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Thread: new linear bearing gantry

  1. #11
    Join Date
    Dec 2011
    Location
    Piedmont, SD
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    650

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    Brady says:
    it's more trouble than it would be worth.
    Gary adds:
    After seeing how much material removal it took to get a flat surface, I vowed to never again put linear rails on aluminum extrusions.
    I think this answers a question rumbling around in the back of my mind (and likely a few others) since this topic has come up a number of times recently.

    Is there a point where the advantages are outweighed by the process of re-building the darn thing? Or am I taking these sentences too far out of context?

    Ultimately, if it's worth it, I'd strongly consider it. Seems to be a pretty sexy upgrade. However, if it's just to say I've got the latest and greatest, but no more than 10 -20% gain in accuracy, then my machine is fine as it is with the V-rollers.
    I think....

    Seems this may be an "if it ain't fixed, don't break it" situation(?)

    jeff

  2. #12
    Join Date
    Apr 2007
    Location
    Marquette, MI
    Posts
    3,374

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    Jeff...
    Let me add ".... without milling a proper surface" to that. I would further say that there is no doubt of the increased capability of speed, cut quality and rigidity. But unless you plan on installing a heavier extrusion for the X, milling it also, you may just be throwing money at the machine.

    From a wide view linear rails seem to be a simple bolt on accessory or upgrade to most users. Getting them mounted within a couple thousandths of parallel and flat is paramount. Which may be the reason they don't exist on the X rails, yet. It would be very difficult for most purchasers of new machines to mount linear rails straight enough and even more difficult to get a pair of them parallel enough to run properly without binding. It is no accident that the majority of machines that are so equipped are welded and machined.
    Gary Campbell
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  3. #13
    Join Date
    Jan 2004
    Location
    iBILD Solutions - Southern NJ
    Posts
    7,924

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    Block & Rail do make a big difference...but there are caveats, as Gary mentioned.

    The v-roller bearings offer a LOT of leeway to being misaligned or sloppily assembled. The problem with the PRS gantries is that on production tools (people using them day in and day out) OR on tools where the YZ car roller bearings are set too stiff, the rails get sandwiched into the gantry beam extrusion to the point where the eccentric bearing is out of adjustment & there's no way to get the v-rollers to be tight on the rails again without jumping through major hoops. Also, they don't exactly 'wear in' linearly - so some areas of the rail are tight while others are loose. ...it also isn't balanced properly & reminds me of a giraffe...doesn't take much to knock one over...but that's another thread.

    If you aren't having problems like I described, then don't worry about it. Just run that thing as long as you can. Nearly anything under the sun can be repaired, rebuilt or retrofit to make it better...just like anything else, how much time, effort and money do you want to put into it? In some cases it's a better value to just buy a new or good used machine and sell what you have for what you'll get for it...and in other cases, it makes more sense to either acknowledge the limitations of what you have or to rebuild/retrofit the parts of the machine that need it. Personally, nobody is going to give me squat for my 18 year old PRT...I knew this 5 years ago - it doesn't owe me a dime - so I have NO QUALMS about welding on new parts to beef it up, hacking off old parts that are worn out or really anything I want/need to get a job done. It's just an appliance...and for most work it does just fine. For fine work, there are other machines...

    So in terms of a gantry...and if I needed one or mine was worn out, I would personally go down to the steel yard and get a big honkin piece of steel rectangle tubing at least 1/4" thick, with preference being 3/8" wall. Something 6x10" would probably be good. I'd get it decked so it was flat & true and machined for block/rail. Unless you're starting with 3/8 or 1/2" wall thickness, aluminum has no place as a gantry beam...plus it's way more money than steel these days. Keep your eyes peeled...you'll see plenty of popular manufacturers making the switch from AL to steel because it's cheaper & better. Not everyone works in metal, so your options may be limited...what one man can do, another can do...(with enough desire & determination) - otherwise you'll have to pony up and pay whatever it is to get it right.
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