Tap Terminology: For Light Fixture Threaded Tube

[nickel-city-fab]

Several ways to get there, but you do need gears not on the standard setup.

Yes indeed, and I thank goodness for the SB documentation and support. I know Paul has that lathe, same as me -- so the specific info might be useful to him. In a similar vein, I have wondered for years about how to calculate the gears for oddballs, when you already have the QCGB.All the available pitches on the SB step by increments of two, so I wonder how to calculate the necessary gears to get all the "in betweens".

[J Tiers]

Yes indeed, and I thank goodness for the SB documentation and support. I know Paul has that lathe, same as me -- so the specific info might be useful to him. In a similar vein, I have wondered for years about how to calculate the gears for oddballs, when you already have the QCGB.All the available pitches on the SB step by increments of two, so I wonder how to calculate the necessary gears to get all the "in betweens".

In many cases you can do as you did in your first post, find a pitch that is very close, then figure the "offset" from that to get the new number of teeth needed.

Or start from the fact that you are wanting a certain number of turns of the leadscrew per turn of the spindle. (or more usually, turns of the spindle per leadscrew turn)

[Paul Alciatore]

Gary,

In case you did not notice in my photo, I HAVE a standard, inexpensive nut. It came with the fixture which came with the house.

I WISH to make a different type of nut that, according to several hours or searching, CAN NOT BE PURCHASED. I looked! I asked at more then one home supply! They tried, but all I got was head shaking.

The point of this post is to know what TAP to order, not to find a nut that is exceedingly common and usually fairly inexpensive. I am not stupid, just not completely informed on the fine points of pipe/tubing threads.

Jihe,

I have a metric 10x1 tap and it may make a loose fitting thread that would work. But for my idea, the difference (27 TPI - 25.4 TPI = 2.6 TPI) is probably too much. It would weaken the grip and I will only have a few threads engaged.

Buy the nut, cheaper than the tap. It is a very common fixture part. When I was a kid I worked weekends with my dad wiring houses. My job was assembling all the lighting fixtures, chandeliers and the like.

[Paul Alciatore]

I do have the gears (16, 54) to do 27 TPI on my SB-9, but I would rather take the easy route and get the tap.

First I would have to do an actual, three wire measure of the thread. Then make one or two (go - no go) male test plugs and then grind an internal threading tool. Or I could just use the sample in my photo and make it a somewhat loose fit. I may be retired, but I have better ways to use my time.

the "brass threads" series is different from most others. A lot are 27 tpi, which just happens NOT to be available with a lot of QCGB lathes unless you add gears to the QCGB drive.

[nickel-city-fab]

Paul -- I may have one that you can have. It's labelled "1/8-27 NPS"
If you think that'll work, just PM me a mailing address and I'll drop it in a small envelope.
Brand new, it was a mistaken purchase.
I wanted NPT and the gave me this instead.

I do have the gears (16, 54) to do 27 TPI on my SB-9, but I would rather take the easy route and get the tap.

First I would have to do an actual, three wire measure of the thread. Then make one or two (go - no go) male test plugs and then grind an internal threading tool. Or I could just use the sample in my photo and make it a somewhat loose fit. I may be retired, but I have better ways to use my time.

[wierdscience]

https://www.amazon.com/uxcell-Machine-Straight-Thread-Flutes/dp/B07VDSWY2B/ref=pd_bxgy_2/147-0166383-2474359?pd_rd_w=pqEmk&pf_rd_p=c64372fa-c41c-422e-990d-9e034f73989b&pf_rd_r=R2JGCNK83G4WSFAXJFRD&pd_rd_r=ff565e14-0713-4396-887c-2d059877e380&pd_rd_wg=6VeYB&pd_rd_i=B07VDSWY2B&psc=1

[Paul Alciatore]

Dave,

Thanks for the link. I had looked on the web already, but I clicked on your link. And I looked at five pages of lamp (shade) nuts. Some are quite beautiful.

But MY nut isn't there. Not only is it not there, but none of the ones that are would be even a good starting point for making it.

I AM going to buy a tap and make one the way I want. So, I am asking about a TAP. In the Army, in the 9th Infantry Division, 709 Maintenance Battalion, in Vietnam I was the real "scrounger" of Hollywood military fame. If they needed it, I found it. In my civilian career I often had to find "impossible" items and I did. I do not think my nut exists anywhere in the world. I AM going to make one and I need the tap. I just lack the proper terminology for that particular thread. That is all I am asking for here.

Amazon.com : lamp shade nut Take your pick, no tap needed.

[nickel-city-fab]

Well, I can maybe save you a few bucks if you're interested in the tap I have. Not sure if NPS will work but maybe.

I AM going to buy a tap and make one the way I want.

[Beazld]

You can use a regular 1/8” pipe tap, just run it in deep enough to thread on the nipple. It’s not a high torque joint or something that will leak, and 1/8” NPT taps are cheap. Carbon tap is all you probably need.

[reggie_obe]

The tap you seek is not listed at Grand Brass?

[Paul Alciatore]

Hijacking my own thread:

For better or worse, there are advantages and disadvantages both ways, my SB-9 does not have the QC gear box. It uses manual change gears. So the 16, 54 tooth gears I posted does the trick.

Using Excel, I have calculated a table that includes all possible gear combinations with the actual change gears that I have, including three compound gears which provide fixed ratios (1::3, 1::4, and 1::6). I then picked the more useful threads from that list and made a somewhat short table of all the threads I should be able to cut. I say "should" because some gear combos can not be set up on a two arm banjo and I have not actually tested all of them. There are a number of duplicate combinations in that short list so if one set-up does not work, I can try another.

Anyway, the ah-ha moment in this undertaking is to realize that all the prime numbers in the TPI number MUST be present either in the lead screw's TPI or in the gear tooth counts. A 10 TPI lead screw provides only two primes, 2 and 5. An 8 TPI would provide 2, 2, and 2. That's three 2s. Other lead screws provide other combinations of primes.

27 TPI is 3 x 3 x 3 = 27. You need three 3s somewhere. My lead screw and probably yours is 8 TPI and that does not provide any 3s. So my 16, 54 gear combo gets the needed 3s from the 54 tooth gear (2 x 3 x 3 x 3). The 16 tooth gear provides four 2s which are also needed to cancel out the three 2s in the lead screw and the other 2 in the 54 tooth gear. This is a example, but not the way that I calculated the gear ratios.

The actual calculations look something like this:

TPIcut = TPIleadscrew x screw gear / stud gear

So with my 27 TPI set-up it is:

TPIcut = 8 TPI x 54 / 16
or
TPIcut = 2 x 2 x 2 x 2 x 3 x 3 x 3 / (2 x 2 x 2 x 2)
which reduces to
TPIcut = 27

Where screw gear is the gear on the lead screw and stud gear is the gear on the stud next to the tumbler reverse gears. And you probably need an idler gear between them to make them meet, but it's tooth count does not matter so any gear that makes it fit will work there.

For a lathe with a QC gear box you need to work with the TPIs that are provided by that box and use a different change gear combo leading up to the box to change the existing TPIs into the desired ones. This work has been done and there are a number of published tables on the web for 8 TPI lead screws. When doing this, the only numbers that matter are the TPIs that are available on the QC gear box and the change gears used with those settings. The TPI of the lead screw does not matter at that point: it is already present in the QC box settings. A good starting point for any specific TPI would be to find a TPI on the QC gear box that has as many of the prime numbers as desired, "in between" TPI that you want. So an 18 TPI setting may be a good start for 27 TPI. Or perhaps 36 TPI.

27 TPI = 18 TPI X 3 / 2

So a 3 / 2 TPI combo gear would work. But no gear has 2 or 3 teeth so you multiply up to keep the same ratio. Perhaps a factor of 8 for 2 x 8 = 16 and 3 x 8 = 24. Then you look at the change gear chain leading to the QC box and see how you can change it to incorporate that ADDITIONAL gear ratio. Often that can be done by just changing one gear. Depending on where it is located in the gear train, an existing 24 tooth gear could be changed to 24 x 3 / 2 = 36 or 24 x 2 / 3 = 16.

Yes indeed, and I thank goodness for the SB documentation and support. I know Paul has that lathe, same as me -- so the specific info might be useful to him. In a similar vein, I have wondered for years about how to calculate the gears for oddballs, when you already have the QCGB.All the available pitches on the SB step by increments of two, so I wonder how to calculate the necessary gears to get all the "in betweens".

[nickel-city-fab]

Wow, thanks Paul! Best explanation I've seen in a long time, copied and pasted and saved! Thanks again!

[Paul Alciatore]

I am getting the education I needed for this. Apparently there is no official "NPS". Everything in Machinist Handbook has a fourth letter which qualifies what it is intended for. "NPSM" seems to be the thread standard used for this type of lamp thread. Both MH and the chart Chipps posted above seem to agree on this. But "NPSL" is a looser version of that which allows a slightly larger OD, along with other differences. I think both would work for me and I suspect your "NPS" tap is actually "NPSM" so it should work.

I have sent a PM with my address. I will be glad to pay what you paid for it. Or a swap if I have anything you need.

Thanks a lot.

Paul -- I may have one that you can have. It's labelled "1/8-27 NPS"
If you think that'll work, just PM me a mailing address and I'll drop it in a small envelope.
Brand new, it was a mistaken purchase.
I wanted NPT and the gave me this instead.

[754]

Get a mic and measure the tap , it HAS TO BE at least 2 thou bigger than your thread.. or should be .
so my 1/8 NPS F measures at .3938..... got to be close to 10mm.
then I measured a Butterfield just marked 1/8 NPS..... UNDERNEATH IT HAD I THINK GH... it measured at .4035..
pretty sure that should be marked C for Coupler... meant to spin together easily.
what size does rod measure..

[nickel-city-fab]

What really gets my attention is that, here is a thread series I had never heard of nor dealt with.
That is very unusual, I collect tap sets like an addict.
I have:

UNC/UNF
M
ME (both series!)
BSW/BSF
BA (hehehehehe....)
And pre-war Singer Sewing machine tap sets.


I have heard of BSB
which could be either British Standard Brass,
or British Standard Bicycle
both of which are a constant-pitch 26TPI series if I recall.
And there is BSP (straight pipe taps)

... NEVER in a million years have I heard of this NPS series!