Boring Head-Bar Set-up

[bjmh46]

barrydc1,

measuring + or - .0005 with a telescope gage is a tall order! I was going to comment on this earlier in the thread, but must have had a senior moment and forgot. One of my boring heads is a beautiful Chandler-Duplex boring and facing head that has the capability of reading directly in tenths--this far exceeds my ability to measure the hole with telescope gages. In a situation like yours, I would carefully turn up a go/no-go gage if I wanted to hit that dimension accurately. I think the ring gage that Mikey refers to is actually a standard setting ring for a tri-mike, or an indicator based bore gage. Thirty years in the machining industry, and any really critical bore, the tool room always set a bore gage to be used on the shop floor. Post machining inspection these days is mostly done by CMM. (coordinate measuring machine)

So, what I'm saying is don't feel bad about overboring a couple of holes by .001, if all you have to measure with is a telescope gage. It's even difficult to get two experienced people to get the same number, when measuring the same hole with telescope gages.

Regards
Bob

 

[mikey]

Yes, a ring gage is a standard typically used to set bore gages. They are accurately ground and hardened and the XXX rings are calibrated in tenths. In your case you would use them to teach you how to use your telescoping gages. You set your gage in there and, knowing what they should read, you refine your technique until you can repeatedly read that gage to the degree of accuracy you choose. As to how accurate you can get with telescoping gages, folks have their opinions. I won't tell you that you can read to tenths but lots of guys profess that they can. Whether they can cut to that tolerance is another story!

Do yourself a favor and buy a micrometer stand and use it. Trying to read a telescoping gage with a caliper is asking for trouble. Use your micrometer and learn how it needs to be used to read your gages. Most micrometers read a gage accurately when you just touch the anvils to the ends of the gage. See how yours need to be handled by using your ring gage.

Boring is an art, a skill, and not a precisely controlled process. It takes some time and experimentation to learn how to do it on your own but the bedrock of the whole thing is measurement. Nail that down and the rest comes much easier.

 

[barrydc1]

Do yourself a favor and buy a micrometer stand and use it. Trying to read a telescoping gage with a caliper is asking for trouble. Use your micrometer and learn how it needs to be used to read your gages. Most micrometers read a gage accurately when you just touch the anvils to the ends of the gage. See how yours need to be handled by using your ring gage.

You guys probably don't know it, but my wife hates you I have a problem. I go to the forum. I get great solutions. I buy more tools! Well, I'll get to practicing. I might try the idea of cutting gauge myself, as OD's are definitely easier to read than ID's for me. Anyway, you guys are great, thanks for the help.:thumbsup:

 

[mikey]

I've been thinking about work habits and thought I would pass on one final tip.

It is common practice to withdraw the boring bar while it is still in contact with the bore before setting up the next pass. The bar will usually take off a bit more as it is withdrawn. It will also chip a carbide insert occasionally so I don't do this, on the mill or the lathe.

It turns out that moving the bar away from the wall before withdrawing is a more accurate way to bore, at least for me. I have to back off on the DOC setting and reset it for the next pass anyway (to deal with the backlash in the feed screw) so I do it before withdrawing the bar. I found that my Criterion head will cut very accurately this way and my finishing passes can be much larger because I know that I'll get what I dial in most of the time. Give it a try and see if it works for you.

 

[Tony Wells]

I have to toss this out there. Working to +/-0.0005 with go/no-go plugs isn't really practical. Let's say you want a 1.0000" hole, +0.0005. What size gage pin would you want to use for the go and no-go? 1.0000 and 1.0005? Nope. If the hole is 1.0000, it's within tolerance, but you're never going to get that go gage in there with your hands. And if that hole is 1.0006, it's out, and you still will have a tough time trying to get that no go to get in there. Simply put, clearance is required to hand fit, or "slip fit" a pin into a hole. Plus you can't detect out of round conditions with pins, nor taper where the hole is larger at the bottom.

Most people have seen in catalogs sets of gage pins. The smallest standard pin is 0.0110, and the largest I believe is 1.0000". Now there is another variable to introduce into the usage of pins. You will see offered a "Plus" and Minus" set. That means of course that they aren't necessarily the size they say they are. How far off nominal depends on the grde you have. A shop grade gage pin set will be either +0.0002/-0.0000 (the "Plus" set), or +0.0000/-0.0002 (the "Minus" set). Some people believe this means that the 0.2500 pin is actually either 0.2502 or 0.2498. Not so. That simply is the tolerance of that grade of pin set. It may very well be very, very close to nominal size. But that only guarantees that the Plus set isn't smaller than nominal, and the Minus set isn't larger than nominal by the amount specified in the grade limits, or in our example, 0.0002. This can work to our advantage though. In the example above, the 1.0000 hole, we might be able to get a 1.0000 (nominal) Minus pin in there, IF it happens to actually be 0.9998. 0.0002 is enough to slip a fit in, if you're careful. So there is a reasonable chance that it's safe to say that the hole is above its low limit of 1.0000 if a 1.0000 gage pin from a Minus set goes. But unless you have (and they are made, if you want them) a 1.0005 Minus pin, AND know that it actually is 1.0003, you don't have any reasonable confidence that the hole is not oversize.

Telescoping gages, in the right hands, can be used with confidence, but it is a skill that must be acquired through practice and comparison with known sizes, like the plain ring gages mentioned earlier. In use with a boring head, it's a little awkward to get in there and measure with nearly anything, because the head will likely be in the way, unless you dial off location to gain the room. Probably not the bet practice for precise locations. Same with dial or digital bore gages. They require headroom, so it's just a little awkward nearly any way you go when using a boring head.

 

[EmilioG]

XXX ring/bore gages are very hard to find at a bargain price. They can be expensive. I've been looking for almost two years.
I have one small ring gage, and it's not XXX. I use it to check caliper ID jaws. At 2" and more, they get very expensive.

 

[Wreck™Wreck]

I just recently for the first time used a boring head in my milling machine to bore a hole. This act has me wondering about some things about boring heads. The bar has no flats at the mounting end and is held in the head with a set screw. This allows for the cutting tip flat to be in any 360 degree position relative to the offset motion of the head. Though the operation of the task worked quite well, it has me thinking this through a little more. What I did was visually (by sight) set the cutting tip flat parallel to the head offset motion with the cutting edge outward of center.

Questions:

Are there set-up techniques for proper cutting tip orientation of the boring bar to the boring head?

What is the proper angle of the cutting tip to be set at?

Though I used this set-up to bore an ID, has anyone turned an OD this way?

Bravo, you used experience and intuition to eyeball a tool setup and it worked well with your machine.
All to often it appears that many people learning how to do this sort of work fixate on the NUMBERS. Work on the technique and the numbers that work will come in time.


And yes boring is merely turning on the inside, turn the bar around and have at it.

 

[CJ5Dave]

I know this is an old thread, but I just bought a Chinese 3 inch boring head with a bunch of 3/4 boring bars(brazed tips). They are all oriented with the cutter to run the correct direction out the bottom of the head. I need to bore a boss that will require extending the bar out the side hole. Looks to me like the cutter will be upside down and have to run backwards rotation. I assume this will unscrew the head and make a wreck. How to do this? Get or make anther bar with the cutter running the other way? A way to lock the head thread?