bowl gouges sharpening - "other shapes" graph

[JR DUBUY]

Hello all ,
as a newbie in the forum I first send my Hello to all

My question is about the graph in the chapter "bowl gouges" of the manual (page 20 in the English version 3.1 or page 82 in the french version - Cf attached pdf file))
This graph show the patterns of various shapes of bowl gouges sharpening in a table 4 columns and 7 raws.

Before launching this thread, I've tried to fond out the logic of this table but until now it remains impossible for me to understand ?

If you consider one same column (i.e. the first left column), how is it possible to obtain the same edge angle (35°) with varying 4 différents JS presets (JS0 to JS3), (knowing that the protrusion P is allways maintained to 65mm) ?

thanks for your explanations

JR Dubuy
 

[Rob]

Hi there and welcome to the forum.

The geometry of elliptically ground gouges is moderately complex.  But it boils down to the fact you need to know that 3 adjustments affect the geometry and by that I mean the bevel angle and the degree to which the wings are swept back.

They are:


- the distance the tool is protruding from the jig (P)
- the distance between the pivot point and the grinding media (hole A or B with Tormek's quick set jig) which is the distance the USB is from the grinding media
- the angle at which the bevel is presented ie the angle between the tool axis and the grinding medium axis. (knuckle setting in the elliptical grinding jig).  That's what the manual refers to as JS 2 or 3 or 4 etc

If the chart shows the same angle for any of these variables, then one or both of the other 2 variables must have been altered.

To add to that is also an operator component ie the time spent focusing grinding on different parts of the bevel.  This is classically demonstrated by spending too much time on the nose (goes flat and dips) or not enough (gets pointy and is very frisky during turning).  Or too much wing grinding can wear them out at the backs and not enough means they dont sweep right round and have no cutting edge at the back.  But the angles are managed by adjustment of those 3 variables.  That also holds true for every other jig based grinding system in the market.  one has control of these 3 factors.  Tormek just happens to do it very well because of the precision engineering and good design.

[JR DUBUY]

Hi Rob

Thank you for your prompt answer.

I am certainly new to the forum, but I practice the sharpening of my woodturning tools since several years with TORMEK machines.
Considering this I can humbly pretend to master the TORMEK principles and settings, especially for the sharpening of bowl gouges with the SVD-186 jig.

You remind me of the 3 variables to be adjusted :
- "jig setting (0 to 6)"
- "hole A or hole B"
- "protrusion of the tool" (55 , 65 , 75 mm)
I know thoses settins well and practice them every day, thank you anyway for taking the trouble to remind me that.

Unneeded also to tout the benefits and high qualities of the TORMEK products, I'm convinced and very satisfied with their system.


But my questionning about the graph in the manual persists and I'm still in search of a satisfactory answer .

Let's consider a single row, by example the 4th :
- the tool protrusion is set to 65mm
- the jig setting is set to JS3
- the hole used is A
With thoses 3 variables settled in this way How then is it possible to obtain such several edge angles as 35° , 45°, 55° and 75° ?

It is in conflict with saying that the 3 adjustments are sufficient to determinate a profile and only one.

Thank you for taking the time to carefully consider my questioning ... with the manual in one hand and the SVD jig in the other hand 

Still waiting for a rational approach and explanation of this graph.

JR Dubuy

[AKMike]

That chart, which is labeled "Other Shapes", specifies the SVD-185/6 jig setting and the protrusion, but omits the USB to stone distance, which I guess is left to you to discover. Only the two starred examples are attainable with the TTS-100.

By varying the USB to stone distance and with some trial and error, the other shapes can be achieved, theoretically. If anyone does the work and finds the appropriate distances, please let us know.

Mike

[Ken S]

Good point, Mike.

Over the years, I have been intrigued with things which supposedly cannot be done with the Tormek. Two examples come to mind, the Alan Lacer skew and the Stuart Batty 40/40 bowl gouge grind. The Lacer grind can be done with the Tormek, just not with the Multi Jig. At first glance, this would seem to be because the Lacer skew is too large to fit in the jig. The real problem is that the Multi Jig and combination flat and curved Lacer grind do not work well together. It can be done by using the Torlock platform.

I requested more in depth literature on the TTS-100 from Tormek. None is available, at least to the public. The TTS-100 and SVD-185/6 were designed to simply and repeatably duplicate commonly used gouge shapes. This has been a major advance for the average user. Unfortunately, a few shapes to not fall into the standard options.

I believe that if a guide to more fully utilizing the jig setting options is eventually forth coming, it will come from forum members skilled in mathematics and/or doggedly determined with trial and error. For anyone with the computer math background, I suspect these calculations would fit well in tables or a computer app, like our members have done with setting knife bevel angles. I hope some of us will take up this challenge.

Ken

[RichColvin]

JR,

I've tried to simplify that chart on this page :  http://sharpeninghandbook.info/WW-BowlGouge.html

Does that help?

Kind regards,
Rich

[JR DUBUY]

YES !
I use to refer to your SHARPENING HANDBOOK , very clear and very complete
thank you again for this work .

By the way may I suggest a topic to add to :
I've tried to use the new SVD186 for sharpening of my rough gauge
this is made possible by the larger opening for introduce the tool

The best settings I've found are
- hole A
- protrusion 75mm
- JS6

Have you experienced also ?
what are your settings ?

thank's again
regards from France
JR

[RichColvin]

JR,

Let me try that.  I only document what I've tried.  Sounds like a great idea though. 

Kind regards,
Rich

[JR DUBUY]

Hi
After experiments several settings for sharpening the roughing gauge with the SV186 tool, I finally prefer the following :
- JS 6
- hole B
- protrusion 55mm

The result is closer to TORMEK recommandations when using SVS-50  (alpha angle=35° and a positive rake angle)
It works very well and the SV186 is helpful for the repeatability

regards
JR

[Rob]

Slightly confused.

Roughing gouges are traditionally ground straight across at 45 degrees.  If you use the SVD then you'll get an elliptical grind.  Is it your intention to sweep the wings of the roughing gouge back?  If so....it's not strictly speaking a roughing gouge any more.  Not sure what you'd call it.....a wide spindle gouge maybe??

[Ken S]

Rob,

Twenty plus years ago, I took a turning class with Ernie Conover. I brought my garden variety set of eight 1930s vintage carbon steel turning tools with me. My set did not include a roughing gouge. I was using my 3/4" "continental" gouge. As I used it for roughing, Ernie advised my to gradually grind it straighter across. Ernie talked about two shapes of roughing gouges, one eliptical and one straight across. I don't recall what Ernie called the eliptical shape. He called the straight grind, which he preferred, as the "English" shape. To keep things in perspective, Ernie is an Anglophile woodworker. He likes High Wycombe lathes and narrow empire dovetails.

Later I purchased two used Sorby M2 roughings (English pattern). Like you, I am sure these will outlast me. I have also used a Blue Chip bench chisel and a big skew for roughing. Definitely not English, but they worked.

[RichColvin]

JR,

I tried what you noted, and I like it a lot.  I updated this page, and noted that the idea was yours.

https://www.sharpeninghandbook.info/WW-SpindleRoughingGouge.html

Rob,

With the SVD-186, when the JS is up at 6, it is basically not grinding elliptically any more.  When I tried what JR had recommended, it worked really well.  I do sweep the wings back with a positive rake angle of 20° as I think it works better for me.  The wings were still flat and not curved, btw.

And I like that the edge angle is 45° with this method.  I was only able to get it up to 35° when using the SVS-50.


As a final note, I prefer the way the SVD-186 mounts to the support bar, rather than resting against it.  Prevents slippage, especially when grinding in the vertical position.


So, for this tool, the Sharpening Handbook shows two jigs that can be used.  Thank you JR for the recommendation.

Kind regards,
Rich

[Ken S]

Interesting. I will try this the next time I sharpen my roughing gouge. Actually, I have a now spare unhandled roughing gouge. The previous owner must have tried to use it with a bowl and bent it. I straightened it and used it until my conscience persuaded me to purchase an unhandled replacement.

Ken

[Rob]

Interesting thread.

There is another perspective on roughing gouges that can "go round corners" which I guess is one of the purposes of grinding the wings back.  There is a health and safety issue because they're never meant to be used on face grain work (ie bowls) but strictly only on spindle, between centre work.  The reason is the metal is tanged into the handle rather than solid stock so is relatively weak.  it's considered highly dangerous to be used against the potentially massive catches you can get from a bowl.  The only reason I even mention this is because I think the moment you grind the wings of any gouge back, it immediately makes it tempting to use it on face grain work.  Now, I appreciate that we're not actually talking about grinding the wings off specifically with this jig setting recipe.  I just thought it worth mentioning that's all.

The positive benefit to having a wide tool like a roughing gouge with smooth wings is of course you can go round corners .......but on spindle blanks.  But if you're putting gentle curves into big stuff like a table lamp or similar, the big gouge is a great tool to go trundling in and out of curves because it removes a lot of stock and is easy to guide.

[Ken S]

Rich,

I agree with your preference of having the SVD-186 being secured in the support bar. I will try it!

Ken