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Metalworking (rec.crafts.metalworking) Discuss various aspects of working with metal, such as machining, welding, metal joining, screwing, casting, hardening/tempering, blacksmithing/forging, spinning and hammer work, sheet metal work. |
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#1
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Ball Screws in Bridgeport mill?
I went to an auction recently and picked up a set of screws that
turned out to be ball screws for a 9x42 Bridgeport. http://igor.chudov.com/tmp/Bridgeport-Ball-Screws/ I am a little surprised about it, as, I thought, ball screws could only be used in CNC mills whose screws were held by stepper motors. So, do they have use in a manual mill and are they in any way better than regular drive screws? Or are they for CNC conversion only? -- Due to extreme spam originating from Google Groups, and their inattention to spammers, I and many others block all articles originating from Google Groups. If you want your postings to be seen by more readers you will need to find a different means of posting on Usenet. http://improve-usenet.org/ |
#2
Posted to rec.crafts.metalworking
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Ball Screws in Bridgeport mill?
On 2008-12-20, Ignoramus25214 wrote:
I went to an auction recently and picked up a set of screws that turned out to be ball screws for a 9x42 Bridgeport. http://igor.chudov.com/tmp/Bridgeport-Ball-Screws/ Nice find! I am a little surprised about it, as, I thought, ball screws could only be used in CNC mills whose screws were held by stepper motors. Stepper or servo motors. Note that the shanks have two spaces for keys -- one for the timing belt gear which drives it from the stepper or servo motor, and the other for the handwheel (with a spring-loaded folding crank handle, so you don't get beat to death when the thing starts up unexpectedly. :-) So, do they have use in a manual mill and are they in any way better than regular drive screws? Or are they for CNC conversion only? The problem with ball screws in a manual-only lathe is that they are too easy to reverse drive. Replace your current leadscrews with these, and you can grab hold of the vise on the table and pull it to where you want it -- driving the screws from the table's motion. A stepper naturally holds in specific positions -- like detents. A servo with no power is a drag on the screw, so you can use the machine in manual mode if you so desire. Note that the X-axis ball screw used by Bridgeport in the Series I (BOSS-3 and later) does not rotate. Instead, the ball nut is mounted in a pair of opposed high-precision preloaded bearings, and driven by a cog (timing) belt. This way, you don't have the screw whipping during rapid motions. But -- you also don't have manual control of the machine at all (other than with the jog switches). As for benefits of the ball screws -- consider near zero backlash, and very long life, as well as the low torque needed for the motor to move the table. If you set up an adjustable clutch on each screw, you *could* use them for a manual machine, I guess. But normally that is too expensive -- unless you luck into a set of the screws like this. :-) Oh yes -- also the Bridgeport Series I BOSS-3 and later have a large diameter hollow ball screw around the quill, and the nut is driven by a motor outside the headstock housing. This way, the Z-axis force is truly concentric with the quill, unlike the aftermarket adaptations which I have seen, which replace the depth stop screw with a ball screw, which provides the force off center, and I expect hastens the wear of the quill and housing in certain directions. Enjoy, DoN. -- Email: | Voice (all times): (703) 938-4564 (too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html --- Black Holes are where God is dividing by zero --- |
#3
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Ball Screws in Bridgeport mill?
On 2008-12-21, DoN. Nichols wrote:
On 2008-12-20, Ignoramus25214 wrote: I went to an auction recently and picked up a set of screws that turned out to be ball screws for a 9x42 Bridgeport. http://igor.chudov.com/tmp/Bridgeport-Ball-Screws/ Nice find! I paid $35 for the lot. The lot included these two aforementioned feed screws and seven Bridgeport drawbars (one of which I now use on my mill, it has a taller hex part). Talk about deflation. I am a little surprised about it, as, I thought, ball screws could only be used in CNC mills whose screws were held by stepper motors. Stepper or servo motors. Note that the shanks have two spaces for keys -- one for the timing belt gear which drives it from the stepper or servo motor, and the other for the handwheel (with a spring-loaded folding crank handle, so you don't get beat to death when the thing starts up unexpectedly. :-) OK, I think that I can visualize it, after installing a Z axis power feed. So, do they have use in a manual mill and are they in any way better than regular drive screws? Or are they for CNC conversion only? The problem with ball screws in a manual-only lathe is that they are too easy to reverse drive. Replace your current leadscrews with these, and you can grab hold of the vise on the table and pull it to where you want it -- driving the screws from the table's motion. A stepper naturally holds in specific positions -- like detents. A servo with no power is a drag on the screw, so you can use the machine in manual mode if you so desire. Note that the X-axis ball screw used by Bridgeport in the Series I (BOSS-3 and later) does not rotate. Instead, the ball nut is mounted in a pair of opposed high-precision preloaded bearings, and driven by a cog (timing) belt. This way, you don't have the screw whipping during rapid motions. But -- you also don't have manual control of the machine at all (other than with the jog switches). As for benefits of the ball screws -- consider near zero backlash, and very long life, as well as the low torque needed for the motor to move the table. If you set up an adjustable clutch on each screw, you *could* use them for a manual machine, I guess. But normally that is too expensive -- unless you luck into a set of the screws like this. :-) Oh yes -- also the Bridgeport Series I BOSS-3 and later have a large diameter hollow ball screw around the quill, and the nut is driven by a motor outside the headstock housing. This way, the Z-axis force is truly concentric with the quill, unlike the aftermarket adaptations which I have seen, which replace the depth stop screw with a ball screw, which provides the force off center, and I expect hastens the wear of the quill and housing in certain directions. I think that this is definitely for a CNC application only, given what I know by now. I had a brief moment of insanity where I considered replacing my screws with these. -- Due to extreme spam originating from Google Groups, and their inattention to spammers, I and many others block all articles originating from Google Groups. If you want your postings to be seen by more readers you will need to find a different means of posting on Usenet. http://improve-usenet.org/ |
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