Beginner design advice for small 24" x 24" machine

[CanadianMan]

Hello. I am very new to the CNC world and am in the process of designing a CNC Machine for myself.
I have been going through a design process and have changed my mind many times but, finally I think I am on the
right track.I apologize if my terminology is incorrect, I will do my best to use accurate terms.

My design plan so far is as follows:

- CNC Router (Will not be using a dremel) Preferrably varialble speed spindle
- Materials I will use are plywoods, Hardwoods, Plastic, Plexiglass and aluminum (Unsure of thicknesses at this point)
- 24 inch x 24inch working area
- Aluminum tubing and aluminum frame construction
- Linear rail and gantry (I think that's the term. Bed is stationary and the spindle is moving)
- 16mm hardened rod for rails
- Linear slide bushings 16mm
- 16mm ballscrew for X, Y - 30" long (Will most likely make my full X, Y dimensions extend to 30" x 30")
- 16mm ballscrew for Z - 9.6" long
- NMEA 23 Stepper motors for X, Y and Z axis
- Arduino control of the system through uploaded G-Code and Inkscape
- System operates of of 120VAC 15A circuit

I have stopped at this point because it seems a bit overkill for my situation. I have not done any torque
calculations to know whether this is too much or not enough. My policy is always "more is better". I do have budget to consider however.

I also need to figure out my current specs for the motors which will depend on the gantry and weight of moving components and
spindle resistances.

My questions are, is this overkill? Am I on the right track?

Thanks in advance for any responses.

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[wizard]

Doesn’t look too bad at all!

When you say materials you will use is that to build the machine or are these materials you will machine? This is an important question because a move to machining aluminum in my opinion requires a step up in machine stiffness amongst other issues. One of those other issues is the need to use coolant/lube to machine metals in any quantity.

As for the question of overkill unfortunately you left out very important considerations. The size of the aluminum tubing is critical to making a machine stiff enough to machine aluminum to a meaningful degree. That may also apply to successful machining of some of those other materials. I’d go so far as to say you have things a bit backwards here. That is you should do the mechanical design of the frame before even worrying about the motion control components. Also unless you luck out aluminum is pretty expensive for machine frames especially for the gantry beam. The better the results you want to achieve in aluminum the more you should consider steel in critical areas. Understanding the results you want to get is very important in choosing build materials and the path you take.

As for that build path there are two types of common CNC routers, one being moving gantry designs and the other moving table. Your machine right now is small enough that a moving table design is feasible. Moving tables have so one advantages in stiffness and ease of build, they however often take up too much space in the larger table sizes. In any event this comes back to mechanical design of the machine structure first. You want to nail the mechanical form factor so that you know how much mass you will be moving around, clearances and such. This may require many iterations to fit everything together in a robust manner.

As for things like lead screws 16mm might work fine at this size but 20 mm wouldn’t hurt. If you want to get more specific reference design specs that the manufactures have on their web sites. You will find sizing information for the various shaft fixations possible.

[pippin88]

Sounds like unsupported round rails? Bad idea.

[routalot]

Sounds like unsupported round rails? Bad idea.

Agreed. Supported hardened rod should be a much better idea. As for the structure of the machine,any material within reason can be made to work if the engineering behind it is sound.Think rigidity and triangulate to achieve it.

[CanadianMan]

Thanks for you replies. I do have supported rods in my plan. I was more concerned that I was going bigger than necessary for my parts.

For the materials that I wanted to cut, I threw aluminum in there as a nice to have mostly. Cutting more than 1/8" thickness was not my plan if I were to use aluminum at all. I did however not consider any sort of cooling for cutting aluminum. So I'm probably just going to stick to softwoods, hardwoods, plastic, MDF, and plywoods.

As for designing the supports and framing first, I agree that is the approach that I should take. I want to stick to a moving gantry design because if this build goes well, I'd like to use the experience to make something with more capability that works along the same design type, (ie laser cutter or larger machine).

I'm still digging into accuracies for cutting. The supplier that I am using only seems to carry C7 nuts for the ball screws. I'm hoping that that will be sufficient for my needs. But again, I'm still learning. Checking out other manufacturer specs is a great idea that I will definitely do for this process.

[ger21]

Thanks for you replies. I do have supported rods in my plan. I was more concerned that I was going bigger than necessary for my parts.

If anything, I would say you could go bigger. Everyone wishes their machines were more rigid, and more powerful.



Almost everyone uses C7 screws, unless you want to pay 5x more. But unless you can build the entire machine to a higher accuracy than the C7 screws, better screws don't really gain anything.

[wizard]

If a laser cutter is in your future I would think seriously about an entirely different design. The reason is the rigidity of a router isn’t needed. Depending upon the laser chosen you can do well with a very light machine. Also to be eye safe a laser needs to be totally enclosed thus you have a bias against size due to the enclosure.

Don’t forget that once your router is up and running making parts for a new build is easy. In the case of a laser that means being able to innovate and be more creative with your laser design. So I wouldn’t let the design of today’s machine box you in when it comes to future builds that are dramatically different. Simply having a CNC router expands your build capabilities.