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metalmagpie
03-08-2015, 12:47 PM
For you Nardini owners: I have a 1440E Mascote. I have all ten change gears. The threading chart does not include 11-1/2 or 27 TPI. Is it possible to cut these threads (useful for fabrication, making pipe threads) as is? Would it be possible with a different change gear?

BTW if you need a copy of the manual let me know.

metalmagpie

Forrest Addy
03-08-2015, 02:05 PM
Both pitches are prime numbers. You need an index gear some multiple of the threads per inch. 11 1/2 and 27 are usually covered with a train having a 23 or 46 tooth gear and 27 or 54 tooth gear respectively. If the product thread length is short you may get close by mixing and matching your existive gears.

Got a mill and a dividing head? DIY.

Jim Hubbell
03-08-2015, 03:18 PM
Please give the spindle gear tooth count, change gear sizes and lead screw TPI. May be something in there.

metalmagpie
03-08-2015, 04:05 PM
Lead screw: 4 TPI

Change gears: (it can use 4 gears or 3, if 4 the middle 2 are fixed together)
40
47
50
71
75
76
100
113
120
127

It's a gearhead lathe, so there isn't a spindle gear as such. That is, you can put any of the change gears on top (the output of the gearbox). The threading/feeds plate has 4 combinations: 40-100-127,
47-127-76, 50-113-100 and 71-113/75-120. In the 4th combination the 113 and 75 tooth gears are
fixed together.

The gearbox can be set to 1:1 or many other gear ratios.

MM

oldtiffie
03-08-2015, 10:13 PM
Both pitches are prime numbers. You need an index gear some multiple of the threads per inch. 11 1/2 and 27 are usually covered with a train having a 23 or 46 tooth gear and 27 or 54 tooth gear respectively. If the product thread length is short you may get close by mixing and matching your existive gears.

Got a mill and a dividing head? DIY.

As a last resort use metric thread cutting.

11 1/2 is a prime number but 27 is not (it is divisible by 3 and 9).

11.5 tpi is pretty well 2.21mm (say 2.2mm) pitch - use 2.25mm pitch?

27 is 0.94mm pitch - perhaps use 0.9mm or 0.95mm pitch.

Why are a mill and a dividing head needed? I can understand it is a universal horizontal mill and a universal dividing head were used - but there are some pretty solid maths there - see Machinery's Hand Book for guidance/info.

metalmagpie
03-09-2015, 12:05 AM
As a last resort use metric thread cutting.

11 1/2 is a prime number but 27 is not (it is divisible by 3 and 9).

11.5 tpi is pretty well 2.21mm (say 2.2mm) pitch - use 2.25mm pitch?

27 is 0.94mm pitch - perhaps use 0.9mm or 0.95mm pitch.

That makes a lot of sense to me! My lathe can cut 2.2mm pitch which is real close to 11.5TPI.
And it can cut 0.95mm pitch which is real close to 27TPI.

It seems to me that following what Forrest said that given that to do 10TPI I use a 50 tooth gear
driving a 100 tooth gear via an idler, that I could interpose a compound gear 46/40 which has
the ratio 11.5/10, and thus I should get exactly 11.5TPI. But I'd need a 46 tooth gear, which is
probably why Forrest said I'd need a dividing head - to make another gear or two.

MM