# Lathe boring tool vs mill boring head?



## Aaron_W (Dec 23, 2017)

Understand these tools work differently the lathe tool being fixed as the work turns, the mill tool turning and the work is fixed in place.

I know there are going to be parts where the lathe is not a good choice, holes offset from the center, non-round part not easily chucked into a lathe etc. Or where everything is already being done on the lathe and switching to the mill would be an unnecessary step.


So my questions are:

As far as holes go is the end product essentially the same?

Is there any reason you would choose one over the other beyond which machine was going to be the easiest to use with the piece?

Given a piece that was equally suited to being held on a mill or lathe (say a hole in the center / end of a piece of hex bar stock) which would you opt to use and why?


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## mikey (Dec 23, 2017)

A bored hole is a bored hole, regardless of which machine produced it.

Boring bars differ, depending on what your application is. Solid, one-piece bars of HSS, cobalt or carbide can be used in lathe or mill. Inserted bars are also available for both but those intended for a boring head are shorter and typically made of steel, whereas those intended for lathe use are available in many lengths and diameters and in various materials. There is a LOT to choosing a boring bar, especially for use on the lathe.

When an accurate hole is required and it can be done on the lathe, that is my preference. It is easier to control the boring process on the lathe vs a boring head, for me anyway.


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## Aaron_W (Dec 23, 2017)

Ok thanks, that is the answer I expected, but wanted to confirm that they don't provide a different finished product. 

Just trying to prioritize tooling purchases. I've got boring tools for the lathe, so I should be good until those don't fit the application. 

Buying tooling seems to be a never ending process....


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## DAT510 (Dec 23, 2017)

It's easier to keep holes concentric on round parts when boring on a lathe, as your spinning the part.  On a mill your trying to center the part on the axis of rotation of the boring head.  Hopefully that makes sense?


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## mikey (Dec 23, 2017)

Aaron_W said:


> Buying tooling seems to be a never ending process....



You underestimate the process, Aaron!

If I could advise a Sherline owner on which boring bars to buy, I would suggest the AH375 cobalt set from Borite. This will work on the lathe and in a boring head, including the boring head from Sherline and any other boring head that takes 3/8" tooling. These bars are accurate, can be resharpened many times over their life span and are well worth their cost. These cobalt bars are the only ones I use in my boring heads and I occasionally use them on the lathe when I need a really fine finish or am trying to take micro-cuts to come in on size for a critical bore. Have a look at these, Aaron.

For deeper holes, I would suggest you consider carbide bars but this is a huge discussion.


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## projectnut (Dec 23, 2017)

When buying "boring tools" consider a set similar to this.  They're carbide tipped and come in different lengths and diameters.  They also come in a variety of shank sizes.   I have several sets of 1/2" diameter and 3/4" diameter.  They get used in both the mill and the lathe.  One of my boring heads and one of the lathes use 1/2" tools.  The other boring heads and a different lathe use the 3/4" tools.

http://www.shars.com/products/cutting/boring-bars/3-4-c-6-carbide-tipped-boring-bar-set

I use this style tool holder on the lathes:

http://www.shars.com/heavy-duty-boring-bar-holder-4-and-41-type-204-bxa

And these style boring heads on the mill:

http://www.shars.com/products/toolh...stable-boring-heads-with-removable-r8-shank-1

http://www.shars.com/products/toolh...stable-boring-heads-with-removable-r8-shank-1

About their only limitation is that they are shorter than the older style that use HSS tool blanks


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## Aaron_W (Dec 23, 2017)

DAT510 said:


> It's easier to keep holes concentric on round parts when boring on a lathe, as your spinning the part.  On a mill your trying to center the part on the axis of rotation of the boring head.  Hopefully that makes sense?



Nope, that makes perfect sense, one less step to make a mistake with.




mikey said:


> You underestimate the process, Aaron!
> 
> If I could advise a Sherline owner on which boring bars to buy, I would suggest the AH375 cobalt set from Borite. This will work on the lathe and in a boring head, including the boring head from Sherline and any other boring head that takes 3/8" tooling. These bars are accurate, can be resharpened many times over their life span and are well worth their cost. These cobalt bars are the only ones I use in my boring heads and I occasionally use them on the lathe when I need a really fine finish or am trying to take micro-cuts to come in on size for a critical bore. Have a look at these, Aaron.
> 
> For deeper holes, I would suggest you consider carbide bars but this is a huge discussion.



Well since this is getting a little deeper...

In another post you recommended a Criterion S 1-1/2 boring head so I've been been keeping my eyes open. 
I'm finding boring head nomenclature confusing. I assume the S 1-1/2" refers to the maximum size / adjustment, but also seeing I have to look at the shank which varies from 3/8" to 5/8", R8, BT40 etc, plus the boring bar size which is often not mentioned when used although at least at this size seems to be standard at 3/8". 

I see this one, are they always threaded at the head like this so if I find a good deal on one with the wrong shank or as in this case no shank I can replace it with the right type? Price isn't bad even with the silly shipping.

Criterion 1-1/2" boring head

Sherline makes a morse  / drawbar blank that should be adaptable to this. Assume that would be the best option as a straight shank into a collet is going to eat up a lot of vertical height.





projectnut said:


> When buying "boring tools" consider a set similar to this.  They're carbide tipped and come in different lengths and diameters.  They also come in a variety of shank sizes.   I have several sets of 1/2" diameter and 3/4" diameter.  They get used in both the mill and the lathe.  One of my boring heads and one of the lathes use 1/2" tools.  The other boring heads and a different lathe use the 3/4" tools.
> 
> http://www.shars.com/products/cutting/boring-bars/3-4-c-6-carbide-tipped-boring-bar-set
> 
> ...




Thanks, size is an issue for me. I've got a Sherline lathe and mill so 3/8" tooling is my heavy duty tooling. I've bought a few smaller endmills and such from Shars but am limited to shopping in their petite department.


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## mikey (Dec 23, 2017)

For a Sherline mill, I think the Criterion S 1-1/2 is about as big as the mill can handle. It allows you to bore anything from 1/8" out to 3.25" ID. As your bore enlarges the centripetal forces get pretty feisty so a small head like this works pretty well. The body of the S 1-1/2 is 1-1/2" Square - pretty innovative nomenclature, eh?

 Yes, the S 1-1/2 has a threaded back and you will need a 7/8-20 to MT1 adapter to fit the head to the Sherline mill. Little Machine Shop used to sell one. 

This head came in 3/8" and 1/2" versions; get the 3/8" version to keep tooling weight down.


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## Aaron_W (Dec 23, 2017)

mikey said:


> For a Sherline mill, I think the Criterion S 1-1/2 is about as big as the mill can handle. It allows you to bore anything from 1/8" out to 3.25" ID. As your bore enlarges the centripetal forces get pretty feisty so a small head like this works pretty well. The body of the S 1-1/2 is 1-1/2" Square - pretty innovative nomenclature, eh?
> 
> Yes, the S 1-1/2 has a threaded back and you will need a 7/8-20 to MT1 adapter to fit the head to the Sherline mill. Little Machine Shop used to sell one.
> 
> This head came in 3/8" and 1/2" versions; get the 3/8" version to keep tooling weight down.



Ok I do see they come in two sizes. I just went ahead and grabbed the one I linked to since it is clearly 3/8 (says so in the description) and many don't specify. Just judging by what is up right now it appears the 1/2" size is far more common comparing at the bore size to the set screw for reference. Not seeing any listed cheaper except for more reasonable shipping even with what seems excessive shipping it is cheaper than Sherline's boring head and is a bargain compared to new (seeing them listed retail at $300-450    ). 

Now to track down a 7/8-20 adapter, LMS doesn't seem to offer an 7/8-20 to MT1 anymore, smallest they have is MT2.


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## mikey (Dec 23, 2017)

Aaron_W said:


> Ok I do see they come in two sizes. I just went ahead and grabbed the one I linked to since it is clearly 3/8 (says so in the description) and many don't specify. Just judging by what is up right now it appears the 1/2" size is far more common comparing at the bore size to the set screw for reference. Not seeing any listed cheaper except for more reasonable shipping even with what seems excessive shipping it is cheaper than Sherline's boring head and is a bargain compared to new (seeing them listed retail at $300-450    ).
> 
> Now to track down a 7/8-20 adapter, LMS doesn't seem to offer an 7/8-20 to MT1 anymore, smallest they have is MT2.



I screwed up. It is a 7/8-20 to 3/4-16 adapter that screws onto the Sherline spindle. My mistake, Aaron.

The Criterion head is vastly superior to the Sherline head; its not even close so you went with a better head. You need to completely disassemble the head and clean it out, then re-lube with a good grease (I like SuperLube) and readjust the gib screws. You will really like this head, Aaron.


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## Aaron_W (Dec 25, 2017)

I did find the 3/4-7/8 adapter at Little Machine Shop, unfortunately it has been discontinued. 

Searching online I am not coming up with either a 7/8 to MT1 or 3/4-7/8 adapters so it looks like I will have a threading project. Good thing I got the 4400 that came with the thread making bits.

Is there an advantage to either method? Sherline has an MT1 blank that is large enough to do 7/8", and obviously I can turn a chunk of 1" steel rod into a 3/4-7/8 increaser.

I've got a tube of Superlube so when the head gets here I can clean it up. I found a couple of options for that Borite boring bar set, all I've found are $150-200 range so it will be a month or two before I pick those up. Lots of time to get the boring head figured out and ready for service.

I've found several reviews that share your opinion of Sherline's boring head. Seems that while adequate it is not up to their usual standard.


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## mikey (Dec 25, 2017)

I would screw cut a 3/4-16 thread and register, then put screw it in place on the lathe head stock and cut the 7/8-20 thread. You're more likely to get a concentric piece. 

I own the Sherline head. It is nowhere near the function or quality of a Criterion head, trust me.


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