Ball screw on manual knee mill?

Perhaps I am just ignorant in this area, but how can true ball screws be used on a manual knee mill? If feeding by hand won't there be a problem there?

Vs. using the conventional way if half but and acme lead screw?

Endmill20 said:

Perhaps I am just ignorant in this area, but how can true ball screws be used on a manual knee mill? If feeding by hand won't there be a problem there?

Vs. using the conventional way if half but and acme lead screw?

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No problem. Obviously, ball screws are reversible and one must control that. Somehow.

Ball screws back drive.
The acme gives you more ability to contro forces.
Unless you have some sort of active control a ball screw could break your wrist.

Huh? I have ball-screws on my BP. I can use all day by hand. Still have all my wrists and fingers.

Plenty of threads on this over the years here on PM.
Some people love them, some people do not.
I like them for some work, don't like them for other work.
No real consensus but you will find individuals passionate on both sides.
Bob

Like a lot of things the details matter, a circa 5TPI - 5mm pitch ball-screw won't readily back-drive on most sensible Bridgeport cutting, drag from its self, the thrust bearings and a power feed is plenty to keep it still. If your trying to use big cutters in hardned materials diffrent story, but keep things sensible and use good sharp cutters and i have no issues with mine in hardox 450 at 45Hrc ish till im feeding so hard its near screaming at me. The zero backlash is so so so good,

Now if you stick something stupid in there like 20mm pitch then yeah back driveing is probably more of a issue. But std 5TPI - 5mm sure works good for me and these days ball-screws are cheap, really cheap! If i bought a new Bridgeport tomorrow it would be the first thing i would swap out along with ditching the R8 spindle for a QC30 one.

On a mill larger than a bridgeport with more power - higher cutting forces it would be a different story, retrofitting a horizontal with them could well be a bad idea too where you have seriously large high torque cutter engagements.

IMHO its something you need to try and use and then make a informed decision on, not just apply logic too.

When I had my own shop, I bought a heavy import mill- like a BPort, only heavier and more powerful. It came with ball screws, and was nearly unusable, at least for me. The dealer told me it was only rated for a maximum 1/2" diameter end mill. I said in that case, take it back. They installed Acme thread screws, and it was a great machine after that. I was cutting large pockets in mold plates, and even with a 1/2" EM and over-tightening the table locks, it would still back drive. Granted, I was working it hard, but why put in a 5 hp spindle if you're not going to use it?

5hp heavy pockets again thats not a Bridgeport is it? Equally what pitch were those screws?

I am one of the guys that can't figure out why so many people want to "improve" a knee mill. They are NOT a rigid machine. They don't make good CNCs and they are not real good at most of the things they do, but they do it all.
JR

adama said:

Like a lot of things the details matter, a circa 5TPI - 5mm pitch ball-screw won't readily back-drive on most sensible Bridgeport cutting, drag from its self, the thrust bearings and a power feed is plenty to keep it still. If your trying to use big cutters in hardned materials diffrent story, but keep things sensible and use good sharp cutters and i have no issues with mine in hardox 450 at 45Hrc ish till im feeding so hard its near screaming at me. The zero backlash is so so so good,

Now if you stick something stupid in there like 20mm pitch then yeah back driveing is probably more of a issue. But std 5TPI - 5mm sure works good for me and these days ball-screws are cheap, really cheap! If i bought a new Bridgeport tomorrow it would be the first thing i would swap out along with ditching the R8 spindle for a QC30 one.

On a mill larger than a bridgeport with more power - higher cutting forces it would be a different story, retrofitting a horizontal with them could well be a bad idea too where you have seriously large high torque cutter engagements.

IMHO its something you need to try and use and then make a informed decision on, not just apply logic too.

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The mill I'm looking at ordering comes with ball screw, but they don't tell me what pitch. I'm waiting for a response back from the company. However this is a 58"x12" table #40 taper 5hp motor. And I do a large amount of work by hand feed not auto feed, I've never had ball screw before I do alot of face milling with large cutters and large (ish) keyways (3/4 to 1 1/2 ) do you feel ball screw is still going to handle regardless of knowing the pitch?

Miguels244 said:

Ball screws back drive.
The acme gives you more ability to contro forces.
Unless you have some sort of active control a ball screw could break your wrist.

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Bullshit!!!

JRIowa said:

I am one of the guys that can't figure out why so many people want to "improve" a knee mill. They are NOT a rigid machine. They don't make good CNCs and they are not real good at most of the things they do, but they do it all. JR

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Same reason back in the day, guys hot rodded that POS flathead Ford 4-banger and later the V8; small, light, available everywhere, easily understood, cheap, plenty of new and used parts, easy resale. All those overcame better, but less common and more expensive designs.

jack vines
Obsolete Engineering Division
of Mager Engine

In my case its simple, a cross between funds, 210 square feet of space and needing more than 3 axis a typical VMC gives me, the head on my Bridgeport gets to nod one way or another most months. Today its set at 15 degrees, tomorrow its back square but theres anouther job coming up with it nodding once more probably end of the week.

Worth adding mine came retrofitted with a anilam crusader control and 5tpi ball screws as part of that, putting it in perspective i paid £437 something on a sealed bid auction for her nearly 2 decades back, straight out of a technical collage and she had very very low hours on her. I only got to use acme screws on a Bridgeport post using ball-screws. In my case yes i run mine part the time under Linux cnc control, its not a vmc, more just like another usefull function to add to a bridgeport, last week was profiling a 11 tooth 520 chain size sprocket, couple of days ago it was a nasty and repetitively shaped pocket cut out. CNC means you don't need a horizontal rotory table and you can drive - mill any shape you wish, + the power feed like functions running in MDI mode gives you. Its great to buzz key ways in whilst your doing something else etc.

40 taper and 5hp you may well be high enough force wise to encounter back drive. 2-3 hp and typical Bridgeport you really won't unless really doing something nasty with 5tpi ish screws. Jumping much coarser - decreasing the helix angle and back-drive becomes a lot lot easier. That said you still have the advantage of the screw thread helix ratio so wrist breaking is a bit bleak a outlook, way more likely if your say feeding in x, Y may move a bit on you.

Typical Bridgeport sized work and i never bother with the carriage locks, there just not needed to resist any back drive in my experience and i climb mill a lot. Its really only hard work with inserted cutters and vibration that will get mine to even begin to back drive, the same kinda cutting that would get a acme screw to back drive too in my experience. Had many a acme threaded top slide move on heavy nasty interrupted cut on most the lathes i have used, really not much different with my ball-screwed Bridgeport.

Cutters wise i run everything from 0.3mm 30 degree engraving bits upto a 63mm SEHT 45 degree face mill in everything from acrylic to the hardox at 45HRC, have flattened several anvils etc,

adama said:

In my case yes i run mine part the time under Linux cnc control, its not a vmc, more just like another usefull function to add to a bridgeport, last week was profiling a 11 tooth 520 chain size sprocket, couple of days ago it was a nasty and repetitively shaped pocket cut out. CNC means you don't need a horizontal rotory table and you can drive - mill any shape you wish, + the power feed like functions running in MDI mode gives you. Its great to buzz key ways in whilst your doing something else etc.

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youtube video, or it didn't happen!!!!!
I'd actually like to see the linux setup

I had a Cincinnati Contour Master with a clapped out hydraulic tracer unit. It had ball screws and it worked just fine as a manual mill.

5hp and a 40 taper? It's going to move on you, most likely. I have a ball screw setup on the VN 2G that was done before I got it. It's only 3hp and it will indeed push the unused axis, even with small endmills, unless it is locked down tightly.

Lakeside53 said:

Huh? I have ball-screws on my BP. I can use all day by hand. Still have all my wrists and fingers.

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moonlight machine said:

Bullshit!!!

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We had one and it would gladly back drive.
Lock the gibs or engage the centroid.

Lakeside53 said:

Huh? I have ball-screws on my BP. I can use all day by hand. Still have all my wrists and fingers.

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My Webb 4VH was fitted with Ball screws from the factory. The CNC parts were missing when I got it and they wanted $1,200 for Acme screws and nuts. I left the ball screws in place and they work fine. Zero lash on the Y and 7 or 8 thou on the X. They work fine. I just flip the locks over when milling. Still have all fingers, both wrists and nothing else missing.