[viroy]

Hello,
I have been slowly gathering parts for my first CNC build and need a little help determining a good lead-screw & motors for my needs.

I already have rails, bearings & complete Z-axis, frame will be made entirely of 8020 t-slot. X rails = 4' & Y rails = 2', max travel has not been determined yet but I am not too worried about having as much as i can get... my parts to be cnc'd will be small. applications are PCB & small aluminum cases, need to be as precise as possible, the aluminum cases will hold optics and have very small tolerances.

I have gone through alot of threads and am not too much clearer on determining a proper motor & lead-screw combo. I am not pinching pennies, so I would rather spend a little extra to do it right the first time.

Can someone recommend a good ball-screw & backlash nut with proper pitch, & a set of motors to match?
I dont mind reading and learning myself, but everything I have come across is specific to the authors needs... which primarily seems to be wood, and of course different lengths.

Any help is greatly appreciated
p.s. - I do have a nook catalog but its mostly greek to me :/

[viroy]

My design is near identical to this one, however I have decided to put the X rails below the table.
That means the X axis lead-screw, and the X axis rails will be on the same plane.

[frequent flyer]

Have you looked at www.pdjinc.com ?

[ger21]

How fast do you want to cut and rapid at? And what are the tolerances you're looking to hold?

[viroy]

wow thanks for the fast reply's!

I'm not really clear as to those ger... i dont know how to translate the cut/rapid to an actual work time.
I have seen other PCB makers go for with tolerences of .01 i believe?
that will also suit my aluminum case needs.
Im more concerned with accuracy than speed, however i also dont want to wait 24 hours for a 3" square box to be completed

[ger21]

.01", or mm? if inches, anything will do that. Most people building Joe's 4x4 machines are using 1/2-10 5 start acme, and DumpsterCNC AB nuts. much cheaper than Ballscrews, and will still give good performance. As for motors, it really depends on how much you want to spend, and how much force you need. A keling G540 package will work.
http://www.kelinginc.net/CNCNEMA23G540Package.html

If you want more speed and power, I'd go with Nema 34 motors and Gecko G203V's. 400-600 oz motors, rated around 6 amp will get you the highest speeds.

[viroy]

That's one thing in not sure on is how much force it sill take to cut soft aluminum... I know pcb's take near nothing.
I looked at the G540, but looks like it will come with 2 more motors than i need since i already have a Z axis completed. Maybe im understanding it wrong but it says 4-axis, so im assuming 4 motors?

any location i can read more about those leas screws?
Thank you for your help

also, i took a look on my micrometer and .005 or less would be preferred

[CarveOne]

That's one thing in not sure on is how much force it sill take to cut soft aluminum... I know pcb's take near nothing.
I looked at the G540, but looks like it will come with 2 more motors than i need since i already have a Z axis completed. Maybe im understanding it wrong but it says 4-axis, so im assuming 4 motors?

any location i can read more about those leas screws?
Thank you for your help

also, i took a look on my micrometer and .005 or less would be preferred

The G540 has four individual stepper motor driver boards in one assembly. It can drive up to four motors, but you can just use three and not use the fourth driver, or use the fourth driver on a dual motor X axis machine. You can also use the fourth driver for a rotary axis if you wish to. It has lots of possibilities.

If you buy it from Gecko Drives it comes with no motors. They only sell the driver modules. If you buy it from another source that sells the G540 you have the option to buy a 3 or four motor bundle.

Home switches allow the software to run the motors to a known position that is detected when the three switches open as the motors reach that predetermined position. Home switches can be set up in software as home and limit switches in combination. Limit switches tell the software to stop the motors before running into the end of mechanical travel and potentially causing damage.

There are software limits also, and are set to define a "box" that will define how far the motors can go. This can be the only limits, or it can be used in addition to the limit switches as two levels of avoiding damage.

CarveOne

[Ayjay]

I just ordered the G540 directly from http://www.geckodrive.com/for $210.00 (They are currently having their customer appreciation sale). You could order 2 motors from http://kelinginc.net/ for $39 or $49 each which would give you a very nice package for about $300. The G540 also includes connections for limit switches as well as outputs for relays.

Incidently, I received my G540 (in Canada) about 26 hours after I placed the order. I was impressed!!!

Ayjay

[revwarguy]

You won't go wrong with the g540's. I am very impressed with them and the company service. You can see my build log for more about the 540's at www.liming.org/cnc

I just wish they were that cheap when I bought them!

[viroy]

ooh ger, I just read a post from you in another thread about making sure to have 'home' switches. I realized i completely forgot about that, are those supposed to connect to the drivers? or are they just an emergency crash switch that cuts motor power?
I am using the allegro bi-polar chopper from pminmo.com
http://pminmo.com/ss3977/ss3977.htm

[ger21]

You already have the drives for all the axis?

[viroy]

hmm 5/8 is just over 1/2"... maybe I should go thicker to 1"? ...something like 3/4-?-5, or 1"-?-6. Are all lead screws perfectly balanced for rotational force?
I dont understand how to determine the amount of threads per inch I should go with.

I happen to read that polished stainless last much longer than coated, due to the coating material flaking off over time?

In these forums I read about a very neat way to avoid racking with a "moving knot".
Seems very practical and quite easy... would this be recommended for me since I will be using a single, centered X-axis lead screw?

Sorry for all the noob Q's
I really appreciate the help

[jsheerin]

If the x is 4' and the y is only 2', you might not have too many problems with racking. Leave room for the cable setup in case you need it, but I'd try without first.

I have a 48" long axis with a 1/2-10 5 start screw that works fine. I run it up to 200ipm, but it could probably go a bit faster - 300ipm max. Above that the screw whips. So if that's fast enough for you, I wouldn't get a bigger screw. If you want to go faster, check out the critical speed charts that Nook has on their site to get an idea how fast you can spin a screw before it whips (called the critical speed).

Picking a lead screw depends on how fast you want to go, what resolution you want, how much force you want, and what motors you have. Here's a thread with some helpful links for figuring this stuff out - especially the cnc mechanics pdf.

[viroy]

Cool i didnt know that (critical speed)... helps alot.
Can you post that link? It didnt go on the last post

[viroy]

I dont know how 200ipm will look while cutting, but I will be doing very tiny grooves for optic mounting... and I'll only be needing a few at a time so im not planning to run this full time mass production.

I found this for nooks critical speed chart... i though it would be easier to read as I cannot find anything comprehendable. looks like "INCH SRT, XPR AND SGT CRITICAL SPEED" is the relevant chart... but what do the numbers on the right side denote? are those product num's?
http://www.nookindustries.com/ball/ballcharts.cfm

[viroy]

Ok I happen to have a nook catalog that I ordered last year...
I looked through and found something that appeals, maybe someone can help confirm?

Lead Screw
Pg# 105
Pn# GT06320R48
Lead accuracy - .0005"
Ball circle dia - .631"
Lead - .200"
Root dia - .5"
Nom ball diameter - .125"

Ball Nut - Preloaded flanged internal return ball nut with wipers
PG# 105
SSN10304

Mount - Double Universal
PG# 210
PN# - EZM-3012

[viroy]

for motors I was thinking from http://kelinginc.net/:
4A: NEMA 34 HIGH TORQUE STEPPER MOTOR 640 oz-in, Shaft with a flat, 80 mm
KL34H280-60-4A (Single Shaft) Specification Price: $89 Rated Current: 6A, Rated Voltage: 2.4V

Is that strong enough or should i go for the:
3B: NEMA 34 HIGH TORQUE STEPPER MOTOR 906 oz-in, ½” shaft with a flat, 95 mm, , Water, Dust proof
KL34H295-61-4A (Single Shaft) Specification Price: $125 Rated Current: 6.1A, Rated Voltage: 2.1V

[jsheerin]

Those are the screw sizes, I think. You'd have to look up their product codes for that line to see what sizes they are. Here's acme screw info that's easier to read:
http://www.nookindustries.com/Acme/AcmeCharts.cfm

Previous link: http://www.cnczone.com/forums/showthread.php?t=33412

[ger21]

If you use those ballscrews with a 5mm pitch, a smaller motor will usually offer better performance, as they have higher torque at higher speeds.