Couple of machinist ( real easy) questions

[Billy NY]

Well, someone here ought to know these, here goes:

1.) Common grease zerk size for a typical pto universal joint, for some reason I can't match it up, the hexagonal portion of it measures 9/32, a 1/4-28 fitting will fit in the hole, and partially thread, then stop or you will gall the threads. I have one of these left on the shaft, the other must have flew out. At the threads it measured, 0.233" on the digital micrometer just below the hex and 0.19" at the last thread or bottom of thread. Thread pitch gauge appears to read 28 TPI, so it looks tapered has to be a common size right, NPT ? Tapered ? I did look on Lincoln's site, there is a nice reference .pdf file for fittings.

2.) What is the correct drill bit size for tapping a 5/16"-18 hole in steel, going to mount a rear work light so I can see better, just know I'll be out there on this old tractor at night.

 

[Don-Wi]

Probably metric. 6mm is .236, there are M6x1 grease fittings, which is very close in pitch to a 1/4-28 thread pitch.

I believe the proper drill for a 5/16-18 is an F drill.

Donovan from Wisconsin

 

[Wile E]

Most likely an M6 thread x 1 pitch, use an M5 drill to tap out the M6.
If you want to use a 5/16" - 18 tap then use a .257" tap drill.

 

[Walt Davies]

If you don't have set of letter or number drills then 1/4 in. will
work just fine.
Walt

 

[MMB]

Regarding the zerk fitting depending on age could be a 1/16-27 national pipe thread.

 

[Rusty wheel]

Zerk fitting takes a 1/8 tapered pipe tap. Be careful not to run the tap in too far. F drill for a 5/16-18 tap. 1/4 inch drill will work unless you're tapping something hard or stainless steel. Those small taps break pretty easy.

 

[Don-Wi]

Zerks come in many different size threads.

http://www.mcmaster.com/#zerk-grease-fittings/=j8l041

1/4-28, 1/8 NPT, M6x1, etc...

More sizes out there than most would think.

As far as the tap drill for 5/16-18, I'd rather go up to a 17/64 drill, than go down to a 1/4" drill (if you don't have an F drill). Drill it too small, and you're much more likely to break the tap while hand tapping.

Donovan from Wisconsin

 

[retired farmer]

Could be a metric grease zerk.

 

[Billy NY]

Thanks fellas, probably metric, always throws me off, when expecting to be SAE.

 

[greygoat]

Some Zerk"s are "Drive in", not threaded! Look
at it close..has it got real threads, or just
tapered grooves?

 

[Billy NY]

You are right about that, this is definitely a threaded hole, as I removed the remaining fitting by unscrewing it to try and match it up.

Those drive ins/barbed-cause they remind me of plastic pipe fittings, I've noticed a tight grease gun tip can and will pull them out, I particularly do not like them for any kind of ag or construction equipment, our challenger compact has them on the loader bucket pins, quick tach pins and so on, some have come out, and of course I'm the only one who will drive one in even if temporarily, to grease, or even remove, clean and re lube a bucket pin because I can't keep a fitting in there, obviously time to drill and tap some in. I know they save money on the mfr.'s production, darned replacement tail wheel on my rotary mower has one, same darned problem, I don't think, from these experiences, they are worn a darn, maybe its the small ones or something I am missing, I would not buy a new piece of equipment if they were all driven fittings. Some of theses fittings, threaded or not, don't hold up either, makes a lot of work, searching/repairing sometimes for the simple task of greasing a pin, or what have you when the grease gun tip will not release and pulls the fitting out. Something seems off on that too, maybe an old tip may have some wear or the fitting dimensions are off, tip slides on, have to hold a certain position or the grease goes out the side, all the monkeying around, they often times come out, real pain in the neck and can be time consuming.

 

[Billy NY]

Donovan, thanks for the link, boy if they don't have it, no one does, (like those kinds of places know of them but have never ordered from there)

It turns out to be a metric, M6 was a little wobbly threading in, but the original was too, so I backed that one out, put the M6 in, then carefully felt my way through tightening it up, after doing the same for the original. I haphazardly mixed up from another package, a 1/4-28, LOL gee, not an M6, now what, then reached for another, did the above. The darn things are so small, even with a thread pitch gauge you need a magnifying glass to see if it fits.

I went and picked up a 17/64" bit, I have a jug of old rigid cutting oil, boy does that stuff reek ! I have 2 old tap & die sets, one a No. 7 from memory, a Greenfield in a wood box, which was my grandfathers, whom was a chief engineer on ships, it was never used, until I got it, in the box, cosmolene (sp?) paper, brown sticky lube on the taps, he passed 2 years before I was born, won't take any chances with breaking those taps, incidentally, I like old school machinist and similar tools like these, reminds a person of the quality we were producing in those days !