# Boring bars, another very beginner question!



## Mauser lover (Apr 6, 2019)

I understand the concept of boring bars. I have searched for all the videos I can think of concerning boring bars. I now have a "need" for a boring bar setup. I have shopped on Amazon, eBay, Shars, Grizzly, etc. for boring bars, but nowhere can I find someone who explains how to hold the thing in a four-way toolpost, or where to buy such a toolholder! I've got to be missing something. 

Does anyone have a link to a video I can watch about this? Is it absolutely impossible to hold a boring bar in anything but a quick change toolpost or a lantern style toolpost? Do I clamp it down in the four-way without a holder? Is there something special that a boring bar holder is called for a four-way? 

I've got to be missing a piece of the puzzle. Any help is appreciated!


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## Cobra (Apr 6, 2019)

Mauser lover said:


> I understand the concept of boring bars. I have searched for all the videos I can think of concerning boring bars. I now have a "need" for a boring bar setup. I have shopped on Amazon, eBay, Shars, Grizzly, etc. for boring bars, but nowhere can I find someone who explains how to hold the thing in a four-way toolpost, or where to buy such a toolholder! I've got to be missing something.
> 
> Does anyone have a link to a video I can watch about this? Is it absolutely impossible to hold a boring bar in anything but a quick change toolpost or a lantern style toolpost? Do I clamp it down in the four-way without a holder? Is there something special that a boring bar holder is called for a four-way?
> 
> I've got to be missing a piece of the puzzle. Any help is appreciated!



Your boring bar can certainly be held in a four way holder.  You need to use shims under the bar to get the tip of the cutter exactly on centre.  A lot of bars have a flat on the bottom to help with alignment of the angle of the cutter.  In most cases a little down angle on the cutter (point still on centre) has worked best for me.  Still use four way holders on my small Emco 5 inch lathe and use QCTP on the the 12 inch.


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## benmychree (Apr 6, 2019)

A vee block sort of device that brings the bar to center is all that is required.  A four way toolpost (turret toolpost) is the least desirable type of toolpost for ordinary work in a lathe for one off or even limited production, Get a Aloris style toolpost, they have holders with a vee groove on the bottom, and adjust to center easily.


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## jwmay (Apr 6, 2019)

Here’s a fellow using boring bars in a 4 way.


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## mickri (Apr 6, 2019)

I never had any trouble using a boring in my four way.  It has been awhile since I did this so I don't remember exactly how I set it up.  I know that I shimmed it to center line.  Just don't remember which shims I used.  I have also seen boring bar holders for a four way that looked like this.




The dimensions would be specific to your lathe, four way tool post holder and the size of the boring bar.

I made a norman style QCTP and made tool holders for the different size boring bars that I have.  Not hard to make.  https://www.hobby-machinist.com/threads/tool-post-holder.69487/


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## mikey (Apr 6, 2019)

Here is the sleeve that Chuck referred to. The problem with this type of sleeve is that it will only work with a bar that fits the hole in the sleeve. That may or may not fit the bore you need. Best idea is to make your own. If you buy a QCTP, you can use the #2 V-bottomed holder or use a circumferential holder with sleeves to suit your bars.


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## Tozguy (Apr 7, 2019)

Use a square or squared boring bar that clamps right into the 4 way tool post. Find/make a shim to get it on centre then dedicate that shim to the boring bar. Easy on and off from then on.
For example: https://www.mesatool.com/product-page/1-2-turn-boring-tool-right-hand


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## Mauser lover (Apr 7, 2019)

Couple of questions now... 

I went and measured my toolpost. From the bottom of the slot for the tool to the top (cutting side) of the tool is 3/4 inch when the tool is lined up to cut correctly. If I'm just getting a square boring bar and clamping it straight into the toolpost does this mean I should get one that is 3/4? Trying to shim minimally. 

For the Aloris type tool holder, what do I measure to make sure I get the right size? I'd like to eventually get one of these, but... maybe next month.


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## darkzero (Apr 7, 2019)

Mauser lover said:


> Couple of questions now...
> 
> I went and measured my toolpost. From the bottom of the slot for the tool to the top (cutting side) of the tool is 3/4 inch when the tool is lined up to cut correctly. If I'm just getting a square boring bar and clamping it straight into the toolpost does this mean I should get one that is 3/4? Trying to shim minimally.
> 
> For the Aloris type tool holder, what do I measure to make sure I get the right size? I'd like to eventually get one of these, but... maybe next month.



No, that just means whatever you measured gives you an idea of what the largest boring bar is that you can mount directly on your 4-way tool post. The size bar*s* you buy should be dependent on what you need to bore. If you buy only the largest boring you can fit, what happens when you need to bore smaller holes? Notice I mentioned bars in plural, you'll need more than one size.

I think I started off with 3/8" & 1/2" boring bars, then I purchased smaller & bigger bars as I needed them.

For QCTP sizing, don't go based on what swing recommendations they give for the different sizes. It varies depending on the lathe. Measure the distance from the top surface on your compound slide (where your tool post sits on) to spindle center line.

For AXA you need at least 15/16" height to run 1/2" shank tools which is the max standard capacity for AXA (not including oversized holders).
For BXA you need at least 1-1/8" height to run max 5/8" shank tools (again not including oversized tool holders).

I could go one but not sure what size your lathe it.


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## Mauser lover (Apr 7, 2019)

From the bottom of my tool post to the top of my tool (this seemed to be the easiest and most precise way to measure from the top of the compound slide to the spindle center) I have about 1.340. Just measured with the calipers. It didn't sound like it needed to be too precise. 

I looked at the ones from Shars (so I could start drooling for when the funds arrive) and it looks like they come with their own t-slot that I will need to machine to fit. Obviously I'd prefer to be lazy, as my mill is kinda "down" right now, so I'd prefer to get away with no milling. Is there any chance that the bolt to hold the Aloris style holder will be the same as what I've got on it right now? 

I've had some time to cogitate on boring bar diameters. If the insert for a carbide insert boring bar is halfway down, then to get a 3/4" bar up to center, I'll have to have 3/8 of shim under it. But! I don't know, and I've never seen someone say, that the insert is halfway down the diameter of the bar. I've just seen pictures and taken a wild guess that it is. 

And yes, I do understand that I will need more than one eventually. Just using a "for instance" so I can start to understand what's going on, and my current project is a large enough hole, so I didn't want to get too far into tooling for a four-way tool post if I am going to be switching to an Aloris soon. 



> I could go one but not sure what size your lathe is.



Please, go on! If you need more lathe info, I'm more than happy to go get it!


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## darkzero (Apr 7, 2019)

1.34", that would be BXA territory (or 250-200 series for the Asian imports). Sounds like you have a 12"-14" lathe.



Mauser lover said:


> I looked at the ones from Shars (so I could start drooling for when the funds arrive) and it looks like they come with their own t-slot that I will need to machine to fit. Obviously I'd prefer to be lazy, as my mill is kinda "down" right now, so I'd prefer to get away with no milling. Is there any chance that the bolt to hold the Aloris style holder will be the same as what I've got on it right now?



Bolt on out of the box, unfortunately no unless they sell one specifically for your model lathe. QCTPs usually come with blank t-nuts & you have to machine them to fit. There are so many different lathes out there all with different t-slot sizes so the t-nuts come blank.

If you don't have access to a mill there are ways to make t-nut using the lathe. I'm sure you could find help here to get it mill it for you.









						How do YOU make a "T" nut for your QCTP?
					

You buy a new QCTP and it comes with an oversize "T" nut that you have to mill to size.  How do you do it? (Photos if possible). How do you measure the correct dimensions of the T-slots, set up the job on the milling machine or other machine that you use, and remove the excess material.  This is...




					www.hobby-machinist.com
				




A couple of more examples from the net. I do remember seeing someone selling QCTPs 9n ebay with premachined t-nuts like these but that was a long time ago & don't remember the details.


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## kd4gij (Apr 7, 2019)

I use boring bars in a four way on a 14x60 lathe at work all the time. 3/4" square tools cut on center. A 1 1/4" boring bar sets on center. Smaller bars I shim. Works great.


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## Mauser lover (Apr 7, 2019)

No, not the t-nut. I realize that the odds of that ending up being identical are slim. I'm wondering if the bolt that attaches to the t-nut and holds on the tool post might be the same as the one I have. 

Thanks for reminding me that you can make square things on the lathe. I forgot I would be able to machine a t-nut on the lathe itself. 

My lathe is a 12x36 import. Don't know from whence it came, Taiwan or China, I'm sure. Probably from the '80s. Not the greatest thing in the world, but I don't think it's a bad setup for a hobbyist like me. Badged as "Millport". 

My biggest question (I guess, if I can rank them by size) was whether or not I could safely hold a round tool directly in the four-way, and it seems like that guy in the video in post #4 did it without issue.


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## darkzero (Apr 7, 2019)

Mauser lover said:


> No, not the t-nut. I realize that the odds of that ending up being identical are slim. I'm wondering if the bolt that attaches to the t-nut and holds on the tool post might be the same as the one I have.



Oh, missed where you were asking about the bolt. No idea on that but I highly doubt it would be the same, both in height & dia. Otherwise you'd hear of people just popping the QCTP right on which I have never heard of or experienced. They vary even on QCTPs from China mfgs as well as USA made ones.


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## kd4gij (Apr 7, 2019)

On my 12x36 craftsman lathe the bolt with the Aloris axa tool post fit the T nut from the 4 way that was on it. 
And yes I use round boring bars in a 4 way all the time.


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## mickri (Apr 7, 2019)

I used round bars with no problem with my 4 way.  

The talk of measurements in previous posts got a little confusing.  So I took a picture of my 4 way and a picture of just the compound.   The distance between the red lines from the bottom of the slot on the 4 way to center line is the maximum distance that the boring bar can be from the bottom of the bar to the point on the bar.  This is not the overall height of the bar.  On my 4 way that happens to be 3/8."  My slot is only 1/2" tall.




On the picture with just the compound the distance between the red lines is used to determine the size of a QCTP that will fit on your lathe.  On my lathe this happened to be 1 3/16."




Hope this helps you out.


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## mikey (Apr 7, 2019)

darkzero said:


> The size bars you buy should be dependent on what you need to bore.



@Mauser lover, please see this quote.

A few things to keep in mind about boring bar set ups:

The tip of your boring bar insert will need to be about 0.005" - 0.010" above the centerline of your lathe. You can shim the bar to this height but a QCTP makes it a lot easier and a lot more precise.
The rigidity with which the bar is held makes a big difference in both accuracy and the finish you are able to achieve. Therefore, the tool holding method you use to hold the bar is important. The *least* solid way to hold a boring bar is to bolt or screw directly down on the bar itself; this is also guaranteed to mar your bars and can break a carbide bar. This is what you are setting up to do in a 4-way post unless you use a sleeve of some kind, and even a sleeve is not ideal because you are still clamping with screws. The *most* solid way to hold a bar is circumferentially, so that the tool holder surrounds and clamps down on the bar completely. The best design for this type of holder is from Aloris and will only fit a QCTP. You can make one if you wish.
Boring a hole is not difficult. Even the most basic methods will work. However, if you need to bore a _precision_ hole then that requires understanding and the best set up you can manage. My suggestion is to buy a decent QCTP and a good tool holder; that will get you part of the way to where you want to go. Then you need good bars. Then you need to learn to use them. Sort of in that order.


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## Titanium Knurler (Apr 8, 2019)

Mauser lover,

Look at the thread "Setting-up my PM 1236-T lathe" post 145 on this Forum.  It shows a BXA QCTP from PM that has a t-nut that does not need to be machined  https://www.precisionmatthews.com/shop/251-222/ .  I ordered the PM QCTP but ended up not using it.  If it fits your lathe you are welcome to it.  TK


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