Threads on miniature nuts & bolts

[jhearl]

This question may be a bit "out there" but I am wanting to make a part on the boat I'm building that is a (approximately) 1mm diameter rod with threads on each end. I can't use all-thread for it because most of it needs to be unthreaded. I've searched around on the web and found any number of jeweler's tap and die sets in the 0.6mm & up range. That would work fine. But I was thinking to use some hex nuts from Scale Hardware. It occurred to me that I could wind up with a die that cut a different number of threads per inch than the hex nuts were tapped for. None of the suppliers I've found for dies mention the number of threads per inch - nor does Scale Hardware.

 

I sent an email to Scale Hardware and got a quick and helpful reply as follows:

 

"Metric threads are measured by pitch (the distance between two threads) rather than threads per inch.  I can say the .6mm thread is approximately 169 tpi and the 1.0mm thread is 102 tpi. "

 

I've sent an email to the Otto Frei company (one of the suppliers of jeweler's taps & dies) but haven't heard back from them so far. Since they are just a seller, not a manufacturer, they may not know the answer. So, I thought, just for grins, I'd ask if anyone here might have tried using a jeweler's die and matching it with nuts from Scale Hardware? It might seem like all metric dies are the same, but the Otto Frei page says "Jeweler's tap & dies sets have broader threads than watchmakers or machinist taps & dies, which have finer threads."  http://www.ottofrei.com/Swiss-Made-Colibri-Jewelers-Screwplate-With-Taps-Set.html

So I'm worried that the two could be different. Of course, I can, if forced into, struggle to make my own nuts, but I know they won't look as good as those from Scale Hardware.

 

Thanks in advance -

John

[grsjax]

I can't answer the question but it may be possible to recut the threads in the nuts with the jewelers tap depending on what material the nuts are made of and how close you can get to matching the original thread.  I have done this with regular sized bolts and nuts when I could not get an exact match.  Can't guarantee it will work for you but it might be worth a try if all else fails.

[PAnderson]

Your .6MM thread is in reality 42.37 threads per inch and your 1MM thread is in reality 25.4 threads per inch. All threads have standard TPI or pitch per the machinist handbook, even sub 1MM threads. Chances are really good any nuts you buy will fit any external thread in the same class OD's. Unlike larger threads, where there may be a fine pitch and a course pitch, smaller threads only have 1 common pitch.

 

Paul

[jhearl]

grsjax and Paul - thanks for your thoughts. The nuts would be brass, so maybe it would work to try to rethread them if necessary. Paul - the statement on the Otto Frei website about jeweler's threads being different from watchmaker or machinist threads is what worries me. If that's the case, it seems the thread pitch would be different even on the same size bolt for different types?

 

The other thing I've considered is faking it by buying slightly smaller nuts and drilling out the internal threads enough so they'd fit over the threads of the rod. I suspect no one could tell. But it would be nice to be able to say they were truly threaded, so that's what I'm shooting for.

 

Cheers -

John

[PAnderson]

John,

I think I misunderstood the sizes you specified. I thought you were reffering to the pitch of the threads. Jewelers threads and watchmaking threads are mostly proprietary and don't always follow standards. I believe it would be in your best interest if you followed the machinist standards except in rare circumstances. Below are the smallest imperial threads. I have bought nuts and screws in these sizes before, mostly the 00-90 and 0-80. Of course there are metric equivalents.

[bizibilder]

If the jewellers thread plates originate from Europe then the threads may well be to BA standard (British Association).  These are Imperial threads made to a metric standard and sized in a geometric progression.

 

Believe it or not they are in very common useage!!

 

The trouble with threads (especially smaller ones) is that no-one seems to keep to any standards and seldom publishes enough data about their products to allow you to match sizes.

 

I have even seen 1.5 mm bolts where the dimension given referred to the length rather than the diameter!!!

 

All rather confusing.

[jhearl]

Just as a follow-up, Otto Frei replied after a couple of days but they only said they couldn't find any information about the thread pitch of the taps and dies they sell (which are Swiss made). My belief is that it would be different from that used by Scale Hardware. The gentleman from Scale Hardware subsequently told me that his metric nuts and bolts use the Unified National Miniature (UNM) standard. Taps and dies from 1mm up are readily and inexpensively available for that standard.  I've decided I can get away with 1mm as the smallest size for this project so I've ordered some nuts from Scale Hardware and a set of taps and dies elsewhere. Whether or not I'll be successful at threading with them is another story!

 

Thanks -

John

[Landlocked123]

Hi John,

 

I'm not sure this will meet your needs, but I was playing with the jewler's tap and die set I bought on e-bay recently. To make the nut and bolt pictured below I used 1/32" brass rod and 1/16" square brass tubing. The length is completely arbitrary. Using a jewler's saw I cut two lengths of the tube about 1/16" long. In one I ran a tap equal to the die I used to make threads on the wire and then forced the other end into the hole on the other piece which I then silver soldered in place. A couple of passes on some 400 sand paper and your done. I can't testify to the strength of nut, but it's definitely strong enough to stay in place.

 

Best,

John

 

[jhearl]

Just wanted to report back. I decided that .6mm was too small for my project but 1mm and 1.6mm would work well. I ordered a set of UNM miniature taps & dies from Amazon and some nuts from Scale Hardware. Using the 1.6mm die wasn't hard but the 1mm die was pretty tricky. Teeny, tiny! One thing I determined is that using half-hard, non-annealed brass rod seems to be the way to go. I bought some silver-plated copper wire (18 guage) and it turned out to be too soft - it twisted as I tried to turn the die and eventually broke off before I could finish threading. I also tried annealing the 1.6mm brass rod and it too twisted as I turned the die. So using the brass rod just the way it comes from K&S seems to provide the best results.

 

When I ordered the nuts, I made a mistake and ordered stainless steel 1mm nuts instead of brass. Didn't really matter since I planned to paint the finished assembly anyway. But the 1mm nuts seem smaller proportionally, than the 1.6mm nuts. In other words, I wish the outside dimension as a little larger. Nevertheless, they worked on the threads I created.

 

Here's a picture of the final assembly. This is a main sheet horse for the scow schooner Alma. The rod in the front is the 1.6mm rod. The one in the back is the 1mm rod. It does have the 1mm nuts on it but, as you can see, they look small compared to the 1.6mm nuts. Still, I'm happy with the results.

 

 

[jhearl]

That's a great idea for making square nuts! and bolts with square heads Never thought of using square tubing.  They look really great. Thanks for sharing the picture. I suspect I will use this technique before I'm done with this model.

 

Cheers -

John

[wefalck]

Dealing with the restoration of antique watchmaking machinery, I came across some pretty odd threads, but they seem to have been somehow standardised, as they re-occur in various machines. Modern engineering handbooks are largely useless to identify such threads. Finally, I got hold of a 657 page book from 1924 that only deals with threads. The multitude of threads that were used in different industries before Whitworth and SI (DIN/ISO norms) is quite amazing.

The book also has a section on watch industry threads. It appears that each major factory has (had) its own standards ! However, in the Swiss watch industry the so-called Thury-thread seems to have become prevalent. Here is a Web-site with some information on it and dimensions: http://sizes.com/tools/thread_thury.htm. Chances are that these screwcutting plates that are being sold by watchmakers supply houses (and on eBay) have Thury threads.

Proper taps and dies (as opposed to the plates) are made down to 0.2 mm diameter, I believe. I have some down to 0.3 mm, but would use them only on my watchmakers lathe, to ensure absolute concentricity and no side forces in order reduce the risk of breaking them. A die cost about 15 EUR in the late 1990s, when I bought them. Taps are cheaper.