[pettyofficernick]

Hi, can anyone recommend a design for a small 3 axis cnc router, around 750mm x 500mm maximum footprint, of all metal construction and available as dxf files so I can get the parts cut by my local laser cutting works. I have built several 3D printers so the electrnic side is no problem. I want to use the mechine for cutting out parts for models in 1 to 5mm ply and thin brass and aluminium sheet.

[millhouse_]

Hi. You could search grabcad: https://grabcad.com/library?page=1&t...y=cnc%20router

[wizard]

I don't have any CAD files for you unfortunately.

However one thing stood out in your post. IF the local laser shop works primarily with sheet metal you may be on the wrong path. To get good results in wood your machine needs to be substantially stiffer than a 3D print and stiffness requirements go up with aluminum. Brass is an interested discussion all on its own due work hardening and various allows being notorious for machining difficulty

In any event to deal with the stiffness issue it is common to use tubular steel sections. It should be noted that some laser shops do in fact have machines to handle structural steel tubing but they are not as common as sheet goods machines. If not a laser the tubing can be cut to size as needed on a band saw or cold cut saw. Some of the pieces may require post cutting work to square up the ends. The good thing here is that a small machine means you can get away with smaller dimensional tubing. To put it another way using sheet metal isn't a good idea unless you have the facilities to bend and weld it up into suitable structures.

The weight of a steel frame bothers some people. However a CNC needs to move a relatively heavy head (Z-axis) around, so to minimize vibration and machine walking you actually will need to be more mindful of the weight you put in the machine, especially its base. Weight is only a negative here when you need to move the machine.

One thing you need to settle on is the machine basic structure which can be moving table or moving gantry. On small machines I like to suggest moving table but your machine is getting up there is size so you need to consider space used. Generally I find moving table designs to be easier too final assemble and align. They also end up stiffer for and equal amount of material.

A few things to consider when coming from a 3D printer build:

1. The increased requirement for stiffness means that you have implement linear guides that are much stiffer. This results in the requirement for high precision alignment. Smallish machines are less tolerant of misalignment so you need to work to a higher degree of precision.

2. The high degree of precision may require that you purchase measuring tools or metrology tools you don't have. Generally these tools are a good investment but you may need more that your are anticipating. The more basic tools here are dial indicators and squares.

3. For pretty much all of the axises, you are driving a lot more mass than on a 3D printer. This requires larger motors and on most systems lead screws of some type. You can't realistically machine with 3 mm wide belts (even if some machine exist with such belts).

4. Be mindful of mass. It is great in a machines base but can be a problem in the gantry if the base is too light. Bolting a machine down (bench, floor, surface plate, concrete slab & etc) may be an acceptable solution to this problem. This is about machine walking, you also have the issue of mass causing acceleration problems. On a machine this size you likely will not have significant acceleration issues for any reasonable design.

Well that is off the top of my head. Lots of luck with your search! There are some plans out there but most are not spectacular designs.

[pettyofficernick]

Hi,thanks for the replies. I intend to use MGN type linear rails, Nema 23motors and ball screws to transmit motion. I have various vernier callipers, both digital and old style, micrometers, height and depth gauges. I haveseen some designs made from 12mm MDF but would rather use say 10mm aluminium, I only intend using a 500Watt spindle, I will be cutting mainly model boat parts from up to 5mm ply and 25 thou brass and aluminium sheet.

[fretman_2]

Navy or USCG Petty Officer?

[pettyofficernick]

Navy or USCG Petty Officer?

Sea Cadets,20 years as a volunteer adult instructor, UK, now retired.

[fretman_2]

Good deal. Retired US Coast Guard Petty Office here...

Sea Cadets,20 years as a volunteer adult instructor, UK, now retired.

[wizard]

Hi,thanks for the replies. I intend to use MGN type linear rails, Nema 23motors and ball screws to transmit motion. I have various vernier callipers, both digital and old style, micrometers, height and depth gauges. I haveseen some designs made from 12mm MDF but would rather use say 10mm aluminium, I only intend using a 500Watt spindle, I will be cutting mainly model boat parts from up to 5mm ply and 25 thou brass and aluminium sheet.

You look ot be well prepared here. You have defined your usage well but I look at the size of the machine you are interested in and think that you need to keep an eye on robustness and stiffness. If I did my math right you are talking an almost 20" span on the gantry, and that is where it really starts to make sense to use box section construction. The material you build the machine from isn't a factor here as any material will benefit from box sections. If you are going to be doing metals to any great extent, I'd avoid products that are not water proof, this mostly due to the use of cutting fluids.

10mm sheet goods are just a bit over 3/8" stock and frankly that just strikes me as too thin for a 20" span of flat stock. If that 500mm is the working area you are after, the gantry beam will be even longer. Now if that 10mm plate was backed by an extrusion you might have something interesting for a gantry beam. Other areas of the machine may or may not be suitable for 10mm plate. I only focus on the gantry beam here because that often ends up being a DIY machines weak link. Your described machining needs is admittedly modest but it is easier to live with a little too much machine than something that isn't up to the task.