How to Use a Boring Bar on a Lathe?

man boring on a lathe machine

Boring is really an easy procedure if enlarging an existing hole is the only purpose. And we don’t have to worry about other parameters of the tool. But, when you have to think about a particular size with tight tolerance, everything matters.

From boring bar selection to chip evacuation, everything should be accurate and precious. That’s why they say; it’s good to have little OCD problem if you want a precise boring on the lathe.

For a flawless performance in the boring process, knowing the use of the boring bar is important. Today’s article is all about using a boring bar on the lathe.

You can read also:

Beginner’s guide to the metal lathe
How to measure lathe swings

Now let’s go with where this topic.

Using Boring Bar on Lathe

Boring is a kind of basic lathe operation. For a successful operation following a few procedures is a must. Hence we are going to talk about the procedure of using a boring bar on the lathe.

Step 1: Selection of Boring Bar

There are three types of boring bars with their own specifications and benefits.

High-Speed Steel (HSS)

HSS is cheaper and tougher. It can be easily re-tipped on a standard grinder and honing stone if the cutting edges wear.

Brazed Carbide Boring Bar

It can cut 2.5-5 times faster than HSS. That means it can tolerate much more heat. Brazed carbide has 2.5 times more modulus of rigidity than steel. But when its cutting edges wear, this type of boring is either reground (which is very difficult) or discarded.

Indexable Carbide Boring Bar

It is like HSS but, when the radius of cutting edge has a smaller corner, a better surface finish is ensured. Also, it produces a more accurate bore size. While cutting edge with a large corner radius is good for roughing.

Hence choose the perfect boring bar according to your operation precision. Stiffness is the key to the boring process. So for better stiffness, using a boring bar with the largest diameter and shortest extension length is a perfect choice.

Step 2: Measurement of Boring Bar

Determining the accurate measurement of the boring bar is also necessary while using a lathe machine. Because requirements vary from product to product. Hence choosing the perfect size of the bar will lead to a precise result.

Measurement of the boring bar can be done using several tools:

  1. Dial or Digital Calipers
  2. Small Hole Gage
  3. Gage Pins
  4. Bore Gages
  5. Telescoping Gages

Step 3: Setting Up the bar

Here are the steps for setting up the bar:

Orientation

Generally, boring bars do not have alignment flats on them. So orienting the top surface of cutting edge parallel to the XZ plane of the lathe is necessary.

There are three possible orientations of the boring bar. These are- negative rake, neutral, and positive rake. Among these three, neutral is the safest. But if you want to try any of the other orientations, you have to set the tooltip on the vertical spindle centerline.

Make sure that you have provided adequate cutting tip clearance.
Cutting weaker materials like aluminum and plastics, it the best to use positive rakes. And to cut stronger materials like higher strength steels, use negative racks.

Height

Height, another considerable parameter while setting up a boring tool on the lathe. Choose a boring bar with a height that is adjustable enough. Which means, as close to the vertical spindle centerline as possible.

While setting up the bar, be very watchful. Because, if the boring bar is not on the vertical centerline, it will surely fail to match your desired size. You will not only regret the wrong operation but also damage the bar permanently.

Step 4: Cutting Parameter Selection

Here are the factors you need to consider before parameter selection:

Cutting Speed

For boring bars, preferable cutting speed should be equal to half of the computed value. But if the tool life allows, you can always work with a limited higher speed than the typical value.

Depth of Cut

Like cutting speed, depth of cut is also an important parameter for the boring bar. In a lathe machine, for the boring bar, it is twice the corner radius, which is considered as the maximum safe depth of cut.

Depending on the material it is said that 0.1-0.2 mm depth of cut is the safest. And around 0.002-0.005 mm is the minimum depth of cut, considering the material.

Note that, below the minimum depth of cut you will get a very inconsistent size and finishing. Because the tool transition remains constant between cutting and smearing.

Feed Rate

One-quarter of the corner radius is the maximum feed rate for a boring bar.

Conclusion

For a successful and precise operation, knowing a few parameters about the tool before starting, is always helpful. It also makes your entire operation much more comfortable.

Hope this article will help you whenever you try to use a boring bar on the lathe.

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