More begineer questions

[blfuller123]

I have been reading around the site for a few months and have finally started gathering parts for my first cnc router. I just bought all of my rails and here is what I have so far. The x axis rails are 49 inches, the y axis rails are 41 inches and the z axiz rails are going to be 18 inches. I am looking around at lead screws and dont really know what to go with. The y and z axis's are going to be made out of aluminium. I am trying to get the largest cutting area possible with these rails. I plan on using this on acrylic and wood for the most part and will be using a porter cable router motor.

I guess the first question is can I get away with one lead screw on the x axis? If so, can I put it on one side of the rails, or does it need to be in the center (under the cutting area)? I ask because I am worried about the weight of the y n z axis with the router motor.

The second question I have is what size and what pitch should the lead screws be on all of the axis?

Third question, do I really need ball screws or can I get away with using just a leadscrew with derlin nuts?

I am sure I will have many more questions as I get more done but this is it for now. Any suggestion are greatly appreciated. Thanks!

-Brett

[ger21]

First question depend on how rigid your machine is.

Second question depends on how fast you want to go and what size and type of motors you'll be using. And maybe also how much resolution do you need?

Third question. The majority of routers you see here use acme with delrin nuts. Ballscrews are more efficient, but also more expensive.

[blfuller123]

Thanks for the response. The frame of the machine will be made of steel tubing that is welded toether. I plan on using 2x4 tubing that is 1/4 inch wall. As far as motors, I havent bought them yet. I was wanting to get the mechanical part built first so I might have a better idea of what motors to get. As far as speed, I dont need anything really fast so looking for suggestions?

[blfuller123]

Any other opinions?

[epineh]

Best advice I can give is to check out machines similiar to what you had in mind, go through their build logs and see what problems they had.

You are generally better to have the leadscrew in the middle, to eliminate "racking" effect

Pitch really depends on you, finer pitch will mean you can use smaller motors/drivers but will cost you in slower speeds.

I would go acme or similiar first, you can always upgrade to ballscrews later, you may find you get addicted to this stuff (like the rest of us ) and decide to build a completely new and bigger better version.

Have fun!

Russell.

[ger21]

The type of linear bearings you use and how they are mounted also comes into play here in regards to stiffness. If the bearings are too close together (per side) then you may still get some flexing, or even binding.

Everyone says they don't need to go fast, but waiting a minute or more for your router to move from one end to the other gets old fast.

There are several online motor sizing sites.

http://www.orientalmotor.com/support..._recommend.htm
http://www.danahermotion.com/design_..._selection.php

[ViperTX]

Center mounted ACME or ballscrew is always the best way to go.

[Greolt]

Allways????

[ger21]

I's say only if the machine is rigid enough that absolutely no racking can occur. Otherwise, I'd go with 2 screws.

[blfuller123]

I think I will use 2 screws, how are the motors configured? Can you run the motors in parralle or how does that work?

[project5k]

if your using mach 3, you will need the second motor, the driver for it, and to set in mach 3 to "slave" the second motor to your x axis... then they will turn the exact same # of steps each time... you will have to make sure that the 2 parallel screws are of the same specs...

[blfuller123]

That answeres my question. I do plan on using Mach3. Thanks for the info.