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  1. #1
    Hi,
    I'm almost done with what i think is a reasonable design for a benchtop CNC mill. Bear in mind that i say that with no real idea what I'm talking about. I started off with an SX1 manual which i wanted to improve and the project, "grew legs" as they say.

    My hope is if I post a few shots of the model and some general info you more experienced folk will be able to give me some tips / highlight the weak spots. I have taken note of the point that is often said that there is no replacement for mass so while this is a benchtop machine it will have to be a fairly solid bench.

    To put some words to the pictures-

    The column is 2 No SX3 columns which are 100 x 50 cast iron box with a 10mm wall - width over the two 270mm
    The Gusset plates at the back are 10mm steel
    The Z Risers are 100mm high 25 x 100 steel with a 25mm plate on top for the columns to fix to.

    All the ways are linear slides all with 4 carriages
    Z 42 x 10 THK, cant remember the model
    X Hiwin 20mm
    Z Hiwin 25mm

    All Axis have Ballscrews
    Z 1605 from CNC4you
    X & Y 1204 probably from BST Motion

    The Base is a cast iron Surface plate with a 25mm thick top plate

    the belt drive is a DIY to give 2:1 up gearing and about 2:1 down. driven by a 500w BLDC sewing machine motor. which runs 200-5000 RPM

    I hope to be able to cut steel, but have no particular speed in mind.

    Solidworks puts the mass at C.142kg

    The base is 24" x 18" and the Z is about 600 high.

    Any questions or comments welcome

    Click image for larger version. 

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    Cheers,

    Luke

  2. #2
    Looks like a good start. Some comments from me:
    500 Watt motor seems a bit underpowered if you want to cut steel regularly. It is BLDC which should help so is it a special high torque version ?

    The plates holding the pulley assembly look cantilevered off the motor body. Can they join back to the black housing to stop them vibrating?

    Main black housing is quite narrow and the footprint ends up some way inboard of the Z rails. Can this be widened at the rear or diagonal bracing added?

    Think about how you will cover the rails with bellows or way covers.

    Think about if you will add flood coolant and provision for a tray around the Tslot table.

    Is the space above the spindle for a future power draw bar? If not make sure there is space to add one.

    Make sure there is provision to tram the spindle and column relative to the table. Either a fancy method or bolted joint with shims.

    Otherwise looking good.
    Building a CNC machine to make a better one since 2010 . . .
    MK1 (1st photo), MK2, MK3, MK4

  3. #3
    Double post sorry
    Building a CNC machine to make a better one since 2010 . . .
    MK1 (1st photo), MK2, MK3, MK4

  4. #4
    Double the vertical size of your Z axis carriage, at least.
    You think that's too expensive? You're not a Model Engineer are you? :D

  5. #5
    Muzzer's Avatar
    Lives in Lytham St. Annes, United Kingdom. Last Activity: 7 Hours Ago Has been a member for 4-5 years. Has a total post count of 370. Received thanks 47 times, giving thanks to others 7 times.
    Yes, the carriage height in Z (top to bottom of the moving body) is very short and quite a bit less than the overhang of the spindle. Also the depth in Y from the spindle to the column is fairly limited. Once you have a vise in there, you will lose some of that, reducing it even further. The Sieg cast columns are standing on spindly pillars - solid blocks would be sensible.

    Looks like a plan though - get cracking and show us how you get on! You are bound to evolve the design as you go so the sooner you start the better.

  6. #6
    Everything the others mention plus a few more.
    #1
    Widen the Y-axis rail spacing, you have plenty of space so use it. Also, this will allow easier access to the bearings bolts, the way you show it now looks like you the X-axis bearings will block access to the Y-axis bearing bolts.?

    #2
    The triangle plates at the rear I would move to the outer edges and fasten to the side of the columns, this will give a wider footprint, I'd also think about adding some lateral bracing to add sideways support. Like muzzer mentioned the column risers look a bit flimsy so maybe beef these up.

    #3
    It's been said but worth mentioning again because it's a Biggy. The Z-axis plate needs to be double the height and the spindle housing needs to be wider.
    Also, the spindle motor plate needs supporting or the vibrations will kill the spindle bearings and vibrate on the machine general.

    Good luck.
    -use common sense, if you lack it, there is no software to help that.

    Email: dean@jazzcnc.co.uk

    Web site: www.jazzcnc.co.uk

  7. The Following User Says Thank You to JAZZCNC For This Useful Post:


  8. #7
    The z axis ratios are way wrong -- as others have said.

    You need about 1.5 x width/depth vs height for best results.
    Aciera comes to mind.
    Deckel.
    Schaublin.
    About 2x for most commercial machines.

    So if you have 600 height you should have 300-400 mm width and depth for best results, and not less than about 250-300 in each dimension.
    Itīs dirt cheap , relatively.
    All modern machines use similar methods with large sections and relatively thin walls around 10 mm.

  9. #8
    Thanks to everyone for the responses. You've mentioned a couple of things that i'd considered but definitely brought some new ideas up as well.

    RouterCNC,


    The whole head is a weak point i think, The project started off as upgrading a Clarke CMD10 and the only bit that remains in the head and spindle as part of tis design. I think ultimately it will be changed later on for a bt30 spindle.

    Click image for larger version. 

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    This is the head from the CMD it has a 30mm travel on the Z for drilling and the spindle moved relative to the head, that's the reason the pulley drive is canter levered that way. I left that function as it was there but on reflection it wont really be that useful on CNC so i can drop it to its lowest height an fix the back of the pully base plate to the head.

    The 500W motor was to be an upgrade from the 150W motor on the clarke mill which seemed a reasonable size for the mill, Its a JACK sewing machine servo motor but think it has gone the other way now. I think at this point id prefer to have the motor underpowered to the mill frame than the other way round but i may upgrade the motor later depending on the spindle



    Main black housing is quite narrow and the footprint ends up some way inboard of the Z rails. Can this be widened at the rear or diagonal bracing added? - I'll add diagonal bracing.

    Think about how you will cover the rails with bellows or way covers. - I do intend to include this but haven't modelled it yet,

    Think about if you will add flood coolant and provision for a tray around the Tslot table. - Yep the plan is for this to be in an enclosure the floor of which will fall to a central drain.

    Is the space above the spindle for a future power draw bar? If not make sure there is space to add one. - Will do

    Make sure there is provision to tram the spindle and column relative to the table. Either a fancy method or bolted joint with shims. - [B]This ive been thinking about, i can work in provision for adjustment even if it is, like you say, shimming but I cant work out how to measure it[. I can tram the head with a dial checkng front, back and side to side in the normal way but what worried me is ensuring the Z rails are vertical. If not it may tram ok but at the head moved in the Z it will move relative to the X and Y. ANy tips on that would be great/B]

  10. #9
    magicniner.

    Thanks, when i first modelled it i had the wrong linear rail blocks and the height of the z carriage came out at 175mm, when i actually put it together ang butted the blocks up it turned out it was 100, so I re-modelled it to suit.

    It did strike me that is looked wrong then but I've already made the dam thing.

    I think that will be the first job of the mill, to make a new Z carriage mounting plate. Ill change it on the model to make sure nothing else will clash later on

  11. #10
    Muzzer

    Cheers for you comments. The one about the pillars surprises me i thought 25 x 100 solid steel bar would be over the top if anything. My logic was that the columns only contact at those points and are relieved in the middle of the base, so with the 25mm thick flat bar fixing the top of the risers, and the plate at the bottom i thought it would be as strong as having them on straight to the base plate.

    carriage height in Z (top to bottom of the moving body) is very short and quite a bit less than the overhang of the spindle. Yes I will increase this to 150 - 200mm from the 100 it is now

    Also the depth in Y from the spindle to the column is fairly limited. Once you have a vise in there, you will lose some of that, reducing it even further. - I tried to space it so the axis of spindle was relatively central to the limits of the Y travel, see below. Would it be more useful further out. Lack of experience on my part to know this

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    Spindle axis to table edge - 23.5mm

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    Spindle axis to table edge - 10.42mm

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