Thread: sliding gantry or sliding Base ?
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05-11-2012 #1
Hello Folks,
sorry if this question has been discussed before, if so, i couldnt find it :)
I am currently thinking out my Design and I am not sure how to make the X Axis.
Either the whole Gantry slides, or the Gantry is fixed and the "Baseplate" slides (lack of the right english word, sry) ?
I will probably use 600mm TBR20 supported round rails for x and y, so thats what the size will be.
Anybody has empiric experience comparing the two methods ?
I want to design the gantry it self as per the paper posted in the faqs, problems, solutions forum regarding "heavy duty design".
I mean just the structural design, not the materials used.
Built from 40x40 Alu Profiles triangular reinforced, i already drew it that way but of course I forgot to make a screenshot :)
I personally prefer the "fixed gantry and sliding baseplate" design, that way I can make a really sturdy gantry.
Another slightly off topic question, that just popped in my head, would be how to fix the TBR20 Rails to the profiles, I dont know if I like the idea of just bolting them down with T Nuts, otherwise I would have to make adapter plates, which in turn would add some of the much desired mass to the system.
THanks in advance,
Regards,
Clemens
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05-11-2012 #2
Ok sliding Gantry will give you almost double the working X travel for a given length of rail so how much workable area do you need
With Moving Gantry you will get 600mm travel and 600mm working X axis minus the thickness of the gantry and the spindle offset, i can do pics if you need them, with the moving X worksurface you will get 300mm workable area/length if you want 600mm workable area then you will need 1200mm rails. and possibly a bigger area to put the machine in than you have..
Regards RickAlways bear in mind that your own resolution to succeed is more important than any other - Abe Lincoln
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05-11-2012 #3
I am aware that the machine footprint will be almost double the length if i am not using a sliding gantry.
My question is, is the advantage in structural rigidity worth it , or are there arguments against it, except the larger machine footprint.
I am mostly interested in
Anybody has empiric experience comparing the two methods ?
*edit*
Regarding the mounting question of the supported Rails,
i probably will just use 40x80 Profile where the rails are, and just mount the rails with t nuts, as the spacing of the TBR20 is 40mm.
Any arguments against that ?
I want to avoid machining that large adapter plates.
Thanks,
Regards,
ClemensLast edited by JohnJ; 05-11-2012 at 06:56 PM.
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05-11-2012 #4Always bear in mind that your own resolution to succeed is more important than any other - Abe Lincoln
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05-11-2012 #5
I didn't mean to offend you Rick,
just wanted to clarify that I already know the disadvantage of the machine being larger for the same workspace, i just didnt mention it in my first post, as it seems kind of obvious to me, sorry for the misunderstand regarding machine size, i should have said i would use 600mm rails if the gantry moves.
Could you tell me what experience you have made with the two methods please, thats whats most interesting for me.
Is the advantage of building a fixed gantry big enough to justify a larger machine foot print ?
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05-11-2012 #6
As you have probably noticed on your travels moving Gantry machines are almost always used for machines such as plasma cutters no load at tool tip, routing machines low to mid load at tool tip. Aluminium seems to be the bridge between both types and i have certainly seen more Steel machines with a moving X rather than a moving gantry.
Always bear in mind that your own resolution to succeed is more important than any other - Abe Lincoln
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05-11-2012 #7
Thanks for your answer,
so, if space wouldn't be an issue for you, you would opt for the fixed gantry, right ?
Regarding my experiences,
i only know a few industrial Milling Machines that are built with a bridge design,
for example the Datron Machines, which are good worthy Mills, have a bridge design, but they have a moving gantry and fixed table, which is probably due to size, as size is a big sales argument for industrial machines.
You are right, all the bridge type machines I can think of, have either no load at the tool tip, or only light load.
I can just think of industrial machines, as thats where my experience is from.
For now i will complete a 3D Design of a fixed gantry type machine, lets see if I like it at the end.
Nevertheless, i would love some more people to join the discussion and share their experiences.
Regards,
Clemens
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05-11-2012 #8Always bear in mind that your own resolution to succeed is more important than any other - Abe Lincoln
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05-11-2012 #9
With a fixed gantry you can make the gantry as strong as you want without worrying about its mass too much, since it's not moving. Clearly since the rails now need to be bigger it's likely to cost more, so you're using more space and money to get better rigidity which is nothing new. Also the motors now have to move the mass of the bed and whatever you cutting, which could add up to a considerable amount with an aluminium bed. Clearly this means you may have to spend more on the motors, although since the bearing blocks can be spaced out a lot, you should only need one ballscrew so that saves a bit compared to a moving gantry.
It will be significantly cheaper to use steel for the main frame, instead of extrusion. With a fixed gantry you can afford to get some big box section...
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05-11-2012 #10
Thanks for your answer Jonathan,
i'd rather spend a little more money for a sturdy machine, than being dissapointed afterwards, so that wont be a problem for me to justify a little more money.
I am not sure about the steel box section, i could only bolt them together, because I dont think I can weld good enough so that it wont distort and warp in every direction :)
Whats your opinion on that ?
Regards
Clemens
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