[Georgie]

Ok, I now bought 3 nema23 300 oz/in dual shaft servo's. To run them for the momemt I have bought a Delagrange stepper controller. This controller will drive 4 axis at 10 amps per axis so that should be fine.

I would appreciate some help on the ball screws for all 3 axis. There is so much information that things begine to get unclear.

My mill is the Eagle 25/ much like the RF25. It's screws are imperial/inches.

What advice can anyone give for ball screws. Cost & where to buy/simple to install and easy to work with are probably the 3 main things that come to mind in that order.

Any help would be very much appreciated.


Encoders would be my final addition so a good source would be welcome.

Happy Christmas to all....

George

[Runner4404spd]

Hey george,

i am going to use a 5/8 ball screw. i got mine from Mcmaster Carr, but there are other places. you'll find most people use the same one since its cheaper than the rest. i will have no drawings available on my setup, unfortunately. even if i did i find there is enough variation to make my parts incompatible. when i get through with parts though i will be more than happy to post some pics. so far i have completed the electronics. i plan on using the rest of this week to do the hardware.

[Neil_J]

Hey george,

i am going to use a 5/8 ball screw. i got mine from Mcmaster Carr, but there are other places. you'll find most people use the same one since its cheaper than the rest. i will have no drawings available on my setup, unfortunately. even if i did i find there is enough variation to make my parts incompatible. when i get through with parts though i will be more than happy to post some pics. so far i have completed the electronics. i plan on using the rest of this week to do the hardware.

Runner4404spd, I have looked at the McMaster ballscrews a few times, but the 0.004" per foot accuracy scares me. Is that including backlash or just how much the nut will be off at 12 inches? If they are in face zero backlash I might have to pick up a set.

[Runner4404spd]

you should be able to take up the .004 accuracy with tuning and anti backlash ball nuts. like i said i haven't installed mine yet but hope to by the end of the week.

[Neil_J]

you should be able to take up the .004 accuracy with tuning and anti backlash ball nuts. like i said i haven't installed mine yet but hope to by the end of the week.

Are the ones on McMaster anti-backlash type? If not, are there any other sources for them?

[Georgie]

Hey george,

i am going to use a 5/8 ball screw. i got mine from Mcmaster Carr, but there are other places. you'll find most people use the same one since its cheaper than the rest. i will have no drawings available on my setup, unfortunately. even if i did i find there is enough variation to make my parts incompatible. when i get through with parts though i will be more than happy to post some pics. so far i have completed the electronics. i plan on using the rest of this week to do the hardware.

Many thanks Runner, I appreciate your response.
What size steppers are you planning on using ?

[Runner4404spd]

if you search around you can find ways to make the ball nuts "anti backlash" this usually involves using two nuts and some springs between them. then you need to find a way to restrain the ball nuts together. i can post some pics later this week when i finish up my holders. i copied mine from someone else and the design seems to work.

the servo motors i am using are minertia series with 500 cpr encoders. these run at 3000 rpm and i will be using a 3:1 gear reduciton. i might need to go more but then i will most likely need the G340s for the step multiplication function. these motors are 150 oz in peak torque i believe. i don't think i will need more than this at this stage of the game. if i do then i will buy bigger motors. don't forget with the 3:1 gear reduction that 150 oz in becomes 450 oz in.

i also am converting the RF-25 and another member adryan did his not too long ago. he has a very detailed pictorial posted.

[Neil_J]

i also am converting the RF-25 and another member adryan did his not too long ago. he has a very detailed pictorial posted.

How would you guys rate the RF25 so far? I've heard a mix of biased opinions...

[yukonho]

Guys, I am doing a round column mill conversion in the near future. I am going to use these ballscrews and pre-loaded nuts. http://www.homeshopcnc.com/page2.html
Colin

[Runner4404spd]

the RF-25 is not a bad mill. however i find its small size limitting to what i want to do. i am converting it to cnc because thats what i have. in retrospect i think i would have at least bought and RF-31 if not the rf-45 the dovetail column mill. i don't have a problem with the head not being fixed its primarily in the table travel. i get 20x6 and will will be maintaining this after the cnc conversion, i am building an offset motor mount so it doesn't limit my travel.

those ball screws look to be the same inexpensive ones that everyone else sells too. basically i would get them from the cheapest place. roton and mcmaster carr carry those too and i think grainger does too.

[yukonho]

The reason I am going with these guys is that they offer a pre-loaded ball nut. I dont want to tinker around with ball nuts, so this is the obvious choice for me.
Colin

[Runner4404spd]

the single nut isn't a preloaded ball nut. a single nut with oversized ball bearings is not considered preloaded. it kinda works like a preloaded ball nut by taking up the slack somewhat more than the standard bearings but not as much as spring preloaded ball nut pair.

and if i were you i would look at adryans thread. he bought the stock ball nuts and then loaded one with i believe 1/8 ball bearings to tighten it up. alot cheaper than paying someone else to do it.

[NC Cams]

To a point, I can agree with runner4404spd re: osize balls not preloading a nut.

If you have a ball screw with simple, radius ground or rolled raceways, the installation of oversize balls reduces radial clearance it but will not necessarily preload the system in the proportion hoped/intended.

Reason: The radius of the raceway is slightly larger than that of the ball. Thus, the ball tends to ride in the "crotch" of the raceway and, as axial thrust is applied, it rides up the side of the raceway - ala a bowling ball running down the gutter. A larger ball will make the radii closer but there is still going to be room for the ball to move axially up the side of the raceway.

HOWEVER, if the raceways are ground with a gothic arch, the installation of o'size balls will preload the system and reduce if not eliminated any backlash.

The g-a system effectively puts the balls into a "4 point" contact with the outer and inner raceways. Thus, you are sort of putting an "oversize round peg into a square hole" and can't help but experience axial preload/slop reduction.

Anotherthing to remember with o'size balls, we're talking o'sizes in terms of 0.0001" or so. It is also adviseable when installing o'size balls to alternate the size. That is if S=std and O=+0.0001, you'd load them SOSOSOS. This helps them roll more freely into, out of and thru the raceways.

Helpful hints to use when you're trying to turn a Ford into a Ferrari.

[Runner4404spd]

i would bet on the cheaper ball screws the raceways aren't groung but rolled.

[Eskerinola]

Hi there;
As a general question, I wonder how easy it would be to go back to manual in case you have to do simple jobs.

[Neil_J]

Hi there;
As a general question, I wonder how easy it would be to go back to manual in case you have to do simple jobs.

It really depends. Most CNC conversions will use some combination of a jog wheel (MPG), joystick (like on a claw grabber machine), buttons, and/or a keypad. That's enough to use the machine comfortably for manual jobs, as you can tune the velocity high or low as needed.

But it really depends on your exact setup. I don't know of anyone who rips their motors off to do simple manual jobs .. I've seen a few (smaller) machines that had handwheels on the steppers, but that's not common on big machines. Just get good software and a good set of controls and you'll be fine.

P.S. you're replying to an 11-year old thread from 2005 You might have better luck starting a new thread .. it's been pretty dead on this sub-forum lately but there are still a few of us hanging around.