Yesterday was Arbor Day

June 8th, 2017

A Boring Story

I’m writing because I’m tired. I figure if I write, I will be able to tell myself I’m doing something productive while I’m really resting.

Today I will tell you about my adventure with the boring head. Not the Indian boring head with integral R8 shank which I got from Grizzly. The US-made Flynn boring head I got off Ebay for seventy bucks.

The Indian boring head works fine. Boring heads are very simple, so bad ones work just as well as good ones. I wanted a nice one because nice ones are more pleasant to use. Also, they’re nice.

The Indian boring head has a jerky action which I have been unable to fix, and it’s just generally not elegant.

Criterion is the name everyone thinks of when they think about boring heads. Criterion makes very good boring heads, and they cost a lot of money (for no reason I can discern). I’ll go look up a price. A 3″ boring head will run you $582 at MSC. That’s a ton of money for something with about ten parts. I tried to find a good price on a used Criterion, but even the used prices are bad.

When it comes to machine tools, name and price are related. A well-known product may sell for more than a product of equal or better quality which is not as well known. It’s like Steinway and pianos. Steinways are not the best, but they bring good money. Name is a very big deal in the used machine tool business.

I found a neat used boring head made by the Flynn company. As far as I know, it’s as good as a Criterion. The seller wanted $70, which is a lot better than I would expect to do on a Criterion. It looked good in the photos. It appeared to have wear from banging around in a drawer with other stuff, but little no wear consistent with use. I bought it.

Problem: the boring head had a funny arbor on it. It was a 5/8″ shank 2″ long, with a thread inside the top end, and there was a mysterious taper down by the boring head itself. “No problem,” I thought, “I will modify it or remove it.”

When the boring head arrived, it resisted all sorts of removal schemes. I even filled the inside of the boring head with a combination of ATF and acetone, which is supposed to be better than Kroil at loosening threads. I got nowhere with it. Even professional machinists had no answers. That’s disturbing, because you will find a good answer in this very blog post if you keep reading.

I considered cutting the arbor flange off or at least reducing it to nearly nothing. I thought the friction between the flange and the boring head might be holding things in place. No one else suggested this, so I decided not to take a chance.

The taper was a little over an inch long. I knew it was okay to run a 1/2″ drill chuck with a short 1/2″ straight shank, so I wondered if I could get away with cutting the taper and turning it into a 3/4″ stub about an inch long. Machinists assured me it would work. That surprised me, but I figured they knew what they were doing.

A 1/2″ shank would have been more convenient, because a 1/2″ collet will accept a lot of tools that are very useful, and it’s a good idea to try to get new tools fit that size collet. It results in less time spent changing collets. I didn’t trust a 1/2″ shank and collet to stand up to boring torque, so I went for 3/4″.

Chucking the boring head in the lathe was a pain. It has lots of features on it, so you don’t want to just slam it in a lathe chuck and tighten down on fragile things you paid good money for. You have to chuck it carefully. Also, I didn’t want the hardened jaws on my 4-jaw chuck to bite into it and mar it.

The best ways to hold an object you don’t want to mar are to use soft jaws or pie jaws. Soft jaws are steel jaws that have not been hardened. You pop off your hardened upper jaws, and you put the soft jaws in their places. Then you cut the jaws to fit your part. If you’re holding a 2″ tube, you bore the jaws out to roughly 2″. You have to put something inside the jaws while you bore them to push them out and hold them in place. You end up with jaws that touch the part with a lot of material instead of three or four small jaw points. Of course, the contact area is limited by the width of the jaws, which are the same size as hard jaws.

Pie jaws are big aluminum jaws that screw to your bottom jaws. They form a 3-slice “pie” when installed. You bore them out just like soft jaws, I believe. Anyway, they cover 60 degrees each, so when you bore them to fit a part, they contact nearly the whole circumference.

I am too lazy to use soft jaws or pie jaws. Also, I only have one set of soft jaws, and they’re too pretty to actually use.

I found a neat tip: aluminum tape. This is real duct tape, unlike the rubbery cheap stuff no one should ever use on ducts. It’s made from aluminum foil. You can get it at Home Depot. You put a piece on each of your hardened jaws, and it helps keep the tips from biting into your work.

There were other problems with chucking the part. If you look at the photos, you will see that the arbor had a flange that screwed up against the boring head. I assumed this flange (and the shank) were concentric with the boring head body, because that’s how machinists do things. It’s sloppy to make cutting tools with arbors that aren’t concentric with them.

When I tried to indicate the part in my 4-jaw chuck, it was impossible to get the arbor flange, the shank, and the body of the boring head lined up at the same time. It’s normal to have to do some work to get two ends of an object indicated, but this time it was impossible. Finally, I put the boring head in my mill with a 5/8″ collet, and I measured it. The arbor flange was not concentric with the boring head, and neither was the shank.

I guess this makes sense. A boring head uses a cutting point which is offset from the spindle axis, so you don’t need the arbor to be concentric with the body. Still, it’s a strange way for a quality manufacturer to make a tool.

Realizing I was up against it, I decided to indicate the face of the boring head, which was virtually certain to be square with the sides of the body. I indicated the face as well as possible, and I indicated the sides to within a few thousandths. Good enough. Indicating the face made sure the shank I was about to turn would not be angled with respect to the body of the boring head. That made me feel good, although it wouldn’t affect the performance of the tool.

I ended up cutting the shank down to a 3/4″ stub an inch long. Now I’m happy. But wait! There’s more!

After I did all this work, someone told me he had removed shanks by cutting the arbor flanges down to a thickness of a few thousandths. He said he then unscrewed them with his fingers. Removing the flange pressure took away the friction that held them in place.

Bummer.

Anyway, here is a photo of my new shank. I think it will work.

I don’t know for sure that I got a good result, but there are a lot of good tips in this blog post. Boring heads aren’t concentric with their shanks or arbors. Use soft jaws or pie jaws to chuck delicate round parts. Aluminum tape prevents marring. A short shank will work fine with a 3″ boring head. ATF and acetone make a top-notch penetrating oil which is dirt cheap (Some people add lard.) Finally, if you want that arbor out of your boring head, take the flange off.

We’ll see whether my shank works or not. Now that I know how to remove it, I don’t care.

One good thing about the short shank is that the boring head will not take up much vertical room on the mill. Boring heads with bars installed can be very long, and that can result in the machinist having to crank the mill’s knee up and down a lot, and in some situations it can make it impossible to use the boring head.

That’s the story. If you see a nice boring head with a funny arbor on Ebay, don’t be afraid to buy it. Now you know how to get that shank out.

7 Responses to “Yesterday was Arbor Day”

  1. Og Says:

    People use red loctite to hold them in place, because it’s not uncommon to use a boring head backwards, and you don’t want it unscrewing. Red loctite can bne removed by warming the part briefly with a propane torch.

  2. Steve H. Says:

    I have read about that. Kind of a cruel prank.

    Here’s an interesting feature of this boring head: there is a screw that comes out and exposes the arbor threads. That’s what I used to fill it with penetrating fluid. I was able to see the threads, and I didn’t see Loctite. I don’t know what the purpose of the screw is. I don’t think it tightens on the threads, but I didn’t check.

  3. Og Says:

    You might not see it, and it only takes a drop. And yes, a screw that opens onto the threads is usually used to lock them in place,.but there’s also commonly a brass or alumimum “Plug” to bite into the threads so they aren’t damaged. The arbor will be adequate for what you’re doing, mostly, but it is much more rigid to have the proper R8 attached to the boring head. And of course, as you mention, shorter.

  4. Steve H. Says:

    This screw doesn’t have any soft material in front of it. I wonder if someone failed to install it.

    It is possible that there is a tiny amount of Loctite in there, but the flange itself would be enough to make life miserable. I did try heating the boring head, but not a lot.

    If you have any explanation of that taper, I would love to hear it. No one else knows what it is.

  5. Og Says:

    Back in the day, Bridgeport had the patents to everything. Bridgeport taper, R8 taper, etc..

    A lot of people built mills but had to come up with their own special toolholders to do the job so they didn’t infringe on Bridgeport patents, so for a not inconsequential time there were many mills out there that used special, oddball tooling. Without measurements, it’s hard to tell, but that looks like an Iso 15.

    The possibility also exists that it was a standard r8 but someone cut it down much like you did.

    Loctite works on flat against flat too. So they might have just put it on the flange., But what you did will work fine.

  6. Steve H. Says:

    The taper looked like the bottom of an R8 arbor, but it didn’t mate with the spindle at all.

  7. Og Says:

    Yeah, I’m betting it was a custom made arbor for some special machine.