This is interesting. Somewhere I read that gun makers sometimes need 7.5 pitch threading capability and that it was very difficult to find tooling to do it. I see from your charts that one of the gearboxes does 7.5 TPI. When I go out to my shop today I’ll have to look to see what gearbox I have on my SB9A. If it isn’t the one that does 7.5 TPI and I ever do get a need for that pitch and if I were to find a gearbox with the 7.5TPI are they interchangeable?
Thank you,
Chuck Lippmeier
From: SOUTHBENDLATHE@yahoogroups.com [mailto:SOUTHBENDLATHE@yahoogroups.com]
Sent: Monday, April 24, 2017 9:25 PM
To: SOUTHBENDLATHE@yahoogroups.com
Subject: Re: [SOUTHBENDLATHE] Fw: 1948 9A Quick Change Gearbox analysis
On 04/24/2017 09:35 AM, john kling jkling222@yahoo.com [SOUTHBENDLATHE] wrote:
Is the strange combinations of DPs only a feature of the work shop lathes? I wonder if the heavy (standard) lathes have a pure 16DP set up.
Change gear lathes do any pitch.
There four or five Southbend quick change gear boxes that I know of. All the inch boxes have 16tpi. Most lathe builders got away with a lot fewer pitches. So to answer your question - all the Southbend lathes with quick change gear boxes do pitches that may seem odd or in between. Also, nobody normal is going to need to cut 224 TPI threads - those finer feeds are for finishing.
* 2 TPI minimum single tumbler box. I seriously suspect that this is the same gear box as the 4tpi minimum single tumbler box but with a different stud gear and chart. Early and uncommon. All settings give half the TPI as the more common 4 TPI minimum single tumbler gear box.
SLIDING
GEAR
TOP
LEVER
THREADS PER INCH
FEEDS IN THOUSANDTHS
IN
LEFT
2
0.1706
2.25
0.1517
2.5
0.1365
2.75
0.1241
2.875
0.1187
3
0.1138
3.25
0.105
3.5
0.0975
CENTER
4
0.0853
4.5
0.0758
5
0.0683
5.5
0.0621
5.75
0.0594
6
0.0569
6.5
0.0525
7
0.0488
RIGHT
8
0.0427
9
0.0379
10
0.0341
11
0.031
11.5
0.0297
12
0.0284
13
0.0263
14
0.0244
OUT
LEFT
16
0.0213
18
0.019
20
0.0171
22
0.0155
23
0.0148
24
0.0142
26
0.0131
28
0.0122
CENTER
32
0.0107
36
0.0095
40
0.0085
44
0.0078
46
0.0074
48
0.0071
52
0.0066
56
0.0061
RIGHT
64
0.0053
72
0.0047
80
0.0043
88
0.0039
92
0.0037
96
0.0036
104
0.0033
112
0.003
* 4 TPI minimum single tumbler box. The common single tumbler gear box.
SLIDING
GEAR
TOP
LEVER
THREADS PER INCH
FEEDS IN THOUSANDTHS
IN
LEFT
4
0.0853
4.5
0.0758
5
0.0683
5.5
0.0621
5.75
0.0594
6
0.0569
6.5
0.0525
7
0.0488
CENTER
8
0.0427
9
0.0379
10
0.0341
11
0.031
11.5
0.0297
12
0.0284
13
0.0263
14
0.0244
RIGHT
16
0.0213
18
0.019
20
0.0171
22
0.0155
23
0.0148
24
0.0142
26
0.0131
28
0.0122
OUT
LEFT
32
0.0107
36
0.0095
40
0.0085
44
0.0078
46
0.0074
48
0.0071
52
0.0066
56
0.0061
CENTER
64
0.0053
72
0.0047
80
0.0043
88
0.0039
92
0.0037
96
0.0036
104
0.0033
112
0.003
RIGHT
128
0.0027
144
0.0024
160
0.0021
176
0.0019
184
0.0019
192
0.0018
208
0.0016
224
0.0015
* Double tumbler box. Does all the same pitches as the 4 TPI minimum single tumbler box, but getting the top row requires changing the stud gear.
STUD
LEFT
HAND
TUMBLER
THREADS PER INCH
FEEDS IN THOUSANDTHS
40
A
4
0.0427
4.5
0.0379
5
0.0341
5.5
0.031
5.75
0.0297
6
0.0284
6.5
0.0263
7
0.0244
20
A
8
0.0427
9
0.0379
10
0.0341
11
0.031
11.5
0.0297
12
0.0284
13
0.0263
14
0.0244
20
B
16
0.0213
18
0.019
20
0.0171
22
0.0155
23
0.0148
24
0.0142
26
0.0131
28
0.0122
20
C
32
0.0107
36
0.0095
40
0.0085
44
0.0078
46
0.0074
48
0.0071
52
0.0066
56
0.0061
20
D
64
0.0053
72
0.0047
80
0.0043
88
0.0039
92
0.0037
96
0.0036
104
0.0033
112
0.003
20
E
128
0.0027
144
0.0024
160
0.0021
176
0.0019
184
0.0019
192
0.0018
208
0.0016
224
0.0015
* Extended range. More rows and columns - does all of the pitches 4 TPI and finer that the other inch boxes do without stud gear changes, and adds in between pitches:
STUD
LEFT
HAND
TUMBLER
THREADS PER INCH
FEEDS IN THOUSANDTHS
40
A
4
0.0853
4.5
0.0758
5
0.0683
5.5
0.0621
5.75
0.0594
6
0.0569
6.5
0.0525
6.75
0.0506
7
0.0488
7.5
0.0455
40
B
8
0.0427
9
0.0379
10
0.0341
11
0.031
11.5
0.0297
12
0.0284
13
0.0263
13.5
0.0253
14
0.0244
15
0.0228
40
C
16
0.0213
18
0.019
20
0.0171
22
0.0155
23
0.0148
24
0.0142
26
0.0131
27
0.0126
28
0.0122
30
0.0114
40
D
32
0.0107
36
0.0095
40
0.0085
44
0.0078
46
0.0074
48
0.0071
52
0.0066
54
0.0063
56
0.0061
60
0.0057
40
E
64
0.0053
72
0.0047
80
0.0043
88
0.0039
92
0.0037
96
0.0036
104
0.0033
108
0.0032
112
0.003
120
0.0028
40
F
128
0.0027
144
0.0024
160
0.0021
176
0.0019
184
0.0019
192
0.0018
208
0.0016
216
0.0016
224
0.0015
240
0.0014
40
G
256
0.0013
288
0.0012
320
0.0011
352
0.001
368
0.0009
384
0.0009
416
0.0008
432
0.0008
448
0.0008
480
0.0007
* The metric gear box. Obviously a different animal. I don't have a table handy for this one. I need to find a good clean picture so I can make one.
