Author Topic: Help! Problems with fingernail grind  (Read 1512 times)

Offline Blake

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Help! Problems with fingernail grind
« on: February 25, 2021, 12:07:48 PM »
Hi - I'm having an issue getting the fingernail grind on my bowl gouge correct and for the life of me can't work out what I'm doing wrong, I'm using a Robert Sorby 447 Sharpening System which I am fairly confident i have set up correctly to give a 45' bevel - however try as I might I always end up with the top of the bevel being in an 'S' shape rather than a smooth arc; I tired to upload a photo but keep getting an error message

All advice appreciated!
Blake

Not sure how that happened - but pic has uploaded now!
« Last Edit: February 25, 2021, 12:50:44 PM by Blake »

Offline Bill21

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Re: Help! Problems with fingernail grind
« Reply #1 on: February 25, 2021, 12:19:14 PM »
A picture would really help. What error message are you getting?
Common problems are the picture file is too big or the wrong type.

Provided the jig angle hasn't changed from its factory setting (although you can alter this to experiment) and you use the recommended tool extension it’s normally fairly fool proof.

Offline Blake

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Re: Help! Problems with fingernail grind
« Reply #2 on: February 25, 2021, 12:30:49 PM »
Just tried again - I get the message: Fatal error: Allowed memory size of 94371840 bytes exhausted (tried to allocate 16384 bytes) in /homepages/4/d355110901/htdocs/awgbweb/AWGB/awgbforum/Sources/Subs-Graphics.php on line 420

I've reduced the pic down to 400KB so well below the limit of 2000k

Offline Bill21

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Re: Help! Problems with fingernail grind
« Reply #3 on: February 25, 2021, 12:56:23 PM »
Looking at the picture it seems you are just not spending enough time grinding on the “wings”. This is not uncommon when folks use the jig the first few times. Give it another try and get back to us with your results.  ;)

Offline Twisted Trees

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Re: Help! Problems with fingernail grind
« Reply #4 on: February 25, 2021, 12:56:28 PM »
Sorby recommends that you split the sharpening into 3 sections, do each wing then do the nose, their proedge video shows it quite well and also how to recover when you get it wrong about 2 minutes into the video. https://www.youtube.com/watch?v=k-nTHpfcwkQ
TT, AKA Pete, but that name is taken :-)

Offline Blake

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Re: Help! Problems with fingernail grind
« Reply #5 on: February 25, 2021, 01:09:15 PM »
Thanks Both - I'd been taking the 3 section approach outlined but seems to be spending a long time on the sides but only increasing the S curve - worth noting that the Sorby Jig I have is only the Jig and I'm using it with a grinding stone (can't afford the full Pro Edge setup!) - I was wondering if this would have any bearing on the approach?

Offline Bill21

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Re: Help! Problems with fingernail grind
« Reply #6 on: February 25, 2021, 01:45:02 PM »
The grinder shouldn’t make a difference. Only once you’ve achieved the desired result will you appreciate how much time needs to be spent on the wings. At least that’s been my experience! Keep trying and do come back if you have any problems. I’m sure we can get this sorted for you.

Offline BrianH

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Re: Help! Problems with fingernail grind
« Reply #7 on: February 25, 2021, 01:51:09 PM »
It may seem a daft question but are you falling into the trap of spending too much angst on what the tool looks like rather than how it cuts? It also helps to remember that a jig helps with angles but the actual shaping remains in your own hands.
All the best with it
Brian

Offline Les Symonds

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Re: Help! Problems with fingernail grind
« Reply #8 on: February 25, 2021, 02:41:18 PM »
My suspicion is that you're spending too much time on the tip...this grinds away rapidly and can begin to undercut the wing, which ends up causing that concave-to-convex shape that your photo shows. Perhaps more importantly.....slow down and grind the wings back a bit, but a little at a time. It looks like you've been a bit over enthusiastic and you're bluing the steel. If that's old, high carbon steel you might well be causing it to lose temper and soften, if it's HSS, you might be okay!

So....forget the tip, work the wings back until you grind back beyond the "S" shape.
Les
Education is important, but wood turning is importanter.

Offline Blake

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Re: Help! Problems with fingernail grind
« Reply #9 on: February 25, 2021, 04:02:26 PM »
Thanks all for the advice, I've tried not to get too caught up in exact angles and shapes generally instead focusing on how the tool works for me, but in this case with the bowl gauge it's not cutting well currently - I shall slow down and take your tips on board and let you know how I get on.

Offline Lazurus

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Re: Help! Problems with fingernail grind
« Reply #10 on: February 25, 2021, 05:50:50 PM »
I use the same jig and have done for decades, the above advice is spot on as long as you have the correct angle on the are, and the correct amount of the gouge protruding it just takes a few seconds to retouch the cutting edge, but the wings need longer to get the fingernail grind, then a quick sweep from side to side to finish.
Living and working on the Norfolk Broads

Offline julcle

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Re: Help! Problems with fingernail grind
« Reply #11 on: February 25, 2021, 08:01:49 PM »
Also, don't just set the protrusion to 2" and then spend 10 minutes grinding it because the metal at the tip will have worn away and the gouge will no longer be 2" but a lot less, keep checking the 2" setting. Hope you sort it, I have had the Sorby Jig for ten years without a problem. -- Julian
Location: S. Wales
Crowvalley Woodturners
Julian

Offline Blake

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Re: Help! Problems with fingernail grind
« Reply #12 on: February 26, 2021, 07:04:19 PM »
After some patient grinding I'm pretty much there I think - at one point I'd ground the wings to much which in turn caused an S shape >:( however I think I can now spot the happy medium - many thanks all for your help & advice - very much appreciated!

Offline Bill21

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Re: Help! Problems with fingernail grind
« Reply #13 on: February 26, 2021, 07:12:33 PM »
Glad you’re sorted, and happy we could help.

Offline Wood spinner

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Re: Help! Problems with fingernail grind
« Reply #14 on: February 28, 2021, 06:22:54 PM »
This may be worth a look , Its not your jig but you can see how they do it

https://www.youtube.com/watch?v=k-nTHpfcwkQ