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Thread: Pondering some Machine Design stuff

  1. #1
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    Pondering some Machine Design stuff

    I just cannot leave this section empty.

    Something I have been pondering lately is the construction of the guides on a machine.

    I have only limited time as my lunch break is almost over.

    I work in Industry and I buy machines as well as support the technical side, of applications. I also do a limited amount of Design engineering.

    So - what I think about CNC machine building I am not a KIT sort of guy. I am a degreed engineer with a machine design engineering background.

    On the guides most CNC routers are using a roller ball or guide in one way or another.

    The other day I was made aware of a company that makes non roller guides. I will get a LOT more into this as time goes on. The company is IGUS and thay make a plastic guide that slides on a hard coated aluminum rail.

    The IGUS guides remind me of the industrial Boxway construction machines. I call those machines industry WORKHORSES.

    Linear guides are really popular these days and almost exclusive in CNC routers.

    In about 2015 I plan to build a 48 x 48 x 12 CNC router - to "MY" specifications. It will be over powered to drive these IGUS slides and to be able to hog out stuff as I need to.

    I am going to go all out on that machine - but I MUST also make it look REALLY pretty.

    I named it.

    It is the Osprey.
    It will have a sculpted Osprey Bird on top and move along with the axis motion.
    The machine will have color - design - and just be awesome.

    Anyway - back on the IGUS slides.

    I will be doing some force testing on the differences between roller guides and boxway guides in the coming months.

    I will post that testing and also make youtube videos about it.

  2. #2
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    Leo, any chance of you taking some pictures of your current set up and taking us through its operations? Kind of a rundown on its positives and negatives versus what else is out there?
    Then if we can get Stu to do the same with his machine and others that have some so us wannabes can maybe make some informed decisions?
    Jon

    God and family, the rest is icing on the cake. I'm so far behind, I think I'm in first place!

    Host of the 2015 FAMILY WOODWORKING GATHERING

  3. #3
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    Lacking any background in the physical requirements of a CNC machine ...

    The IGUS claims are interesting "For example, self-lubricating plastic bushings routinely deliver a longer service life than oil impregnated sintered bronze bearings, with cost savings up to 40%". Being somewhat of a fossil I'm surprised at all that because I still generally think of actual bearings as superior (although also realize that even "ancient" technology like babbit has some advantages over roller bearings - the plastic ideas seem to be similar in theory). IGUS also appears to have some pre-built linear sliding tables - dunno how the cost compares to the components..

  4. #4
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    Ryan - yes the bearing is a much lower friction bearing. When it is new and clean - the performance is superior as in movement of the slide.

    BUT - I have already had issues with my machine, with the fine dust getting into the balls in the linear guides.

    The IGUS slides don't care about a dirty environment, but they do take more force to move them. SO - use bigger motors to move the slides and it all equals out - with the benefit of slides that remain in a constant level of force needed to move and a high level of accuracy. The plastic guides are at zero or real close to zero clearance between the slide and the rail. The balls guides start to jam as you get close to zero clearance.

    I bought a set of IGUS rails and carriages to do some testing. I actually visited IGUS and spoke to the rep there about the products. They actually gave me samples to do some testing. I bought the rest.

    When I can cut some time I will build a small cross slide and test forces needed to move the slides. Then I am going to test my machine to fine out what forces stall the motors. The machine I plan to build is going to be at least 4 times more powerful than my current machine.

  5. #5
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    Quote Originally Posted by Jonathan Shively View Post
    Leo, any chance of you taking some pictures of your current set up and taking us through its operations? Kind of a rundown on its positives and negatives versus what else is out there?
    Then if we can get Stu to do the same with his machine and others that have some so us wannabes can maybe make some informed decisions?
    Jonathan,

    I have about 55 videos on youtube - mostly about CNC routing and my machine and about me.

    http://www.youtube.com/user/arcticfox46/videos

    Enjoy

    Leo

  6. #6
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    Quote Originally Posted by Leo Voisine View Post
    Ryan - yes the bearing is a much lower friction bearing. When it is new and clean - the performance is superior as in movement of the slide.

    BUT - I have already had issues with my machine, with the fine dust getting into the balls in the linear guides.
    Ok that about lines up with that my preconceived notions were. The plastic seems to basically offer not having to maintain sweeps in front of the bearings and not having to worry about the bearings running dry as well as limiting the contamination problem (I'm not 100% sure I buy it eliminating it, but maybe I'm just overly pessimistic in general ). I see a lot of complicated systems for reducing contamination issues in various linear bearings.... fascinating. It will be interesting to see what the performance variances between a couple of the options are for sure.

    One other thing that might be interesting to try to measure is acceleration resistance/speed. It seems that you are mostly working well under the top speed of any of these bearing systems but the acceleration profile would largely define the performance envelope of the machine (at least for detailed work).

  7. #7
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    When I was in my machine design classes we did this sort of testing. I will repeat the testing in my shop - perhaps a little bit over the weekend.

    This slide design is NOT the norm for a CNC router and will not sit well with too many people - cause it does not look like the rest of the group.

    I do notice that the CNC router builders do keep reinventing the guides on their machines - so - there are no hard and fast rules. It is also evident that the builders also don't have it down yet.

    ME - personally - my entire life makeup is to go against the flow.

    I will go out to the shop and try to grab a couple of pictures.

    Hang on - I'll be right back.

    OK - I'm Back

    Click image for larger version. 

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    This is the guide rail with carriage in place.

    I have two of these sets - 18" long. This will eventually become my "Z" axis.


    Click image for larger version. 

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    This is the innards of the carriage.


    There is no need for wipers - the plastic skids in the carriage simply push the dust aside. The dust really cannot get between the plastic and the rail. It gets pushed aside.

    On a roller bearing - the dust gets between the roller and the rail really easy - the roller simply rolls onto the dust and it gets pressed onto the roller and sticks there.

    On a roller guide the dust does not get totally wiped away with the wipers and some of the dust gets inside the little roller ball cage. This I know on both accounts.

    My Larken machine has roller guides and I needed to clean them out.

    On by band saw - the roller guides get deposits of buildup on the rollers. At work we have similar issues.

    In my testing of the IGUS guides I will make a cross slide using the two sets of what I have in the pictures above.

    I will adjust the carriages to get zero deflection side to side. I have a decent compliment of tenths indicators. I will test side to side at a specified load. I have a scale to measure the load. I will also load the cross slide with varying weights - and test the force(s) to move the cross slide. I will test from stop, to find the inertia to get the slide moving. I will also test the steady sliding motion.

    These slides are rated for 900 pounds - but I think I will load to no more that about 25-50 pounds.

    I will also test my machine to see how much force stalls the machine.

    All of this testing will give me some idea how much motor torque I will need.

  8. #8
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    This is going to be a very interesting thread to watch.
    When the going gets weird, the weird turn pro. - Hunter S. Thompson
    When the weird get going, they start their own forum. - Vaughn McMillan

    workingwoods.com

  9. #9
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    Wow! This is interesting!

    Enjoy,
    Lurker---sorry, JimB
    First of all you have to be smarter than the machine.
    VOTING MEMBER

  10. #10
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    Just please don't be expecting fast - that just is not my speed.

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