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Any spur gear experts out there ?

cuslog

cuslog

Super User
Premium Member
My lathe is broken down. 1640 Nardini about 1990 vintage (made in Brazil).
Rack & pinion for longitudinal feed skipping, no broken teeth just badly worn. Company is dead, no parts supply.
Up near the chuck is where its worn, tailstock end looks new (still factory paint on it).
I'm thinking I can flip the rack around if I re-drill mounting and dowel pin holes but I'll have to cut a new pinion gear and shaft.
I've cut a few Dp spur gears before (and they worked) but I'm far from an expert.
I was expecting Module (metric) but the numbers seem closer to Dp (Imperial)
Pinion gear: 1.343" dia. x 14 teeth OR 34.12mm dia. X 14 teeth (measured across a small area that saw no wear)
I get 34.12 / 16 = 2.135 module OR 25.4 / 2.135 = 11.910 Dp = 12 DP ?
Rack is 48.5 " long x 186 teeth = .260" linear pitch
Or maybe my math is wrong ?
Forgot to mention: this thing does have a 4TPI (Imperial) leadscrew. All fasteners do seem to be metric though.
 
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DP=(N+2)/OD; (14+2)/1.343”=11.913, rounded to 12DP. Your math is correct.

I have some 12DP involute cutters; all are 14.5* pressure angle though. I would guess that in the 1990s they would have switched to the “new standard” of 20* pressure angle.

BostonGear sells 12DP gear rack

ECatalog

www.bostongear.com www.bostongear.com

Motion Industries, BDI Canada, WAJAX Industrial Components, & Applied Industrial Tech here in Calgary are BostonGear distributors.
 
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Thanks Rudy, it's been awhile since I cut one and none of the numbers were "solid". Then imperial or metric etc.
Yes, and just "eyeballing this thing, I was thinking 20 * pressure angle.
Now off to Ebay.
 
cuslog said:
My lathe is broken down. 1640 Nardini about 1990 vintage (made in Brazil).
Rack & pinion for longitudinal feed skipping, no broken teeth just badly worn. Company is dead, no parts supply.
Up near the chuck is where its worn, tailstock end looks new (still factory paint on it).
I'm thinking I can flip the rack around if I re-drill mounting and dowel pin holes but I'll have to cut a new pinion gear and shaft.
I've cut a few Dp spur gears before (and they worked) but I'm far from an expert.
I was expecting Module (metric) but the numbers seem closer to Dp (Imperial)
Pinion gear: 1.343" dia. x 14 teeth OR 34.12mm dia. X 14 teeth (measured across a small area that saw no wear)
I get 34.12 / 16 = 2.135 module OR 25.4 / 2.135 = 11.910 Dp = 12 DP ?
Rack is 48.5 " long x 186 teeth = .260" linear pitch
Or maybe my math is wrong ?
Forgot to mention: this thing does have a 4TPI (Imperial) leadscrew. All fasteners do seem to be metric though.
Click to expand...
here's the best place for all your gear calculators (free)
enjoy Dan
evolventdesign.com

Spur Gear Calculator Hub | Evolvent Design

Tools to help you get started with gears – .STL and .DXF gear generators, detailed gear geometry, measurement over pin and span inspection tools, and more
evolventdesign.com evolventdesign.com
 
Thanks guys !
I think I'm stuck with making a new gear as it's not just a gear, its actually ~ 3.625" of shaft that passes through a boss / bushing in the apron casting, ~.600" wide gear cut on the end. Shaft portion and the bushing have ~.050" of wear on them as well.
 
I think I'm stuck with making a new gear as it's not just a gear, its actually ~ 3.625" of shaft that passes through a boss /
Click to expand...

maybe I'm not see ing the clearly, but can't you machine the gear off the shaft, take a bought gear and whittle away all the excess material and loctite or press onto where the turned off gear was? Assumes you have you another lathe but you'll likely need access to one to get the lathe running in any event.

cuslog said:
I get 34.12 / 16 = 2.135 module OR 25.4 / 2.135 = 11.910 Dp = 12 DP ?
Rack is 48.5 " long x 186 teeth = .260" linear pitch
Or maybe my math is wrong ?
Click to expand...

I looked at the rack: 48.5 X 25.4 = 1231.9mm / 186 = 6.623 / PI = 2.1 ...... close to Module 2.

Forgot to mention: this thing does have a 4TPI (Imperial) leadscrew. All fasteners do seem to be metric though.
Click to expand...
I've seen companies in metric countries product imperial lathes, but everything not needed to imperial is still metric. The oddest is Schaulblin slide rests, the feed screw is a 6mm x 20tpi thread. Try and find that tap. I mean come on, just use 1/4 20!

Maybe they put a DP gears on so as to have truth the feed claims (seems a bit excessive), or maybe mod 2 is close enough.

Its got to be mod 2 or 12 DP, but they are different enough I'd guess you can't really interchange them.

What to do? My suggestion ...... there is about 15 thou pitch difference between 12DP and mod 2 (CP 0.2618"
vs .2474" respectively). What about taking a half a foot of unworn rack at the end and very carefully measuring across say 20 teeth with a caliper. that difference will about .144" which should easily be discernible.
 
That was my first thought but the shaft is fairly worn and also the steel bushing it runs in is worn, all contributing to the gear deflecting away from the rack.
So, how about this for comparing dp or module: I'm sitting here with the section of rack off the gap in my hand. Its 100.23mm long, it has 16 full teeth. Root center to root center.
PICT0243.JPG
 
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