11.5 TPI

[Just for fun]

Looks like a good idea Ken, I'll have to check out the spreadsheet after while though as I'm on my phone now.

 

[Ischgl99]

I made the same mistake Mark did in his spreadsheet and had my formulas set up to slow the lead screw and not speed it up as would be needed to go from 14 to 11.5. Once I realized that, I found a combination you can get pretty close with your using your existing change gears. If you put the 32 gear on the 120 gear in the top position, and the 30 gear on the 127 on the banjo, you will get about 11.57. For a short hose fitting, that should be close enough to work, at least it’s worth a try since you already have the gears you need. I verified it on my lathe and it comes out almost spot on to the calculation.

 

[B2]

I did not come up with 11.5175 TPI with your gearing options. Here is what I had. 30-127 and 120-32 Norton box at B7, looks more like 15 TPI.

Doing the math on that gear combo, 30/127 * 120/32 * .125 * .6153848 = .068141 pitch, hence (14.676)

Hi Tim,
Thanks for the posting. This is helpful and seems to confirm my Excel work book.. Since I only have my lathes to work with I cannot check the other lathe sheets for accuracy with out your contributions.

I think maybe we have miss-communicated as to how the external gears are arranged. I am sorry if my first posting was not clear.

Interestingly @Ken226 pointed out that the 14.676 would be close to your measurement. I think the 30/127 * 120/32 external gear combo is what your photo shows, where the 32T is connected to the Norton gear box and the 30T is at the spindle. I think he used 1.25*0.6153848=0.80890 as the pass through pitch ratio for all the other gears, including B7 of the Norton box. My spread sheet also predicts 14.676TPI for this configuration. So it appears to be in agreement and ok .... atleast for this configuration!

My suggestion for gear arrangement had the 32T/120T at the spindle and the 30T/127T at the Norton gear box input, the opposite of your photo...... again, I am sorry if this was not clear.

Note:
30/127 * 120/32=.8858 Ken's value, where as
32/120 * 127/30=1/.8858=1.1289 and so .8858/1.1289=0.7847. (0.7847*14.676=11.5157TPI), better still
Using Ken's equation:
32/120*127/30*0.125*0.6153848=0.086838 pitch(in/thread) or 11.5157 TPI

I realize that my Excel workbook is complex. However, if you open it and select the tab (sheet) uwPM1340 you will have the calculations for the PM1340 which is the same as the PM1236. The cell at Column "I", line 30 show what Norton gear # has been selected, cell N30 is for the Norton Letters. These are pull down menus and if you click on it, to high light it, it should give you an arrow to choose from a list of Norton gear position 1 through 7. If you select a a different number then you should see the new TPI value in cell F24, (Column F, line 24). (The thread pitch appears in cell F25. Metric equivalents are shown at the far right in column W) You can make similar selections in each of the cells I30 to V30 to set up a set of gears. With each of these selections the TIP value of cell F25 will change.

The order of these columns (or gears) start at the right, V30, corresponds to the gear at the spindle moving from gear to gear to the input to the Norton Box at "O30". Below these cells in the rows in orange color you will find the gears via tooth number available for selection. If the you want to add to these possibilities you my do so by just typing in the integer number of teeth on the new gear... i.e. 30, 32, 40, 46 etc. and they should appear in the selection list. The Zzz indicates the last gear available for the macros so do not delete it, just type it farther down if need be.

Thanks again for making the thread cut and the excellent pictures!

Dave L.

 

[Just for fun]

Thanks Dave,

I thought that was probably the case about me mixing up the gears especially after reading @Ischgl99 post about the gearing he has used.

I was just checking out your spreadsheet but I'm not getting it. On the spreadsheet, I changed the gears to 32-120 and 127-30 then for the Norton box I set to Seven and B. In position F24 shows 14.675556

 

[Just for fun]

I just got it..... I'm not sure what I changed but I have the right numbers now..

 

[B2]

Great! Thanks. The 14.675556 that you had was the same as the 14.676 that Ken had. So you may have had the gears at the top and bottom reversed in the spread sheet cell locations. Anyway, the column names (cells just above the pull down menus) for the gear cells are a little cryptic ... in order to get them to fit in the column width.

"Spindle" gear, 32T, is spread sheet cell V30;
"A2Spin" (gear A contacting to Spindle gear, "2" => contacting to), 120T, is spread sheet cell U30
"C-C" gear, 127T, is spread sheet cell P30
"Screw2C" gear, 30T, is spread sheet cell O30
and the Norton gear box levers at B7 should yield the 11.5157 TPI

Because in the 1236 (and 1340) there are no other shafts for intermediate gears nor coupling gears, the columns
C2B, B-B, B2A, and A-A all contain gears or gear ratios of 1. This then causes C-C to be in contact with A2Spin and so both turn at the same rate. It is the two halves of the 120/127 change gear.

These extra shafts columns, C2B, B-B, B2A, and A-A allow folks with lathes which do not have gear boxes with levers (like the Norton box) to alter the spread sheet to make more complex sets of manual exchange gears. Be grateful for having a Norton gear Box! The PM1440GT has a gear box, but not a Norton and it is not nearly as intuitive to use!

FYI:

Attached is a screen shot of the part of the spread sheet of interest with the gear set up just described. This should look similar to the first lines of the threading spread sheet that I first posted for you the other day. "TPI PM1340GT-1236 M421_1443 M921.pdf". It was generated via the macros : Run1 : "GenAllTIP_14" to generate a list of all possible TPI values in the sheet called AllTPI located at the left of the WorkBook Tabs, then Run2 : "SortAllTIP_1Col" to sort each line by increasing TPI, then Run3 : "SearchTPI_At_TPI_Col" . You do not need to do the sort, each macro runs independently.

By the way, in the file name the M921 means today's date: M=>22nd year (2022), 9=> September, 26=> 26th day.

Likewise, in the file name M421_1443 is the date and time I last made significant changes to the spread sheet. 2022, April 21, at 1443 hundred hours (2:43PM). This short hand date-time stamp is how I keep versions of files in order without typing out a long file name. This should be the same date and time stamp that was on the spread sheet that you downloaded from my posting back in April.

Dave L.

PS. It is nice to know that someone else has actually run the workbook. I got very little feed back on it. Thanks.

 

[Just for fun]

I tried the gears you recommended and it looks pretty darn close.

 

[B2]

Hi Tim,

Fantastic! Congratulations and thanks. And now you also know how to use the workbook! What a high quality photo.

Looks dead-on to me, but then you probably need to turn the spindle at least 11.5157 x100 =1151 times and measure the 10.0 inch length accurately to be completely sure! I can do that with my digital spindle counter and the DRO pretty quickly. However, there is something very satisfying about a scratch cut confirmation.

Dave L.