people found to be the most ridged Z axis arrangement? Ive noticed in lots of builds the spindle sicks out rather far.

    Ive still got lots missing in the attached image. I am currently trying to concentrate on the base, gantry and Z axis.

    Any help is very much appreciated.

    Rohan

  2. #2
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    Join Date
    Jan 2005
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    12539

    Re: Cast Bench Top CNC Build

    Quote Originally Posted by KiwiEngineer View Post
    Kia ora,

    Thought id share some concepts of a new build im currently doing. This is my first build so please feel free to steer me in the right direction if you see my going the wrong way.

    As all the work i currently do is aluminium and plastic and the build volume is too big for a mini mill conversion.

    Goals:

    -Eat aluminium for breakfast.(Possibly Steel with light cuts)
    -Cast in SG iron
    -Working area of 700mm x 550mm x 160mm
    -Fully enclosed with flood coolant.
    -Easily replaceable fixture plate.
    -Base to be machined in 1 operation and gantry to be machined in 2 operations.
    -Cut out in bed to allow for larger parts.
    -Gecko Drive G540
    -UCCNC
    -Double nut ball screws with angular bearings and low backlash motor coupling
    -Hiwin linear guides.
    -4 pole 800hz spindle
    -Landrover engine mounts

    Things i need some help with.

    1. I was planning to put 25mm linear guides with double blocks on both X and Y axis with a 2005 ball screw. 20mm linear guide with 1605 ball screw for Z axis. I know that this is slightly over kill but is there a disadvantage to going overkill with these bearings? Assuming i can machine my tolerances high enough to mount them correctly.

    2. What have people found to be the best homing switches? I was planning to use some inductive switches. As i plan to try mount some fixtures and possibly a 4th axis in future.

    3. What have people found to be the most ridged Z axis arrangement? Ive noticed in lots of builds the spindle sicks out rather far.

    Ive still got lots missing in the attached image. I am currently trying to concentrate on the base, gantry and Z axis.

    Any help is very much appreciated.

    Rohan


    Looks good. with some of my machine builds I use a similar Design style, but I fabricate in steel, my current build is 1 m x 2 m

    The Zaxis is always a challenge to get it as compact as possible without sacrificing rigidly

    You can use two Gantry Beams with the spindle in the middle, you have no stick out then, you need more rails Etc. with this design
    Mactec54

  3. #3
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    Jul 2018
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    3030

    Re: Cast Bench Top CNC Build

    Hi Kiwi Cus - Why the many webbed gantry? It won't be as stiff as a hollow section, especially in torsion and you will need substantial torsional stiffness for this machine& will be relatively heavy? The only way I think to reduce the stick out is to place the gantry rails on the top and bottom of the gantry, but this presents problems in machining the rail lands accurately. Depends on the type of mill you have access to to do this sort of machining... One advantage of the rails on top and bottom is that it puts the action centre of the Z axis closer to the shear centre of the gantry making it more efficient in resisting torsion... The bed and gantry are going in the right direction but the rigidity of the Z does not match them. It needs to be much much stiffer to get to where you will need....Oz Peter

  4. #4
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    Re: Cast Bench Top CNC Build

    Hi Rohan - Have you spoken to a caster about the design? Usually they don't like casting square or rectangular grids as when the metal solidifies and shrinks it pulls and distorts the shapes as it does not solidify evenly. The elements are usually made offset or slightly curved so as the metal shrinks it does not pull the geometry as much as they then have some stretch. Thats why wheel spokes are curved so they do not pull flats onto the rim... Peter

  5. #5

    Re: Cast Bench Top CNC Build

    Quote Originally Posted by mactec54 View Post
    Looks good. with some of my machine builds I use a similar Design style, but I fabricate in steel, my current build is 1 m x 2 m

    The Zaxis is always a challenge to get it as compact as possible without sacrificing rigidly

    You can use two Gantry Beams with the spindle in the middle, you have no stick out then, you need more rails Etc. with this design
    Thanks!

    I did look into a twin gantry style setup but it got a little complex and the extra added machining/required accuracy began to put me off a little. Definitely a good option if i had a decent machine i could use for low cost. Which unfortunately i dont

    Rohan

  6. #6

    Re: Cast Bench Top CNC Build

    Gidday Peter,

    Sorry the webs were simply there as a 2 second sketch up. Ive done a few quick mock ups what do you think? I guess no matter what way i do this im going to have to make some guide ways covers.

    Im guessing the base is going to be around 300kg and the gantry 100kg.

    Im really trying to avoid as many setups as i can. As currently i am planning to do this on a large manual mill. If it ends up i cant do it as simply as i imagined i know a work shop with a few 4 axis work centers that should hold it fine its more the $$$$.

    Cheers for the casting info! Surprisingly i did my apprenticeship at a large foundry and never understood why the flywheels looked like that til now.. thanks The caster is a good friend of mine and will no doubt let me know if my starting to get out of control with my designs.

    Ive got another idea for the Z axis ill share soon.

  7. #7
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    Re: Cast Bench Top CNC Build

    Hi Kiwi - "orthogrids" don't help you much in the stiffness dept. You need to triangulate as much as possible. This will help the structures rigidity and it will help keep the cast straight as it cools... If your good at making patterns why not try UHPC? mineral cast? much cheaper then CI and most of the CNC builders are going this way & you can do it in your garage... Peter

  8. #8

    Re: Cast Bench Top CNC Build

    Hi Peter, Ahh gotcha, yes i can change them to triangles. I will probably do the same to the base aswell. I was originally going to weld a steel frame, stress release it, cast it into a mold of epoxy granite then machine it. Have people had much success doing this? I cant say ive seen any done in UHPC yet.
    Rohan

  9. #9
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    Re: Cast Bench Top CNC Build

    Hi Rohan - Yes there are many machines of mineral cast or UHPC out there. Europe tends to go UHPC and EG there's a few threads here on EG and concrete. I'm playing with this one at the moment and its available in NZ... Rapidset have one as well but not sure its in NZ. Bluey have been very helpful with technical info.... So you use steel inserts for rail mounts etc then cast them in, then finish machine the inserts once grout has set.... A bag is cheap to play with so much cheaper then epoxy and 35GPa out of the bag.... same CTE as steel so good match there and only 2300kg/m3 so its light so just do solid casts nothing fancy unless your chasing light weight......If you look at my Milli thread it covers the testing I've done and the rabbit holes. Peter

  10. #10
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    Re: Cast Bench Top CNC Build

    Hi Rohan - Here's a company in Europe that does this sort of thing... Peter

    https://www.rampf-group.com/de/produ...stellbauteile/

  11. #11

    Re: Cast Bench Top CNC Build

    Hi Peter, Have been looking into some of the concrete and epoxy casting. I think i still actually prefer to go down the casting in SG iron method. Simply because if my one isnt a complete disaster i have a couple mates that would use my pattern to make one also. It saves on money but requires alot more time and effort to do the expoxy/concrete version.

    I think i need to do some more concepts of the gantry and base that i will post here if your still interested if i go down the the SG Iron path.

    Rohan

  12. #12
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    Re: Cast Bench Top CNC Build

    Hi Rohan - Always interested in what people are doing no matter what the material. Keep at it... Looking back at your build list: I use UCCNC and have found it to be easy and reliable. I have built a router with the G540 but I wouldn't (and haven't) done that again.

    1) You can't add a 4th axis to it easily
    2) Its limited to 3A per axis and some would say 48V is not high enough voltage. It says 3.5A per axis but I have had issues in the past running 4 axis at full amps and had to put 3A limiting resistors in place to stop occasional overcurrent stops by the gecko. This chopped my potential motor power down a bit...
    3) You can build it cheaper from individual parts then the G540 usual price. This then gives you 5 axis in future if you use a 5 axis BOB which costs $18AUD https://www.makerstore.com.au/produc...axis-breakout/
    4) The small plugs for the motors are a pain to solder if you have big fingers, prefer units with screw connectors and use shoestring ferrules https://www.jaycar.com.au/search?tex...1-197379ba64fc
    5) engine mounts?

    Where are you getting the 4 pole spindle? I'm looking for a 4 pole 12000rpm unit at the moment for a mill...

    Peter

  13. #13

    Re: Cast Bench Top CNC Build

    Hi Peter,

    As this is my first build i wanted to go down a path i thought would be the simplest or at least the path with the most documentation and resources. My original plan was to go towards servos and us Acorn but i think ill save servos till me electronic skills have increased. I am rather new the whole electrical side of things.

    I already have the G540 along with the stepper motors, powersupply and spindle. All i really need to do is finish designing roughly my router frame so i can order some ballscrews and linear guides from BST. The plan is to have all the mechanical and electronics components here and bench tested before i cast the frame and machine it so i can make sure everything fits and works together.

    1. I did buy the UT400ETH controller. So im hoping adding the the 4th axis to the second parallel port wont be too hard.
    2. All i guess i can do is hope i dont encounter this problem haha
    3. Maybe for my next build when i have a little more experience under my belt.
    4.The shoestring ferrules look good! Might have to give them a go.
    5. I had a couple lying around from an old engine conversion i did a few years back. Thought id use them between the router and the frame to dampen some noise.

    I brought the gpenny spindle. But its 800hz so 24k rpm. I did ask if they would modify the spindle for me to be 400hz, but they would not reply. Maybe its worth asking them, im sure they would be popular.

    Rohan

  14. #14
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    12539

    Re: Cast Bench Top CNC Build

    Quote Originally Posted by KiwiEngineer View Post
    Hi Peter,

    As this is my first build i wanted to go down a path i thought would be the simplest or at least the path with the most documentation and resources. My original plan was to go towards servos and us Acorn but i think ill save servos till me electronic skills have increased. I am rather new the whole electrical side of things.

    I already have the G540 along with the stepper motors, powersupply and spindle. All i really need to do is finish designing roughly my router frame so i can order some ballscrews and linear guides from BST. The plan is to have all the mechanical and electronics components here and bench tested before i cast the frame and machine it so i can make sure everything fits and works together.

    1. I did buy the UT400ETH controller. So im hoping adding the the 4th axis to the second parallel port wont be too hard.
    2. All i guess i can do is hope i dont encounter this problem haha
    3. Maybe for my next build when i have a little more experience under my belt.
    4.The shoestring ferrules look good! Might have to give them a go.
    5. I had a couple lying around from an old engine conversion i did a few years back. Thought id use them between the router and the frame to dampen some noise.

    I brought the gpenny spindle. But its 800hz so 24k rpm. I did ask if they would modify the spindle for me to be 400hz, but they would not reply. Maybe its worth asking them, im sure they would be popular.

    Rohan
    Don't worry about Ac servos they can be less complicated to setup than using steppers, not all are created equal though

    For your casting if in doubt, you can get software and do a flow analysis, for designing the best use of webs Etc.

    Casting Simulation
    SolidCast
    Flow-3Dcast
    Mactec54

  15. #15
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    Re: Cast Bench Top CNC Build

    Why SG iron instead of gray iron? Gray iron is less expensive and has better damping qualities. Is the ductility of SG an advantage here?

  16. #16

    Re: Cast Bench Top CNC Build

    Hi Mactec, I think some servos in future would be good! Something like the clearpath ones seem to be an easy physical replacement. Ived used stepper motors before so i feel comfortable with those. Baby steps for me haha.

    My friend who is creating the pattern is a wiz with flow simulation so ill leave that to him.

    Rohan

  17. #17

    Re: Cast Bench Top CNC Build

    Hi dixdance,
    You are correct, grey iron is low cost, better in vibration and better machine ability. With SG iron having a higher tensile strength and elongation then grey iron. In all honestly i will probably go down the grey iron path, the more i research the difference between the 2.

  18. #18
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    Re: Cast Bench Top CNC Build

    Quote Originally Posted by KiwiEngineer View Post
    Hi Mactec, I think some servos in future would be good! Something like the clearpath ones seem to be an easy physical replacement. Ived used stepper motors before so i feel comfortable with those. Baby steps for me haha.

    My friend who is creating the pattern is a wiz with flow simulation so ill leave that to him.

    Rohan
    I don't call Clearpath a servo of choice low pole count, low encoder PPR not really suitable for CNC machines
    Mactec54

  19. #19
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    Re: Cast Bench Top CNC Build

    Hi Mactec

    I am curious. I looked up the Teknic web site for the ClearPath motors, and was a bit confused. It seemed as though they were telling me what they wanted to say, but I could not get answers to my questions.

    It may be of course that I was expecting something different from what they offer. I was looking for details like angular resolution (I did find it, but the spec was obscure) and how to connect a ClearPath DC motor to a Gecko servo driver for a CNC. I imagine that the stuff might be fine if you want to automate a production line, but I could not see how to hook it up to, say, Mach3 or Mach4.

    Help?

    Cheers
    Roger

  20. #20
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    Re: Cast Bench Top CNC Build

    Quote Originally Posted by RCaffin View Post
    Hi Mactec

    I am curious. I looked up the Teknic web site for the ClearPath motors, and was a bit confused. It seemed as though they were telling me what they wanted to say, but I could not get answers to my questions.

    It may be of course that I was expecting something different from what they offer. I was looking for details like angular resolution (I did find it, but the spec was obscure) and how to connect a ClearPath DC motor to a Gecko servo driver for a CNC. I imagine that the stuff might be fine if you want to automate a production line, but I could not see how to hook it up to, say, Mach3 or Mach4.

    Help?

    Cheers
    Roger
    You can use any software you want to use, they have there own built in drive, so no other drive is needed, this is the part most fall for, you are correct automation would be there ideal use

    They have more than one Encoder resolution option, the cost goes up with each step up, even there highest resolution is no where near what you want it to be for CNC machines, the magic number for encoders is the minimum of 14Bit so any number above this is Ideal for CNC machines and of cause the pole count of the servo motor there Pole count is ( 3 ) the normal Ac servo motor is ( 10 ) Pole to ( 12 ) Pole
    Mactec54

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