Tips on boring aluminum

[Harold_V]

What is the best method to determine the center? I've been using a live center in the tail stock and setting it a tad low.
-Capel

One does not set the tool low when boring. If anything, go slightly above center. When you set below, you lose relief rapidly due to the radius of the bore.

Harold

[lakeside53]

What is the best method to determine the center? I've been using a live center in the tail stock and setting it a tad low.
-Capel

As Harold said, tad low works fine for external work, but take care with that on inside bores - neutral to slightly high is best. Look at the direction of the material as it approaches the tool.

The tail method can work if you're sure of the tail, and your eyeball is calibrated There are many ways to set center, but the easiest is to simply face across some scrap and see if you leave nub or try to rub it off. Start low, and adjust up until the nub just disappears. You can get it dead-nuts by starting low, deliberately leave a nub, measure that nub and raise your tool by exactly half of the diameter (using a dial indicator on the tool). If you want to be say 10 thou higher than center, just add 10 thou to 1/2 the diameter measured.

[Hot Brass]

Yes, I understand. There are those that want to drive in a race before they know how to operate a car. For me, it makes no sense, especially considering the harrowing experiences I had in the process of becoming a journeyman machinist.

No one should attempt to run when they can't walk----what you are avoiding is the basics of machining---basics that can't always be replaced by insert tooling. Had you started out by grinding tools, you'd understand why this project is running like a pig on stilts. You can tailor a tool to remove the aluminum without making strings, or loading the boring bar. You may even be able to buy a carbide insert and holder that would do the same thing, but you'd be far better served to learn how to grind your own tools. For your own good, do give the idea a go. Now--not when you have become totally dependant on insert tooling that is likely to be, at best, a compromise for your particular application.

Harold

Ok, that's fair. I honestly don't know any better. My motivation for coming to this forum was to learn.
-Capel

[Harold_V]

Ok, that's fair. I honestly don't know any better. My motivation for coming to this forum was to learn.
-Capel

It's not always easy to swallow advice dispensed by others---especially if you have predetermined notions of how you wish to approach a project. I'd like to encourage you to stay the course, but, in clear conscience, I can't do that.

Having come up through the ranks by sharpening my own tools, I realize how important it is. Unless you are running a CNC, where interchangeability is important, you can achieve perfectly good results in almost all cases by grinding your own HSS tools. It's cheaper, far more convenient, and you gain knowledge in the process. Most importantly, however, is that it sets you free. You can create tools of any description in a moment's notice.

Aluminum is one material where you gain very little, if anything, by using carbide. That's especially true if you're using brazed carbide tools, which often have grinds that leave a great deal to be desired.

Aluminum responds so well to HSS with high positive rake and chip breakers that it can, in general, out-perform carbide. Cutting pressures are reduced, and finishes can be better, although that's a function of spindle speed and rigidity. All in all, if you are running a small machine with modest construction, HSS is the definite winner.

I'd encourage you to do some reading on grinding---then to jump in with gusto! You can't learn it strictly by reading---it requires hand to eye coordination and experience----which you can get only by trying.

Feel free to ask questions. There's a large number of journeyman machinists on this site that can help.

Good luck!

Harold

[ZipSnipe]

Listen to Harold's wise advice!!! I remember when I first learned that you can sharpen drill bits(when I was younger and dumber , I just tossed worn out bits and bought new ones) But once I learned to sharpen drill bits I was hooked on sharpening my own tools.

Same goes for lathe bits, I used to have a link to a web site that showed you diagrams of which bits did what and how to sharpen them unfortunetly I've lost that link.

Another thing have great respect for the lathe its an awesome tool but can easily be the most dangerous tool in the shop.

Good luck and never where long sleeve's when working on the lathe!!!!

[Hot Brass]

Ok guys, I've taken your advice and started down the path of learning how to grind my own tools. I only have a basic Delta grinder with a very coarse stone that is very worn. More on that in a second. I took the carbide boaring bar and ground it so I got better relief and insured that only the cutting edge was contacting the part. My results improved dramatically and the chatter went away. The finish is still rougher than I want, but until I can get up to speed on grinding my own cutters, it will do.

I've been looking for a boring bar that I can put home ground HHS tools in, but I must not be looking in the right place. I found one http://www.mcmaster.com/#boring-bars/=889vyy, (at the bottom of the page), but it looks like it uses round stock for the bits and I have a ton of square bit stock in sizes from 1/4" up to 1/2". Thoughts?

Now, about the grinder. Like I said, I have a Delta shop grinder that turns at 3450 rpm. See http://www.amazon.com/DELTA-GR275-Varia ... B0007WWHZC for a similar model. Can I outfit this grinder to work or do I need to build one as described in posts found in the resource library?
-Capel

[randyc]

Glad to hear that you're having better luck with sharpening. There are lots of nice boring bars out there but I just made my own, sized for my small lathe. It's simply a length of 1 inch diameter CRS, drilled and reamed eccentric for a standard 1/2 shank diameter boring tool, secured with three 8-32 set screws. When I use HSS (most of the time), I use a 1/2 diameter bushing that is slotted for a 1/4 square HSS tool as shown below:



The 1 inch bar can be slid in/out of the toolpost block to any desired length, rotated to any angle, then secured with the five socket head clamping screws. The toolpost is attached directly to the compound (no QC mechanism) for max rigidity.

Cheers,
Randy

[EdK]

I've been looking for a boring bar that I can put home ground HHS tools in, but I must not be looking in the right place. I found one http://www.mcmaster.com/#boring-bars/=889vyy, (at the bottom of the page), but it looks like it uses round stock for the bits and I have a ton of square bit stock in sizes from 1/4" up to 1/2". Thoughts?-Capel

Capel,

Here are a couple of examples that will take square HSS tool bits.

http://www.use-enco.com/CGI/INSRIT?PART ... A=377-2060
http://www.use-enco.com/CGI/INSRIT?PART ... A=378-4012

Hope this helps some.

Ed

[Hot Brass]

Capel,

Here are a couple of examples that will take square HSS tool bits.

http://www.use-enco.com/CGI/INSRIT?PART ... A=377-2060
http://www.use-enco.com/CGI/INSRIT?PART ... A=378-4012

Hope this helps some.

Ed

The Enco tool looks just like the McMaster tool, but McM does not specify if the bar accepts round or square bit stock. Enco is also cheaper and you can select square vs round.

Randy,
When using your boring bar, is the axis of the bar parallel to the axis of the spindle or is the compound at a small angle to prevent contact with the shank?

[BadDog]

Actually, if you get into the item detail, MC does show round vs square. Basically, the smallest are round, the larger are square.

As for orientation, you would ideally have the bar angled a bit away from the bore surface (limits depend on bore size, bar size, and depth of bore) so that the force vector is along the bar axis as much as possible to reduce the tendency to flex. Likewise, depending on relative sizes and build quality, orienting the compound the same as the bar can make a difference due to putting forces along the compound ways rather than rocking across. I've also seen support blocks run under the bar, and even jacks braced off the apron helping support.

Oh, and one ore thing, did you try to grind that carbide on a standard AO wheel?

[randyc]

Hello Hotbrass,

You inquired about the boring bar in my photo - when the brazed carbide tools are installed, there is enough clearance so that the 1 inch bar is pretty much in line with the spindle axis. If using the 1/4 HSS cutter, I angle the bar very slightly, just the minimum amount to keep anything from rubbing. (My compound normally stays at around 30 degrees and is always locked when not in use so I adjust the boring bar angle by slightly loosening the clamping nut and tapping the bar.)

Note that the 1/4 HSS tool can't be used for very deep holes in the configuration shown in my photo - about 1-1/2 inches max. When going deeper, I normally use the brazed carbide tools, clamped in my 1 inch bar.

No doubt you'll find that one size bar never fits all purposes. I have a couple of 2-flute small diameter end mills that I use for boring small holes (one of the flutes has been ground off). These get clamped in a 3/8 holder that fits in my 4-way toolpost. I've also used bars like the ones that Ed referenced and they work fine, the most useful being the ones where the cutter is angled at around 45 degrees. The only problem with those bars - and ALL bars, in fact - is that they flex, so every boring job is a compromise between the time it takes to do the job and how much chatter one can accomodate, LOL.

The inexpensive sets of C6 brazed carbide for $20 or so are handy if you're willing to spend a few minutes cleaning up the set. Need to take a good look at the cutting edge, under magnification, and sharpen with a diamond file. At those prices (about $2 each) I consider them a throwaway and if I get a half-dozen good bores out of each one, I'm completely satisfied.

If you use a lot of carbide tooling, they are almost always rounded at the cutting edge - partly for cost considerations and partly for wear. A real sharp edge on carbide won't last under any shock impact, such as an interrupted cut - HSS is king for that purpose. Keep a diamond file handy for touching up the carbide tooling and performance can be improved (also remembering to crank up the spindle speed about three times faster than HSS).

There are very few times that a home machinist needs to reach for carbide tooling. Once one has acquired the basic sharpening skills, a half dozen 1/8 (for boring bars), 1/4, 3/8 and 1/2 square HSS blanks and a couple of parting tool blanks will accomodate 95% of your needs. With the exception of some types of steel, HSS will produce a better finish, require less horsepower (and less stress on the machine) and generally hold tolerance better for fine cuts. The drawback is the lower speed requirements and this usually doesn't concern a hobbyist.

Getting back to boring bars, I wouldn't be surprised if most of the experienced guys have around ten bars of various lengths and diameters with various types of cutters. I get by with three or four but all of my work is small.

Cheers,
Randy

[Hot Brass]

Oh, and one ore thing, did you try to grind that carbide on a standard AO wheel?

The only wheel I have is what came with it, so if it is AO, then the answer is yes. The wheel has never been dressed, so it is only flat on the sides. Definitely to rough and misshapen for grinding lathe tools.
-Capel