# Boring Head And Bars



## Armourer (Nov 28, 2016)

Quick question, I purchased a 2" boring head that takes 3/8" boring bars for my 3 in 1 machine. The bars are of course the cheap Chinese ones. Any way, I am trying to bore a hole in some hot rolled steel thats 2" thick to a size of around 1.450". I only have a drill bit thats 1" so I figured I would drill it to 1" then use the boring head to finish it to the proper size. Only problem is that its taking for ever to do! I can only make .010 cuts, and getting to 1.450" will take me for ever, and also the "chips" the bar is giving is pretty sad looking. Not really chips but dust almost. Would better quality bars give me a better cut? I have the bar right now set up so it has a 0 degree rake. Would changing that help? Any one have any other suggestions? Thanks a bunch and be easy on me I am as green as grass in the machining world!


----------



## Uglydog (Nov 28, 2016)

Welcome to HM!!
No question is to simple. We've all started with no knowledge of this stuff.
That includes the professional machinists who are on this site (once upon a time they were also green). 

Have you got her set up correctly (angles)?
Are you running her at the correct speed?
Look carefully at your cutter. Is she chipped?

Here is a link to a past thread: http://www.hobby-machinist.com/threads/boring-head-bar-set-up.15169/
And to a Don Bailey free video:   




Please be sure to check back and report on progress and/or frustrations.

Daryl
MN


----------



## Bob Korves (Nov 28, 2016)

Asian boring bars are often not ground correctly.  They often rub on the I.D. at the bottom of the carbide or on the steel shank below the carbide.  Mark it with a Sharpie and see if it rubs.  You can grind some of that away, or you can twist the cutting edge downward a bit, and also raise the bar so the cutting edge remains on center.  That often is enough to make the bar stop rubbing on the work, and, somewhat amazingly to me, they also cut quite well in that negative rake configuration.


----------



## rgray (Nov 28, 2016)

Yes those chinese bars are dull as purchased. Grinding some relief behind the leading edge will make it cut.
It will still be a long process as you will probably be cutting .030 at a pass.


----------



## Christian Poulsen (Nov 28, 2016)

rgray said:


> Yes those chinese bars are dull as purchased. Grinding some relief behind the leading edge will make it cut.
> It will still be a long process as you will probably be cutting .030 at a pass.


Yes I agree with everybody's above suggestions....and how long are (is) the 3/8" bar sticking out of the head?...Cutting it (one) off as short as possible to still get through your 2" part while having it up it the boring head as far as possible will help (rigidity)...Even a good 1/2" diameter boring bar in a adjustable boring head likes to "push off" with depth and Hot Rolled isn't the easiest steel either....


----------



## Joncooey (Nov 29, 2016)

Sorry, I maybe don't know what a three in one machine is... Any way, another method that you could use (if you have it) would be to chuck it up in a four-jaw on the lathe and use a boring bar and a HSS cutter.  Might be a more robust setup and allow for the removal of more material in less time.


----------



## Armourer (Dec 1, 2016)

Thanks for the help and suggestions. I haven't had anytime to take a look at it any farther. Hopefully I will have a chance to get back in the shop in the next couple of days! BTW does anyone have any pictures of how a sharpened boring bar should look?


----------



## Armourer (Dec 3, 2016)

Well thought I should update this if anyone is interested! I couldn't find much googling how to sharpen a carbide boring bar with pics, but did read a few threads on other forums to use a green wheel on your grinder as the carbide is hard. I don't have a green wheel for my grinder, but did have a few green wheels for my Dremel, so I looked at a few pics of boring bars with carbide inserts and sharpened mine to look similar to them, and finished it off with a diamond hone I bought. Took about 5 tries but finally got it to cut pretty good. So I hogged away at it taking .030 cuts at a time, cutting it three times at that to ensure I kept taper to a minimum. I finally got it to 1.433, set my boring head to take a .014 cut. Did the pass, measured the hole and it came out to 1.463!! Not 1.500 I was hoping..... Oh well it will still work fine! I also measured both ends of the holes, and I have about .015 taper in it. I don't think thats too bad considering I was boring 2" solid chunk of steel with a 3/8 boring bar. I do wish it was less, is there any way to get rid of the taper? I was thinking about flipping the piece around and try cutting from the smaller end first. If not I can live with the way it is.


----------



## T Bredehoft (Dec 3, 2016)

To eliminate the taper I'd made what are commonly called 'spring' passes, feed and and out  without advancing the tool. Taper on a mill is hard to troubleshoot, I'd check that the quill is as snug as you can make it and still feed. 
Keep doing the spring passes until there are no more chips. If the taper persists, there's another problem.


----------



## mikey (Dec 3, 2016)

Taper in a bore is often due to deflection, especially when cutting with a carbide tool. Carbide needs speed and an adequate depth of cut to work well, even brazed carbide. The problem with speed when using a boring head is centripetal force which can cut a larger bore if you don't account for it. You need to use as high a speed as you can without causing excess vibration due to centrifugal forces and start with that higher speed early, when you have room to cut and adjust the bore for that speed. For example, if you dial in 0.010" doc at 700 rpm and get a 0.010" increase in bore, you may get a 0.015" increase in bore size with that same depth of cut if you turn it at 800 rpm. You need to settle on a speed and doc that you can work with and do so early enough so that you don't bore oversize.

The problem is that going fast enough can cause a lot of vibration at times, especially as bore size increases. Go big enough and fast enough and the mill will walk across the floor. The smaller the mill, the more important this becomes. For this reason, I prefer cobalt boring bars that cut well at much lower speeds and with much less deflection. I have those Chinese bars, too, but they are used for rough work in small bores when I can cut deeper and go faster. Otherwise, a sharp cobalt bar or a solid carbide bar is used.


----------



## Armourer (Dec 4, 2016)

Ok thanks, I did take 3 spring passes each time I adjusted the boring head out. I did only run it at 250RPM so that may have been way too slow! I will centre the piece back up in my mill and crank her up a bit and try again! Only thing I am worried about is making the hole bigger then what it already is.... Oh ya I would of tried to do all this in my lathe but the piece I am working on wouldn't fit in the chuck.


----------



## lcorley (Dec 4, 2016)

Is your boring head calibrated for radius or diameter cuts? If its calibrated for radius cuts and you had it set for .014, then it would had cut the hole .028 bigger (in diameter).
The fact that it cut .030 when you were expecting .014 sounds like this is worth checking.

regards,
Leon


----------

