Boring A Long Tube

[Tozguy]

For boring a 2'' hole to a depth of 4'' it would be much better to use a bar larger than 1/2'' of mild steel. Considering the level of precision you are after it seems to me that you need a more ridgid tool. For example, a 1/2'' square bar would be more ridgid than a round bar.

Or a 1'' round bar can have one end turned to 1/2'' to fit the tool holder but leave the unsupported part at 1'' for rigidity.

Also, do you absolutely need to use the square boring bar holder or can you clamp the boring bar directly in the post as Joshua mentionned?

 

[prasad]

For boring a 2'' hole to a depth of 4'' it would be much better to use a bar larger than 1/2'' of mild steel. Considering the level of precision you are after it seems to me that you need a more ridgid tool. For example, a 1/2'' square bar would be more ridgid than a round bar.

Or a 1'' round bar can have one end turned to 1/2'' to fit the tool holder but leave the unsupported part at 1'' for rigidity.

Also, do you absolutely need to use the square boring bar holder or can you clamp the boring bar directly in the post as Joshua mentionned?

Tozguy

Thanks. I am not boring it much in the real sense. The amount of material I will remove is very small. The bore is already just under 2" and I have to enlarge it very slightly, just enough to let my 2" accessories enter in. So, I can take very small cuts to prevent flexing of the 1/2" boring bar that I want to make/use. I feel it should work.

True if I have to really cut much more - e.g., enlarging a 1.5" to 2" then I may not use a 1/2" boring bar.

Any case I will soon share my experience.

Thanks again
Prasad

 

[joshua43214]

This holder can fit both 1/2" and 3/4 bars. You just drive out the sleeve to use the bigger bar.
The AXA currently shown on the LMS website looks similar to this one.

 

[Charles Spencer]

If you buy the Shars brand as in the picture it says "Shars" where the others say "China".

 

[prasad]

This holder can fit both 1/2" and 3/4 bars. You just drive out the sleeve to use the bigger bar.
The AXA currently shown on the LMS website looks similar to this one.

No Joshua,

I can not use boring bar holder of this type. My G4000 has not been modified for QCTP. I still use the good old 4-way tool post.

Meanwhile I made a long boring bar and ground the tip of the cutting tool bit. Tomorrow I will have to try to hold the tube in the 4-jaw chuck and see if my newly made boring bar will be able to travel the entire length without touching anything. I hope I can. I keep my fingers crossed.

Thanks again
Prasad

 

[joshua43214]

No Joshua,

I can not use boring bar holder of this type. My G4000 has not been modified for QCTP. I still use the good old 4-way tool post.

Meanwhile I made a long boring bar and ground the tip of the cutting tool bit. Tomorrow I will have to try to hold the tube in the 4-jaw chuck and see if my newly made boring bar will be able to travel the entire length without touching anything. I hope I can. I keep my fingers crossed.

Thanks again
Prasad

Doh...
I am so sorry. I just made a stupid assumption.
The 4way will atleast give you a more rigid set up. Good luck getting the hole done.

 

[prasad]

<snip>
The 4way will atleast give you a more rigid set up. Good luck getting the hole done.

Joshua

That is an interesting comment you made. I have been toying with the idea of making a Norman Patent style QCTP. Can you educate me why a QCTP would be less rigid than 4-way?

Thanks
Prasad

 

[mikey]

Prasad, you might want to test this bar on a piece of scrap first. I say that because the physics of boring are about to become reality for you. Not saying you cannot do it with a 1/2" bar; we've all broken the rules and gotten away with it but depending on the cutter you're using it might turn out less than optimal.

You are using a steel bar, which will flex about twice as much as a similar tool made of carbide; this has to do with the modulus of elasticity of the bar material. Normally, steel can extend in a ratio of about 4:1 (extension: diameter of bar), while carbide can go 8-10:1. The diameter of your steel bar influences deflection to the 4th power, such that a 1/2" bar will deflect 16 times more than a 1" bar at maximum extension, which you are at. Add to this the fact that you are holding this bar in a 4-way post that is not rigid so chatter is a distinct probability. Finally, the cutter itself will alter cutting forces in unknown ways so you cannot predict them.

The bottom line is that you should test your set up first.

 

[Wreck™Wreck]

Add to this the fact that you are holding this bar in a 4-way post that is not rigid so chatter is a distinct probability.

I beg to differ.
A four way post will hold the tool just fine, often more accurately and rigidly than a quick change tool post of the same size (the four way is the original quick change, 4 tools indexed by bearing balls, sans easy height adjustment). a right pain in the keester to use however unless you consider shimming the tools every time you use one "fun", I do not.

 

[David VanNorman]

Make an adapter to hold a 3/4 bar in a piece that your 4 way will hold.