I may have under sized my gantry beam. - Page 3


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  1. #25
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    Default Re: I may have under sized my gantry beam.

    Quote Originally Posted by tkms002 View Post
    OK so how do we define rigid?
    That is an interesting question, rigidity is acceptable when the machine can get the job done. That is probably not extremely helpful but in the end you the user needs to decide what sort of quality you want to achieve. Even quality has an individuals definition that might vary with respect to what a third party would call quality.

    Now I may be jumping to conclusions here but I suspect that most people want a Machine rigid enough to produce good surface finishes. That would be followed up by a machine that is highly repeatable. In most cases absolute precision comes In last, at least after the first two.
    The reason here is that routers by definition are not replacements for milling machines so you can’t really compete with a milling machine precision wise. However that do ant mean surface finish isn’t important. So people aim to make the machines as rigid as possible given the context of a “router”.



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    Default Re: I may have under sized my gantry beam.

    Quote Originally Posted by wizard View Post
    That is an interesting question, rigidity is acceptable when the machine can get the job done. That is probably not extremely helpful but in the end you the user needs to decide what sort of quality you want to achieve. Even quality has an individuals definition that might vary with respect to what a third party would call quality.

    Now I may be jumping to conclusions here but I suspect that most people want a Machine rigid enough to produce good surface finishes. That would be followed up by a machine that is highly repeatable. In most cases absolute precision comes In last, at least after the first two.
    The reason here is that routers by definition are not replacements for milling machines so you can’t really compete with a milling machine precision wise. However that do ant mean surface finish isn’t important. So people aim to make the machines as rigid as possible given the context of a “router”.
    OK Here is what I hope to do with it. I want to make non-ferrous sheet metal inlays( Aluminum, copper, brass) in wood(table tops, bench backs, etc). I don't need speed(within reason) but I do need the inlays to fit "perfectly" in the recess I cut.
    That being said, how big of a gantry beam will "get er dun"?
    Thanks



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    Default Re: I may have under sized my gantry beam.

    Quote Originally Posted by nlancaster View Post
    I have never seen a CNCROuterparts that used less then 3x6inch beam for the 4ft axis, they had plans for a machine that was 24x36 with a 3x3 beam. And I have been reading about cncrouterparts since he started by just making and selling his skate bearing units.
    OK I stand corrected. It was not a CNCRouterpars kit. It was a FineLineautomation kit using CNCRP parts.
    My apologies

    .



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    Default Re: I may have under sized my gantry beam.

    So you will be cnc machining both the recesses and the inlays?
    Then you mention "Fit Perfectly".

    There are other factors involved in doing this kind of material combining. It isn't something that you can just jump right into and get a perfect result on the first try. Hopefully you have already walked the walk.
    CNC will make this kind of work a little easier by getting the parts close to what you need. Possibly perfect for you.

    You will always have a crack between the materials. I would not shoot for a perfect fit, but rather a relaxed fit and fill the gaps with epoxy. This will allow at least some different expansion between the materials without buckling or busting out a seam.

    If it is not too intricate, you may pull it off with your current gantry. The bottom of the recesses will be covered, so not critical for surface finish.

    Lee


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    Default Re: I may have under sized my gantry beam.

    That being said, how big of a gantry beam will "get er dun"?
    It's really almost impossible to answer. You can somewhat adjust your feeds and speeds to compensate for a weak machine. Or make multiple shallow passes.


    I think if you reinforce what you have, as I mentioned earlier, it may be adequate.

    You said earlier that it can't be taller than 3"? If that's the case, then I'd say use what you have. Ideally, you want it to be taller, not wider.

    Gerry

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    Default Re: I may have under sized my gantry beam.

    Quote Originally Posted by ger21 View Post
    It's really almost impossible to answer. You can somewhat adjust your feeds and speeds to compensate for a weak machine. Or make multiple shallow passes.


    I think if you reinforce what you have, as I mentioned earlier, it may be adequate.

    You said earlier that it can't be taller than 3"? If that's the case, then I'd say use what you have. Ideally, you want it to be taller, not wider.
    OK What if I internally braced the entire beam every 6 inches with rebar then added a full length piece of 3x5 or 3x6 angle welded to the back like so.
    I may have under sized my gantry beam.-gantryupgrade-jpg



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    Default Re: I may have under sized my gantry beam.

    Quote Originally Posted by ger21 View Post
    It's really almost impossible to answer. You can somewhat adjust your feeds and speeds to compensate for a weak machine. Or make multiple shallow passes.


    I think if you reinforce what you have, as I mentioned earlier, it may be adequate.

    You said earlier that it can't be taller than 3"? If that's the case, then I'd say use what you have. Ideally, you want it to be taller, not wider.
    So the one thing I dont understand is the taller than wider comment. I really dont know what I am talking about but it seems to me most of the forces are in the X and Y axis directions rather than in the Z direction as the router is being pushed and pulled through the material.
    Can you set me straight?
    Thanks



  8. #32
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    Default Re: I may have under sized my gantry beam.

    No, not really. Maybe I'm wrong. But usually the weight hanging off of it is more than your cutting forces will be.

    The only way to really know what will work is to build it, or model it and use FEA on it.

    Gerry

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  9. #33
    Gold Member LeeWay's Avatar
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    Default Re: I may have under sized my gantry beam.

    If I were intending to beef up the structure of the beam, then I would find the closest fitting pipe that I could slide inside of it. Then fill the outside of that pipe with epoxy or even concrete. That will give you added defense against flexing. Then possibly include the angle iron as a last resort. Remember too that everything you do now is adding weight to the gantry, which also impacts the forces it needs to overcome.
    As I said initially, I would not bother trying to beef that one up. Most measures would yield far less benefit than the effort and cost put toward it.

    Lee


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    Default Re: I may have under sized my gantry beam.

    Quote Originally Posted by LeeWay View Post
    If I were intending to beef up the structure of the beam, then I would find the closest fitting pipe that I could slide inside of it. Then fill the outside of that pipe with epoxy or even concrete. That will give you added defense against flexing. Then possibly include the angle iron as a last resort. Remember too that everything you do now is adding weight to the gantry, which also impacts the forces it needs to overcome.
    As I said initially, I would not bother trying to beef that one up. Most measures would yield far less benefit than the effort and cost put toward it.
    OK
    Trying to add information here so that all you good people can help me out as best as possible.
    For me to "try it out" I have to build the whole thing and if it does not work it will require a LOT of rework and expense. So, I would rather scrap the current beam in favor of
    making a new one that has a great possibility of working without going over board.
    It will not be a production machine but rather a hobby machine that I may make some money with so it does not have to be lightning fast.
    If it takes me 5 passes to cut through .125 aluminum, I am good with that as long as it is a good enough cut quality to do the inlay thing.
    I don't have any idea how often it will be used for this but I don't want it to fail either.
    After calling Speedy Metals(I have one close by) I got the following real prices(not the internet prices) for some steel tube.
    Each at 6 ft( I may need a little more but this gives me a close estimate).
    4x6x.250 $110 online price $290
    5x5x.250 $100 online price $325

    So the questions are.
    Will either of these work?
    Is one better than the other?
    Could I use 3/16 thick?
    Will they still have to be internally braced?
    I really dont want to go much larger as the weight is getting up there (about 70 lbs each.)
    Dang, they are heavy.

    Thank you again.



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    Default Re: I may have under sized my gantry beam.

    Quote Originally Posted by tkms002 View Post
    So the one thing I dont understand is the taller than wider comment. I really dont know what I am talking about but it seems to me most of the forces are in the X and Y axis directions rather than in the Z direction as the router is being pushed and pulled through the material.
    Can you set me straight?
    Thanks
    Taller is better because it spreads out your contact points to the z-axis (assuming your linear rails are wider) which helps with leverage.

    For example, hold a broom with both hands together at the end of the broom, then kick the head of the broom and see if you can resist the broom moving. Then try the same thing with your hands further apart. It’s easier with your hands further apart.



    Sent from my iPhone using Tapatalk



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    Default Re: I may have under sized my gantry beam.

    Quote Originally Posted by BrokenHorn View Post
    Taller is better because it spreads out your contact points to the z-axis (assuming your linear rails are wider) which helps with leverage.

    For example, hold a broom with both hands together at the end of the broom, then kick the head of the broom and see if you can resist the broom moving. Then try the same thing with your hands further apart. It’s easier with your hands further apart.



    Sent from my iPhone using Tapatalk
    OK
    That makes sense. Wasnt sure if that was the only reason.
    Thanks



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I may have under sized my gantry beam.

I may have under sized my gantry beam.