Re: Fw: 1948 9A Quick Change Gearbox analysis


Chuck Lippmeier
 

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.

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