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  1. #11
    Ah Kitwin, the siren call of ‘just make it a bit bigger’! But I take your point, extra Y length does not change the design or performance significantly.

    And thanks for the appreciation Brian, I had hoped this would be of value to others. However others have already steered you away from gantry routers for steel

    So where has Jazz left me:

    Budget and spec is realistic (Hurrah) but time under significantly! I can live with the greater time commitment, though I expect I will be tempted into stretching the budget when it comes to the motors.and electronics. Definitely worth press on then:

    Frame
    Wood and plastic cutting router, so aluminum extrusion frame keeps things simpler for me.(avoids welding and steel work) Plates I will definitely be looking to cut/drill my own so will want to keep design simple.

    Quote Originally Posted by JAZZCNC View Post
    It's also very very important how it's all fastened together and plates etc. Done correctly it's very strong and perfect for wood routers.
    .
    Sure I will need to come back to what joining methods for extrusions are best once I have a first stab at the design.

    Mechanics
    Ballscrews all round, but only 3
    Single Y ballscrew will save a bit of budget, however I do need to cut ends of boards set vertically. With an under-table ballscrew and cross brace, I will needs to have the spindle sitting forward of the bearings enough to do this. I only need 65mm of cut distance beyond table. Is that a sensible design option?

    Gantry

    Quote Originally Posted by JAZZCNC View Post
    However, it's important that you have a piece of material which is a nice tight fit that goes into the slots between upper and lower profile.
    I get the material in the slots to lock the two extrusions together, but see that 10mm aluminium bar is not a standard size so what to use? Options seem to be either machine a ½” aluminum bar down to 10mm slot size on a router table or forget the slot filler and have multiple bolts. By creating a gantry length ‘washer’ with regular clearance holes along it, I could use it as a guide to drill the access holes in the lower extrusion, then install bolts in it to mate with slot nuts in the upper extrusion, so they are bolted every 50mm or so. Avoids having to machine material to tolerance?

    Electrics
    Tempted by closed loop steppers - looks like for 2nm nema23 steppers it is about £40 stepper plus £20 driver vs £80 for closed loop motor and driver, so maybe extra £20 per axis well spent. Where will I see the benefit besides getting error rather than inaccuracy due to missed steps?


    Electronics
    There are enough challenged already, UNCNC it is.

    Quote Originally Posted by JAZZCNC View Post
    Design is VERY VERY important and if done with a forward-thinking attitude then you can have a great machine for not a lot of money.
    But still all down to the design, so guess I need to fire up Fusion360 and start designing. Plan to start from the Z axis and work out axis by axis. The Z seems a simple matter of sandwiching 15mm linear rails and 1605 ballscrew between two plates and getting the heights and clearances right...we shall see.

  2. #12
    BDH's Avatar
    Lives in Mansfield, United Kingdom. Last Activity: 30-05-2021 Has been a member for 3-4 years. Has a total post count of 26. Received thanks 3 times, giving thanks to others 22 times.
    The mill that would be most suitable for converting is a Graham Engineering one with a round vertical column but I thought that I would need to replace the leadscrews & nuts etc. As a manual machine with DRO it is very useful.
    The other machine is a Tom Senior Major Mk2 ELT in horizontal mode.
    If anyone has any ideas about how one of these could be CNC'd then I'd be most interested.
    Brian

  3. #13
    Andrew,
    As my wife, an accountant, has often said, you have the triangle of Time, Quality and Cost. Decide on the level of any one and the other two are inversely proportional.
    An optimist says the glass is half full, a pessimist says the glass is half empty, an engineer says you're using the wrong sized glass.

  4. #14
    Quote Originally Posted by Kitwn View Post
    Andrew,
    As my wife, an accountant, has often said, you have the triangle of Time, Quality and Cost. Decide on the level of any one and the other two are inversely proportional.
    Wow! Mine just nags.

  5. #15
    Quote Originally Posted by Andrewg View Post
    Mechanics
    Ballscrews all round, but only 3
    Single Y ballscrew will save a bit of budget, however I do need to cut ends of boards set vertically. With an under-table ballscrew and cross brace, I will needs to have the spindle sitting forward of the bearings enough to do this. I only need 65mm of cut distance beyond table. Is that a sensible design option?
    Single or double ball screws it doesn't make any difference to if you can overhang or not. This is down to gantry design.
    Many will sweep the gantry beam back from the centre of the bearing plates to recover lost tablespace. However, in your case this can't be done because you need the spindle to project past the end of the bed so your better with the gantry beam inline with the bearing plates.

    There are other design methods, like having the long axis frame rails extend past the end of the bed. In this way you can have both methods and have any overhang amount you like(within reason). The cost is it takes up more physical room and slightly longer rails which cost more money.
    I've used this design on several machines so that a 4th axis can be used on the end for turning and fluting etc. The same can be done with extending the gantry at one side and using the length of machine for longer work. (See pics)

    Quote Originally Posted by Andrewg View Post
    Gantry

    I get the material in the slots to lock the two extrusions together, but see that 10mm aluminium bar is not a standard size so what to use? Options seem to be either machine a ½” aluminum bar down to 10mm slot size on a router table or forget the slot filler and have multiple bolts. By creating a gantry length ‘washer’ with regular clearance holes along it, I could use it as a guide to drill the access holes in the lower extrusion, then install bolts in it to mate with slot nuts in the upper extrusion, so they are bolted every 50mm or so. Avoids having to machine material to tolerance?
    Your way way over thinking this.!! . . . For machine this size it's not required. To be honest at this size you would get away with NO bolts. If not using the spacer method then 2 x M10 bolts spaced evenly along length and tapped into the upper profile will be more than enough.

    Quote Originally Posted by Andrewg View Post
    Electrics
    Tempted by closed loop steppers - looks like for 2nm nema23 steppers it is about £40 stepper plus £20 driver vs £80 for closed loop motor and driver, so maybe extra £20 per axis well spent. Where will I see the benefit besides getting error rather than inaccuracy due to missed steps?
    Depending on which you get then the main differences will be smoothness and speed/torque.

    The smaller closed-loop motors (<=3nm) all tend to be 3 phase and the motors use 0.9Deg step amount or 1.2 rather than 1.8deg found on typical hybrid steppers. This gives a smoother action but requires more pulses from the controller to get the same speed. But controllers like AXBB or UC300 etc have more than enough frequency so this isn't an issue.

    Being 3phase they provide more torque and allow higher rpm's. Typical RPM where torque starts to drops away is 1000-1100rpm for hybrid stepper motor. With closed loop it's around 1500Rpm, but this does depend on other factors like quality and voltage etc. But in genral they are faster and stronger.

    Larger (=> 4Nm) Closed-loop motors can be found either in 3phase or two phase versions.



    Quote Originally Posted by Andrewg View Post
    But still all down to the design, so guess I need to fire up Fusion360 and start designing. Plan to start from the Z-axis and work out axis by axis. The Z seems a simple matter of sandwiching 15mm linear rails and 1605 ball screw between two plates and getting the heights and clearances right...we shall see.
    Don't use 15mm for the Z-axis as it makes more difficult to build regards clearances and they are fiddly. 20mm cost very little extra and make for a much stronger and easier to build Z-axis.
    Whatever you do don't cut corners on the Z-axis, it's THE one area you don't want to get wrong because it holds the tools so if it flexes or vibrates this will be seen in your work.!


    Below are 2 machine designs, both can be single or twin screws and placed under the bed for protection. The larger one will extend past the end of the bed and the side, it also adjustable length 4th axis.

    Edit: also a larger version with extended side rails for more front extension.

    Click image for larger version. 

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    Last edited by JAZZCNC; 11-04-2020 at 01:44 PM.

  6. #16
    Quote Originally Posted by JAZZCNC View Post
    Your way way over thinking this.!! . . .
    That is what I need - Keep me focused on the real issues

    Click image for larger version. 

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    Yes this is what I aspire to:Neat, clean, capable looking machine!
    From your previous posts I am assuming I am looking at
    - 45x90 extrusions on Y axis with two for the L gantry.
    - 12mm Plate for ends and gantry sides
    - 20mm linear rails all axis
    - 1610 ballscrew, 1605 on Z driven via belt and pulleys so steppers can be tucked out of sight, 1: 1 gearing? is it worth added parts?

    A little worried about the X/Z carriage getting complicated. If rails on front face and ballscrew on top, then couldn't it be a single plate again?

    I am assuming this design cannot cut beyond the table, but by removing the gantry sweep back and maybe mounting the rails on the face of the gantry (and removing the control panel) I could create sufficient over run.


    Quote Originally Posted by JAZZCNC View Post
    The smaller closed-loop motors (<=3nm) all tend to be 3 phase
    The ones I was looking at for price were like these appear to be just steppers with encoder and therefore not 3phase though these look similar but are described as 3phase and are £40 more so guess your advantages of 3phase closed loop will cost a little more. Know little about steppers besides frame size (NEMA) and torque (Nm) plus a vague idea that inductance needs to be worried about.

    Quote Originally Posted by JAZZCNC View Post
    Don't use 15mm for the Z-axis as it makes more difficult to build regards clearances and they are fiddly. 20mm cost very little extra and make for a much stronger and easier to build Z-axis.
    Again feedback from real experience appreciated. How much should I be worried about keeping Z axis weight down? I was assuming that on a small machine, I want to keep the weight being flung about to a minimum to ensure good acceleration and performance whilst allowing modest (lower cost) motors and drivers to be spec-ed.

    Working on a Z axis, need to upgrade the rails to 20mm!

  7. #17
    Quote Originally Posted by Andrewg View Post
    From your previous posts I am assuming I am looking at
    - 45x90 extrusions on Y axis with two for the L gantry.
    - 12mm Plate for ends and gantry sides
    - 20mm linear rails all axis
    - 1610 ballscrew, 1605 on Z driven via belt and pulleys so steppers can be tucked out of sight, 1: 1 gearing? is it worth added parts?
    Yes 45 x 90 with 10mm slot Bosch Rexroth or equivalent with this style of machine. This is type and size is required to allow easy fitting ball screws because the slots match up with Bk12 bearing blocks so no extra plates are required.

    12mm could be used for the end plates but I wouldn't use it for the gantry sides and Z-axis. Normaly I would use 15mm for the end plates and making motor mounts etc and use 20mm for the gantry sides and the Z-axis.


    Quote Originally Posted by Andrewg View Post
    A little worried about the X/Z carriage getting complicated. If rails on front face and ballscrew on top, then couldn't it be a single plate again?
    Well yes and No.
    Yes could be done but with this design, it compromises the machine in other ways. Rails on the front face only mean the distance between the rails is narrow so there's less support to the Z-axis rear plate.
    Next the ball screw on the top means extra plates will be required so the bearings can be mounted, this means extra work and it also raises the screw high up the Z-axis rear plate causing an imbalance in how the forces are applied.

    Quote Originally Posted by Andrewg View Post
    I am assuming this design cannot cut beyond the table, but by removing the gantry sweep back and maybe mounting the rails on the face of the gantry (and removing the control panel) I could create sufficient overrun.
    No, it can't, well it does but not by much. This design doesn't suit cutting past the front. If you want to cut past the front then use a gantry design like what's used on the other machine along with a slightly different base frame for rail placement.

    That machine uses ITEM style profile 120 x 80 with an 8mm slot. It makes a very stiff gantry and if you look closely you'll see one rail is on the front face and the other is on the top.

    If you like I could quickly knock you up a model of how it would look.?



    Quote Originally Posted by Andrewg View Post
    The ones I was looking at for price were like look similar but are described as 3phase and are £40 more so guess your advantages of 3phase closed loop will cost a little more. Know little about steppers besides frame size (NEMA) and torque (Nm) plus a vague idea that inductance needs to be worried about.
    Those would work reasonably ok even thou 2 phase. The more important spec to look for is the voltage the drives can be run at. I
    inductance is important but it goes hand in hand with voltage and I won't get too deep into why now, let us just say more volts allows higher rpm's and negates slightly if inductance is on the high side.

    Now those drives allow Max 60vdc but that is the maximum and you never want to run at or near the maximum so we allow roughly a 10% tolerance on the voltage. So the ideal voltage for those drives is 54Vdc which will still allow the motors to give decent RPM.

    However, if I was going with 2phase these are what I would use. The extra Nm means you can push the machine harder but more than this the extra Voltage range allows for higher speeds. Another advantage and money saver is that they will run on AC or DC so if you run on AC you only need a transformer. Whereas with DC you need to build the PSU with capacitors and bridge rectifiers which costs more money.

    https://www.aliexpress.com/item/3279...69e73421AESKcL


    Quote Originally Posted by Andrewg View Post
    Again feedback from real experience appreciated. How much should I be worried about keeping the Z-axis weight down? I was assuming that on a small machine, I want to keep the weight being flung about to a minimum to ensure good acceleration and performance whilst allowing modest (lower cost) motors and drivers to be spec-ed.
    With 3Nm with 50+ Vdc or the motors, I suggested then for normal woodworking conditions with a typical 2.2Kw spindle, etc you don't need to worry at all.
    Only if you have special needs or are going to use the machine for work like 3D which has lots of high-speed positional moves and attach a heavy spindle-like ATC spindle will you need to consider weight or fitting higher rated motors that can handle it and give you the speeds you need?

  8. #18
    Quote Originally Posted by JAZZCNC View Post
    If you like I could quickly knock you up a model of how it would look.?
    If you have the time it would be very helpful!

    So the X/Z carriage with rails top and bottom and ballscrew behind, ends up being an inverted G rather than C - do you have a picture of the back?

    Lichuan 5.5N.m closed-loop step motor
    Ok those are seriously stronger motors than I was thinking off, but I guess it is good you are revising my expectations for when I finally try and calculate what power I need/can afford! I wont worry about weight then, as I can see you are directing me toward a seriously solid solution.
    Last edited by Andrewg; 12-04-2020 at 02:37 PM.

  9. #19
    Ok, Just banged out a rough budget.
    I'm sure there is much to add and adjust, but for now we are still near enough the £2k mark (£2,112 as I post this)

    It is Google Spreadsheet here

    Break it to me gentle what I have missed or under estimated

    Also: Links were just what I used for budget numbers, and does not indicate intention to use supplier or endorsement of them
    Last edited by Andrewg; 12-04-2020 at 09:31 AM. Reason: Link now allows comments on GSheet

  10. #20
    As of 9:30 - I guess your spreadsheet will be live and therefore subject to change as you respond to comments?

    I note the comment re. suppliers, but buying from China - usually the best option - figure on getting stung for import duty especially for big/heavy/shiny items like these.

    Those particular stepper drivers need DC so, depending on the transformer selection you might be cutting it fine (by £20 or so) for the rectifier & caps. Unless you've found a suitable toroidal transformer for £50. Hmmm, 36V?, and those stepper drivers?, you'll be compromising the potential performance - but that's a different question to the one you've asked here.

    You've completely over-egged your CY cable costs - but that's no bad thing. You can cover the costs of all cabinet wiring and marking with the budget you have.

    Oh, What about a cabinet to hold the control gear (+£75)? E-Stop ("oh shit!") button, miscellaneous switches, relays and bases, add £100 (or take that off your budget for the PC). Connectors etc, into the cabinet - add another £60, unless you're hard-wiring everything (I'd not recommend this option!).

    You'll need a 24V and 5V supply also. Think if you're using DIN rail and terminals in the cabinet.

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