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12teethperinch
01-15-2014, 11:57 PM
I have a imperial quick change southbend 10k. I would like to cut this 15 tpi thread, there isnt 15tpi on the chart. Does this need to be done on a change gear lathe or is there a way to do it in my lathe?

winchman
01-16-2014, 03:13 AM
Assuming your lead screw is 8tpi, you'll need to get a ratio of 1.875... to 1 between the spindle and the lead screw to get a feed of 0.0666... or 15tpi.

Please tell us why you want a 15tpi thread on something. The only reason I can think of is so that it won't fit anything else that's ever been made.

RussZHC
01-16-2014, 07:17 AM
At one point there must have been something w 15 tpi, my 1930s Sheldon has it "native" two ways with change gears and semi quick change box but for the life of me I can't find any reference to that thread count currently (and, if I have not misread, it is not even quite close enough to a metric thread to be used that way). Its not tough w a 8 tpi lead screw, 32 tooth and 60 tooth will do it and those are very common change gears, of course depending on ratios in the quick change others too (16 tooth and 60 tooth in my case)

John Stevenson
01-16-2014, 07:49 AM
Please tell us why you want a 15tpi thread on something. The only reason I can think of is so that it won't fit anything else that's ever been made.

The reason he wants a 15 tpi is someone got there first. :p

EVguru
01-16-2014, 07:53 AM
Many people seem to get fixated on standard threads. The truth is there were all sorts of threads around before standards were drawn up. Many would have continued in use to save the cost of re-tooling and to maintain compatability. Then there are all the specials chosen for specific reasons (or on the whim of the designer).

martik
01-16-2014, 08:44 AM
If that's the 40 pos gear box with 18tpi at B2, a 24 tooth stud gear will make a 15tpi thread at position B2. Easy to cut with a form tool and piece of delrin.

12teethperinch
01-16-2014, 09:31 AM
Reason for the thread is to match the shaft of an old sheet metal bead roller i acquired. Some folks must 15 tpi otherwise why would they have a thread gauge for it:) i gave a couple of spare gears i will count the teeth and see what i have on hand to work with and report back.

rode2rouen
01-16-2014, 11:58 AM
At one point there must have been something w 15 tpi, my 1930s Sheldon has it "native"


My Sheldon R15 has it covered, along with quite a few other Imperial pitches.

http://i721.photobucket.com/albums/ww216/bjorn_toulouse/Sheldon%20R15%20Lathe/threadsfeeds.jpg


Rex

JoeCB
01-16-2014, 12:28 PM
Just checked an old screw thread book, sure enough nothing 15 tpi, dispite all kinds of other unusual threads. My 10" Atlas does have 15 tpi on the QC box, right along with it's multiples, 7.5, 30, 60. It seems that if your lathe has the more common 30 tpi , it should be simple to get 15 by 2X'ing the feed.
Joe B

winchman
01-16-2014, 04:21 PM
Now I'm confused. The picture Rex shows in post #8 has 15tpi at B10, but it's showing the feed as .0320. I thought the feed for 15tpi was .06667.

The other feeds appear to be off by a similar factor.... 4tpi is shown as .1200.

macona
01-16-2014, 05:46 PM
Feeds are when using the feed drive in the carriage and not the leadscrew and half nuts.

15 TPI is almost exactly .6mm pitch. Bet it is metric.

danlb
01-16-2014, 06:16 PM
Now I'm confused. The picture Rex shows in post #8 has 15tpi at B10, but it's showing the feed as .0320. I thought the feed for 15tpi was .06667.

The other feeds appear to be off by a similar factor.... 4tpi is shown as .1200.

If this is like other lathes, there is a lever for setting to either feed or thread. The same chart is used for both. When in feed mode it uses a different ratio so you get less carriage movement per revolution.


Dan

John Stevenson
01-16-2014, 06:47 PM
Feeds are when using the feed drive in the carriage and not the leadscrew and half nuts.

15 TPI is almost exactly .6mm pitch. Bet it is metric.


?? I get 1.69 mm

0.6 is 42.3 tpi

Don Young
01-16-2014, 09:51 PM
I don't know the purpose but Atlas gearboxes have the 15-30-60 ... position. Maybe that's one capability the Atlas has that many other lathes do not!!!

RichR
01-16-2014, 11:13 PM
I don't know the purpose but Atlas gearboxes have the 15-30-60 ... position.
These guys found a purpose for 30TPI:
http://www.practicalmachinist.com/vb/gunsmithing/5-16-30tpi-screw-126384/
The Atlas will also do 120TPI in case you need to make a #000-120 screw:
http://www.custompartnet.com/tap-size-chart
If you look at the quick change gearbox, it relies on selecting a row and a column forming a matrix. Each successive row doubles
the number of TPI of the row above it. There can be no holes in the matrix. Even if 15TPI is not needed for anything, it still has to
be there in order for 30, 60, and 120TPI to exist.

macona
01-17-2014, 12:09 AM
?? I get 1.69 mm

0.6 is 42.3 tpi

Doh, got it all backwards.

12teethperinch
01-21-2014, 11:04 PM
Ok I have a little more information. The first photo show the contraption I am trying to make the nut for the second shows the plate on my quick change.http://i1017.photobucket.com/albums/af296/12teethperinch/IMG_3797.jpghttp://i1017.photobucket.com/albums/af296/12teethperinch/IMG_3799.jpg Trying this on a new computer if the photos work I will comment further in the next post.

12teethperinch
01-21-2014, 11:35 PM
Ok That wasn't very good I will practice a bit and try posting photos. Anyone know how you paste from photo bucket so as to show the photo in the thread?

RichR
01-22-2014, 12:16 AM
Hi 12teethperinch
There is a sticky at the top of the General Forum on that topic. Basically, you place the address of the picture between image tags.
If you hit Quick Reply, it's the third button from the right.

kitno455
01-22-2014, 09:51 AM
Your images:

http://i1017.photobucket.com/albums/af296/12teethperinch/IMG_3797.jpg
http://i1017.photobucket.com/albums/af296/12teethperinch/IMG_3799.jpg

kitno455
01-22-2014, 12:58 PM
If you replace the 20 tooth stud gear with a 16 tooth gear, every pitch made by the gearbox will be 1.25 times as fine. So, the 12 tpi position will cut 15 tpi. The 16 tooth gear was part of the standard 9B and 9C set, and will fit your 10K. There are a couple of them on ebay right now.

allan

12teethperinch
01-22-2014, 02:36 PM
Thanks allan! I have a 32 tooth gear for a southbend. Will that work as well since its a mulitple of 16.
Darrell

kitno455
01-22-2014, 06:35 PM
Yes, if you replace the 20 with a 32, every pitch on the gearbox will be .625 times as fine (20/32=.625). The 24 tpi position will cut 15 tpi. (24*.625=15)

allan