Cutting 27tpi On Grizzly G4003g

Lamp brass tube fittings are 27 TPI. Lathe makers ought to include this thread,much as it is used.
 
Re: using an approximate thread pitch, 1/8-27 NPT threads are a sealing thread and an approximate thread may begin to bind up before full contact of the mating threads is made. Use of a good pipe sealant or silicone gasket sealant may allow a seal to be made, however.

Another possible solution would be to cut the approximate thread and chase the thread with a 1/8-27 NPT die.

Bob
 
dave2176 said:
If my math is correct here, (somebody feel free to jump in) 27 tpi is .03703" pitch.
45 gear on F and 60 gear on G with QCGB set at C3 it will produce a metric thread pitch of .9473mm. So .9473 times .0393 thousandths in a millimeter equals a pitch of .03722" which is less than .0002" off per thread. Should be close enough.

The bad thing is you are cutting metric so not so easy as with full thread dial use.

Dave
Click to expand...

Dave, I couldn't get your solution to work until I realized I needed the reduction of the 86/91 intermediate gear. With a 45T at F meshed with the 91t intermediate, and the 86T of the intermediate meshed with a 60T at G it comes out to 26.8 tpi. You probably accounted for that which is why you mentioned metric threads but it went over my head. I haven't checked this in real life yet but it looks like the answer. Thanks for the help to you and all the others that responded.
 
epanzella said:
Dave, I couldn't get your solution to work until I realized I needed the reduction of the 86/91 intermediate gear. With a 45T at F meshed with the 91t intermediate, and the 86T of the intermediate meshed with a 60T at G it comes out to 26.8 tpi.
Click to expand...
I just looked on page 32 of the PDF manual where it like gear combinations for metric threads. There are a lot of blanks in the table so I was looking for something between 1.0-2.0mm threads to calculate the blanks spaces. Yes you have to use the 86/91 gears. In the 45/60 combination it list C1 as 1.125mm so C2 = 1.125 / 1.125(ratio difference) = 1.0, C3 is 1.125(C1) / 1.1875 = .9473 which is as close as I could find.

BTW, 11.5 above was mentioned as one that is missing on most lathes. 2.2mm is .08646" pitch which is only .00049" off per thread. Should be doable.

Let us know how it works,
Dave
 
dave2176 said:
I just looked on page 32 of the PDF manual where it like gear combinations for metric threads. There are a lot of blanks in the table so I was looking for something between 1.0-2.0mm threads to calculate the blanks spaces. Yes you have to use the 86/91 gears. In the 45/60 combination it list C1 as 1.125mm so C2 = 1.125 / 1.125(ratio difference) = 1.0, C3 is 1.125(C1) / 1.1875 = .9473 which is as close as I could find.

BTW, 11.5 above was mentioned as one that is missing on most lathes. 2.2mm is .08646" pitch which is only .00049" off per thread. Should be doable.

Let us know how it works,
Dave
Click to expand...
You saved me a lot of time. I started working out every possible gear combination of F, G and intermediate gears. I started at the low end with 26T at F and 40T at G. I worked out each combination of the intermediate with 86/91, 91/86 and no change. By the time I would have gotten to F45T and G60T my calculator would have blown up. As soon as I read your post I left where I was and went right to 45/60.. Thanks for the rescue.
Ed P
 
Back when I was working as a design engineer at HP, my job duties frequently included mentoring newly graduated/hired mechanical engineers - very intelligent and industrious individuals every one. But their curriculum had lots of gaps. One of the fun things I'd tell them was that there was nothing about a ½" pipe that was actually one half inch.
 
Just a followup. The 45/91 86/60 set up works. With the QC gearbox set at 19 tpi It produces 26.8 tpi and I can screw it in to a 27tpi fitting about 3/8 inch by hand. Thanks all.
 
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