Thread: new build opinions required
*** sorry double posty ***
Last edited by george uk; 18-12-2013 at 10:30 AM.
i will whip up the gantry and x in scetch up and post it later. i prefer to do initial engineerings and calcs in pencil and paper, Think of it as 2 C clamps per x rail, spaced at maybe 200mm
Last edited by george uk; 18-12-2013 at 10:43 AM.
reading this will answer your questions about the forces in play. what you suggest will not work , as you have to decrease moment B and the best way to do it is to increase distance D4.
Last edited by Boyan Silyavski; 18-12-2013 at 12:36 PM.
Wont be a problem as it will have equaL up forces from the guide underneath
in that drawing, my x would be were moment A is, and were the two yellow arrows are ( d3 ) would be the top and bottom connection to the X Rails.
The Y gantry, will be between the 2 x rails ( above and below ) , putting its COG were moment/force A is. I think i will only need the tool going below the gantry, not the spindle, the aim was always to get the bottom point of the spindle finnishing at the y gantry and bringing any material up to it
At the bottom of that drawing is Force D and Force C, these are are right angles to the rails.
With your proposal these forces would be along the rails, parallel to them and pointing in opposite directions
Last edited by EddyCurrent; 18-12-2013 at 01:24 PM.
The Following User Says Thank You to EddyCurrent For This Useful Post:
Eddy - yes exactly, and if i increase the distance of the gap on the bottom rail bearings, that should change the force angle a bit. ( cutting force ).
Also, the rails can run on the top of x, and the side of x, if its to hard to get the bottom level to the top. The intention being, the second rail would absorb some of the stress, and the ammount of extra stress relief should be proportional to the allowable gantry weight reduction.
If it will work this way, i can loose loads of weight from the gantry but maintain its rigidity. I still think there must be something am not seeing,
Last edited by george uk; 18-12-2013 at 02:47 PM.
Yes, yes, they will change direction/the forces. But... on a typical router the bearings that move the gantry are spaced 260-300mm/including, if rectangular supported/. On a heavy duty, like my current build for example, they will be spaced 400mm and above. So you have to space them obviously. What you are not taking into account is the overall height of that and the gantry and what i am speaking of is RESONANCE. It will resonate like crazy cause the forces of the tool and the assembly will be in paralel lines. Something like this resonator , where one fork will be the tool and its plate and the other the gantry assembly
there are some other forces which you don't take into effect- inertia and gravitation. Which are not problem in normal L shape gantry.
Just imagine a tank speeding on its noze vertically, when it has to stop. Tanks are low and long. Thats what best sturdy gantry design is.
While gravity and long L take care of the balance spreading it over the bearing blocks, the non achievable balance will f^^^ck what you propose. Vertical tank on its nose, it doesn't matter that it will be supported in the middle. if not that, then the resonance.
I am music instrument maker and here what will tell you. to lower resonance, you divide a long force arm into short ones and put each of them in different plane, so they will not help each other
I will put it in sketchup, as my current build of typhoo boxes and cartons and kitchen items, looks a bit to heath robinson ( I can write the Math on them, makes it easier to visualise stresses )
Of all the point you mention above, i think resonance is the one i can not design around, but, If the rails art fixed hard, the bearings will take out some. And although my design may increase the occurrence of resonances, it also reduces the requirement of weight of the gantry, therefor, having less effect ( less mass to carry the force of the resonance beyond the barings ), and also lowering the inertia problem
My works table is within the box of the frame ( half way ), the Y ganrty will be the top of the frame, not above. To keep forces and resonance down, my Z does not extend beyond the gantry frame. only the tool.
My z, will be between the two Y walls of the ganrty, fixed to both walls, the gantry, is a box itself, ( 100/150mm deep - 40mm wall width ), giving me the gap in the center to fit the Z gubbins
Last edited by george uk; 18-12-2013 at 03:51 PM. Reason: spullig
Unfortunately George I was meaning it was a bad thing that the forces were parallel along the rails unless you have 2 bearings on the top and 2 on the bottom but that would be overkill.
Unless your drawing, when you post it, makes it clearer.
Last edited by EddyCurrent; 18-12-2013 at 04:24 PM.
hi eddy, yes i am going for 2 bearings per rail, 4 bearings per X side, and when i ment spacing them out, earlier, its the gap between the bearings per rail, not the rails themselves ( top bottom ) .
I think that overdoing it on the bearings and rails, will allow me to make the gantry lighter, and a stable box, If i can get the gantry lighter, i dont have to worry about inertia , am also thinking that, in might want to be able temporarily add weight to the Gantry for some jobs, like surfacing stone,
I did go down the heavy road at first, and gantry weight, can cause as many problems as it solves, every time i work on the calculations with heavy gantry, am hitting performance limits on bearings, then bar, way before the machine design going to hit any problems. Then when you look at the costs of baeringfs an rails that will perform ok with the weight, ooooaaaarrr , then, when your bearings and rail can take it, your machine may need supporting. chicken and egg game.
whereas, the more rigid the Y, the less weight it needs to be stable
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