View Full Version : Boring head Size

12-25-2006, 08:28 PM
I'm looking for a boring head for my mill. I don't understand what the designated size ( 2", 3" 4") means. Looks like there are two holes in the end to choose from and one in the side to install the boring bar. Can the offset of a 4" be set small enough to bore as small of hole as a 2" one?


12-25-2006, 08:55 PM
Boring head size primarily determines the size of boring bar used and maximum offset. Most will hold a bar in the center position, and have cross holes to permit large diameter hole boring.

As with most tooling, the most rigid set up is the best, and if the majority of boring will be large diameter, the heaviest boring bar will yield the best results.

12-25-2006, 09:47 PM
My BridgePort boring head is a bit over 3" diameter. I had a smaller one before, and it was a bit limiting. The B'Port head will let me go down to 'Zero', or as small as the boring bar itself will go, 1/2" with one of those cheapo brazed carbide jobs. The B'Port head came with a couple of toolholders that use a regular 1/4" lathe toolbit. By using the appropiate hole and tooling, you can bore pretty large holes, I've done at least 4", IIRC.

Spin Doctor
12-26-2006, 10:37 AM
A 3" boring head is just what it says. The head is 3" in diameter. The size of the minumum and maximum hole size it will cut will vary depending on the hole arangement for the bars. And then some boring heads have no bars but hold the tool right in the head. A lot of these are insert boring heads. As to the size of the bars to use. In most cases the 1/2" bars are too wimpy IMO. If possible aslways use the heaviest bar that will fit in the situation. Another nice feature is the ablility to pass a bar through the head at right angles to the spindle. It allows the boring of larger holes with the head more centered in the assembly. Also if possible use a shank on the boring head that matches the mill (or lathe) you have. Any thing that reduces the metal to metal interfaces in your tooling is good

12-26-2006, 10:51 AM
As others have noted, the size you want depends on what you're going to do.

I've got a 2" dia. "quality import" from Travers Tool Co. It takes 1/2" dia. boring bars and will bore holes from the size of the boring bar up to about 6" or more, if you use the hole in the side of the boring head and a left-hand boring bar. The need for a left-hand boring bar in the side hole will become obvious the first time you try to use the side hole. I made one from a piece of 1/2" drill rod and a piece of carbide silver soldered on.

It's been plenty big enough for the stuff I've wanted to do, but if you contemplate regularly doing really big holes you'd probably want a larger one. Or get two! :D

Ian B
12-26-2006, 10:53 AM

In reality, the limiting factor on how large a hole you can bore usually comes down to tool speed - with many vertical mills, you soon exceed the maximum cutting speeds. This will vary from mill to mill, also depends on what materials you cut and if you're using carbide tips or not. A few calcs will tell you what the largest diameter that you can cut is. Size the boring head to this or one size larger for rigidity.



12-26-2006, 11:30 AM
Good point, Ian.