Need some advice on DIY 24"x24" CNC Router Table...

[kanankeban]

Hi,
I don't want to spend the big bucks on something that's really new for me...I think that for now and for learning before the big one...I should start with something more reasonable.
I'm thinking in a 24"x24" capable Router Table...I don't want a toy, but something more stable a ruged...I plan to use a rotozip or a 1.5hp router...So my bigggest doubts.. (Thinking in staying in a low budget).
1. What capacity of steppers to use, how many oz/in? for x and y, and z? (I intend to cut maybe 3/4" ply, of course in several passes and slow )
2. What driver kit is reccomended? Xylotex, FET ???
3. What type of linear devices to use? linear slides or bearings? and what size of, rods, slides or bearings?
This is one of my first posts...so go easy , asume that I'm a complete ignorant in this matter.... :P
Regards...
Hector

[DDM]

Well you've got a lot of choices ahead of you. Read through the treads on the forum and you'll get a lot of great ideas. Here's my two cents

1. Stay with steppers above 100 oz/in. You can pick 116 oz/in ones up pretty cheap and they will do the job for a time but if you can get more power do it. I'd also prefer to use bipolar motors.

2. For the driver I would suggest the xylotex, one because it's a bipolar chopper drive and that there are a lot of people using them so support would be good. You could go with geckos if you got some rather large stepper motors but they are spendy.

3. Linear bearings are costly if you go with THK's but they are super precise and super strong. On the other end is gass pipe and roller skake bearings. Look through the treads for ideas on what you want your machine to be.

You've also got several different choices for the power transmission, from (preloaded ballscrew to ready rod) for a first machine I would use acme rod with two nuts preloaded or offset to reduce the backlash. I think I've said enough to get the gears turning inside your head.

[kanankeban]

DDM,
Thanks for your info, but could you be so kind to explain to me some further details

1. Stay with steppers above 100 oz/in. You can pick 116 oz/in ones up pretty cheap and they will do the job for a time but if you can get more power do it. I'd also prefer to use bipolar motors.

Why bipolar, whats the main difference between unipolar and bipolar, and if chossing bipolar what benefits do I get?

2. For the driver I would suggest the xylotex, one because it's a bipolar chopper drive and that there are a lot of people using them so support would be good. You could go with geckos if you got some rather large stepper motors but they are spendy.

what's the deinition of "chopper" I've read that there are some drivers that are not choppers and other that are...an the choppers are the ones preffered...

3. Linear bearings are costly if you go with THK's but they are super precise and super strong. On the other end is gass pipe and roller skake bearings. Look through the treads for ideas on what you want your machine to be.

ç

Dou you have a rough idea of the precision you can get with gass pipe and roller skate bearings? Of course if you do a good job

You've also got several different choices for the power transmission, from (preloaded ballscrew to ready rod) for a first machine I would use acme rod with two nuts preloaded or offset to reduce the backlash. I think I've said enough to get the gears turning inside your head.

what's acme rod, is it a regular rod with nuts yo can get from home depot or is a special rod? what kind of thread does it have? and what's backlash, I've read this word all the forum around and I don't know what it means...and I can sense that is something pretty important to consider...

Regards...
Hector

[arvidb]

Hector,

What do you want to cut?

The "precision" of the guides is only one thing to consider. Two other equally important properties are deflection and backlash.

People may not agree, but in this context I define

* precision: as irregularities in the guides, for instance the surface of gas pipe may not be completely flat or the pipe may not be straight.

* deflection: if you push hard on your gas pipe, it will act as a spring and "give in" (deflect) somewhat, and return when you stop pushing. If you're cutting things like aluminum, use supported guides to reduce deflection to practically zero.

* backlash: play between different parts of your guides.


acme is a special form of thread, designed for moving a nut instead of locking a nut (as ordinary M-thread or all-thread). It is not as "triangular" as all-thread, but more square (trapezoidal I think).


Backlash is play between and in components - for instance between nut and rod and axial play in ball bearings. Backlash is bad for repeatability and precision, and backlash and deflection is bad if you are cutting harder materials since it will lead to vibrations that will quickly wear things out and cause ugly cuts.

Arvid

[balsaman]

backlash is "play" or "slop" between the moving part and it's drive screw. Usually found between the nut and the lead screw. Some people buy or make antibacklash nuts to try and eliminate it. Backlash results in inacurately cut parts.

Don't go with too large a stepper motor becaue the xylotex is only good for 2.5 amps. For small, simple machines 60-114 oz/in works.

Eric

[kanankeban]

Thanks..guys
great explanation... 100% understood. Could you explain me whats's a "antibacklash nut", well thanks to the great explanations now I know that is a nut to try to elimiate backlash, but the question is how it works and the mechanics involved in its functionality?
Regards...
Hector

[arvidb]

An anti-backlash nut is basically two nuts that are spring loaded - thread on one nut, then add a spring and then thread on the other nut so the spring is caught between the nuts. Then make sure the nuts cannot rotate in relation to each other. This way the nuts are pressed apart and any slop is absorbed by the spring.

You often hear the term "preloaded" nut for this. The same principle can be used for all backlash elimination.

Arvid

[Cold Fusion]

Here is an example of a preloaded nut.

[Sanghera1]

This thread is helping me understand some things better too. Great thread. I have a question aswell :
How many oz/in would you need to cut alumminum and mild steel on a lathe or mill. Would 200 oz/in do it?
Thanks.

[DDM]

200 oz/in would probably be more than enough for your purpose. You could probably get by with 100 oz/in steppers but you wouldn't be able to run at the speeds that you could with the 200 oz/in. Plus with the higher oz/in you could cut deeper and not have as much of a possibility of missed steps. Steppers have great torque at low RPM but they loose it when they get to higher RPMs. If you can find out where you want your maximum cut speed and where the most usable RPM of the steppers is then you can determine what rod/gearing/rack and pinion you would like to have to get those cut speeds. Have I confused you yet? Some of the other members on here would probably be better to tell you all of the in's and out's of gearing and speed but thats the lowdown.

Carl

[cnczane]

You wrote:
I don't want to spend the big bucks on something that's really new for me...I think that for now and for learning before the big one...I should start with something more reasonable.
I'm thinking in a 24"x24" capable Router Table...I don't want a toy, but something more stable a ruged...I plan to

That's what ~I~ thought too. (: I've got between 800 and 900 bucks in a 30x30x9 (24x24x6 cut). Moving gantry type of gas pipe and MDF and scrounged aluminum bits here and there. Bought kit controllers from embeddedtronics. For me the big tickets seem to have been used 150 oz-in motors and a used 24V 50A supply both of which I could have got cheaper if I had only listened to myself. I still want to get a real spindle for this thing too.

You'll probably do the same but if you CAN manage to hold off on the urge to pile up all the electrical stuff until your machine is at least HALF built, you should be able to find what you need easily on ebay.
--
Dan

[kanankeban]

What do you want to cut?

That's a good question...Well my idea is to cut maybe aluminum for the next cnc router . I think if I get the cheap one made I can get two main ingredients for the next one...a 4x8 ft. table...
1. Is experience
2. a 24x24 table where I can cut and mill aluminum to construct the big project
Is this a reasonable thought?
Regards...
Hector