View Full Version : Boring Bars
02-13-2005, 01:24 PM
Hey guys, I've posted here a couple of times and I am always amazed at the knowledge of some of you guys. I thought I would tell you about myself a little and then ask a question. I work in a maintenence shop at a large chemical plant and have been in machining for about 10 years now, I am 29 years old. We do a lot of machining on stainless, inconel, haynes alloy, hastelloy and stellite to name a few. I run a variety of equipment such as a Giddings and Lewis cnc lathe with fanuc control, a horizontal cnc mill with autocon control, and I am currently training on a new Charmilles wire edm. I have just recently started into home machining with my main interest being model i.c. engines. It is taking me a while to build up my shop and tool supply. We use all insert tooling at work on our lathes but at home I bought a set of the cemented carbide 3/4in. boring bars to save money and I am not having good results with them. I am thinking that it is probably because there is no relief ground on the top of the tool. Do I just have a cheap set of bars or are these kinds of bars just inferior to good insert bars? I am thinking now of buying me a couple of insert bars and giving up on the cemented carbide bars but I thought I would get your opinions first.
02-13-2005, 01:41 PM
If they are the type of cemented carbide boring bars meant for use with boring heads there are good ones out there and bad ones. And it does ssem to be a matter of you get what yo pay for.
For boring tools I prefer to use HSS and if you are getting in scale IC than that's the route I would (heading there myself). I would think in your situation it should be fairly easy to come up with pieces of shafting steel in 3/4 and 1 inch sizes and make some bars out of them. If you are going to have access to a wire edm you should be able to burn the square holes in the bars otherwise you either have to broach them or use a silver soldered square hole sleeve. Also if you go with these type of bars you can always use the C2 or C6 grade cemented carbide lathe tools. I've got a set of bars I started at work out of 4140 TG&P. I'll take some pictures tommorow and link them to phototbucket
02-13-2005, 03:44 PM
One of the basic problems with the " 3/4" bars" is that they're 3/4" diameter only at the noncutting end. The actual shank on the smallest ones measure 0.356", next size is 0.468", etc.
And there's no way to shorten up or choke up to get the tip closer to the toolpost, so you're at maximum projection even if you don't need to be (like boring a shallow hole).
The inserted bars, made or bought, give you full shank diameter from toolpost to cutting edge, with the ability to lengthen/shorten as needed.
02-13-2005, 06:24 PM
I make mine out of 1/2" Square Hot Rolled shanks and 1/4" Square HSS bits Silver Soldered to the shanks.
02-13-2005, 06:40 PM
I have both insert bars and some Cobalt bars. The insert bars are APT brand i believe, made to work in 1/2 or lrger holes, different depths from 1.5 inch to 3" - 2 bars. They are relatively inexpensive, about $30.00 each, and the inserts are TPU or TPG (triangular) inserts 221 type, small nose raduis so I do not have nose rub on finishing cuts. Inserts are cheap at about $1.95 to 2.30 each, and a box of 10 should last a home shopp guy quite a while.
I also have a smaller set of 3/8 shank cobalt boring bars. these work in .210 diameter holes on up, and I bought cobalt because i could dress them up when they dull out a bit with a sharpening stone or a light ginding. I can also ad a bit more relief as needed, and one I bought seperate for .375 diameter holes in an aluminum job I put a chip breaker in it. They have lasted me 10 years, and if a tiny one breaks, as has only happened once, they are a cheap $9.00 replace. The set of 6 of these cost as much as my two larger bars together.
I have also used two flute end mills to bore in a crunch, had to do a .140 bore, used a 1/8 2 flute end mill, and once did a ..093 bore with a 1/16 2 flute I got from a local shop - it was a dulled one that I dressed up a bit.
For large diameter deep boring, the ATP (I believe this is the brand name) has a great 3/4 bore bar that uses TPG or TPU 321 inserts, and it is very solid, and costs about $50.00 as i recall. have one of those as well.
If you ever want to know about internal groove nd threading, I can mention product there as well, but I use kennemetal for that, so get out your pocketbook (but they and the inserts last forever, and the work and tool quality and life far outweigh the cost)
02-13-2005, 08:25 PM
Thanks guys for the input. I believe I will invest in a good insert bar and look into one that I can use rex in too. I believe a good set of cemented carbide would serve my needs to but my set is cheap and the carbide seems soft. Also I am trying to go with a setup that can be used on my lathe and in my boring head on my mill although I know I will need some short ones for the mill too.
02-13-2005, 09:38 PM
I have a couple kennametal insert bars and love them for deep work.
I have some cemented carbide bars, the type used for a boring head in 1/2" and 3/8" sizes. I like them for smaller shallower holes but I do have a 1/4" insert bar also. I like the cemented type cause I can still grind a special form on it if I need to, O-ring groove.
And I also have a variety of bars for holding HSS/cobalt. They are from 1-1/2" on down. They are all "homemade" but not all by me. I don't really use these much due to the carbides I have.
02-13-2005, 09:46 PM
What is the specific problem?
02-13-2005, 10:21 PM
The main problem with the set I have is that the carbide seems to be to soft. The other problem is that it seems to be tearing the metal instead of cutting freely. The material is mild steel, .5 thick and I am using one of the short bars with .75 shank. The setup and machine are plenty rigid enough for the cut I am taking.
02-13-2005, 10:28 PM
<font face="Verdana, Arial" size="2">Originally posted by japcas:
The other problem is that it seems to be tearing the metal instead of cutting freely. </font>
Remember, carbide was not meant for us home types although we make it work. Your problem might be speed, and not enough of it.
Crank her up. Also, make up for a slower spindle buy takin a deeper cut, make the carbide work, it likes it.
Do you have nice purple chips?
If you are used to working with carbide at work your machines are prolly movin.
[This message has been edited by JRouche (edited 02-13-2005).]
02-14-2005, 06:00 PM
I said I would post these from p'bucket. The bars are 1" diameter 4140 TG&P @35RC. They have a flat milled on 4 sides at 90D .030 deep. The holes at 90D were broached with a square broach (unfortunately they didn't come out quite as parellel as I would of liked to the bottom flat). The nds with the angle are meant for boring to the bottom of holes or ID threading as seen in the last image
Also knocked this out to generate the threading tool shown
Some will question the need for jigs to grind tools but frankly my eyes ain't so good anymore
02-14-2005, 08:27 PM
Thats nice work. They can also be used for broaching internal keyways.
02-14-2005, 11:04 PM
No need to worry about what to do in retirement ... really nice work & great pics too. Ever think about doing an article for HSM? If Rudy K. were still alive he'd smile at your work.
02-15-2005, 05:32 AM
Actually I have. Possibly a series of them if Niel will bite on the first one. Primarily dealing with machine mods
02-16-2005, 08:56 AM
Looks like you're ready to start! HSM says they're always looking for contributors, and your work is as nice as any I've seen in years.
02-16-2005, 07:27 PM
japcas...I just went through the same thing. The carbide would dull while boring 6061 aluminum. It was really bad doing mild steel. I got ahold of the supplier and let them know what crap these where and they agreed to replace the whole set with higher (hopefully) quality carbide. I tried higher speeds, different angles etc...nothing helped...the carbide was just crap. I could grind a big section of it with an ordinary grinding wheel and it wouldn't even mark a medium hard wheel. If these new ones don't work I'm going to buy a US set. I wouldn't bother but damn they are handy little things for tight work.
02-16-2005, 09:01 PM
I run them all,insert,carbide tipped,HSS,and crap I picked off the floor.I can tell you that the brazed points don't like to be pushed near as hard as the insert bars,.002" per rev rather than .015"
I also found the bars to be only rough ground,they are un-usable as recieved.
At home I stick to brazed and HSS bars,the insert bars are great for industry because industry can afford a broad range of tooling.When ever I order up an insert bar I call up the Kennametal application eng.and have them tell me what insert/bar I need,save lots of money and time that way.
I also found that KBC sells bars similar to the ones Spin made,they are cheap and can be cut up and modified for special tasks.I also have some Kennametal 3/16 and 1/4 sq solid tin coated carbide toolbits to fit them.They make Titainium and Stainless disappear http://bbs.homeshopmachinist.net//biggrin.gif
02-16-2005, 10:14 PM
I think I will look into getting some of the bars that use hss and cobalt stick tooling. They are easily grindable and a lot cheaper than insert, plus my little 9x20 doesn't seem to like carbide very much. I borrowed an insert bar from work to try before i oredered one and it didn't cut as good on my lathe as a piece of ground hss. I am still trying to get used to this smaller lathe and the lack of rigidity that I am use to having at work. Do any of you know where I could buy some of the bars like spin doctor posted at a reasonable price? Also, is there a big difference in tool life between standard hss tool blanks and the cobalt ones? I don't believe I have ever used cobalt.
02-17-2005, 03:46 AM
Forget brazed tools - I only use them to clean rust off of gamey metal. You have not lived until you have used top quality insert type bars - there is a world of difference.
That being said, you can do superb work using HSS such as M-42 or better yet T-15 bits. A properly honed edge makes them cut far better and produce a superior finish. Hone them to mirror like finish for best results.