Well here goes... Aluminium frame router design

[Boyan Silyavski]

Given the short length of your desired travel it will work ok. Bus as you have drawn it, the bit should touch the finished machine bed. Cause lower it will not go obviously. Is it so?

The case is if say you want it to travel 200mm for example or longer , then the 4 blocks on the Z will go higher than the gantry, hence the tuning fork.

[CharlieRam]

The case is if say you want it to travel 200mm for example or longer , then the 4 blocks on the Z will go higher than the gantry, hence the tuning fork.

So, is that the issue that will cause the vibration, the rails going above the gantry top? If it is then I will have a look at what I can do.
Cheers, Charlie

[CharlieRam]

Well... I'm at a bit of a crossroad in my design, I have altered the Z axis to the conventional method which should please Jazz! but the machine is now 1004mm wide by 1400mm long with overall cutting area of 620mm x 1100mm and I'm now thinking do I need it that big?
The original idea was to have a machine capable of machining soft metals or even steel if it could cope but I also wanted it to be big enough to machine 600mm wide sheets of MDF so I could machine my arcade cabinets, the problem is I would need a machining area of 1800mm lengthways to produce them in one cut but I am now thinking should I make a smaller machine with say a cutting area of 400mm x 600mm for aluminium and possibly steel (Is steel doable or a definate no go?) and when that is built, use it to make parts for a dedicated mdf/wood router that would take the full length sheets at a later date, This machine could hang of the wall with a slight incline to get over the space issue.
I am also thinking that 1610 ballscrews with 1.8 deg steps will only give a resolution of 0.05mm, If I built it for metals and plastics then 1605 ballscrews could be used bringing the resolution down to 0.025mm.
What are your thoughts on this?

One other thought, If I only have a cutting width of 400mm would I get away with a single ballscrew, if not, what is the maximum width I could get away with or is it just better to go with 2 when machining metals?
Cheers, Charlie

[irving2008]

For machining metals, esp steel, you need rigidity, so a mill arrangement, table that moves in X & Y and a rigid fixed Z column is the best solution. a rigid router style machine can mill ali if strong enough but its a compromise at best.

To improve resolution for machining metal you need to gear the motors down. a 4:1 reduction improves resolution by 4 and increases torque, necessary to overcome the inertia of a heavy moving table and increased cutting forces.

[Boyan Silyavski]

Single ball screw is out of question if you machine metals on the cnc, meaning aluminum, not steel. many though machine iron from time to time. Steel is out of question if not annealed.

1610 ball screw makes one turn and moves 10mm. so for 1mm it makes 1/10th of turn. To make one turn a 1.8 degree motor- 360/1.8=200steps per turn. When you apply 1/8 micro stepping which is the usual 200x8=1600 steps per turn.Any decent driver will do that. So to move 1mm then 1600/10=160steps per turn. 1mm/160steps=0.00625mm resolution. 1/4 microstepping will give you 0.0125 mm resolution

I would worry more about rails and ball screws parallelism and perpendicularity in all directions, as this is the culprit for the real life imprecision of a machine. Do yourself a favor and equip with precision straight edge long enough that can be laid on both the long axis rails perpendicular, and 2 precision squares, cause without this i dont see how you can even be in the <0.5mm ballpark when you reach the moment to mount everything together.