Trouble with my SB 9” QCGB Tumbler bearings

My SB 9” x 4 foot bed, model CL644A, s/n 38987NAR9 (April 2, 1956) QCGB tumblers came with Torrington GB-88 needle bearings. During my tear down, clean, repaint and refelt effort I noticed that the needles were frozen in the tumbler gears. Amazon’ed some Koyo (made in USA) GB-88 replacements. (Some concern about the length; the tumbler gear is 0.495” thick, catalog says GB-88’s are 12.7 mm long (0.500”). When received they check out as 0.495” long, so far, good.)

Pressed out the old Torrington’s, checked the Koyo’s that they roll fine. Pressed in the Koyos (gently with an arbor press). Locked up tight like the old Torrington’s.

What to do???

John

Someone correct me if I am wrong, but I think you will find that the original bearing was just a plain bronze bearing.

Earlier lathes, yes, by 1956 they had gone to needles...

Thinking about the bronze though, as long as it gets oiled they are fine.

John

comstockfriend said:

--snip

Pressed out the old Torrington’s, checked the Koyo’s that they roll fine. Pressed in the Koyos (gently with an arbor press). Locked up tight like the old Torrington’s.

What to do???

John

Click to expand...

The bore in the gear is to small and squeezing the needles together.
Research the proper fit for the bearing then open up the bore of the gear to that fit.
You'll likely need new bearings.

Ken-Bergen said:

The bore in the gear is to small and squeezing the needles together.
Research the proper fit for the bearing then open up the bore of the gear to that fit.
You'll likely need new bearings.

Click to expand...

I think you have it. I had only installed one. Popped it out and the rollers now roll. Mikes out same as the unused one. According to the bearing books, the cup is to be 0.6875", the housing is 0.687" min, 0.688"max. South Bend has the tumbler gear at 0.6827" bore so we are 5 to 6 thou tight. 11/16 is a reamer I'll have to acquire!

Thanks for getting me to do what I should have done at the first. Not sure how much interference you get with a 0.688 housing and a 0.6875 bearing but that's what the books (Timken and Koyo) say! The books say you can't mike the cup, it has to be put in a ring gage with go/no go's in the bore. Miking the cup the max OD dimension I get is 0.685", 25 thou less than the published. Tolerance is supposed to be -0.010" max. Looks like a nominal ream will be too big.

John

11/16 is a reamer I'll have to acquire!

Click to expand...

You've got a lathe. Feed might not work, but you can still center the gear up in a 4jaw indicate it flat, and single point bore it.

If the carriage handwheel seems tetchy, tram in the compound and bore it with that, with the carriage locked.

smt

Had the same problem when I did mine. I found ultra precision bearings that fit the bore after trying standard ones that locked up. Mine was for a heavy 10, not sure if they are the same as yours. Probably still have the box around and can get you the part # if you want.

Teryk

stephen thomas said:

You've got a lathe. Feed might not work, but you can still center the gear up in a 4jaw indicate it flat, and single point bore it.

smt

Click to expand...

Oh, I have two other working lathes. Will be going out to do just that.

John

mTeryk said:

Had the same problem when I did mine. I found ultra precision bearings that fit the bore after trying standard ones that locked up. Mine was for a heavy 10, not sure if they are the same as yours. Probably still have the box around and can get you the part # if you want.

Teryk

Click to expand...

What I don't understand is that Timken and Koyo say the OD is Nominal is 0.6875" and to press them into a 0.6880" ring gage. Both the brand new and pressed out new bearings are around 0.685", they will drop through the ring gage. They are 25 thou undersized (WAY out of commercial tolerance).

Seems the nominal interference for the press is about 5 10ths, or about a 0.8745 housing to fit these.

John