Re: I may have under sized my gantry beam.
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I put a 30lb dumbbell on it in the middle and got .005 inches of flex. I get about .001 inches when moving my z axis across it with no spindle on it so the question is what is too much flex and what should I shoot for?
That's something only you can answer. Different people have different expectations.
The bigger issue is that it's going to twist when that same 30lb load is pushing on it from the end of the Z axis.
And the sag or twist isn't the only issue. The fact that it can move, means it can vibrate as well, causing poor quality cuts.
Re: I may have under sized my gantry beam.
Right.
That was static weight too. Add the weight o the Z axis as well. Then when you add in the driving forces of the weight of the whole gantry, it uses that weight against itself when it changes direction abruptly. Even though it is relatively light, the span makes it susceptible to many different types of error at the tool. I would venture to say the tool itself would not be rigid enough to get any kind of tool life from carbide tooling in aluminum. Anything less than rigid is going to quickly be fatal for carbide.
Re: I may have under sized my gantry beam.
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Originally Posted by
LeeWay
Right.
That was static weight too. Add the weight o the Z axis as well. Then when you add in the driving forces of the weight of the whole gantry, it uses that weight against itself when it changes direction abruptly. Even though it is relatively light, the span makes it susceptible to many different types of error at the tool. I would venture to say the tool itself would not be rigid enough to get any kind of tool life from carbide tooling in aluminum. Anything less than rigid is going to quickly be fatal for carbide.
OK so how do we define rigid?
Re: I may have under sized my gantry beam.
I think it may be easier to describe what is not rigid.
And again it is about what the machine is designed to do and it's size as well as speed and accuracy while doing that.
On the gantry in question, it might be able to machine aluminum up next to one of the gantry supports rather well if the spindle is strong, fast and we have very low backlash and run out.
If cutting full size material, you will not see the same cut quality across the entire span. Cut quality will diminish toward the center and get better when approaching the opposite support.
Re: I may have under sized my gantry beam.
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Originally Posted by
tkms002
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”.
Re: I may have under sized my gantry beam.
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Originally Posted by
wizard
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
Re: I may have under sized my gantry beam.
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Originally Posted by
nlancaster
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
.
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.
Re: I may have under sized my gantry beam.
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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.
1 Attachment(s)
Re: I may have under sized my gantry beam.
Quote:
Originally Posted by
ger21
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.
Attachment 407934
Re: I may have under sized my gantry beam.
Quote:
Originally Posted by
ger21
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
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.
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.
Re: I may have under sized my gantry beam.
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Originally Posted by
LeeWay
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.
Re: I may have under sized my gantry beam.
Quote:
Originally Posted by
tkms002
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.
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Re: I may have under sized my gantry beam.
Quote:
Originally Posted by
BrokenHorn
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.
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OK
That makes sense. Wasnt sure if that was the only reason.
Thanks
Re: I may have under sized my gantry beam.
OK so what do you think of my post #34?
Thanks
Re: I may have under sized my gantry beam.
I'd go with the 1/4", and yes, add the internal bracing, as that will help to resist twisting.
Re: I may have under sized my gantry beam.
Quote:
Originally Posted by
ger21
I'd go with the 1/4", and yes, add the internal bracing, as that will help to resist twisting.
the 4x6 or the 5x5?
Thanks
Re: I may have under sized my gantry beam.
I would go for the 4x6 and mount the 6” dimension vertically.
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