Apron Gits Oil Cup in Apron on 9" Lathe

Hello crew; hope all is well.

I'm just about finished with re-felting the apron on my 9" Model B SB lathe.
Looking good and almost everything is A-OK. However, this morning I was carefully
trying to thread in the 90-degree Gits oil cup, below/right of hand wheel.
It did not start as easy as I would have liked. I checked threads on the cup and threads
in the apron casting, and even used a 90-degree dental pick to clear threads.
(They looked okay)

However, I'm getting this sinking feeling that I have partially cross-threaded
the hole in the casting. What I would like to do is to get the correct size tap
to chase these threads. But before I do, I need to make sure of the thread size...some of this
does get confusing.

Measuring across the threads, I get .310 (5/16ths?); the TPI is 32; and a 5/32 drill shank is a
sliding fit in the hole.

So checking the GITs website and McMaster Carr, both show a 5/16ths Male UNEF threaded
oil cup. Is this the correct size for this particular oil cup? And the correct size for a tap?
(I sometimes get terribly confused with pipe thread sizes)

Thanks...any advice appreciated!

PMc

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A 16" has 1/8th pipe threads. Looking at your pic, it looks like 1/8 pipe also.

To drill for 1/8 pipe you need either a LTR. R drill, 21/64, or 11/32" depending on how deep you want to fit in the hole, as the threads are tapered. That is around .3 of an inch.

1/8 pipe thread is 27 tpi though. But i would guess not an odd ball size from South Bend.

I couldn't tell you why pipe threads are labeled the way they are.

Obtw, pipe threads being tapered, don't feel like bolt threads, they begin tightening as you get tighter in taper. Might be why you feel cross threaded. Put pipe tape, or pipe sealant on threads too. Might try tightening it, then fill apron to check for leaks.

I seem to recall that some of these really are 5/16 - 32 straight thread. Other more knowledgeable folks will no doubt chime in here.

jim rozen said:

I seem to recall that some of these really are 5/16 - 32 straight thread. Other more knowledgeable folks will no doubt chime in here.

Click to expand...

I think these are straight threads; I see no taper whatsoever.

Thanks.

I just ordered a set of 5/16 -32 taps from McMaster Carr. I think they will do the trick.
Thanks.

PMc

View attachment 308835

It finally occurred to me what I did wrong with this Gits oil cup, and I knew better.
The refresh book says to use teflon tape to seal the threads, and that is just about the worst
and most useless stuff you can use for extra-small 32 threads per inch.

Knowing me, I probably tried to use too much, and it was just enough to keep the starting threads
from mating correctly, hence the apparent cross-thread. Damn!

Nope, from here on out, it's just a dab of non-hardening Permatex on the threads. I tend to like the aviation type
with the little brush in the cap. It's not as thick as the stuff in the tube.

PMc

View attachment 308916

Finished The Job

Since I started this thread, I figured I might as well finish it up with a conclusion.

I ordered/received the 5/16-32 taps from McMaster-Carr, and I bought the set of three. Only took
two days to get them; about 25 bucks. (I really didn't need the set). The first thing I wanted to do
was check the threads on the 90-degree Gits oiler to make sure they weren't crossed up. I decided this
was done easiest on the lathe with a 1" dia rem. After threading the 9/32" hole, the oiler fit the threads
just right; no probs.
View attachment 309183 View attachment 309184

I knew that the probable correct way to chase these threads would be through the back of the apron casting,
coming out the forward side. But I had just buttoned up the installation of all of the gears, and had
"adhered" the small reservoir plate in place. To get to this threaded hole, I was going to have to take
a lot of this assembly apart again. And, there was no guarantee that I would even have a straight shot
at the threads. I was not looking forward to repeating all of this.

So instead, I used my fingers to feel the tap threading into the hole. Luckily, it started straight
and I was able to jiggle it down 4-5 turns. I did hit a little snag and used a small ignition wrench
to turn the tap. (I did not want to have to remove the handwheel either). A few Q-tip cotton
swabs down the hole removed whatever tiny chips I created to my satisfaction.
View attachment 309185 View attachment 309186

Finally added some Permatex to the threads; screwed it in; and cleaned off the Permatex excess with a
little swab. Needs a paint touch up, but I'm glad that's about the extent of the issue. I didn't want
to have to buy a new oiler or a 5/16-32 die or have to use an insert. We all know that the simplest of
tasks like this one can quickly turn into a nightmare from hell! It could have been much worse.
View attachment 309187

PMc
(Now I have a set of 5/16-32 taps that will never get used again!)