Boring/Facing head questions

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wally318
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Boring/Facing head questions

Post by wally318 »

The other day while doing some searches, I came upon a picture of a unique item
called a BoreMate. Anyone ever use one of these?
It got me thinking of practical uses, and then about boring/facing heads.
I've looked at a few videos of boring facing heads in use. Most of them dealt
with the facing and cutting internal grooves. But none of them touched on
just pure boring with that type of head.
My question would be can you use a boring/facing head for boring only
by taking succesive cuts and advance the boring tool to make a larger
hole without stopping to unlock/ adjust/and lock the slide?
Buy just advancing the slide as in facing with the ring in between each boring pass?
John Evans
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Re: Boring/Facing head questions

Post by John Evans »

You could I guess if you had a lot of material to remove but remember you will not have very good control over depth of cut. And to get final size you still will need to used it as a boring head.
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wally318
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Re: Boring/Facing head questions

Post by wally318 »

Maybe what I meant to ask was: By feeding vertically into the bore
with either the quill or the knee(so therefore control over depth of cut)
can succesive cuts be taken without stopping the mill and unlocking and relocking
the diameter setting just by using the feedring?
SO ... bore a diameter/adjust the feedring bore again etc. w/o stopping,
except for maybe the final few cuts. To measure and get an accurate finishing pass.
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Harold_V
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Re: Boring/Facing head questions

Post by Harold_V »

You don't understand what he means by depth of cut. Depth of cut is the amount of material removed per pass, and is NOT related to the depth of a given bore. By feeding the head while it's running, you may not be able to control the amount you can take, so it may not be a good idea. When trying to hold tight tolerance, it's a good idea to take equal passes so tool loading is constant. That's particularly true when using a slender boring bar.

H
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wally318
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Re: Boring/Facing head questions

Post by wally318 »

So what you're saying is that by not stopping and locking the head after each adjustment,
that the tool is somewhat free to wander and the bore can/will become uneven.
And this can become more pronounced with more flexible boring bars?
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Harold_V
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Re: Boring/Facing head questions

Post by Harold_V »

I didn't try to address the wander of the head, just the constant feed, or depth of cut. I have NEVER (sadly) used a facing type head, although I have seen them, so I hesitated to address that issue. What I did try to address is the fact that the depth of cut determines the degree of deflection of any cutting tool, and that includes even cutting tools on robust machines using 1" shank (and larger) holders.

With a boring head, it's usually the case that the tool is rather slender. Depth of cut is really important if you hope to take reliable passes. For that reason, one who expects predictable results tends to take controlled cuts. If the rotating head can be relied upon to do that, you most likely could make on-the-fly adjustments, but if you can't, you'd struggle with holding size.

Said another way, if you have .050" to remove from a hole and you have a tight tolerance, if you take a pass to determine where you are, then remove .045" in one pass, measure, then take the remainder, the chance of hitting your target diameter is not good. The heavy loading of the .045" pass will yield a hole size that does not represent the size of a hole that has been taken with uniform cuts.

Rule of thumb, and it takes time to do it. You spend time to avoid random results. When you are trying to hold a tight tolerance, take a pick- up pass on the part, be it turning/boring on a lathe or boring on a mill. Measure. Determine the amount of material that must be removed to achieve size. Take 1/3 of that amount in one pass. Measure again. Take half the remaining material (which should be 1/3 of the original amount). Measure again. By now, the cutting tool is uniformly deflecting for the load it sees, so the amount you feed should be predictable and reliable. Take the final pass.

Spring passes may or may not be a good idea. A great deal depends on the nature of the tool in use, as well as the material being machined. Some material (like carbon steel) simply does not respond well to light passes, so the chance of ruining the work piece is quite real. In those cases, it's best that you avoid a spring pass. Taking uniform passes, as I suggested above, is a way to avoid those spring passes.

One thing to keep in mind. If a boring bar is cutting properly, there is no reason for it to not cut a straight hole. If it isn't cutting properly, it's entirely possible that it will generate a tapered bore. A spring pass isn't the solution. A proper sharpening is. Make sure that the only place a bar makes contact with the part is the cutting edge. If there's the least sign of a shiny surface immediately behind the point of the tool, it most likely isn't cutting properly and will gradually spring away from the part, generating a taper. Once it starts, due to the lack of rigidity, it's not uncommon for the bar to continue to deflect until it can overcome the cutting pressure and stop floating. A sharp tool has no reason to do that, nor does the depth of the hole being bored. There's no more pressure on the bar at the bottom (of the bore) than there is at the top, assuming you don't have any issues with chip accumulation.

H
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BadDog
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Re: Boring/Facing head questions

Post by BadDog »

There are various boring/facing heads including Wohlhaupter, Gamet, Narx and a french name I can't seem to tease out at the moment. Anyway, I'm not fortunate enough to have one, but as I understand it, they are able to take pretty precise boring cuts using the advance ring, and including a stop to be used for consistent repeated operations to some tolerance without locking. Whether or not your needs are within that tolerance or not will depend on the quality of device, condition, cutting tool, and skill of operator (including consistent passes for consistent outcome). These heads are not cheap even now in the world of CNC, which has made them largely irrelevant for most tasks for which they were once required.

I've never heard of a Bore Mate, but a post hear doesn't give me the warm fuzzy about it.
https://www.hobby-machinist.com/threads ... ate.19330/

I do have a Volstro rotary head I lucked up on and bought cheap a long time ago. It's a rather delicate fussy/fiddly little thing, but goes WAY beyond boring/facing, though without even close to the accuracy possible with most any boring head. My dreams are filled with things like K&T or Cinci rotary head, maybe a Bridgeport Cherry Head. Again, different animal, but both appear to eclipse what you get with a Bore Mate, then using a more traditional boring head when tolerance requires.
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rmac
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Re: Boring/Facing head questions

Post by rmac »

Harold_V wrote: Wed Jan 20, 2021 4:43 pm Rule of thumb, and it takes time to do it. You spend time to avoid random results. When you are trying to hold a tight tolerance, take a pick- up pass on the part, be it turning/boring on a lathe or boring on a mill. Measure. Determine the amount of material that must be removed to achieve size. Take 1/3 of that amount in one pass. Measure again. Take half the remaining material (which should be 1/3 of the original amount). Measure again. By now, the cutting tool is uniformly deflecting for the load it sees, so the amount you feed should be predictable and reliable. Take the final pass.
Harold, you taught me this same lesson eight or nine years ago on this board, and to this day it remains the best machining tip I ever got from anyone, ever. I'm curious today, though, about your words, "be it turning/boring on a lathe or boring on a mill." What about regular milling with an end mill? Wouldn't the same considerations apply?

-- Russ
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Harold_V
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Re: Boring/Facing head questions

Post by Harold_V »

rmac wrote: Thu Jan 21, 2021 8:36 am Wouldn't the same considerations apply?
Yep! They sure would (and do). I didn't expound beyond boring/turning, but maybe I should have.

Deflection is always an issue, and it manifests itself in virtually all machines. Needless to say, as the machine becomes more robust, it is usually less of an issue, as the flex inherent to a machine's construction limits how much the machine itself lends to the problem, but the most robust of all machines can't control the flex in the cutting tool proper. That's were cutting tool geometry enters the picture, and is often the solution to problems that might, otherwise, not get resolved. I say that because one with an understanding of how and why a tool cuts can introduce controlling factors to modify the behavior of how a tool performs. As an example, it isn't uncommon for greater relief to be applied to aluminum cutting tools, to accommodate the larger chip volume and feeds that are possible. It's not limited to this alone, as you likely understand.

While this is off the topic, I have endlessly discouraged hobby shop machinists from relying on carbide insert tooling. If for no other reason, it can get prohibitively expensive, but the real tragedy is that those who resist learning to fashion cutting tools won't gain a firm understanding of why cutting tools perform. Without that knowledge, they will be held captive, unable to resolve issues that are easily managed by those who do. Beyond that, the comparison of performance between a **properly** ground HSS tool and the typical insert if often so drastic that one would wonder why carbide would be desirable.

Mind you, I'm not trying to suggest that carbide has no place. Of course it does, but for light duty machines, especially those with little power, there's generally little benefit in using carbide unless there is reason, which would include machining highly abrasive materials (fiber glass is a great example), or hardened materials, where a harder cutting edge may spell the difference between success and failure.

H
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johnfreese
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Re: Boring/Facing head questions

Post by johnfreese »

On many boring and facing heads the facing (or grooving) motion is easily controlled. The operator holds a knurled ring to start facing. Every time the operator feels or hears a click the tool moves a definite amount. On some heads it is possible to set up multiple clicks per revolution. By counting the clicks the operator can tell how much the tool has advanced. On d'Andrea boring and facing heads the feed for boring is done with a crank with a graduated collar. The TA100 is manual feed only. The TA120 has the capability of power feed as well as manual. On both the crank is used to adjust the depth of cut when boring.
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rmac
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Re: Boring/Facing head questions

Post by rmac »

Harold_V wrote: Thu Jan 21, 2021 5:37 pm Yep! They sure would (and do). I didn't expound beyond boring/turning, but maybe I should have.
Thanks, Harold. Just wanted to make sure I wasn't missing something.

-- Russ
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