Boring a hole 0.8" by 3.5"

[chris123]

Hello

Is the Taig lathe capable of boring a hole 0.8" wide and 3.5" deep
If so what tools will I need?

[Dean W]

In what? Steel, aluminum, plastic?
A through hole, or flat bottom?

The lathe won't be the weak point in any case. A boring bar that long is going to flex a good deal. More details needed for an answer that is more than just a guess concerning tooling, but it's within the lathe's work envelope.

Dean

[chris123]

Aluminium with a flat bottom
Does taig provide sufficient tools or will I have to go else where
I am a new to all this

[chris123]

1. thats not what im after
2. i already have a taig lathe

[Jeff-Birt]

For stock large enough to accept that size hole you will need to use a steady rest to pupport the work piece. I would suggest drilling to close to your finished size. You will also need a longer boring bar than what Taig sells.

[Dean W]

As Jeff says, drill it as close to finished size as you can. That would probably be 3/4". The extra support provided by the steady rest is an excellent idea, too.

You will need an aftermarket boring bar with a reach to make it to the bottom of the hole. These are common enough where I live (U.S.A), but if you have trouble getting one there, you can make one easy enough from solid rod. You may actually need two boring bars, depending on how you plan to do the flat bottom of the bore.

A simple boring bar can be just a piece of steel round stock with a hole drilled through in one end for a tool bit, and a second hole to be used for a set screw to hold the tool bit fast.

You will probably have to rig up a tool post to hold it, since it will be too large to fit in a standard Taig tool post. That can be just a block of metal with a hole drilled through to hold the boring bar. It will also need a way to mount it to your cross slide. You could make that similar to how the stock tool post works.

Another option for this boring bar is to use a drill bit and grind the end flat. If you think for a minute what that will look like, you can imagine how the flat end offers two edges that can be used for boring.

Often, for a hole like you describe, with a flat bottom, you will need to do the boring first, and finish up the bottom of the hole after the boring is done. Depending on the boring tool you end up using, you may end up repositioning the bar somewhat to clean up the bottom.

Feel free to ask more questions. Be specific, if possible. I realize you are not an old hand at this, but all the info you can offer helps in providing good answers.

Dean

[chris123]

The end does not need to be super flat
I like the idea with the ground drill bit, would a HSS 1/4" or 2/5" be sufficent for al, I have no idea what type it is
If i flattened the end I should be able to mount it into the std taig tool holder

[Dean W]

The end does not need to be super flat
I like the idea with the ground drill bit, would a HSS 1/4" or 2/5" be sufficent for al, I have no idea what type it is
If i flattened the end I should be able to mount it into the std taig tool holder

That's kind of a small diameter bit for the depth you need, but with light cuts you will probably manage. A larger bit would be much better, (more rigid, less chatter).

When you grind off the end of the drill bit, you need to grind a little clearance so it doesn't rub as it cuts. If you hold the flat end against something and study it a bit, you will see what I mean. Think of the part rotating in the lathe and you will see that as the ground off drill bit enters the hole you are boring, only the tip of one of the flutes is going to be doing any work. As you reach the bottom of the hole, the end of the bit will rub. Grind a slight angle on the end, starting at the flute you intend to use for cutting, and angle it back away from where it would hit the bottom of the hole.

Be careful not to get your drill bit too hot when you grind it. If you do, and it's a carbon steel bit, it will anneal it, making it fairly useless. If it's a HSS bit, you have a little more leeway, but best not to get it too hot, either.

Dean

[chris123]

i meant after i drill with a 3/4" hole use something smaller to bore it out.
so you suggest use a 3/4" drill and a modified 3/4" drill bit as the bore tool

[Dean W]

You have it right, Chris. I just meant that a 1/4" bit for boring is going to whip around a bit. You're going to have to take light cuts for the last .050" and you many get some chatter. If you have a 3/8" or 1/2" bit to use for your boring bar, it will give you a better shot at a nice finish.

Dean