Cutter profile for line boring?

[homebrewed]

A few days ago I bought an attachment for my little 7x12 lathe. It's a version of the compound slide that has two 8mm tee slots, instead of the 10mm threaded hole for mounting tool posts. I had thought of making something like it from scratch, but the cost for the materials was comparable to what this thing cost.

The idea was to enable me to perform some operations on long workpieces (like drilling accurately-positioned holes on their ends). My benchtop mill doesn't have much Z axis range, which is further reduced when a drill chuck is installed, so with this approach I can clamp pieces down using tee slot type workholding clamps. Very long pieces could be accommodated (with end support). The main limitation is the height of the compound, but, still, it will add some capability to my shop w/o spending a whole lot of money on it.

Anyway, I'm also thinking the new slide could be used for line boring, too. Which brings up the question, what sort of cutter profile is best for this? Symmetrical, like what's used to cut threads? Left hand? Right hand?

 

[ChazzC]

A few days ago I bought an attachment for my little 7x12 lathe. It's a version of the compound slide that has two 8mm tee slots, instead of the 10mm threaded hole for mounting tool posts. I had thought of making something like it from scratch, but the cost for the materials was comparable to what this thing cost.

The idea was to enable me to perform some operations on long workpieces (like drilling accurately-positioned holes on their ends). My benchtop mill doesn't have much Z axis range, which is further reduced when a drill chuck is installed, so with this approach I can clamp pieces down using tee slot type workholding clamps. Very long pieces could be accommodated (with end support). The main limitation is the height of the compound, but, still, it will add some capability to my shop w/o spending a whole lot of money on it.

Anyway, I'm also thinking the new slide could be used for line boring, too. Which brings up the question, what sort of cutter profile is best for this? Symmetrical, like what's used to cut threads? Left hand? Right hand?

Left hand like a boring bar bit. Quinn (Blondiehacks) has a video about line boring the cylinder on her Vertical Engine (I think).

 

[WobblyHand]

Like a boring bar bit, but it is actually called right handed! A right hand internal threading or boring bar has the cutting tip pointing towards the operator when inserted into the bore towards the chuck. The terminology is confusing at best. As for the best shape of the tip, that depends on the internal geometry of the bore. If you are grinding your own, that's no problem. If not, it would be good to think stuff through so you don't get stuck midway with not having the correct shape bit.

 

[homebrewed]

Like a boring bar bit, but it is actually called right handed! A right hand internal threading or boring bar has the cutting tip pointing towards the operator when inserted into the bore towards the chuck. The terminology is confusing at best. As for the best shape of the tip, that depends on the internal geometry of the bore. If you are grinding your own, that's no problem. If not, it would be good to think stuff through so you don't get stuck midway with not having the correct shape bit.

I definitely would grind my own cutter.

After thinking about it a bit, I suspect the "handness" of the cutter would depend on what direction you're cutting. Since the line boring setup passes completely through the work, either direction is possible, right?

 

[WobblyHand]

I definitely would grind my own cutter.

After thinking about it a bit, I suspect the "handness" of the cutter would depend on what direction you're cutting. Since the line boring setup passes completely through the work, either direction is possible, right?

I believe a normal cutter (RH) is RH no matter which way it is used (flat up). Your right hand doesn't change because you look at it upside down, it is still a right hand.

This a RH boring bar

But this kind of threading tool (home made) can be right handed or left handed, because the bit is removable.

At the moment it is set up as a LH threading tool, for internal threading. (Outward, with the spindle in reverse.) You could make something conceptually similar and just grind a custom bit for it. I used 0.1875" round M42 HSS.