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How To Counter Bore?
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06-04-2013, 05:07 PM
I'm wondering what's the best way to counter bore the end of this chunk of steel? That threaded hole is tapped 10-24. I need to counter bore into the face of that part roughly .050". What's the best way to start the counter bore? It's too shallow to start with a drill bit and then proceed with a boring bar.
 Thanks, Ed 
One thing I have done in the past when needing to do something such as that and no tooling is available, is take a small HSS or carbide endmill that you really don't care too much about.....2 flutes is the quickest and easiest to make this out of.
Grind away all but one flute and mount it in your toolpost and use it the same as you would a boring bar that you don't have......  Best Regards, Russ Thanks given by: EdK
06-04-2013, 05:54 PM
Here's some pics of ones I've made and believe or not.....actually used in my Cnc Okuma Lathe........but SHHHHH!! Don't tell KEN!!
![[Image: 20130604_185043_zps2335fc3b.jpg]](http://i203.photobucket.com/albums/aa90/wrustle/Crosby%20Machine/20130604_185043_zps2335fc3b.jpg) ![[Image: 20130604_185114_zpscc4ecc85.jpg]](http://i203.photobucket.com/albums/aa90/wrustle/Crosby%20Machine/20130604_185114_zpscc4ecc85.jpg) Later, Russ
06-04-2013, 05:58 PM
Russ,
Thanks. That makes sense. I'm sure I have some butchered end mills around here that I can further butcher.  Ed 
06-04-2013, 06:12 PM
You could also grind a tool out of a HSS lathe tool bit, or cut off a drill the proper size to a stub and make it into a flat bottom drill.
Tom ![[Image: TomsTechLogo-Profile.png]](http://tomstechniques.com/wp-content/uploads/2013/11/TomsTechLogo-Profile.png) Thanks given by: EdK
06-04-2013, 06:17 PM
After contemplating a lot of grinding on an old end mill, I vaguely remembered that I had bought a couple of small solid carbide boring bars off of ebay some time ago. Surprisingly I was able to find them in quick order.
Anyway, it looks like the smallest of the two might do the job. My question is whether a boring bar this small is up to the task without risk of snapping in two? The material is 1018 CRS direct from our friend Russ. Any thoughts? Thanks, Ed
06-04-2013, 06:34 PM
(06-04-2013, 06:17 PM)EdK Wrote: After contemplating a lot of grinding on an old end mill, I vaguely remembered that I had bought a couple of small solid carbide boring bars off of ebay some time ago. Surprisingly I was able to find them in quick order. Ed, do you have "any" flat bottom drills under 1" dia.? Tom brought up a good point (but it may be cost prohibitive to grind a 1" drill....they're not cheap) and could get you done pretty quick. I'm sure you thought of it already, but never know.....sometimes it is the simple things that get overlooked. Rough with the drill to remove as much as possible then finishing up with a larger boring bar would be much easier. You certainly can use the tool pictured, but keep your DOC low and your speed high, especially in the center or you risk snapping that bad boy in half. I would not go much more than .010" deep but keep your RPM maxed (how much do you have?) and your feed around .002"/rev. The high speed steel will be much more forgiving at that size.....slower to machine.....but will allow you small errors in your approach. The carbide will go bye-bye in a blink if not optimized, and you may just end up dulling it up feeding by hand whereas the HSS can be run slower and feed by hand. If it were me.....I'd opt for making a HSS tool.....a dull EM can be made into a boring bar in few minutes and even if it's dull as a fart, once you have one flute left touch it up a bit to sharpen by hand....no need to worry about anything as long as it's the highest point on the bar and pointed in the right direction! Later, Russ BTW.....we'll be expecting pictures, and video.......at least I'll understand what the hell you'll be saying.....unlike that other film making foreign guy from across the pond!  Later, Russ 
06-04-2013, 06:43 PM
Could you not counter bore it with a regular left had tool bit (one that cuts toward the headstock) Do as a facing cut from the center out. You have a hole to start in.
Free advice is worth exactly what you payed for it.
Greg
06-04-2013, 06:56 PM
(06-04-2013, 06:34 PM)wrustle Wrote: Ed, do you have "any" flat bottom drills under 1" dia.? Tom brought up a good point (but it may be cost prohibitive to grind a 1" drill....they're not cheap) and could get you done pretty quick. I don't think I'll risk the small carbide boring bar. I just know I'd snap it off in an instant. Grinding a HSS tool bit sounds like by best option. I have some 1/4", 5/16" and 3/8" HSS tool blanks I can choose from. Thanks for all of the advice. Ed
06-04-2013, 06:59 PM
(06-04-2013, 06:43 PM)f350ca Wrote: Could you not counter bore it with a regular left had tool bit (one that cuts toward the headstock) Do as a facing cut from the center out. You have a hole to start in. I might be able to with a small enough tool. I'll see if I have one small enough to do the job. Otherwise I'll just grind one out of a blank. Thanks, Ed |
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