And then there were three

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egnald

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Hello all and Greetings from Nebraska! I'm finding that making tools is as much fun as making pens. Maybe it's not quite as much fun, but it sure makes turning pens a lot more enjoyable when I'm turning with tools that I made myself. I made the first one a few weeks ago out of maple and finished it with spray lacquer. The ones that I made last week and today were made out of hickory and were finished using Hut Crystal Coat. I still have one more that I want to make, for a diamond cutter (like EWT Ci4, but with sharp points instead of radiuses). I really like how the hickory turns compared to the maple.

I glued a custom glass cabochon on the ends of the tools to identify each specific cutter.

Regards,
Dave (egnald)

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jttheclockman

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OK Dave I have to ask, why the negative rake in a scraper cutter?? To me looks like an accident waiting to happen. I know you will not use them on pen blanks so where else would these be used?? Learn me something :)
 

egnald

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OK Dave I have to ask, why the negative rake in a scraper cutter?? To me looks like an accident waiting to happen. I know you will not use them on pen blanks so where else would these be used?? Learn me something :)
I use them for extremely brittle plastic blanks (inlace). EWT actually manufactures cutters with a 20-degree negative rake ground into the cutter itself for this purpose. Adding a 20-degree attack angle provides pretty much the same result but with standard flat ground carbide cutters - Dave
 

jttheclockman

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I use them for extremely brittle plastic blanks (inlace). EWT actually manufactures cutters with a 20-degree negative rake ground into the cutter itself for this purpose. Adding a 20-degree attack angle provides pretty much the same result but with standard flat ground carbide cutters - Dave
It is really not the same at all. Get below center and disaster. You tilt that cutter into a brittle blank you can say good bye to it. With a negative rake cutter the bevel of the cutter rides on the blank, not the tool. But if it works for you good luck. Not my cup of tea.
 
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egnald

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For clarification of the design, I have attached my original design notes for the first tool I made back in May. It shows the differences between:

1) The profile of a Standard Carbide Tool, i.e. a Standard Cutter (zero degree Rake Angle) mounted to a tool shaft held level (perpendicular to the workpiece).

2) The profile of the EWT Negative Rake Carbide Cutter mounted to a tool shaft held level.

3) The profile of a Standard Carbide Cutter mounted on my modified tool shaft so that it presents with a negative rake angle to the workpiece.

The most obvious difference between the EWT and my design is that there is a steeper angle between the Flank (Bevel) of the cutter and the New Surface of the workpiece. Since carbide has a considerably high sheer strength and the materials in pen turning are relatively soft think any impact on the cutter should be negligible.

Regards,
Dave (egnald)

Note: These were my design sketches used for proof of concept only (not drawn to scale).

NR Notes (Scan) 001.jpg
 

jttheclockman

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To me and this is only my opinion you are doing nothing by changing the angle. You still are cutting with the same edge of the cutter. Just that you are now lowering the handle because if you cut below center you risk a grab or catch that will destroy the blank. If a tool such as a bowl or spindle gouge or even a roughing gouge is used in that way it rides on the tool bevel to give it support. There is no support with those tools. It is all cutter head. I am sorry but but just do not buy it. Now again if you find it works for you then great you found and made a tool for your turning needs. Just think there are better options to get that negative rake you desire.
 

More4dan

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To me and this is only my opinion you are doing nothing by changing the angle. You still are cutting with the same edge of the cutter. Just that you are now lowering the handle because if you cut below center you risk a grab or catch that will destroy the blank. If a tool such as a bowl or spindle gouge or even a roughing gouge is used in that way it rides on the tool bevel to give it support. There is no support with those tools. It is all cutter head. I am sorry but but just do not buy it. Now again if you find it works for you then great you found and made a tool for your turning needs. Just think there are better options to get that negative rake you desire.
For me the advantage is with brittle materials like Inlace. It does reduce the chance of catches and leaves a ready to polish finish. It’s the first time I’ve had ribbons come off Inlace. One could angle the tool to replicate the angle or cut below the center axis for a similar cutting geometry. Angling the cutter on the tool allows less experienced turners to just hold the tool flat for more consistent passes. I’ve tested moving the tool below center axis and I don’t get nearly the finish as the negative rake tool. I can get similar results on my metal lathe where the tool is absolutely rigid and cuts are precise without the negative rake. The negative rake tool is much more forgiving. I’ve found little to no advantage on softer materials. Just my experience from experimenting with this same design last year. If you want to use a negative rate scraper, this is a more economical way to go. The inserts are cheaper and you can resharpen them to get more life.

Danny


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jttheclockman

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For me the advantage is with brittle materials like Inlace. It does reduce the chance of catches and leaves a ready to polish finish. It’s the first time I’ve had ribbons come off Inlace. One could angle the tool to replicate the angle or cut below the center axis for a similar cutting geometry. Angling the cutter on the tool allows less experienced turners to just hold the tool flat for more consistent passes. I’ve tested moving the tool below center axis and I don’t get nearly the finish as the negative rake tool. I can get similar results on my metal lathe where the tool is absolutely rigid and cuts are precise without the negative rake. The negative rake tool is much more forgiving. I’ve found little to no advantage on softer materials. Just my experience from experimenting with this same design last year. If you want to use a negative rate scraper, this is a more economical way to go. The inserts are cheaper and you can resharpen them to get more life.

Danny


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Being you quoted me Dan, all I can say is good luck and you have to be an experienced turner to be able to cut below center and have good results. Just the natural forces of downward pull makes me skittish and I will stick with standard tools. As I said it may work for others and I have never seen these so have no experience with them and really have no desire. I understand the negative rake cutters but the tool is beyond my turning skills. Work safe and happy turning.
 

More4dan

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Being you quoted me Dan, all I can say is good luck and you have to be an experienced turner to be able to cut below center and have good results. Just the natural forces of downward pull makes me skittish and I will stick with standard tools. As I said it may work for others and I have never seen these so have no experience with them and really have no desire. I understand the negative rake cutters but the tool is beyond my turning skills. Work safe and happy turning.
I’m not experienced enough to cut below center and get good result either. I struggle above center too but I’m amazed at folks that can ride the bevel of a skew. Maybe one day. For best results I try my best to hit the center axis. Different angles of the cutting edge for different material properties is something I learned from grinding cutters for metal turning bits. I’ve been experimenting with the same principles for wood, plastics, and ebonite. I have found changing the rake can make a difference in surface finish as well as the angle on the cutting edge. These are secondary at best after sharpness and cutting depth/feed rate (which translate to skill when hand turning).

To each to their own experience and comfort levels.




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egnald

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Different angles of the cutting edge for different material properties is something I learned from grinding cutters for metal turning bits.
A metal fab shop is where I was exposed to cutter shapes and angles as well. The force angle that the cut applies to the tool is perpendicular to the rake face which is also a difference between the physics of a zero and negative rake angle tools.

As has been previously stated, one can achieve essentially the same thing by raising the handle on the tool to provide a downward cutting angle. Using a conventional carbide tool held at an angle makes it significantly more difficult to maintain control and consistency compared to keeping the tool level as is done with carbide cutters.

It is also a given that that the shearing cut from a traditional skew will yield a better surface than one where the material meets the cutting edge straight on, as it does with carbide scrapers. I started with traditional high speed steel tools, but it was short lived after only a few projects. Instead of investing in a Wolverine or other sharpening system, I opted for carbide tools. I guess my familiarity with carbide from the machine shop was also a factor.

To all: I appreciate the passionate discussions related to this but I think we have officially run the topic to death, so let's use the tools and techniques we are all comfortable with and as Cap'n Eddie says, lets get out there and be makin' some shavin's! - Dave
 

ramaroodle

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Feb 15, 2018
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Seattle
I am so jealous of the quality look of your work. Mine are nowhere near as pretty but they do work as well as the negative rake.

To me and this is only my opinion you are doing nothing by changing the angle. You still are cutting with the same edge of the cutter. Just that you are now lowering the handle because if you cut below center you risk a grab or catch that will destroy the blank. If a tool such as a bowl or spindle gouge or even a roughing gouge is used in that way it rides on the tool bevel to give it support. There is no support with those tools. It is all cutter head. I am sorry but but just do not buy it. Now again if you find it works for you then great you found and made a tool for your turning needs. Just think there are better options to get that negative rake you desire.
There definitely is a difference in the way it cuts vs not having the angle on it. It leaves a much smoother and less aggressive cut with less tear-out especially on acrylics and softer woods. I bought a negative rake bit but sent it back after comparing the two as they cut the same as far as I could tell. Plus, I can sharpen with the hone like my other carbides unlike the neg rake one. The ability to sharpen it makes all the difference in the world. Like I said, it ain't pretty but it works great.
 
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