View Full Version : Another Boring Day

12-17-2008, 09:51 PM
Was trying to Bore (ive done so many successfuly YET) a 4 inch deep 1.375 diameter hole today. Couldnt get boring bar to work right?? I have tried so many and it seems to usually give me lots of grief. I think i need some new tips on Hole Boring. I find doing the Longer Bores causes me loads of trouble Any tips guys thanx Mike

12-17-2008, 10:14 PM
Make sure the tool is on the center line .

Use the biggest bar you got that will fit the hole

Take light cuts if using a small bar

I usually hog as much material out of the hole that I can with a drill , then use a bar .

12-17-2008, 10:19 PM
I seem to run into troubles in my home shop due to using a old bridgeport and substandard chinese boring bars. Also when bore depths get into 4 inch plus region chatter and tip breakage seems always a problem I run the mill at the slowest spindle speed and tried fasrter slower and so on,. Nothing works squeals and so on. Tips Please?? Thanx

12-17-2008, 10:52 PM
I take from you 2nd post your using a mill, not a lathe. I prefer to bore on the lathe and Js's tips are right on. Usually, a ratio of 3:1 or 4:1 depth:diameter should be adhered to so a 1" boring bar(HSS) would fit this for 4" depth.
What dia. are you using?
Also, watch your clearance angles.
What material are you trying to bore?

12-17-2008, 11:31 PM
Use hss toolbit with lots of top rake, reduces the load on the bar. Of course you will have to slow down. 200 for mild steel less for alloy steel. I have had 0 luck with china carbide boring bars. bought one set and they are for decoration only. I have no trouble with hss. Peter

12-18-2008, 08:16 PM
CRAP_ Boring Bars. i even tried re silver soldering tips onto the ends. No Luck Later Pissed off Mike

12-18-2008, 08:43 PM
One trick someone showed me was that if the stock started to ring and cause chatter to wrap the stock tightly on the outside with a rubber strap like maybe a bicycle inner tube opened up and cut to width. Never seen that mentioned here but it works well for me when i'm boring out a piece of 3" AL. When I get within 1/2" from the outer diameter it starts ringing like a bell and the cut goes to hell. Wrap it and all is good.

12-18-2008, 08:48 PM
You should be doing that in a lathe, not a mill. Is that a through hole or blind hole?

12-18-2008, 08:52 PM
You should be doing that in a lathe, not a mill. Is that a through hole or blind hole?

Carl was that directed at my post??? If so that was on a lathe and blind holes

Spin Doctor
12-18-2008, 09:33 PM
Rule #1 when boring. Rigidity, rigidity, rigidity. Rule #2, see rule #1. as noted as big a bar as you can fit in the hole with the minimum amount of length possible.

12-18-2008, 11:25 PM
I made a boring bar holder for my mill, starting with a chunk of steel larger in diameter than the spindle. Into that I turned a recess so that chunk would be a snug fit over the spindle. A drawbar holds it in place, and a pin keeps it from rotating on the spindle. The rest of the chunk is machined like a boring tool, and uses 3/8 shank boring bars. I've had no problem going the full depth into aluminum, and it works in steel also, but I haven't gone the full 3 inches deep in steel.

This setup is more rigid than the other boring tool I made which mounts inside the spindle, like all the other accessories such as end-mill holders, fly cutters, etc. I recently made another boring tool, for larger diameter holes up to about 6 inches, using the same method. I've been equally impressed with how smoothly a cut can be made. Let me coin a phrase, if it hasn't already been done- 'flex makes wrecks'. Ok, so that's cheesy, but it says the same thing- rigidity is good.

Another thing which helps and has already been stated is that damping is good. I actually haven't tried damping the workpiece, but several times I've put damping material on a boring bar and improved things a lot. I used to use a lot of window sealing strip in a previous job, the black tarry type stuff, and that's what I use for damping. Playing with its location on the boring bar will be worth the effort.

Some of my projects involve either turning or grinding on a small diameter workpiece, which is often several diameters out of the chuck. Many times I'll use a finger on it to dampen, and that works well- however I can show you one or two fingers without any fingerprints left :) - not funny really, getting burnt or making zillions of tiny slices in the skin from the rough surface of the workpiece, but it does show instantly what damping can do to improve things.

12-19-2008, 01:27 PM
Can you post a pic of your device?

Thanks, Paul

loose nut
12-19-2008, 01:55 PM
Rapping string or better yet heavy solder ot lead wire around the bar or work will dampen vibration quite well.

David Powell
12-19-2008, 04:51 PM
If your mill is a bit worn, or perhaps not made in USA or Canada you may find it far better to bore by raising the knee rather than lowering the quill. Some quills dont fit very well and most arent adjustable for fit. Its harder work, unless you have power to raise the knee. Regards David Powell.

12-19-2008, 05:17 PM
dockrat, no, I was refering to madman's problem. You did your boring job right. Doing a job he and you described is best done on a lathe with a positive carriage stop. One still has to be carefull at the bottom of a bore on a blind hole.

Even if his is a through hole that long of a bore is a problem on a mill. Not that it can't be done on a mill, it's just harder because you have to use a smaller boring bar with the boring head.

12-19-2008, 07:20 PM
Yup that bore is pissing me off. I thought i had finished it , then when i took it out of my setup the bottom of the 4 inch deep plus bore had a amazing taper in it. I didnt even bother putting it back on the mill. i just shut er down and went to the Beer store BURP and thats that. Later and thanx for the tips ,Chinese tools suck later Mike

12-20-2008, 11:01 PM
I made good parts for years on Chinese junk ....so don't give up yet.

12-20-2008, 11:35 PM
I'm pretty sure Mike has a Bridgeport mill. He's using chinese brazed carbide boring bars.
Mike..I had a set of those that where so bad you couldn't believe it.
I sent them back to KBC...they replaced them with ones from India...much better....tho still brazed carbide.

12-20-2008, 11:53 PM
It's not the quality of the boring bar or carbide. It's the length of the bar and the boring head and the slop in every mill between the quill and the housing. There is no way you can ever produce a bore that long on a mill as good as you can do it on a lathe.

A mill boring head has a 5/8" hole to mount the boring bar in. The bar is very slender because it has to move in a circle inside the bore so it can't be very large diameter and even if it were large diameter the mounting is still only 5/8".

A lathe, on the other hand, can use a boring bar almost as large as the diameter and the mounting of the bar is very rigid. There is no way a mill can ever compair to a mill boring that 1.375" x 4" deep hole.

If your content to make 3 or 4 finish passes without adjusting the bar and letting it clean the bore out you MAY come out with a decent bore. But, it's not a mill job, it's a lathe job.

12-21-2008, 01:07 AM
Carl...I have to agree...but my boring head uses 3/4" bars. The same as I was using in my lathe. I recently bought a good quality 1" bar with inserts. I cannot believe the difference that extra 1/4" in diameter makes when you have the stick the bar out a ways. Of course...that's only in the lathe.

12-21-2008, 10:46 AM
Most boring heads have 5/8" or smaller. The larger heads like yours are more rigid. He said he is using the Chinese bars and I use them also. I have not found them any weaker than the more expensive USA bars but the carbide is not always as good.

Part of his problem is the angle of attack the cutting edge is on the bore. That is negative, neutral or positive angle to the bore. It is very easy to set the wrong angle thinking your right on. The other thing is variations in metal quality.

Boring with a mill is always tricky.

12-21-2008, 10:50 AM
Boring on a mill...gee...now I know why I avoid it like the plauge.
I don't have much patience with that...when I know I can do it a whole lot faster and easier on a lathe.
Too bad not everything will work on a lathe.