I Need Boring Bars For My 7x10 Lathe: Brazed Carbide, Hss, Or Carbide Inserts?

Cavediver

Cavediver

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The thread title pretty much says it all! I need to pick up some boring bars for my 7x10 HF lathe, and I don't know what I should get. Aluminum will be the material I use most, followed up by plastics and brass. Steel will come into play somewhere down the road, but that likely won't be for a while.

I'm inclined to buy the inexpensive brazed carbide bars as trainers. I know the carbide will probably need to be sharpened, but I think I can handle that by hand with some diamond sharpening paddles. Any reason I should skip these and move on to one of the other choices? I would buy the HSS version, but my grinder / sharpening skills are way below adequate. They'll eventually get better, but I need to get rolling on this project sooner than that...

As far as the insert bars are concerned, I have no idea where to begin. Soooo many choices for both insert and tool, so many material possibilities, etc. I'm quite lost at this point, and am not sure if I should go this route or not (following the "buy once, cry once" method).

If it matters, I'm still using the stock tool post at this point. A QCTP setup is in my future, but not for a while yet.

Thanks!
 
I am in the same boat and interested to see what the group says.
 
I recommend SCLCR insert bars. They use CCMT (steel, CI, anything really)/ CCGT (alu, plastics) inserts which are cheaply available. You can get a 5pc set with inserts for $30 from Banggood
http://www.banggood.com/5pcs-SCLCR-...content=saul&utm_campaign=Electronics-US&ebay

I've been using a 3/8 bar from Shars for the last couple of years and it works just fine and recently received a 7mm and 12mm pair (1/4 and 1/2in) from Banggood that uses the same inserts, all for $17. Haven't had a chance to use them yet, but they look good, inserts fit tightly, nice Torx screw. I'll get a pack of 10 CCGT inserts at some point as I mostly work with alu and the high rake CCGT form works better with softer materials and low hp. You can even get turning holders that use the same inserts, which brings the cost down a bunch.

I tend to use HSS for turning, but the insert boring bars are much more versatile than ground HSS and I've been down the brazed carbide route and never want to go back!
 
Carbide requires a higher tool pressure to work.

With the small size of the lathe and the materials you list plastic, brass, Al
HSS is best for all of those..

Grinding is not that hard, just read a book, look at a chart, watch a video and try it, test it
It's not critical.
 
grinding HSS boring bars from blanks is not trivial and it's hard to grind one to bore more than 2in deep. You can get or make the HSS bit holder boring bars (I've made one for threading/ grooving) which work ok, but making one to bore and face a bore isn't trivial and you still end up with a larger minimum bore size than you would for an indexable boring bar.

I'm all over HSS and have ground a ton of HSS bits, but those SCLCR bars just make life so much easier. Never had a problem using my 3/8 bar on steel, CI, alu, brass or plastic and that's with a CCMT insert. CCGT inserts should require even less cutting force/ pressure.
 
I also have a set of Everede boring bars and they are very nice. They have small triangular stock inserts, both carbide and HSS, like Karl said. They are not cheap but are worth the money. Everede also makes bars for standard inserts as well.

Boring does not need to be difficult. I started with a set of made in India cheap boring bars from ENCO. They take square or round bits you grind yourself, one end at 90 degrees, the other at 45 degrees. The whole set of bars up to 1" was only like $30-40 or so. They work just fine. I still use them, especially the 1" one, because my Everede set does not go that big. Those tools are also pretty easy to make if you have some stock lying around.

Boring tools need much more relief than outside tools or else they will rub below the cutting edge. That seems to be the biggest problem people have -- me too, when I started out. Import brazed carbide tooling are really projects, not finished tools. They work very nicely when they are sharpened properly and have correct clearance and relief. A machinist needs to be able to grind, adjust, and troubleshoot his tooling, and needs to be able to make a tool from scratch where and when necessary. Face up to it and get it behind you.
 
Bob Korves said:
A machinist needs to be able to grind, adjust, and troubleshoot his tooling, and needs to be able to make a tool from scratch where and when necessary. Face up to it and get it behind you.
Click to expand...

I hear that and I am trying to get it right, but have produced mediocre results thus far. I know what needs to be done, but my hand-eye coordination needs to get with the program! :(
 
Hey Cavediver, don't feel bad. I've ground many, many boring tools and as Matt said, its a lot of work. And don't kid yourself - boring is the most complicated "simple" process there is in machining. There are few areas that have its own knowledge base and specialist machinists and boring is one of them.

You are asking a simple question with a very, very, very complicated answer with a lot of "it depends" thrown in. It would help to know:
  • How deep do you need to go and how large is the bore?
  • What are your tolerance and finish requirements?
  • Is the bore a through bore or does it have a closed bottom?
  • Do you have a good boring bar holder?
  • What is your budget and do you have the knowledge to choose the right bar and insert geometry for your needs should you choose an inserted tip bar?
  • Do you have any idea about the cutting forces inherent in the boring process and how the tool and the user alters them?
In my opinion, this is the one area in machining where doing some homework before choosing a bar/bars will pay off. Mistakes made here can be very expensive so learn first and choose well. In the meantime, I would just buy a cheap Chinese inserted boring bar set like Matt suggested (SCLCR-type), keeping in mind that this is to get your feet wet. Once you learn about boring you can focus on buying bars that will work well for your needs.

Trust me; there will come a day when you will need to bore a hole with very, very tight tolerances. To do that you need the right bar and you must know how to use it.
 
From a practical standpoint the bore depth is the most important factor.
If you require + 10 diameter depths then carbide body/insert bars work nicely yet will be well beyond your price range.

I have never used any of these tools but may encourage my employer to try one, we often do very long bores.
http://www.toolingsolutions.com/catalog/dorian_tool_DEEP-HOLE-BORING.pdf

If the bores are sub 4 diameters deep then brazed tools will work fine, with bores smaller then .500 and less then 1 1/2 diameters deep I use solid carbide bars made by Accupro.
http://www.mscdirect.com/browse/tn/...ars-Grooving-Tools/Boring-Bars?navid=12105888
I have no connection to this company aside from using their products, bare in mind that small solid carbide tools are very easily broken.

Good luck
 
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