Thread: Accurate Strong Gantry
Extending the gantry uprights down seems good idea -this node should be rethink with the bracing and reinforcement plates in profiles.
My aim is to design parts that can be done by both DIY and machining method.
machine bad is Ok -it has surfaces to be leveled on top -preferably positioned on the same level-that is way stand the gantry leg here at the moment
Y beam is the same -can be done on both way
Z beams will be separated and bolted so it is similar to Y -I do not want to weld a U form and do something with frame -it makes my life hard
rather to make strong flange nodes and the careful assembly and adjustment will give the accuracy (especially the two parallel surfaces)
Nodes will be oriented and fixed with parallel pins.
That is only may plan for now -God knows nothing about it.
Last edited by vargai; 19-12-2014 at 08:38 AM.
That design will be a night mare to build and setup which isn't required and will have no gain over other simpler designs. C channel is bad choice due to it being bendy/twisty in relation to boxsection.
I don't think you have really thought about the complexitys and realitys of building this design.?
The C section inner surfaces won't be flat so will need milling for the rails. Then you have the problem of making sure the uprights are perfectly parallel in 2 planes and perfectly perpendicular in the other.!! . . 99.9999999% Nailed on that you won't be able to weld this up and keep parallel/perpendicular in all planes.
Any surfaces that where milled flat and true won't be flat and true after welding so this will be a waste of time and you have no way mill when welded up.
There is a no provision for adjustment and the design is such that there is no room for any error to be taken out.
Boxsection will work far better and be much easier to setup or deal with alignment errors after welding.
The slight difference from ideal bearing loading which Ross suggested won't make any differance to the machine in real world performance or longevity but it will to your mental health and sanity when setting up.
Also the Uprights need far more bracing as any deflection here will show at the cutter and finish quality. Personally for best strength and bearing loading I would have double uprights each side of gantry with 1 rail on each upright and the uprights would be braced in 2 directions.
I feel If you go with this design you'll regret it come setting up time.!
This is a design evolution process with analysis, checking, listening to the pointers . I am not able to put a ready for production plan on the desk right now and I am patient and have time. Bad design leads to a better one. (in a good case)
This is still a study where I try to find the place for all the function.
Some detail explained in written form and never meant to weld this construction otherwise I would need medical treatment right now.
Yes, box section is better than C no question-even when equipped with bracing
For some reason I supposed that box section is more inclinable to resonate than a thicker opened one
The stronger the better so I am opened to the closed section
Just a sketch about how I understood double upright braced in two direction
Last edited by vargai; 19-12-2014 at 07:23 PM.
Now you have got me with that constant changing of the design. Why don't you like one design, stick to it and further develop it to suit your needs. If you liked the before suggested design from the video in post #41, then just see what is good and what could be bettered. i would suggest even contacting the guy and asking him if he were to make it again what he would change and what he liked. That will save you a lot of unnecessary trouble and give you invaluable real life feedback. Thats why people stick with certain designs, cause they are good and there is feedback.
I understand that the overhang of his design is bothering you, and it should be. Cause it bothering me. Not only the spindle, but the hole gantry overhangs. That kind of kills the good points of that particular design.
One thing from a design point of view people should understand is that the fixed gantry design we discuss here has one really strong point. I am sure most people don't understand this point properly. Its not that the gantry is fixed. Its that the rectangle it forms is very big so its moment of inertia is incredibly big. So when changing that fixed gantry design/where it forms a portal with 2 legs/ in any way that compromises it main strength is not a good idea.
Another basic point to understand is that all rests on a couple of bearing blocks in all 3 different coordinate planes. So no matter how strong you make the machine frame, the bearing spacing, placement and forces there will form the real weak spots.
the purpose of the strong frame is to hold enough for the forces. next purpose is to minimize bend and twist which leads to minimizing vibration.
What people fail to understand, i see it here and in the other forums, is that the machine frame should be sturdy to a certain point and then the aim should be to be integral. No need to make 1 ton machine when same could be achieved with integral 200kg one.
Sturdy machine that is extremely rigid will ring like crazy if not integral. So thats when all make them heavy instead of making the design integral.
By integral i mean designed so that all forces spread equally, neutralize themselves and no weak spots and overbuilds in any direction possible.
Thats why there are some principle designs that all use, cause they are integral. Not that always people take full use of the possibilities with that design.
I assure you that a properly designed L gantry will beat any day the fixed gantry design if its not properly designed.
And IMHO after playing a lot and rethinking all designs and reinventing the wheel, my conclusion is that if all things taken into account we must not forget that we usually use only 2.2 -3kw spindle, using only 6-12mm bits, so we should not forget the strongest point of each design and choose it when needed, cause at the end they will all work if made properly.
Last edited by Boyan Silyavski; 19-12-2014 at 11:37 PM.
The Following User Says Thank You to Boyan Silyavski For This Useful Post:
Im very new to this, but that was a great post silyavski.
This design and the over hang are no problem what so ever.! . . Milling machines and Many large commercial horizontal designs use much much larger overhangs but rest of the machine is built to match.
Like Boyan rightly points out your design is weak where it matters most and not very well thoughtout in other areas. This why I would support and brace the uprights on 2 planes and support the gantry on 2 sides with rails.
The over hanging spindle wouldn't bother me in the slightest with correctly sized and spaced bearings. But if you want the best layout which is slightly more complex and costly then have the Axis which the spindle travels on supported both sides so effectively having a Box in Box arrangement.
Personally like Boyan says don't re-invent the wheel just make it fit your purpose.!!
Last edited by JAZZCNC; 20-12-2014 at 10:44 AM.
The Following User Says Thank You to JAZZCNC For This Useful Post:
Well to be fair the first post did say 1000N cutting force so guessing big cutters will be used and with 0.05mm accuracy that's not much error budget within the whole machine.
Without getting in to complex design calcs the quickest and most economical solution is to over engineer the frame. The extra weight can be benificial and also a problem with regard to acel-decel and dynamic loading but this design stops all the loading being transferred to the x axis like a moving gantry. So wont be as much of a problem.
The natural progression of a diy machine is to upgrade so having a strong sturdy frame means you get bigger steppers or higher powered spindle at a later date.
I know that the machine will be limited by its spindle power and cutter diameter and in fact tool deflection will be the ultimate limiting factor to cutting and feed speeds but this isn't a commercial machine.
I always believe that the machine should be designed from the cutting tool back through the spindle and the rest of the machine. Maybe It would be better to start again with the design spec to confirm what spindle and cutters will be used and go from there. :0)
The Following User Says Thank You to Ross77 For This Useful Post:
3 kW motor + belt driven spindle with a later ATC option
Cutters "anything" that the motor can drive ( in plastic I can use 50 mm face mill :)
100-10000 rpm( so conventional machining range)
one option is AC motor +VFD -only the motor is 25 kg I know
other:s cheaper type servo motor or similar- designed for this purpose
I need some help in this subject to choose.
I made some searching but still have not find too much here.
Something I found on Blakburn's post but its reading is not aloud for small children.
So pls point it to if any is here
Last edited by vargai; 28-12-2014 at 09:44 PM.
With my cheap drill press, cut off saw and stick welder I have needed some tolerance building my frame and I have seriously taken my time!!!
You are doing the right thing sharing on here though you will get some v helpful advise.
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