Is self leveling epoxy a must?


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Thread: Is self leveling epoxy a must?

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    Default Is self leveling epoxy a must?

    Hi all,

    I have been working on my cnc project for a little over 1.5 years. The machine is a 4x4 cutting bed and is built using a mix of steel tube and aluminum plate. I will attach a picture below. I have completed the control box and have machined all the pieces for the base but have yet to purchase or machine any of the actual CNC parts due to this confusion since I will require a design change.

    My question is do I need to level my rails with self leveling epoxy? I have done lots of research on it but only find topics regarding the methods used to level rails, but not if its a must. And what conditions make it a must?

    I always thought that if rails aren't level, I can always level the entire bed (waste piece) using a large fly cutter. This should allow for work pieces to be square to the inaccuracy of the rails. As long as I use good methods to make sure both rail mounting surfaces are parallel and on the same plane, I should have a pretty level machine right? I understand that if the rails are very out of parallel and out of plane, that the gantry or Z-axis can bind, but I figure I could always use shim stock and fine tune the position until it I get smooth motion.

    Any input would be appreciated. Thanks for your time.

    Matthew

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    Default Re: Is self leveling epoxy a must?

    It's usually good practice to surface the spoilboard before using the router, but it's not a cure for rails that aren't flat. All it does is make sure that whatever shape the rails are corresponds to the shape the spoilboard is. To picture this, imagine that your rails are "U" shaped; high on the ends and low in the middle. Surfacing the spoilboard will create a base that's also "U" shaped. If you try to make a part on it, either the workpiece will span the depression, or (if it's not stiff enough) it will conform to it. In either case, you'll end up with a warped part. Of course, the rails might not have a "U" shape; they could have one low corner, or a wicked twist - any of that will be reflected in the parts you make with it.

    Get the rails as close as you can to flat and parallel, then use the epoxy on top of them to get it the rest of the way. Once your rails are really flat and parallel, then your spoilboard will be flat and parallel as well. There are other ways to do it - lots of patience and shims can work - but the epoxy method is a good shortcut.

    Andrew Werby
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    Default Re: Is self leveling epoxy a must?

    Put a long straight edge against the tubes you want to mount your rails to. How flat are they?

    You're confusing machining your spoil board with getting your mounting surfaces flat. Even after getting flat mounting surfaces, you will probably need to machine your spoil board anyways to account for any differences in height between the two sides and the plane of your table, which is not the same thing as getting a flat mounting surface for the rails.

    If you got lucky and you have some really flat surfaces to mount your rails to, then no, you don't have to. The conditions that would make it a must is if you put a straight edge against the surface you want to mount your rails to, and it's not flat. It's that simple.

    I have some solid aluminum pieces 2" x 3" that are super flat from the factory. Steel tube typically isn't.

    Another trick that can be done is to put some stainless steel shim tape at both ends of the tube you want to mount your rails to, then, for example, the 2"x3" really flat pieces I have, cover one 2" face in mold release, then use a thick epoxy that gets squished flat over the area you want to mount your rails. That is an alternative to self leveling epoxy and there are a couple of variations on that, like using a granite slab, etc.

    You can also use cosmetics (I head chalk might work too) and a really flat piece of metal to rub on where you want to mount your rails, and use an angle grinder with a sandpaper flapper disk to take down the high spots. I did this for places on my build but used 1.5"x0.5" flat bar stich welded in place and then painstakingly took down all the high spots while checking for square with the opposite side. If you're not a patient person, or really good with an angle grinder, then this method isn't for you. Also, this method is more suited to where you have a raised surface for your rails to mount on, like the flat bar I described.

    Or, you can take in your tubes that you want to mount your rails to, into a shop and have them machined flat. In your case, seeing as everything looks bolted together, that's not a bad option, if you can find a shop with the equipment to do it (the length is the issue) and give you a good price. The only shop I found in the city I live in that could do it wanted a huge sum of money, for probably only a couple hours of work, so I did it myself with an angle grinder and it took a few days of tedious work.

    People often use T slot for builds because generally it comes flat enough from the factory, where steel tube generally doesn't.

    When I say check for flatness, you use the straight edge and you see if you can slide a piece of paper anywhere under the straight edge, or you shine a light from the other side along the edge and look for where it is coming out.



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    Default Re: Is self leveling epoxy a must?

    Quote Originally Posted by awerby View Post
    It's usually good practice to surface the spoilboard before using the router, but it's not a cure for rails that aren't flat. All it does is make sure that whatever shape the rails are corresponds to the shape the spoilboard is. To picture this, imagine that your rails are "U" shaped; high on the ends and low in the middle. Surfacing the spoilboard will create a base that's also "U" shaped. If you try to make a part on it, either the workpiece will span the depression, or (if it's not stiff enough) it will conform to it. In either case, you'll end up with a warped part. Of course, the rails might not have a "U" shape; they could have one low corner, or a wicked twist - any of that will be reflected in the parts you make with it.

    Get the rails as close as you can to flat and parallel, then use the epoxy on top of them to get it the rest of the way. Once your rails are really flat and parallel, then your spoilboard will be flat and parallel as well. There are other ways to do it - lots of patience and shims can work - but the epoxy method is a good shortcut.
    Quote Originally Posted by NIC 77 View Post
    Put a long straight edge against the tubes you want to mount your rails to. How flat are they?

    You're confusing machining your spoil board with getting your mounting surfaces flat. Even after getting flat mounting surfaces, you will probably need to machine your spoil board anyways to account for any differences in height between the two sides and the plane of your table, which is not the same thing as getting a flat mounting surface for the rails.

    If you got lucky and you have some really flat surfaces to mount your rails to, then no, you don't have to. The conditions that would make it a must is if you put a straight edge against the surface you want to mount your rails to, and it's not flat. It's that simple.

    I have some solid aluminum pieces 2" x 3" that are super flat from the factory. Steel tube typically isn't.

    Another trick that can be done is to put some stainless steel shim tape at both ends of the tube you want to mount your rails to, then, for example, the 2"x3" really flat pieces I have, cover one 2" face in mold release, then use a thick epoxy that gets squished flat over the area you want to mount your rails. That is an alternative to self leveling epoxy and there are a couple of variations on that, like using a granite slab, etc.

    You can also use cosmetics (I head chalk might work too) and a really flat piece of metal to rub on where you want to mount your rails, and use an angle grinder with a sandpaper flapper disk to take down the high spots. I did this for places on my build but used 1.5"x0.5" flat bar stich welded in place and then painstakingly took down all the high spots while checking for square with the opposite side. If you're not a patient person, or really good with an angle grinder, then this method isn't for you. Also, this method is more suited to where you have a raised surface for your rails to mount on, like the flat bar I described.

    Or, you can take in your tubes that you want to mount your rails to, into a shop and have them machined flat. In your case, seeing as everything looks bolted together, that's not a bad option, if you can find a shop with the equipment to do it (the length is the issue) and give you a good price. The only shop I found in the city I live in that could do it wanted a huge sum of money, for probably only a couple hours of work, so I did it myself with an angle grinder and it took a few days of tedious work.

    People often use T slot for builds because generally it comes flat enough from the factory, where steel tube generally doesn't.

    When I say check for flatness, you use the straight edge and you see if you can slide a piece of paper anywhere under the straight edge, or you shine a light from the other side along the edge and look for where it is coming out.
    Thanks for the replys. I don't have the rectangular tubes yet but I should be able to snag a straight edge from work to check for flatness once I purchase them. Approximately how much thickness is added vertically by pouring epoxy? I will need to account for the thickness in my model and change a few parts. I will research shops in my area to see if I can find a mill or surface grinding service to create a flat mounting surface as an alternative as well.

    Also, NIC 77 - since you are in Canada, have you found a source for epoxy in Canada? I have researched but all I have found are American re sellers.

    Thanks



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    Default Re: Is self leveling epoxy a must?

    Quote Originally Posted by Matthew_ View Post

    Also, NIC 77 - since you are in Canada, have you found a source for epoxy in Canada? I have researched but all I have found are American re sellers.

    Thanks
    It depends on what method you're going to use and how much your tubes are off by.

    If you are going to use the stainless steel adhesive shim method with a long flat piece of metal, then you will also need to check the squareness to the other side so that your flat surfaces aren't canted to each other. If they are, you can do a small shim(s) on the outside edges of the longer shim(s) to make it square. With this method, I'd say you're looking at 1mm or so thickness, of course the thickness will vary and it depends on how warped the steel is. I have tried this with a wax based mold release and JB weld. Any normal epoxy should do, you can even mix in metal powder to the epoxy if you want.

    If you're going to use the gravity setting epoxy (as opposed to squishing a thicker epoxy flat), then you need to buy the right stuff so that it will spread out evenly under it's own weight. I have not used this method.

    The best example of that I have seen is in 1Jumper10's build thread:

    http://www.cnczone.com/forums/cnc-wo...are-forum.html

    Probably good for you to have a read through that thread, I think it will help you out with your build.

    Like I said, the solid aluminum pieces I have are really flat, and it looks like your design bolts together. Perhaps go to your nearest metal merchant carrying a long straight edge with you, and see if you can find something the same size, but flat already. That would make things easier. The differences in thermal expansion between steel and aluminum could be a small issue, but personally, I would risk it. I'm not talking about T-Slot, But solid aluminum billet. Of course, measure the steel you have first to see where you are.

    Honestly, I can't really tell what it is that the rails are sitting on from your CAD work. Is that steel tube or plate?

    What province are you in, just out of Curiosity? I'm in Ontario.



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    Default Re: Is self leveling epoxy a must?

    Quote Originally Posted by NIC 77 View Post
    It depends on what method you're going to use and how much your tubes are off by.

    If you are going to use the stainless steel adhesive shim method with a long flat piece of metal, then you will also need to check the squareness to the other side so that your flat surfaces aren't canted to each other. If they are, you can do a small shim(s) on the outside edges of the longer shim(s) to make it square. With this method, I'd say you're looking at 1mm or so thickness, of course the thickness will vary and it depends on how warped the steel is. I have tried this with a wax based mold release and JB weld. Any normal epoxy should do, you can even mix in metal powder to the epoxy if you want.

    If you're going to use the gravity setting epoxy (as opposed to squishing a thicker epoxy flat), then you need to buy the right stuff so that it will spread out evenly under it's own weight. I have not used this method.

    The best example of that I have seen is in 1Jumper10's build thread:

    http://www.cnczone.com/forums/cnc-wo...are-forum.html

    Probably good for you to have a read through that thread, I think it will help you out with your build.

    Like I said, the solid aluminum pieces I have are really flat, and it looks like your design bolts together. Perhaps go to your nearest metal merchant carrying a long straight edge with you, and see if you can find something the same size, but flat already. That would make things easier. The differences in thermal expansion between steel and aluminum could be a small issue, but personally, I would risk it. I'm not talking about T-Slot, But solid aluminum billet. Of course, measure the steel you have first to see where you are.

    Honestly, I can't really tell what it is that the rails are sitting on from your CAD work. Is that steel tube or plate?

    What province are you in, just out of Curiosity? I'm in Ontario.
    Sorry been busy the last couple weeks. Thanks for the thread to look through. Skimmed through it but will look at it more thoroughly when I have a chance.

    I'm in Ontario as well. The rails are sitting on steel tube. I jusdt got an invoice for the rest of the metal. $2,000. Thats $3500 total for just the metal on the machine. More than I was expecting.

    I do have a long piece of 3x3 0.25 wall tube that I put my rails on and I get no wobble. The tube seems fairly straight and flat so I'm hoping the larger rectangular tubes will be the same since I feel I may be able to shim them if the warping is minimal.

    I did find this american supplier of epoxy that seemes like what I'm after if I do go the epoxy route. Precision Epoxy Products

    Thanks again for the info



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    Default Re: Is self leveling epoxy a must?

    I ordered my epoxy from www.plasticworld.ca/store

    I used the 206 (Slow) hardener as it flows better than the 205 (Fast).



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    Default Re: Is self leveling epoxy a must?

    You can achieve basically the same effect by using shims. No need for epoxy.

    Lee


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    Default Re: Is self leveling epoxy a must?

    There are many factors here but generally you want your rail pairs in the same plane to avoid binding and early wear. How you get those rails in the same plane is up to you. Nothing is perfect here either, for example epoxy can deform under load, weldments and castings can change due to built in stresses.

    As for your rails and the plane they are mounted on, how much mislaignment they can tolerate varies with the rail design, machine stiffness and the distance between rails. So rails six inches apart should be mounted with higher precision than something sixty inches apart. This would be especially the case on a Z axis built up on tooling plate that is very stiff, you will notice issues with very slight misalignments especially parallizm.

    In a fabricated machine your problem often comes down to how accurate your fabrication is. Remeber you are looking to keep those rails in the same plane, ideally under one thou. At least for some uses of a router you are.

    The trick here is understanding what the router tool is doing. It basically traves parallel to the plane defined by the linear rails. Any warpage in that plane will be followed by the cutter. You can not correct this by flattenting the spoil board with the router. Now the thing here is that how important this is varies with the routers usage. For machine sheet goods a warped spoil board isnt a big deal it might be significant though for carving musical instruments.

    So is epoxy leveling required, the answer here is no but that answer is also highly qualified. Unless you are extremely good at welding a fabricated structure will not be accurate enough for most users. However the other thing to understand here is that epoxy leveling isnt your only option, there are many methods that could give you what you need. Also understand this these metal frames aren't infinitly stiff, a large machine will need to be leveled mechanically where it will be installed. As such holding off with the epixy until the frane is in place might be a good idea.



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    Default Re: Is self leveling epoxy a must?

    I am most likely going to wait until the machine base is built with the tubes that the linear rails sit on before deciding the method to level and square the rails. I can measure how out of plane the two mounting surfaces are off by using piano wire in a cross pattern along with a precision level and a 6ft long Starrett straight edge from work. Then I can shim the rails until both top surfaces of each rail are co-planar. Parallelism in the side surfaces of the rails (and not the top surfaces) can be achieved by bolting one rail completely on one side (rail 1) and the other rail (rail 2) at only one end with one screw. By pushing the gantry to the opposite end of the machine of the first bolt should give me my bolt location for the opposite side of the second rail.

    I think shims will be my first attempt. I have never used epoxy and it's an expensive one shot deal. Shims are non permanent and a more precise method, albeit lengthy.

    The X axis (i.e. the rails mounted closer together on the gantry tube) rails must have perpendicularity between the planes that the top surfaces of the rails have in both X and Y. The X rails must be co-planar in their top surfaces, as well as perpendicular to the plane of the Y rails surfaces. Shims can be used here again.

    The epoxy would cost me around $400 Canadian for the West Systems 209 extra slow hardener from plastic world. This is based on 68" x 2" x 0.25" surfaces for each rail plus 3 dams running across the machine for each pair of rails.

    Do you guys think epoxy is really that flat or worth it for the price?

    Thanks



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    Default Re: Is self leveling epoxy a must?

    That cost seems pretty high. I did a similar size machine using a different brand of epoxy for about ~$150.
    Its worth it if you need a flat surface. West systems is premium epoxy but their aimed toward the bonding applications market more so than leveling. If you were in the US, I'd recommend Precision Epoxy's SC15P. I'm at a loss to recommend a brand in Canada.



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    Default Re: Is self leveling epoxy a must?

    West Systems is about the most expensive epoxy you'll find.

    If done right, the epoxy will be perfectly flat. Whether you need to do it or not, depends on how flat the frame is, and how flat you want it to be.

    Gerry

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


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