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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?

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.

RE: Gib is Sliding in Old Jig Boring Machine: Will Recessing Center Gib Screw Retain the Gib Better?

Is there not an oiler on the case for the sleeve bearing?

RE: Gib is Sliding in Old Jig Boring Machine: Will Recessing Center Gib Screw Retain the Gib Better?

(OP)
Grease fittings only. The grease fitting is aligned with a slot in the bronze bearing to distribute the grease away from the center and towards both ends.

RE: Gib is Sliding in Old Jig Boring Machine: Will Recessing Center Gib Screw Retain the Gib Better?

What you suggest for the gib plate may work but you really should just find out why the plate is moving when it is not supposed to and fix the problem rather than trying a modification when you do not understand what the problem is. When I was a kid I "fixed" a steel tape measure that had a loose hook by hammering the rivets tight. I later figured out that the hook was loose by design so it would read accurately which ever side of the hook was used for measurement.

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?

A jig borer isn't really meant for milling.

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?

Oh. It's fairly common for a gib to be restrained axially by a half-dog pointed setscrew projecting into a blind hole in the gib.

Mike Halloran
Pembroke Pines, FL, USA

RE: Gib is Sliding in Old Jig Boring Machine: Will Recessing Center Gib Screw Retain the Gib Better?

In that case, find the hole that is suposed to be there, don't just drill a hole. Perhaps the gib was replaced and not properly installed. Then you may have to drill a hole to finish the job. See what is keeping the other gib from sliding and you will know for certain.

RE: Gib is Sliding in Old Jig Boring Machine: Will Recessing Center Gib Screw Retain the Gib Better?

(OP)
Found them! (The 2x "missing" holes were in place, but hidden beneath the table. Until the grease fittings were removed, the table could not move sideways far enough to show the recessed holes - which, as implied above, were missing their cap screws .

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?

Jig borers are, indeed, used for milling. Very well suited to the job.

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?

"Is generic automotive grease the wrong choice for such a load in a machine tool under machining loads?"

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.

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