All possible Threads on PM1030V? (Edited out PM25V)

B

Bill Kahn

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On my (edited out the reference to PM25V—dumb error on my part) PM1030 many useful TPI are listed and the appropriate change gear set ups are listed. (And metric too.)

I was trying to figure out how to get 27 TPI. I did find some change gear combinations whose ratios work properly, but none of them geometrically fit. (Hard to explain, but the gear train can be too "short" in total length for example. Or, two small gears can not be gotten close enough together. And other funny constraints.)

There are many TPI that are possible that are not listed. 27 TPI just doesn't happen to be one of them. (Well, I don't think it is, but I feel like I worked through the options exhaustively. Maybe I missed a branch of the option tree)

Does there exist anywhere a comprehensive list of all TPI that are, actually, possible on this lathe? (And metric too.) I guess I could try to program in all the geometric constraints and enumerate, but perhaps someone has already done this.

Thanks.

-Bill
 
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I am not familiar with your lathe, but generally, say if the gear on the change box is say, 32 teeth, you set the change box for 32 TPI and replace the gear with a 27 tooth gear, or a multiple of that number, and setting the change box accordingly; bottom line, you need a 27 tooth change gear to cut 27 TPI. Very few lathes are set up to cut that number of threads.
 
I thought the PM25V was a milling machine? I'm corn-fused
-Mark
 
:)
I would call PM and ask- you might have to buy a gear from another vendor like Boston or Martin if PM can't provide one to cut 27 tpi
 
Ok, simple question. What are you threading that is 27tpi? I don't see anything on my tap chart with that pitch except a NPT which you can't really do on normal lathe.

Joe
 
Liljoebrshooter said:
Ok, simple question. What are you threading that is 27tpi? I don't see anything on my tap chart with that pitch except a NPT which you can't really do on normal lathe.

Joe
Click to expand...
Well, I am a hobbiest. Not doing anything that actually matters. Just playing. So, two reasons:
  1. Just interested in the capabilities of the machine. As simple as a lathe may be in theory—round and round, scrape and scrape—in practice it is endlessly fascinating. One of the hundreds of fascinations is simply what are all the possible TPI possible with any particular set of change gears. I realized I had not worked that one out and figured, perhaps, someone has been there before.
  2. And, as you guessed, I happened to have a small project running that, quite by accident, happens to be using 1/8-27 NPS (not NPT). I needed a small locking nut. But, that costs a dollar at the local big box. So, maybe better to make it. Could buy a tap instead for $10. OK, that does seem better. But hey, I am retired, and, I have a lathe. Instead I could spend weeks figuring out change gears and seeing if I could single point it instead. Maybe even figure out the key extra change gear I need, and buy the appropriate accountrements, and make the gear myself? I will not cast the steel to make the gear—there are limits to my silliness.
I am impressed you saw the silliness driving the interest.

-Bill
 
27 tpi, as it turns out, is more common than you might think. Microphone stands use it, and those little filter screens on the spout of your bathroom and kitchen faucets often have it too- Just call me Mr. Trivia :)
-Mark
 
There is a 1/8 - 27 NPS thread used in electrical fittings. You can buy 1/8-27 NPS threaded tubing at any electrical supply house. It was commonly used for lamp fittings.
 
I did some scratching at the numbers, with all the change gears there is a multitude of combinations and all one really cares about are those that you will be using/need. It is also very time consuming to put together an Excel spreadsheet, and the spindle drive gear tooth count is unknown. I looked at the 26 and 28 TPI and looked at the gear combination that would be in between the two. Looks like any combination that gives a 1:1 input drive and a 2:1 output drive should give a 27 TPI. If you have no duplicate gears then you can adjust the combinations to give a 2:1 final output if I have my numbers correct.

Gear Chart.jpg
 
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