Anyone got a thread micrometer?

[John Beardslee]

A 1/4-32 roll form tap might be a chase, in a short search I didn’t find any listed. I think ours were manufactured by Butterfield and were all metric. It’s worth the time if you find them. They generate outstanding strong clean threads and don’t make any chips in the process.

 

[K F Wheeler]

I've had plenty of experience hand tapping 3/8" thick stainless steal !!! !/4-28 I think. Up around 925 holes!! Yeah I broke a tap or two... Or Three. Or...
All cutting taps. Always used Tap Majic. Never had a chance to use anything else. Ken

 

[Terry Keeley]

Well I did a bunch of reading in the Machinery's Handbook and got semi edumicated on threads. Picked up a "Pee Dee" wire kit and checked several O'Donnell plugs.

I get a PD between 0.2269" & 0.2279", basic (or nominal) PD for a 1/4-32 thread is 0.2297" so they are between 0.0018" & 0.0028" under nominal. From the Machinery's Handbook this is a standard Class 2A thread.

The problem is the tightest H1 tap is between nominal and +0.0005", so even if I could find one I could still be 0.0033 big, no wonder the standard H3 is sloppy, at max. tolerance it is over four thou big.

Everything you wanted to know about taps but were afraid to ask, styles of taps, class of thread , gh numbers , basic point in thread measurement , constants for finding pitch diameter and minor diameter of screw threads , thread constants for various percentages , relation of tap pitch diameter to basic pitch diameter , tap limits product limits and class of thread , how to order special taps - Newman Tools

Guess I'm doomed to single pointing them unless I had a L2 or 3 tap made...

 

[K F Wheeler]

That sloppiness in the threads is why I CRINGE almost EVERY time I see someone tighten a glow plug!!!!! That copper washer is there to help keep that plug from backing out. It's there to provide a slight crush. Along with better heat transfer between the plug and the head. You don't keep re using that same copper washer because each time it's tightened it's going to have a little less crush to it. You want to check the plug after a run? Go ahead! I leave that copper ring with the plug and put the plug back in if the plug is good. Just don't keep using that same washer with the next ten plugs!! That washer is getting slightly thinner each time the plug is tightened. Doubt that will have much if any change in performance. You leave that same ring in there with the next four or five plugs it may... I've never stripped that hole out. But, I've NEVER had one back out!
The tapered plugs, I can't say anything about. Never had an engine that used them.
Now I'll get down off my shoebox and go back to bed... Ken

 

[Wasted wages]

Same here Ken, I could never figure out how someone could put that much torque on a glow plug to pull the threads in a head button.

I don't know,, maybe it's just the "mechanics feel" that some people are lacking ??
After pulling wrenches for close to 40 years I can honestly say that I have seen some idiotic stuff that people are prone to doing.

It's almost like they had to sit back and figure out how to screw something up so bad...

I should take an old head button, and my inch lb torque wrench,,and see how much torque it takes to pull the threads....I'm not sure if I could pull the threads with a 5/16" nut driver by hand...

 

[John Beardslee]

Wait until you’ve had surgery on both hands and have to use a T-handle, it’s easy to loose that sense of feel. It cost a first place with my twin at the Nitro Championships a few years ago when I didn’t get one of the plugs tight enough and it decided to exit after 4 laps. That year Glenn Quarles and I did torque studies in February at Speedweek and settled on 36-40 inch/lbs. my small torque driver only goes to 36 inch/lbs so we decided to double click it. Knock on wood I’ve not pitched a plug since. I called all the old dogs to see if anyone had a torque spec and none had any.
Thanks John

 

[Jeff Lutz]

Well I did a bunch of reading in the Machinery's Handbook and got semi edumicated on threads. Picked up a "Pee Dee" wire kit and checked several O'Donnell plugs.

I get a PD between 0.2269" & 0.2279", basic (or nominal) PD for a 1/4-32 thread is 0.2297" so they are between 0.0018" & 0.0028" under nominal. From the Machinery's Handbook this is a standard Class 2A thread.

The problem is the tightest H1 tap is between nominal and +0.0005", so even if I could find one I could still be 0.0033 big, no wonder the standard H3 is sloppy, at max. tolerance it is over four thou big.

Everything you wanted to know about taps but were afraid to ask, styles of taps, class of thread , gh numbers , basic point in thread measurement , constants for finding pitch diameter and minor diameter of screw threads , thread constants for various percentages , relation of tap pitch diameter to basic pitch diameter , tap limits product limits and class of thread , how to order special taps - Newman Tools

Guess I'm doomed to single pointing them unless I had a L2 or 3 tap made...

The numbers you got on the Odonnell plugs are in tolerance. And there is nothing wrong with a little clearance/slop as it allows the plug to seat flat on a washer that may not be dead flat . On a different note I personally like .213” for my minor hole size on my custom heads though.

 

[Thomas Augustin]

Well I did a bunch of reading in the Machinery's Handbook and got semi edumicated on threads. Picked up a "Pee Dee" wire kit and checked several O'Donnell plugs.

I get a PD between 0.2269" & 0.2279", basic (or nominal) PD for a 1/4-32 thread is 0.2297" so they are between 0.0018" & 0.0028" under nominal. From the Machinery's Handbook this is a standard Class 2A thread.

The problem is the tightest H1 tap is between nominal and +0.0005", so even if I could find one I could still be 0.0033 big, no wonder the standard H3 is sloppy, at max. tolerance it is over four thou big.

Everything you wanted to know about taps but were afraid to ask, styles of taps, class of thread , gh numbers , basic point in thread measurement , constants for finding pitch diameter and minor diameter of screw threads , thread constants for various percentages , relation of tap pitch diameter to basic pitch diameter , tap limits product limits and class of thread , how to order special taps - Newman Tools

Guess I'm doomed to single pointing them unless I had a L2 or 3 tap made...

I’ve single point machined acme / buttress/api oil pipe/metric/ British/UNJ controlled root radius aerospace/and Threads for decades. Very good advice from your fellow model boaters. I rather make my own parts instead of buying

 

[360modena]

Hey Guys,

A great source which we use for size and tolerances of all threads is Gage Maker. It is the best information regarding every class of threads. Check it out.

Virgil Ericksen