heartbroken

A

AMMASHOOTA

Gary Gruber
it's been 30+ years since i have broken a tap in a hole. tonight i broke a $120 carbide tap the first time i used it. fortunately, i was able to extract the broken piece and save the item i was tapping.
 
As you might know, I am in the Machine Shop Business. We do, on rare occasions, break taps. We usually have them disentegrated, there is a company in Houston that has portable Carbon Arc burners that do it for about $150.

The main culprits in tap breakage are the tap going crooked into the hole. Second is too small of a tap drill, and of course, bottoming one out and a dull tap.

I have to ask. $150 seems quite expensive for any tap that would be used in Gun work. What size was it? We just bought a new 1 1/2 6tpi plug tap for about $125.
 
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jackie schmidt said:
As you might know, I am in the Machine Shop Business. We do, on rare occasions, break taps. We usually have them disentegrated, there is a company in Houston that has portable Carbon Arc burners that do it for about $150.

The main culprits in tap breakage are the tap going crooked into the hole. Second is too small of a tap drill, and of course, bottoming one out and a dull tap.

I have to ask. $150 seems quite expensive for any tap that would be used in Gun work. What size was it? We just bought a new 1 1/2 6tpi plug tap for about $125.
Click to expand...

it was a blind hole. i bottomed it out. didn't want to pay another $120 for another carbide tap to finish the thread. got it from MSC. 8-32. it was the right size drill (#29).

Ruger bolts (rimfire) are hardened. i purchased carbide spot drill and tap drill to attach a 'racker' to the bolt. the after market rackers use clamping action that weakens the aluminum surrounding a might large dovetail. Invariably, the clamp portion of the racker fails at the joint from excessive pressure to keep it together. they are $80 each and rarely last more than 3-4 months in heavy competition.

i figured i would drill and tap the bolt head for a racker, that would solve the problem. the initial taping went fine -- i blew it when i tried to get 'one more thread'. i forgot how brittle carbide is.

expensive lesson.
 
jackie schmidt said:
As you might know, I am in the Machine Shop Business. We do, on rare occasions, break taps. We usually have them disentegrated, there is a company in Houston that has portable Carbon Arc burners that do it for about $150.

The main culprits in tap breakage are the tap going crooked into the hole. Second is too small of a tap drill, and of course, bottoming one out and a dull tap.

I have to ask. $150 seems quite expensive for any tap that would be used in Gun work. What size was it? We just bought a new 1 1/2 6tpi plug tap for about $125.
Click to expand...

http://electroarc.com/tabletop.cfm

http://www.metal-disintegrators.com/metal_disintegrators/Models.cfm
 
Carbide taps are really for production work in a machining center. They are certainly not intended to be hand taps. They'll snap off easy as pie if you apply side pressure on them. If you really have to use a carbide tap manually, at least set it up in the mill and use a dead center to hold the tap wrench.

Any of the really nice quality taps will tap your action materials without any problems. Emuge taps for high alloyed materials are very nice and not near so pricey. You can get a 10-32 for $35 or so on sale. I'd say you can tap materials in the high 40s with them. 4100 series steels max out around 46, so even if its at max hardness, they'll do the job. Not saying it'll do it for long, but, a hole or 3 should be no issues with good tap fluid. Personally, I like coolant at full strength for most steels.
 
4Mesh said:
Carbide taps are really for production work in a machining center. They are certainly not intended to be hand taps. They'll snap off easy as pie if you apply side pressure on them. If you really have to use a carbide tap manually, at least set it up in the mill and use a dead center to hold the tap wrench.

Any of the really nice quality taps will tap your action materials without any problems. Emuge taps for high alloyed materials are very nice and not near so pricey. You can get a 10-32 for $35 or so on sale. I'd say you can tap materials in the high 40s with them. 4100 series steels max out around 46, so even if its at max hardness, they'll do the job. Not saying it'll do it for long, but, a hole or 3 should be no issues with good tap fluid. Personally, I like coolant at full strength for most steels.
Click to expand...

it was set up in a mill and the tap started and ran very smoothly. the problem here is that once i get the process down correctly, i will probably have around 10-12 guns to do for other club members, so i'm not sure buying taps every couple of holes is justified for the $85 i will charge for the racker and installation. However, if i can get 6 holes per tap, i guess that would spread the cost out a bit. I don't know the hardness index of the Ruger bolt, but the spot and tap drills ran through like butter.
 
"Ruger bolts (rimfire) are hardened. i purchased carbide spot drill and tap drill to attach a 'racker' to the bolt. the after market rackers use clamping action that weakens the aluminum surrounding a might large dovetail. Invariably, the clamp portion of the racker fails at the joint from excessive pressure to keep it together. they are $80 each and rarely last more than 3-4 months in heavy competition."

I'm curious, what do you mean by a "Racker", and what model of Ruger rimfire are you attaching it to?

Is this on a pistol, or rifle?

You might look into the possibility of spot annealing the area you'll be drilling and tapping.
 
gunsmither said:
"Ruger bolts (rimfire) are hardened. i purchased carbide spot drill and tap drill to attach a 'racker' to the bolt. the after market rackers use clamping action that weakens the aluminum surrounding a might large dovetail. Invariably, the clamp portion of the racker fails at the joint from excessive pressure to keep it together. they are $80 each and rarely last more than 3-4 months in heavy competition."

I'm curious, what do you mean by a "Racker", and what model of Ruger rimfire are you attaching it to?

Is this on a pistol, or rifle?

You might look into the possibility of spot annealing the area you'll be drilling and tapping.
Click to expand...

Ruger pistols (MK II, III, 22/45) have a bolt with a 65 degree heavily serrated dovetail on the end. Grabbing the serration to initially chamber a round or release the bolt between mag changes tears your fingers up very quickly. A racker is nothing more than a rectangular piece of aluminum that extends past the end of the bolt attached in some manner to to the back of the bolt to permit one finger action.

Traditionally this has been accomplished by ears that wrap around the dovetail and are held in place by set screws. Aluminum wears very quickly under these conditions and the racker becomes loose and /or the threads strip. they usually need to be replaced frequently.

i have done spot annealing on other items in the past but hesitate to take that approach on something this large.
 
JerrySharrett said:
There are some rally cool videos at the Emuge web site. I especially love the Z-axis/C-axis portion.

http://www.emuge.com/videos/32rc.html
Click to expand...
Jerry,
What I wouldn't give to have a 5 axis machining center like that. The 5th axis for chamfering is more than just fluff, that's some time/tool saving stuff there.

Ammashooter,

A little known fact about tapping I'd like to add to this thread (tho it's likely you know this already), is that tapping depth past 55% of thread diameter is basically a waste. It gains no strength vs stopping at 55% depth.

Tapping to a depth of 55% requires only 60-70% as much torque as tapping to 75%. Tapping to 85% requires double the torque it takes to tap 55% depth.

A trick I use when doing materials that are really hard, is to go one size lower on the drill chart. In your case, I'd be using a 28 Drill. I wouldn't worry too much about that 45rc 4140 stripping out. But, expecting a tap to cut full depth threads in stuff like that can be asking a bit much. When I do this, I usually go past 100% depth, but, it's not challenging for the tap when the hole is a tick oversized.
 
ammashoota,
MkI & early MkII bolt tabs were serrated square,not tapered.
The bolt tab is welded to aft end of the bolt.
A 5/16" stud locates the tab & is fusion TIG welded,blended.

Don't add too much weight,or the tab will break off-I've TIG welded <100.
 
Dans40X said:
ammashoota,
MkI & early MkII bolt tabs were serrated square,not tapered.
The bolt tab is welded to aft end of the bolt.
A 5/16" stud locates the tab & is fusion TIG welded,blended.

Don't add too much weight,or the tab will break off-I've TIG welded <100.
Click to expand...

Sounds like a reasonable solution -- but i haven't found many people willing to go that length for a bulletproof racker. I should not have included MK II. as you say, they were not tapered. III and 22/45 are 65 degree.
 
Dumb question: Why don't they have a tap that cuts half the thread depth and another to cut the remaining depth or do they?
Ron
 
ncnbrsa said:
Dumb question: Why don't they have a tap that cuts half the thread depth and another to cut the remaining depth or do they?
Ron
Click to expand...

They do :) that's how I was taught to tap on guns. You buy three taps, grind one down for starting shallow holes and snap one of square for use as a bottoming tap.

And then there's number of flutes to consider, straight or helical, and lubricant...... all important with small taps and variable steels. The last tap I snapped was a 1/4-28, because I didn't figure it was possible to break a tap that huge!

LOl

al
 
Last tap I broke was a 1/2-13 making a barrel vice out of "mystery metal". I used a 1/4" carbide end mill to hog it out. I then decided to scrap the whole thing and started over with a 4140 block. I don't think I will try to tap any more steel of dubious origin, too much work only to have to scrap it!
 
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