[vroemm]

Hi..

I would like to make a cnc router frame with the best accuracy and stability.

Which these two frame types is best for a CNC router ?

The type A where one slider bar is above the other ?
Or type B where the slider bars are next to each other and the drill is in between ?


Thanks..

[jans123]

I don't really think it matters. So many parameters are involved regarding stability that you have to to make decisions about suporting the rails etc. One thing that strikes me is that "A" gives better acces to both work-pice and router/tool. With "A" the router actually can work outside the table both at the tables end (if you are milling something high" and the router also can be very accesible from the long edge of the table. I built one like that once since I wanted room for my hands while changing tools. It is also easier to attach new routers, drills, multitools or whatever if you have an "open front", but you are the one to make i work and to worke safely.
/Jan

[andy_ck87028]

I prefer B. I could have gone either but I have elected B as I believe the torsional strength is better for supporting the Z axis, especially when Z is working fully extended.

I think with A there are too many lever factors in the design which arises in both the Z design and the gantry supports.

Agreed re. access for tool change but I have minimised that by having the tool head protude from the base of the Z. Although that brings the lever factor back in it is minimal.

I have also raised the X axis rails so there are virtually no gantry supports (thus removing the gantry lever factor) and enabled the cutting table to be raised manually to enable the Z to not have to extend unecessarily (thereby reducing the impact of the Z lever).

I think that by inadvertantly introducing unnecessary lever factors into the design, it will limit the potential of the machine.

Andy

[vroemm]

I think with A there are too many lever factors in the design which arises in both the Z design and the gantry supports.

Yep, i was thinking also about this lever fector.
But mainly its influence on the X axis bars.

With type B there is a other problem with lever action.
The top of the Z-axis is far away from the X axis bars.
Which makes it more difficult to make a construction which will limit the movement of the top of the Z-axis.
You wil need more and heavier material to hold the top of the Z-axis stable.

Has this been discussed before in a other thread ?
Does anyone know the link to this thread ?

[keebler303]

i am going to bed so i won't elaborate in detail but if you just look at the play in the guides (slides,bearings, etc.) there will be less play at the tool end in the A type. this is for a given bar separation and tool distance below the lowest guide rail. the leverage on the rail is also greater in the b type, assuming similar dimensions.

[ViperTX]

One covers torsional forces the other covers rotational forces......duh....

[andy_ck87028]

What do you mean ViperTX?

Sounds interesting.

[keebler303]

here are the forces generated by a side load on the cutter that the guide rails would see. higher forces mean more deflection and less accuracy. sorry for the crappy drawing.

Matt

[keyne]

Nice drawing keebler, thanks.
The smaller side loads for option B suggest that it may be better suited for Vee-rollers. amazingly, this is also the option selected by shopbot and ez-copycat.

[High Seas]

Style B! For sure. But, the trick is to try and duplicate , or include a similar solution for reducing torsional loads on the Z axis as well. It can be done, but there is always a bill to pay, ease of access to router, bit, etc - but, do-able.
:cheers: Jim

[vroemm]

Experience is the BEST Teacher.

This is often on my mind lately.
If i am not sure of a solution, i can just build it, try it, and see if it works or not.
If it does not work, i can always build a new cnc router frame :-)
Its one of the fun parts of building your own cnc router :-)