Boring troubles (still)

clr8ter · Oct 9, 2015

I am still having troubles boring holes on my lathe. I have tried various tool angles and such, but no luck. The bit tends to walk to the inside, and leave a really nasty finish.

Here are the details;

Heavy 10
chinese boring bar set, carbide, the type used for non-ferrous metals. (I'm boring aluminum)
Slowest feed speed, or fed by hand
Fast spindle speed
tool as close to on-center as I can see
chinese quick change tool holder, AXA

Is the end (face) of the cutter supposed to be square to the bore? or is the cutting edge of the cutter supposed to be parallel to the bore? Cutter angled up slightly into the work, right?

Admittedly, I'm boring a very small hole, less than .500", and using the smallest boring bar in the set. I don't see any clearance issues, and everything is tight.

I don't really see any other way to get non-standard holes. I cannot go out and buy a drill bit or reamer every time I have to drill a hole. But this just isn't working...

johnoder · Oct 9, 2015

Sounds like clearance issue

You have to KNOW the cutting tool is only touching the bore at the cutting edge

If the bottom of the insert, or any portion of the bar is rubbing on the bore not much will happen in the way of cutting

Smaller the bore the worse it will perform

tar356 · Oct 9, 2015

John is right...make sure you have clearance.

What type of bar are you using...brazed carbide? Insert type? What spindle speed?

Carbide likes to eat...if you're using your highest spindle speed already, try increasing your feed rate...try a test cut at around .010" per rev and see how that goes.

fwiw- if I was boring something that small on my SB, I would be reaching for HSS.

Todd
Orange, CA

Mechanola · Oct 10, 2015

Less than half an inch? Why don’t you drill?

billzweig · Oct 10, 2015

With small holes the problem is usually not enough clearance on the boring bar bottom or the lower edge of the cutting face or insert. As well, the tool tip must be exactly at the centre hight.

clr8ter · Oct 10, 2015

I am using a brazed bit. I'm not using a drill because I'm making a counterbore for the head of a shoulder bolt.

"Exactly at the center height". Yeah...I try, but my eyes suck, and I haven't found a way to do it that works for me, yet. Honestly, I'm always doubting whether the tool is at center height.

OK, I'll they increasing feed, checking clearance, and possibly trying HSS. I might have a bit that'll work...

Thanks for the replies.

Ringleboy26 · Oct 10, 2015

Best way would be to buy a set of counter bore reamers.

moonlight machine · Oct 10, 2015

Setting center height is pretty basic. lots of ways to do it. Do you have a caliper? measure your OD, divide by 2, use the depth rod on your caliper to set the tool height from the top of your work. If you can't manage that put the cutting tool edge against the work using it to pinch a 6" scale between. Is the scale vertical? If not the cutting edge is not on center. That said I drill, ream and use counterbores for all holes smaller than 1/2"

doug8cat · Oct 10, 2015

Since you didn't state the depth or number of holes on average, how about a HSS end cutting EM?

Mechanola · Oct 10, 2015

Ringleboy26 said:
Best way would be to buy a set of counter bore reamers.

+1, piloted counterbores, cutting oil, slow speed. You’ll make hundreds of them holes.

Dobermann · Oct 10, 2015

If you're talking about through holes, I'd suggest getting a good quality adjustable reamer. Drill slightly undersize and finish ream.

Boring small diameter holes is a VERY difficult process to get right because the small hole size requires a small boring bar or tool and deflections of the bar under the cutting load cause all sorts of trouble----as you already know!

Greg Menke · Oct 10, 2015

Tool edge is really important with the smaller tools. Since you're cutting something soft I'd switch to a small bar w/ HSS cutter, ground and honed into something suitable w/ minimum engagements. Its easy to chip the edge off a carbide cutter and not know it which increases the cutting effort and so flex. I'm with all above- check clearance 1st, tool edge second, on center third.

kitno455 · Oct 10, 2015

Zero or low rake brazed carbide requires a stiff bar and a good depth of cut. I would grind a boring tool from a stick of HSS instead, and use more rake.

allan

clr8ter · Oct 10, 2015

So, I do not disagree with pretty much anything here. The trouble is that I can't afford to go buy expensive tooling, and my projects tend to be one-offs, with each requiring something different than the last.
That method of setting the tool height with the dial calipers may work good for me, I'll have to try it. Gringding a boring bar out of HSS may be the ticket, too. I already have a tool that I probably can alter.

I also thought about an EM. Not sure if I have the right size, but....I tried this years ago, and the EM made a HORRIBLE hole. out of round, way bigger than the EM, etc. Granted, that machine may have been out of whack, but the EM I was using was not that bad, and that machine was in a working production machine shop. I have wondered ever since if doing this with an EM is or is not an accepted way to go.

Whysosharp · Oct 10, 2015

I have 3 drawers full of random resharps. They've been piling up since my grandfather started the company 45 years ago. What size c'bore do you need Dia and length I'll dig around for an EM suitable if you can cover the cost of a stamp or whatever it costs to ship something small nowadays. You shouldn't have a problem boring with an EM it may have just been a speeds and feeds thing.

clr8ter · Oct 10, 2015

Thanks for the offer! I did, however, just get 'er done. I also have a bunch, (but not 3 drawers worth), of random tooling. I found the HSS bit I was thinking about, and ground off some more for clearance. It worked pretty good. At this point, I'n guessing it was either the clearance or the carbide causing the issues. I'd bet the clearance. I find it very hard to see things like that, especially at odd angles, and in so-so light.

Moonlight Machine, that height-setting method worked great, thanks for the tip!

Rudd · Oct 10, 2015

"chinese boring bar set, carbide, the type used for non-ferrous metals. (I'm boring aluminum)"
Probably most of your problem right there. They don't arrive sharp, and require a minimum of a green wheel to sharpen.
Save your money and use HSS unless you run into some really nasty cast iron.

clr8ter · Oct 10, 2015

HSS DOES tend to cut better on aluminum, I agree. Now I wonder if anyone makes a set of HSS boring bars similar to the brazed carbide ones. You have to admit, they are convenient.

Yes, I am aware that there is a company who makes HSS inserts, but again, out of the price range.

iwananew10K · Oct 10, 2015

Even if you bought them presharpened you would still have to keep them sharp.

I wish I still had my stuff and I would show a pic of my small counterbore tool.

Just a plain stick of 1/4" HSS ground kind of like a cross between a trepanning tool and boring bar.

In aluminum a single plunge was all it took for a nice flat bottomed counterbore.

Greg Menke · Oct 10, 2015

Victor Tools has a wide variety of boring bars that take regular hss tools, the smallest of them use the annoying round hss but its not that much work or $$$. I've found it well worth immediately replacing the lock screws- the ones they ship with often seem to be made of butter...

I did a basement cleanout a few years ago, the estate of a US Navy machinist. He liked to take larger HSS blanks and grind them into boring bars, internal threading tools, all kinds of parting and grooving. Beautiful stuff. His shop didn't have a fancy grinder- plain old bench grinder was all, I suspect he made the nice tools elsewhere.

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