# Cheap 60 degree tool or correct threading bit shape?



## cdhknives (Feb 11, 2015)

My 60 degree gauge 'thread fish' has rounded bottoms in the vee notches.  When I round/blunt my threading bit tips to match, my threads look bad and are too tight, so I end up cutting too deep (per 3 wire measurement vs. 'book' dimension) to get a nut on.  I'm beginning to wonder if the no-name gauge should have a relief in the tip.  With a sharp bit the tip catches the radiused bottom before I can get the edges against the notch to really check my angles.

In the picture below I'm trying to build a 1/2-28 mandrel.  To get the thread protector on, I had to cut to the point the thread measures .011" undersize...for a 2 hour to build paperweight!

Should I relieve the tip of the vee notch in my thread fish, or is that radius the proper tip geometry and I have another problem with my threading?


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## Ulma Doctor (Feb 11, 2015)

a threading tool should be pretty sharp. some will have the smallest of radius at the tip- almost unnoticeable.
is the fish tail for UNC/SAE threads???

Whitworth threads have a pronounced radius in their threads and is at 55*v rather than a 60*v like the UNC/SAE


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## Bishop (Feb 11, 2015)

Can you post a photo of your fishtail gauge.


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## higgite (Feb 11, 2015)

The tool point isn't supposed to be shaped like the fishtail gauge cutout. The notch at the base of the cutout is so you can snug the tool up to the gauge to check the side angles without hitting the tool point and dulling it.

Tom


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## Bishop (Feb 11, 2015)

higgite said:


> The tool point isn't supposed to be shaped like the fishtail gauge cutout. The notch at the base of the cutout is so you can snug the tool up to the gauge to check the side angles without hitting the tool point and dulling it.
> 
> Tom




He mentions the tip of the tool hitting the bottom of the relief hole before the tool touches both sides of the v notch.


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## Brandon1 (Feb 12, 2015)

First obvious problem is the poor choice of beer.:rofl:


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## higgite (Feb 12, 2015)

Bishop said:


> He mentions the tip of the tool hitting the bottom of the relief hole before the tool touches both sides of the v notch.



My bad. I misread it. In that case, I would cut a relief notch if there is none or buy a better fish gauge.

Tom


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## NightWing (Feb 12, 2015)

The tool tip should have a radius of .125 times the pitch.


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## mikey (Feb 12, 2015)

I'm with Ulma Doc - sounds like a British Whitworth fish tail.


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## Bishop (Feb 12, 2015)

What I don't get is if the OP is using the gauge to check the threading tool and his grind, how is it bottoming out before touching both sides of the gauge?


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## JimDawson (Feb 12, 2015)

Bishop said:


> What I don't get is if the OP is using the gauge to check the threading tool and his grind, how is it bottoming out before touching both sides of the gauge?




Three possibilities that I see:  1) it's a crappy gauge with no relief in the bottom of the V, 2) the OP is grinding a 30 degree tool, 3) as said above, it's a Whitworth gauge.


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## projectnut (Feb 12, 2015)

Here's a link to a Starrett gauge.  Note the relief at the top of the V.  The sharpened tool should fit the V with the tip going into the relief.  I have several B&S and Starrett gauges,  They all look the same.  However I don't recall paying more then $5.00 for any of them when I bought them new.

http://www.amazon.com/Starrett-C391-Degree-Center-Gage/dp/B0002CSBN4


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## 4GSR (Feb 12, 2015)

If your root width of your thread is coming out too wide. Just chase the thread with a die nut to finish out the root.  I used to have to do this almost every time cutting fine pitch threads.  Now, I have a good selection of pre-formed threading inserts that do a pretty good job cutting threads.  I still use die nuts once a while when needed.  I have cut 1/2-28 thread before without any issues.


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## mce5802 (Feb 12, 2015)

I have el cheapo fishtails from China n they have the relief. I'm betting you're right about it being a whitworth gauge.


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## cdhknives (Feb 12, 2015)

Thanks guys.  The gauge is not marked with anything except the measurement data...not even a manufacturer's mark.  There is no relief at the tip, just a radius at the bottom of a vee notch.  Hopefully it isn't a Whitworth...you've got me worried now because isn't Whitworth a 55 degree thread?  It was what they had at the local Rex Supply.  If so my threading bits are ground to the wrong angle too.:angry:  I used the thread fish to scribe alignment lines on my grinder to set the angle.


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## cdhknives (Feb 12, 2015)

Here it is:

http://www.rex-supply.com/cgi/CGP2S...PAHDID=000000086395384&PARDID=567190930511425


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## higgite (Feb 12, 2015)

Unless it's mismarked, it is a standard 60* gauge, not a Whitworth gauge. Just a cheap one.

Tom


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## mikey (Feb 12, 2015)

That is not a Whitworth fish tail gauge. It has a 60 degree included angle so it is meant for standard Imperial threading. Whitworth threads have a 55 degree included angle and a pronounced round profile at the bottom of the thread.


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## kd4gij (Feb 12, 2015)

You need to get a better gauge. You don't need a Starrett, Just one that looks like this.


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## 18w (Feb 12, 2015)

File a relief with a small jeweler or swiss type file..... done.



Darrell


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## cdhknives (Feb 12, 2015)

I have a Mitoyo gage en-route.  $13 shipped via Amazon Prime.


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## G MORSCH (Feb 12, 2015)

A good quality gage is important.  When I set my threading tool, I loosen the tool post and set a 30/60/90 ground triangle against the chuck face, I only need to set the leading edge since I use a form ground insert.  Place a white piece of paper on the ways, and slide the 30 deg. edge of the threading tool against the 30 degree edge of the triangle until the gap blocks out the white paper and lock 'er down.  A tooth brush and a couple drops of TapMagic really help reduce built up edge when running low manual threading speeds.  When you are a thou or two from full depth, take a couple straight in cross slide passes at the bottom to shave both the leading and trailing thread flanks.    
Good Luck!
Best Regards,  Gary


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## Andre (Feb 13, 2015)

higgite said:


> My bad. I misread it. In that case, I would cut a relief notch if there is none or buy a better fish gauge.
> 
> Tom



A knife edge, or nut file would work well for this as long as it is not hardened. If so a Dremel cutoff wheel would work.


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## basildoug10 (Feb 18, 2015)

Hi all, A most interesting topic here on sharpening a tool bit for threading. I am new to  machining and milling, and I have the same problem with my thread gauge when checking  the grind of the tool bit. Usually I find a tiny "feather" on the tip of the tool bit which forms as a result of grinding. This feather is barely visible and the tool touches the bottom of the "V" on the gauge, and prevents the tool from going any deeper into the the gauge and results in the sides of the toolbit from making contact with the sides of the gauge. What I do is to wipe across the whole point of the toolbit with a fine honing stone and the feather is removed. The tool then fits into the gauge all the way. It amaizing just how much the slight feather on the tip  prevents the toolbit from sitting deeper into the gauge. 

Also, can someone advise me about " thread measuring wires" what are they?
Regards


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## darkzero (Feb 18, 2015)

basildoug10 said:


> can someone advise me about " thread measuring wires" what are they?



Here's a recent video that covers them.


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