9/16 end mill for 5/8-18 breech?

[ddoyle]

Hoping that it is OK to use a 9/16 4 flute end mill to final size and form the shoulder in a breech to be tapped 5/8-18. Book says that would give a 80% thread. Hole will be .5 deep.
I have the sharp mill on hand and it's short length in a collet makes the job doable on my short lathe bed so I am hoping it is OK.
Any tragedy potential or poor practice potential here?

[okieboy]

 Are you putting the end mill in the head stock or in the tail stock? If the mill is in the tail stock (not rotating) it will function as a boring bar, not as a drill; meaning, if it is perfectly on center it may cut on size, if it is not perfectly on center (MANY tail stocks are not) it will cut oversize. Cutting a test piece would of course let you know. Don't know why you don't want to drill an undersized hole and bore to the diameter that you want.

[jerrywh]

 I should work great if you cut slow and your tail stock is on center.  Check the tail stock with a dial gauge or make a full length cut on a 12" rod and mic. the diameter. If the diameter is the same on both ends it is on center.

[ddoyle]

Huge thanks guys, I am new to this turning business.

I was planning on the barrel thru the head stock I made spiders for both sides and the end mill in the tail stock. My tail stock has been painstakingly adjusted/shimmed but now that I read the warning I am certainly going to run a test before I stick it in my barrel!

Okie you know I never even thought of boring it I think your right though I need to learn to bore to a shoulder. Kind of silly to be looking to drills and end mills eh. Like I say, brand new and learning.

So I guess the remaining question for me (if I can be so bold) is what is the ideal % of thread for a breech?

[Clark Badgett]

Also be warned that is there is any give in the tail stock (it does happen) the cut could go large. A small boring bar will give you results that are exactly as you want, the end mill has much higher chance of something going wrong.

[ddoyle]

End mill is back in it's sleeve. Gonna work on my boring. Thanks much.

[Old Ford2]

Hi,
Clark B's suggestion is right on.
Also when holding your barrel in the lathe chuck, three wooden wedges holding the barrel at the far side of the head stock will help keeping the barrel on center.
Cut the wedges ( hard wood ) about two inches ( 2" ) long.
Tap them in tight at 60 degrees intervals. Make sure the wedges are in the spindle hole the same distance.
This sounds much more complicated than it really is, but it really helps the barrel from wobbling in the chuck.
Afterwards rotate the chuck by hand with a dial indicator on the breech end  "OR" just bring the tool bit holder, with a pointed tool bit in place as close as possible to a corner of the barrel.
If it is the same distance from the tool bit, you are ready to bore your breech.

NOTE: it is rather hard to turn a 30"+ barrel in a lathe and not have some degree of wobble, without support on the outside end of a lathe.
Generally for chambering, breeching, or threading of a barrel I have a special fixture with set screws at the outer left side of the spindle, that holds a barrel true.
Good luck on your venture!
Fred

[Bob Roller]

Are you putting the end mill in the head stock or in the tail stock? If the mill is in the tail stock (not rotating) it will function as a boring bar, not as a drill; meaning, if it is perfectly on center it may cut on size, if it is not perfectly on center (MANY tail stocks are not) it will cut oversize. Cutting a test piece would of course let you know. Don't know why you don't want to drill an undersized hole and bore to the diameter that you want.

Put a dead center in the taper of the headstock after making sure it's CLEAN and another dead center in the tailstock and then see if the two points come together.IF the two points align the there is no reason not to use a 9/16 end mill after boring the hole with a 35/64ths drill. 9/16 is .5625 and the 35/64ths is .5469.
Good luck and go slow if you are in new territory.

Bob Roller

[okieboy]

 I am not sure that a novice lathe operator will want to do this, but if you use a solid carbide internal grooving tool as your boring bar, you could easily cut a relief at the bottom of your bore, so you end up with no partial threads. An internal thread relief groove isn't a necessity, but it would be nice.
 You can look at internal grooving tools at MSC or several  other cutting tool supply houses.

[ddoyle]

go slow if you are in new territory.

Yes, I am creeping respectfully! Part of the attraction to this machining business is the- you can't take eggs out of cake aspect. Helps keep my hack and slash and fix it later tendencies in check. To be honest I was so tickled when I got the bore dialed in with the spiders I could just sit and watch the barrel spin as if it was fine art lol. When I squared up/ faced the breech with a tool I ground and it 'worked' I was about in heaven. 

Again much thanks for all the input,  I am gonna dig out the books and investigate this idea of internal thread relief and spend some time practicing on scrap before I dive in any deeper.


Cheers all