Steel Framed Router

[Ricardoco]

:confused:

If I was to mount a plate (as shown in pic) to the back of the axis with many fixings would that stiffen up the gantry sufficiently?



The current design supported round rail, but this was down to cost and if available I would use profiled rail.
I also think the 25mm ballscrew is OTT but now that it has been mentioned I'll look at 20mm with 5mm pitch with pulleys and belts. I am concerned about whip in the 16mm screws, but again it could be a saving.
I am hoping to use a single ballscrew on each axis but if I find problems I think it would be easy enough to add an additional one, so I'll look out for a 4 motor and driver package.
Never thought about resonance, but kiln dry'd sand could be a good solution.

Thanks for all your input and please feel free to continue.
Jim


I can see this becoming a bit of a monster and it has to fit in my garage with all my junk.

Ok let me show some diagrams..


With no load and Spindle central this is the look of the machine from above.


Now cutting brings in to play these forces and consequences.

As the others have touched on instead of using 1 screw in the center if you use 1 on each side that will sort it out but at the end of the day it is all down to cost and accuracy. if you take the above examples and apply them to the other two axis you will see the weaknesses in your structure at the time of design not when you have spent the money, most of us on here have been through the building process and made the mistakes for you...:whistling:

BUT. my first attempt at building a machine was flawed and at the end it was not accurate but it was cool looking and i played for hours with it just amazed ide built it and to me for that split second it was PERFECT!!

then i took it to pieces and joined this forum... the rest is history...

""MOST"" of these guys on here really do know their stuff, but dont just settle for one opinion get lots of opinions and you will soon see the way or be extreamly confused :confused:


Rick

[mocha]

Rick, A silly question perhaps... most of the utube vids I've looked at seem to position the work at 0,0 giving the forces you describe in the pic 2. Would I be right in thinking that if the work was positioned mid Y (above the ball screws) with x=0 or where ever, it wouldn't be so so much of a problem? And, would that imply that best accuracy / precision would be in the centre of the table rather than at the edges??

[JAZZCNC]

Rick, A silly question perhaps... most of the utube vids I've looked at seem to position the work at 0,0 giving the forces you describe in the pic 2. Would I be right in thinking that if the work was positioned mid Y (above the ball screws) with x=0 or where ever, it wouldn't be so so much of a problem? And, would that imply that best accuracy / precision would be in the centre of the table rather than at the edges??

Have you posted in the right thread.? Not sure what your saying or meaning.?

[mocha]

Oops, sorry gents, dropped the quote somewhere along the line, what I should have posted is:

:confused:



Ok let me show some diagrams..


With no load and Spindle central this is the look of the machine from above.


Now cutting brings in to play these forces and consequences.



Rick

Rick (anyone), A silly question perhaps... most of the utube vids I've looked at seem to position the work at 0,0 giving the forces you describe in the pic 2. Would I be right in thinking that if the work was positioned mid Y (above the ball screws) with x=0 or where ever, it wouldn't be so so much of a problem? And, would that imply that best accuracy / precision would be in the centre of the table rather than at the edges??

[JAZZCNC]

Rick (anyone), A silly question perhaps... most of the utube vids I've looked at seem to position the work at 0,0 giving the forces you describe in the pic 2. Would I be right in thinking that if the work was positioned mid Y (above the ball screws) with x=0 or where ever, it wouldn't be so so much of a problem? And, would that imply that best accuracy / precision would be in the centre of the table rather than at the edges??

Ok understand better now.! If using just a single centrally placed screw then yes the most accurate position is in the centre of the machine and as you approch the outer edges the gantry will flex and twist~(racking) reducing precision.
How much racking depends on several factors but obviously the wider the machine the worse it gets, wide gantry or wide placement of the bearings the gantry sits on helps reduce this to a degree.
Basicly if you have central screw on narrow machine with wide bearing placement then the racking affect can be controlled to acceptable levels. Wide machines are better suited driven from both sides of the gantry using 2 screws.

Regards work positioning I think you'll find when you see a referanceto 0,0 position it will often relate to work coordinates which are often differant to Machine coordinates.

Excuse if you know this.! . . . Machine coordinates define the overall cutting area of the machine. .Work coordinates define a referance point on your material that you want to start work cutting from.
So say you have 400mm * 400mm cutting area with machine coordinate 0,0 defined in the lower left corner (looking down from the top) and place 100mm x 100mm material in the centre with the cutting start point in the lower left corner of the material.
Then the work coordinate is at 0,0 but it's actual position on the machine is at 150,150. Where you position the work 0,0 coordinate will be determined by where abouts you position the 0,0 in you cad program and the part your drawing.
Often Machine coordinates are positioned in the lower left corner so you'll never have negative machine coordinates, so If your work as negative coordinates IE Circle with centre defined as 0,0 work coordinate then you need to offset the 0,0 work coordinate far enough away from 0,0 machine coordinates other wise the machine will crash into the limits.

Hope this helps if i'm teachng dad to suck eggs then i'm sorry.!