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  1. #1
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    Pros and Cons: Extrusions as linear rails

    Ok I've had the benefit of participating in recent posts voicing concerns with using extruded aluminum profiles as the linear rails for CNC builds. Even though I'm a fan of the practice I also agree with the opposing views. Maybe we could start a fresh dialog of the pros and cons of the matter here.

    To begin with, "wheel and plate" kits just aren't able to withstand the daily use and abuse of an industrial quality machine [linear system] built to handle around the clock high stress workcycles. But then again they aren't meant to.

    The popularity of the kits comes from allowing new users an inexpensive and far less complex system to learn and maintain. Plus if they mess up and break something not needing to take out a second mortgage to repair the machine adds to the appeal.

    Like I said I'm a fan and have evolved my own designs to this kind of linear setup. I won't claim that any past build will take the punishment that the machines at work do for me but I still see potential in this type of linear motion system.

    Anyone up to discuss?

    *Post links to horror stories if you must. But if you do also offer up thoughts for improvements along with it thx.


    MC
    Slow work takes time

  2. #2
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    Re: Pros and Cons: Extrusions as linear rails

    Alright then; I'm free to ramble on here a bit.

    Stated before, I like the current wheel on extrusion linear setups available, yet there is a lot that I don't like about building machines with it exclusively.

    1 - Nylon and polycarbonates are decent economical choices for wheels on lightweight builds that exert very little force [engravers, 3D printers, laser/plasma cutters]. Larger/heavier mill builds can deform or crack those materials sooner than later when put to task on regular, high force machining. Also any direct steel wheel contact would gall the anodized aluminum surfaces quick fast and in a hurry.

    2 - The sections of alum extrusions used for linear motion are too thin and unsupported. These channels can warp and deform with prolonged high force use rendering accuracy null. Plus depending on where the framing comes from to start with, manufactured/delivered quality and consistency can be largely hit or miss. You really have to QA every inch of any new stock.

    3 - Less complaint and more "wish they would have"; I appreciate the specifically designed extrusions for this application but really would have liked to see a better wheel system developed for existing products too.

    4 - The preferred use of "20 series extrusions" is way too small for realistic goals. Within that dimension all compact wheel designs are confined to using std/deep groove radial bearings only. A larger framing series could facilitate a larger wheel that would use a matched set of angular contact bearings to better address the dynamic loads of a CNC linear system.

    5 - Quarter inch thick alum plating for body parts still lacks significant anti-deflection characteristics under high cycle loads. Add to that relying on the use of spacer bushings to account for frame depths in build up is a potential weakness.

    These are my top 5 gripes, and things I've been working on in house for a few years. It would be great to hear any other complaints and imagined solutions about this from y'all. At the same time I aim to keep this topic friendly and not solicit anything in anyway.

    *Admin", please pigeon hole this thread as needed. I'm certain to have missed a posting rule or two.

    MC
    Slow work takes time

  3. #3
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    Re: Pros and Cons: Extrusions as linear rails

    While cheapness is great, the hassle of building a CNC machine and then having to tear it down and rebuild it when the rinky-dink slide system fails makes me think that doing this part right in the first place is worth the cost of real steel rails and wheels. They aren't all that expensive, and can be fitted to aluminum extrusions; that's how the Shopbot machines are constructed: Finally get to un-crate my shopbot . You can get the system from Bishop-Wisecarver : DualVee
    Andrew Werby
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  4. #4
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    Re: Pros and Cons: Extrusions as linear rails

    I am Interested in the V wheels every thing I have done in machining over the years leads me to believe that the swarf would go under them and cause them to lift ,they say it does not Jury is out Yes to the answer buy good gear the first and last time is the key.

  5. #5
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    Re: Pros and Cons: Extrusions as linear rails

    @awerby; Congrats on the SB man. We have a PRS Alpha at work and it's a great machine, you should really enjoy it. Very straightforward design; easy to maintain and keep in good working order affordably IMO. The SS v wheels on steel rails are really trustworthy. In our high saltaire environment however they need looked after and oiled daily to keep the rust at bay.

    Agreed, T-Slot slide bearings are a poor choice for larger high cycle machine builds. Even custom made close tolerance slide systems can be terrible to dial in and keep that way under heavy use. And yes "cheap" [poor quality] parts will always bite you at least twice.

    I started this thread because I am developing a new wheel and plate style machine and have dealt with and learned a lot from the experience. I am truly hoping to hear anyone else's thoughts on the matter and wish to share my own for scrutiny.

    I've been inspired by the @work SB (and a MultiCam 5000 we leased for a few years before it) and am confident in bringing any work home when needed to be finished. The biggest issue so far with passing this build series onto others is the need for a much better wheel. The machines I've had access to thus far still lack the needed accuracy to mill such small parts.

    Have been experimenting with a number of phenolics, torlon, and oil impregnated bronze on a wheel designed specifically for std 80/20 type profiles but as mentioned earlier, the machines I have had use of do not hold the accuracy needed for the project. And since it's way more fun to do things in house, I haven't really tried to outsource the project's design to date. Instead I aim to automate my little Grizzly x2 mill in the coming weeks for the task.

    Just received a new 3MT to ER20 collet set, boring head/bar kit, and large ass XY table for the project. Guess I ought to post that build log elsewhere though.

    Thanks for the reply Andrew, again enjoy the heck out of that ShopBot.

    MC
    Slow work takes time

  6. #6
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    Re: Pros and Cons: Extrusions as linear rails

    There are many problems with using extruded aluminum profiles as the linear rails for CNC.

    The material is too soft, never really straight, expands a fair bit as heat increases, so it will change size due to friction generated heat and ambient temperature changes. The structural stability is not the best. Steel is much better, even if bolted together. It is also much cheaper, will give you a more rigid machine. The problem is that steel is not as easy to work with as it is with aluminum, that's why I used extruded aluminum profiles for my CNC, though the idea of using it as linear rails would never occur to me as an alternative. If money is a concern, home made steel V-rails, or steel rods (minimum 12mm but 16mm preferred dia) would be my choice. It would be still very cheap and would improve accuracy and rigidity a lot more that just using aluminum profiles.

  7. #7
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    Re: Pros and Cons: Extrusions as linear rails

    I agree with Mr. Camera; the idea of running wheels on aluminum rails needs serious re-thinking. If you were just trying to construct a machine for your own use as a learning experiment, and had serious budget constraints, I'd say fine - try it out and see how long it takes to find out why everyone says it's a bad idea.

    But if you're seriously considering making a machine for sale to others, then no way - spend the money for a linear motion system that will last as long as the rest of the thing. Otherwise, you'll just be another one of those companies that puts out a fatally flawed product, sells a bunch of them, then folds up when they all start failing at once and the customers want their machines repaired or their money back.

    I am enjoying the Shopbot, and am using it quite a bit lately. The steel V-wheels work fine with a little wood dust; they're a lot less sensitive to it than ball-screws are. If I was spraying metal swarf around, then sure - protecting the rails with bellows or something would probably be required.
    Andrew Werby
    Website

  8. #8
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    Re: Pros and Cons: Extrusions as linear rails

    Thank you guys for the back-n-forth here, but truth be told this topic has not stemmed from a point of question or doubt toward using a wheel and plate type of linear motion system on personal or "for hire builds". I have already invested in the cost development and considerable testing of many separate drive and linear motion setups on different designs for years. And have busted my butt to assure that every custom build performs exactly as claimed or better for the price charged regardless of componentry. The loudest and most outstanding issue to date has been not being able to build a machine fast enough or cheaper for a client than was projected.

    Absolutely, there is a growing need for quality and easy to use and maintain machine options for under 5 grand. IMO the best effort toward that I have seen stateside is anything CNCRP is doing. Sincerely, if you are in fast need of a great machine and on a strict budget, do not hesitate to look twice at their stuff. It's very professional!

    Back to the topic at hand though: everyone with the means and tenacity for a DIY build over 5k; please research this forum heavily and consider all other options available for drive and linear motion systems on your own build.

    From a personal POV, bolting on an overly expensive linear/drive system to an MDF, Wooden, or even Laminate frame is wasting more time effort and money than is needed and will still end up in several rebuilds of what you have to achieve the results you want. Just buy a SB and have fun.

    However if you are looking to build something strong and reliable within this genre or have already done so and have a constructive critique/horror story about it, please speak up.

    MC
    Slow work takes time

  9. #9
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    Re: Pros and Cons: Extrusions as linear rails

    Sincere apologies to everyone for the personal ugliness of the last post reply. While I have definitely found this forum to be greatly helpful to the DIY effort over the years, it has perpetually and continuously been intolerant of any new direction from the "norm" and largely advocates toward a singular point of view.. A point I clearly dis-agree with.

    Great respect to all. Apologies again.

    MC
    Slow work takes time

  10. #10
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    Re: Pros and Cons: Extrusions as linear rails

    While I have definitely found this forum to be greatly helpful to the DIY effort over the years, it has perpetually and continuously been intolerant of any new direction from the "norm" and largely advocates toward a singular point of view.. A point I clearly dis-agree with.
    I clearly disagree with that.

    I'm building a 4x8 machine from wood, with Hiwin linear bearings and AC servos. In your previous post, you say I'm wasting time and money. I say I'm building something in a new direction from the "norm"

    With the proliferation of low cost machines, people come here all the time thinking they can build a $10,000 machine for $2000. While it's impossible to know someone's expectations, we try to steer them in the right direction, so that their machine will hopefully meet their expectations. I've yet to see any "new ideas" that result in a better machine. There are plenty of innovations that result in cheaper machines, but not better machines. We try to steer people in the direction of higher quality machines.
    By all means, feel free to re-invent the wheel. Provided you can make a better one.
    Gerry

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    http://www.thecncwoodworker.com/2017.html

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

  11. #11
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    Re: Pros and Cons: Extrusions as linear rails

    Quote Originally Posted by wednesday View Post
    ... bolting on an overly expensive linear/drive system to an MDF, Wooden, or even Laminate frame is wasting more time effort and money than is needed and will still end up in several rebuilds of what you have to achieve the results you want.
    The subject here was NOT wood or MDF machines. Just because I think your idea about using extrusions as rails is wrong that does not mean that I'd build a machine out of MDF or that I think it is in any way a better idea then yours. Apparently some people like to use wood or MDF and for some tasks it may be just as good as any other material. I have seen people building machines using ordinary drawer slides and many other material and while I would not do it, I wish them good luck and hope they have fun, and even though I don't believe in your revolutionary idea, I still wish you good luck.

    Quote Originally Posted by wednesday View Post
    However if you are looking to build something strong and reliable within this genre or have already done so and have a constructive critique/horror story about it, please speak up.
    Wood and MDF can in fact be VERY strong, as strong as aluminium. Of course, you have to think about HOW to make it strong but of course, since wood can be used to build high rises, it can also be used to build strong CNC machines as well.

  12. #12
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    Re: Pros and Cons: Extrusions as linear rails

    Quote Originally Posted by wednesday View Post
    While I have definitely found this forum to be greatly helpful to the DIY effort over the years, it has perpetually and continuously been intolerant of any new direction from the "norm" and largely advocates toward a singular point of view..
    I think your generalisation is a bit too simple. Yes, there are some intolerant and narrow minded persons on this forum, just like on every other forum, but the mainstream is definitely interested, open minded and tolerant for different ideas, new as well as old. That does not mean that everyone must cheer and praise every idea.

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