Why can one not use their thread gauges to cut thread?

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fixxer

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By that; I mean, why do all these videos I see show people using measuring wires or dedicated pointed anvils for finding the ID of the thread. I'm talking about home-gamers when I see this and not talking about guys making aircraft parts for Boeing or JPL.

Do my Mitutoyo thread gauges show me my threads are deep enough plus OD readings with normal layout tool mics not get the job done? Do I need to invest in a dedicated screw-thread micrometer with different thread-form anvils? It seems like overkill to a home gamer. I haven't done much threading yet it just seems like 60 degree threads are habitually being over-complicated when I look at what's being touted. Am I missing something?

I'd love to hear your thoughts.

Thanks folks.
 
I had the same thought many years ago when I first started in this hobby. I tried it, too, and found that the resulting threads were extremely loose. Using the thread gauge caused me to cut way too much material off. You can try it if you like but it doesn't work well, at least in my hands.

To be honest, its actually faster and easier to cut threads to tolerances using a thread mike. They are cheap (Asian variety), direct reading, easy to use and the mating part fits every time. For me, this is a no-brainer.
 
"Do my Mitutoyo thread gauges show me my threads are deep enough plus OD readings with normal layout tool mics not get the job done?"

Are these thread gauges you talk about, what you would use to determine the thread pitch of an existing and unknown threaded bolt ? If so, they are not designed to be thread depth gauges. For most single point threading, turn to the proper OD, take some cuts, check it with an appropriate sized nut, when the nut fits, you are good to go.... simple...

If, however, you need to fit a bolt that you are making, into a machined and threaded hole in a machine, for example, this is where the "Machinery's Handbook", and a set of thread wires comes into play. You simply can't go wrong if you follow the charts.

Brian
 
Properly functioning threads have to have the correct pitch diameter. A 6-32, an 8-32, and a 10-32 screw will all fit the thread gage the same way but they're clearly not interchangeable. If you closely at an ideal thread, it has a small flat on the o.d. The width of the flat has a has an effect on the pitch diameter even though the major diameter is correct which is why thread mikes are used. The wires engage the flanks of the thread which are directly related to the pitch diameter so the wires plus conventional mike also gives you pitch diameter.

For the hobby machinist, an acceptable way to check threads is to use a mating nut. It may not give you a textbook fit but it will work. After cutting a few threads, you will get a feel for the desired fit. It would be to your advantage to assemble an assortment of nuts and check the fit on some mating screws to get a feel for the fit. Set them aside as your own personal gage set.
 
I use a Starrett #40 thread pitch gage both to check the form of the tool I've ground and the threads I'm cutting. Works great
 
RJSakowski said:
Properly functioning threads have to have the correct pitch diameter. A 6-32, an 8-32, and a 10-32 screw will all fit the thread gage the same way but they're clearly not interchangeable. If you closely at an ideal thread, it has a small flat on the o.d. The width of the flat has a has an effect on the pitch diameter even though the major diameter is correct which is why thread mikes are used. The wires engage the flanks of the thread which are directly related to the pitch diameter so the wires plus conventional mike also gives you pitch diameter.

For the hobby machinist, an acceptable way to check threads is to use a mating nut. It may not give you a textbook fit but it will work. After cutting a few threads, you will get a feel for the desired fit. It would be to your advantage to assemble an assortment of nuts and check the fit on some mating screws to get a feel for the fit. Set them aside as your own personal gage set.
Click to expand...
Yes, I used nuts for a long time, but it is good to run a sharp tap through them before the first use. Before e bay came along, I used thread wires, but now I use thread mikes, especially when I am making a thread plug gage. Most of the time I simply use a nut.
 
markba633csi said:
I use a Starrett #40 thread pitch gage both to check the form of the tool I've ground and the threads I'm cutting. Works great
Click to expand...
Any more, I simply use the Aloris form ground threading tool, you just sharpen it on top and its good to go. for some special thread I use the "fish tail" gage to grind a tool and have both 60 deg and 55 deg tool ( for Whitworth threads) For common Acme threads, I use the Aloris form ground bit of the proper pitch; they make them in several (common) point widths, but the crest can be surface ground wider for odd pitches if necessary. I also have a grinding jig made by the Clark Tool Co. to sharpen tool bits to acme form.
 
Machining 101 .

When using wires , pitch mics or ring gages , you are checking the pitch diameter of the thread . There is no ID of any thread , the term does not exist ! There is a major , minor and pitch diameter . Ring gages , pitch mics and thread gages and wires should NOT be used to verify thread form . Only an optical comparator will . Not that any of this matters as long as it's not for the military . Use a bolt or a nut to verify fit .
 
Thanks for the replies guys. I put a thread depth mic in my online shopping cart weeks ago and then decided to hold off on it until I asked around.
I have the 29th and 30th ed. of Machinery's, SB How to Run a Lathe (which took me weeks to finish a little at a time). Many references on hand in my shop but wasn't sure why I keep seeing people not use the thread gauges to check the threads they make.

I get using thread gauges following a scratch pass to check lineup but not why they cannot grind pitched gauges to indicate you have a deep enough thread belly, correct pitch and correct form angle. It seems to me if they actually ground them to the correct pitch and depth that it would do this too. Yes, the gauges are used to find thread pitch on existing equipment... Except on almost any inside thread you can't bring to the bench. Good luck with that. I still have to figure that out. I have a master set of strung nut and bolt checks that I use for this. They go from nearly too tiny to distinguish up to 1-1/2" (or more I think) along with a metric set. As far as fasteners go, that's how I spec what I need or sort what I have. Very quick since I can just about ball-park most of them before hand on most.

Someone should make a truly pitched set that does this. Or maybe a collection of nut and bolt cross sections that have been Q/A'd. The wires seem very time consuming so if/when I go this route, I'll probably go with a micrometer type tool. Maybe even digital for this one since I don't think I'll be working on anything for production. I know I'll be making some acme (possibly buttress) threads in the future for leveling feet on a 1400lb (and counting) welding table I have gathered most all the materials for. I might as well just get the layout tool that can support this. I may only use it 4 times.

Yes. Understand technically it is considered minor diameter and major diameter for threads. And when you're cutting inside threads, it starts to get confusing to keep them separated. I guess that's why it would be a good idea for someone like myself to work from notes instead of re-referencing the same tables throughout the cut. I'll be shutting down the machine and rethinking every cut if I don't jot it down and roll. Still though, thanks for the feedback. It's easy to blow past these things and make them habitually incorrect. Good thing I don't have to supervise this kind of work or I'd end up with a soup sandwich.

BTW, I should have bought the large print edition of Machinery's Hand Book. Do yourself a favor and do this if you're on the fence. I suspect I'm going to re-buy 30th in large print now. It's almost as bad as trying to follow a tiny table inside McMaster or similar. Maybe it's just me...
 
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benmychree said:
Any more, I simply use the Aloris form ground threading tool, you just sharpen it on top and its good to go. for some special thread I use the "fish tail" gage to grind a tool and have both 60 deg and 55 deg tool ( for Whitworth threads) For common Acme threads, I use the Aloris form ground bit of the proper pitch; they make them in several (common) point widths, but the crest can be surface ground wider for odd pitches if necessary. I also have a grinding jig made by the Clark Tool Co. to sharpen tool bits to acme form.
Click to expand...

I'm going to look for some grinding jigs. I've come across a few online. I'll take a look at these. This will help me greatly.
 
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