Which boring bar?

SubtleHustle

SubtleHustle

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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.
 
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.
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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
 
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
 
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.
20190119_072319.jpg
20190119_075028.jpg
 
Look for Circle Machine bars. Nice stuff and the price reflects that.
 
Could anyone tell me what the letters mean, or point me to somewhere that explains them? Ex: CCMT, QCMI...
 
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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