Thread cutting on a Stanko 1A616

[ksor]

I'm trying to figure out how thread cutting is done on this lathe.

 The change gears on the left side of the gearbox give me some problems - I think I miss some of them !

 I only have 2 dobble gears and 1 bigger to connect them.

 The 2 dobble gears have this stamped on the side:

 M2 20-55

 and

 M2 25-36

 and it's the number of teeth on each single gear ... what is the "M2" standing for ?

 I have got some copies of some tables on how to set up for thread cutting and I can see
 there is mentioned some teeth number that I don't have !

 So my question is:
 How many change gears is normaly delivered with the machine ?
 Only the one set I have (M2 20-55 and M2 25-36) or ... ?

 You can see some Pictures here - Google translation is avaiable to the right just
 under the menu line:

http://kelds.weebly.com/gevindskaeligring.html

 Best regards
 KSor, Denmark

[philf]

 ... what is the "M2" standing for ?

 

Ksor,

If the 55 tooth gear is 114mm outside diameter the M2 might mean 2 Module - which is the size of the teeth.

Phil.

[RussellT]

Hi KSor

That looks an interesting problem.  I think from your website that all the information you need should be on the plate on the top of the gearbox.  Have you got any better pictures of it.  I can see references to 36: 55 on the plate which is presumably the changewheel set up.  If you have two double gears 20-55 and 25-36 you have four possible setups depending on which way you put the gears on.  (20:25, 20:36, 25:55, and 36:55).

I suppose that's really 8 as in principle they could go the other way too.  The plate should tell you what you're missing.  I think I can see a reference to 30:55 but that might be a 20.

It looks a very capable lathe.

Russell

 

[ksor]

Ksor,

If the 55 tooth gear is 114mm outside diameter the M2 might mean 2 Module - which is the size of the teeth.

Phil.

  I don't get you !

Do you mean that IF I should make a new or extra set of change gears I would have to use the M2 gear cutters or ... ?

[ksor]

Hi KSor

That looks an interesting problem.  I think from your website that all the information you need should be on the plate on the top of the gearbox.  Have you got any better pictures of it.  I can see references to 36: 55 on the plate which is presumably the changewheel set up.  If you have two double gears 20-55 and 25-36 you have four possible setups depending on which way you put the gears on.  (20:25, 20:36, 25:55, and 36:55).

I suppose that's really 8 as in principle they could go the other way too.  The plate should tell you what you're missing.  I think I can see a reference to 30:55 but that might be a 20.

It looks a very capable lathe.

Russell

Yeah, maybe ... I have used this table to set the levers for my test cut - and I'm aware of all the combinations I can get with these gears

BUT the table DON'T tell very clear whitch gear should be placed where - at least I don't see the pattern .. yet - I have to do a light cut and then measure the pitch to see if I have to swap the gears.

Maybe there is a convention (whitch I then just don't know) that tells that when the table says 20:25, then the 20 teeth gear should be placed FIRST in the direction of power - do you get what I mean ?

I think I will only use the metric threads, so I just wanted to know IF there should have been more change Wheels/gears delivered for other type of threads.

It isn't an easy job to make gears for other types of threads because the gears sits on a "multi-keywayed" (I don't know the right term here   ) axle - so for now I stick to metric threads.

Tomorrow I try to cut a sample - a big one 40-50mm diameter - both inside and outside - if I succeed I take some pics or video 

[philf]

Ksor,

If the 55 tooth gear is 114mm outside diameter the M2 might mean 2 Module - which is the size of the teeth.

Phil.

  I don't get you !

Do you mean that IF I should make a new or extra set of change gears I would have to use the M2 gear cutters or ... ?

You asked what M2 might mean. I was guessing it may be 2 Module and was giving you a method of checking.

The OD of a gear is (n + 2) * Module (where n = number of teeth). So for a 55 tooth gear the OD = (55 + 2) * Module and if the Module is 2mm then the OD would be 114mm. You would need a 2 Module gear cutter (or set of cutters) if you were to make more.
 
I guess the term you may be looking for for "multi-keywayed" might be "splined".

Phil.

[ksor]

You asked what M2 might mean. I was guessing it may be 2 Module and was giving you a method of checking.

The OD of a gear is (n + 2) * Module (where n = number of teeth). So for a 55 tooth gear the OD = (55 + 2) * Module and if the Module is 2mm then the OD would be 114mm. You would need a 2 Module gear cutter (or set of cutters) if you were to make more.
 
I guess the term you may be looking for for "multi-keywayed" might be "splined".

Phil.

OK, thx I thought it has to do with the threads - making new sets of change gears will have to wait a while

[RussellT]

Yes, I do understand, I would expect it the first one written down to be the driver and the second to be driven as you suggest.  If you used one that was 30:55 then if they were the wrong way round the error would be huge and easy to see.

Russell

[ksor]

Yes, I do understand, I would expect it the first one written down to be the driver and the second to be driven as you suggest.  If you used one that was 30:55 then if they were the wrong way round the error would be huge and easy to see.

Russell

Yeah, that's right, but it's not that easy to "see" the difference between a pitch 1,75mm and 2mm without doing a light cut and measure - let's say 10 of them.

I'll try to take a Picture of that table - maybe you can see the pattern in the notation.

[RussellT]

Well you could save stock and make it easier to test a lot by putting a fine marker pen or a pencil in the tool post and cleaning off between trials, or if you stuck a piece of paper on a piece of stock you would have a record for each setting you tried.

Yes, please try and post a picture of the table.

Russell

[ksor]

Well you could save stock and make it easier to test a lot by putting a fine marker pen or a pencil in the tool post and cleaning off between trials, or if you stuck a piece of paper on a piece of stock you would have a record for each setting you tried.

Yes, please try and post a picture of the table.

Russell

Thx, what a bright idea  for documenting !

I'll go over to the shop right away to do some test threadings ! 

[ksor]

Now I did some test cutting, but I have some problems in finding out how much Deep to cut !

I found a formula saying:

Pitch * 0,8660

But it's way too Little, so I proceeded to the threads "look nice" - 

You can see some details down on this site - Google translation to the right just under the menu line:

http://kelds.weebly.com/gevindskaeligring.html

[RussellT]

Hi Ksor

I’ve had a look at the thread cutting chart on your website.

When you change from normal to coarse thread the thread pitch is 8 times as big.

As you go from I to IV the thread pitch doubles for each step.

Settings 1 to 6 provide pitch increases by factors of 1, 1.4, 1.6, 1.8, 1.9 and 2.4 in metric mode and pitch decreases by those factors in imperial mode. (The drive through this part of the gearbox must reverse in imperial mode.)

When you change from metric to imperial it applies a correction factor of 4.064.

All the other corrections are taken care of by change wheels and you appear to have the complete set.

So to take a metric thread as an example:

Let’s say metric,coarse, III, 4, changewheels 30:36

0.375 *8 *2*2*1.8*30/36

gives you a pitch of 18mm, which is what the chart says.  0.375 is a constant related to the pitch of the leadscrew and the basic gearing in the gearbox.

Let’s try another

Imperial, fine, II, 6 changewheels 30:36

0.375*4.064*2/1.8*30/36

gives you a pitch of 1.4111.  Divide that into 25.4 and you get 18 threads per inch.

For module and diametral pitch the sums are exactly the same, but the numbers on the chart are different because of the need to bring in PI.  For example to cut a worm to mate with a module 2 gear the settings are

metric,coarse, II, 3, changewheels 36:55

0.375 *8 *2*1.6*36/55

gives you a pitch of 6.28364

For module gears module = circular pitch /Pi

6.28364/PI = 2

You can do a similar calculation for diametral pitch but you need to bring in 25.4 as well as PI because you need to convert from inches to millimetres.

Russell

[ksor]

>> Russell

 

Thx for your time - I will study your post together with the tables and levers on the Stanko .. to see if I can get some knowledge out of it 

But I thank you for your time involved !

As you can see on my website I have managed to do some threading ... but I made BOTH the inside and the outside and THAT isn't so hard to do !

I think it's worse to make some threads witch shall fit with some factory made ones ... inside or outside ... so I think I'll challenge myself by making some of these types next.

 

I'll give it a try one of the first days.

[Ned Ludd]

Hi Ksor,
If the formula does not produce a deep enough thread,could it be that you need to go twice the dial reading. The reason is that the convention on a metric lathe is that the cross slide dial reads in diameter reduction not actual movement, so to get a specific depth you have to double the dial figure.
Ned

[ksor]

Hi Ksor,
If the formula does not produce a deep enough thread,could it be that you need to go twice the dial reading. The reason is that the convention on a metric lathe is that the cross slide dial reads in diameter reduction not actual movement, so to get a specific depth you have to double the dial figure.
Ned

Yeah, I have thought about that as you can see on my web site (only if you can read Danish OR you did the translation AND the Google translation is good enough  )

but this doesn't Work either - the 'best' result is somewhere between !

But IS this formula OK:

Cutting Depth = Pitch * 0,8660

 - maybe this formula is wrong - I just found it on the internet 

I wonder why the diameter is NOT a part of the formula as a sort of min and max limits - obviously you can't do a thread with a Pitch=2mm on a diameter less than 4mm - it has to be much larger.  - right ?

[Ned Ludd]

Hi Keld,
Are you going straight in or off set top slide cutting?
If going straight in, 0.866 X pitch would be about right, but if going in at an angle the top slide movement would be close to the pitch as it is an equilateral triangle. Figures are only close to theoretical as the thread is not a perfect triangle because of the flats at crest and root (for Metric and US threads), but should give a good starting point.
Ned
PS with the cutting insert you appear to be using, going straight in would not cause any problems because of the chip breaker design, but cutting close to a shoulder might be problematical.

[ksor]

Hi Keld,
Are you going straight in or off set top slide cutting?
If going straight in, 0.866 X pitch would be about right, but if going in at an angle the top slide movement would be close to the pitch as it is an equilateral triangle. Figures are only close to theoretical as the thread is not a perfect triangle because of the flats at crest and root (for Metric and US threads), but should give a good starting point.
Ned
PS with the cutting insert you appear to be using, going straight in would not cause any problems because of the chip breaker design, but cutting close to a shoulder might be problematical.

At this one I was going "strait in" - in next sample I'll try to set the compound slide to 28-29.5° and the try to match a factory made nut