How To Bore Using a Mill by a Total Newb

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seal killer
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How To Bore Using a Mill by a Total Newb

Post by seal killer »

All--

A couple of you have asked me to update you on my boring experiences. I herewith comply!

I bored a hole. Fairly succuessfully, at that. Along the way, I discovered many things that I did not know. A few of them are so OBVIOUS that I have never seen them mentioned on this forum, but for a person new to the boring assembly, they are vital.

First, I beg the experts to forgive me for writing this in a style that conveys I know what I am doing, for I most definitely do not. This is just my writing style that I have used for decades to convey things about which I DO know something, a lot, in fact. (Machining is certainly not one of them!)

I invite everyone to jump in and correct my mistakes and other blunders.

Here is a teaser picture to get us started. A few months ago, I started work on a skid-steer robot. I needed some bearing blocks. So, I step-drilled holes (step-drill: start with a small drill bit and work your way up to the size with which you finish). I did not like the finished appearance. All I had to work with at the time was a drill press. Our friend Harold reluctantly told me I might try reaming the drilled hole. (Harold is a self-admitted non-fan of reaming.) So, I bought a chuck-mounted reamer the same size as the holes I had drilled and "finished" them with the reamer. Although I was pleased with the results, they were still not PERFECT like you see in photographs or in some products you buy.

Harold told me the only way to get a very good finish on a hole was to drill it large enough to get a boring bar in it first, then, using a mill, bore it to size. Having just acquired a mill and boring bar assembly and a bunch of other stuff, I decided to give it a try. Below you will see a picture of the BEST hole I ever drilled with a drill press and subsequently reamed with a drill press. On the right, you will see my very first mill-bored hole. I guess you might say Harold was right . . .

Image

By the way, the two pieces shown above are from the same 2"x2" solid bar of aluminum.

I began the boring process with the setup, which often takes longer than the job (but not in this case).

Image

The picture above was taken prior to me clamping the square aluminum bar down. A hint I gleaned from this forum was to use a C-clamp to tighten the angle plates then bolt them down. I did not have C-clamps large enough so I used a vise-clamp, which was later removed after I trammed the aluminum bar along two perpendicular sides.

Here is the setup with the clamping bars and other components included. Note that I used a piece of 0.375" flat steel bar in the setup, as well. (Just ignore that 3/4" hole I already drilled!)

Image

I wondered about the safety of using the step blocks in this manner. They proved very sturdy and reliable. There was no vibration or shaking during either drilling or boring.

Speaking of drilling, here is the assortment of drill bits I used to get up to 0.750" . . .

Image

Here is one of those vital things I learned that I have never seen mentioned on this forum. (That does not mean it hasn't been mentioned, I just have not seen it.)

The dial you see in both pictures below, clearly on the left, is the adjustment that moves the boring head assembly (which actually holds the boring bar cutter) in and out. It does this with incredible precision, yet is simple to use. Note the picture on the right, the one with the blurry dial but the clear boring bar cutter. Notice how the leading edge of that cutter is aligned perpendicularly to the surface of the dial? In other words, the actual cutting tip of the cutter is nearest the dial.

If it is not that way, or exactly opposite, but I can't figure out why anyone would want to do THAT, then you cannot adjust the tip of the cutter. If you can't adjust the part of the cutter that cuts, then you can't cut! Simple, but vital and not talked about to my knowledge.

Image

It took me about an hour to figure that one out! (I was not boring, but I was slow.)

Now, time to bore! But, how much do you take off with each revolution of the cutter? I did not have a clue. So, without paying any attention to how MUCH I turned the dial, I gave it a crank and carefully plunged (lowered; engaged) the cutter to the surface at the edge of the hole with the following result . . .

Image

A closeup . . .

Image

Wow! That was horrible! I was trying to take, way, way, WAY too much off! So, I cranked the dial back withdrawing the tip (cutting part of the cutter). When it looked like it would plunge into the hole without touching it, I began to bring the tip of the cutter back towards the edge of the hole. When I felt it touch, I stopped, raised the tool, and locked the boring bar down with its THREE set screws. Then, I slowly plunged the boring bar back into the hole to see what would happen.

I bored! Not much, but a little and it gave me a great place to start experimenting with a bigger cut . . . but, not nearly as big as the first one! The only thing big about that one was the mistake!

Without adjusting the first successful setting, I plunged the cutter--using my microfeed--down into the 1.75" deep hole. I was worried about when I would know to stop, because although the microfeed has a nice dial and I had previously figured out how many complete revolutions to make and how many thousandths to add to that, I WANTED to watch that cutter (because I was worried--needlessly--about it).

After hitting bottom I brought it back out. Here is what things looked like at that point . . .

Image

I had done it, or at least a tiny, tiny bit because the hole needed to be enlarged from 0.750" to 1.100". (I THINK this is a lot for a boring bar. However, as it turned out, I went even further, to 1.150".)

I experimented with depths of cuts ranging from 0.005" to 0.030" and settled on 0.030" to simply remove metal. (I could have probably taken more.) I used WD40 as a lubricant and to cool the tool. Additionally, since I was boring a blind hole (blind hole: one that does not go all the way through the material; as you might expect, there are through holes, as well), I stopped to clean out the swarf, frequently. If I hadn't, pretty soon the boring bar would have been resting on a bed of chips at the bottom and not cutting to the full, intended depth.

At 1.085", I stopped to begin taking 0.005" and even smaller cuts to give the hole that great looking finish. (It looked very good when taking 0.030" cuts!) In reality, I should have stopped sooner. Say, 0.050" to 0.030" sooner. (Harold's guidance. Thanks!)

Here is the finished product. I have better pictures, but this one actually has a few chips on it!

Image

I would certainly appreciate feedback on both my technique and use of the equipment.

--Bill
ps The underline indicates a sentence edited to make sense.
Last edited by seal killer on Fri Nov 23, 2007 9:48 am, edited 1 time in total.
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Jose Rivera
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Boring

Post by Jose Rivera »

Hey, you're doing fine!

Just don't hit the boring head on the clamps! :-)

The faster RPMs the better finish but need to be kept bellow any point in here vibration begins created by the off-set of the boring bar.
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BadDog
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Post by BadDog »

Great post!
First, I beg the experts to forgive me for writing this in a style that conveys I know what I am doing, for I most definitely do not. This is just my writing style that I have used for decades to convey things about which I DO know something, a lot, in fact. (Machining is certainly not one of them!)
BOY do I know what you mean! I'm always feeling like I'm sounding way like I think I'm WAY more an authority than I have any illusions of being. So I sprinkle little disclaimers around. But that begins to look "not right" too, particularly since I don't generally post unless I actually think I'm pretty well understanding the topic.

Anyway, on the topic...

One thing I might offer, no way would I have gone through that many drills. Each "step" need only be large enough to fit the web of the next drill, plus "a little bit". I would probably have started with a spotter, then 1/4 split point, then maybe a 1/2, and then the 3/4. A week or so back, I drilled a 1.25" hole in 1/2 plate steel by spotting, running a 3/8" split point, and then followed by the 1.25". That big ol' drill didn't even grunt and I doubt that big hole took 30 seconds to drill. :D Sure beats the heck out of my old HF 17" press!

And yes, the cutting edge needs to be aligned with the axis of adjustment. To do otherwise, you don't get the exact offset dialed in, and you can get into rake angle and clearance issues.

On DOC, edge geometry has a lot to do with it, but with the typical boring head bars, the point radius seems to pretty well define your max DOC. Assuming that edge corner is acute (roughly 80*) like most of the bore/face bars, then if you have an 0.020 radius, your "roughing" cuts won't want to be more than about 0.030. So that nets you 0.060 per pass without pushing it to hard (vibration/chatter). At least that seemed to work well for me on both the boring head and the lathe, though a leading angle can really help with deeper cuts if you are not bottoming. As a matter of actual cuts, I've generally managed 0.030 easily in aluminum even with small/sharp corner radius, but steel won't like it at all. On those final finish cuts, a TINY corner radius is good, just sharpen to a point and lightly lap the sharp point under a magnifying glass.
Russ
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Jose Rivera
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Nightmare

Post by Jose Rivera »

Let me describe I nightmare that I been having off and on for the last 30+ years.

I am running this 58" swing lathe where I cut my teeth as a journeyman.

I am just a few thousands away from hitting the jaws on this huge chuck and I for some reason cannot stop the feed. I usually start trying to stop the hand wheel with all my strength.

My two cents on boring a hole, drill if available to 1/6 under finish size.
1/32 may be OK but deviation on the drill may damage the finish envelope.
Last edited by Jose Rivera on Fri Nov 23, 2007 10:34 am, edited 1 time in total.
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seal killer
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Post by seal killer »

BadDog--

Ha! Harold told me I didn't need all those drill bits, as well! But, using that many bits makes for very little wear on each bit. However, I am doubtless going to start following your advice . . . and Harold's.

--Bill
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RET
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Post by RET »

Bill,

You actually get better results by using fewer drills. When the drill point of the big drill is "held" by the pilot hole of the small drill it makes a truer hole. If you drill a hole with a big drill where the point isn't held, you tend to get a triangular hole because the point moves around.

With deep holes, the drill trues up, but it often makes a 3 sided hole at the start.

Richard Trounce.
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Post by mechanicalmagic »

Bill,
One reason that you don't see max depth of cut when boring, is that it is very dependant on the ridgidity of the mill, the boring head, and mostly on the length and stiffness of the boring bar.

With a 3/4" short bar, I have easily taken .050" (two turns, = .100" diameter) in aluminum. But if it's a 1/2" bar sticking out 4", depending on the phase of the moon, (radius, sharpness, etc.) a .010" cut might chatter.

This is the essence of this craft. Just about everything is a shade of grey, dependant on: speeds, feeds, tool sharpness and tip radius, machine stiffness and tool ridgidity. And of course, the need to get it done quickly. If the customer (or your wife) is waiting, NOTHING will work quite right.
DJ
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Post by Harold_V »

Bill,
Congrats on a well executed first attempt.

One correction.

In your first picture, your problem has nothing to do with depth of cut. Had you examined your boring bar, you'd have seen where it was dragging on the bore. The evidence is clear with the badly raised edge of the bore. As diameter increases, so to does clearance.

Don't be afraid to take large passes when boring, as long as the bar will tolerate the load, there's no reason why you can't take at least .100" off per side when roughing. The tip radius of your bar should not dictate depth of cut---and, if it does, something is wrong with the tool. Again, much depends on the tool geometry.

In keeping with that thought--you must control the chips when moving metal in large volumes, particularly where they aren't fee to exit. That's where learning to grind proper chip breakers pays huge dividends.

Harold
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Post by goodfellow »

Good job -- looks very nice and clean.

WD40 isn't that good of a cutting fluid. Try some TAP Magic or equivalent. You results will be better.

A good milling vise may also help in proper setup
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BadDog
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Post by BadDog »

Maybe it's the bars I'm using (yeah, cheap import sets) but there is no way I can see taking 0.100 DOC with my equipment. Maybe it's the bars, equipment, my skill, or combination of all the above. I don't remember exactly, but I would guess that about 0.030 in steel and 0.060 in aluminum is about all I can manage with the sharp acute angle cutters, and that would be pushing it based on what I recall. Now if I angle the cutter (lathe of course) to add lead angle (also better force geometry on angled bar to minimize flex), add in a radius, grind for lead angle, or otherwise modify the cut, then I can take more depth; all things depending. But with a boring head and using the typical boring head bars (the ones I seem to see in most every hobby/HSM shop) I certainly have not been able to take that big a DOC. Perhaps with a nice inserted bar, perhaps in carbide? That would probably work much better. Perhaps I need to look into what is causing my perceived limitation? <shrug> Oh well, it's not like I have to do much boring on the mill, and I get by ok when I do, so probably not worth working too hard on improving...
Russ
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seal killer
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Post by seal killer »

goodfellow and Harold and mechanicalmagic and Richard and Jose--

Jose, simple, DUMB LUCK allowed the boring head to miss the clamps with so little clearance that I could barely detect it! However, I guarantee you that I watched very closely!

goodfellow, I have a 57 pound vise. I did not use it. I did a test setup with the long bars and discovered that the vise was too tall even for my mill. (15" spindle to table.) I SHOULD have tested the short bars! (Dumb move on my part.)

Harold, re: "you'd have seen where it was dragging on the bore". I am not quite sure I know what you mean. Is it that the cutter was RUBBING on the perimeter of the hole? (The tiny relief angle was rubbing . . . to some degree, on the hole instead of the cutting portion of the tip?) In other words, I did not have the tip plane lined up well with the adjustment dial? Perhaps the tip plane was somewhat less than perpendicular to the plane of the dial surface?

mechanicalmagic, I VERY easily took 0.030". ONCE, I very easily took 0.040", I just did not report it in my little essay. I believe I could take 0.050". Next time, I will try it. I know enough now to stop if things don't sound, look, or feel right.

Richard, I am going to reduce the number of drill bits drastically, as both you and Harold recommend . . . well, and others, too. (I had no clue about the problem you explained in your post.) I THINK I have witnessed the problem you described with my drill press.

QUESTION: How do you know when to change from a narrower tip to a wider one? Is it when the adjustment dial "looks" like it is sticking out too much? (I know this is a dumb question, but you will realize what I mean and I will get an intelligent answer.) I changed bars three times. The first bar I chose was the only one that would fit in my 0.750" drilled hole. The second one I chose was due to the fact that the dial looked too extended. The third one I chose was due to the simple fact that it would fit the larger hole.

Thank you all very, very much.

I will start another thread concerning my next moves and the cutters I need to perform those moves.

--Bill
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Post by Harold_V »

seal killer wrote:Harold, re: "you'd have seen where it was dragging on the bore". I am not quite sure I know what you mean. Is it that the cutter was RUBBING on the perimeter of the hole? (The tiny relief angle was rubbing . . . to some degree, on the hole instead of the cutting portion of the tip?) In other words, I did not have the tip plane lined up well with the adjustment dial? Perhaps the tip plane was somewhat less than perpendicular to the plane of the dial surface?
I've since taken a second look at the part, and I'm not sure I was correct, but my point is a common problem. As the hole diameter decreases, a greater and greater amount of relief is required for the trailing edge of the tool to avoid making contact with the bore. When it touches, it doesn't cut at the tip, but displaces material by rubbing at the point of contact. It's generally accompanied by a serious grinding noise, and, in steel, would result in a failed cut. Aluminum is forgiving enough to be displaced adequately to permit the cut in many cases, depending on the degree of contact. None is best, however. It would have been dead easy to determine if that was the case in this instance by simply looking at the boring tool once removed from the head. There will be distinct signs of tool rubbing under the tip if that be the case-----it need not be described----you'd automatically question why a given area of your bar was smeared with aluminum.

As the hole enlarges, the need for such drastic clearance is lessened, and eventually becomes a non-issue. You will encounter instances where a pass runs poorly, yet the succeeding pass will cut effortlessly. That condition is often the reason.
QUESTION: How do you know when to change from a narrower tip to a wider one? Is it when the adjustment dial "looks" like it is sticking out too much? (I know this is a dumb question, but you will realize what I mean and I will get an intelligent answer.) I changed bars three times. The first bar I chose was the only one that would fit in my 0.750" drilled hole. The second one I chose was due to the fact that the dial looked too extended. The third one I chose was due to the simple fact that it would fit the larger hole.
Boring tends to be somewhat different from outside machining in that you are always restricted by the bore size and depth. Rule of thumb: Use the shortest and most stout tool you can get in the hole, and change to a larger one when possible if you're limited by the present bar. There will be times when you need not make any changes-----and times when you go through more than one. keep in mind that getting the bar in the hole, alone, may not always solve your problems. If the hole is deep enough, it may present problems in evacuating the chips. You may have to use a compromise on bar size to circumvent the problem.

Fact is, aside from your conservative approach (very wise, I might add), you did very well------you made good decisions where needed.

I can't stress enough------you will become very comfortable with these operations with experience. It's not like playing a musical instrument, where there is no room for error-----and endless practice is the only way to achieve results. There are many folks on this group that turn out exceptional work-----and have little experience. The big difference is that those of us that have worked in industry are inclined to take larger cuts, faster speeds, heavier feeds, due in part to having to run to expected levels of performance, considering we're supposed to be qualified for the work at hand.

In reality, in almost all instances, there's nothing wrong with slow speeds and conservative feeds-----not as long as you're not against the clock. We were! :wink:

Harold
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