Need some startup advices...

[b_cybe]

Has started planning to build my first CNC router, I plan to use it for woodworking and (hopefully) milling aluminium.
Since I intend to use it to mill aluminium I decided to build the machine with aluminium since this is both strong and not to hard to work with. After some reading on the forum I also desided I would go for a gantry style cnc. When I started planning I decided to build a machine that was 1000mmX500mmX100mm. But I already have changed the Z-axis to 88mm since I bought a ballscrew with that travel length, I have also bought some linear glides for the Z and Y axis. The Z axis ballscrew is 6mm diameter (the load on the Z ballscrew is going to be vertically so I dont think it matters that that the diameter only is 6mm) and has a lead like 1mm/turn. The reason I chose that slow Z ballscrew was because I thought that this would increase the accuracy for the Z axis, wich for me is more important than speed, and since the Z axis dont travel so long I think it will be fine. Anyways are now looking for Y axis ballscrew that need to be around 470mm (the length of the linear glides) and I am therefore looking for a ballscrew with around 16mm diameter and 5mm/turn. I am planning to use mach3 since I have heard with that program I can compensate for different leads on the ballscrews. I am planning to build a 3 axis L297/L298 bipolar driver for the stepper (probably will build : http://www.hans-w.com/9908-09A.gif). But I am unsure if Mach3 will suport that type of driver? I am further probably going to buy 3 of these stepper motors wich are running on 4.05V and is using 1.5A. Would these motors work alright?
I will probably make some sketch of my design that I will build after once I find and buy the ballscrews and linear slidings I need...

[b_cybe]

Well I think the final size for my CNC machine will be 660,4mmX470mmX88mm (or 66"X18,5"X3,47" aproximately for those you prefer inch...). I am planning to buy a 16mm diameter ballscrew that is 660mm long, but I dont know the movement/turn, I am therefore wondering if I can calculate this by using for example a caliper and measure the length of movement for one turn (or several turn and then divide by the total turns to get the number for one). Will this be accurate enough or will this decrease the accuracy detectable?
Any other start advices also receives with thanks!

(Sorry for my bit bad english...)

Edit: With the size I mean the total movement in the x, y and the Z axis...

[ger21]

Originally Posted by b_cybe I dont know the movement/turn, I am therefore wondering if I can calculate this by using for example a caliper and measure the length of movement for one turn (or several turn and then divide by the total turns to get the number for one). Will this be accurate enough or will this decrease the accuracy detectable?

This will get you close enough to set up the machine, then you can cut some parts, measure them and fine tune it until it's perfect.

[b_cybe]

Ok, dont know how to measure it from the finished part, but I guess that will be solved(either I find it out myself or get some help on teh forum...) after the building is complete. I am a bit unsure of the motors I have choosen to, since they are driven by such low voltage, I see that many others use motors that are driven from higher voltages, should I buy motors with higher voltage too? I dont personally know too much of motors, but I guess the speed atleast will increase with higer voltages, is the holding torque also larger for motors with higer voltages?
How high holding torque should my stepper motors have to be strong enough to mill aluminium? (Well if that is possible with these kind of machines...).

I am also a bit unsure what driver I should use, I have already linked to one in my first post, and I have also seen a bit on this site.
Or are those commercialy available like gecko much better?

[bearwen]

b_cybe,
I am unsure about motor size and what not for milling aluminum. However the higher voltage that you hear about for the motors are motors such as yours rated for 4v however by running them at there rated current but much higher voltage ( dont exceed 20 times the rated voltage good practice) your torque curves change meaning you can spin them faster before the torque drops off.
Pminmo site is great I like the picstep but there not cheap (cheaper than gecko) try the 3977 boards they cost about $30.00 a piece to build. The 3977 chip you will have to search the net for a supplier that will allow you to purchase just a few of them.
Checkout these motors I purchased the nema 23 262oz/in dual shaftshttp://www.homeshopcnc.com/page3.html They also build ballscrews but I used Acme 1/2-10 from http://www.use-enco.com pretty good price.


Good luck

[b_cybe]

Thanks for the reply, I think I try out the motor I originally planned, I get those cheaper than other since I receive "friend-discount" since I know the seller, very practical when buying electronics
Well I think I have a look at that picstep... thinking of implementing it with the 4 axis PC interface, don't think I will get the 4th axis yet, but are interested in implementing it afterwards...

[Oldmanandhistoy]

Originally Posted by b_cybe Thanks for the reply, I think I try out the motor I originally planned, I get those cheaper than other since I receive "friend-discount" since I know the seller, very practical when buying electronics Well I think I have a look at that picstep... thinking of implementing it with the 4 axis PC interface, don't think I will get the 4th axis yet, but are interested in implementing it afterwards...

Hi

The stepper motors you mentioned in your first post are only 139 oz in.

They might be ok for your Z axis with a small pitch but try to get more advice before you buy them as they may not be enough for your X and Y axis.

They might be cheap for you to buy but could get expensive if you can’t use them and they sit on a shelf.

Not sure about what you mean with the voltage rating. Are you thinking that if you buy stepper motors with say a 24v plate rating they will run faster?

Low voltage plate rating would be a good thing, so the 4.05v rating of the stepper you have been looking at is about right.

To get more speed out of your stepper motors you can run them up to 20 to 25 x their voltage rating so the 4.05V stepper could be powered by up to about 80v.

The max volts you can use would depend on the driver you use and their max volt rating.

Hope this helps, John

[b_cybe]

Learning more and more Reading as much as I can about stepper motors...
And I just understood that TPI propably stand for Travel Per Inch . And from that I got that my X axis ballscrew that is 26" long has 5 TPI or 5.08mm/turn.

I have found some unipolar NEMA 23 stepper motors on ebay that have a holding torque of 200 oz./in unipolar operation or 283 oz./in in bipolar operation. Would this be enough? The motor runs at 3V and uses 3A. From post on teh forum that I have read it seems that people starts off with motors wich hace atleast 200 oz./inch. But now are aluminium a bit more heavy than wood that many uses to build their machines...

[Oldmanandhistoy]

The power you need from your stepper motors depend on a number of things like.

Weight of your gantry

Size of your screws, the larger the diameter the more power needed to turn it.
Also the number of turns per inch, more T.P.I. less power needed.

The 283 oz inch stepper will probably be ok but do lots more reading before you buy anything.

Think about how fast you want to cut and what you will be cutting.

If you can not find the information you need, post a question in the right category on this forum.

Have a good look on the cnc wood router project logs.

Look for machine similar to what you want and ask the builder questions about their choices for parts.

John.

[b_cybe]

Thanks for the help, yes I will read more I buy any motor... I found this with that attached pdf file... that was very informative... think I will finnish those calculations before I do anything...

[b_cybe]

I am a bit confused about those motors... is there a way to calculate how much torque I need per axis? I tried posting a question about wich motor to chose under the sticky thread "What stepper motor should I use" but havent got any replies.
I am also considering using steel for the mainframe since it is cheaper and more sturdy (but can also rust...), but use aluminium for all the moving parts...

I really woud like some help with those motors though... I have tried to read around the forum, but I cant seem to find what I am looking for. I see those cnc made from wood use around 200 oz. in., but since my is gonna be made of aluminium it is going to be heavier...

[Oldmanandhistoy]

Hi again

Have you had a good look in the “cnc router projects log” section?

Unfortunately I am only a cnc beginner myself so can not give you the best advice. Hopefully some one more qualified will jump in and give you the help you need.

Best of luck , John