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Making a tap using a screw plate


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Hello Blacksmiths, Locksmiths, Clock and Watchmakers,

I am quoting from  George Daniels: "Watchmaking" book

"Screw Plates

The screw plate is not so much used now that standard sized taps and dies are available. For small threads up to 0.6 mm diameter the screw plate offers no advantage, but for larger diameters they are often useful because of their finer thread pitch. A plate is illustrated in Fig 48 and it can bee seen that the thread holes are numbered for association with the appropriate tap. The threads are duplicated and one set have clearance holes to help in the cutting. These duplicate holes are used for final forming of the cut thread. The plates are supplied with taps when purchased but it is better to make taps from the plate as required.

To make the tap turn the shaft to be threaded with a tapered end as described earlier. Start the plate and measure the first full thread as a guide to the correct diameter. The shaft can now be reduced ready for threading, but the extra reduction will need to be increased to allow for the action of the plate which will not cut freely as a modern die. The reduction can be determined by experience with the plate and the material to be threaded. In forming the thread the plate will partly cut and partly force the metal into shape. Use oil-hardening steel. The readily available silver steel is quite unsuited for threading with screw plates because of its resistance to deformation.

Keep the shaft well lubricated and withdraw it each full turn to avoid the tearing of the thread. It will be useful to keep a firm pressure against the back of the plate to help its advancement. Failure to do so will result in poor threads of the form illustrated in Fig 47. Too much pressure will tear the thread, Here again experience is the only guide to success. After the thread is formed with the cutting hole, the duplicate thread in the plate can be used without pressure to complete the final form of the thread.

File two flats to bring the thread to a flat taper leaving the end approximately one-third of the diameter as shown in Fig 49. Now reduce the width at the end for the starting threads, and finally relieve the back edge of the starting threads only. Harden the tap in oil temper to a pale-yellow colour. After hardening dress the two flats with a sharp oilstone slip to remove the burr from the file and ensure a keen edge. The tap is now ready for use but it should be noted that the thread of the tap is the same size as the thread in the screw plate and consequently a screw made with the plate will not freely enter a hole made by the tap. This can be rectified by polishing the screw thread. 

These plates are particularly useful for replacing screws in old watches. The pitch of the diameter of the required thread in the plate can be ascertained by screwing a piece of hard wood into the hole."

Could someone please enlighten me what does this mean in the text: "and finally relieve the back edge of the starting threads only." What is the back edge oh the thread and what does relieve mean? Probably it does not help that I am not native English speaker? I want to follow this procedure and make a tap.

Take care,

Lui

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Edited by luiazazrambo
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8 hours ago, luiazazrambo said:

What is the back edge oh the thread and what does relieve mean?

Seen in section a thread is an isoscele triangle. The back edge is the one of the two equal sides, the one that faces the head of the screw. The front in the one that meets the female thread first when fitting.

Relieveng is removing material on a face that does not directly cuts, on a cutting tool.

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Thank you. I think I get it now. So relieving our tap this way would help us to form the thread with less force at the beginning minimizing the risk to snap it as the length of the cutting edge would be reduced and the removed material could leave more easily? I marked the back edge and the relieved section with red. Could you please confirm? I dont want to mislead somebody.

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Furthermore I thought I understand this but I am not so sure now:

"reduce the width at the end for the starting threads". What does it mean? What is the end of the starting threads? And what is the width of it? I must understand this. 🙂 

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Yes, the first few threads will be tapered but also grind a little from the trailing edge of the thread to the cutting edge, exactly what you've emphasized in the pic above.

 

The blue steel you have isn't useful for making taps, it will just kill your screwplate. The standard steel in the U.S. would be O1, which is available from multiple suppliers and costs very little. I'm sure you can find it in the U.K. but probably minus the "cheap as chips" aspect. I'm sure there are suppliers to model engineers who carry "silver steel", which is a catch-all term for hardenable steel.

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1 hour ago, luiazazrambo said:

I marked the back edge and the relieved section with red.

Foreword, sorry I never made a tap, but I think you understood correctly.

Before I didn't even realize that there are edges on tap threads (it's a cutting tap not a forming one) so I wrote face instead, but in fact relieving the whole "back face" even for a single thread be not just difficult but wrong.

 

1 hour ago, luiazazrambo said:

What is the end of the starting threads?

The point where threading starts, or ends if you consider that starts from the head.

 

1 hour ago, luiazazrambo said:

And what is the width of it?

I think he means diameter. In other words make the tip tapered

 

29 minutes ago, luiazazrambo said:

I'd like to make and replace screws, and re-tap holes with this method and this is my screw plat in mint condition:

How do I get oil-hardening steel is another question. I got a bunch of blue pivot steel.

The plate won't stay mint for long if you try to thread pivot steel with it. If you bought from Cousins that is actually Indian spring steel, very hard and difficult to machine. I recommend that you use standard tap and dies, even if you want to make your own tap. Start getting the feeling of what is what by experimenting on brass first, then bronze maybe, then leaded steel (which can be hardened to an extent), then O2, tool steel or the like. You're in the UK and can get all these materials easily.

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8 minutes ago, nickelsilver said:

I'm sure there are suppliers to model engineers who carry "silver steel", which is a catch-all term for hardenable steel.

Yes, when one tries to go by precise steel nomenclature and equivalences, this historical term becomes quite confusing. So I'm attaching a couple of data sheets which I've found with Google.

 

SILVER_STEEL.pdf Silver-Steel-Data-Sheet.pdf

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11 hours ago, jdm said:

The plate won't stay mint for long if you try to thread pivot steel with it. If you bought from Cousins that is actually Indian spring steel, very hard and difficult to machine. I recommend that you use standard tap and dies, even if you want to make your own tap. Start getting the feeling of what is what by experimenting on brass first, then bronze maybe, then leaded steel (which can be hardened to an extent), then O2, tool steel or the like. You're in the UK and can get all these materials easily.

I thought that pivot steel could maybe could be annealed, but I dont know what material it is made from neither the one I have, what is probably half a century old or the Indian ones. Probably I need to learn metallurgy now. We electric engineers always pretended to hate mechanic engineers and vice versa, but in fact we were best friends. I did not like to clean their big lathes over the mandatory summer practical sessions because we found nothing better to do though.

Buying standard tap and die sounds not to be painful enough so its a no no 🙂, but I might do that later. I like the comment that I should start with something softer first. George Daniels says i can check the screw plate with hard wood. I probably start with that with the biggest hole I have on the screw plate.

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I would avoid the Indian screw plates - I own one and they are shite. The thread doesn’t conform exactly to any standard and they are not very nicely made. The associated taps snap very easily and I guess are likely to be hardened carbon steel (nothing wrong with that instead of HSS, but the exact temper is important….. excellent makers like Presto used high carbon steel, so it’s certainly good enough). 
 

I mainly use German-made tap/die sets these days but do also have Martin screw plates for odd jobs. I also make my own crown pipe cutting taps from stems where it is a non-standard pitch, eg. for some older JLC and IWC watches. There is a SE Asian-made tap/die set which I think only goes down to 1.0mm and up to 2.2mm but for the money it is excellent.

Edited by rodabod
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11 hours ago, luiazazrambo said:

I thought that pivot steel could maybe could be annealed, but I dont know what material it is made from neither the one I have, what is probably half a century old or the Indian ones. Probably I need to learn metallurgy now.

You can try annealing it of course but in the end is made to make pivots not screws. It is much easier to turn hard steel rather than threading or drilling it.
If one opens a metallurgy box head drops on the 2nd page, but not much metallurgy knowledge is needed for watchmaking, as it reduced to recognizing like two heating colors, and the tempering process is almost always skipper altogether.

 

11 hours ago, luiazazrambo said:

Buying standard tap and die sounds not to be painful enough so its a no no 🙂, but I might do that later.

One thing is enjoying masochism, another nice is being able to resolve small problems quickly. As mentioned the cheap Chinese M1 - M2.5  taps and dies (white tray clear cover) set works well on soft material, and lets you make and repair tools and stuff beside watches.

 

10 hours ago, rodabod said:

I would avoid the Indian screw plates - I own one and they are shite. 

OP has a quality WIRU plate. I mentioned Indian pivot steel not plate, although I also bought the latter because it has a nice wooden box, like most Indians sets for that matter.

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On 1/13/2022 at 11:51 AM, luiazazrambo said:

"reduce the width at the end for the starting threads".

I agree with jdm. All he's talking about here (I think) is putting the taper on the end of the tap. In the diagram you marked in red, you can see the crests of the first four threads have been removed, increasingly towards the tip of the tool. For width he could also have said diameter. It's important, so that the cutting / forming happens in small steps and the tap finds the centre of the hole.

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1 hour ago, LittleWatchShop said:

Yet another thread that will cause me to spend money...OH!! Forgive the pun!

This looks like a nice set.

That's a WIRU No 2 set, but if the objective is making things as opposed to collect / invest in expesnive tools, why spending a lot when one can do for less? I buy lose HSS taps and dies on ALiX for few bucks a piece. HSS-E is also available for a premium and with that one can cut 316 SS - lower grade SS does not even need that. https://www.aliexpress.com/item/4001076576072.html

Threading a watch screw is not that much of a deal especially with a die holder on the lathe, more difficult is to precisely cut the head slot (files for that are expensive and milling as it even more), then finish to perfection, blueuing, etc all these things that exigent eyes like.

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1 hour ago, Klassiker said:

I agree with jdm. All he's talking about here (I think) is putting the taper on the end of the tap. In the diagram you marked in red, you can see the crests of the first four threads have been removed, increasingly towards the tip of the tool. For width he could also have said diameter. It's important, so that the cutting / forming happens in small steps and the tap finds the centre of the hole.

I would say I agree but we start with a tapered shaft already, does he mean that we even have to remove more material (reducing the width / diamater), and removing the back edge of those starting threads is the releaving.

Edited by luiazazrambo
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48 minutes ago, jdm said:

That's a WIRU No 2 set, but if the objective is making things as opposed to collect / invest in expesnive tools

I guess you have figured me out!

The set you point to does not go down as one might need for watch screws, no?

I bought a file for making slots.  Indeed, that is challenging.

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18 minutes ago, luiazazrambo said:

I would say I agree but we start with a tapered shaft already, does he mean that we even have to remove more material (reducing the width / diamater), and removing the back edge of those starting threads is the releaving.

Yes, it has to be the case as the original taper made for the shaft was only made to find the first full thread so to get the correct diameter of the shaft. You have to turn your shaft to the size of the first full thread if I am correct. I think I now understand the full process.

Edited by luiazazrambo
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12 hours ago, luiazazrambo said:

How do you make these if they are not standard? 

You take a scrap stem and then cut a “relief” with a sharp edge to help remove material. 

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I just bought a set of watch makers taps from  Eslinger, $26.  Ya, well ya get what pay for.  Absolute junk.  Please don’t buy these tools, they are not tools they are garbage.  
 

756F8FEB-5273-4CA8-B96A-955B49F29597.png

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20 hours ago, luiazazrambo said:

How do you make these if they are not standard? 

You can get by for threading a short object by reducing diameter on near a sized one that has the right pitch, but for a complete thread you need to single point thread a complete new one on the lathe. Below a good example, the author then proceeded to make a die from the tap, because he needed to make a new make threading.

 

Also very interesting an insight on how tap are (were ?) made in the industry

 

I will stop with links now because YouTube is better than me at suggesting!

 

 

4 hours ago, BillM said:

I just bought a set of watch makers taps from  Eslinger, $26.  Ya, well ya get what pay for.  Absolute junk.  Please don’t buy these tools, they are not tools they are garbage.  
 

756F8FEB-5273-4CA8-B96A-955B49F29597.png

These are the Indian ones discussed above. What material and diameter you are trying?

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I wanted to put an access hole in a brass case, 1mm or smaller and seal it with a flat head screw, which I did, but the threads the tap cut are shallow and jagged because the tap is dull and does not cut properly. 

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