# Boring Bar Carbide tip Center Height



## Stockyj (Oct 13, 2017)

I have bought a few Carbide tool holders, my lathe has a center height of 12mm (i do not have an adjustable quick change tool post). 
The straight, LH & RH holders are the correct height but the boring bar requires a 6.4mm packer to achieve center. 
Is there a logical reason for this as I find it strange.


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## mikey (Oct 13, 2017)

Can you clarify your center height - 12mm? Or do you mean 12 cm?

Are you using a 4 way tool post or some other kind of tool post?


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## Zathros (Oct 13, 2017)

Stockyj said:


> I have bought a few Carbide tool holders, my lathe has a center height of 12mm (i do not have an adjustable quick change tool post).
> The straight, LH & RH holders are the correct height but the boring bar requires a 6.4mm packer to achieve center.
> Is there a logical reason for this as I find it strange.



Not strange Some need that as the packer can help you adjust the right position for the boring bar asuming it has à round clamping side. If it has à square one well not much you can do about it other than make  it round on your lathe and buy à barrel clamp wit one flat side. I have 2 square ones myself and hardly use those. Rather use the round ones.



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## Stockyj (Oct 13, 2017)

The boring bar is a round shaft with a flat bottom.
The 12mm is from the mounting surface on the tool post to the centre height, its tool size, not center height my mistake.


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## mikey (Oct 13, 2017)

Many tools sets will come with a boring bar that is smaller than the turning tools. For example, you may have 1/2" turning tools but a 3/8" boring bar in the set. I am not sure about the reasoning for this but I suspect that they are shooting for versatility. A smaller bar will bore a smaller and larger hole, whereas a larger bar will only bore a larger hole. The important thing is that your tool post will allow you to set the tip of the boring bar above center height, which you need to do to accommodate tangential cutting forces.


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## Moper361 (Oct 14, 2017)

I have a similar issue I cannot set my small boring  bar above centre height using my 4 way tool post so I flipped it over and cut on the far side of work peice and run the chuck in opposit direction it works ok .One day I will mill a bit of it so I can get it above centre height using my 4 way post ,Oh how I'd love a quick change tool post hmmm


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## Wreck™Wreck (Oct 14, 2017)

No mystery there.
An OD turning tool is unconstrained by the work piece.

A boring bar however must fit into the existing hole being bored. If using a round bar with a shank diameter close to or the same as the tool diameter this will often require a tool holder for the tool holder.

Remember above all that this is machine work, if some tooling doesn't fit as expected make it fit, you are a machinist.

As a side note a 4 way tool post is faster then a quick change if it will hold the number of tools required for the work.


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