Design questions for a 3x2m Router

[koosjr]

I know this is a bit of all in one post, but the main issue here is the motion requirements.

I bought myself a small hobby router about three weeks ago. By then, I was an absolute novice in the field of CNC routing. I do have a little experience with CNC plasma cutting though, but cutting wood and aluminium where large forces comes into play, adds a mountain of interesting effects to indulge into.

I bought the router (1300x650mm cutting area) to learn the trade as we have plans for an interesting range of products. This router is lead screw driven on all axes.

As a CAD Package I am using BOBCAD V24, which is OK, but there are a few important bugs that I am not satisfied with and that BOBCAD support is not quite handling the way I like. They are great with sales though... That I will take up in the software threads.

My router is driven by Mach3 and now that I am getting to grips with all the finer settings of the software, it starts to become a real joy to use.


For some reason, I am one of those oaks who cannot help doing things myself. So rather than buying a large machine, I want to build it and it certainly is not difficult. That is what makes CNC such a beaut. I am hard in the planning stage for making a 3-Axis 3x2m Router that will be upgraded to 4-axis later if the need gets there. The basics will be:

1. Aluminium Retrofit Frame with provision for a A-Axis
2. Drive on X and XX axis because of the 2m Y-span
3. 1050W Kress Router with auto tool changer and speed drive.
4. 150mm Z-Travel


At this longs lengths, the drive gets really important.

For a Stepper motor package, I am looking at the 1200 Oz-In 4-axis package of these oaks.

Page Title

For X an Y guides, I am leaning to the type in the link below in stead of the fully supported chrome bar type.

Profile Rails, Carriages, Hiwin rail rails hiwin carriage bearing cnc machine linear


For the drives there are basically only 2 affordable and easily obtainable options: Lead Screw or Rack and Pinion. Belt drives are not on my list yet. I am well aware of motor curves and know how quickly the torque drops as the drive pulses increase.

From my experience in other fields, I see issues with using a lead screw on a 3m length. Unless one have additional sliding support for a long screw like that, it (literally) goes bananas or wobbles as soon as a bit of torque or revs are applied. I would not go less than a 28mm screw on a 3m length, but that is already a pretty heavy shaft.

The automatic gear reduction of the lead screw is a handy benefit though in terms of low speed torque and resolution, but it seems to me if one wants to get some speed out of that large bed for rapid travelling when drilling a hole matrix, a double entry lead screw is the best option.

What I also like about the lead screws, are the no backlash nuts and in terms of that, my feeling is that one can much easier get a long lasting zero-backlash setup than with Rack and Pinion.

Rack and Pinion on the other hand, will easily give the speed one needs, but it most definitely needs to be geared down to improve resolution. For resolution, I would prefer 3:1. That said, would Microstepping be recommended for this setup?


Based on the above, it does seems to me that Rack and Pinion will offer me the simplest construction while it will be easy enough to get both the speed and torque I would need. I am only worried about setting it up so that backlash is negligible over the entire 3m length. Is this an issue?

Are there any other options I should know of or thing I need to consider?

Needless to say, I am quite excited at the moment. It is always nice to dig deep into new fields.