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  1. #1
    Hi all.

    I'm really in need of some advise and reading through the threads here it appears I might have found the right place!

    I previously had a useless MDF(!) CNC router that was a complete waste of money and I have regretted buying it ever since!

    That was a few years ago and I am now after something new that actually works.

    I already have a set of 4 Nema23 steppers (KL23H2100-30-4B @3.5N.m. They don't seem too bad and drove a 4ft MDF gantry OK. I would like to reuse them to keep initial cost down and upgrade them if necessary later. Same goes for the 36v supply and driver (not sure of the drive make/model as I type).

    As for the rest its a clean sheet design.

    Requirements
    Cutting area: 800x600x100mm minimum.
    To cut: Mostly sheet plastics (5~8mm Acrylic) - This is the primary use.
    Aluminium parts (hence the 100mm Z requirement)
    PCB boards
    Some engraving (but I know a guy with a laser engraver so hopefully not)

    Budget
    I am looking to spend between 800 - 1000.

    Construction Ability
    I only have a drill press, Mitre/Table saw and no access to a machine shop so anything I can construct needs to either be done by someone else or using these tools. I know a guy who makes gates and things professionally (but haven't approached him yet) so it might be possible to get things welded but I don't know.

    Questions
    So before I start planning I have a few questions.
    1. I have seen routers on here that use aluminium extrusion and I think I can cut that accurately enough on the table saw but they use aluminium plate for the gantry sides and end plates which I can't construct. If I was to go down that path how much (as a ballpark) should I expect to pay to get them made for me? I need this to come in at least on budget.

    2. I have also seen routers on here that are made from steel profile which (assuming I can get it welded) works out cheaper? Is there an advantage to using it over aluminium profile or is the profile better for my needs?

    3. Screws. I was thinking of dual x-axis screws and singles on the rest. As for diameter and pitch I'm not sure what should be best over these distances. Some of you seem to favour 1610s, others 2005s. I don't mind using pulleys to drive them so I can adjust the ratio between stepper and screw as long as it doesn't add too much to the cost.

    4. Rails. Profiled or supported? Cost is really the decider here I guess, and perhaps how I'm mounting the gantry. Perhaps when I have a design in mind I should ask this again! A bigger question is how do I mount either? I don't know how accurate either the profile or extrusion would be and have never used epoxy and don't have access to any milling or grinding machines.

    I hope someone on here will be able to answer these for me or impart some advise on these issues. It will help me make some design decisions before I make a start.

    Thanks all.
    Tom.

  2. #2
    Welcome to the forum Tom, my advice would be to have a read through some of the build logs as you will learn a lot just by doing that & probably answer some of your questions as well.
    The nema 23 motors will be fine so will the power supply & drivers although you might want to think about upgrading the power supply & drivers at a latter date, better off running the motors at 70v rather than 36v.
    Your budget should be fine as you already have the electronics sorted for now.
    Can't answer your question on what you would pay for gantry side plates but there are guys on the forum that will machine parts for people so just ask for a price when you get to that stage.
    Problem people have with steel is keeping it square & flat especially when welding which will distort it making mounting rails more difficult. Some people use an epoxy coat to achieve the flat surface they need. Some people will build the frame from steel but then use aluminium extrusion or square tube for the table & gantry.
    Profile rails are much better than supported rails but it comes down to price, they are more expensive & supported rails will still do a good job. Some people will opt for supported rail for the x & y axis & profile rail on the z axis.
    At the size your planning 1610's will be ok & will give you better speed & feed rates than 2005 ballscrews.

    Once you have read a few build logs then you can start a new thread with a design for your machine, best to design it before you start buying parts, once you have posted a design or the start of a design then some of the more experienced members will help you make sure the design is suitable for your needs before you start manufacturing it.
    Hope that helps a bit, good luck with it all.

  3. #3
    Martin has pretty much said it all.

    Profile rails are much better but are are less tolerant to mounting errors so if you have limited access to tools then you will need to shim and grout to make them level. Otherwise you will lose the advantage of them.

    Supported rails can absorb some mounting error but at the cost of rigidity as they have a larger radial clearance. TBR blocks have adjustable clearance so you can maximise their rigidity (data sheets show lower load capacity but I think that is because they are rated with max clearance, need to check that tho.)

    For plastic and ali I would go for the 5mm pitch screw to keep the torque advantage. You can always gear up if using belts. Diameter is dependant on length/speed but 16mm should be ok.

    There are so many options its probably best to Post some designs to help further. Good luck

  4. #4
    For plastic and ali I would go for the 5mm pitch screw to keep the torque advantage. You can always gear up if using belts. Diameter is dependant on length/speed but 16mm should be ok.

    Ross obviously I got this one wrong, still learning myself & haven't started machining yet other than a few test pieces. Reason I had said 10mm pitch screws was because I was under the impression that you had to use fast speed & feed rates for cutting plastics. Have I got that wrong or would you just gear up 2:1 for that.

  5. #5
    Quote Originally Posted by martin54 View Post
    For plastic and ali I would go for the 5mm pitch screw to keep the torque advantage. You can always gear up if using belts. Diameter is dependant on length/speed but 16mm should be ok.

    Ross obviously I got this one wrong, still learning myself & haven't started machining yet other than a few test pieces. Reason I had said 10mm pitch screws was because I was under the impression that you had to use fast speed & feed rates for cutting plastics. Have I got that wrong or would you just gear up 2:1 for that.
    No not wrong at all. I just think that for Ali and plastic 5mm would be safer as the Cutting force is higher with Ali than plastic. If the speed is an issue then yes it is a simple job to gear up as plastic is lower cutting force and the steppers are 3.5N

    You could take the other approach of gearing down a 10mm pitch which gives the same speed/force but the 10mm ballscrews are less rigid than the 5mm so you would lose out there.

    Theres no real right or wrong way but I figure it is best to make it as mechanically as strong as poss and then pick/upgrade motors later.

  6. #6
    Thanks for the advice Martin and Ross.

    I have made a start on some designs after reading through a heap of build logs. Seems that for my size of machine I would be pushing the budget too far to get HIWIN 15mm rails on all the axis. Perhaps I will have to have HIWIN on the Z and build in some upgrade paths for HIWIN on X and Y in the future if I find the machine needs it.

    Also thanks for the info on welding problems in regards of accuracy. I think I should be aiming for something similar to this one, in particular JAZZCNC's machines in the second post of this thread http://www.mycncuk.com/forums/diy-cn...ign-build.html

    The info on the screws is useful too. I hadn't anticipated the torque required for aluminium, I was worried about whipping. Speed is of secondary concern after the accuracy. I would rather run for 10hrs and be accurate than 5hrs and be sloppy. I will design with pulleys so I can have a bit of choice over it.

    I am having trouble finding Aluminium profile with prices listed to get a feel for what is affordable. Are there any preferred suppliers? I need to get a feel for how much I can expect to spend to help with design choices.

    Thanks.
    Tom.

  7. #7
    Try doing a search Tom, suppliers have been mentioned but can't really remember who as it's not something I have bought myself. I do remember JKN Ltd & value frame being mentioned but can't say for what reasons. May help with the search though. Aluminium warehouse are pretty good if you need full lengths of flat bar or tube but don't think they do profile.

  8. #8
    Quote Originally Posted by PilotTom View Post
    Thanks for the advice Martin and Ross.

    I have made a start on some designs after reading through a heap of build logs. Seems that for my size of machine I would be pushing the budget too far to get HIWIN 15mm rails on all the axis. Perhaps I will have to have HIWIN on the Z and build in some upgrade paths for HIWIN on X and Y in the future if I find the machine needs it.

    Also thanks for the info on welding problems in regards of accuracy. I think I should be aiming for something similar to this one, in particular JAZZCNC's machines in the second post of this thread http://www.mycncuk.com/forums/diy-cn...ign-build.html

    The info on the screws is useful too. I hadn't anticipated the torque required for aluminium, I was worried about whipping. Speed is of secondary concern after the accuracy. I would rather run for 10hrs and be accurate than 5hrs and be sloppy. I will design with pulleys so I can have a bit of choice over it.

    I am having trouble finding Aluminium profile with prices listed to get a feel for what is affordable. Are there any preferred suppliers? I need to get a feel for how much I can expect to spend to help with design choices.

    Thanks.
    Tom.
    Hi Pilot Tom
    Hope you are getting on well with your design. I have worked up the final drawings and going with Jazz's approach on the use of 80x40 heavy extrusions arranged in an L pattern, with 20mm toolpate for the Z axis and 20mm plate for the gantry sides. After just purchasing a VFD and 2.2kw spindle, it sure is heavy! so stiffness of the gantry is important.

    The guys on this forum give honest critical advice which has made the difference in my design and will ultimately save time and money. My buiild will start in a couple of months so watch the build log.

    Kind Regards
    Mike

  9. #9
    I have worked up the final drawings and going with Jazz's approach on the use of 80x40 heavy extrusions
    Ditto on using heavy sections, I bought a job lot cheap on ebay a year or two ago and it was a mix of light and heavy, the light is much weaker and only really any good for display cabs.

    Perhaps I will have to have HIWIN on the Z and build in some upgrade paths for HIWIN on X and Y in the future if I find the machine needs it.
    If you can, go for the profile rails on the z axis as this is always going to be the weakest section, loaded as a cantilever and also eccentric loading from the weight of the z axis.

    20mm plate for the gantry sides.
    Ok this is only my opinion and I realise that there are lots of machines thathave been built this way and work fine but to me it is a very inefficient way too do it. The gantry sides are the final link in the chain of transmitting force to the ground so really need to be treated as beams/columns. I would go for using 4040 extrusion with 6mm plates either side, probably the same weight but much stiffer. Again I'm not criticising using plate, it just not the way I would do it.

  10. #10
    Having nearly finished a build similar to what your describing (mine having a cutting area of 1200X700X200)
    Welded box section steel frame (50x50x3)
    45x45 heavy aluminum profile frame (on top of box section)
    20mm profile rails on all axis
    2x1500 2010 ballscrews for x axis, 1x1000mm 2010 ballscrew for y axis, 1x250mm 1605 ballscrew for z axis
    20mm side plates (milled with my home made MDF router) (very very slowly)
    electrics, stepper drivers x3, (from diy MDF special)
    2x nema 34 (for x and y axis) 1x nema 23(from mdf special)
    belts and pullys ect. ect ..... a bit over engineered?? oh yes !!! cost...................way more than i had expected (around 2.5k) 5 months to build....
    suppliers i got materials from
    http://http://aluminium-profile.co.u...KJN990520.html
    http://http://www.zappautomation.co.uk/en/
    http://http://www.aluminiumwarehouse...php?cart_qty=2
    http://http://www.beltingonline.com/...leys-bars-272/
    http://http://stores.ebay.co.uk/line...earings?_rdc=1
    and a big thanks to iwant1 as his build log was exactly the sort of thing i wanted to build
    http://http://www.mycncuk.com/forums...my-head-7.html
    hope this helps
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    Last edited by davethefixer; 21-05-2013 at 11:53 PM.

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