# Brazed carbide boring bars



## lensman57 (Jan 13, 2013)

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


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## Tin Falcon (Jan 13, 2013)

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


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## Philjoe5 (Jan 13, 2013)

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


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## lensman57 (Jan 13, 2013)

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


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## lensman57 (Jan 13, 2013)

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


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## Philjoe5 (Jan 13, 2013)

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


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## chipenter (Jan 13, 2013)

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 .


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## Brian Rupnow (Jan 13, 2013)

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


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## lensman57 (Jan 13, 2013)

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


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## Brian Rupnow (Jan 13, 2013)

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 (Jan 13, 2013)

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.


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## lensman57 (Jan 13, 2013)

Brian Rupnow said:


> 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


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## Runner (Jan 14, 2013)

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?


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## gus (Jan 14, 2013)

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.


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## Brian Rupnow (Jan 14, 2013)

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


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## goldstar31 (Jan 14, 2013)

I've deleted my postings. Obviously NO problem exists.


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## Brian Rupnow (Jan 14, 2013)

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


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## Propforward (Jan 14, 2013)

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.


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## gus (Jan 16, 2013)

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.


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## Propforward (Jan 17, 2013)

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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## lensman57 (Jan 17, 2013)

Hi,

Just to add a further point to my OP, I am not quite sure if the geometry-design of a boring bar differs from a lathe where the tool is rigidly held but only moves along a single axis to a boring head on a mill where the work is stationary and the boring head and tool rotate and plunge at the same time.
The moments of inertia of the boring head and the tool must put a great deal of load on the mill head, bearings and  tool shank therefore the design of the boring head becomes even more important in particular with reference to the dynamic balance of the boring head.
I would be grateful for any advice.

Regards,

A.G


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## JLeatherman (Jan 17, 2013)

I've long had a very love/hate relationship with this style of boring bar.  Two things I have found they are very sensitive to.  The most important is rake.  Since they are round you have to set the rake by hand, and if you mount them in the holder wrong the rake can end up way off and produce a terrible quality of hole even with a sharp bar.

The second is feed rate.  Being a small boring bar they will flex a surprising amount.  If you don't feed at a constant and proper rate the flex can cause chatter.  I try to feed these with the power function whenever possible and make sure to take a few spring passes at the same crossfeed setting when you are getting close to your intended diameter.


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## goldstar31 (Jan 17, 2013)

Far, far too complicated. I am guessing that you simply do not understand the geometry of a cutting tool.
Can I suggest you rig your mill or lathe with a bit of faced chip board as the workpiece. At the spindle end, you drill a small dimple with a drill chuck- as a reference point. You then leave the workpiece where it is and remove the drill chuck and replace it with a boring head. Don't put the boring bar cutter into the boring head- but draw a line from the point. Then insert the boring bar tool and align the top edge of the cutter with your line. That is going to be the reference- for subsequent adjustments of the diameter of the cut. You do NOT disturb the alignment. You can now- manually turn boring head in a cutting motion to scribe a circumference.
Now look at where you have got. Does any part of the cutting tool touch inside the circumference- other than the tip of the cutting tool? If it does, you have the wrong tool shape.

All that I have described- but differently-is  the action of a lathe tool or a twist drill.

Try it- tell me your discoveries.


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## lensman57 (Jan 17, 2013)

HI ,

I have actually done that this afternoon, prior to that I dressed the tip as best as I could and reduced the length of the shank to just enough to fit in the small holder to reduce the flex and chatter. I did bore the hole to exactly 15.85 mm that I wanted and the finish as not bad with the exception of the bottom of the hole. This was not a very deep hole to bore but I am glad it worked out. BTW the tips really do need serious sharpening with these bars, they must have sharpened them to bore in to "set custard" at the factory.

Regards,

A.G


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## goldstar31 (Jan 17, 2013)

Of course, this is a long and expensive journey into the realms of boring holes.

From the information- just recorded, you were boring nothing more than a hole of 5/8th of an inch.
If I had to do this, I would not have gone to all this rigmarole of boring bars and  boring heads - and Uncle tom, Cobley and All-- and bought a bit 5/8ths in cheap carbon steel or a 13" piece of 5/8ths silver steel-- and made a D bit from enough of the rod turned it down to 15.85mm and halved- or almost halved it. I would have put a 5 degree cutting edge on it- heated it on the gas cooker-- and bunged it carrot red into a raw potato and worked from there.

This- I have to say- is 'engineering' and cheap at that.

If you disagree- re-read George Thomas- you have the book. Page 94 Figure 7.11 refers.
----------------------------------------------------------------------------------------------------------------------
I made up his small boring head from the scrap box - which is really for bores of up to 50mm and I made up the two boring bars- inline for the Quorn- and a funny one to do the rotary table.


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## lensman57 (Jan 17, 2013)

Hi Goldstar,

The size of the hole ,15.85 mm , was incidental as it was the the diameter of the pyrex test tube that arrived from a vendor on ebay, I bought a parcel of 10 of them and evryone is different from each other, therefore I needed to bore it to the exact size of the tube. If I break this glass during cutting then I'd have to choose the next one which is about 15.89 mm, these were sold as nominal 16 mm tubes, and the bore has to be enlarged, so the idea of making my own reamers , although appealing is not quite practical, infact I bore the adjacent hole of 20.03 mm on my lathe using a 6" 4 jaw independent. At the time it seemed like a good idea to try and do the small hole on the milling machine using a boring head and then proceed to make the bolt pattern to finish the job.

I will at some point make my own reamers for small holes of about 5 mm and under.

Regards,

A.G


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## gus (Jan 17, 2013)

Propforward said:


> 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.



I am turning at 600-rpm. Bore finish looks OK. I did improve grind the BT.

Will use the BH and test bore with the BT.


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## Propforward (Jan 17, 2013)

Hm. That's what I was turning at, on a 3/8 bore. Going by what you say, and also others, I will see about dressing the bits up first, and see if that helps.


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## goldstar31 (Jan 18, 2013)

At the risk of boring everyone else, doing a 3/8th bore is a task for a simple D bit.  If you want a mirror finish, you bore undersize and make up a hone to do the last bit.


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## Propforward (Jan 18, 2013)

If you say so.


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