Thread major/minor for apparent M16L-11tpi thread?

[JasonPAtkins]

Hi all, a previous thread was closed, hopefully this will be more the the admin's liking.

Previous thread here: http://www.practicalmachinist.com/vb/general/frustrating-nut-320454/

The consensus was that my pedestal grinder from Portugal (in the 70's, when they were still using some inch stuff) might be threaded M16 but 11tpi. I'm as sure as I can be that it's 11tpi and not 2.0mm - the 11tpi thread gage definitely fits better.

The major is 0.6299" (16mm). I just used 11tpi thread measuring wires to get a thread diameter of 0.5703". I'm not very experience with non standard threads.

What will my ID of the nut be (external thread minor dia plus tolerance?) How much will I eventually feed a 29.5 degree compound once I touch off of that bored ID to cut the thread?

Thanks a lot, a weird thread like this is new territory for me, but I'd like to get my grinder fixed.

 

[Milland]

Perhaps the safest way to deal with this is make a test thread on a short shaft that matches your grinder thread on OD and measured pitch diameter. Then use this shaft for fitting the nuts you'll machine. You can make the nuts a little loose to ensure they'll work, a super-close fit to the grinder spindle isn't needed here.

After you've made the test thread, lay it into the grinder thread to ensure the longer section of 11tpi still matches.

 

[John Garner]

There's a rule of thumb for determining "tap drill diameter" -- which I'm pretty sure is what you're asking about -- for both the Unified (aka ISO Inch) and ISO Metric threadforms: tap drill diameter = Major Diameter minus Pitch. Using that rule of thumb, your tap drill diameter would be calculated as 16 millimeter minus 1/11 inch.

1/11 inch is very nearly 2.3 millimeters, making your tap drill diameter very near 13.7 millimeter.

As for the required infeed of the toolbit . . . it can theoretically be calculated, but it's dependent on the actual diameter of the yet-to-be-threaded hole, the infeed angle, and the length of the flat at the tip of the toolbit. It's a calculation I hesitate to make, and have found it's far more direct to simply make a short counterbore a proverbial hair over the Major Diameter at the mouth of the hole to be threaded. Color the counterbore surface with a permanent ink marker that contrasts with the metal color, use a toolbit with a proper-length flat at its tip, and stop cutting once the tip of the toolbit grazes the color.

John

 

[kevin66]

I could be wrong but Im willing to bet its a 5/8-11 thread.

 

[StinkyDan]

U been trying to figure this out for 2 years?

 

[JasonPAtkins]

I could be wrong but Im willing to bet its a 5/8-11 thread.

That would be wonderfully easy, but the Dewalt grinder sitting right next to it uses 5/8-11 nuts (one left and one right), and it won't thread. Half a revolution, but once yet get past the chamfer, it won't go any further.

The RH threaded nut for this Siemens grinder in question, the nut that I do have, will thread onto the 5/8-11 thread of the Dewalt spindle, but the reverse is not true - which makes sense given that this spindle measures over the OD it should for a 5/8-11 thread.

Wish it were that easy! If I, for some reason, had an M16L-11tpi tap, I'm pretty sure I could run it through a normal 5/8-11 nut and I'd be off to the races. Don't seem to have that tap sitting in my toolbox though!

 

[JasonPAtkins]

U been trying to figure this out for 2 years?

Living in West Africa for a decade has taught me the value of refocusing on something you *can* push forward when you hit an unsolvable dead end.

It's also greatly heightened my tolerance for working with half-broken equipment, unfortunately.

The other side of the grinder works fine, and I have five pedestal grinder spindles in my shop. To be honest, I don't really need the 6th, I just don't like it having beaten me!

 

[HuFlungDung]

Even a true 16mm male thread probably shouldn't be a full .6299" OD, as any bit of contamination or denting in handling can make the nut want to seize on. Does the male thread appear to have a sharp crest? It might just have a burr raised that could be filed off. I'd probably just file the damn thing down to .624" OD anyways, to avoid having to have a 'special nut' for one damn machine.

Edit: scratch that, I checked the PD you gave, it does appear to be a bastard metric.

 

[DMF_TomB]

i have seen rod start out .625 diameter and get bigger cause the dull thread die pushed the metal around a bit and made it bigger diameter like .630 dia.
.
dont matter its still a 5/8-11 thread cant get nut on, run a file on it while turning or use a hand thread die. only take maybe 10 seconds either way

 

[MrWhoopee]

Triangular file, thread chasing file or threading die...
Make it fit a 5/8-11 one way or another.