Another thread cutting calculator - Metric & Imperial

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Andy B
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Another thread cutting calculator - Metric & Imperial

Post by Andy B » Thu 05 Jul , 2007 16:10 pm

Hi All,

In response to various questions from paulmo101, I put together a threadcutting calc sheet for imperial and metric gearboxes.
As far as I can tell, the gearboxes and their drives are common to all models of Viceroy manual lathes from the 1960's 5" models through to the 280 models of the mid 1980's.

It works in a slightly different way to the calculator created by dazz (see post in 'Machines' section, "Imperial threads from a all metric lathe") - his will enable you to try out various combinations of compound gears.

It's a bit big (805KB) as it includes copies of various threadcutting charts.

Hope others find it useful.

Andy

Edited 20 June 2009 - new version uploaded with metric 4-position gearboxes included
Attachments
Screwcutting calculator (Viceroy Gearbox Lathes).xls
Threadcutting calculator for gearbox lathes
(942.5 KiB) Downloaded 2386 times
Last edited by Andy B on Sat 20 Jun , 2009 10:51 am, edited 5 times in total.

paulmo101
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Spreedsheet

Post by paulmo101 » Sat 20 Jun , 2009 10:03 am

Hi Andy

very nice spreedsheet I think I will find this very useful. Also good explanation of calculations to work out tpi usiong different gear combinations.

Cheers

Paul

molyneux.mike
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Re: Another thread cutting calculator - Metric & Imperial

Post by molyneux.mike » Mon 05 Apr , 2010 15:36 pm

Hi Andy
I have made a 38 tooth stud gear to give me multiples of 8 T.P.I. Imperial Thread, according to your calculator. I can also make gears fo the Thread Dial Indicator which is out of sink (30 tooth gear) for 8 TPI. Can you calculate what gear I would need on the indicatorc to start these threads?

Thanks Mike




In response to various questions from paulmo101, I put together a threadcutting calc sheet for imperial and metric gearboxes.
As far as I can tell, the gearboxes and their drives are common to all models of Viceroy manual lathes from the 1960's 5" models through to the 280 models of the mid 1980's.

It works in a slightly different way to the calculator created by dazz (see post in 'Machines' section, "Imperial threads from a all metric lathe") - his will enable you to try out various combinations of compound gears.

It's a bit big (805KB) as it includes copies of various threadcutting charts.

Hope others find it useful.

Andy

Edited 20 June 2009 - new version uploaded with metric 4-position gearboxes included[/quote]

Andy B
CNC Guru
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Posts: 383
Joined: Mon 20 Nov , 2006 18:19 pm
Hardware/Software: 280 VS lathe, Denford Senior E-type mill, Senior Major Universal Mill
Location: East Midlands, UK

Re: Another thread cutting calculator - Metric & Imperial

Post by Andy B » Tue 06 Apr , 2010 10:17 am

Mike,

Quick calc shows that a 19T or a 38T gear on the thread indicator will both do the job - the indicator error will be around 0.0000000000002%, which is rather less than the thread error 0.26%.
I trust you will run a few trials without full tool engagement to check it looks OK!!

Have you cut a thread using your 38T stud gear yet (by reversing the lathe)?
I'm interested to know just how well it works - I've done all the sums, but never tried it myself.

I'm not sure yet how to incorporate a thread indicator gear lookup into the main spreadsheet - the calc itself is very simple: The factor given by [Indicator gear teeth * (leadscrew pitch/cut thread pitch)] must be an integer - just needs a few hours playing with possible solutions.

Andy

molyneux.mike
Posts: 15
Joined: Mon 22 Feb , 2010 9:51 am

Re: Another thread cutting calculator - Metric & Imperial

Post by molyneux.mike » Tue 06 Apr , 2010 14:15 pm

Hi Andy
I have fitted the 38 tooth stud gear, which only just meshes with the gear train, and cut a partial thread on a piece of bar and then measured it, got an exact or a very, very close 8 T.P.I. So I am pleased. I hit my chuck the last time I tried cutting a thread with a fixed Lead Screw, turned the air blue!!!
Thanks for the info on the indicator gear, a 38T gear would not fit the standard Viceroy unit, so I will make a 19T and give it a go, have to work out what the diameter of the gear would be and if it will be OK for the 0.5" dia. indicator spindle. Would the 19T indicator gear do all the threads shown for a 38T Stud Gear? It would be very usefull if the indicator gear size could be incorporated into your spread sheet calcs.

Mike


Quick calc shows that a 19T or a 38T gear on the thread indicator will both do the job - the indicator error will be around 0.0000000000002%, which is rather less than the thread error 0.26%.
I trust you will run a few trials without full tool engagement to check it looks OK!!

Have you cut a thread using your 38T stud gear yet (by reversing the lathe)?
I'm interested to know just how well it works - I've done all the sums, but never tried it myself.

I'm not sure yet how to incorporate a thread indicator gear lookup into the main spreadsheet - the calc itself is very simple: The factor given by [Indicator gear teeth * (leadscrew pitch/cut thread pitch)] must be an integer - just needs a few hours playing with possible solutions.

Andy[/quote]

molyneux.mike
Posts: 15
Joined: Mon 22 Feb , 2010 9:51 am

Re: Another thread cutting calculator - Metric & Imperial

Post by molyneux.mike » Wed 07 Apr , 2010 14:55 pm

Hi Andy

19T for the thread indicator gear does not leave much 'body' in the gear. At 26 DP, it's O/D is only 0.808" and the tooth depth - .0820" with the idicator spindle at 0.5" dia. not much body left. Is there a bigger tooth size between 19T and 38T that will work?

molyneux.mike wrote:Hi Andy
I have fitted the 38 tooth stud gear, which only just meshes with the gear train, and cut a partial thread on a piece of bar and then measured it, got an exact or a very, very close 8 T.P.I. So I am pleased. I hit my chuck the last time I tried cutting a thread with a fixed Lead Screw, turned the air blue!!!
Thanks for the info on the indicator gear, a 38T gear would not fit the standard Viceroy unit, so I will make a 19T and give it a go, have to work out what the diameter of the gear would be and if it will be OK for the 0.5" dia. indicator spindle. Would the 19T indicator gear do all the threads shown for a 38T Stud Gear? It would be very usefull if the indicator gear size could be incorporated into your spread sheet calcs.

Mike


Quick calc shows that a 19T or a 38T gear on the thread indicator will both do the job - the indicator error will be around 0.0000000000002%, which is rather less than the thread error 0.26%.
I trust you will run a few trials without full tool engagement to check it looks OK!!

Have you cut a thread using your 38T stud gear yet (by reversing the lathe)?
I'm interested to know just how well it works - I've done all the sums, but never tried it myself.

I'm not sure yet how to incorporate a thread indicator gear lookup into the main spreadsheet - the calc itself is very simple: The factor given by [Indicator gear teeth * (leadscrew pitch/cut thread pitch)] must be an integer - just needs a few hours playing with possible solutions.

Andy

Andy B
CNC Guru
CNC Guru
Posts: 383
Joined: Mon 20 Nov , 2006 18:19 pm
Hardware/Software: 280 VS lathe, Denford Senior E-type mill, Senior Major Universal Mill
Location: East Midlands, UK

Re: Another thread cutting calculator - Metric & Imperial

Post by Andy B » Wed 07 Apr , 2010 16:56 pm

Mike,

The table below shows the error that the indicator would have for different gear sizes.
A 1% error would mean that the tool is trying to engage with the part-cut thread at 3.6 degrees out of position, so I would imagine that anything more than about 0.25% error would cause problems -but you might get away with a 21t or a 35t and prove me wrong!

leadscrew pitch (mm) 3
Pitch of thread to cut (mm) 3.166666667
Ind gear| Ratio---------|--Nearest-|----% error
teeth--|---------------|-Integer--|
19------18----------------18------2.1711E-13
20------18.94736842------19------0.277777778
21------19.89473684------20------0.529100529
22------20.84210526------21------0.757575758
23------21.78947368------22------0.966183575
24------22.73684211------23------1.157407407
25------23.68421053------24------1.333333333
26------24.63157895------25------1.495726496
27------25.57894737------26------1.646090535
28------26.52631579------27------1.785714286
29------27.47368421------27------1.724137931
30------28.42105263------28------1.481481481
31------29.36842105------29------1.254480287
32------30.31578947------30------1.041666667
33------31.26315789------31------0.841750842
34------32.21052632------32------0.653594771
35------33.15789474------33------0.476190476
36------34.10526316------34------0.308641975
37------35.05263158------35------0.15015015
38------36 ---------------36------2.1711E-13

[edited to make table readable as all my spaces disappeared]

Maybe a more complex indicator is needed, with a compound gear set - something like a Metradial - http://www.dgrdesigns.co.uk/metradial.html

Andy

molyneux.mike
Posts: 15
Joined: Mon 22 Feb , 2010 9:51 am

Re: Another thread cutting calculator - Metric & Imperial

Post by molyneux.mike » Thu 08 Apr , 2010 12:54 pm

Hi Andy
Here is an idea, a joint venture, you design a compound gear train for a universal thread indicator, and I will make it!!!
:P
Mike
Andy B wrote:Mike,

The table below shows the error that the indicator would have for different gear sizes.
A 1% error would mean that the tool is trying to engage with the part-cut thread at 3.6 degrees out of position, so I would imagine that anything more than about 0.25% error would cause problems -but you might get away with a 21t or a 35t and prove me wrong!

leadscrew pitch (mm) 3
Pitch of thread to cut (mm) 3.166666667
Ind gear| Ratio---------|--Nearest-|----% error
teeth--|---------------|-Integer--|
19------18----------------18------2.1711E-13
20------18.94736842------19------0.277777778
21------19.89473684------20------0.529100529
22------20.84210526------21------0.757575758
23------21.78947368------22------0.966183575
24------22.73684211------23------1.157407407
25------23.68421053------24------1.333333333
26------24.63157895------25------1.495726496
27------25.57894737------26------1.646090535
28------26.52631579------27------1.785714286
29------27.47368421------27------1.724137931
30------28.42105263------28------1.481481481
31------29.36842105------29------1.254480287
32------30.31578947------30------1.041666667
33------31.26315789------31------0.841750842
34------32.21052632------32------0.653594771
35------33.15789474------33------0.476190476
36------34.10526316------34------0.308641975
37------35.05263158------35------0.15015015
38------36 ---------------36------2.1711E-13

[edited to make table readable as all my spaces disappeared]

Maybe a more complex indicator is needed, with a compound gear set - something like a Metradial - http://www.dgrdesigns.co.uk/metradial.html[/color]

Andy

molyneux.mike
Posts: 15
Joined: Mon 22 Feb , 2010 9:51 am

Re: Another thread cutting calculator - Metric & Imperial

Post by molyneux.mike » Sat 10 Apr , 2010 15:35 pm

Hi Andy
Seen this link, a Metradial patent?

http://www.freepatentsonline.com/4218942.html
molyneux.mike wrote:Hi Andy
Here is an idea, a joint venture, you design a compound gear train for a universal thread indicator, and I will make it!!!
:P
Mike

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