# Tapping question ??...



## 56type (May 8, 2017)

Having a bit of trouble tapping and was hoping I could get some clarification on where I'm going wrong...this is my first machining project...

OK, making a muzzle nut which has an internal thread of 14 X 1.0mm LH. Got the hole drilled on the lathe (Atlas 10100) with a 0.50 cobalt drill bit, which by my math comes up to 12.7mm when converted to metric. I have a metric tap in the needed 14 X1.0mm LH size and aligned it using the lathe tailstock so it would start straight & square to the hole.

Problem is the tap doesn't want to start ?? I'm NOT trying to tap using the lathe's power...It's a small Atlas with a screw-on chuck, so no running it in reverse for left-hand thread. Also at this time I have not bought any tooling for threading, so I won't be threading it on the lathe. To top it off the drill chuck I'm using to hold the tap keeps wanting to unscrew itself from the MT shank that mounts it in the tailstock, even doing the tapping by hand (lathe unplugged, turning 4-jaw chuck in reverse by hand while holding drill chuck with other hand to keep it from turning).

Am I correct in thinking the hole is possibly to small at 0.50in. (12.7mm) ?? I checked & re-checked the measurements and it does measure at 12.7mm, so I was thinking maybe I'll have to bore it to 13mm to get the tap to start ?? Guess what I need to know is what size hole for 14 X 1.0mm LH tap...Thanks


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## DAT510 (May 8, 2017)

What type of tap are you using?  Taper, Plug or Bottoming?  Ideally you want to make sure you are using a Taper Tap as it will be the most easy to get started.  A plug tap will work but it has less of a taper, so it will be harder to start.  A bottoming tap will be next to impossible to start.

Yes, at 12.7mm you are smaller than the recommended tap drill of 13mm.

Here's a Metric Tap Chart.  http://www.kasthurimmc.com/tap-drill-chart.html


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## brino (May 8, 2017)

I'll add that a chamfer at the start of the hole is also a good idea.
-brino


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## 56type (May 8, 2017)

It may in fact be a bottoming tap since it doesn't have very much of a taper, maybe one or two threads & shallow taper... 

Guess I'll pick up a 13mm drill bit and try again with the larger hole size. Thanks.


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## 56type (May 8, 2017)

brino said:


> I'll add that a chamfer at the start of the hole is also a good idea.
> -brino



The tap did accomplish that quite nicely !! Wouldn't start but did chamfer the the edge of the hole. Hoping that will help some when I go up to 13mm and try the tap again.


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## mikey (May 8, 2017)

I should think that a 33/64" drill would be good enough (13mm = 0.512"; 33/64 = 0.516"). Personally, I would go a step bigger and use a 17/32" drill to be sure I can run the tap in steel.

As Brino says, chamfer the hole before starting with a taper or plug tap and it should go okay.


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## 56type (May 8, 2017)

mikey said:


> I should think that a 33/64" drill would be good enough (13mm = 0.512"; 33/64 = 0.516"). Personally, I would go a step bigger and use a 17/32" drill to be sure I can run the tap in steel.
> 
> As Brino says, chamfer the hole before starting with a taper or plug tap and it should go okay.



My drill bit inventory is embarassingly small & consists of one 25pc. cobalt set up to 1/2in. and a Dewalt set with pilot tips up to 1/2in. Just ordered a 25pc. HSS metric set from amazon a few minutes ago though that includes the 13mm bit.


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## carlquib (May 8, 2017)

Are you using the lathe tailstock to push the tap into hole or just by hand? I would think your half inch hole would work, but might produce a more than 75% thread. 

Sent from my SM-G930P using Tapatalk


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## JR49 (May 8, 2017)

56type said:


> The tap did accomplish that quite nicely !! Wouldn't start but did chamfer the the edge of the hole. Hoping that will help some when I go up to 13mm and try the tap again.



56type,  If it is a bottoming tap, you can easily taper 3 or 4 of the first threads on the tap with a fine wheel on a bench grinder.  I've taken many taps that broke up where the full threads are and tapered the first few threads and they worked fine.  Good luck,  JR49


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## 56type (May 8, 2017)

carlquib said:


> Are you using the lathe tailstock to push the tap into hole or just by hand? I would think your half inch hole would work, but might produce a more than 75% thread.
> 
> Sent from my SM-G930P using Tapatalk



That was the initial plan but the tap refuses to engage... Even advancing the tailstock  into the workpiece to maintain pressure and keep the tap straight & square to the hole didn't help, it just chamfered the edge of the hole but wouldn't advance any further. Since it is LH thread when pressure was increased from the tailstock it just started to unscrew the drill chuck from the MT2 shaft. I wouldn't have thought the difference between 12.7mm and 13mm would have made that much of a difference as far as starting the tap, however the tap seems to notice it enough to refuse to start.

I'm thinking of using the high-strength (red) Loctite to lock the drill chuck to the MT2 shaft in order to use it for starting LH threading with taps. Since starting a LH tap causes the drill chuck to unscrew from the shaft.


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## 56type (May 8, 2017)

JR49 said:


> 56type,  If it is a bottoming tap, you can easily taper 3 or 4 of the first threads on the tap with a fine wheel on a bench grinder.  I've taken many taps that broke up where the full threads are and tapered the first few threads and they worked fine.  Good luck,  JR49



That's the next piece of equipment on the "buy list".  After some of the posts by other members I think the problem is that as you said I have a bottoming tap, and a slightly undersize hole that just aren't playing well together. Thanks for the tip, I definitely see myself trying that in the future when I can get some experience on the bench grinder. Be a great to salvage broken taps that way.


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## carlquib (May 9, 2017)

Since you are using a threaded chuck, open the jaws all the way and see if your mt adapter is threaded, many are. If it is, it will probably be a left hand thread for just what you are experiencing. You screw the chuck tightly onto your arbor and then apply the left hand screw to keep your chuck from backing off the mandrel when running in reverse. 

Sent from my SM-G930P using Tapatalk


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## 56type (May 9, 2017)

carlquib said:


> Since you are using a threaded chuck, open the jaws all the way and see if your mt adapter is threaded, many are. If it is, it will probably be a left hand thread for just what you are experiencing. You screw the chuck tightly onto your arbor and then apply the left hand screw to keep your chuck from backing off the mandrel when running in reverse.
> 
> Sent from my SM-G930P using Tapatalk



What I have is a Craftsman 1/2in. drill chuck that is thread onto a shaft that has a MT2 taper on one end that goes into the tailstock. Workpiece is being held in a 4-jaw chuck threaded onto the headstock spindle of the lathe. No reverse on my lathe since running it in reverse could cause the 4-jaw to unscrew itself from the headstock. The thread on the MT2 shaft that goes into the tailstock is RH.

 I tried turning the 4-jaw on the headstock spindle by hand in reverse and as soon as the tap tried to cut into workpiece it locked hard and began unscrewing the Drill chuck mounted in the tailstock from the threaded MT2 shaft. Then I tried leaving the MT2 tapered shaft loose in the tailstock bore to act as a guide to keep things straight, this time turning the drill chuck holding the tap by hand into the workpiece. Still no luck, the tap refused to start & just chamfered the edge of hole without cutting any threads.

At this point I thought I should take a step back and find out where I'm going wrong before damaging either the workpiece, the tap, or both. Here's a pic showing the drill chuck mounted in the tailstock (note I have since cut threaded portion of the MT2 shaft to gain a bit more rigidity)...


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## 56type (May 9, 2017)

Pic of the workpiece....before I attempted using the tap. Hole now has a chamfered edge thanks to the tap.


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## DAT510 (May 9, 2017)

If you are having trouble getting enough torque on the tap turning the drill chuck by hand, you might try mounting the tap in a standard tap wrench, and then mount a tap guide in the tailstock chuck to keep the tap aligned with the bore of the barrel.

The tap guides are spring loaded so the guide stays in contact with the end of the tap wrench (and therefore aligned) as the tap cuts deeper into the barrel. Just make sure the tap wrench you use has a guide hole on the top.

Tap Guide  http://littlemachineshop.com/products/product_view.php?ProductID=1963


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## 56type (May 9, 2017)

DAT510 said:


> If you are having trouble getting enough torque on the tap turning the drill chuck by hand, you might try mounting the tap in a standard tap wrench, and then mount a tap guide in the tailstock chuck to keep the tap aligned with the bore of the barrel.
> 
> The tap guides are spring loaded so the guide stays in contact with the end of the tap wrench (and therefore aligned) as the tap cuts deeper into the barrel. Just make sure the tap wrench you use has a guide hole the top.
> 
> Tap Guide  http://littlemachineshop.com/products/product_view.php?ProductID=1963



Thanks fr the link !! I bookmarked it to add to the next order from LMS. Also I'll make sure any tap handles I buy come with the tap guide hole.


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## Zathros (May 9, 2017)

Just à answer from à eu dude who Works with every tread that is thinkable. First for Some treads we use 2 or even 3 differend irons. Foretap, middle tap and end tap. Often when Used one tread iron 'sorry for My bad english' I use the lathe Lets say for the first half of the tread. I saw à huge amount of Good tips here, grinding à sharper edge or bevel to both If needed. But I see you want to make à m14 and most lathe machines can hold tools to start female tap treads at   M12 (½ ") and it Looks that your machine can do that. And for the left hand tread you can scree à bolt at the MT 2 other end throug the hollow axle of the machine. That Will hold your left hand turn Ok. I have not read all the posts but I night even double up in answers My apologies for that.
Grts.
Ted.


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## brino (May 9, 2017)

Zathros said:


> Grts. Ted.



Welcome to the group Ted!
Your english is way better than most people's second language. (I have none!)
I am glad you're jumping in and contributing.

-brino


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## Zathros (May 9, 2017)

Thanks,
Me is always happy talking about any tecnology. My main work is in small metal parts. Any metal. Done à lot of tech stuff and diy projects. Worked in construction, ships building, cars, bikes of any kind, spray paint and body shop, as à kid already with electronics, the chip didn't exist yet. So from building or changing à machine up to working with it and everything in between I most lightly done it.
Really threading withwort, tpi, iso or exotic threads like in bycicles or ships and all in between it's done. Left and righthanded.
Just à Tiny bit of My background for your info all.
Grts
Ted.


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## Wreck™Wreck (May 10, 2017)

You don't need a chart for tap drill sizes they are the major diameter minus the lead, in your case 14mm Major diameter X 1mm lead thread. A 13 mm drill.

This is true of all 60 Degree threads, a 3/8-16 tap drill would be 5/16. The lead is 1/16, 3/8-1/16 = 5/16.

There are exactly 25.4 mm per inch as set by international standards use that number for converting dimensions back and forth.


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## T Bredehoft (May 11, 2017)

Wreck™Wreck said:


> a 3/8-16 tap drill would be 5/16.



True, if you want 100% thread contact. It might be hard to thread the two together, though. 60 to 75% is norm, depending on  material and usage.


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## benmychree (May 11, 2017)

One thing that I do not see in this discourse is the desirability to BORE the hole to the size required and not rely on drills which are likely to result in a non concentric part.


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## markba633csi (May 11, 2017)

The MK2 Atlas shown above actually has MT1 taper in the tailstock. Same as the 618.
MS


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## Wreck™Wreck (May 11, 2017)

T Bredehoft said:


> True, if you want 100% thread contact. It might be hard to thread the two together, though. 60 to 75% is norm, depending on  material and usage.


Not really, this generally yields a 75% thread, also the question is about taps where the size is fixed by the tool, the Pitch Diameter of taps are not easily changed.


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## T Bredehoft (May 11, 2017)

Wreck™Wreck said:


> the Pitch Diameter of taps is not easily changed.



My Starrett card does say 5/16 is the tap drill for 3/8 16.  Hmm.


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## Wreck™Wreck (May 12, 2017)

T Bredehoft said:


> My Starrett card does say 5/16 is the tap drill for 3/8 16.  Hmm.


I have no idea why I remember this, in order to determine the Major Diameter of a number sized screw thread multiply the number by .013 then add .060, whoever thought this was a good idea in 1870 something deserves to be forgotten.

You will also notice that with a metric drill/tap chart the tap drill size is the Major Diameter minus the lead of the thread, for example an M5 .08 thread tap would like a 4.2 MM hole and so on. The metric screw thread standards and Unified Screw Thread standards are both 60 Degrees included angle, they differ in diameter and lead which cannot be mixed.


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## 56type (May 12, 2017)

Thanks for all the help & suggestions...I got it threaded and it actually works !! Took a bit of head scratching though, I ordered a cheap set of HSS metric bits and drilled the hole to the needed 13mm then had to figure out how to lock things down for the LH thread. Wound up taking a small block of wood and 1/4in. drive ratchet extension and placing the extension in the 4-jaw chuck key hole and block of wood on lathe bed to protect it. Placed the 14x1.0mm LH tap in the drill chuck on the tailstock and got it to start a few threads before the drill chuck tried to unscrew itself again. At this point I started looking locally for a tap handle that would fit and came across one at Harbor Freight that fit the tap. It's a ratcheting type and seems fairly heavy duty (despite HF bad rep.). Started the tap back into the workpiece and using the extension & wood block to lock the 4-jaw to keep it from loosening (which it initially tried to do), threading it was straightforward from there. Other than backing up the tap to break the chips and making sure the handles didn't contact the lathe bed while turning the tap handle it threaded great. Here's a pic of the muzzle nut on a cut barrel piece that has the male threads I keep on hand to check threads...


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