Ball screw for a lead screw
Has anyone used a ball screw for a lead screw on BP series 1. What are your results. Does it work good, is it solid?
I have a ball screw that is new old stock I believe it is a warner and is set up for a bridgeport. I do very little machining and it is mostly 1 odd piece type work. I can use it or I can sell it and buy some other goodies. I have a new regular screw also. It is a toss up based on what you guys tell me.
Great for backlash, but there isn't adequate friction to keep the screw in place.
You would need to introduce friction, not so much to lock the handwheel, but to keep force on the table from moving the table.
Some sort of plastic block rubbing/gripping the shaft would be a good start; get a spring in the system to keep the friction consistent.
If you can't figure out a way to introduce friction, don't install the ballscrew.
Interesting. I guess the motor on a cnc machine is the friction. it locks the screw. Keep them coming and lets see
DOnt do it. Keep the acme.
The ball screw is free running. My not be correct term. But if you stand an acme screw and nut on end and give a quick turn it will revolve a few turns and stop. The ball screw will spill the nut onto the floor.
So when cutting (particularly climb) it is possible to do something similar. Maybe pull the handle out of your hand.
A friend of mine rebuilds Bridgeports professionally. He STRONGLY recommends against ball screws. In fact he refuses to install them even when asked to.
I've been designing a self-locking mechanism that would hold the table in place under stress, but haven't come up with a working version as yet.
Here are some good reasons posted for not installing a ballscreww in a Bridgeport.
But I have to jump on the other side of the fence for this one.
Of the seven Bridgeports in our shop, I installed X and Y ballscrews in a 2HP Bridgeport.
It was a 48" or 56" table, I do not remember the actual length. The results were outstanding. The machine ran two shifts with a wide variety of work.
However, The ways of the machine need to be in very good shape as well as the gib.
I would point out that the fit of the ways is what will provide 'friction' or drag and not the nut and leadscrew. If there is friction between the nut and leadscrew then the nut just wears out that much faster.
Backlash for the initial installation was minimal.
After five years the backlash was .0005.
Drawbacks, I do not believe enough oil is delivered to a ballscrew with the standard Biljur oiling system. I did change the metering valves to allow more oil to pass to the ballscrews so they could 'self clean'.
My 1987 Webb mill came to me as a former CNC machine which I converted back to manual use. It has ball screws. I have learned to lock the X or Y axis before cutting and it works perfectly for my purposes. While not ideal for a manual machine, it's nice to have a machine with only four divisions of lash on the X axis and 0 lash on the Y. I checked them when I was cleaning the machine up and they were getting plenty of lubricant from the oiling system. It works for me.
For my purposes, converting it to standard acme screws and nuts would be cost-ineffective. I would probably still lock the tables when making cuts anyway.
All depends on the pitch of the ball screw. IMHO the 5mm pitch ones i have on my Bridgeport are lovely and you can keep your acme. Now if your running a silly pitch like 20+mm then yeah its probably a whole different story. I have never seen any sign of them being back driven.
Personally i think those that disprove have never actually been there and tried it, mealy thought about it. Stick to a sensible lowish pitch and backlash free ball screws are great.
I've thought about converting my ancient M-head to be a hybrid manual/ XYCNC machine and eventually ballscrews would be nice.
Originally Posted by The real Leigh
What I wonder is, why nobody has figured out a way to use a capacitive sensor (like the touch-to-turn-on lamps) on the handles of a hybrid machine....that way you could lock the steppers when nothings touching the machine, and unlock the axis that has a human hand on the handle.
I haven't given much more thought to it than the initial idea, as I have neither the time nor the money to buy myself ballscrews, get a lathe set up to modify the ends of raw ballscrew stock, steppers, Gecko drive and build the controller to lock/unlock the steppers when needed. But when I do get the time and cash to do such a conversion I'll be posting details up here.
I agree with adama. Opposition to ball screws seems to be more theoretical than experience based.
I run a student machine shop. Four of our Bridgeports are CNC retrofits with ball screws and another one was a CNC and is converted back to manual with the ball screws still in it.
These machines are run manually by students who had never even run a drill press and I have never seen a single instance of a free running ball screw.
I use the machines often myself and the ball screws are a definite improvement. You can take larger climb milling cuts without the part pulling into the cutter like you get with an acme screw. The funny thing is that the table locks don't work as well with the ball screws. It's easy to overpower the locks because there isn't as much friction when you turn the handles.
I have not run a BP with ball screws but have always wanted them for my clones. My Willis has been retro-fitted with a Proto Trak 3 axis CNC. So far I have had no trouble with table movement when hand feeding either x or y axis. I dont feel the servos are 'holding' the axis when hand feeding. They do when the controler is engaged and you can feel that in the handles. But I have no problems with movement while hand feeding.
The idea that a ball screw will spin itself to the floor when you do as stated in a previous post makes me wonder why anyone would do that when the screw is not used in the vertical and removing the 'ball nut' from the screw will 'destroy' the assembly for all practical purpose. These type of screws come with warnings not to remove ball nuts from the screw. That makes me think some have no experiance with thses screws.
You needn't take my word for it, contact a supplier of ball screws for better explainations of their use and applications.
Removing a ball screw nut won't destroy it (they don't machine them together in one solid block now do they? or do they grow them???)
It will drive you frigging nuts putting all the balls back in properly though :-O
I tend to agree that it won't actually destroy it, but every supplier I've looked at has had that statement or something similar in their notes. I repeated it to point out that it would not be adviseable to do so. The CNC retro that I installed on my Willis also had such warnings. For the typical (what ever that means) HSM to try to disassemble a ball screw unnessecarily will result in their rejection of ball screw use also.
Originally Posted by adama
I have used Mobil synthetic grease to hold the balls in place when the leadscrew is removed. It is thin and red in color and will mix with or be flushed by oil. It looks like blood when it is on your skin. One of the guys was working on a machine and a salesman was pestering him. Lefty did the grease trick on his hand and started screaming. Mischief managed, salesman gone. The 'knuckle bracket' for the Bridgeport X and Y axis was installed first and then the leadscrews. The work area better be spotless in case you drop a ball.
When I was cleaning up my ball screw-equipped Webb Mill last year, I saw no reason to remove the lead screws or the center ball nut portion of the assembly. I just cleaned the leadscrew carefully with solvent.
I was well aware of the danger of dumping the balls out on the floor from reading admonitions on this site. I also understand that the people who make those units will sometimes need an over or undersized ball to get the clearance correct. With my luck, that's the one I'd lose on the floor. LOL.
The Webb has two locks on the X axis, two and one on the Y axis and those are sufficient to keep things where I put them when working with the machine.
Had my machine been set up with regular acme units, I wouldn't have changed to ball screws for use as a manual. Now that I have them, I think they're neat. They sure work smoothly.
I installed ballscrews on a '50s vintage BP about 20 years ago. At the time I didn't know about admonitions against ballscrews on a manual machine. The supplier implied that I was a dummy for doing it but sold me the screws anyway. They worked just fine.
The ballscrews that I have worked on have had a simple (better than useless) hard plastic wiper. I have removed just those to clean. There is usually some type of debris to clean out. Then just replace the plastic wiper.