[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

[yukonho]

The best words of wisdom I can offer are these.
"Small is good"
I built my first machine, a moving gantry type with 14 X 36 X 3 travel. I am now almost finished my second machine that will have 11 X 22 X 3" travel.
I chose a moving table type for machine number two. That, combined with the smaller size and a bunch of reading and research is going to give me a very rigid and reasonably fast machine. These are the two biggest considerations I think that need to be dealt with. Rigidity and speed.
Using the Xylotex controller (which is a steal at $125 I would not consider anything else) and a cheap 24V 5A power supply I got off ebay for 20 bucks, my total electronics bill was under $250. Keeping your machine small allows you to use gas pipe and rollerblade bearings and still get good accuracy without a bunch of flexing. Again flex bad, rigid good.
There is no way I could have cut aluminum on my first machine without taking super light passes and taking forever. I did cut some delrin, but again, very slowly. I am sure that this machine will easily be able to cut aluminum, although I probably wont, cutting fluid and MDF dont mix so well.
I got a rotozip 5A for a song and cant wait to see how it performs, I am sure it will be leagues ahead of the Dremel I used on number 1.
Consider a moving table design, and think about cutting your Y travel in half. Moving table designs are inherently more rigid (there is that word again) and cutting that Y travel in half will help with the rigidity too.
You can see some pictures of my design here http://www.cnczone.com/forums/showth...2&pagenumber=7
And keep asking questions and reading these threads, it is the best way to get info to help you make your decision.
co

[arvidb]

Hector,

if you want to be able to cut aluminum, go for rigidity! Use supported rail (vee-type, THK, supported rod - buy at Ebay), build as small as you can stand, and go for a moving table setup. Also very important is to use backlash-free components - pay attention especially to the lead screw nuts AND the lead screw bearings (normal radial bearings have some axial play). The above advice comes from using a manual mill; I've seen and felt how quickly things deteriorate from just a small amount of flex or backlash.

Sanghera1 asked "How many oz/in would you need to cut alumminum and mild steel on a lathe or mill."
Now, what we are really interested in is how much force we need at the table. From this we can then calculate the required motor torque, taking into account the lead of the screws and any gearing. Unfortunately I cannot answer the force question - I have asked the same in several forums and nobody seems to be able to give guidelines here.

Arvid

[kanankeban]

Hi,

build as small as you can stand, and go for a moving table setup

By stand do you mean the gantry? or the print size of the table?
and what's the benefit of using a moving table design, don't I need more torque in the motors if doing so?
Regards...
Hector

[arvidb]

I meant build as small as you can live with.

A moving table design is more "parallel" than a moving gantry - in a moving gantry machine, the Z axis is mounted to the Y axis, which in turn is mounted to the X axis. With a moving table there's only two axes in series - the Y and Z for instance. This makes it easier to build a more rigid construction.

You *might* need more torque. Or less. What is heavier, the gantry including the router, Z axis motor, and Y and Z guides, or the table including the material you are cutting?

My guess is that the biggest demands on the motors will be not accelerating forces but cutting forces. Unless you want to build a very fast machine that needs to be able to do very fast acceleration - but this doesn't fit very well with an aluminum cutting machine of the size you had in mind. Better go for strength here.

Arvid

[balsaman]

It is not easy to cut aluminum with a home made wooden machine. It can be done, but most times it's not realistic unless you have high quality components all around. I don't think it can be done with gas pipe and bearings for rails, but I could be wrong.

Build small. Learn a lot. Smaller always means more rigid for similar components. Build first, buy electronics and motors last. Moving table is the most rigid solution, but takes more space.

Eric

[kanankeban]

It is not easy to cut aluminum with a home made wooden machine. It can be done, but most times it's not realistic unless you have high quality components all around. I don't think it can be done with gas pipe and bearings for rails, but I could be wrong.

Actually I'm not thinking in MDF, I want to use a welded steel frame for table and gantry. How difficult is to weld a precision frame with mig, I've done some arc, mig and tig welding, not a profesional but did It in a course a couple months ago...I have a paper (degree) that's says so but to be honest I just remember half but I'm sure I can weld, and weld good with mig...but I'm unsure of how difficult is to get really square and aligned structures for this aplication
Also thinking In THK rails if I can get a good ebay auction and win it, of course...
Regards...
Hector

[balsaman]

It is imposible to make a welded frame with any precision, however, it is not required either. You weld it up, then shim all the components (rails etc.) to get it assembled acurately.

Eric

[kanankeban]

Originally posted by balsaman
It is imposible to make a welded frame with any precision, however, it is not required either. You weld it up, then shim all the components (rails etc.) to get it assembled acurately.

Eric

Sorry...for my english but what do you mean by "shim all components"?
Regards...
Hector