Got The Chuck & Fear For My Bearings

Good thinking. You've come to the conclusion that extra power - supplied in the form of increased speed, is used to compensate for a dull or dulling edge. Shouldn't be. It's a warning that it's time to renew it. You can increase object speed, but it's a compromise, as the surface gets rougher and the tool hotter.

As far as cutting air or any other form of interrupted cutting, like roughing the outside of a bowl, the bounce should be your cue that you are not holding the tool properly on the rest. A lot of trouble like this comes from that "ride the bevel" folklore. Not a bit of sense pressing air. The tool should be _Anchored to the toolrest, the _Bevel guiding on available surface. Less available surface, the more you hug the rest as you _Cut until you get one. Once you have a continuous surface to reference, doesn't mean you should press the bevel to it, either. Difference in end/face grain resistance and the broadening of the distance between annual rings can get you out of round pretty quickly if you do.

You need to rethink your bevel angle theory. Blunt does not equal dull. It is the edge that cuts. Scrapers, in spite of the nomenclature, can and do cut with bevel angles approaching 90 degrees. It's in how they're presented to the work.

"What we have here is a failure in communication". :)

I think Leo referred to the angles that form the edge ("the included angle of the cutting edge") not the supporting bevel behind it, what machinists refer to as the 'cutting angle'. The old knife, cold chisel and nail analogy: The metal in a knife is harder than a nail, but it won't cut a nail, while a cold chisel of softer steel will. In life, to succeed you've got to have an angle. :)

My (mis)understanding is that to cut wood any tool's edge must first enter the surface using a sharp edge; the cutting angle. After that it's mosty a wedging and/or shearing action. This action, of course, depends on many factors beside angles and bevels, but I convenently omit them here.

I think of cutting as wedging more than shearing. To cut (wedge) along the grain, after entry the edge isn't much needed so a narrow supporting bevel can be used. To scrape (shear) across the grain the edge is needed and thus requires a wide supporting bevel. Both actions require a sharp edge (cutting angle) to get things started. Now, I'll explain rocket science. :)

Returning to earth having explained all I know.... I tend to neglect an important edge and an important half of an edge and the tools to make them. I mean the burr on my scrapers and my burnisher. Also the flute side of my gouge edges and my gouge slip. Just a gentle reminder.

Turn to Safety, Arch Fortiter

"George" wrote: (clip) You need to rethink your bevel angle theory. Blunt does not equal dull. It is the edge that cuts. Scrapers, in spite of the nomenclature, can and do cut with bevel angles approaching 90 degrees. It's in how they're presented to the work. ^^^^^^^^^^^^^ I was trying to question your use of very sharp carving tools and knives to prove a point with respect to turning. Let me try again: Turning tools rest on a toolrest, and when things are right, the cutting force is directed downward, so the tool can be held in place with a gentle grip. The cutting force is downward, at about 90 degrees to the tool. Carving tools and knives have the cutting force straight into the cutting edge. They're not the same.

G'day George,

I have to disagree with what you have presented. I'll let anyone reading the posts decide what to accept and what to dismiss. Further, I see little benefit is likely when you have to commence with sweeping unsupported statements about the poster's knowledge and lead off with a selected edit from a longer post.

Are you suggesting that a well sharpened tool will cut wood fibres cleanily and equally at any lathe speed? Please advise which law of physics you are relying upon that describes the energy necessary for the cut to take place? I assume it must be independent of timber's surface velocity and derive the energy from some other source (since the cutting tip of the tool is stationary).

A given amount of energy is required to cut a fibre cleanly without causing significant subsurface damage (pulling the fibre as it cuts). Stop here and consider if this is correct or false in a real turning exercise rather than with one cut from a freshly sharpened carving tool. I believe it is true, others may not.

Subsurface damage is harder to repair than a clean, even rippled cut so I'd opt for a speed that will more cleanly cut the fibres. Taking this to the next stage, at some velocity, the energy available will be below that necessary to cleanly cut the fibres. This follows as a logical statement if you thought the earlier statement was considered to be true.

You cannot keep a "carver's" quality edge on a turning tool so any comparisons other than to compare edge sharpness of each are not really a useful example when discussing turning. Obviously a tool sharpened for carving will cut the fibres as you push. Sounds nice but take a few cuts into a piece of jarrah with the tool and it won't have such a keen edge for long.

I'm unsure what was meant by, "a couple of strange turning ideas" as I doubt I would be alone with the views contained in the section of my earlier post you copied.

Regards, Alan

He Might no be but it is fact a well sharpened tool will go where you lead it and a blunt tool will go ehrer it can. so if the tool is sharpend correctly and presentrd correctly a clean cut is possible at low speed. Think about the old lathes BEFORE motors with speed much slower than the modern lathe (Even at what we call SLOW SPEED) yet clean finishes were the norm for experianced turners without causing significant subsurface damage (pulling the fibre as it cuts).Remember these slower speeds also have the benifit of less impact on an inapropriately presented cutting surface.

Slower speeds and a light delft touch with sharp tools WILL GIVE A CLEANER CUT than not so sharp tools heavy hand and High speeds (Actually this is asking for ignificant subsurface damage (pulling the fibre as it cuts) in soft woods. Some thing to think about Alan

I take it you don't carve? First thing I was taught was that the tool moves in two directions for the best cut. Just as in whittling, where you draw the knife across the work as you push or pull it along. Or skew a plane in flat work.

Same on the lathe. Not sure why you'd want to cut at 90 degrees to the tool on a lathe. You want your edge at a nice steep skew so the rotation will bring the material along the edge as you advance it, producing the same slicing motion you use with the other tools.

You say it yourself. A certain amount (quantum?) of energy is required to make the cut for a specific wood and orientation. I agree, it's what I said at the beginning. Are you arguing with yourself? However, the source of that energy is immaterial. Can be your elbow or the lathe.

Speed does not cut the fibers. the edge does. Unless and until you get this basic concept firmly implanted, you're chasing your tail. It seems you know it to be true, because you keep talking about sharper edges doing better work. Why not just go with it? It's correct.

Of course, if you did, we'd be back to the same, which is that energy in excess of that required for the cut increases potential danger. The proper mindset is to sharpen the tool rather than increase the speed to compensate. I guess that's it. You know better, you just don't care to admit the corrolary.

This all started when I contended that slower isn't always better. I never advocated fast is always better. My position has come from considering quite a good deal of written and verbalised views (including those posted in this group). A few spurious arguments seem to have been presented and I can only hope the open minds spot them.

I'm uncertain why comparisons between sharp and blunt tools entered the discussion. My point was that a turner would not usually be sharpening a tool to an edge as fine as a carver's chisel and even if he did, it would be gone very quickly. What I've written about speed and finish assumes the tool is "sharp" and has a good bevel (otherwise there are too many variables).

I can't comment upon the results from pole lathe craftsman, but I'd have to suspect that "Thomas Average", a backyard pole lathe turner, would struggle to get a great finish (or were there only true craftsman using pole lathes to create the work you mention?). His tools would lose the edge faster than our HSS and sharpening must have been more difficult (I fear I am widening the front to encompass sharpening technique now!). As with all of the crafts, a few people will perform better than the many if given identical equipment.

I see little benefit in comparing a sharp tool at slow speed and a not so sharp tool at fast speed (whether yelled or not)..... would not sharp and fast be better than less sharp and slow?. Rather an obvious answer in both cases I would have thought. It really doesn't do anything more than find a point I certainly know we can fullly agree upon (which isn''t bad, but doesn't really advance anything).

Unless someone has something new to add I'd say we may have wrung this topic out, for a while anyway.

Safe turn>He Might no be but it is fact a well sharpened tool will go where you lead

George,

George,

I think you probably prefer to be contentious. Unfortunately you misinterpret or intentionally twist what is posted so you can commence another lecture to impress.

The use of the term "quantum" adds nothing to everyone's understanding of the point, but does indicate a lot about you.

Safe turning, or whittling, Alan

But it is definitely SAFER

Well sharpened as opposed to something that is not well sharpened EG BLUNT

I DO it achieves a better cut at SAFER SLOWER speeds

and even if

Not with quality tools.

What I've written about speed

Another words a well sharpened tool!

Not all lathes before motors were pole lathes having used a treadle lathe with WELL SHARPENED tools I was amazed at the quality of the cut obtained the very first time I used the lathe. Here as I said "a light delft touch with sharp tools WILL GIVE A CLEANER CUT"

NOT necessarily so as the wood is turning slower there is less "Grinding " action on the edge as can be seen when turning wood with a high silica content on an old lathe with the tools of the time. the remain sharp for a longer time than HSS tools turning the same wood at high speed. (Much less grinding action)

than our HSS and sharpening must have

No I wont go into the argument of High speed grinding as opposed to low speed wet grinding.

As with all of the crafts, a few people

NO that is not what the discussion is about which is Fast and less sharp Vs Slow and Very Sharpe

Rather an obvious

A good way to avoid saying you are wrong.

Slower is Much safer than Faster it just takes a bit more skill in developing a lighter touch.

:-))

Well said Alan. I suspect you have really hit on the fine point of it with this post.........

For further posts, please visit alt.binaries.semantics

;) Alan

Interesting evaluation here,

"Chuck" wrote: Gotta say it: B I N G O ^^^^^^^^^^^^^^^^ Anybody named "Chuck" must know something about lathe RPM, by George. ;-)

Gotta say it: B I N G O

If only he'd show it....

This thread seems to have skipped back to my earlier post regarding RPMs vs Safety. My limited experience, specifically with a sharp skew chisel, is that at slow speed (500 rpms) I get more catches than I do at higher speed (1200 rpms)

Making shearing cuts "downhill", it seems to be easier to get a smoother surface using higher rpms than lower.

When cutting coves with a detail gouge I get better surfaces and smoother curves at higher rpms than at lower rpms.

Still having fun getting use to turning a tool while making a cut. Guess that's a carry over from a metal lathe.

Fun stuff this turning thing. Instant gratification, relatively speaking. Of course when things go to hell in a handbasket it often means significant change to the original idea or throwing the piece away and starting over. In solid wood furniture a screw up usually doesn't require starting all over.

charlie b

Except when the piece is thrown hard by a high-speed tool?

As the lathe speed goes up, the temperature at the cutting edge goes up. At temperatures as low as 150 degrees Farenheit some woods lose up to half their strength, making them easier to cut. So at higher speeds you will get better finishes. This information comes right out of one of Mike Darlow's books. regards Kevin