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radkins
12-06-2010, 11:53 AM
I need to buy a tap 15/16" 16 TPI to cut new threads in some 4140 HT, this is an open ended hole about 7/8" deep. I have a choice between spiral flutes or straight flutes and I am a bit confused about which might be better, any suggestions?

Mark McGrath
12-06-2010, 12:04 PM
Spiral point would be best for a through hole.Straight flutes would be my next choice.
Spiral flute would do it ok but as it is designed to feed the cutting back up the hole,there is a chance that when you reverse the tap after breaking through that the cutting gets trapped in the back of the tap and causes it to chip.

Boucher
12-06-2010, 12:23 PM
On the larger taps with a through hole I would go with a straight tap. It is easier to blow the chips out. After I get things started with a tap handle, I switch over to a 1/2" air impact to run and reverse the tap. Use lots of dark cutting oil or Moly Dee. Makes a mess but turns out some slick threads.

becksmachine
12-06-2010, 12:54 PM
Is this a custom made tap?

15/16-16 is a "special" size to begin with, and finding it in anything other than straight flute would seem unlikely to me.

Spiral point would be my choice for a through hole, not spiral flute. I also must admit that I would never be brave enough to run a tap with an impact wrench. Well, maybe to clean out an existing thread but never to cut a new thread. :D

Dave

Boucher
12-06-2010, 01:01 PM
I wouldn't either for something as short as the OP is working on but for something 2 1/2" thick it works. Guess I was not paying enough attention to the original question.

radkins
12-06-2010, 01:08 PM
I have found these taps available at several places in threads ranging from 9 TPI to 40 TPI and spiral flute or straight flute but I have not seen spiral "point". Pardon my ignorance here but I am a bit confused by spiral "point".

Kind of embarrassing to admit that I am confused by spiral "point" but then I guess if I already knew these things I would not have needed to ask in the first place. :)

RobbieKnobbie
12-06-2010, 01:27 PM
I think they're talking about 'gun' taps... taps that have a secondary angle ground into them for the first four or six threads that cause the chips to roll our ahead of the tap. This is especially beneficial for tapping through holes because the chip never gets in the way - it always stays out ahead of the tap and drops out the far side when the hole is finished. No good what so ever for blind holes though.

for a nice tap primer, try McMaster's wonderful catalog (http://www.mcmaster.com/#gun-taps/=a14r1y)

JCHannum
12-06-2010, 01:36 PM
What is the application? 15/16"-16 is thread size for a Winchester High Wall action. I just made a tap last weekend to chase the threads. If initially threading an action, it should be single pointed on the lathe.

Willy
12-06-2010, 01:40 PM
The spiral point taps are the ones to get for through holes as they do force the chips out ahead of the tap.

In addition to the McMaster page left by RobbieKnobbie here is one I refer to for issues with tapping problems, it's Carbide Depot's tapping trouble shooting guide.

http://www.carbidedepot.com/formulas-tap-troubleshoot.htm

radkins
12-06-2010, 02:04 PM
What is the application? 15/16"-16 is thread size for a Winchester High Wall action. I just made a tap last weekend to chase the threads. If initially threading an action, it should be single pointed on the lathe.



You pegged it, I am tapping new threads for the barrel in a High Wall action.


My only choices so far are either a straight flute or a spiral flute and these are only available (from where I have checked so far anyway) in a plug style which is not my first choice, that of course would be a taper tap. If anyone has any suggestions on where I might find the best tap for this application or any suggestions on completing this threading operation I would appreciate it.

doc0455
12-06-2010, 02:20 PM
Spiral fluted taps are great for blind holes but for through holes I would pick the straight with a spiral point. The reason is that the spiral flute tap is a little more fragile than the straight and less forgiving.

JCHannum
12-06-2010, 02:26 PM
The flute configuration would make little difference in this application. A plug tap can always be ground to taper configuration. However, I would not recommend tapping the threads for the barrel shank. They should initially be single pointed in the lathe. They can be cleaned up with a tap if desired after 90% or so depth has been reached.

Toolguy
12-06-2010, 03:01 PM
The spiral point or gun tap takes the least amount of effort or force to cut a thread from a drilled hole. I do agree with JC and others, the hole should be threaded on a lathe or thread milled first to make sure it's perpendicular to the action. If you then chase it with a tap for final size, any style will work. The plug tap would then be a good choice.

radkins
12-06-2010, 03:26 PM
OK, you guys have me thinking about this and I guess I better rethink cutting new threads with the tap, I have put waaaaaay too much work into this thing so far to screw it up now! Also I just finished reading up on taps from those links that were provided, good stuff and I leaned some things.

Thanks everyone.

JCHannum
12-06-2010, 03:53 PM
This is me doing it a couple of years ago. I set it up on the surface plate, then transferred it to the faceplate. I bored and threaded in one setup.

http://i320.photobucket.com/albums/nn351/jchannum/P1030739-1.jpg

radkins
12-06-2010, 08:59 PM
Thanks for the pic since deciding not to attempt this with a tap I have been scratching my head trying to think of the best way to do that setup. I was thinking along those lines already but still a little puzzled about what to use, seeing that pic is the perfect example of the old saying "A picture is worth a thousand words"!

Thanks again

DR
12-06-2010, 09:37 PM
What is the application? 15/16"-16 is thread size for a Winchester High Wall action. I just made a tap last weekend to chase the threads. If initially threading an action, it should be single pointed on the lathe.


If this is for a gun, yes, the threads should be single pointed.

That size tap will be fairly hard to turn, and maybe harder to get the threads concentric with the barrel (which I assume is the idea).

Single pointing will assure concentricity.

beanbag
12-06-2010, 11:58 PM
AFAIK, the spiral FLUTE taps are meant for bottoming, so the lead (initial chamfer on the tap) is about 2 threads. This means it takes a bit of force to tap. Since you have a thru hole, then you can afford to use a tap that has a longer lead.

jdunmyer
12-07-2010, 10:35 AM
JC Hannum said:


This is me doing it a couple of years ago. I set it up on the surface plate, then transferred it to the faceplate. I bored and threaded in one setup.


Jim,
What reference points did you have to begin with? Is the hole smooth that you could indicate off it, or what?

JCHannum
12-07-2010, 02:47 PM
Jim; I machined it from the inside out. It was a set of Storie castings and the mortise for the breechblock was pretty good as cast.

I fitted the breechblock by filing, stoning and scraping the mortise in to fit. I then worked off the mortise for the barrel. The breech block is at 7 degrees to the bore. I used a 7* angle block located on the rear of the mortise to set the angle and set the bore on center of the breech block.

I bored and threaded in one setup, and then transferred the setup to the milling machine and faced the action.