Metric Thread Pitch on PM1340 Lathe

[Dpaul7]

Thanks for getting back. The spread sheet I was referring to came from the following thread - (See link below) - regarding a metric threading question posted by David Best.
https://www.hobby-machinist.com/threads/metric-thread-pitch-on-pm1340-lathe.59976/

The link to the spread sheet in question is part of the last post at the bottom of the above thread. (see link for spread sheet below)

http://s000.tinyupload.com/index.php?file_id=41165643326520255331

Re: my lathe: I purchased the 1340GT 2 years ago with the standard gears 40T and 32T w/ the 120T / 127T
I am interested in being able to cut 0.8 and 1.75 mm thread pitch same as in the post. Also need a 46 tpi which is not readily available as far as I know. Thanks again David P.

 

[B2]

@Dpaul7

Yes, that is a very old link and it does not work for me either. However, others have posted simple spread sheets for your lathe. The issue with the Lathe manuals is that they only provide a few of the gear combinations for the exact threads that are available and usually none of the approximate threads.

Meanwhile I provided you what you need if you just look at the table I posted for you last night. Remember that TPI=1/(mm/T)/25.4). Just look for the equivalent TPI value and then scan across the table and you will find the MM/T calculated, just after the last gear tooth list column. The PM1340GT is suppose to come with 30, 32, 40, 40, 120/127 gears. So how close can you get to what you want without the 35T gear. I content close enough and sometimes exactly. The pdf table I supplied you has the TPI listed in the first column. Or you can search this table for 3 digits of what you are seeking. For example use the pdf find command on 31.7 and see if it does not work. So:

31.75TPI is the same as 0.8mm/T You will find multiple options for cutting this thread with the gears that you have. See Pge 18 of the pdf table.

1.75mm/T is the same as 14.51286TPI So when you look up this TPI in the table you will find options that are very close, but unless you have the 35T not exact. However, within less than 0.03% error. Is this not close enough??? Try 14.55208 (5-B-30/120/127/32) or 14.40000, where the last gear listed is at the top near the spindle. Even the error on the last one is only 0.1/14.5123~ 0.6%. Unless you are really very good at threading want the threads really tight this should be fine. Besides who says the mate for this thread will be this good. See page 12 of the table.

As for 46TPI. Your 30,32,40 gears will yield 45.9619TPI (3-D-40-120/127-32), which is very close. 0.04/46 <0.088% If you have the 35Tyou can be exact but is there really much difference!. You can also reach 46.5667TPI (~1.2%) with your gears. See page 22 of the table.

There is a lot of info in that table.

Dave L.

 

[Dpaul7]

That is an awesome table! That should get me where I need to be. Thanks!

 

[mksj]

Paul,
I had posted a complete gear table years ago for the 1340GT and a few other lathes. A 30-127 and 120-32 will give you a 46.03 TPI under D7. In metric a 0.8 pitch is a standard gearing 40-127 and 120-30 with D4. A metric 1.75 requires a 35T gear, I had one and sold it with my 1340GT but you might check with QMT if they might become available down the line. My current lathe has a universal gearbox, so if there is something you need threaded I might be able to help you.

 

[B2]

@mksj & @Dpaul7

Interesting Mark. I had just over looked the 7-D 30-127 and 120-32 listing, in the pdf table I posted for Paul , but it is there. The difference is that my calculations indicate that this yields a 46.06299~46.063 not 46.03. Are you sure about your number? I did not check your work.
It all is rather moot as it is unlikely that there are very many lathes/operators that will work with that precision anyway!

Paul, it also appears that my statement that a 35T would get you an exact 46 was not correct either. At more like ~ 46.3 it it would not be as good! It appears that with the 30, 32, 35 40, 40 gears you cannot get an exact 46TPI. You can look at my table and see all values that are possible, then select one and you have a gear set that got that number.

Dave L.