better, bigger cnc router?

[jimmyaz]

Hey guys,

I currently have a home build cnc router (12x15in) cutting area. Using 180oz nema motor and unbiopolar. It running ok, but quite slow and take a lot of time to cut stuff. So I was thinking to build a new and better machine, higher resolution so I can cut more tolerance stuff.


I was thinking to go all ball screw and higher torqe and bigger motor. I was wondering what determine the speed of the motor, how fast it can move. currently my machine take for ever to jog arround, I want something that can jog and cut with a little better speed.

I'm planning something like 24x36 cutting area... what kind of stepper motor do you guy suggest? Direct drive is good? or do I have to gear? what's the benifit of using gear on stepper motor?


Another question, is metal/alum a much more better way to go? MDF build can't be as good? I was wondering where can I buy the aluminum materials and how to cut it?

thanks all,

Jimmy

[dertsap]

you can probably get it from a local scrapper , also you could cut the aluminum on a mitre saw or a table saw with carb tip blades , i use both on a regular basis , while many may disagree with the use of a table saw it does work well and is as safe as the guy using it , biggest thing is to use eye protection , i'm not a huge fan of eye glasses but it's a must have thing ,there are lots of chips and they can get pretty hot

have you concidered steel tubing , it would be a much more economical way to go , and you can get a 110v stick welder dirt cheap if you haven t got one already

[jimmyaz]

No other reply???

Is 1/2in per one rotation is to much for a leadscrew? would the resolution of the movement drop because of this?

[dertsap]

depends upon the drivers as to how much microstepping they will do
my screws are 2"/rev , which gives me a resolution of .001"/step @ up to 1000 ipm on the x and 1400 ipm on the y , i keep them both set at 500 ipm for full torque and to avoid any lost step due to momentum,and it runs smooth
some guys aim for .0001/rev but personally i see it as pointless ,on a diy your going to need high end hardware to uphold dimensions withing tenths and within a few thou is plenty if your cutting wood , on most metal part drawing the general tolerance is .005

take a look at the specs of the professional machines

[jimmyaz]

Hey, thanks for all the reply dertsap.

What about this driver, is this good?

http://cgi.ebay.com/3-AXIS-CNC-ROUTE...QQcmdZViewItem

Thanks

[dertsap]

i would entertain the idea of ebay drives , gecko's are the best for what we need and they are a solid company if you need help or have trouble , they are a little more pricey than other drives but are by far worth it , if they aren t in your budget range then look at this thread from the guy who builds the geckos , he's developing a cheap high quality driver which may be worth waiting for
http://www.cnczone.com/forums/showthread.php?t=51083

[jimmyaz]

Thanks.

BTW, I bought a new lead screw planning to use for a X axis for the new bigger machine. It's 1/2 inche per rotation, I just hook it up to my X axis stepper just to see how it can move. Unfortunately, it's isn't any faster then my old lead screw I got from hardware on the old machine which is 125mm. I do believe my driver is doing full step.

Now I do unstand how fast it move will all depend on the lead screw you got. Is this why people use geared system pulley and belt? So let say they have a fine lead screw and you can gear it up? Or I got this all mix up?


I am currently looking at this for my Y axis, this would awsome be slow if I hook it directly to the stepper motor right? Anoter question is, if my X set up is slow and my Y set up can move fast, then that would slow my machine down anyway correct? because it will pick the slowest axis as primary?

Danaher Motion Precision Plus Ground Ball Lead Screw Assembly
Model #1/2-100 BSJ
Double Circulating Ball Joint - ACME Lead Screw #2
Ball Screw Thread Type
Preloaded, Round Ball Nut with Integral Flange
Major Diameter: 1 1/2"
Minor Diameter: 1 5/16"
Ball Full Radius
Pitch: Count = 5, Pitch = 1 in/5 = .200 in.
Length: 60"
Right Hand
Carbon Steel
Dynamic / Design Load - 4250 lbs.
Max Static Load - 27.250 lbs.
Preload Force - 750 lbs.

[dertsap]

Originally Posted by jimmyaz Thanks. Is this why people use geared system pulley and belt? So let say they have a fine lead screw and you can gear it up? Or I got this all mix up?

thats a serious dia screw , i don t think flex will be an issue
generally most people gear down to get a higher resolution ,and or more torque ,
i would imaging you will be needing larger motors in order to turn those screws , if you bought 600oz + then you'd be rockin ,i'm setup with 770 oz motors on the x and y and wouldn t use anything less for my system ,
the problem you end up facing running larger motors is the fact the cheaper drivers won t run them
i do beleave the nema23 450oz motors from keliginc can be run with low amp drivers and they are relatively cheap , i understand guys are having pretty good success with them

[jimmyaz]

Hey... back for your help again.


I think I will wait on the motor and driver after I finish the machine I will get them. I will probably will go with that 450 0z Nema.


I don't think I want to go with ball screw, they are so expensive, so I will go with a lead screw. It's 3/4 OD and 5 turn per 1 inche. Do you think this is decent? how many IPM do you think I can cut with that 450oz with that lead screw?

My current machine is only doing like 16ipm max... and I feel like it really slow. So do you think there will be a big different with this new set up?

Thanks

[dertsap]

there will be a huge difference in speed ,ive used the 3/4-6 on my first setup and it worked very well ,
if you look up joe's machines you will see he uses the hobbycnc board and those 450oz motors are pushing those machines around 150 - 200 ipm with a 1/2-10 acme

[jimmyaz]

Thanks Dert

Check out my build log on my new machine.

http://cnczone.com/forums/showthread.php?t=52759