@evan-e-cent
Hi, Thank you for responding. I had forgotten all about contributing to your thread.
I am still curious if you too have found that the cross-feed rates listed on many lathe model front plates are inaccurate?
WRT to your interest in alternative gearing for metric-imperial conversion gears you may find my excel program useful for testing your concepts. In any of the lathe model spread sheets in my work book you will find three shafts/axles set up just to provide for this. For example if you look at a lathe tab such as uwPM1440GT you will find these at columns P thru U. Shafts A, B, C correspond to two columns each (front and rear gears). Look at columns T and U for the traditional 127/120 combination. The gear in a column U will contact the gear at column V (the spindle gear). etc.... The gears at columns T and U are on the same shaft and so are tied to each other. (Each time one revolves a single turn so does the other.)
If you did not spend time with this before, the spread sheets can be operated manually via the pull down menus at cells (row 30, columns I thru V). You can insert new gears in the cells below row 30 for each of the shaft columns and move the "z" flag down. So by putting new, various gears, at the three external gear shafts you can create upto 3 compounded translation gears. You select the gears to compute with via the pull down menus at cells of row 30 and the resulting TPI and mm/T results cells, E24 and X24 respectively . You can do this for any of the lathe models and since you are using it manually you do not have to use the macros, so can use spread sheet that is not zipped. However, for the tables etc. the macros will save a lot of effort.
Obviously because, the conversion between metric and imperial is 25.4 mm/inch exactly the gear with 127 teeth is special. 127*2= 254. or 10x25.4. However, a 127 tooth gear is pretty big in diameter for most lathes. The 120 tooth gear is of less importance and is used to match up to the other gears. Many of the Imperial lathes use a 30 or 60 tooth gear at the spindle or gear box and so 120 matches these via factors of 2.
The ratio of the 120/127 = .94488 . So a close approximation to this is 95/100=.95 while 95/101=.94059 both of which are only off by about 1/2 of a percent. So some smaller lathes use transfer gears with these number of teeth. By the way, most hobby machinist probably do not cut threads long enough, and tight/accurate enough, to ever notice this amount of error and since most simple thread matching indicators do not have enough teeth to measure this.
If you download the zipped version of my spread sheet and then run it to generate an AllTPI table. You can then use the srchlist macro generate the search corresponding to sheet named uwSrchList to get the standard threads. For example, I will post an image below. In column B are listed the number of possible gear combinations to get to the metric thread (approximate) value listed at column A. For example, Cell A7 is for 4mm/thread where the * indicates the approximation decimal place. Cell B7 indicates the 4 possible gear arrangements are available to get to this extremely accurate value. (As shown at Cell E1, this was done for the lathe model uwPM1228VF-LB). There is another sheet generated which lists these gear arrangements, along with all of the others in this list.
I look forward to hearing about your work on metric conversion.
Dave L.
Hi, Thank you for responding. I had forgotten all about contributing to your thread.
I am still curious if you too have found that the cross-feed rates listed on many lathe model front plates are inaccurate?
WRT to your interest in alternative gearing for metric-imperial conversion gears you may find my excel program useful for testing your concepts. In any of the lathe model spread sheets in my work book you will find three shafts/axles set up just to provide for this. For example if you look at a lathe tab such as uwPM1440GT you will find these at columns P thru U. Shafts A, B, C correspond to two columns each (front and rear gears). Look at columns T and U for the traditional 127/120 combination. The gear in a column U will contact the gear at column V (the spindle gear). etc.... The gears at columns T and U are on the same shaft and so are tied to each other. (Each time one revolves a single turn so does the other.)
If you did not spend time with this before, the spread sheets can be operated manually via the pull down menus at cells (row 30, columns I thru V). You can insert new gears in the cells below row 30 for each of the shaft columns and move the "z" flag down. So by putting new, various gears, at the three external gear shafts you can create upto 3 compounded translation gears. You select the gears to compute with via the pull down menus at cells of row 30 and the resulting TPI and mm/T results cells, E24 and X24 respectively . You can do this for any of the lathe models and since you are using it manually you do not have to use the macros, so can use spread sheet that is not zipped. However, for the tables etc. the macros will save a lot of effort.
Obviously because, the conversion between metric and imperial is 25.4 mm/inch exactly the gear with 127 teeth is special. 127*2= 254. or 10x25.4. However, a 127 tooth gear is pretty big in diameter for most lathes. The 120 tooth gear is of less importance and is used to match up to the other gears. Many of the Imperial lathes use a 30 or 60 tooth gear at the spindle or gear box and so 120 matches these via factors of 2.
The ratio of the 120/127 = .94488 . So a close approximation to this is 95/100=.95 while 95/101=.94059 both of which are only off by about 1/2 of a percent. So some smaller lathes use transfer gears with these number of teeth. By the way, most hobby machinist probably do not cut threads long enough, and tight/accurate enough, to ever notice this amount of error and since most simple thread matching indicators do not have enough teeth to measure this.
If you download the zipped version of my spread sheet and then run it to generate an AllTPI table. You can then use the srchlist macro generate the search corresponding to sheet named uwSrchList to get the standard threads. For example, I will post an image below. In column B are listed the number of possible gear combinations to get to the metric thread (approximate) value listed at column A. For example, Cell A7 is for 4mm/thread where the * indicates the approximation decimal place. Cell B7 indicates the 4 possible gear arrangements are available to get to this extremely accurate value. (As shown at Cell E1, this was done for the lathe model uwPM1228VF-LB). There is another sheet generated which lists these gear arrangements, along with all of the others in this list.
I look forward to hearing about your work on metric conversion.
Dave L.