Brazed carbide boring bars

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lensman57

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Hi,

I have a set of import brazed carbide boring bars ( the type for the boring head ), the stuff is useless, the edges are just dull and even the lightest cut causes chatter even in aluminium. Is there anyway that these could be sharpened up or shall I just throw them away and put it down to bad experience.

Regards,

A.G
 

Tin Falcon

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unfortunately some of the cheap import tools are not very useful as shipped. and In one shop I worked even though we purchased quality boring bars they were imediatly reground when taken out of the box.

Is there anyway that these could be sharpened up or shall I just
A green wheel or diamond wheel are the tools for the task. harbor freight has inexpensive diamond wheels.

Also you have to keep the bar as short as possible

Tin
 

Philjoe5

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AG,

What size hole are you starting the boring bars with? If you try to start boring in holes that are too small for the size of the bar, you'll present an improper cutting edge to the workpiece and you'll get rubbing or poor cutting.

I myself had a long learning curve with these bars but having gotten the knack I now get good results. Many of the bars I had marked with red ink as questionable (couldn't bring myself to tossing them) now give me good results.

The rule of using the biggest bar to reduce flexing is good when you're near the end of the job, but often you need to start it with a small one to open up the hole.

Hope this helps

Phil
 

lensman57

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Thank you both Tin and Phil,

I was using the shortest of the bars ( they are 8 mm shank size ) to open up a hole that I had drilled 9.2 mm to 10mm. I was using a chinese made mini boring head of 35 mm diameter and I shortened the shank to make it just stick out of the boring head for the length of the reduced section to minimise flexing. I honed the tool on the diamond stone on both surfaces before use and it still, with my help of course, managed to make a mess of the hole. The boring head has a lot to answer for as well, one of the reasons that I have started a thread for the design of a really small but rigid boring head. My mill is a Taig with a sherline DC motor and controller. I do have a bench grinder with green stone.
The point that Phil made about the tool rubbing rather than cutting rings a bell as this is exactly what I experienced, I found it very difficult to sneak on to the final size and the tool finally cut oversize.
Any help and advice is greatly apprecited.

Regards

A.G
 

lensman57

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Hi,

Further to my previous post I would like to add that I have a Sherline supplied brazed carbide external threading tool that was truly sharp and ground to a mirror finish when I got it, it is chipped now but perhaps it could be salvaged once I learn how to do it. I don't know if these are uS made or sourced from some other part of the world but I am sure that if there was a boring bar of that quality it would work.

A.G
 

Philjoe5

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Boring holes on my mill, a Sieg X3, has always been a challenge. On the other hand, boring on my lathe always seems to go quite smoothly. Some time ago I discovered why this is so, for me with my tools.

When I'm boring free machining steel like 1144 on the lathe I usually use one of the slowest feed rates I can use. If I go to an intermediate feed rate, say 0.006"/rpm and take a cut of say 0.020" I can watch the boring bar climb up on the work without cutting. If I reduce this feed by half, I get a nice cut.

On my mill with hand feeding (I have no powerfeed), it is difficult to approximate the slow feed rates I can get on the lathe, and I suspect this is why I often get better boring results on the lathe.

BTW all of my carbide tipped boring bars are inexpensive imports from Enco and Little Machine Shop.

Hope this gets you to thinking and improves your results. In my case, boring holes on the mill led to the longest learning curve I had for cutting metal and I still approach it with as much patience I can muster.

Phil
 

chipenter

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I to bought a set of boring tools they had very little clearance angle on them , I put 5 degrees witch allows me to put a little top rake on .

boring tools.jpg
 

Brian Rupnow

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I have a set of el cheapo brazed carbide boring bars, but they serve me surprisingly well. I did buy a "green" grinding stone for sharpening carbide on my bench grinder. ---Brian
 

lensman57

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Hi,

If I were to regrind these beauties, what are the correct angles ? I maybe able to salvage something out of these lot.

Many Thanks,

A.G
 

Brian Rupnow

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That I can't say. It just appeared to me that they were a bit too "fat" in the diameter. When the cutting edge was lined up "on center", the bulge about 30 to 40 degrees below the cutting edge was rubbing on the side of the hole. I ground enough relief on them to let the cutting edge cut.
 
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jack620

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I use cheap Chinese boring bars on my lathe. I think they are ground for boring much larger holes than us modellers tend to bore. They work well on small holes if you grind away heaps of metal from the underside to give them enough clearance. Then you can grind a nice sharp cutting edge on the carbide. No idea what angles. Just nice and sharp with plenty of clearance.
 

lensman57

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That I can't say. It just appeared to me that they were a bit too "fat" in the diameter. When the cutting edge was lined up "on center", the bulge about 30 to 40 degrees below the cutting edge was rubbing on the side of the hole. I ground enough relief on them to let the cutting edge cut.
Thanks Brian,

That is interesting, I will try a regrind tomorrow.


A.G
 

Runner

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I have recently embraced carbide tipped tools because I had a set of CI locomotive wheel castings that had hard spots and destroyed the HSS lathe tools that I had. The carbide tipped tools did the job but in machining 6 wheels I blunted 6 tips. These are indexable tools (they have 3 tips) so I was interested to see this post and the indication that carbide tipped tools can be sharpened with a green stone. Can indexable carbide tipped tools also be sharpened or is the carbide just a coating and and once blunted you replace the indexable tips?

028.jpg
 

gus

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Hi Gurus,
I sincerely hope the "look alike" boring tools I bought for the DIY 2" BoreHead works well.
Now checking the business end and regrind to suit.. Will try boring on the lathe.
Will report.
 

Brian Rupnow

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Goldstar31---I think you are being somewhat of an alarmist. I have been "touching up" these cheap boring bars on the green stone in my grinder for 5 years now, with no "utter disasters".---Brian
 

Brian Rupnow

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Goldstar31--I'm sorry. That was not intended as a personal attack. Perhaps your description of an "utter disaster" differs somewhat from mine. These brazed carbide boring bars were no good to me as purchased. I had to buy a green stone for my grinder anyways to "touch up" other carbide turning tools, so I thought that since the boring tools were no good to me as they were, I had nothing to lose by attempting to correct them, and it worked fine.---Brian
 

Propforward

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I'm personally glad you posted this. I just got a set of carbide tipped boring bars. I had some success, but definitely problematic, but then again I'm new to machining. Had you not posted this thread, I might have assumed all the problems I was having were due to my inexperience, when in actual fact if I dress the tools up a bit I might get some use out of them.

Although I still think I'll splurge on some HSS boring tools when I get the chance. I have been having a lot more success with that as a cutting bit material.
 

gus

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Hi Fellow Members,
I must be lucky. Made a special tool holder to try out the shortest brazed carbide boring bar from Arceurotrade.
Test cuts was OK with aluminium bar and brass hex bar.. Will regrind to provide ample relief later.
Will go on to test same tool on my new DIY Boring Head.

IMG_1288.jpg
 

Propforward

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For my part, I am beginning to think my spindle speed was not high enough. I will be trying again at the weekend, looking forward to making more swarf.
 
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