9A QCB threads are wrong (my fault )

[animal12]

I just tried to do my first threading with my lathe . It's a 40 something 9A . I did the rebuild following directions in the Ilion book but somewhere I messed something up & my threads don't match the gear chart . I have the Army TM parts list
but it dosn't tell the teeth count on all of the gears . Can someone point me towards a Parts drawing of the gear box that has the teeth count of all the gears ? I'm sure it's something that I got crossed up on & a drawing with gear counts would
get me back in the running .
thanks
animal

 

[iwananew10K]

what do you end up with when the gearbox is set for 8tpi?

 

[animal12]

I'll got back to the shop tomorrow & see . I was trying for a 16 tpi & the results came out much finer .
thanks
animal

 

[SLK001]

The parts list shows the number of teeth in each gear. The number of teeth is also in the part number of the gear. For instance, part # PT615K22NK1 is a 22 tooth gear.

My army tech manual is from December, 1980 and it shows all the numbers of gear teeth.

 

[animal12]

OK it looks like I'm getting 32 tpi & I'm trying to get 16 , so I'guessing I have one of the non internal gear box gears off . MY Army manual does not have all the gears numbered that way . No 37 in drawing shows part # as PT621NK1 for example , so teh number after the 6 is the tooth count ?I also have gear numbers for the gears in the gearbos numbered PT615K20NK1 & this is where my confusion comes in . I even tried looking up one of the gear part #s through google & it came up with another tooth count .I'm trying to figure out where I saved the owners manual I DL'd so I can read up on the gear settings for the left side of the lathe .
thanks
animal

 

[SLK001]

Here's a screen capture of the .pdf page you are needing:

You might try to download the later manual.

 

[johnoder]

Go to Steve Well's page (by way of Steve's Serial Number thread), then catalogs and pull up catalog 50. Page 25 has a good sized view of QC tag

so I can read up on the gear settings for the left side of the lathe

There are only two differing "stud" gears for left end - a 40 and a 20 - same as shown on left side of QC tag

 

[animal12]

I think I have made a MAJOR ROOKIE MISTAKE , I've veen using the clutch instead of the half nuts . Will retry & report back tomorrow .
thanks
animal

 

[johnoder]

I think I have made a MAJOR ROOKIE MISTAKE , I've veen using the clutch instead of the half nuts . Will retry & report back tomorrow .
thanks
animal

Yep - one is repeatable threads and the other is a mess

 

[SLK001]

Yep - one is repeatable threads and the other is a mess

I'm curious as to how the OP could have cut any threads at all. He must have been very good and very fast on that clutch!

animal, here's the thread and feed chart for a Heavy 10. Using the clutch, the feed is about 1/3 the rate as using the half nuts. On a 9", it is also about 1/3 the rate as the half nuts, but the two (9A and H10 feed rates) aren't exactly the same.

At least you can say your rookie mistake didn't damage anything!

 

[animal12]

Thank you folks for all the insight . I got a bit of time to get out in the shop today & it appears that all is well in the universe !!
Question , if I am threading but using a crank in the spindle & not under power do I still use back gear ? I pulled the hand wheel off my home made tapping setup cause it was way to small for tapping anything over 10-32 & I made a locking sleave that fits in the outboard end of the spindle . It's really too small for that & thinkin if Im not in back gear it may turn easier .
thanks again
animal

 

[johnoder]

Not using back gear just means you lost the 6 or 8 to one mechanical advantage if you are trying to turn the spindle cone pulley - try it

 

[SLK001]

Yeah, what Jon said above. If you can thread manually out of back gear, go for it. However, your arms will thank you for using the back gears!

 

[500mpxlcameraguy]

Disengage the drive belt when you are threading by hand and you will not have turn the motor. I’ve done that many times in “metric” mode and my shoulder was very appreciative of a little less work.

 

[SLK001]

Disengage the drive belt when you are threading by hand and you will not have turn the motor. I’ve done that many times in “metric” mode and my shoulder was very appreciative of a little less work.

If you're going to a lot of threading by hand, it helps to have a spindle crank on hand. Here's one I made for my H10.

 

[animal12]

Cool , thanks for that ! Saved & printed & on the stack for the next time I get out to the shop .
animal