Thread gauges, taps and drills?

[lazylathe]

Hi,

I have been looking for an easy to understand guide or answer to this question for quite some time now.
No luck on the internet so far so i thought i would ask here!

I have a jewellers saw from work that broke and i want to fix it.
It was a bad design with an aluminium handle and a stainless steel screw that screws into the handle.
The people that use it have threaded it into the handle skew and have stripped the threads in the handle.
Easy fix i thought!
Drill out the handle and make a SS insert that is threaded and loctite it in.
Seems simple enough...

And onto my question!

I have a Union Tool thread gauge that measures the threads at 26.
Nowhere on the gauge does it say Metric or Imperial...
How do i decipher what it is?
And then how do i convert the mysterious 26 into a suitable tap size?

Way confused...

Andrew

[steamer]

OK...I assume it's 26 threads per inch ......is that correct?

What's the OD of the thread?

Additionally,....considering your the new owner.....does it have to be 26 threads/inch.. or could it be a pitch for the closest thread you have a tap for?

OR

You could make a tap to fit that specifically

[Don1966]

Andrew Dave is correct my Myford chart has 26 TPI  as imperial threads. Like Dave says make a tap.
However I did find this http://www.steadfastcycles.com/cart/index.php?main_page=product_info&cPath=133&products_id=4419

Don

[steamer]

If it were me...I'd grab my 5/16 -24 tap to make the hole...A jewelers saw is all about getting the correct tension on the blade...but that is controlled by the frame anchor....not the screw.   It can be anything.

Once you've set the frame anchored...you never adjust it...you just use the screw to loosen and tighten the blade to the predetermined tension.....so actually the thread doesn't matter at all.....

Dave

[lazylathe]

Not sure if it is inches?
The gauge does not tell me anything just the manufacturer.

The OD of the screw is 0,220" or 5.63mm.

This saw has a spring frame and the screw that goes into the handle is the one used to generate the tension in the blade.
It has pin lock blades so you need to loosen the handle in order to change blades.

I guess the closest thread would also do.
If i really wanted to get into it i could also make a new blade holder and then i could use whatever thread i wanted!

Andrew

[steamer]

That's kinda where I was heading....but it's your saw....

Dave

[lazylathe]

 

[Pete49]

Just to confirm I pulled my moore & wright thread gauge and it is 26ANF but as been suggested use a similar fine thread in metric or inch and it will work just like a bought one
Pete
ps I made an error it should read UNF sorry bout the fusion.

[arnoldb]

Good advice all round Andrew.

I'll just add a note too:

Metric thread gauges are normally marked with the pitch as distance between teeth in mm.  Thus the bigger the number on the gauge, the further the teeth are apart and the coarser the thread.  Some of the standard smaller threads would be M3 x 0.5, M6 x 1, M10 x 1.5 etc, and the thread gauge plates will be marked 0.5, 1.0, 1.5. 

Imperial gauges are normally marked in TPI (threads per inch), and the smaller the screw the higher the number - e.g #0-80 (80 TPI) #4-40 etc, and the gauges plates marked with the number of teeth per inch e.g. 80, 40 and in your case 26.

So the general rule of thumb for unknown thread gauges are that if the numbers on the gauge plates gets higher and the teeth gets finer, its likely imperial, and if the number gets higher and the teeth gets coarser, it's likely metric.
In your case, the imperial 26TPI you mentioned is close to a metric 1mm pitch - 25.4TPI = 1mm pitch.

Another general rule of thumb is that if you know the country of origin where a thread comes from, you can have a good guess at the thread form. 
Goods from the US will usually be threaded with UNC or UNF form (that's a 60^o form measured in TPI with imperial dimensions). 
From Asian countries, it's normally metric (60^o form, pitch in mm and metric dimensions).
Goods from the UK are a bit more difficult...  Older goods are normally in BSW (normally just called Whitworth) or BSF (50^o form, pitch in TPI and imperial dimensions).  Newer goods tend to be fully metric.  I can't recall the rest of the British thread forms off the top of my head, but there's also BA, BSB, BSP, ME etc - all with their own sets of measurements - I always have to reach for threading charts for these.
From Continental Europe, things are by-and-large metric.
Things from most of the Commonwealth countries tend to be metric for newer items, and one of the British forms for older items. I'm not sure about the distribution in Canada; from what I've observed online, its usually US or metric - even though Canada is a member of the Commonwealth...

Screwy subject, isn't it ? 

Kind regards, Arnold

[Stuart]

26 tpi is BSB   British Standard Brass

your mic size looks like a worn 1/4 inch

but as you say you have a lathe so you can make what you want


eg  I have a job on at the mo. 30mm by 32 TPI

yes you read it correctly metric dia and imp threads so to confuse the a little more the thread depth for 32 TPI is 0.20"  so with the lathe being metic and Dia marked on the dials the thread depth as indicated is 1mm ( 0.5 cut )

the male thread then becomes a 31 mm 32 TPI 


Stuart

[Bluechip]

1/4" 26 TPI BSB could well be 1/4" BSF, as they are identical ... 

Both 26 TPI 55^o WF [ Whitworth Form ].

List of info on threads here:

http://www.watchman.dsl.pipex.com/thread.html

Download the Spreadsheet version , then you can sort it ...

Note that BSCycle [or CEI] is a 60^o thread, not 55^o WF.

Best of luck ..

Dave

[Arbalest]

If it were me...I'd grab my 5/16 -24 tap to make the hole...A jewelers saw is all about getting the correct tension on the blade...but that is controlled by the frame anchor....not the screw.   It can be anything.
Dave

Yep, same here. I'd just use the nearest size tap I had to hand and make a new screw.