More on Grinding Angle

[Dennis J Gooding]

The recent thread started by Randy Anderson regarding the measurement of grinding angle got me thinking about what we mean by grinding angle and its relationship to the actual cutting angle of the tip of the tool when a wheel grinder is used. (If flat belt grinder is used, both angles are the same.) In either case, the grinding angle usually is measured by laying one arm of a protractor across the ground face and the other leg parallel to the shaft of the tool. For or a wheel grinder, this angle is always larger that the resultant cutting angle –the angle between the top of the arc and the top of the tool. The latter angle is what determines the performance of the tool but is difficult to measure directly. The difference between these two angles depends on the size of the grinding wheel, the thickness of the tool being ground, and the grinding angle.

The engineer in me insisted that I calculate how big is the difference between the grinding angle, as defined above, and the cutting angle. It turns that for most cases of interest the difference is minor, so we can all heave a sigh of relief. Here are some typical results for an 8-inch grinder for two values of tool thickness:

Grind**Cut Angle*Cut Angle
Angle**¼" Thick**½ Thick

*30°****29.1°****28.2°

*40°****38.8°****37.7°

*55°****53.5°****52.1°

*60°****58.45°***56.9°

A further point—If the heel of the tool is ground off, then tool thickness for purposes of these calculations is the distance down from the top of the tool to the point where the heel grinding intersects the arc produced by the sharpening.

(Am I the only one who lies awake at night solving trigonometry problems?)

 

[Lars Hansen]

(Am I the only one who lies awake at night solving trigonometry problems?)

Yes and no. Awake and thinking about sharpening and angles, yes. Solving, not so much. But then I get up and turn on my tablet, and there...
Thanks!

 

[Randy Anderson]

Dennis, not usually but recently found myself out here at night trying to figure this out so I could at least be consistent and know what I wanted to set my platform at for different tools. Also so I could understand what more experienced folks like yourself mean when they speak before I starting putting a lot of expensive metal dust on the floor. After discovering a very embarrassing mistake in my logic I ended up OK. All reshaped, working MUCH better.

 

[Dennis J Gooding]

For some reason, the system does not show the text as it was originally formated. There should be three well spaced columns with a heading at the top of each and a series of angles below each heading. The system insists on deleting the spacing between the columns.

 

[Bill Boehme]

(Am I the only one who lies awake at night solving trigonometry problems?)

I've been known carry a calculator to bed with me. Maybe that's TMI

For some reason, the system does not show the text as it was originally formated. There should be three well spaced columns with a heading at the top of each and a series of angles below each heading. The system insists on deleting the spacing between the columns.

Try switching to a fixed space typeface for your table (i.e., Courier New) Also, create fake non-breaking spaces by typing some character such as an asterisk and changing the color to the background color (white). I edited the table for you.

 

[William Rogers]

I have “people” for that sort of thing so I can remain angle worry free.

 

[Mark Jundanian]

I edited the table for you.

Which made it a little harder to read on a tiny phone screen. It was a good try.

 

[Dennis J Gooding]

Thanks Bill, but it is still screwed up.

 

[John King]

Thanks Bill, but it is still screwed up.

Not on my screen. Perfect alignment and clarity. - John

 

[Dennis J Gooding]

I just discovered that the formatting of the table shows correctly on my Windows computer, but almost unreadable on my ipad.

 

[Bill Boehme]

How about now? I made the columns narrower. I haven't checked on my iPad yet, but mine has a large screen.

When we upgrade to XenForo 2.X it will support creating tables in a post.

 

[Dennis J Gooding]

Looks good now Bill. Thanks.

 

[Mark Jundanian]

How about now?

It's still off on my phone screen. It would be a challenge to get the formatting to work on every possible screen size.

 

[Bill Boehme]

OK, I made one final tweak by shortening the column headings. Dennis will kill me if I do any more butchering to his table. He might kill me anyway. The table looks OKAY on my wife’s iPhone.

 

[Dennis J Gooding]

OK, I made one final tweak by shortening the column headings. Dennis will kill me if I do any more butchering to his table. He might kill me anyway. The table looks OKAY on my wife’s iPhone.

No way Bill. I appreciate your help. It never occurred to me when I made the tables using my PC that ipads and phones may have a smaller maximum line width. Another approach would have been to convert the tables to an image and upload it.

 

[Emiliano Achaval]

I have done almost 40 demos in this Covid era; there is always someone asking the angles of my tools, so I have started to say what I'm using. Usually, the same guy would want to know what speed am I turning at, LOL

 

[Bill Boehme]

I have done almost 40 demos in this Covid era; there is always someone asking the angles of my tools, so I have started to say what I'm using. Usually, the same guy would want to know what speed am I turning at, LOL

Be sure to state the angle and RPM to two decimal places. And tell the guy that any deviation greater than ±0.01 is too much.

 

[Dave Landers]

Be sure to state the angle and RPM to two decimal places. And tell the guy that any deviation greater than ±0.01 is too much.

Or give the RPM in Degrees per Second and explain how that needs to relate to the tool angle.

 

[Doug Freeman]

All smart *** responses aside, what rpm (within 10%) and bevel angle (within a few degrees), along with an explanation about how important or unimportant you think both are and why you are using what you are, should be provided by the instructor. It does matter whether the rpm is 500 or 2000, and the bevel angle is 40 or 60. People watching demos aren't masters of the craft. Glib responses dont help them.

 

[Randy Anderson]

Ouch... I've been turning for a few years. Made a few hundred bowls, sold a lot of them and proud of my work but still a lot to learn relative to the folks I find here. I like coming to this site a lot since I feel safe asking dumb questions that I should know by now or forgot. I'll keep asking but don't want to feel embarrassed about what I don't know.

 

[hockenbery]

Ouch... I've been turning for a few years. Made a few hundred bowls, sold a lot of them and proud of my work but still a lot to learn relative to the folks I find here. I like coming to this site a lot since I feel safe asking dumb questions that I should know by now or forgot. I'll keep asking but don't want to feel embarrassed about what I don't know.

I’ve been turning a long time. I still learn things. I still ask dumb questions....
You seem to be at a good place.

One thing I’ve learned from teaching is people need a foundation before they can add new information and we all have vastly different bases.
We need to be ready to learn specific things before we can take them in.

 

[john lucas]

Ditto.what Al.said.

 

[Phil Hine]

I had the privilege to be able to teach some first year electrical apprentice classes at our state college. After observing one of my sessions my coordinator told me that I needed to "dumb it down a bit". His comment was "That you have known this stuff for so long, you have forgotten that at one time you didn't know it". I always try to remember that when I get a question that seems to be a simple one or perhaps redundant. Always something else to learn.

Phil