Author Topic: Sharpening a Glenn Lucas Negative Rake Scraper with a french curve.  (Read 1256 times)

Offline greydarrah

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I just bought Glenn Lucas's GL1 negative rake scraper with a french curve (I'm hoping the attachment works so you can see what it looks like).  It has a 33 degree angle on both sides of the steel as well as going around the curve on one corner.  I can't figure out how to get it smoothly sharpened on my T8.  Being 1 3/8" wide, it wont fit in my SVS-50 multi jig for skew chisels, though I doubt that jig would work because of how long the curve extends around one corner of the steel.  I tried the SVD-110 Tool Rest, getting it set to the 33 degree angle to the wheel, but when I try to round the corner on that curve it makes a mess of the grind on the steel.  This may be all my fault.

Anyway, I was wondering if someone knew of the best jig to use for this type of tool, if one exist.

Thanks for any help
Grey
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Offline AKMike

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Re: Sharpening a Glenn Lucas Negative Rake Scraper with a french curve.
« Reply #1 on: July 02, 2018, 09:18:14 pm »
The SVD-110 is the proper choice. Were you using it horizontally or vertically? Scrapers are normally done vertically, but the GL1 is really a skew chisel and should best be done horizontally. Try practicing the sharpening motion with the T8 turned off, and when you get the feel for smoothly swinging the tool, try again with the machine on. Swinging that long handle around with the changing blade curve is not easy. You can also try sharpening one end of the curve, then the other end, and then blend the two in the middle.

Mike

Offline greydarrah

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Re: Sharpening a Glenn Lucas Negative Rake Scraper with a french curve.
« Reply #2 on: July 02, 2018, 09:24:15 pm »
Thanks for the response.  I'm using it horizontally.  I'll try it again.  That big curve is tricky and I was hoping there was a better jig.

Grey

The SVD-110 is the proper choice. Were you using it horizontally or vertically? Scrapers are normally done vertically, but the GL1 is really a skew chisel and should best be done horizontally. Try practicing the sharpening motion with the T8 turned off, and when you get the feel for smoothly swinging the tool, try again with the machine on. Swinging that long handle around with the changing blade curve is not easy. You can also try sharpening one end of the curve, then the other end, and then blend the two in the middle.

Mike
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Offline AKMike

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Re: Sharpening a Glenn Lucas Negative Rake Scraper with a french curve.
« Reply #3 on: July 02, 2018, 10:01:14 pm »
I just went out to refresh my memory of sharpening the GL1. Just make sure that you are standing to one side so that you can stay out of the way of the handle swing.

Mike

Offline greydarrah

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Re: Sharpening a Glenn Lucas Negative Rake Scraper with a french curve.
« Reply #4 on: July 02, 2018, 10:43:26 pm »
Thanks, I'll do that.  It is a pretty big handle.

Grey

I just went out to refresh my memory of sharpening the GL1. Just make sure that you are standing to one side so that you can stay out of the way of the handle swing.

Mike
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Offline RichColvin

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Re: Sharpening a Glenn Lucas Negative Rake Scraper with a french curve.
« Reply #5 on: July 03, 2018, 10:11:11 am »
The SVD-110 is the proper choice. Were you using it horizontally or vertically? Scrapers are normally done vertically, but the GL1 is really a skew chisel and should best be done horizontally. Try practicing the sharpening motion with the T8 turned off, and when you get the feel for smoothly swinging the tool, try again with the machine on. Swinging that long handle around with the changing blade curve is not easy. You can also try sharpening one end of the curve, then the other end, and then blend the two in the middle.

Mike

Mike is right.  It is about the continuous movement of the tool whilst grinding.

As for horizontal vs. vertical, I use this guidance for regular scrapers:
  • When grinding angles >60º, grind in the horizontal position.
  • When grinding angles <60º, grind in the vertical position.

But with negative rake scrapers (NRS), I’ve found that sharpening with the SVD-110 attached to the support bar in the vertical position (with the grinding direction being towards the edge of the tool) does two things :
  • it makes raising the burr faster and easier, and
  • makes sharpening easier as the tool is being pushed into the tool rest, not being pulled away from it. (My experience when trying this from the other position was that the tool was being constantly pulled away from the tool rest and holding it there was difficult.)

These are based on my experiences.  You should find what works best for you.

Kind regards,
Rich
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Rich Colvin
www.SharpeningHandbook.info

You are born weak & frail, and you die weak & frail.  What you do between those is up to you.

Offline greydarrah

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Re: Sharpening a Glenn Lucas Negative Rake Scraper with a french curve.
« Reply #6 on: July 03, 2018, 05:47:38 pm »
I ended up talking with Glenn Lucas himself.  He uses the tool rest (SVD-110) in the vertical position.  He said that with a piece of steel that big, it's easy to keep steady with the Tormek wheel coming into the tool, so it's being pushed down onto the rest.  He send me a number of images.  I'm attaching one that sums it up best.

I tried it and now have a perfect edge.

Thanks for you input,
Grey
« Last Edit: July 03, 2018, 08:36:00 pm by greydarrah »
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Offline Ken S

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Re: Sharpening a Glenn Lucas Negative Rake Scraper with a french curve.
« Reply #7 on: July 03, 2018, 09:48:26 pm »
Grey,

Welcome to the forum. I am not an active turner, so I could not answer your question. In the past, we have occasionally had questions about sharpening large skew chisels. One tool comes to mind, the Alan Lacer skew. As I recall, I measured the opening on the multi jig and found it a bit too small for the skew. As a tinker, if I owned one of these skews, I would have tried filing out the opening in the jig. The posters never seemed to stick around, so I have not posted this suggestion before.

Tormek has redesigned several of the turning jigs to hold larger tools. They did not do so for large skews. Perhaps not enough turners expressed interest. Glenn Lucas has worked with Tormek. I am surprised the jig has not been modified.

I don't know if this modification would work. (I don't own a big skew. If I was a turner, it looks useful.) I realize your question involved a scraper, not a skew. I think it yould be worth a look.

Ken

EDIT: Since I wrote this, I have purchased a large Lacer skew. I have also come to realize that the combination straight section and radius does not fit the multi jig. I have had good luck using the Torlock platform. Enough grinding is involved that as Glenn Lucas stated, the vertical position works better.
« Last Edit: March 30, 2019, 03:07:39 am by Ken S »

Offline blackhawk

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Re: Sharpening a Glenn Lucas Negative Rake Scraper with a french curve.
« Reply #8 on: March 30, 2019, 02:27:18 am »
When grinding the negative rake scraper in the vertical position, a burr is not created, correct?  In this case, do you produce the burr using a burnishing tool?

Offline RichColvin

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Re: Sharpening a Glenn Lucas Negative Rake Scraper with a french curve.
« Reply #9 on: March 30, 2019, 03:53:02 am »
I get a burr.  Small one, but it is there.

Kind regards,
Rich
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www.SharpeningHandbook.info

You are born weak & frail, and you die weak & frail.  What you do between those is up to you.

Offline OneRogueWave

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 I had a experience on shaping and sharpening a convex curved surface, it may help....or not. I had a Stanley No. 40 plane using a 3 inch radius for the cutting edge. Since the previous sharpening distorted the geometry I reverted to my roots and with a fine sharpie laid out radial lines to maintain perpendicularity to the grinding surface and that allowed me to free-hand the iron and recreate a smooth arc using the SVD-110. Even though a french curve is not created the same way the principle still applies. 

Offline Ken S

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ORW,

Your comparison of sharpening the curved negative rake scraper with the Stanley 40 roughing plane is quite applicable. In both cases, we seem to have forgotten some useful ancient knowledge. Over the years we have become so fascinated with jigs. Sometimes the best and only practical way to shape and sharpen a tool is freehand.

I once watched a Tormek demonstrator fumble with trying to sharpen a small woodturning cut off tool. The tool was too small to fit in the prescribed jig. All he needed to do was rest the tool against the universal support bar and sharpen. The operation would have taken less time to do than to write this post.

I wish I could locate a video (movie) of Torgny Jansson using the original Tormek before all of the jigs were introduced. Do not misunderstand me. I like using the jigs whenever practical. Recreating the same sharp profile with minimal steel removal is the intelligent way to sharpen. I just think a well trained Tormek sharpener should also develop freehand skills.

Ken


Offline Twisted Trees

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Have to agree with Ken's post free'ish'hand sharpening with the Tormek is an essential skill and because it's a slow wheel actually pretty easy to achieve without much risk of chewing away a lot of expensive metal.

I often just use the guide bar set somewhere close even for bowl gouges (especially those that have been used so much they don't really fit the jigs anymore)

Negative rake scrapers are so easy to freehand just marker pen the end, move the guide bar so you get a comfortable standing position to the correct angle on the wheel, and touch the scraper to the wheel often to maintain the burr so much easier than setting it in a jig if you are doing it regularly you soon learn and it is literally a single pass of the blade on the wheel to maintain, rather than re-profiling which is when I would reach for the jig.

In woodturning time sharpening is non productive time, keep it short by doing it often.