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  1. #21
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    on EBAY they have a 3 axis 6040 router, all the way from jolly China, which gives you approx 2 feet X 14 inches X 3 1/2" of working capacity and will cut aluminium as well as the usual blah blah etc.
    you probably right , it s wiser to start with buying such a machine , but I can not give up on learning to design one that easily even if I eventually ended up buying one .

    You haven't stated a budget or your machining capabilities......design is totally dependent on both options.
    I donno what u mean by my machining abilities but I m good with measuring and cutting if it s what you mean , I can weld too but I don have any welding equipment , If it makes such a huge different I may buy a cheap one for this job , doesn't hurt to have one around , and as for my budget I m thinking of around 4 to 5k and maybe a little more to expand .

    you could glue the sheet metal to a sacrificial MDF board, using a glue that is heat sensitive and melt the glue off after you finish.
    thanks for the tip

    anyhow I was very busy but I ended up with this one , I tried to explain some of the materials on the pic , as you see I tried to go with a full supported base and minimize the gantry arms , I ended up with putting the Y axis rails on left and right sides instead of top and bottom config , I donno if it has a weak point that I couldn't think of , I didn't see anyone design it this way .
    I used 1.5x1.5 steel square tubes at bottom , My biggest concern is the 1/4" brackets I used for ballscrews end supports , I donno if they are strong enough to hold them or not .
    this is what I ended up for now , I learned lots of my mistakes from your replies , so don look at this as a final design just be kind and try to point me my mistakes or what I could have done better .

    Regards

    Attached Thumbnails Attached Thumbnails New CNC Design - Design Check (Again :D)-cnc-3-5-f-01-ii-jpg   New CNC Design - Design Check (Again :D)-cnc-3-5-f-02-jpg   New CNC Design - Design Check (Again :D)-cnc-3-5-f-03-jpg   New CNC Design - Design Check (Again :D)-cnc-3-5-f-04-jpg  



  2. #22
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    Hi, never be put off by someone else's idea of the ideal machine, whatever, most times they haven't even got a machine and can only go by what they think will work.......Henry Ford proved it can be done a different way.

    Your final rendition is unorthodox, but interesting.......you need to justify your design concept ...to yourself.

    Once you have the "ideal" design that surpasses all other designs...LOL.....walk away, put the computer file to bed, and sleep on it.

    The sub conscious will work out a lot of ideas without you knowing it, and a couple of days later when you open the file again, you'll see it in a different light........getting too close to the design for an extended period will blur you to either concept or proportions.

    That's how I see a situation that is new and conceptual.......it always could be done a different way once you have committed to making it.

    The old rule of think twice and cut once pays here.

    BTW, by abilities I tend to assume the other guy is a fully qualified machinist with design qualifications and a fully operational work shop with nothing to do all day but work on projects for the fun of it........rarely in the real World.

    With a budget of at least 4G's you can delve in the pool of the imagination quite a bit, but if you blow your total budget on a machine build concept and it doesn't fly, you won't be able to recover your outlay, except for break it up and retrieve the parts for another build etc.

    In the end it sometimes pays to get the feel of a working out of the box model and adapt the design for your own needs, selling the original one when you outgrow it.

    It's fun to design and build, but frustrating when it doesn't perform.
    Ian.



  3. #23
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    Hi, just been looking at your final design concept.

    I like the way you have "eliminated" the gantry side supports and made the Y axis slides directly under the X axis crossbeam.

    In my opinion this will stop the side flex that normal gantry design all have.

    Dropping the table down below the Y axis rails will give a close structure, and should be a big improvement on the gantry side plate current designs.

    I think this opens a whole new concept and a solution to the moving gantry rigidity problem.

    I have to wonder if this design is current practice, but if not it needs a more closer evaluation.

    One of the problems with a wide X axis is the slewing affect of a central ballscrew, but there are also potential problems with the twin screw design if one stepper fails and the other is unable to drive against the other stationary screw.

    That is, unless the method of coupling the two screws to a toothed belt and driving with one central stepper to guarantee drive under all circumstances.

    Having two steppers and coupling with a toothed belt will work but if one stepper fails the other is at twice load.

    I think the long toothed belt will have problems too from stretching, and I'd think that a cross drive shaft with two mitre gears to the screws will eliminate the need for a long belt, still using two steppers but making the system fail safe.....backlash in the gears won't be a problem as they are only a synchroniser in case of one stepper failing or missing steps.

    Looking at the first drawing in post #21, I would make the X axis crossbeam a bit more of a box section to resist torsional deflection from the cutter under load and keep the configuration of the linear rails on either side of the beam at the top as it now is, but possibly add a third one at the lowest point on the front face of the beam.

    You show the side rails for the Y axis travel as 3"X 6" extrusions, so for the crossbeam, if this extrusion is doubled to give a 6"X 6" section that would make the X axis stiffer and less likely to bow or twist under load.

    Without the rail on the front face bottom the Z axis will be too unsupported in its lowest position.

    This means you will now have two rails on the front face, one above the other as is normal configuration and another on the back face at the top.

    It's possible that having only two rails, one above the other on the front face, will be a better design, but you'd need to make the crossbeam a square box section to do that, which is OK too.

    In the design you show in post #21, the X axis crossbeam is the main strong point as you now have no gantry side to worry about.

    I would have to think that with this design concept you could possibly mill steel if the material sections themselves were strong enough.

    I would even suggest that the total build be made in steel, not only from the economy, but also from the ability to weld it and the greater strength achieved.
    Ian.

    Last edited by handlewanker; 08-27-2013 at 09:12 PM.


  4. #24
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    Quote Originally Posted by boof View Post
    you probably right , it s wiser to start with buying such a machine , but I can not give up on learning to design one that easily even if I eventually ended up buying one .
    Only you know what your goals are. Just building a machine can lead to far more learned and an and a greater depth of understanding when it comes to carving out your designs. However it is a big detour if you goal is a machine to get product out the door.
    I donno what u mean by my machining abilities but I m good with measuring and cutting if it s what you mean , I can weld too but I don have any welding equipment , If it makes such a huge different I may buy a cheap one for this job , doesn't hurt to have one around , and as for my budget I m thinking of around 4 to 5k and maybe a little more to expand .
    Welded structures almost always require some after the fact machining to square up or flatten the structure. This isn't an issue for small weldments if you have a mill. Bigger structure may require a trip to a professional machine shop. That and ideally the weldments should be stressed relieved.

    thanks for the tip

    anyhow I was very busy but I ended up with this one , I tried to explain some of the materials on the pic , as you see I tried to go with a full supported base and minimize the gantry arms , I ended up with putting the Y axis rails on left and right sides instead of top and bottom config , I donno if it has a weak point that I couldn't think of , I didn't see anyone design it this way .
    I used 1.5x1.5 steel square tubes at bottom , My biggest concern is the 1/4" brackets I used for ballscrews end supports , I donno if they are strong enough to hold them or not .
    this is what I ended up for now , I learned lots of my mistakes from your replies , so don look at this as a final design just be kind and try to point me my mistakes or what I could have done better .

    Regards
    If you are looking to do precise machining of sheet goods this design looks far better than the previous one. Just make sure it meets your needs for Z height and clearance for X&Y.



  5. #25
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    Hi, there is one area I would voice concern about and that is the width of the X axis.....it appears to be very wide compared to the length of the frame/table.

    It is not a good policy to have the X axis crossbeam wider than you need, due to it having to span the two Y axis rails without any centre support.....any extra width increases the "springiness" of the beam when the Z axis is in the middle of the beam and applying it's maximum force from the cutter loading.
    Ian.



  6. #26
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    first of all thk u Ian and wizard for your replies and honest opinions
    Quote Originally Posted by handlewanker View Post
    You show the side rails for the Y axis travel as 3"X 6" extrusions, so for the crossbeam, if this extrusion is doubled to give a 6"X 6" section that would make the X axis stiffer and less likely to bow or twist under load.
    I would even suggest that the total build be made in steel, not only from the economy, but also from the ability to weld it and the greater strength achieved.
    I totally agree , I m now thinking that investing money on bolts and corner brackets is a bit of a risk and maybe by a couple more bucks I can invest on small mig welder and build the total base with steel tubes , it s a bit tricky to build it that accurate but if I make it , it would be much steadier and I wouldn't worry about wide X axis and if it bow or anything .

    but I m not sure about the Y axis beams , It s far more steadier if I make it by steel but it will become much heavier , so what do you suggest ? steel based bed and aluminum extrusion for moving parts ? or I should go for steel and use larger steppers ? and if I go for steel should I worry about ballscrews life time ?


    Without the rail on the front face bottom the Z axis will be too unsupported in its lowest position.
    It's possible that having only two rails, one above the other on the front face, will be a better design, but you'd need to make the crossbeam a square box section to do that, which is OK too.
    mmm , that s something to be rethink , I think I would go with one on top and the other one on other side at bottom .

    Quote Originally Posted by handlewanker View Post
    Hi, there is one area I would voice concern about and that is the width of the X axis.....it appears to be very wide compared to the length of the frame/table.
    the machine working envelope is about 25x25 , but i will change the design again and keep that in mind .

    so again thanks for your inputs , they really helped me understand what I m doing . tell me what do you think again , what should I keep in mind and watch out for if I go for a steel based machine and any other suggestion would be great



  7. #27
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    Hi, glad to see you are working your way through this design. May I ask what software you are using for your drawings as they are very nice indeed. I am about to start with 3D software for the first time so any help would be appreciated.

    Thanks.



  8. #28
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    Hi , i m using solidworks ,link : "3D CAD Design Software SolidWorks" , very good and very easy to learn (it was almost my first 3d software as well), it has a huge online library for almost anything you look for ,link : "Free 3D Models, Free CAD Models", it has a " hole wizard" that is a big time saver for making any kinda holes in your project , mass calculators and motion study as well ... and the standard version is around 3 to 4000$ I think , but the standard version doesnt have the photoview360 rendering ability (what you saw in my pix) neither the built in toolbox library (not that necessary but good to have it ) different versions comparison link : "3D CAD Matrix | SolidWorks"
    one other thing is if you buy one I suggest to buy Lynda.com solidworks essential training as well ,it s very good explained and very good point to start learning the package.
    Hope it helps



  9. #29
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    how about this for an ideal machine

    Datron M8



  10. #30
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    Hello Guys
    It s several revision after my last attempt here , whole steel frame (all welded together) , by my estimate it s gonna cost cheaper than a aluminum body even if I have to buy a small cheap mig welder but it s gonna be much more rigid , I didn't put my mind on how to transfer the motion from motors to ball screws except using direct drive system and I think i m gonna leave it as it is for now .
    the whole machine is gonna be around 200 pounds , i m worrying about the weight of gantry and donno if nema 23 motors are gonna be enough or not , so tell me what do you think , and any suggestion about the ball screws , motors and etc would be appreciated .

    Regards

    Attached Thumbnails Attached Thumbnails New CNC Design - Design Check (Again :D)-cnc-4-2-03-jpg   New CNC Design - Design Check (Again :D)-cnc-4-2-01-jpg   New CNC Design - Design Check (Again :D)-cnc-4-2-02-jpg  


  11. #31
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    With a G540 driver, NEMA23 380 or 381 oz-in steppers, and 48vdc your machine should have no problems since you are using two motors to move the gantry. That size machine, even built with steel, isn't going to have a gantry heavy enough to justify NEMA34 motors.

    CarveOne
    http://www.carveonecncwoodcraft.com


  12. #32
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    Hi Boof, I have to admire the layout of this latest design.

    I absolutely like the frame with all the cross braces.....should make it pretty rigid and able to resist deflection.

    The X axis crossbeam is good too......having the vertical spacers to firm up the long tubes makes for a rigid structure without adding too much weight.

    I would definitely address the twin stepper drive for the table......if one fails it will cause you a headache big time.......some form of synchronisation by toothed belt is needed, but this is just my opinion.......the issue may not be one in real life.

    BTW, a Mig welder does not have all that much capability for penetration, and you will probably get better results and cheaper too with a stick welder.........a Mig welder with more oomph will cost a packet along with the extras like gas and wire.

    The tubing for the frame work will need to be thick wall anyway if it's to do it's job.

    Is this going to be the final design layout for the router per se, or are you going to also have a base framework to mount it on so that it is a stand alone unit as opposed to standing on a bench?

    You will need some jacking points under the base (6?) to allow alignment once the welding is complete........it will twist if not supported properly.
    Ian.



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    You do not need to physically synchronise the X axis steppers. If you are in a situation where you will lose steps, a belt ain't going to save you.



  14. #34
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    Hi pippin88, the problem is with the Y axis (the table drive, not the X axis where a single screw is used), but where twin screws and twin steppers are intended to be used, one either side of the table, to off set the aspect of slewing the gantry such as when a single centre drive screw is used and the spindle is to one side of the bridge.

    If one stepper fails or misses steps you will have slewing and possibly damage to the linear rails when the gantry side plates go out of alignment.

    Coupling the twin screws to a toothed belt ensures both screws will stay driving even if one stepper misses a step or fails completely.......it doesn't matter if the other stepper consequently misses steps due to the increased load, at least the gantry stays parallel to the table.

    The table is intended to be 635mm (25") wide so this is not too wide to employ a toothed belt as back up.
    Ian.



  15. #35
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    If one stepper fails or misses steps you will have slewing and possibly damage to the linear rails when the gantry side plates go out of alignment.
    No way you can ever damage linear bearings from a stepper missing steps. Linear bearings can handle thousands of pounds of force. I'd expect the machine would be torn apart before a bearing would be damaged. If one motor gets out of position a little, though, the bearings will bind slightly, and both motors will end up stalling before any damage would be done.

    The reality is that a properly setup stepper machine should NEVER lose steps.

    Gerry

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  16. #36
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    I hate to think of the damage that can occur if one stepper fails .....for some reason.....and the gantry is caused to slew.

    The talk is about a home built router, so given that some error can occur....Murphy's law will find it out.

    Personally, I think I would drive the two screws from a single stepper placed in the centre and two short toothed belts to the ballscrews of the Y axis.

    That way you can have a more powerful stepper to drive twin screws with short belts to reduce springing, and achieve synchronisation all in one hit.

    BTW, the linear rails were not my main concern in a stepper loss, it was the warping of the gantry if/when one stepper stopped driving and the bridge warped across the frame.

    As you said, the other stepper would stall and also miss steps, but not before the Y axis bridge became distorted.

    In this final design, the length of the X axis bridge would guarantee that if one stepper stopped working, causing a virtual clamping effect, the other would, by way of the longer leverage it could exert to one side of the bridge, bend it like a banana.
    Ian.



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    I think it's extremely rare to have a stepper just fail; of course barring any electronic failure or wiring issue. That said, if you size your steppers correctly they will not stall. Also if your frame is stout enough the steppers will stall before any racking of consequence occurs; the 'danger' is if you use servos. Thousands of machines are built with dual gantry steppers with success.



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    Ian,

    The steppers will not be strong enough to cause damage to any decently sized gantry - they'll just stall. And stalling a stepper doesn't do it any harm.

    Running from a single stepper (rather than 2) means half the torque to move the large gantry.

    (Also the convention on routers is the X axis is the longest, the Y axis is usually the gantry).



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    Quote Originally Posted by pippin88 View Post
    Ian,

    The steppers will not be strong enough to cause damage to any decently sized gantry - they'll just stall. And stalling a stepper doesn't do it any harm.

    Running from a single stepper (rather than 2) means half the torque to move the large gantry.

    (Also the convention on routers is the X axis is the longest, the Y axis is usually the gantry).
    Hi, the "popular" convention......seems the Chinese who supply most of the routers on EBAY think otherwise.

    I think people who think the X axis is the long one are confused by the direction the slots in the table run.....I may be wrong in this assumption.......one day there will be standards of recognition that are standard.

    BTW, l I still would not rely on twin steppers to drive the table without some form of coupling.
    Ian.

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    I don't think there's a hard and fast "standard" other than, if you are standing in front of the machine, the axis running from your left to your right would be the "X" and the axis running towards you to away from you would be the "Y"; this is to reflect the coordinates used in your CAM. Obviously you cna configure it any way you want based on your needs.

    As to the coupling issue - there are thousands of commercial machines out there that run dual motors to move the gantry, and all without issues. These ae machines well over $100K, using servos, pushing gantries weighing upwards of a half ton or more, at speeds us DIYers mostly only dream about. I can see possibly an MDF machine tearing itself apart. If your motors can tear your machine apart, I would reconsider my motor sizing or machine design.



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