Flycutter as hole saw?

It's very easy to make your own adjustable boring bars. A length of 3/4" or bigger steel bar, drill a 5/16" or 3/8" cross hole at one end and drill and tap for a grub screw to hold the cutting tool that goes in the cross hole. If you drill the cross hole at 45 degrees to the shank instead of 90 degrees to it then the non cutting end of the tool sticks up out of the way of the workpiece i.e. you can use longer tools with more diametrical adjustment on them. Cutting tools can be ground up from old milling cutters, drill bits or use carbide tipped tools on round shanks which are cheaply available from engineering suppliers.

Start your hole with the biggest drill bit or milling cutter to hand and then enlarge it as required with the boring bar.

I've made loads over the years in various sizes to bore from 3/4" up to 4" or more. Whatever size bar I use for the shank I generally turn a 3/4" end on it and run it in an R8 collet.

-- Dave Baker

Depending on the construction of the fly cutter, you may not be able to install a tool such that it will serve as a hole saw. Fly cutters are generally intended for tools that somewhat parallel the face being machined. If you have one that permits the tool to be installed at a right angle, parallel to the spindle, it might serve your needs, but you may not have the option to select the diameter you desire. An operation such as that is called trepanning, where you remove a core piece without reducing it to chips. It can be accomplished easier with a boring head, but even that can be challenging---especially when machining tough materials like the majority of the 300 series stainless alloys or the chrome moly series.

Regards clamping the piece that comes loose---it's usually a good idea to use a slightly angled tool, so the cut will be quite thin at one edge, the outer one preferred, so you don't leave a lot in the hole. When it's about to break through, you stop cutting and remove it manually. By setting a quill stop, that's easy. Often, when you break through, the core piece will shift enough to bind and break the tool, so it's not a good way to get the piece out. If stop cutting at the right point, it's real easy to remove the core with a light tap of a hammer on one side. Needless to say, you should be on parallels, not working off the table face. Be mindful of the tapered edge remaining--it can be quite sharp if you stop at the right place.

Using a boring head for fly cutting isn't likely to work much better than using a fly cutter for trepanning. For one, it may not run smoothly if you are running at reasonable speed. The advantage of fly cutting is the ability to run fast, so your single point tool will permit a faster feed rate. As mentioned in a different thread, you're limited by the tool's ability to cut at the limits of the material, but some materials have literally no restrictions. Aluminum, for example. If speed isn't a concern, you might get away with the boring head, but I'd advise keeping the slide locked to avoid movement sideways, under cutting pressure. Surface finish would likely suffer otherwise.

If you don't have a boring head now, and you're debating between a face mill and the boring head, that should be a no-brainer. Buy the boring head. You can face mill with a fly cutter, which can be shop made with ease, or even end mills, A face mill won't bore holes, so running without the boring head would be the greater restriction.

Harold

Harold,

I need to read this more and ask some more questions. However, my question is not so much about using a boring head for flycutting, as it is using either a flycutter or boring head to make large round holes in thin steel and some truly awful gunk passing as metal: when cut, it reduces to a mix of what seems like cast iron dust and razor sharp oat meal - terrible stuff.

A hole saw might be the right answer, but I have relatively few such holes to make, and have more faith in a carbide bit than the hole saws at Lowe's.

All of that said, I might see the problem with the flycutter for the job. I'll think it through some more and post again once I can explain it. Boring bars can be had cheaply, and given that I don't care about precision in diameter, I might do well to rig my own holder as suggested elsewhere. Also, I can afford an import boring set; I was simply hoping to put it off a while given the additional measuring tools I just bought. No worries about the flycutter; it was cheap and I will certainly get use out of it, so it was a great place to start for facing if nothing else.

I bought a $27 (for about half price it turns out!) flycutter set and some bits; they should arrive early next week. I reserve the right to be scared silly of it (always thinking of "Lefty" and the blurry area), in which case I might opt for the face mill. If the flycutter and I get along (seems likely), then I agree the boring head would be next.

Thanks!

Bill

Harold,

Are there bits commonly available for trepanning in a boring head? If I wanted to make one, how would it be shaped? I'd start with round stock so that it could be mounted in the head, yes?

Regards,

Peter

Non-standard sized large round holes? Thin metal (steel or aluminum?) boxes? Using a drillpress or a mill or something else?

Hey Bill,

Fly-cutters are normally used to remove a light or relatively thin cut of constant thickness across a flatted surface, controlled by a lead screw to apply relatively constant positive pressure in the feed direction(s), and the contact of the tool to the work is not large.

When you try to use the same fly-cutter to "bore" instead, it goes very easily and rapidly for the first few thou, then the cutter starts to cut over a greater and greater fever increasing face area as it plunges. Doesn't work really well, and the "feed" control is not as constant or steady as you'd like. ie: doesn't work worth a sh$t, and "break-through" can be pretty exciting if you get that far, and edge finish sucks.

A proper hole saw has lots and lots of teeth, so the chip load and cut in Inches Per Revolution can be quite large, and the "surface" being cut never changes as it "bores in", and break-through is both controlled and even, and relatively good finish.

Now-a-days, even good (USA) quality hole saws for metal are not too expensive, and very available. Maybe you could just borrow what you need from a buddy?

Of course, there is always the old stand-by of edge drilling and filing. Even edge drilling, knock out, and then fly-cutter boring to size and finish. Works even better if you can clamp the metal in between two sacrificial wood pieces, and gives you something to both clamp to for work-holding and protects the work at the same time.

My two-bits worth.

Brian Lawson, Bothwell, Ontario.

If you are talking about enlarging an existing hole, it will work fine. You may have to make multiple passes, re-setting the bit after each pass. You will have to measure very carefully on the last few passes if you need any real accuracy. All of which will take time.

The boring head, of course, will be a lot faster as you will just crank out the slide after each pass.

If you don't have the central hole to start with, it's a lot more difficult. You could grind up a trepanning cutter for a fly cutter head, but it would be a lot of work to get the edges right for both inside and outside cutting and it would only work for very thin stuff. In the boring head you can hold the bit end on to the work, and can therefore grind it a lot more effectively.

All of which is to say that you can often make do with what you have, but that it won't necessarily be easy.

John Martin

I was faced with this challenge years ago, when I built a gasketed filter press for my gold refining operation. I had to cut about two dozen washers from an unknown (austenitic) stainless material, roughly 3/16" thick. Finished washers were roughly 3" diameter, with a bore of 1-1/2" as I recall. The press is long gone now, having been sold along with the refining business I sold when I retired, so I may be off on the sizes. No matter, the principle remains unchanged.

I used a 3/8" HSS end mill shank, on which I ground what resembles a parting tool for a lathe, with a slight cant to the cutting edge, so it would leave a very thin section on one side of the part being removed (the washer), so there was little material to machine afterwards. You stop cutting before breaking through to avoid the tool binding on the part being removed from the stock, and the thin section makes it easy to get the piece out. The problems of cutting stainless in this fashion were difficult to overcome. I ended up buying a BoeLube setup, which solved all the machining problems. Sulfur oil alone wasn't adequate. That would likely not be true on other materials.

One runs the boring head very slowly, using the finest feed. With a chip breaker properly ground in the tool, it works great, but would certainly become a serious challenge if the cut was very deep. There's considerable chatter, due in part to the rather flimsy setup. You can often eliminate the chatter with proper speed and feed selection, however.

One of the things you have to address is considerable side clearance on the tool, where it must clear the radius of the cut on the outside edge of the circle. The tool looks somewhat odd, but works fine. Should you decide to try it, remember, the material you select for your tool will leave the tool edge ahead of center unless you reduce it at the point of the cut to the centerline of the tool. That the cutting edge is on center, or not, has a serious effect on how the tool sees the material, and the relief angles. Does this make sense to you? If not, lets talk. It's important that you understand it well.

Harold

I think what you're saying is that if the entire cutting edge is to be square to the cut, the tool itself may need to be curved, and the inside and outside cutting edges will be on the centerline, making the edge look "slanted" in relation to the rest of the tool (I suppose if the tool were short enough that it wouldn't need to be curved, then one would get more chatter...?). Unlike a bit where the cut is straight, although each relief may look different, when measured in reference to its own cutting edge it'll be the same as the other. Am I understanding this or have a disappeared over the horizon on a tangent?

I just finished a job where a setup like this would have made sense. I was drilling 2.250" holes in .250 6061 plate and then finishing them with a boring head. I did 12 of them. The hole saw was pretty sloppy, and although it wasn't all that important that the holes be of similar size, the diameter of the holes made by the hole saw varied quite a bit. The goal was to have holes with a decent finish and it would have satisfied my sense of propriety if the first holes were accurate and finished well enough so that passes with the boring bar were unnecessary. It's probable that I'll end up performing this operation again, so I'm interested in how to do it quickly and cleanly.

As always, thanks.

Peter

"Peter Grey" wrote in message news:QKiCf.4236$ snipped-for-privacy@newsread3.news.pas.earthlink.net...

Sigh! Trust me to say something in such a way that I use up all the words I know, but fail to hit on the point at hand.

OK----lets try it this way:

Boring heads (at least the ones I have) are made such that the centerline of the cutting tool is the centerline of the head. For boring, that's exactly where you want the tool to fall, due to the position of your boring tool. For trepanning, that isn't the case. That means that when you make a tool such as I described, the actual cutting edge will be in front of center unless you grind away half of the shank you use to grind your tool. Does that make sense? You'd grind what is a D configuration, with the straight side of the D the cutting edge, which will parallel the slide of the boring head. This tool, when installed in the boring head, would have the cutting edge on the centerline of the head. You then grind away the sides to establish the width of the tool, grinding greater relief on what will form the outside of the circle you'll generate, so the tool clears the circular slot it generates, and much less on the opposite side, for the same reason. The tool should also have back clearance, so as it goes deeper into the cut, it doesn't drag on the portion behind the cutting edge. In simple terms, the point of contact, the cutting edge, will be the broadest portion of the tool, with clearance in all directions ground on the tool. Hope that makes it somewhat more clear. It's easy to do, just hard for me to describe. One more thing to remember. Make the tool cut in a clockwise direction, so you don't unscrew the boring head from its shank. The tool you'll grind will be handed because one side has considerably more relief than the other.

I fully understand about the hole saw. They're a dreadful tool, although they are good for opening a large hole. Like you, I've experienced various sizes from the same saw, and am never pleased with the quality of the hole.

A note to remember. When you open a hole by the means I've described, it may not come out really pretty. You'll have some trouble with chip flow if your tool isn't perfect, and the cut well lubricated, so the size could vary to some degree ( a few thou) from hole to hole, depending on if you have chip problems, or not. Finish would be a reflection of chip flow and lubrication. Bottom line-----if you want all the holes to have sharp, square corners, with a nice finish, treat the trepanning operation in keeping with what it really is-----a roughing operation. Shoot for a hole that is somewhat undersized----maybe .020/.040", depending on how well it goes. That will allow for a finish pass with a boring head after the fact, providing a uniform hole and finish. That's called good workmanship, and should be practiced unless the hole just plain doesn't matter.

You're welcome, Peter. Hope some of this helps. All of it has been used with success, so if you have any particular problems, let me know. Could be I've been through the same thing and may recall how I got around it.

Harold

Yes. I understand your point now. That makes sense, as does the rest of your post.

Regards,

Peter.

Dave,

Sorry - large holes, not necessarily non-standard, thin metal, one steel, one a mix of various metalic substances. If I really get lucky, I might be able to negotiate the steel out of existence, leaving just the dusty/grity/disgusting metal that must be penetrated. That stuff would probably yield to the cheapest of hole saws, assuming I can get one of a suitable size (likely).

Bill

John,

Accuracy is not a big deal, which makes the discovery of an appropriate hole saw reasonably likely. Hole saws are getting fairly good reviews in this thread, which increases my confidence in them.

Dumb question: when you say a "pass", are you referring to: (1) set the bar at a given radius; (2) quill down to contact; (3) slow feed until breakthrough? Is the bar parallel or perpendicular to the spindle? Does it matter?

The stock is thin, so I have that going for me. I'll try to do some reading on trepanning and then take another crack at this and Harold's answer. Correct me if I'm wrong, but I think you guys are saying pretty much the same thing.

Thanks,

Bill

The hole saw is the way to go. If you need a better finish or a different size, finish up with the fly cutter or boring head.

Your interpretation of "one pass" is correct. And the boring bar or bit can be held in either orientation in the boring head - it all depends on the size of the head and the size of the boring bar. For smaller holes it will have to be parallel to the spindle.

Trepanning can be a difficult operation. In a way, it's like parting, because both sides and the end of the tool are in contact with the work. Which means no side rake. Since it's not as rigid as a typical parting setup, back rake can also be a problem. And then, as you'll be cutting a curve, you need different clearance angles on each side of the bit.

I suggested that you could grind up a trepanning bit for a flycutter if you lacked a boring head. That bit would have to have a tit on the side to do the cutting - sort of like a bit that you might grind up to cut a small internal thread. Maybe an Acme or square thread.

John Martin

According to Bill Schwab :

One thing to consider is that hole saws tend to make rather ugly holes in metal -- at least based on use in a drill press.

What I always like for aluminum or steel panels is a Greenlee Chassis punch -- but that can be *very* expensive.

And if you're working with the die-cast aluminum zinc boxes, I think that the stresses of a chassis punch might lead to cracking.

What I've found to do a nice job of making clean holes in sheet metal on a drill press is something called a "Roto-Bor". I have two sets, covering a size range from about 1/4" to 1". They have a spring-loaded pilot which fits into a center punch mark or a center drill hole to precisely locate the cutter.

The cutter has two flutes for the smaller sizes, or four for the larger sizes.

The major disadvantage of this is that as far as I can determine, these are no longer made.

Note that using a boring head on the mill will not eliminate the need for a hole to start with -- and the bigger the hole the better, because a boring head is rather a rather slow way of removing material. So, a hole saw to produce an undersized hole is a good thing to use

Enjoy, DoN.

You missed the part about trepanning, DoN. I've done it with outstanding success. You can, indeed, create large holes without having a starter hole. That was the point of our discussion above.

Harold