Gib is Sliding in Old Jig Boring Machine: Will Recessing Center Gib Screw Retain the Gib Better?
Gib is Sliding in Old Jig Boring Machine: Will Recessing Center Gib Screw Retain the Gib Better?
(OP)
I am restoring to service an "old" jig boring machine obtained at an estate sale several years ago. Obviously, the former owner can't give me any advice, neither his former shop or the original owner of the tool is known. Can't fins any manual on-line (yet!) either.
Two problems I've found after repacking bearings and replacing the pulleys and belts:
(1) The upper bearing is a simple tapered bronze sleeve, tightened by screwing down on the two retaining collars. But it seems to be running "hot" after 30-45 minutes of light running (no substantial steel cutting, simple spindle rotation.) Feels too hot to the touch (110 - 120 degrees), but if I loosen the bearing much more, the spindle can be felt moving sideways, which will foul up the cut when a tool is being used. How "tight" is "tight enough"? Or reversing the question, when is "too hot" "too hot" for a simple greased bearing? Is generic automotive grease the wrong choice for such a load in a machine tool under machining loads? I don't intend the tool to be used for professional or multi-0.000x accuracy, just low speed milling and drilling with a manual feed.
(2) One of the gibs is sliding with the bed as the tool bed is moved in the "x" direction. The other gibs are all fine. Since there are 3x gib screws, can I drill a recessed hole in the gib wedge (not all the way through obviously) so the center gib screw acts both as a left-right retainer against motion and a pressure point?
If I tighten the gib enough to prevent motion of the gib plate, there is excessive resistance to movement of the bed - equally undesireable.
Two problems I've found after repacking bearings and replacing the pulleys and belts:
(1) The upper bearing is a simple tapered bronze sleeve, tightened by screwing down on the two retaining collars. But it seems to be running "hot" after 30-45 minutes of light running (no substantial steel cutting, simple spindle rotation.) Feels too hot to the touch (110 - 120 degrees), but if I loosen the bearing much more, the spindle can be felt moving sideways, which will foul up the cut when a tool is being used. How "tight" is "tight enough"? Or reversing the question, when is "too hot" "too hot" for a simple greased bearing? Is generic automotive grease the wrong choice for such a load in a machine tool under machining loads? I don't intend the tool to be used for professional or multi-0.000x accuracy, just low speed milling and drilling with a manual feed.
(2) One of the gibs is sliding with the bed as the tool bed is moved in the "x" direction. The other gibs are all fine. Since there are 3x gib screws, can I drill a recessed hole in the gib wedge (not all the way through obviously) so the center gib screw acts both as a left-right retainer against motion and a pressure point?
If I tighten the gib enough to prevent motion of the gib plate, there is excessive resistance to movement of the bed - equally undesireable.





RE: Gib is Sliding in Old Jig Boring Machine: Will Recessing Center Gib Screw Retain the Gib Better?
RE: Gib is Sliding in Old Jig Boring Machine: Will Recessing Center Gib Screw Retain the Gib Better?
RE: Gib is Sliding in Old Jig Boring Machine: Will Recessing Center Gib Screw Retain the Gib Better?
A tight sleeve bearing will run hot. My guess is that the top bearing may not need to be very tight. What effect does it actually have on the tool position tolerance. Are the spindle and sleeve worn?
RE: Gib is Sliding in Old Jig Boring Machine: Will Recessing Center Gib Screw Retain the Gib Better?
The spindle isn't really meant for drilling either.
I don't recall ever seeing one rotate faster than ~100 rpm, always with one of those unbalanced adjustable precision boring heads clamped in the chuck.
For all I know, they were roughing the holes on a Bridgeport and finishing on the jig borer.
Mike Halloran
Pembroke Pines, FL, USA
RE: Gib is Sliding in Old Jig Boring Machine: Will Recessing Center Gib Screw Retain the Gib Better?
Mike Halloran
Pembroke Pines, FL, USA
RE: Gib is Sliding in Old Jig Boring Machine: Will Recessing Center Gib Screw Retain the Gib Better?
RE: Gib is Sliding in Old Jig Boring Machine: Will Recessing Center Gib Screw Retain the Gib Better?
Cap screws replaced, gibs no longer moving.
And, about the wisdom of using a jig borer for light-duty machining? When budget permits, I'll get the right tool for that job. Most likely a combined drill-mill-lathe, since my little-bitty Craftsman-Atlas lathe is far older than I am. 8<)
RE: Gib is Sliding in Old Jig Boring Machine: Will Recessing Center Gib Screw Retain the Gib Better?
It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.
RE: Gib is Sliding in Old Jig Boring Machine: Will Recessing Center Gib Screw Retain the Gib Better?
Not sure about automotive greases, but some automotive oils can have an adverse effect on brass or bronze bearings. The nearest modern equivalent to the lube oil specified for my old (1940's) lathe turns out to be a low viscosity hydraulic oil. You might want to check what is needed on that spindle.