# Which boring bar?



## SubtleHustle (Jan 18, 2019)

I currently do not own any boring bars, and have a project in which I will need one. I will be needing to bore a 2.5" hole through .75" 6061, on ml y mill. I have a cheapo shars boring head, that came with my mill, and will probably be using this. I would also like to use this bar in my lathe, in the future. Could anyone suggest to me a good bar for this operation? I dont want to spend $300 for it, but dont want a HF special either. Thanks in advance for advice.


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## mikey (Jan 18, 2019)

SubtleHustle said:


> I currently do not own any boring bars, and have a project in which I will need one. I will be needing to bore a 2.5" hole through .75" 6061, on ml y mill. I have a cheapo shars boring head, that came with my mill, and will probably be using this. I would also like to use this bar in my lathe, in the future. Could anyone suggest to me a good *bar* for this operation? I dont want to spend $300 for it, but dont want a HF special either. Thanks in advance for advice.



Could you tell us which mill you have and what size shanks your boring head takes? The reason this matters is because boring a 2.5" ID hole on a knee mill is no biggie but it is just about the size that you'll get some vibration on a little benchtop mill if you cannot run it slow enough. 

Boring bars can be used on the mill or the lathe but no single bar will be sufficient for all boring jobs. On the lathe, I prefer inserted carbide bars but on the mill I prefer cobalt bars or solid carbide bars. This is because a sharp HSS/solid carbide bar will generally be lighter than an inserted tip bar for less mass and will take very fine cuts. They will bore from pretty small to pretty big holes while also finishing better than carbide inserts and are easily sharpened in the home shop. I use Borite cobalt bars and Micro 100 solid carbide. Both are expensive but cheaper brands are out there. Little Machine Shop has a set of 1/2" cobalt bars that are less then 1/3 the cost of a comparable Borite set: https://littlemachineshop.com/products/product_view.php?ProductID=2682&category=-1134493617

If you want to use indexable bars there are many sets out there, from cheap $80 Chinese sets to expensive Micro 100 sets. One good quality set for not much money is a Borite inserted carbide set: https://www.amazon.com/BORITE-IB-50...7845538&sr=8-4&keywords=boring+bar+set+borite. These are good bars; I've used them. However, they are 1/2" bars so they won't do bores smaller than about 5/8" ID so they aren't all that useful on a lathe.

Quite frankly, you can do the job you described with a cheap $18.00 set of brazed carbide bars. It will bore the hole and can be used on the lathe as well. Just be sure to hone the sides and top with a diamond stone and put a really tiny nose radius on it and it will bore that hole with no problem. You won't get a fine finish with these tools but they will cut an accurate hole.
https://www.amazon.com/HFS-Shank-Ca...id=1547845840&sr=8-18&keywords=boring+bar+set


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## P. Waller (Jan 18, 2019)

If you are making 1 part and do not have to make time then virtually any tool that will fit in the boring head will work.
Good Luck


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## SubtleHustle (Jan 19, 2019)

Ok, so my mill....well, it's a Central Machinery, bench mill, from 97. It is nearly impossible to find any info on it. I feel like I have the only one around. That said, it's about 800 lbs, and VERY rigid. Its rpms are from 103-1980. I bought it about a year ago, for $250, and couldn't be happier with it. I was sceptical, but figured for that price, it was worth the scrap. It came with a face mill, boring head, and vise. I digress, the boring head holds .500 bars.
I was thinking of picking up the set you've shown above, from LMS, for the mill, then picking up 1 decent indexable bar to start out with, on the lathe. Except, I am a little confused from your "boring primer" thread Mikey.  In it, you stated that if you had to pick 3 bars for general use, to start a new shop, you'd pick these three...

¼”: *CCBI-250-4-5R*
3/8”: *QCMI-375-6-5R*
½”: *QCMI-500-8-5R*
*The reason I am confused, is because I cannot find any "qcmi" boring bars...not sure what I am doing wrong.
oh, and sorry for the bold text now, can't seem to get it off, since I copy/pasted your bars...damn technology...thanks again for you help. I will post a couple pics of the mill.



*


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## Liljoebrshooter (Jan 19, 2019)

Look for Circle Machine bars.   Nice stuff and the price reflects that.


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## WalterC (Jan 19, 2019)

I bought from these guys- I believe these are still made in USA. ?
 Great boring bar- good quality with inserts. Good prices.
https://www.mesatool.com/


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## Cooter Brown (Jan 19, 2019)

I Love Micro 100 Solid carbide boring bars...
But I also Like this one by the same company as above ^^^
https://www.mesatool.com/product-page/1-2-boring-bar-x-3


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## SubtleHustle (Jan 19, 2019)

Could anyone tell me what the letters mean, or point me to somewhere that explains them? Ex: CCMT, QCMI...


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## P. Waller (Jan 19, 2019)

QCMI is a Widia number, carbide shank insert bars.
https://www.widia.com/en/resources/site-search.html?sort=&inchMetric=i&search=qcmi&facetQuery=


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## mikey (Jan 19, 2019)

Sorry, I thought I made it clear in the primer thing that I was referring to Circle Machine boring bars. Circle Machine had numerous series of bars and each series has different sizes. The designation, like QCMI or CCBI, are series designations for Circle Machine bars only. Within each series they had different sizes, all with the same bar and insert geometry. Widia has taken over Circle Machine but in many cases the nomenclature has changed. In any case, a QCMI-375 bar is a 3/8" bar, a QCMI-500 is a 1/2" bar. 

I think the cobalt bar set is a good choice for your boring head, as are solid carbide bars. They will cut well at the lower speeds your mill can run at and will take a very fine cut. Inserted carbide will work on a mill but they are a bit more complicated to use. You are dealing with the same three cutting forces we see on the lathe but also must contend with Centripetal force, and Centripetal Force varies and increases with speed. As we know, carbide inserts like speed. Inserts also require more planning in order to take cuts that will bring you in on size. 

I have an appointment to get to so I'll return to this later. Just wanted to clarify the QCMI thing.


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## warrjon (Jan 19, 2019)

I agree with post #3. I have a set of carbide insert boring bars, but I also quite often use an slot drill as a boring bar. You could put a slot drill in the boring head just make sure the flutes are parallel with the axis of the boring head.

I recently finished a job boring 0.200" deep X 0.750" wide recesses in aluminium and I used a 10mm slot drill in a tool holder to bore the hole. Gives a much better finish than carbide inserts.


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## SubtleHustle (Jan 19, 2019)

Any opinions on whether or not this would be a good first bar gor the lathe?https://rover.ebay.com/rover/0/0/0?mpre=https://www.ebay.com/ulk/itm/382731534368
 I am going to go with the LMS set for the mill.


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## MarkDavis (Jan 19, 2019)

That's a nice tool.
The small diameter is well suited to boring accurate small holes, If that is what you plan to do with it then yes.

A larger diameter boring bar would be more rigid, and give a greater depth of cut. 

Don't forget to get some inserts for it.


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## mikey (Jan 19, 2019)

The F-series bars use a triangle-shaped insert so it has 3 usable tips. The one you linked to is a 3/16" *right hand carbide* shank bar with a *5 degree positive lead* that is *4" long*. It has a *minimum bore size of 0.275* and takes *Circle Machine TDAB, TDCG or TDAT inserts*. TDAB inserts are flat-topped. They come in various nose radii: TDAB-500 is a 0.002"NR, TDAB-505 is a 0.007"NR, and both come in various grades (CG5, CG6, TN7, CM1, ALO). The TDCG is a ground chipbreaker insert (C = chipbreaker, G = ground) that comes in a 0.007"NR (TDCG-505) and a 0.015"NR and 0.031"NR. The TDAT insert is a pressed-type chip breaker with either a 0.007" or 0.015"NR. Most grades will work fine in a hobby shop. I have most grades and use them all but I really like CM1 for harder steels.

I have not used this specific bar but have used bars of similar type and they work fine. They have zero radial rake but should perform well for you if you need a positive lead bar that takes flat topped inserts. For small bars, the ability to use either a general purpose 0.007"NR insert OR a 0.002"NR insert is really useful. It allows you to do general boring and also do really precisely sized bores. For me, a flat topped insert is a real positive. Not many companies produced flat topped boring inserts.

The key reason I chose the CCBI bars over something like the FCBI that you're looking at is because the CCBI uses inserts with a positive axial rake. This reduces tangential forces and really boosts chip clearance. It is a superior design, in my opinion, but the FCBI bar should be just as accurate. The critical thing we are looking for in a small bar is the ability to take inserts with a really small nose radius and the FCBI bar does that.

I think you'll be fine with it but the price for the bar you linked to is pretty high. I would look for another listing that has a new one of these bars for under $100.00. Be patient and it will show up.

Just so you know, the Circle Machine nomenclature is pretty straightforward. The first letter, like C or F or Q is the series that reflects the insert geometry/shape. C is an 80 degree diamond, F is a triangle, Q is a 60 degree triangle or 80 degree diamond, G is a Trigon triangle insert, etc. The second letter is the bar material - C for carbide, S for steel. The third letter is the function of the bar: B = boring, M = multi-purpose (boring, grooving, threading) and so on. I don't know what the last letter stands for.

If you are interested in Circle Machine bars, search for their catalog that should still be available online. Widia took over Circle Machine and still produce the same bars and inserts. They respond to email inquiries so you can contact them to get the current Widia bar and insert numbers.

By the way, I happen to agree with your choice of HSS cobalt bars for the mill. I think you'll find them very useful.


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## SubtleHustle (Jan 19, 2019)

Thanks Mikey! You've really cleared up tons for me! I was really hoping that you'd respond to this thread. I see another bar, that seems similiar, for $50. But instead of a *FCBI-187-4-5R, it's a FCBI-187-4-5L*
any idea what the difference is between 5L and 5R...who am I kidding, of course you do, could you tell me? this is it...
https://rover.ebay.com/rover/0/0/0?mpre=https://www.ebay.com/ulk/itm/292023146875


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## mikey (Jan 19, 2019)

I should add that Circle Machine inserts are like most things on ebay - they come and go. Sometimes there are a lot of them, sometimes it can take a few months for them to show up. The flat topped inserts are getting harder to find and I've noticed their prices are going up. Still, they come up for fairly good prices if you're patient. When you see the one you need, be prepared to jump on it because they will go fast now that I published the Primer thing.

No matter which bar you get, please pay attention to the nose radius on the insert that you're buying.

EDIT: There are some TDAB inserts on ebay right now but they have a 0.015"NR on them - too big for my purposes. I would avoid them.


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## mikey (Jan 19, 2019)

SubtleHustle said:


> Thanks Mikey! You've really cleared up tons for me! I was really hoping that you'd respond to this thread. I see another bar, that seems similiar, for $50. But instead of a *FCBI-187-4-5R, it's a FCBI-187-4-5L*
> any idea what the difference is between 5L and 5R...who am I kidding, of course you do, could you tell me? this is it...
> https://rover.ebay.com/rover/0/0/0?mpre=https://www.ebay.com/ulk/itm/292023146875



Same bar except the 5L is a 5 degree LEFT HAND boring bar. Unless you plan to bore in reverse, go for a 5R. 

By the way, these bars also come with a zero lead. For example, such a bar might be an FCBI-187-4-0R. The 187 means the OD of the bar is 0.187" or 3/16", the 4 means it is a 4" long bar, the 0 means it has a zero lead and the R or L means RH or LH. Circle Machine was really good about their nomenclature, making interpretation easy if you know how it works.


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## SubtleHustle (Jan 19, 2019)

Roger that, gonna be a pass on the 5L then
 Thanks again.


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## NortonDommi (Jan 19, 2019)

That mil/drill is looks like an RF-45 clone.  I've got one with the dovetail column and paid WAY MORE than $250 for it!  Good score.  Excellent rebuild article on a RF - 45 here: http://www.metalworkingfun.com/showthread.php?tid=405   They are all pretty much the same, like you I am very happy with it.
  If I can make a suggestion on boring bars, for the mill those sets of brazed Carbide are good value but do need a bit of a touch-up from new, I'd invest in a 3/4" boring head as well.  For the lathe I like LH boring bars as it allows better optics and with a 3/4" bar can be used in the 3/4" boring head in the horizontal position which reminds me that I need a LH 1/2" bar!
  I agree with *WalterC *about Mesa Tools, well made good quality at a very keen price.


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## SubtleHustle (Jan 19, 2019)

Well, the *FCBI-187-4-5R * guy decided to let it go for $120, and its new/unused so I went for it. Also got my eye on a ccbi-250-4-5r. Hope to get that one too.


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## SubtleHustle (Jan 19, 2019)

NortonDommi said:


> That mil/drill is looks like an RF-45 clone.  I've got one with the dovetail column and paid WAY MORE than $250 for it!  Good score.  Excellent rebuild article on a RF - 45 here: http://www.metalworkingfun.com/showthread.php?tid=405   They are all pretty much the same, like you I am very happy with it.
> If I can make a suggestion on boring bars, for the mill those sets of brazed Carbide are good value but do need a bit of a touch-up from new, I'd invest in a 3/4" boring head as well.  For the lathe I like LH boring bars as it allows better optics and with a 3/4" bar can be used in the 3/4" boring head in the horizontal position which reminds me that I need a LH 1/2" bar!
> I agree with *WalterC *about Mesa Tools, well made good quality at a very keen price.


Thanks for the info,  it does look very similar. I will have to do some reading on the RF-45. I literally cannot find ANYTHING on this mills item #...its "35845", if you're curious.


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## mikey (Jan 20, 2019)

SubtleHustle said:


> Also got my eye on a ccbi-250-4-5r. Hope to get that one too.



I hope you get that 250-5R. It is my most accurate bar and I've been using it for about 20 years now. I cannot count the times I have roughed with another bar and then used that 250 with a 0.002"NR to sneak up on the final bore. It is a truly excellent bar.


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## SubtleHustle (Jan 20, 2019)

Got it for $55! Ok I'm happy for my 2 starters!


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## mikey (Jan 20, 2019)

Congrats!


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