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Thread: Boring Head-Bar Set-up

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    Boring Head-Bar Set-up

    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?
    Randy
    1958 Series 1J Bridgeport
    1969 Logan 6561H
    1989 Ellis Bandsaw
    The more I learn, the less I know.

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    Re: Boring Head-Bar Set-up

    Hi Randy,

    Others with more experience should have better answers but after having used a boring head two whole times now, I'm reasonably sure you want to set the angle of the cutter to have a rake similar to what you would use to cut the same material on a lathe. I read that a boring head can be used to cut a circular boss, but either the boring head must be solid and your machine must have reversible tool rotation (the head doesn't thread onto the shaft), or you have to find a left-handed boring tool to fit the head.

    Walt

    Edit/ Hmm, I see that you were asking how to set the tool angle and I didn't address that at all. I just eyeball it to be at right angles to the work piece, but I'm only making light cuts in aluminum and that may not be good enough for your purposes. /Edit
    Last edited by Walt; 04-26-13 at 01:31 PM.

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    Re: Boring Head-Bar Set-up

    I've seen a boring head used to turn a boss in the shop i work at by some of the older guys. one said he was "cutting the other side of the hole".
    Any way, setting the angle isn't all that tricky. the rake should already be there on the bar and then eye balling the point is good enough...
    However, when i finally get my OWN set, i plan to mill or grind a flat that will orient the point to the ideal position every time.

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    Re: Boring Head-Bar Set-up

    Start out with the top of the tool parallel to the slide on the head, this will give you zero degrees back rake on the tool. If you are cutting non-ferrous metals like aluminum or brass, you may get a better finish by rotating the boring bar slightly to get a little back rake. Sometimes rotating the boring bar a bit one way or the or the other can also help get rid of chatter, so a flat is not necessarily a good idea. When sharpening a boring bar, grind on the end only to maintain the form and keep the point sharp. A very slight radius can be stoned on it to improve surface finish, but too much will cause chatter. If you do encounter chatter, anything that upsets the natural resonance of the bar will kill it, try changing the speed, feed or even adding a rubber band or a couple of O-Rings to the bar to absorb the vibrations. Boring bars work equally well for bores or bosses, i.e. inside or other side of the hole.

    Tom
    Last edited by Tom Griffin; 04-26-13 at 07:51 PM.

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    Re: Boring Head-Bar Set-up

    I'd say you're only limited by your imagination. I've used them both outside and inside I've even used it for broaching. Like Tom says your material makes a difference, along with the tool you're using. Sounds like you're on the right track and thinking beyond.
    dickr

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    Re: Boring Head-Bar Set-up

    When I align the bar in a boring head I take a small, long, fairly straight scrap of metal (you could even use a nail) and hold it against the flat face of the cutting surface on the boring bar. This helps me to see the angle the cutting surface is in relation to the boring head.

    Hope that makes sense,

    -Ron
    South Bend 11" Lathe
    Wells-Index 860 Mill
    Queen City Shaper

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    Re: Boring Head-Bar Set-up

    Guys c'mon!!! A boring bar used in a boring head needs to have it's cutting edge on the centerline if you expect to hold tolerances using the dial. Period. The cheap (flat-less) brazed boring bars are not suitable as purchased. Most of the time, if you orient the top of the bars cutting edge parallel to the slide motion of the head, the cutting edge will be so far above center, you might as well drill the hole. Put the cutting edge on center, and your cutting with so much negative rake, bar spring and chatter will make boring with the head a nightmare. You CAN modify these bars with a little work, but you have to grind away a good bit of carbide. I really like the (more expensive) HSS bars, or bars made by grinding an old endmill.

    Bob

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    Re: Boring Head-Bar Set-up

    Quote Originally Posted by bjmh46 View Post
    Guys c'mon!!! A boring bar used in a boring head needs to have it's cutting edge on the centerline if you expect to hold tolerances using the dial. Period. The cheap (flat-less) brazed boring bars are not suitable as purchased. Most of the time, if you orient the top of the bars cutting edge parallel to the slide motion of the head, the cutting edge will be so far above center, you might as well drill the hole. Put the cutting edge on center, and your cutting with so much negative rake, bar spring and chatter will make boring with the head a nightmare. You CAN modify these bars with a little work, but you have to grind away a good bit of carbide. I really like the (more expensive) HSS bars, or bars made by grinding an old endmill.

    Bob
    This really deserves a "how-to" with pictures. I'm not sure I'm following what you mean by the "top of the bars cutting edge". Is that the flat portion of the carbide? What is the best process for doing this? It seems easy on the lathe. Also could you throw in there what are reasonable DOCs that can be taken with a boring tool of say 1/2" dia x 2". Is there a formula?

    Barry

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    Re: Boring Head-Bar Set-up

    Quote Originally Posted by bjmh46 View Post
    Guys c'mon!!! A boring bar used in a boring head needs to have it's cutting edge on the centerline if you expect to hold tolerances using the dial. Period. The cheap (flat-less) brazed boring bars are not suitable as purchased. Most of the time, if you orient the top of the bars cutting edge parallel to the slide motion of the head, the cutting edge will be so far above center, you might as well drill the hole. Put the cutting edge on center, and your cutting with so much negative rake, bar spring and chatter will make boring with the head a nightmare. You CAN modify these bars with a little work, but you have to grind away a good bit of carbide. I really like the (more expensive) HSS bars, or bars made by grinding an old endmill.

    Bob

    Granted, I may be easy to confuse at times but I'm with Barry on this one. I don't quite understand what you are recommending. You say that "needs to havie it's cutting edge on the centerline if you expect to hold tolerances" but you also state "Put the cutting edge on center, and your(sic) cutting with so much negative rake, bar spring and chatter will make boring with the head a nightmare.". Those two statements seem to contradict one another.

    Pics, or maybe just expanding on this a bit would be a great help.

    -Ron
    South Bend 11" Lathe
    Wells-Index 860 Mill
    Queen City Shaper

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    Re: Boring Head-Bar Set-up

    According to Criterion, the cutting face of the bar needs to be aligned with the center of the bore:

    ScreenShot119.jpg

    The center diagram is the desired orientation. Note also that the face of the cutter is perpendicular to the point of contact.

    When the face of the cutter is on the bore centerline it will allow the depth of cut adjustment of the head to produce accurate cuts. If the cutter face is not on the centerline the doc adjustment will be off, as shown here:

    ScreenShot120.jpg

    I "think" this is what Bob is referring to.

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    Re: Boring Head-Bar Set-up

    I did some work with a boring bar a few months ago and have been wondering ever since if I had done it and set up correctly. I managed to muddle through it, but there were times I thought I was going to break something. These pics help - thanks.
    Never too old to learn I say!

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    Re: Boring Head-Bar Set-up

    Scrapmetal and barrydc1,

    I hope Mikey's pics cleared that up for you. No contradiction in my statements--I was referring specifically to the common far east carbide tipped bars, and describing the two possible setup conditions in a boring head. With the brazed tip bars, as purchased, proper setup in a boring head is not possible. You CAN achieve centerline setup in the lathe, because tool centerline setup is independent of spindle centerline. That is not so with a boring head. Every boring head I've seen has the tool hole on a radial centerline of the spindle when installed.

    Take a new Chinese carbide tipped bar, say 1/2" shank, and lay it on a flat surface. Now take a 1/4"parallel, and lay it on the surface just in front of the business end of the tool. Now roll the tool til the top of the carbide is parallel to the parallel, and you will see how far above center the cutting edge will be if installed in the boring head where you've eyeballed the cutting edge parallel to the boring head slide motion. You can also roll the tool so that the cutting point is at the same height as the 1/4" parallel, and you will see how much negative radial rake the tool will effectively have if installed like this.

    I've always gotten my best boring head results using tools with neutral radial rake, and positive to very positive axial rake, depending on the material. Sharpen to this geometry and a sharp point, then hone a very small corner radius on the tool. As far as DOC goes, you just have to figure this out for yourself. Every setup and tool/workpiece interaction, sharpness, feedrate (hand or power) is different. I will say that a 2" long 1/2" bar will require a very light touch in steel!

    Sorry if I confused anyone with my previous post.

    Regards
    Bob

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    Re: Boring Head-Bar Set-up

    Bob, my experience with Chinese boring bar sets is limited to the single $10.00 set I own (the only Chinese tool I own) but these bars have brazed inserts that are ground to the centerline of their shanks and can indeed be set up correctly in a boring head. They are not as accurate as my Borite or Micro100 bars but I suspect that is due to the cheap steel and less than accurate tempering of the bars but they can rough with the best of them.

    Randy, if you want to use the DOC adjuster of your boring head as intended, and if your boring bars have zero axial rake like most bars do, then the flat face of the cutter must be oriented along the centerline of the bore. If you purposely turn the bar to introduce some rake then the DOC adjustment will be off, which must then be accommodated. Normally, I only do this in small bores in an attempt to reduce tangential forces so I don't run into clearance issues; it works. Most of the time, I just try to make sure the spindle is centered on the bore and then orient the face of the cutter parallel to the travel of the head.

    My boring head is a Criterion square head. The sliding part of the head is milled fairly square and I use a combination square with the base pressed against the head and the end of the sliding blade is brought up against the cutting face of the boring bar to get it aligned with the head. If I have a deep bore then I use a ground parallel held against the sliding part of the head to get the combination square down enough so the blade can orient the face of the cutter. Does that make sense?

    While aligning the cutter as above is not totally accurate it is close enough for my purposes. I do check to be sure that when I dial in a 0.020" adjustment the bore increases by 0.020". Most of the time this is exactly what happens so it works for me.

    One tip that may come in handy someday is to remember that cutting speed can be used to fine tune the bore. As the RPM increases the bar will cut deeper due to centrifugal forces at the end of the cutter. If you are close but just under the desired bore size, try increasing speed a little instead of adjusting the DOC and make another pass. Quite often, just a 25-50 RPM increase can give you that tiny bit you need to come in on size.

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    Re: Boring Head-Bar Set-up

    Quote Originally Posted by bjmh46 View Post
    Scrapmetal and barrydc1,

    I hope Mikey's pics cleared that up for you. No contradiction in my statements--I was referring specifically to the common far east carbide tipped bars, and describing the two possible setup conditions in a boring head. With the brazed tip bars, as purchased, proper setup in a boring head is not possible. You CAN achieve centerline setup in the lathe, because tool centerline setup is independent of spindle centerline. That is not so with a boring head. Every boring head I've seen has the tool hole on a radial centerline of the spindle when installed.

    Take a new Chinese carbide tipped bar, say 1/2" shank, and lay it on a flat surface. Now take a 1/4"parallel, and lay it on the surface just in front of the business end of the tool. Now roll the tool til the top of the carbide is parallel to the parallel, and you will see how far above center the cutting edge will be if installed in the boring head where you've eyeballed the cutting edge parallel to the boring head slide motion. You can also roll the tool so that the cutting point is at the same height as the 1/4" parallel, and you will see how much negative radial rake the tool will effectively have if installed like this.

    I've always gotten my best boring head results using tools with neutral radial rake, and positive to very positive axial rake, depending on the material. Sharpen to this geometry and a sharp point, then hone a very small corner radius on the tool. As far as DOC goes, you just have to figure this out for yourself. Every setup and tool/workpiece interaction, sharpness, feedrate (hand or power) is different. I will say that a 2" long 1/2" bar will require a very light touch in steel!

    Sorry if I confused anyone with my previous post.

    Regards
    Bob
    That cleared it up very well. (FWIW, I already had a real good handle on how to set up a boring bar but I'm always willing to listen to those who most likely know more than me. )

    Thanks much Bob.

    -Ron
    South Bend 11" Lathe
    Wells-Index 860 Mill
    Queen City Shaper

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    Re: Boring Head-Bar Set-up

    Quote Originally Posted by mikey View Post
    Bob, my experience with Chinese boring bar sets is limited to the single $10.00 set I own (the only Chinese tool I own) but these bars have brazed inserts that are ground to the centerline of their shanks and can indeed be set up correctly in a boring head. They are not as accurate as my Borite or Micro100 bars but I suspect that is due to the cheap steel and less than accurate tempering of the bars but they can rough with the best of them.

    Randy, if you want to use the DOC adjuster of your boring head as intended, and if your boring bars have zero axial rake like most bars do, then the flat face of the cutter must be oriented along the centerline of the bore. If you purposely turn the bar to introduce some rake then the DOC adjustment will be off, which must then be accommodated. Normally, I only do this in small bores in an attempt to reduce tangential forces so I don't run into clearance issues; it works. Most of the time, I just try to make sure the spindle is centered on the bore and then orient the face of the cutter parallel to the travel of the head.

    My boring head is a Criterion square head. The sliding part of the head is milled fairly square and I use a combination square with the base pressed against the head and the end of the sliding blade is brought up against the cutting face of the boring bar to get it aligned with the head. If I have a deep bore then I use a ground parallel held against the sliding part of the head to get the combination square down enough so the blade can orient the face of the cutter. Does that make sense?

    While aligning the cutter as above is not totally accurate it is close enough for my purposes. I do check to be sure that when I dial in a 0.020" adjustment the bore increases by 0.020". Most of the time this is exactly what happens so it works for me.

    One tip that may come in handy someday is to remember that cutting speed can be used to fine tune the bore. As the RPM increases the bar will cut deeper due to centrifugal forces at the end of the cutter. If you are close but just under the desired bore size, try increasing speed a little instead of adjusting the DOC and make another pass. Quite often, just a 25-50 RPM increase can give you that tiny bit you need to come in on size.
    WOW! Thanks Bob and Mikey.

    Mikey this is exactly what I was looking for. Very nicely done. THANK YOU!

    Doesn't look like many use it to do OD's though.
    Randy
    1958 Series 1J Bridgeport
    1969 Logan 6561H
    1989 Ellis Bandsaw
    The more I learn, the less I know.

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    Re: Boring Head-Bar Set-up

    I'm with the others who say this is a great forum. Those explanations are exactly what I needed as well. Thanks not only for the clarifications, but the tips and total technique. I am untrained and self-taught, and so much of the things I do are done from watching a video or pictures that didn't have a lot of clarification. If I get some time I may try to do this with a video or pictures and then have some of you check my work.

    One more question. If I start out boring a hole on the mill by centerdrilling, drilling in steps to 1/2 inch or whatever, and then put the boring head in the spindle, can I assume (if my mill is in good shape and a proper tool used) that the cutting tool axial center will be line with the the bore centerline? Then shouldn't the only issue be rotating the tool in the boring head to get the cutting face perpendicular as described above? Am I understanding this right? If I'm not, I'm going to need pictures.

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    Re: Boring Head-Bar Set-up

    You are correct - you'll be exactly on the bore centerline after drilling as long as you do not move the X-Y position after changing to the boring head. This is what most folks do, I suspect, when it is possible. It can be a bit more work to get centered when boring a hole you didn't drill; here, you must indicate it in.

    I totally forgot to address the DOC question you had. As far as I am aware, there is no formula for determining DOC for a boring cut. Every mill differs in its power and rigidity capabilities, and some boring heads and boring bars are better than others. My suggestion is to practice with your particular set up before doing an important project.

    Every bar likes to cut a certain way, even within a set of bars, so you need to know how much that bar will take off for a given setting. I usually do a trial cut with, say a 0.020" cut and see how the cut goes. If it chatters a lot I may reduce the DOC until it cuts freely. Each material has different requirements and I have notes on what speed/feed/doc works for all common materials with a given boring bar set on my mill. I got that by practicing as above. Note that roughing and finishing DOC differs in that as the DOC falls below the size of the nose radius, tangential and radial forces increase so what you dial in is not what you get. You need to do trial runs until you find out how your bars like to cut.

    I'll give you an example. One of my best Borite cobalt bars likes to rough aluminum at 0.015" DOC; here, it runs clean and smooth and can do it accurately all day. I know that this bar will also produce a 0.004" increase in ID if I dial in 0.0045" on a finish pass so I rough until I get to a point where I can dial in 1-3 finish passes to come in on size. This is how I do it and it works for me. I'm sure others will differ but the bottom line is that you need to find out how your mill/head/bars like to cut and make note of it.

    One more point: be sure you can reliably measure a bore before you try tuning your set up. Trust me; even a seasoned guy can mess up with measurement and blow the bore because of it. Buy a XXX ring gage or two and learn how to use your tools so you can trust your measurements.

    With all that said, don't worry, Barry. Most of us hobby guys have no formal training. We learn by standing on the shoulders of all those that went before us. That, and screwing up enough until we figure it out!

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    Re: Boring Head-Bar Set-up

    Randy, I have not used the boring head to cut a boss - sorry to be useless here. However, I suspect that the set up would be fairly simple. If I were going to try it I would orient the cutter face so the cutting point is toward the center and then slowly feed in. I should think this would work okay. The only thing that concerns me is the backlash in the Z-axis, which might just be enough to crash into the shoulder of the work. Granted, a boring bar doesn't self-feed like an end mill does so this may not be a problem but it would worry me some.

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    Re: Boring Head-Bar Set-up

    Boss turning should be approached with great caution if you need to run the spindle in reverse with a threaded shank boring head. With a left-hand tool, and running in the normal direction, no problem.

    Regards
    Bob

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    Re: Boring Head-Bar Set-up

    Quote Originally Posted by mikey View Post
    I totally forgot to address the DOC question you had. As far as I am aware, there is no formula for determining DOC for a boring cut. Every mill differs in its power and rigidity capabilities, and some boring heads and boring bars are better than others. My suggestion is to practice with your particular set up before doing an important project.

    Every bar likes to cut a certain way, even within a set of bars, so you need to know how much that bar will take off for a given setting. I usually do a trial cut with, say a 0.020" cut and see how the cut goes. If it chatters a lot I may reduce the DOC until it cuts freely. Each material has different requirements and I have notes on what speed/feed/doc works for all common materials with a given boring bar set on my mill. I got that by practicing as above. Note that roughing and finishing DOC differs in that as the DOC falls below the size of the nose radius, tangential and radial forces increase so what you dial in is not what you get. You need to do trial runs until you find out how your bars like to cut.

    With all that said, don't worry, Barry. Most of us hobby guys have no formal training. We learn by standing on the shoulders of all those that went before us. That, and screwing up enough until we figure it out!
    Thanks for answering those questions, that is about how I understand it as well. I do have the means to indicate in a hole that I didn't make, so that is also as I suspected. I have been trial and erroring my boring a bit. Unfortunately, I was trying to bore a hole the other day and after 3 attempts still kept getting it too large by about. 001 or 2, but it was round. This was in mild steel with my chinese carbide, but it may well have been due to the issue you mention above and radiuses. The hole was supposed to be 1.002 +/- .0005. Anyway I gave up after 3 holes and need to get back to it with this new info.

    Also you mentioned measuring. I am using a telescoping bore gage and calipers to measure that unless I need finer measurement and then I use the micrometer. What is the XXX ring gage you mention?

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    Re: Boring Head-Bar Set-up

    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

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    Re: Boring Head-Bar Set-up

    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.

  23. #23
    Aluminum barrydc1's Avatar
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    Re: Boring Head-Bar Set-up

    Quote Originally Posted by mikey View Post
    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.

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    Re: Boring Head-Bar Set-up

    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.

  25. #25
    Administrator Tony Wells's Avatar
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    Re: Boring Head-Bar Set-up

    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.
    Late to bed, early to rise puts big dark circles under your eyes! Author - Me!

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