Mounting linear rails on aluminum t-slot extrusions?


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    Default Mounting linear rails on aluminum t-slot extrusions?

    Out of curiosity, how are people mounting their linear rails to aluminum t-slot extrusions?

    I was looking at my rails and the pile of extrusions in the corner of my work area and it doesn't look as easy and intuitive as I would have thought.

    My supported rails have two sets of mounting holes (one on each side of the rail) but they don't line up with the t-slots on either my 10 series or 15 series, or open builds v-slot extrusions. I haven't tried metric extrusions but not sure they would be any better.

    My square thk rails have one set of mounting holes running down the middle. It seems easier until you see that they use those teeny tiny m3 screws which makes them unsuitable for direct mounting with a majority of the available t-bolts (without further mods). I did see one set of expensive m3 t-bolts for both 10 and 15 series but they aren't commonly available.

    I guess you could mount the rails to a steel or aluminum plate and mount the plate on the t-slots but then you loose the benefits of easy construction and easy rail alignment (as the t-slots are already parallel to each other).

    Are any of you guys mounting your rails to the t-slots directly? If so, are you specifically choosing rails with mounting holes that fit your extrusions? Or maybe you just use one of the sets of mounting holes on your supported rails? Or do you drill additional holes in the flat part of the extrusion between the t-slots?

    While I am going with a steel and cf frame for my first build, I was thinking I might use my extrusions for a second smaller build at some point.

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    Default Re: Mounting linear rails on aluminum t-slot extrusions?

    I just bolted my profile rails right to the T-slot when I built an aluminum extrusion machine. My profile rails were 20mm and it worked just fine but 25mm would have worked even better. You could use a piece of steel flat stock, maybe 16ga, with holes that match the pattern of your rails and sandwich that between your rails and your extrusion. With that method you still have the T-slot to help with alignment and even if your rail is on the narrow side the flat steel will bridge the T-slot valley. That is probably better than just bolting your rails directly to the extrusion.



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    Default Re: Mounting linear rails on aluminum t-slot extrusions?

    I've seen 15mm profile rails mounted to an aluminum plate, which in turn was bolted to the extrusion.

    Gerry

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    Default Re: Mounting linear rails on aluminum t-slot extrusions?

    Quote Originally Posted by 1Jumper10 View Post
    I just bolted my profile rails right to the T-slot when I built an aluminum extrusion machine. My profile rails were 20mm and it worked just fine but 25mm would have worked even better. You could use a piece of steel flat stock, maybe 16ga, with holes that match the pattern of your rails and sandwich that between your rails and your extrusion. With that method you still have the T-slot to help with alignment and even if your rail is on the narrow side the flat steel will bridge the T-slot valley. That is probably better than just bolting your rails directly to the extrusion.

    Would the steel not need to be thicker? 16g steel is not much more than sheet metal. I wouldn't have much confidence in it's ability to hold the screws in place without being torn out under a heavy load.



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    Default Re: Mounting linear rails on aluminum t-slot extrusions?

    Sorry, I wasn't clear. The steel isn't threaded. It acts like a big long washer that your bolts pass thru and thread into T nuts that lock into the T slot. The steel makes a flatter mounting surface than extrusion.

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    Default Re: Mounting linear rails on aluminum t-slot extrusions?

    This is how I did it. It's been working great for several years now.

    Here is the first idea I used for attachment of linear rails
    http://www.cnczone.com/forums/cnc-wo...ml#post1014678


    This is the final method.
    http://www.cnczone.com/forums/cnc-wo...ml#post1141165



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    Default Re: Mounting linear rails on aluminum t-slot extrusions?

    Quote Originally Posted by RicknBeachcrest View Post
    This is how I did it. It's been working great for several years now.

    Here is the first idea I used for attachment of linear rails
    http://www.cnczone.com/forums/cnc-wo...ml#post1014678


    This is the final method.
    http://www.cnczone.com/forums/cnc-wo...ml#post1141165
    That's how I imagined it would work. It's a shame things aren't standardized enough for a direct mounting solution.

    I tested one other method which involved using a pair of single lane t-slot extrusions (one mounted on each set of holes on the rails) and then using some additional extrusions mounted at 90 degrees to the rails to attach it to the frame. It's not a particularly elegant solution...

    The only other idea I had was to drill additional mounting holes in the extrusion. I have a 3" x 6" x 36" 15 series extrusion that ai originally intended to be my gantry. The metal on it is probably around 1/8" so it could hold some screws.

    I have a similar method to you for checking that things like rails are mounted parallel except I use aluminum bars and some calipers to double check. I hate all that stuff though. I was hoping that the ready aligned t-slots was some type of shortcut for it.

    Last edited by ger21; 09-29-2017 at 08:19 PM.


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    Default Re: Mounting linear rails on aluminum t-slot extrusions?

    It's a shame things aren't standardized enough for a direct mounting solution.
    Linear rail manufacturers will tell you that aluminum extrusions are not a suitable mounting surface for linear rails.

    Gerry

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    Default Re: Mounting linear rails on aluminum t-slot extrusions?

    I have used steel flat bar on my aluminum extrusion builds. There was no adjustment between the rails and the steel bar, but minimal adjustments could be made with the flat bar in the T slots. Not the best method for precision and rigidity. I consider that method an easily accomplished one and middle of the road system. Direct mounting to aluminum being the least desirable, but considerably easier. No drilling and tapping etc. That is unless using wide rails with double row mounting holes. The best would be stress relieved machined plate to mount the rails on. At that point, it isn't very practical to mount that on aluminum. Possible yes of course, but missing a shot at getting something better with a more solid base.

    Lee


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    Fair warning you will likely get lots of conflicting answers here most of them correct for one situation or another.

    Quote Originally Posted by Goemon View Post
    Out of curiosity, how are people mounting their linear rails to aluminum t-slot extrusions?
    You don't want to do thins unless the extrusions are specifically designed for profile rail mounting. Of course there are lots of variables here but with common framing extrusions i would consider alternatives.
    I was looking at my rails and the pile of extrusions in the corner of my work area and it doesn't look as easy and intuitive as I would have thought.
    If you are trying to do a precision machine build, using profile rails, trying to mount the rails directly on extrusions, is an avenue to heart ache. This is more so on a small machine where there is less spread between components thus an in ability to compensate for mis alignment.
    My supported rails have two sets of mounting holes (one on each side of the rail) but they don't line up with the t-slots on either my 10 series or 15 series, or open builds v-slot extrusions.
    For supported round rails you can drill your own holes in the support extrusion. This would only be useful if the flange is wide enough to line up with two slots in the T-slotted extrusion.
    I haven't tried metric extrusions but not sure they would be any better.
    You might get lucky but this can easily be verified by breaking out a scale and measuring the center to center distances on the rail supports. It probably surprise nobody but these days many parts are fabricated to metric dimensions. So it is possible but maybe on extrusions to light for your needs.
    My square thk rails have one set of mounting holes running down the middle. It seems easier until you see that they use those teeny tiny m3 screws which makes them unsuitable for direct mounting with a majority of the available t-bolts (without further mods). I did see one set of expensive m3 t-bolts for both 10 and 15 series but they aren't commonly available.
    The smaller the profile rails the more difficult they are to mount on T slots. Some T slots are not flat at all across the width leading to serious issues with precise alignment. You are far better off mounting the rails on a piece of tooling platen, steel bar or other interposer to support the rail.
    I guess you could mount the rails to a steel or aluminum plate and mount the plate on the t-slots but then you loose the benefits of easy construction and easy rail alignment (as the t-slots are already parallel to each other).
    This is generally what you want to do but it highlights a point i try to make from time to time. That is Aluminum T-slots really leave a lot to be desired for building machine tool axises on. In this case you mention that you have a much smaller machine that you are thinking about here. Now i don't know how small nor what tasks it will be doing but it might be reasonable to make the axises out of bar stock and tooling plate where needed. That bar stock could be steel or aluminum if you really wanted to use aluminum. If significantly large you probably should consider steel tubing. It is a question of what you mean by smaller, guys have built machines with work areas as small as six inches square.

    Are any of you guys mounting your rails to the t-slots directly? If so, are you specifically choosing rails with mounting holes that fit your extrusions? Or maybe you just use one of the sets of mounting holes on your supported rails?
    .
    You really want to have mounting screws on both sides of the rail supports. As for mounting profile rails directly on extrusions id skip that idea unless you have extrusions specifically designed for such use
    Or do you drill additional holes in the flat part of the extrusion between the t-slots?
    The vast majority of extrusions out there can't hold screws in the webs for crap. This is a seriously bad idea as taped holes in the webs strip out amazingly fast.
    While I am going with a steel and cf frame for my first build, I was thinking I might use my extrusions for a second smaller build at some point.
    That is fine. Even with every thing said above extrusions are still useful for machine tool builds. For example if you use bar stock for the X axis rails the extrusions could be used to separate the two bars. For the gantry you might run two extrusions length wise faced with a bit of tooling plate or a wide bar. As above what makes sense depends upon what you mean by small and what you expect out of the machine.

    I understand the need to use what you already have but sometimes life is easier if you settle for 75% instead of 100% usage. I know i often sound negative with respect to T slotted extrusion usage but that only reflects two concerns. One is that the stuff is expensive and two it is less than ideal for linear rail mounting. On the other hand it can be very useful to a builder that wants a kit and doesn't have a wealth of shop equipment. in the end it is up to you, as you have seen mounting the rails on T slots isn't always as easy as it might seem.



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    Default Re: Mounting linear rails on aluminum t-slot extrusions?

    Some of the best examples is with the XZERO CNC Extrusions, the Extrusions where designed for mounting Linear Rails, and you may be able to buy this Extrusion from him

    Attached Thumbnails Attached Thumbnails Mounting linear rails on aluminum t-slot extrusions?-xzero-png  
    Mactec54


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    Default Re: Mounting linear rails on aluminum t-slot extrusions?

    Quote Originally Posted by wizard View Post
    Fair warning you will likely get lots of conflicting answers here most of them correct for one situation or another.


    You don't want to do thins unless the extrusions are specifically designed for profile rail mounting. Of course there are lots of variables here but with common framing extrusions i would consider alternatives.

    If you are trying to do a precision machine build, using profile rails, trying to mount the rails directly on extrusions, is an avenue to heart ache. This is more so on a small machine where there is less spread between components thus an in ability to compensate for mis alignment.

    For supported round rails you can drill your own holes in the support extrusion. This would only be useful if the flange is wide enough to line up with two slots in the T-slotted extrusion.

    You might get lucky but this can easily be verified by breaking out a scale and measuring the center to center distances on the rail supports. It probably surprise nobody but these days many parts are fabricated to metric dimensions. So it is possible but maybe on extrusions to light for your needs.

    The smaller the profile rails the more difficult they are to mount on T slots. Some T slots are not flat at all across the width leading to serious issues with precise alignment. You are far better off mounting the rails on a piece of tooling platen, steel bar or other interposer to support the rail.

    This is generally what you want to do but it highlights a point i try to make from time to time. That is Aluminum T-slots really leave a lot to be desired for building machine tool axises on. In this case you mention that you have a much smaller machine that you are thinking about here. Now i don't know how small nor what tasks it will be doing but it might be reasonable to make the axises out of bar stock and tooling plate where needed. That bar stock could be steel or aluminum if you really wanted to use aluminum. If significantly large you probably should consider steel tubing. It is a question of what you mean by smaller, guys have built machines with work areas as small as six inches square.

    .
    You really want to have mounting screws on both sides of the rail supports. As for mounting profile rails directly on extrusions id skip that idea unless you have extrusions specifically designed for such use

    The vast majority of extrusions out there can't hold screws in the webs for crap. This is a seriously bad idea as taped holes in the webs strip out amazingly fast.


    That is fine. Even with every thing said above extrusions are still useful for machine tool builds. For example if you use bar stock for the X axis rails the extrusions could be used to separate the two bars. For the gantry you might run two extrusions length wise faced with a bit of tooling plate or a wide bar. As above what makes sense depends upon what you mean by small and what you expect out of the machine.

    I understand the need to use what you already have but sometimes life is easier if you settle for 75% instead of 100% usage. I know i often sound negative with respect to T slotted extrusion usage but that only reflects two concerns. One is that the stuff is expensive and two it is less than ideal for linear rail mounting. On the other hand it can be very useful to a builder that wants a kit and doesn't have a wealth of shop equipment. in the end it is up to you, as you have seen mounting the rails on T slots isn't always as easy as it might seem.
    You don't sound negative to me on this. I prefer honest and useful opinions over undue optimism.

    The concern about stripped screws is the biggest for me with my THK rails. It's not just for when they are mounted to aluminum. I really don't like that they use M3 mounting holes. Those tiny m3 screws are great for creating a neat-looking mount by they are so thin that I worry that they might strip or even snap under a heavy load. Even if they are mounted on a steel frame, I don't have much confidence in them.

    My spare THK rails have 20 pre-drilled m3 mounting holes. With the m3 t-nuts I just bought, they can mount directly on 10-series and 15 series extrusions but whether I do this or use a steel bar in between, I am wondering if I would be better off putting them on my drill press and widening the holes so I can use m5 or m6 screws instead.

    The thing is, these THK rails are used and they came off a working CNC mill so maybe I am wrong and m3 screws will work fine...

    The supported rails with two lines of mounting holes are a different story. A separate piece of metal to mount them on seems like a must.

    The other question that came out of this is whether THK or supported rails should be mounted horizontally or facing up. Looking at the rail designs, it seems like they are meant to be facing up but many people use a horizontal mount. It looks like you lose the benefit of the support on the support rail if it isn't underneath support the load....

    btw, most of my t-slot extrusions are the heavy 80/20 and a mix of 10 and 15-series. I don't know if these are considered framing extrusions or precision heavy duty rail holders but they are a million times better than the open builds v-slot garbage.

    I used all my open builds extrusions for a portable curing oven build for my carbon fiber parts where they don't need to hold any load.



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    Default Re: Mounting linear rails on aluminum t-slot extrusions?

    Quote Originally Posted by mactec54 View Post
    Some of the best examples is with the XZERO CNC Extrusions, the Extrusions where designed for mounting Linear Rails, and you may be able to buy this Extrusion from him
    How do Xzero CNC extrusions differ from the heavy 80/20 15 series extrusions? They look the same in the pic but I guess all extrusions look the same in pics...

    The heavy 3" x 6" x 36" 80/20 15 series extrusion I have feels fairly solid. I would have no worries about it's strength or stiffness for a wood cutting machine but I have never measured it's flatness or how parallel the t-slots are etc. is this where the difference is with Xzero t-slots?

    In reality, if I can't use my existing t-slots for a CNC machine, I'll use them for something else and use steel, epoxy granite and carbon fiber for the next build too. Aluminum T-slots start to lose their charm for me when they don't offer the convenience of easy, quick and tool free assembly.



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    Default Re: Mounting linear rails on aluminum t-slot extrusions?

    Another option if you do want to use extrusions is something I've been using which are milled extrusions by misumi - you could probably find a size that suits your needs.... nice flat milled surface specifically for mounting linear motion components.



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    Default Re: Mounting linear rails on aluminum t-slot extrusions?

    Quote Originally Posted by Goemon View Post
    How do Xzero CNC extrusions differ from the heavy 80/20 15 series extrusions? They look the same in the pic but I guess all extrusions look the same in pics...

    The heavy 3" x 6" x 36" 80/20 15 series extrusion I have feels fairly solid. I would have no worries about it's strength or stiffness for a wood cutting machine but I have never measured it's flatness or how parallel the t-slots are etc. is this where the difference is with Xzero t-slots?

    In reality, if I can't use my existing t-slots for a CNC machine, I'll use them for something else and use steel, epoxy granite and carbon fiber for the next build too. Aluminum T-slots start to lose their charm for me when they don't offer the convenience of easy, quick and tool free assembly.
    The difference is there is a rail alignment boss in the profile. You would need two extrusions and I suppose they get bolted to another plate to stiffen and help with alignment.
    Profile rails are usually installed with a Master rail bolted up against a machined boss and then the opposite rail is aligned to it.

    Lee


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    Default Re: Mounting linear rails on aluminum t-slot extrusions?

    I made a full length tbolt to mount the rails to Misumi 2550 extrusions. This was for a Delta 3d printer, so alignment between rails isn't as critical as for a mill or router.



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    Default Re: Mounting linear rails on aluminum t-slot extrusions?

    I can't find any alignment issues on the 80/20 t-slot extrusions I have here. I only have some digital calipers and a bubble level to measure though. What tools are you guys using to find any issues in the t-slots before mounting rails?



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    Default Re: Mounting linear rails on aluminum t-slot extrusions?

    Lay them on something flat. Sight along them and look for daylight where the surfaces meet. If its perfect you wont see any. Then press down on the 4 corners and see if you can feel any rocking. If yes, this probably indicates twist. A bowed extrusion can be shimmed straight or high spots can be filed down. Twist is much harder to deal with.



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    Quote Originally Posted by Goemon View Post
    I can't find any alignment issues on the 80/20 t-slot extrusions I have here. I only have some digital calipers and a bubble level to measure though. What tools are you guys using to find any issues in the t-slots before mounting rails?
    In wood working circles there is the concept of winding sticks that can be helpful in initial adjustments. Basically two very straight and parallel sticks that you lay across beams, separated by a good distance, to get beams in the same plane. In the case of a machine build, extrusions may be of use if in good shape. Ideally though the edges are fairly square and often painted of dissimilar colors.

    Initially the sticks are used to rough in the frame so in this case the X axis beams are in the same plane lengthwise. You will also be able to see if the beam is twisted either due to mounting or physical twist in the beam.

    While winding sticks are really good for rough in it never hurts to invest in a precision level. Given one of suitable sensitivity you will be able to map out twist in your frame. Precision straight edges can be a big help too. Depending upon what you want to accomplish though one of your extrusions may make a suitable straight edge. This might sound obvious but a flashlight really helps at times when looking for gaps from twists or bends. . Now extrusions aren't perfect for straight edge use as they are thick thus making looking for gaps a chore, one cheap alternative is a piece of cold rolled steel, say about 3/16" thick and maybe 3" wide and length sized to what you need. You would need to verify straightness as cold rolled can be less than straight at times but often cheap and dirty are good enough. Basically anything straight that can span the width of your rails is a help.

    Having done more than a few machine rebuilds over the years you elevate the precision of your alignment tools to reflect what you are working on at the moment. Alignment aids are almost always better than trying to eyeball things. Even something a simple as aligning pulleys on shafts benefits from alignment aids.

    Also the idea of a master rail is important to digest. You want to get one rail installed perfectly and then mount a second rail parallel to that one. This is where a dial indicator and a good stand come into play. However there are alternatives here too. You can space rails parallel with 1,2,3 blocks or custom machined parallels. Often parallelism can be set into a part a saddle for example, when it is machined. Thus you mount your master rail, mount the saddle and then use that saddle to set your second rail.

    Noe one thing that you will run into, especially with 80/20 is that the surfaces of their extrusions are not flat. This is done on purpose for their system but it can lead to massive frustrations with rail alignment. If the linear rail is small in width you can end up with it twisting out of plane as you tighten up the mounting screws. This us why some suggest going to larger than required linear rails to better span the low spots. In other words a narrow rail has to be aligned fairly accurately with the center of the 80/20 extrusion to avoid roll and twist. This is also why extrusion suppliers that offer machining services to flatten their extrusions are often preferred. It is important to understand that this is an issue with the extrusions themselves and varies with brand. Ideally you want linear rails wide enough to span the little built in radius that some extrusions have on their faces. This is also why it is common to face an extrusion with tooling plate or bar stock.



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    Default Re: Mounting linear rails on aluminum t-slot extrusions?

    Quote Originally Posted by 1Jumper10 View Post
    Lay them on something flat. Sight along them and look for daylight where the surfaces meet. If its perfect you wont see any. Then press down on the 4 corners and see if you can feel any rocking. If yes, this probably indicates twist. A bowed extrusion can be shimmed straight or high spots can be filed down. Twist is much harder to deal with.
    That sounds like a good low cost but effective tip.



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Mounting linear rails on aluminum t-slot extrusions?

Mounting linear rails on aluminum t-slot extrusions?