[Ellis76]

I'm in the process of gathering information to CNC my RF45 clone mill.

I have a question about the Z axis, once it has been changed to ballscrews and servo drive, etc. When there is no power to the Z axis servo motor will the head fall? If it doesn't does this put stain of the ballscrews? Thanks

[LeeWay]

I'm pretty sure it would fall without power. The head is pretty heavy. The nuts on some ball screws will spin down sometimes under their own weight. Consider the extra few hundred pounds added. I have a similar mill in conversion now, but round column. I was considering ordering the square column for it. This particular issue was part of the equation on that decision.

There are several ways to counter the issue though. Several counterweight systems have been documented on the Zone.

[jalessi]

Ellis76,

They make a servo with a brake option, when you power up the machine it applies 24 volts to the brake and unlocks it.

When the power is off the brake is locked so the axis wont freewheel.

http://www.isa.org/Template.cfm?Sect...ContentID=9489

Jeff...

[Ellis76]

Thanks guys. I'm guessing most of the machining will be done in the X and Y direction and the Z axis will be held in position by the power of the servo. Is it better to have a brake applied when the Z axis is not moving to save current draw through the servo z axis motor? Would this be quite high(the current) just holding the head there?
Or am I just making this more complicated than it needs to be and people typically park the head @ the lowest position when the machine is off and let the Z axis servo just take care of it during production? And some would add a brake just in case of a power failure? Thanks

[jalessi]

Ellis76,

Conserving power may be good reason to have a brake however it is usually not implemented for that reason.

If you where working on a part and decided to pause the operation and turn off the machine a brake is a good idea because you would not loose your Z zero or Z home position.

The same scenario would apply during a eStop.

Jeff...

[devincox]

I just had this same question as I am putting precision ground ballscrews on my IH mill. I was advised it wouldnt need a brake. I tested it last night and it definately wont need a brake unless your gib is all worn out (and only maybe then). Even disconnected from the ballscrew the head barely moves and thats with me forcing it and my gib oiled up and completely loose.

Devin

[CROSSHATCH]

Like other have said, I think a counterweight system would work well along with maybe a compression spring system.

-Jason

[tray]

When I took apart my machine, I got the approx. weights: Head 170 lbs. Motor 40 lbs. Slip saddle (my manual calls it that) 20 lbs. for a total of 240lbs.

I have a brake on my machine and have the key removed because I don’t have a 24V power supply for it yet. When the axis in disabled, I sometimes get about an 1/8” of downward travel. The other day I removed the drive belt and the head freewheeled down and crashed into my presetter. The gibs are a little loose and if I had to do it all over, I’d omit the brake. I’m not sure about the accuracy for maintaining position when the motor is turned off but sometime, I’ll check it out.

I also do not have a counterweight and can achieve about 250IPM (only 150 on X/Y because of a lower voltage power supply).

[pete from TN]

Ya got a video of that millhead going 250IPM?!! I can get around 150IPm and that is TOO fast for me.... are you running Geckos? When I get too much faster than that the Gecko faults during a direction change and the bad part is that the head will fall when it does..... You must have a very powerful system, what is your belt drive ratio? Motor size? power supply voltage? Inquiring minds wanna know.... Almost hard to believe....peace

[tray]

I’m with you-I think the only time I want a rapid like that is when the head retracts for a tool change and 150 should be just fine. During development of the tool position routines, I’ve been using 150. The mill is a Lathemaster ZAY7045 with Aerotech hardware with 300W brushless servos running at 80V(X&Y) and 160V (Z). My belt ratio is 3.5:1 and the leadscrew pitch is 0.2”. I spent about $300 on the leadscrew but it’s a new Kuroda ground screw. I have cheap angular contact bearings and in the future may replace them or just by a decent CNC. But for now, the learning experience is fantastic. I have a lot to learn and I’ve only made 2 parts. Sometime I’ll post some videos but I am still setting things up and need to research what would be a safe upper limit for the rapids. The 250IPM varies from 240 to 300(once only for a few cycles) and I still need to find the right parameters.

Can you put a brake on your Z axis so when the Gecko faults it stops the head? What voltage are you running? Maybe your acceleration is a little too high when the motor windings warm up due to the higher speeds.

Tray

[pete from TN]

Man that is really fast, especially on the factory millhead. What the hell is aerotech hardware? 160vdc!! Holy smokes!!! No need for a counterweight with that much power for sure.... I am running Geckos at their max recommended 76vdc. My motors are 1125oz inch. I am also using a .2 x3/4 inch ballscrew on the Z. My millhead is considerably lighter than it was stock due to a belt drive conversion and higher HP much lighter spindle motor. See my build thread on here entitled " Finally Getting Started"

I am probably going to get a brake for the Z when funds allow. The acceleration is set pretty high and that of course does not help the direction change problem but as I said it only does that when I try to run it at 200IPM or more.... I am sure if I set the acceleration much slower I could get a higher feedrate but as I said before even 100IPm is plently even for a toolchange for me on this mill... Mine is also a Lathemaster Zay7045l.. Have had it for nearly nine years now and still working great!!!! peace...

[MIRZA ABUBAKAR]

Heelp for every one

[MIRZA ABUBAKAR]

IF any one want any parameter for machine then such person contact to me
my ID is [email protected]
cell # +92-3456224711