Threads

[Security-Man2k]

Ok so apologies for this if it is a bit of a newbie question but how do you work out the pitch of the thread of nib units? I am looking into making my own sections now and i needed to know so I can attempt to source the right taps when the time comes. I already know what bock nib units take so I have those in my sights but if I want to progress further I need to expand on the different nibs I can make pens to fit.

 

Thank you for your help.

 

take care.

 

Dennis

[richardandtracy]

Dennis,

 

Take a look at the Beaufort Ink web site. The nib unit sale pages have links for the relevant taps. I think the #6 nib unit has an M7.9 x 0.6 thread but that's my memory and it's not totally reliable.

 

Regards,

 

Richard.

[Security-Man2k]

Hi Richard,

 

I use Beaufort Inks already and i will be buying the taps they have for the bock #6 nib units. I was wondering how i would work it out so if i had someone who wanted me to make a pen for a nib unit they already had i could work it out and do it for them that way. I don't want to be restricted to just using bock nibs. I want to be able to use Jowo ones too as well as others from other manufacturers.

 

Thanks

Dennis

[richardandtracy]

Then you'll need a 'Thread Pitch Gauge'. I suggest you get a 51 leaf metric & imperial one as it will cover all the sizes you are likely to see, 0.25mm to 6.0mm. I would link to a suitable one, but I am on a tablet and Chrome for Android is really doing its best to irritate the hell out of me by copying and pasting almost anything except what I want at the moment, and correcting the spelling of URL's etc. I HATE predictive text and autocorrect.

Use the leaves to fit into the thread, hold it up to the light and keep changing leaf until you get to the one with minimum light showing through. That will tell you the pitch.

 

For the diameter, get yourself a Vernier caliper, registering to 1/50 mm or better. There are very cheap digital verniers on E-Bay that only register to 0.1mm. This isn't good enough. Get a manual one such as Screwfix 4269V (£12.99) or a digital one such as Screwfix 7093V (£19.99). These will tell you the outer diameter of the thread. Other suppliers may be cheaper for the same quality. I got my manual Vernier from Screwfix in 2002 and use it nearly daily. Cannot complain, and no batteries to change.

 

So, now you need to calculate the tapping hole diameter. With a metric form thread the tapping diameter will be either the diameter calculated below or the next 0.1mm drill size up:

Diameter = Thread outer diameter - Thread Pitch.

Eg tapping drill size for M6 X 1.0 = 6mm - 1mm = 5mm. The recommended tapping drill for M6 is 5mm, but for a free-er thread cut you can use 5.1mm.

 

This is not the way to get the perfect drill size, just one that will work well enough at the sizes we're talking about.

To thread cut the thread on your lathe, select the gear ratio that gives you a pitch within 5% of that, and progressively cut the thread deeper. As you reach the correct OD for the thread, try the housing in the thread after each cut. That way you'll get a fit you feel comfortable with. I said a gear ratio within 5%, ideally you will want exactly the right ratio, but this is not always possible. On my Warco lathe, the metric pitches are a uniform 1.4% in error, but over a normal thread engagement length, it is not a problem at all. I started a discussion on the Model Engineer Magazine forum about this, and the consensus of a number of experienced ME contributers was that 10% is OK for coarse threads, and 15% for fine threads - I was expecting it to be the other way round, but they uniformly agreed fine threads were more tolerant of pitch inaccuracies.

 

Hope this helps a little,

 

Richard.

[Security-Man2k]

By all the gods alive and dead i totally agree with you on the sentiment to auto correct and predictive text. I curse the day when they took the ability away turn the darn thing off.

 

I work in a lab and we have calibrated vernier callipers that have a resolution of 0.01. I will look out for a thread pitch gauge though, so thank you for that.

 

I figured that was how you worked out the hole size you needed to drill. I have done tapping in the past when building rigs around work and whatnot. Again thank you, that has been very helpful.

 

Unfortunately the lathe i have doesn't have a thread cutting function as it is broken and the owner of the lathe (my boss) isn't likely to fix it any time soon. I will revisit this when i get my own lathe though.

 

Overall that was a fantastic answer so thank you and looking over your site you have some beautiful pens there.

 

Take care

Dennis

[fabri00]

It is not easy to have a threading tool to be used in a lathe to thread internally diameters of 7 or 8 mm, at least for me.

 

As the celluloid or hard rubber are soft and easy materials, I would prefer to make a tapping drill of the right size with the late, and then use it to thread internally the section.

 

As models of nibs are not too much, making 4 or 5 tapping drill will be enough.

[richardandtracy]

I agree, it's not easy. Far from it. Using tiny tools helps, the 4mm set here is about the right size, though grinding the point yourself on a stick of HSS would be much more economical:

https://www.arceurotrade.co.uk/Catalogue/Cutting-Tools/Lathe-Turning-Tools/6pc-Internal-Threading-and-Boring-Sets

 

The other method is to make your own tap of the right size to suit. Possible, but probably not economically viable if you need to charge for your time.

 

Regards,

 

Richard.

[Security-Man2k]

I have no idea how i would go about making my own tap. I guess that will have to go on to the 'skills to learn' list. A list which is getting longer daily.

[Pierre---]

An easy answer for Jowo ID is here. You can also buy the nibs and feeds here and measure it with your calipers. In the same shop, you can find the correct tap.

And then, to the workshop.

[richardandtracy]

Making a tap is not rocket science. If you can thread the outside of a bar, you can make a tap.

 

Simplistically, cut the thread on the outside of a bit of silver steel. In the US it's called 'Drill Rod' and is actually a bit better for making taps than the UK's 'Silver Steel', but the advantage isn't great enough to be worth importing it. Put in a 5 degree (-ish, a plug tap will need ti be steeper) taper on the end, so the end of the taper is smaller than the tapping drill diameter. Then remove from the lathe and put in a mill with either a rotary indexer or a rotary table.

 

Mill 3 or 4 slots into the thread with an end mill so the cutter passes the centreline of the thread. Going past the centreline means there's a slight positive rake on the cutting face which will cut plastics slightly better. Mill along the thread, index the tap, mill another slot etc until the number of flutes is complete. Then comes the tedious bit, using a tiny 60 degree file to file away all burrs. Once done, stone the cutting face flat.

Heat to red heat, quench, polish the cutting face so you can see the colour and temper to straw by heating the unthreaded end & see the colours run up the tap.

Stone the cutting faces sharp.

 

And there you have it.

Well, the first few probably won't work terribly well (and maybe not at all), but persist & you'll get the hang of it.

 

If no mill is available, the flutes can be ground or filed, but neither way is as quick or as reliable as milling. An alternative is to use the lathe as a mill, as people used to do in the past.

If you are making your own tap, you can be inventive by putting a guide plug below the thread, to make sure it always goes in straight, that sort of thing.

 

Regards,

 

Richard.

[Security-Man2k]

Oh my god, most of that went over my head lol. I think I will search for taps i need until i have got the hang of using a new lathe which can cut threads.

 

Dennis

[Security-Man2k]

An easy answer for Jowo ID is here. You can also buy the nibs and feeds here and measure it with your calipers. In the same shop, you can find the correct tap.

And then, to the workshop.

 

 

Thank you pierre. This will prove useful.

[richardandtracy]

Oh my god, most of that went over my head lol. I think I will search for taps i need until i have got the hang of using a new lathe which can cut threads.

 

Dennis

Possibly very wise.

If learning on your own, it can take a fair time to pick up general lathe & milling skills. I'm still really a beginner 17 years after getting my lathe. I look at some of the results on the ME forum and realise just how much I have to learn still before I can think of myself as an 'advanced beginner'.

 

Regards,

 

Richard.

[Security-Man2k]

Hey Richard,

 

If after 17 years you are a beginner what does that make me? I had never even touched a lathe as of 6 months ago. lol

 

Regards

Dennis

[fountainbel]

Then you'll need a 'Thread Pitch Gauge'. I suggest you get a 51 leaf metric & imperial one as it will cover all the sizes you are likely to see, 0.25mm to 6.0mm. I would link to a suitable one, but I am on a tablet and Chrome for Android is really doing its best to irritate the hell out of me by copying and pasting almost anything except what I want at the moment, and correcting the spelling of URL's etc. I HATE predictive text and autocorrect.

Use the leaves to fit into the thread, hold it up to the light and keep changing leaf until you get to the one with minimum light showing through. That will tell you the pitch.

 

For the diameter, get yourself a Vernier caliper, registering to 1/50 mm or better. There are very cheap digital verniers on E-Bay that only register to 0.1mm. This isn't good enough. Get a manual one such as Screwfix 4269V (£12.99) or a digital one such as Screwfix 7093V (£19.99). These will tell you the outer diameter of the thread. Other suppliers may be cheaper for the same quality. I got my manual Vernier from Screwfix in 2002 and use it nearly daily. Cannot complain, and no batteries to change.

 

So, now you need to calculate the tapping hole diameter. With a metric form thread the tapping diameter will be either the diameter calculated below or the next 0.1mm drill size up:

Diameter = Thread outer diameter - Thread Pitch.

Eg tapping drill size for M6 X 1.0 = 6mm - 1mm = 5mm. The recommended tapping drill for M6 is 5mm, but for a free-er thread cut you can use 5.1mm.

 

This is not the way to get the perfect drill size, just one that will work well enough at the sizes we're talking about.

To thread cut the thread on your lathe, select the gear ratio that gives you a pitch within 5% of that, and progressively cut the thread deeper. As you reach the correct OD for the thread, try the housing in the thread after each cut. That way you'll get a fit you feel comfortable with. I said a gear ratio within 5%, ideally you will want exactly the right ratio, but this is not always possible. On my Warco lathe, the metric pitches are a uniform 1.4% in error, but over a normal thread engagement length, it is not a problem at all. I started a discussion on the Model Engineer Magazine forum about this, and the consensus of a number of experienced ME contributers was that 10% is OK for coarse threads, and 15% for fine threads - I was expecting it to be the other way round, but they uniformly agreed fine threads were more tolerant of pitch inaccuracies.

 

Hope this helps a little,

 

Richard.

 

Excellent clear explanation Richard , well done !

Francis