[Newbie] Help with Finding and Using Thread-Pitch Gauges

[markba633csi]

Looks like a good selection of gauges for 23$. I have only one Starrett #40 gauge and I only use it occasionally
I do use my "fish" gauge often though
-Mark

 

[JDavis]

also used to gage the angle of lathe and grinder centers when regrinding them.

There are way too many thread forms. Japanese metric has some variations from European metric. European metric uses British pipe/tube threads in either straight or tapered. Some Imperial threads are really close to metric. There are lots of "special" threads that luckily you only find on very specific items. Buy a good wall chart that lists most of the threads, their tap drill and their clearance drill. My chart has drill sizes listed in size order: fraction, metric, letter and number. Get a good 115 pc. set ($250+) of bits and it will cover most drill sizes even close enough to most metric. I have a set of metric but they are by too big of jumps. For 1/2 to 1" I've got a set (Silver & Deming) from Grizzly that are actually pretty good. For most things my go to are screw machine bits in cobalt. I have a few carbide bits for drilling out broken bolts and taps. I have a few left hand bits that work well for drilling out broken bolts. Usually they will just back the bolt out. Much better than easyouts. As you can tell this is part of the rabbit hole phenomenon.

Thanks @Larry$. Do you have a picture of your wall chart? I'd love to try to find a complete chart, or make one of my own in Excel. Thanks!

 

[JDavis]

Gentlemen, I'm appreciative of your thorough and speedy replies! My reply was not so speedy, but I'll improve. This truly is the greatest forum that I've ever had the pleasure of being a part of. I know the concept of using the calipers and thread gauges, but I'm overwhelmed by all the different standards and knowing which ones matter. I guess that it'll all come together through practice. If anybody has some good charts, would you mind sharing pictures or links to them? I'd like to make an excel spreadsheet that has them all, which I will of course share with you all. Much thanks. -Jeff

 

[Bi11Hudson]

I have a couple of SAE gauges from Brown & Sharpes(I think), but keep a cheap set of SAE and Metric on my desk for general use. I don't do really precise work(any more), strictly model building nowadays. With the fine pitches I work with (00-90~), a reading glass is a must to get a good reading. There are many pitches where Imperial and Metric are so close, a glass is needed. Note that the peaks are "shaved off" a fuzz such that the screw is undersized. Not much, but enough to be confusing even to an "old hand".

Tapered/pipe threads are nominally specific to tubing. But not universally. There are straight threads on many(most?) hydraulic fittings. British standard and Whitworth 55 degree are rare in the States, unless you have a British motorcycle or auto. Even they use the 60 degree thread form nowadays for much work.

Thread charts alone make a good sized book. "Standard" threads vary by the use. Thread forms for fasteners are just one of many. It's just another branch tunnel in the " Rabbit Hole". Might I suggest you acquire a copy of Machinery's Handbook. Most thread forms of any use will be listed. A wall chart will cover general usages, after a while bolts and the like will become second nature in use. For my use, smaller sizes are more important. ie, I consider 1/4-20 to be very large. But often use 3/8-16 to make worms for worm drives.

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[Winegrower]

Really, I've never seen a Whitworth thread, to my knowledge, kind of hope I never do. I have a simple small thread gauge that belonged to my dad, and it seems to cover all the possible threads per inch that I have ever needed. I observe that every screw thread comes down to so many threads per inch or thereabouts, and for imperial, that and diameter is all you need to know, and for metric, it's such a clean system that you basically only need diameter and you can get the pitch or have a couple obvious choices. But having some good charts is fundamental. And after all, in a pinch you could use a ruler in most cases and nail it.

 

[ericc]

When I first started out, my first "thread pitch gauge" was a plastic divider box full of screws with labels on each compartment. This turned out to be insufficient for testing scratch cuts on a lathe, so I used a file to flatten a few sacrificial screws. As a bonus, the resulting gauge is two sided. Eventually, I was able to acquire a real thread gauge. It was great!

 

[Illinoyance]

60* pitch gauges can be used for Acme and Whitworth threads. The thread form will not match but the pitch will be correct. The fish gauge doesn't care if the thread is Imperial or metric. The Whitworth thread requires a different fish gauge.

 

[devils4ever]

I started with a thread gage that came with my tap and die set that I bought 30+ years ago. As I got more and more into machining, I was having trouble using it and getting accurate readings. So, I bit the bullet and bought a Starrett Imperial gage and a Starrett Metric gage. What a difference! So, much easier to use.