Grinding chip breakers on HSS toolbits

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pgrey
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Post by pgrey » Thu Feb 15, 2007 10:06 pm

Good stuff Harold! This and your two other posts to which you referred us from Rec.Crafts.Iggy'sTrailer.OT.Metalworking (I may be done over there...) caused me to make a contribution to deforestation by printing them out for further perusal.

You've motivated me to try free-hand tool bit creation. If my nickname becomes "Stumpy", I'm blaming you.

Peter

Harold_V
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Post by Harold_V » Fri Feb 16, 2007 1:12 am

Chuckle!

Go slow, Stumpy, until you get the "feel" of grinding by this method.

Make sure you give it a little time before making any decisions about how well you like it, or how well it works. You may not get immediately accustomed to not having a rest, especially if you're using a wheel that's too hard and you're pressing a lot to do your grinding. That's a recipe for getting hurt, for sure. The proper wheel makes all the difference in the world.

Let us hear from you after you've given it a try.

Harold

Randall Va
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Post by Randall Va » Sun Feb 21, 2010 4:27 pm

New fellow here,sure enjoy these post!Harold I have a peice of 1" drill rod I need a finished bore of 11/16 in the end 2" deep,I have it driled out to 21/32 don't have much experance grinding bit's and boring,mostly what I have did is outside turning, any sugestion's thanks in advance Randall
www.chaski.com

Harold_V
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Post by Harold_V » Mon Feb 22, 2010 2:50 am

Randall,
Welcome to the forum.

In one of my long winded posts, there's a picture of a boring tool with a chip breaker. I suggest you hand grind a similar tool. You should use the largest blank you can accommodate in your lathe, but not larger than a 5/8" square. One ground from a piece of ½" square would work quite well.
If you need a little guidance on how it should be ground, ask. Please note that I will not be available until Monday evening, but there are others on the board that should be able to give you guidance.

Consider that you will be boring steel, so your rake and relief angles would slightly less than those used for aluminum. Width and depth of the chip breaker will determine how the tool performs. Considering you will be taking rather light cuts, make it shallow and narrow, and remember that it's hard to break fine cuts. You may have to settle for a chip that coils, which is much better than creating strings.

Harold

Randall Va
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Post by Randall Va » Mon Feb 22, 2010 4:47 pm

Thanks Harold
I found a 11/16 straight reamer and it did the job.
Randall
www.chaski.com

Torch
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Re: Grinding chip breakers on HSS toolbits

Post by Torch » Sun Jul 11, 2010 11:18 am

Harold_V wrote: (snip)
Functional turning tools are ground to a mental picture, with relief angles ground to fit the requirements of the task at hand. While these angles are important, they are not carved in stone, and vary with circumstances.
(snip)
I also suggest that tools be ground without the use of a rest, which I will address in a different post. Lets see if this has helped anyone, or if it has raised any questions that may need to be addressed. The next tool will likely be a right hand turning tool. Once you have seen a couple designs, you should be able to envision a tool of almost any design, and grind accordingly.
Harold,-

I've been keeping an eye on this subject for a while now, hoping that you would find time to post some similar pictures of a couple of the other "standard" turning tools like the RH turning tool or a facing tool. I think I understand the basic principle, but I don't have a real live mentor available to slap me upside the head when I misunderstand something so I have to rely on pictures and reading until I gain more experience and can start slapping myself.

So, if you ever get the time to post some pictures of other tool shapes, I'd really appreciate it.

Harold_V
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Re: Grinding chip breakers on HSS toolbits

Post by Harold_V » Sun Jul 11, 2010 3:09 pm

Torch wrote:So, if you ever get the time to post some pictures of other tool shapes, I'd really appreciate it.
Do you have anything specific in mind? If you can give me some guidelines, I'll try to post something.

Harold
Wise people talk because they have something to say. Fools talk because they have to say something.

Torch
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Re: Grinding chip breakers on HSS toolbits

Post by Torch » Sun Jul 11, 2010 9:44 pm

A couple of close-ups (similar to the boring tool shown on the first page) of a turning tool and/or facing tool would be great if you have them. I'm just trying to get the idea straight in my head and I haven't progressed to boring tools yet so it would mean more if I saw the chip breaker on a tool shape I'm more familiar with.

Harold_V
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Re: Grinding chip breakers on HSS toolbits

Post by Harold_V » Mon Jul 12, 2010 11:36 pm

Torch wrote:A couple of close-ups (similar to the boring tool shown on the first page) of a turning tool and/or facing tool would be great if you have them. I'm just trying to get the idea straight in my head and I haven't progressed to boring tools yet so it would mean more if I saw the chip breaker on a tool shape I'm more familiar with.
Ok, Torch, I think I understand where you're going with your request. It might help you to understand that the cutting edge is virtually the same on all tools, the only real difference being the orientation of the cutting edge on the tool. For example, the boring bar you mentioned could easily be used to face a part by mounting it rotated 90°. You can then safely assume that if you grind a similar tool with the cutting edge on the end, but with a straight grind top to bottom for relief (instead of a radius-- beneath the cutting edge), you would have created a facing tool. Move the cutting edge to the right side of the tool (as it sits in the machine) and you have created a left hand turning tool.

The upper tool in the picture, below, would be satisfactory for facing. It can be set such that the cut has lead by rotating the tool slightly in the holder, CCW. That is common practice. The other tool is an example of a right hand turning tool. It, too, could be set at a slight angle to allow for lead, or set opposite, so it could turn and face a shoulder.

The idea behind this is pretty simple. The end or side that does the cutting receives a chip breaker, ground parallel. The chip breaker is ground such that it yields positive rake. Width and depth of the chip breaker is dependent on several variables---type of material, depth of cut, feed rate, power and rigidity of the machine, like that.

The best way to become familiar with what works is to grind a few tools and give them a go. In the posts, above, I have commented on the features of chip breakers, and how they affect chip behavior. It might help you to review my comments if you're still lost.

One thing to keep in mind; none of this is difficult, nor complex. You'll come to understand what works simply by trying.

Hope this helps.

Harold
Attachments
Turning and facing tools.jpg
Wise people talk because they have something to say. Fools talk because they have to say something.

Torch
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Re: Grinding chip breakers on HSS toolbits

Post by Torch » Tue Jul 13, 2010 1:38 am

Harold_V wrote: The upper tool in the picture, below, would be satisfactory for facing. It can be set such that the cut has lead by rotating the tool slightly in the holder, CCW. That is common practice. The other tool is an example of a right hand turning tool. It, too, could be set at a slight angle to allow for lead, or set opposite, so it could turn and face a shoulder.

The idea behind this is pretty simple. The end or side that does the cutting receives a chip breaker, ground parallel. The chip breaker is ground such that it yields positive rake. Width and depth of the chip breaker is dependent on several variables---type of material, depth of cut, feed rate, power and rigidity of the machine, like that.

The best way to become familiar with what works is to grind a few tools and give them a go. In the posts, above, I have commented on the features of chip breakers, and how they affect chip behavior. It might help you to review my comments if you're still lost.

One thing to keep in mind; none of this is difficult, nor complex. You'll come to understand what works simply by trying.

Hope this helps.
Yeah, I think it helps like an epiphany: The chip breaker basically takes the place of grinding the entire top into a faucet for the side rake angle, right? In other words, the chipbreaker itself produces the rake, it's not in addition to the rake.

So, one further question, if I may: Do you attempt to hone the chipbreaker? Or just the ground faucets? (Oops, guess that was two questions, wasn't it? Dang! Now it's three...)

Harold_V
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Re: Grinding chip breakers on HSS toolbits

Post by Harold_V » Tue Jul 13, 2010 3:25 am

Torch wrote:Yeah, I think it helps like an epiphany: The chip breaker basically takes the place of grinding the entire top into a faucet for the side rake angle, right? In other words, the chipbreaker itself produces the rake, it's not in addition to the rake.
Correct. If you take a look at the youtube presentation that was discussed, everything he has to say is actually pretty good, but, he avoids chip breakers, and they're the very thing that sort tools that perform from tools that perform extremely well. A properly ground chip breaker reduces cutting pressure, as well as controlling chip formation. It can also serve to limit hogging, especially when combined with the proper amount of relief. .
So, one further question, if I may: Do you attempt to hone the chipbreaker? Or just the ground faucets? (Oops, guess that was two questions, wasn't it? Dang! Now it's three...)
Man, where do I start? :-)

Yeah, if you can, it pays to do so. Some are difficult to hone, so use good judgment. You're better served to use one without than to risk ruining the tool by poor honing. You can almost always hone the cutting edge, especially if you learn to grind the faces without chopping them up. I'll talk about that, below. I try to make each face a single grind. It's not hard to do if you keep the wheel well dressed and running true, and you use the proper wheel. A bouncing wheel that cuts hard makes that difficult, so follow the advice I've dispensed in using a wheel well suited to grinding HSS. It won't be good for much else, because it will be relatively soft in the scheme of things. Grinding mild steel, for example, will quickly break down such a wheel.

I will often hone just the keen edge of a chip breaker, such as the one shown for right hand turning. You can't really get down inside, so I tend to use a finer wheel (60 grit is a good compromise) and leave a decent finish. Too rough of a chip breaker can lead to chip welding, so a polished surface is desirable, if possible.

Do hone all features that you can. Honing extends the useful life of a cutting tool, assuming you do it properly. In spite of what you may read on some web sites, not honing a HSS tool (of any description) tends to lead to premature edge failure. The wire edge that results from grinding is still hard---and destroys the keen edge when it is dragged in to a cut. Further, the rough surface that results from the wheel tends to break down quickly as compared to a tool that is well honed.

By not chopping up the individual faces, the top and bottom of each face becomes a guide, allowing for honing without risk of rounding the cutting edge. The slightest rounding at the edge has the potential to ruin a tool, so try to keep the stone in full contact top and bottom. You need not hone the entire face, just enough to remove grinding marks at the cutting edge. You'll end up polishing only the top and bottom due to the hollow grind that is achieved by the radius of the wheel. Perfect for fast and easy honing!

Luck! You can do it!

Harold
Wise people talk because they have something to say. Fools talk because they have to say something.

Torch
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Re: Grinding chip breakers on HSS toolbits

Post by Torch » Wed Jul 14, 2010 12:53 am

Harold_V wrote:Luck! You can do it!
Turns out I'll have to wait for the new bench grinder to arrive. The one I have was at least third hand when I got it and is probably older than Methuselah's father. It's quiet and seems smooth but it turns out that it has a bit of a wobble and end float. Not a problem on the circumference of the wheel 'cause dressing it trues that surface up nicely. Seems to be somewhat of an issue when trying to use the edge of the wheel to grind a chipbreaker though. I ordered a nice new 8" 3600 rpm grinder a few weeks ago, but it's on backorder.

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