Need help from real machinists

A

alinwa

oft dis'd member
So today I'm drilling and tapping a Stainless Steel PTG .500 recoil lug to 1/4-28.

Drill-----'screeeeeEEEHHH!!! Drilled in steps, center drill did OK (but blue chips at low speed) Had to GET IN! and try not to work-harden the surface.... I tried several brands (all cheap) and one "black one" drilled a lot better than the others but generally just TOUGH to drill. Sharpened bits 10 times.

Tap-----STICKY!! Nearly stuck the taps several times. Had to tap/bottom tap.....tap/bottom tap.....tap/bottom tap several time to get to 5 threads


I'm gonna' order some 2-flute taps and some high quality drills......


Any thoughts/brands/types/techniques come to mind?

I'm drilling on an old Bridgeport, tapping by hand with a guide using Do-Drill.
 
It always helps to know what type of stainless you are drilling. There is a lot of difference in something like 416 and 17-4.

Any quality high speed #3 drill and tap should do the job. In most tool catelogues, you will see different bands of drills and taps, labeled "foreign" or "domestic". Get a top quality drill such as Cleavland.

There are also "cobalt" drills, which are High Speed Steel alloyed with cobalt. They are harder than regular HSS tools.

Of course, you can always get a Carbide drill. When I drilled and tapped the bottom of my Bat Neuvo Action, I just bought a #3 Carbide drill and 1/4 28 tap. Made the job a lot easier.
 
jackie schmidt said:
It always helps to know what type of stainless you are drilling. There is a lot of difference in something like 416 and 17-4.

Any quality high speed #3 drill and tap should do the job. In most tool catelogues, you will see different bands of drills and taps, labeled "foreign" or "domestic". Get a top quality drill such as Cleavland.

There are also "cobalt" drills, which are High Speed Steel alloyed with cobalt. They are harder than regular HSS tools.

Of course, you can always get a Carbide drill. When I drilled and tapped the bottom of my Bat Neuvo Action, I just bought a #3 Carbide drill and 1/4 28 tap. Made the job a lot easier.
Click to expand...

Thanks...

I don't know from PTG website just what these are made of. They're surface ground and take a nice finish so my intuition is that they're "harder" than mild steel or barrel steel. But I don't know if this stuff is "hard" or just sticky-tuff.

I'll happily buy some carbide taps, I've never used them so don't know how brittle they are or how they work for hand-tapping.....you're saying #3 (.2130) drill bit? I've been using #1 (.2280) but I'd love nice deep threads!


I've had a drop-port Neuvo on order for a couple mo now...... hoping they do a run :)
 
Make sure you're using good quality tools all 'round. Especially the tap. If it says "Vermont American" or "Irwin" it belongs in the trash. I'm a big fan of spiral-fluted (not spiral point) taps and they're special enough that I've never run across a poorly made one. I have quite a few from Western Cutting Tool that I think are Korean made and they work great.

GsT
 
Get drills with a 135* point. The spiral flute taps work great. Use a good cutting oil for drilling and tapping. Bacon grease or Lard Oil works great on harder materials. Just clean up well afterwards or the mice will.
 
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my trick for stainless ( non production ) Set up in Bridgeport But I never turn it on - I use a strap wrench on the chuck and turn by hand, no heat generated that way which what is giving you the problem, just a little and the surface becomes glass hard for a couple thousandths deep, a real pia to break through that again. Carbide taps - no thanks in this instance . just too brittle. I have a lard based additive that I add to my cutting fluids- but with stainless it can cause discoloration and will etch it if not cleaned off extremely well. Fells Naptha soap made into a kind of semi soupy paste works well for the tapping/drilling for sticky types of metal. I am just real old school, ain't in any hurry. Chris
 
Just a note, Al. The biggest cause of tap breakage, aside from a tap being too dull, is not getting the tap started straight in the hole.
 
OK, so I ordered some carbide fi'tty-dollar taps and some better drill bits.

And here's a pic to show that even though it's binding the taps, it is still soft enough for displacement to occur.


I'm starting the taps in the mill or the drill press, using DoDrill (Viper's Venom)



As far as WHY???


My Momma done tol' me 45yrs ago, she said "Son, you ain't normal! You don't THINK like other folks..... less'n you learn what the word "conformity" means? Life will be HARD for you...."

And she was right


And now I've infected my KIDS! Life is hard for them too.......


:)





I won't even show you'se what's on the other side...........(s)
 

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I'd contact PTG and ask what your dealing with. Those are made, heat treated and finish ground. Parts like those can be a crap shoot unless you can test them for hardness. Or, at least get a reasonable assurance as to what they are supposed to be.

As stated use top quality 135 deg drills. Screw machine length. I'd look into 140 deg hole starting drill when using 135 deg drills. With hard to machine steels, using the wrong center drills can destroy the drill and you don't realize it until it starts to squeak.

Do "not" resharpen drill, pitch it.

Drill as deep as you can, further if possible. You need room for chips.

Do "not" step bore hole, or use too sharp of an angle center drill.

Find a proper designed and coated tap. Spiral pointed, for thru holes, spiral fluted for blind holes If it has even the slightest indication of being chipped or worn, pitch it. Use only "machine" taps not "hand" taps.

Do not stop and reverse rotation of tap....that's the fastest shortcut to failure.

Now pucker up and CRINGE,...... "power tap the hole"..........Chicken !!!!!!!!

While your mileage may very, but, this is how we do it. Breaking off or sticking taps is not acceptable.

Seems like a lot of BS just to drill and tap a hole.
 
TRA said:
I'd contact PTG and ask what your dealing with. Those are made, heat treated and finish ground. Parts like those can be a crap shoot unless you can test them for hardness. Or, at least get a reasonable assurance as to what they are supposed to be.

As stated use top quality 135 deg drills. Screw machine length. I'd look into 140 deg hole starting drill when using 135 deg drills. With hard to machine steels, using the wrong center drills can destroy the drill and you don't realize it until it starts to squeak.

Do "not" resharpen drill, pitch it.

Drill as deep as you can, further if possible. You need room for chips.

Do "not" step bore hole, or use too sharp of an angle center drill.

Find a proper designed and coated tap. Spiral pointed, for thru holes, spiral fluted for blind holes If it has even the slightest indication of being chipped or worn, pitch it. Use only "machine" taps not "hand" taps.

Do not stop and reverse rotation of tap....that's the fastest shortcut to failure.

Now pucker up and CRINGE,...... "power tap the hole"..........Chicken !!!!!!!!

While your mileage may very, but, this is how we do it. Breaking off or sticking taps is not acceptable.

Seems like a lot of BS just to drill and tap a hole.
Click to expand...



I'm not disagreeing with you!

BUT

I'm a dude with a couple lathes and an antique Bridgeport..... I got no 'power tap' capability :)

And I'm drilling/tapping the recoil lug only to avoid making a lug from easier steel, hoping that the threading process is less work than making the entire thing. I have 1/2" thick 304 SS and 12L14 bar stock if this gets too complicated. (which it kinda' already is..... I was hoping for some magic!)
 
alinwa said:
I'm not disagreeing with you!

BUT

I'm a dude with a couple lathes and an antique Bridgeport..... I got no 'power tap' capability :)

And I'm drilling/tapping the recoil lug only to avoid making a lug from easier steel, hoping that the threading process is less work than making the entire thing. I have 1/2" thick 304 SS and 12L14 bar stock if this gets too complicated. (which it kinda' already is..... I was hoping for some magic!)
Click to expand...

Al, I wish I could come up with an even more complicated and convoluted way to explain how to drill and tap a hole, but TRA has me beat.
 
alinwa said:
So today I'm drilling and tapping a Stainless Steel PTG .500 recoil lug to 1/4-28.

Drill-----'screeeeeEEEHHH!!! Drilled in steps, center drill did OK (but blue chips at low speed) Had to GET IN! and try not to work-harden the surface.... I tried several brands (all cheap) and one "black one" drilled a lot better than the others but generally just TOUGH to drill. Sharpened bits 10 times.

Tap-----STICKY!! Nearly stuck the taps several times. Had to tap/bottom tap.....tap/bottom tap.....tap/bottom tap several time to get to 5 threads


I'm gonna' order some 2-flute taps and some high quality drills......


Any thoughts/brands/types/techniques come to mind?

I'm drilling on an old Bridgeport, tapping by hand with a guide using Do-Drill.
Click to expand...

Send the lug back and have them to anneal it or order that has not been hardened....period

That lug is probably made from a hardenable material 17-4ph, 18-8ph or one of the 400 series stainless steels. When a material is beyond a certain hardness you ain't gonna' cut it with conventional tooling!!!





.
 
jackie schmidt said:
Al, I wish I could come up with an even more complicated and convoluted way to explain how to drill and tap a hole, but TRA has me beat.
Click to expand...

And you drill and tap small holes in extremely tough materials?????? Just using a 60, 82, 90 degree center drill and running a 135 drill "will" destroy even very pricey carbide drills. not only is the drill scrap, it then results in tap failures. It's no different than page after page of chambering advice, as the end result is directly in relation to the basic machining practices. The harder the material, and using the expensive perishable tooling these days, the more a process needs complicated and convoluted practices followed.

He asked for advice from real machinists, not a drill press operators, tricks of the day. We all know you are the best machinist in Texas but he asked the question and I hope he benefited from it. Al did not ask how to drill and tap, plain old hot rolled.

Jackie did you read what I said to Al???? If so, "why"?


"AL"......You can power tap on your lathes and the definition of a Bridgeport is "power tapper". We direct tap, use ARO air tappers.....even a cordless tool will drive a tap. I better stop here as I don't want someone bitching about me bloviating.
 
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Thank you guys all! My idea of using a relatively cheap recoil lug unconventionally is kinda' withering on the vine :)

I can make the lug I need, just not for the 25 bucks these cost me.....but as has been said, I'm fighting an uphill battle on the back end trying to save a buck on the front end.

This clarification has helped, and thank you Jerry for putting it into perspective :) yes, this stuff work-hardens like crazy.
 
FBecigneul said:
And another thing.
How can you be sure the drilling and tapping hasn't expanded the lug to a point that it is no longer ground to a perfectly flat 0.500000?
Click to expand...

If you know how to grind to that precision, I'll pay you for lessons... (Still a valid point, but I'm guessing 0.5000" +/- 0.0002")

GsT
 
FBecigneul said:
And another thing.
How can you be sure the drilling and tapping hasn't expanded the lug to a point that it is no longer ground to a perfectly flat 0.500000?
Click to expand...

Its a judgment call. If the remaining wall thickness is enough it isn't going to distort. Several ways to check. Measure the thickness before and after is one. Throw it on a surface grinder if it has swelled, ferinstance.


.
 
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