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Bowl gouge Sharpening Angles

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MichaelB

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I've only been turning a short time so most of the problems I encounter I put down to my poor technique...however

I have 3/8 standard 45* bowl gouge which I sharpen using the Sorby "universal System". In a moment of madness I created a fingernail profile using the fingernail attachment. It produced a wicked point and was completely unusable (by me). Reground to standard. However and before I try again, perhaps someone can help me understand this.

Grinding at 45* on a standard profile using a V block is pretty simple and I get a smooth bevel from tip to wings. The wings are obviously "pronounced". If I now remove the wings (grinding with the flute against the bed)till they almost meet at the tip, I have two "flat" non-cutting surfaces as the wings of the gouge. Using the Sorby jig I can now sharpen each wing till they almost meet at the tip. From above I now have the nice fingernail shape. I follow the instructions as to how to set the gouge in the jig for 45*

My question (finally) is are whether the angle of the wings is also 45* and whether that angle is constant from one wing through the tip to the other wing. The original bevel angle was 45* measured from the inside of the flute to the bevel. What is the wing angle measured against?

I may be over-thinking it, but I'd like to understand more before having another attempt to see if a fingernail grind would be helpful.
 

Robbo3

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We are getting into complicated territory here but as a general rule stick with the angle that the tool came with until you need to change.

The main reason for a steeper bevel is so that the bevel rubs all the way round the bend in the bottom of a bowl.
Shortening the bevel by grinding away the heel is one solution or having two gouges with different bevel angles is another.

The grind is controlled by the shape of the flute (as shown here)
- A personal view of bowl gouges
& the length of time spent removing metal. The first is fixed & the second is under control of the user.

It helps to know what shape you are aiming for before you start. Perhaps a drawing or photo of the desired end result could be consulted at regular intervals.

The variables are:
• How far the gouge sticks out of the jig
• The angle of the jig (if adjustable)
• The distance from the grinding wheel

Once we have achieved the grind that we want we need to know how we produced the result so that it can be repeated consistently so that we only remove as little metal as possible to achieve a sharp cutting edge.

Presume 'ground as standard' means the wings aren't ground back (often called a conventional grind) similar to a spindle roughing gouge. If the tips of the wings are in front of the nose they are termed 'bull's horns' and need to be ground back so that the wings are at least in line with the nose or slightly behind.

Don't worry about the side angles. They are mainly governed by the jig.
Lyle Jamieson has a video that explains some of it
-
 

Paul Hannaby

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I've only been turning a short time so most of the problems I encounter I put down to my poor technique...however

I have 3/8 standard 45* bowl gouge which I sharpen using the Sorby "universal System". In a moment of madness I created a fingernail profile using the fingernail attachment. It produced a wicked point and was completely unusable (by me). Reground to standard. However and before I try again, perhaps someone can help me understand this.
Don't assume that because you are using a jig that it will guarantee the grind you produce with it is correct! What is happening here is that because the wings are thinner, more metal is removed from that area resulting in the pointed grind you are getting. What you need to do is to shape the tip of the gouge first to a gentle curve and then take the wings back to give the "fingernail" shape. Once you've got this right, sharpening should keep the shape but be careful not to overgrind the wings or the pointy shape will reappear.

My question (finally) is are whether the angle of the wings is also 45* and whether that angle is constant from one wing through the tip to the other wing. The original bevel angle was 45* measured from the inside of the flute to the bevel. What is the wing angle measured against?
The bevel angle at the wings will be less than at the tip.
 

MichaelB

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The variables are:
• How far the gouge sticks out of the jig
• The angle of the jig (if adjustable)
• The distance from the grinding wheel
Thanks Robbo. I think I have the jig (distances) set up correctly but I need to check. Whilst the Sorby system can be adjusted, it is clearly designed to be left alone. I have left it as "supplied" with the datum lines in the original position. The "Standard grind " I referred to is the conventional grind again supplied by Sorby. I am sticking with the conventional grind as I don't have the skill to benefit from any other. I understand that fingernail grinds allow greater flexibility: I need consistency!

Don't assume that because you are using a jig that it will guarantee the grind you produce with it is correct! What is happening here is that because the wings are thinner, more metal is removed from that area resulting in the pointed grind you are getting. What you need to do is to shape the tip of the gouge first to a gentle curve and then take the wings back to give the "fingernail" shape. Once you've got this right, sharpening should keep the shape but be careful not to overgrind the wings or the pointy shape will reappear.
The bevel angle at the wings will be less than at the tip.

Thanks Paul. Several things for me to check! I suspect my initial effort to cut back the wings was too aggressive. I think I under stand more about angles: the tip is in relation to the base of the flute; the wings in relation to the sides. Where the two meet is getting complicated, as the sides of the flute ease round to become the bottom. I think....

This video made sense to me
Thanks Rich
 

Duncan A

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As Paul H points out, jigs need to be used for the appropriate time on each part of the gouge to produce the desired shape. There are countless Sorby ProEdge videos on YouTube, but this one illustrates the concept very clearly from about 3 minutes into the video: Sharpening Woodturning Tools - YouTube
Practice on a cheap tool first!
Duncan
 

MichaelB

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Thank you all for the help. My dilemma is that whilst I am keen to learn to use "improved" profiles, I am having some success in producing bowls (and Christmas presents!) with the current conventional grind. My last attempt at reprofiling was not a success and I only have the one 3/8" bowl gouge (Christmas is coming).

Duncan-thanks for the link. I was following that the last time, but at present I'm blaming (my) operator error. That is based on using the Pro-edge, which looks excellent in that every adjustment has an "indent" for consistent use. I have the "Universal System" (445,5,6). I re-read the instructions to check that the basic platform (446) is positioned correctly in relation to the grinding wheel. It is, but there is no mention of differences for different diameter wheels. I have already discovered that grinding further "up" the wheel makes a noticeable difference to the angle produced when adding the V block to the platform.

I have made plywood jigs that are shaped to the circumference of the (6") grinding wheel with tails at 40,45,80* to ensure the jig table angle is correct (with allowances for the V block). However the position/angle of the fingernail profile attachment is determined solely by the position of the jig frame in relation to the wheel-the platform being folded out of the way.

So to practicalities: I shall create a wooden 3/8" bowl gouge: the flute will not be elliptical, but round. However it should show the resulting bevel angle .

It may turn out to be correct, and I am over-thinking the issue. But I've not been impressed with the lack of instructions about how the various parts of the (albeit older, simpler ,cheaper) Sorby system interact with regards to grinding angles. Or maybe I'm just thick!
 

loftyhermes

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I have two marks a piece of ply at the side of my wheel, the top mark is for skews and parting tools the lower one is for gouges, all of them, roughing, spindle and bowl. No idea what the angle is, it's one that I've always used and used to it. Scrapers are just laid on the tool rest.
Grinding set up.jpg
 

MichaelB

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Don't assume that because you are using a jig that it will guarantee the grind you produce with it is correct!
As I wandered out to the workshop I realised that the angle of the current set up is less important than being able to set it an an angle that I want. So, checked the bevel angle on the bowl gouge to be 45*, used the "Sharpie" technique to reset the angle of the fingernail profiler to the angle of the gouge as it touched the wheel. The "new" angle was noticeably different.

The profiler is adjustable but it would have been helpful is there was a scale (for repeatability) and a bit in the blurb that (a) it will need adjusting, (b) the wheel diameter makes a difference (see (a)). There is an angle gauge supplied but it's too small to use "platform to wheel" angle. And it is only mentioned in the set up instructions in terms of it's overall length being 2"-the needed protrusion of the gouge in the profiler.

So I now have a nice even smooth bevel at 45*. Interesting learning curve! Thanks to all!
 

Terry - Somerset

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Interesting videos.

I have been turning occassionally for a number of years and use a Sorby jig on a 6" wheel. I have deliberately kept the jig settings the same all this time to ensure repeatability, and a block fixed approx 50m from the edge of a worktop to set gouge projection.

This way I know any problems are mine and I can work at technique rather than blaming the tools.

I now realise very much more clearly how the grind can affect the way the tool is used to achieve different outcomes.

I will add additional blocks to my setting system to get (say) 55, 50 and 45 degree bevels and see what difference it makes.
 
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