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  1. #21
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    Quote Originally Posted by TumbiUmbiTek View Post
    May I ask what controller software you thinking of using? Mach3, UCCNC or LINUXCNC
    Cheers
    Linuxcnc, mate.

    Happy Days.



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    Default Re: DIY CNC Design. criticism wanted.

    I'll have to check the calculators but I suspect that I wouldn't gain any speed running it at 60v series over 48v parallel. Yes I'll pick up on torque but I don't think that I'm really short on that.
    Series doesn't really gain you any torque at all. Motors are rated at the the same holding torque whether series or parallel, and in series, the torque falls off faster than it does for parallel.
    I agree, though, that 48V wired parallel should be faster.

    Gerry

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    JointCAM - CNC Dovetails & Box Joints
    [URL]http://www.g-forcecnc.com/jointcam.html[/URL]

    (Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)


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    Quote Originally Posted by joel0407 View Post
    Thanks for the comments all. Keep them coming.

    "Louieatienza" The motors will handle more voltage in series but then the inductance goes up considerably. I'll have to check the calculators but I suspect that I wouldn't gain any speed running it at 60v series over 48v parallel. Yes I'll pick up on torque but I don't think that I'm really short on that.

    "TWIST"

    Now I'm racking (pun intended) my brain over this. I'm going to guess that all that have problem with this have been running single screw on the X axis.

    If I stand at the end of the table and the X gantry is moving away from me. The force in the router bit is toward me. Now the Y Gantry attaches to the X Gantry at 4 places. 2 on the top, on the same plane and 2 on the bottom, on the same plane. So with the X gantry moving away, force on the bit toward me, the force on the bottom rail is toward me and the force on the top rail is away. It's irrelevant if the Y Gantry is toward the left or right as there is an even push from each ball screws on each X Gantry side.

    If we reverse the above and have the gantry moving toward me rather than away. Every thing is just opposite. The only force is forward and back on the top and bottom rails. Now I find the rails already very strong the short distance of 1m and than I'm backing that with 18mm ply sheet and then backing that with 50mm x 18mm support on the top and 40x40 aluminum angle at the bottom.

    I just struggle to see where the flex will come from.

    Should I be doing this with a single ball screw on the X axis. Firstly bellow the drag point of the bit then if the Y gantry is at it's extreme then you are relying on the bearing spacing. I could see this twisting the gantry no end.

    Happy Days.
    Exactly my point about the steppers. You won't need to run them above 48V, so you don't need a drive that runs max at 80V.

    As to twist, I'm referring to the gantry's axis, not "racking..."



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    Default Re: DIY CNC Design. criticism wanted.

    [QUOTE=joel0407;2063282]
    Quote Originally Posted by ger21 View Post
    I agree that the screws should be OK on that size machine. With AM882's, you can run in the 50-60V range, which should get you good speed.

    Yep. I'm going the AM882 drivers mainly for the extra voltage handling. Sure there are plenty of cheaper options but not many that will handle the voltage.

    Regardless of how strong you think your plywood is, it will flex. You don't want ANY flex at all. I'd at least double the side plates, and make a torsion box gantry. At the very least, make the gantry 2-3 layers thick, with no cutouts.
    Another option is to make more cutouts in your gantry piece, and add a skin on each side of 1/4" baltic birch. This would make it a thin torsion box, and would greatly increase stiffness. As it's a smaller machine, this will probably be adequate.

    I'm starting to get worried by the number of people that doubt the strength of the marine ply. I can stand on this stuff with the 50mm back to create a U channel and get no flex. I'm doubting the router would handle 85kg of force. I'm also using 16mm supported rail. I've seen other machines use unsupported rail (with flex mind you). I'm sure my marine play gantry will exceed some of the T-Slot gantries that I've seen
    People are commenting because it can be an issue. First off I can assure you that you are getting flex when you stand on the plywood. How much is open to debate but the real issue is how much deflection can your machine handle before it goes out of spec? This of course is up to you and you requirements but getting 0.005" deflection out of a beam can be excessive for most people, then you have to consider twisting that a gantry beam is subject too.

    From my perspective there is nothing wrong with building in wood but you do need to design to leverage the material. This is why you see all the references to torsion boxes, laminated beams and such. Using good technique, a wood frame machine can do a good job for wood machining.

    If any thing this is where I think your approach needs a bit of work. First don't bother with machine screws unless you have assemblies that MUST come apart. If you do use threaded inserts in the wood. Other wise the various part of your machine should be assembled in the most permanent way possible. For me this means good glues and screws designed for wood. I'm in the habit of using deck screws in a lot of my wood projects but even so you have to use a good quality glue. Often the joints are further reinforced with gussets glued in place. You really want to be thinking structural wood working not cabinet making. Box sections are one thing to keep in mind when designing with wood.
    I'd add some triangular braces or square side panels on the Z axis plate. As drawn, it'll flex quite a bit the way the spindle is mounted.

    Thanks. I'd missed that.
    I seem to be having internet problems at the moment, more comments to come.



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    Default Re: DIY CNC Design. criticism wanted.

    Quote Originally Posted by joel0407 View Post
    Honestly. Initially, I only wanted to cut 6mm Pin Ply wood. LOL.
    Starting out with one requirement is pretty common, once you have a machine (any machine really) you suddenly find that it can do other things for you. Or it could do other things for you if you had the capacity to do so. With most of these DIY machine there is an attempt to balance capability against cost. This is where attention to detail in a wood build can pay off in the long run.

    The thing here is that you won't spend a whole lot extra on wood to produce a far more rigid machine. In the over all cost of things the extra wood (if any at all) will be rather small portion of the over all build. I'm pretty sure that you, like most people, will want to use this machine for all sorts of things beyond its original intention. That is why careful attention of detail is so important.
    That was it. I'm sure I'll use it for what ever I can though.
    That is a certainty.
    I'm liking some of the wooden gear machines I've seen. Most of the gears are cut from MDF but I might do something to look better from wood.

    Happy Days
    Gears are easily done on a CNC machine but you do want a stiff machine that repeats well. Depending on the specific gear you may need to make dozens of passes with a small cutter to get the correct profile and clearances. For this to come or well you need to be able to repeat each run around the circuit precisely.

    Some other comments:

    1. As mentioned above I really believe you wan tot use wood screws and glue as much as possible in your build. You want sound structures that act as a unit. People do use machine screws in wood but that is normally done in hard woods and the threads are know to have limited use capability. For anything you may want to take apart often, or make adjustable, I suggest looking into thread inserts for wood.

    2. Anything that is adjustable, say for a belt drive, make use of heavy and thick washers to spread out the clamping load across the wood surface. Sometimes a hardwood block (really hard wood) can help here. The idea here is that wood, most plywoods really, are pretty soft and could easily be deformed by the clamping screws and washers.

    3. #2 applies to your uprights that support the gantry. You will likely need some adjustability here as you square up and make the gantry parallel to the table.

    4. Once you have your adjustable pieces in the correct positions and everything test out correctly, it is a good idea to pin everything in place. In the automation world we often do this with dowel or taper pins. Wood leaves you with a lot of options here but the goal is to lock components into position after everything has been verified to be true.

    5. I can't overstate how important glue is in making the assemblies for various parts of your machine. This might should like beating a dead horse but you want each component to be have as a single structure. Further glued and screw joints often benefit from gussets and such. For example if you build a box beam, internal baffles acting as gussets of a sort, will stiffen that box beam and greatly reduces the parallelogram effect that can be seen in box beams. I know it may sound like people are obsessed with the stiffness properties of the machine but that is due to experience as one of the common weak links in DIY machine builds is the gantry.

    While wrong in some respects I liken glueing up wood to welding metal. They are a different solution to bolted up joints and offer a different set of mechanical advantage over the bolted up solutions.

    6. Plywood does give you the option of simply laminating up a bunch of pieces to get to a dimension that will be stiff enough for the purpose. For a one off machine it might be a lower traction / effort way to get to the beam dimensions you really want. If you have a big scrap pile or cutoffs bin you can also save some money.

    7. Remember to apply sealants or paints to the bear plywood assemblies. This moderates distortion from yearly humidity changes, it also makes keeping the machine clean a bit easier. Apply the sealants / paint to everywhere you can reach.

    8. Use common wood working joints in all structures where possible. Lap joints, dadoes and the like all improve joint strength and help with structure alignment.


    In any event the above are just some things that come to mind when working with wood to build machinery. The trick is to leverage its good qualities.



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    Default Re: DIY CNC Design. criticism wanted.

    Quote Originally Posted by wizard View Post
    8. Use common wood working joints in all structures where possible. Lap joints, dadoes and the like all improve joint strength and help with structure alignment.
    Normally, I'd agree with this. But not with plywood or even MDF. What gives them their strength are the outer layers. So when you cut through them as with a rabbet or dado, it may strengthen the joint in one direction but weaken the assembly in another. Especially true with MDF and in particular melamine - one reason adhesive such as "Roo Clear" work so well. Maybe one exception would be lumber-core plywood, which I believe does not come in a marine grade. A compromise would be Lamellos (biscuits) that do not cut through the entire veneer surface. Or maybe better the Festool Domino system.



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    Default Re: DIY CNC Design. criticism wanted.

    I'll get back to the comments soon guys.

    Not long out of bed and off to work now.

    Just pushed the button on the AM882 Drivers. Maybe over kill, maybe not. The motors (not purchased yet) are 5.66amp on Parallel.

    Happy Days

    Last edited by joel0407; 06-29-2017 at 03:22 AM.


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    Default Re: DIY CNC Design. criticism wanted.

    Motors and PS ordered. 48v, 7.3amp and previously linked motors.

    Happy Days



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    Default Re: DIY CNC Design. criticism wanted.

    I'm honestly struggling to understand how this is going to flex. I'm not trying to be intentionally rude to you guys and not believing you but I am having trouble to understand it.

    Please help me get my head around at least twist from one axis. Starting with X

    So the X gantry back butts up to the Gantry sides at right angles with 4 bolts that are not only tight in there holes but also provide clamping force. The Gantry sides sit on 2 bearing each that are 300mm apart. Given there will be very slight play in the bearings allowing very slight front to rear roll. I figure that play can't be over come easily and I will live with it. Maybe one day upgrade to square linear bearings and rail. I will consider this play irrelevant and call each end fixed for the purposes of this.

    So each end will not move in any direction front to back. The next possibility will be bend along the gantry. Now I can understand this if one end was fixed but I have both ends fixed. With both ends fixed, I see the weakest point to be the middle of the gantry. So if I was to extend a bar/lever down from the gantry to the bed. (This will be the router but I'll call it a bar for these purposes). Now if I grab that lever and push it back and forwards, the effect on the gantry will be back at the bottom and forward at the top when pushing back on the level and the opposite when the opposite force is applied. In the direction that I am pushing the force on the bottom of the gantry will be greater than the opposite force on the top of the gantry. The bottom of the gantry will be the fulcrum of the leaver working on the top. I think this force is different to twist observed when one end of an object (the gantry) is fixed at one end and a rotational force is applied at the other.

    I do enjoy thinking about this stuff. Exercise for the mind.

    Happy Days



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    Default Re: DIY CNC Design. criticism wanted.

    Quote Originally Posted by joel0407 View Post
    I'm honestly struggling to understand how this is going to flex. I'm not trying to be intentionally rude to you guys and not believing you but I am having trouble to understand it.
    I'm not trying to be intentionally rude to you, but...

    ...that's why I didn't post in this thread. I had a feeling when I read your post for the first time, before anyone posted any comments that you don't really want criticism but confirmation.

    There is only one way to find out who is right (you?) and who is wrong (people with a lot of experience in building machines?). I think you should build it. That will give you experience and you will learn a lot through your own mistakes about flexing, vibrations, twisting and so on. Of course, things which may matter for others may not matter for you, expectations are different, which is a problem when giving advice because what I and others may regard as pretty serious flexing or play, you may see as negligible and irrelevant.

    https://www.youtube.com/c/AdaptingCamera/videos
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    Quote Originally Posted by A_Camera View Post
    I'm not trying to be intentionally rude to you, but...

    ...that's why I didn't post in this thread. I had a feeling when I read your post for the first time, before anyone posted any comments that you don't really want criticism but confirmation.

    There is only one way to find out who is right (you?) and who is wrong (people with a lot of experience in building machines?). I think you should build it. That will give you experience and you will learn a lot through your own mistakes about flexing, vibrations, twisting and so on. Of course, things which may matter for others may not matter for you, expectations are different, which is a problem when giving advice because what I and others may regard as pretty serious flexing or play, you may see as negligible and irrelevant.
    Mate I'm open to critisim but I can't see how gantry twist is a problem. I expected it to be things like the one rail up and one forward kind of things.

    I think someone said I might not understand how much force the Ball screws can apply. Im more worried that my router would not handle that much force. It's only a Makita 700.



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    Default Re: DIY CNC Design. criticism wanted.

    Sorry. Struggling to post from my phone. Still at work

    Even cutting 6mm ply I was expecting that I might need to do it in 2 or 3 passes



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    Default Re: DIY CNC Design. criticism wanted.

    I notice most (not all) of you guys are in the US. I don't know if your marine ply is different as I've read that your ply only uses hard wood for the outer layers. All layers of the ply wood I'll be using are hard wood. I don't know if that makes much difference using machine screws.

    I'm not really a fan of the suggestions to just layer up multiple layers of ply. I've always stood by the motto "Design it strong. Don't just build it heavy". Although maybe you guys are suggesting that's the design to make it strong.

    My biggest worry at the moment is if the pre build with MDF will be strong enough to cut the 18mm Marine Ply. I think I'll be cutting at 1mm step at this stage.

    I should add here. I usually hate working with wood. My father has always been the wood person and I like steel. With steel there is either the equipment to deal with it very accurately or if your cutting and rough welding, you can always fill a mm or 2 with weld or grind a bit more off if you need. If you cut wood too short, well your up a creek without a paddle. Another reason for building the router is I'm hoping it'll cut stuff more accurately than I could ever cut it by hand. Hence partly why I'll whack it together with MDF and then use it to cut the ply for the final build. I guess I'll get an idea if the design will work with the MDF build.

    Happy Days.



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    Default Re: DIY CNC Design. criticism wanted.

    I've always stood by the motto "Design it strong. Don't just build it heavy"
    With CNC, mass is your friend. You don't want it to be light.

    An MDF machine will have no trouble cutting plywood. It's not really the material you build from, it's how you build it. The more rigidity you have, the better.

    If you only plan on using a small, low powered spindle, then you can probably get away with what you have shown. But when you start using it, and want to cut deeper, and faster, you'll start making upgrades, and then you'll realize what we are trying to tell you.

    Gerry

    UCCNC 2017 Screenset
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    JointCAM - CNC Dovetails & Box Joints
    [URL]http://www.g-forcecnc.com/jointcam.html[/URL]

    (Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)


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    Default Re: DIY CNC Design. criticism wanted.

    Quote Originally Posted by ger21 View Post
    With CNC, mass is your friend. You don't want it to be light.

    An MDF machine will have no trouble cutting plywood. It's not really the material you build from, it's how you build it. The more rigidity you have, the better.

    If you only plan on using a small, low powered spindle, then you can probably get away with what you have shown. But when you start using it, and want to cut deeper, and faster, you'll start making upgrades, and then you'll realize what we are trying to tell you.
    Thanks mate. I'm comparing it to other machines with DIY Linear bearings and T-Slot builds.

    I mean this one seems to go OK and without being able to see the back of the gantry, it appears to be a flat sheet.


    This one looks good but i can't see the point of the box gantry when the only thing attaching the X gantry to the Y/X are the unsupported rails.


    This Black toe has far less support in the gantry and a wider span and seems ok.


    I am impressed with this and I think mine gantry is far more ridged than this X-carve.


    I found this very impressive and like how cleanly it's built. I don't like how close the bearings are on the Z axis. Especially on unsupported rails. I think the T-Slot has to have more flex over this distance than my ply gantry will have over a shorter distance.

    I guess this is about as close to mine. He shows the twist he has about 5:50 minutes. All he has is supported rail with aluminum angle bolted straight to the back with nothing in between. Mine the angle plus the 18mm ply.


    These are all the kinds of machines I've been basing mine on.

    Happy Days.



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    Default Re: DIY CNC Design. criticism wanted.

    It's all about your expectations.
    I don't consider any of those machines to be any good. But I'm sure that there are plenty of owners of those machines that are happy with them.

    The Blacktoe is a very poor design, and has a lot of flaws. You can buy 10x the machine for what they charge for their kits.

    You can find a lot of X Carve reviews on Youtube that point out a lot of issues that it has with a lack of rigidity.

    Gerry

    UCCNC 2017 Screenset
    [URL]http://www.thecncwoodworker.com/2017.html[/URL]

    Mach3 2010 Screenset
    [URL]http://www.thecncwoodworker.com/2010.html[/URL]

    JointCAM - CNC Dovetails & Box Joints
    [URL]http://www.g-forcecnc.com/jointcam.html[/URL]

    (Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)


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    Default Re: DIY CNC Design. criticism wanted.

    Like I said...

    you don't really want criticism but confirmation
    So far, as far as I remember, you have dismissed EVERY good advice.

    I really think you should go ahead with building. You will learn as you progress... unless you give up half way.

    https://www.youtube.com/c/AdaptingCamera/videos
    https://adapting-camera.blogspot.com


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    Default Re: DIY CNC Design. criticism wanted.

    Quote Originally Posted by ger21 View Post
    It's all about your expectations.
    I think you are hitting the nail on the head there mate.

    This is my first machine and I'm not expecting to mill aluminum block at 0.001mm accuracy. I have no doubt it will go through some evolutions after it's built. I even have one evolution planned before I'm starting as I'm building it in MDF then using it to re-cut the pieces in ply.

    One idea in my head that is nothing more than an idea is at one day converting it to a CNC plasma. I already have a plasma cutter. Maybe when I get board of cutting wood. Problem is my Plasma draws a heap of power and will still trip the circuit breaker on a 15am point.

    Happy Days



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    Default Re: DIY CNC Design. criticism wanted.

    Quote Originally Posted by A_Camera View Post
    Like I said...



    So far, as far as I remember, you have dismissed EVERY good advice.
    You have a short memory.


    Quote Originally Posted by A_Camera View Post
    . unless you give up half way.
    I've never been known to give up. I'm a little bit stubborn if you haven't noticed. LOL

    Happy Days.



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    Default Re: DIY CNC Design. criticism wanted.

    [QUOTE=joel0407;2063282]
    Quote Originally Posted by ger21 View Post
    I'd add some triangular braces or square side panels on the Z axis plate. As drawn, it'll flex quite a bit the way the spindle is mounted.

    Thanks. I'd missed that.
    First advice taken.



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