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The Knew Concepts Birdcage Fretsaw: a critical look



For reference, if unfamiliar with past reviews, there is an article I wrote about the development of the KC fretsaw for use in woodworking. This details how it came about and how it evolved, and is really essential reading if interested in but new to the KC fretsaw: http://www.inthewoodshop.com/ToolReviews/KnewConceptsFretsaw.html


Having been there from the start of the woodworking models, it is not surprising that I am still interested in its progress even though I no longer have input into the design. My good fortune is to have a great friend in Lee Marshall, who sends me saws and asks my opinion. 

Here is the new (left) and the original (right) versions of the 5" fretsaw:



New (bottom) and original (top) ..



The change in the construction of the titanium model was forced upon Lee by the cost of the material. Lee had to find a better way of using it - a one-piece construction was too wasteful of titanium sheets and too expensive to manufacture in this form. And so the "Birdcage" design came about (my name for it is the "Eiffel Tower"  ).



I raised concerns (from photos) with Lee even before I had a chance to try it out: the reason why the original fretsaw has been such a hit is partly because the frame is so stiff to create high blade tension, and partly because it is so light to create great control. The new saw design threatened to maintain the stiffness but at the expense of the lightness where it counted - at the back of the frame where it would affect the balance.

Lee sent me a fretsaw (actually, he sent me the new coping saw as well - photo later), and I had the opportunity to put it through its paces. This was now several months ago, and it was used in my then current project, the Kist-of-many-dovetails

After using the fretsaw to remove the waste on about 60 through dovetails in hard and interlocked Curly Marri, my opinion was that the back of the saw did noticeably weigh more and that it indeed changed its balance negatively.


It must be pointed out that this would likely go unnoticed by those who did not have the opportunity to use the two saws side-by-side. The differences are not great, but are nevertheless real. I thought that the new saw was not as nice to use as the original version. 

The other change in the new saw was a slightly improved blade adjustment mechanism courtesy of a wider knurled knob. I think that the knurled knobs for the blade were made standard a while ago, but they were originally T-bars, which did not look nearly as nice or work as well as the knurled knobs.

Old above, new below ...



What appears improved further is the blade tension. The original saw created high tension. The new version goes a little better. More tension is good tension.


How to use the new fretsaw


It dawned on me that I could – and should - use the saw in a different way for dovetail waste removal. One of the factors that stirred my thoughts was my preference in handle design.


The original saw came with a handle that I considered to be short ... but then I like longer handles in my chisels, so that should not come as a surprise to those who have read my comments on chisel handle design. Lee agreed that the (original) fretsaw handles could be improved, however he saw this as an improvement in looks/materials and not design or ergonomics. If you want a handle made from a more exotic wood, Elkhead Tools make them, and they are indeed stunning!



There is no doubt that these fretsaw handles are in the same class as the Dave Jeske's Blue Spruce chisel handles, which I consider some of the best around. But the Elkhead are not my design of choice in this instance since they are not actually much longer than the originals (having stated this, they may well now have alternate designs available).

My preference is for a longer handle. Here you can see the KC handles alongside one I made ...




It was this handle that gave me the idea to use the new fretsaw with two hands rather than one ..





What a difference! Now the saw was completely rock solid and balanced. 

I have used this grip on the KC coping saw as well. Again it creates a solid, balanced saw for great control ..



The double-handled grip may be used with the existing handles on the KC saws. They do not need to be changed out. However, the double-handed grip is easier with a longer handle. Easy enough to make if you prefer this. Or get one made (try Elkhead). If others agree, I will work on Lee to offer an optional longer handle.

Bottom line: if you have the original version, you have a great saw. If you have the new version, you have an improved version of a great saw.



Testing the KC - Mythbuster Style

My decision to complete some objective testing of the KC fretsaw came soon after a video was posted on YouTube featuring Adam Savage using an older version ..

http://www.youtube.com/watch?v=VhNNzgNZaLA#t=12

This video came to light on a forum, which one member used to criticise the saw, essentially stating that it flexed more than his vintage jeweller’s saw.

... a TRADITIONAL (cheap $15.00) jeweler’s saw-frame is ... three times more rigid than the comparable red thing ... the handle is connected to the blade and the tension along the blade is more or less irrelevant. The sideways flex is the thing that lets you wander off line and break blades easily.

He continued …
I did the test. I put them in the vice and hung weights on them "MYTHBUSTER - STYLE" and confirmed what I felt.”


The tone of this post was quite emotional, but everyone has a right to his or her opinion. However I also recognised that the method of testing was incorrect as I believed that it was based on a flawed understanding of the dynamics of sawing. The conclusions drawn were, therefore, not simply prejudiced, but more relevantly, they were incorrect.

The following was my response …


Testing in the Real World - Mythbuster's Style

Perhaps it is time to get a real world look at fretsawing dovetail waste, and you, the Reader, can decide whether the KC fretsaw offers an advantage or not.
The poster’s argument is that the "The sideways flex is the thing that lets you wander off line and break blades easily."
So let’s look at this point first. I clamped the frame in a vise and twisted at the handle. And, indeed, when you twist the frame, it does flex just so ...



... and does so more than a traditional jeweller’s saw (mine is a vintage, a good one ...) ..



However – and this is where I disagreed with the Poster - this is not how I view a fretsaw undergoes tension! Let us look at each of these saws in real use ...

When one saws, the tension will be exerted in such a way as to bend the frame inward, not downward or upward (which is how the Poster made his tests) ...

When one saws the force is directed at the blade parallel with the arms and towards its rear. The blade moving backwards pulls the arms inward. Not up-or-down, but coplanar with the frame. This is demonstrated below …






I rigged up a simple experiment to assess how much tension the frame could resist in this axis: The two saws were set up with the same blade and with as much tension as I could create. The knobs were tight (in the case of the vintage thumb screws I used a pair of pliers). The aim was then to apply as much pressure at the centre of the blade until it snapped or came loose. The aim was to see how much each saw blade bowed as a measure of arm flex in the horizontal axis.



The blade on the KC deflected 5mm before popping off. 



Note that the blade on the KC fretsaw was determined to be tighter to start as it twanged with a higher note. In other words, pressing the blade against the block applied a higher stress than if it had begun with a lower blade tension.

The blade of the vintage fretsaw was taut as possible (I used grips to ensure this), and the frame could not cope with more. It flexed considerably - 14mm in all ...



You can how much see the frame has bent inwards ..



... before popping off ...



Note that both saws cut on the pull. This places the frame in tension in a linear fashion, not vertical as the Poster asserted.


One cannot, however, discount the up-and-down movement of the arms. They both do this and the KC does so more. As the arms are pulled inward they will be more vulnerable to twist. The saw is guided by a hand, and hands differ. Some move the saw back-and-forth without twisting the blade. Others do not - and it is this group I imagine that are likely to break blades since this will stress it. The question where this aspect sits in the order of priority.


My reasoning is as follows ..

... a Japanese saw cuts on the pull. This tensions the blade in a linear manner. It does not require any reinforcement at the spine to prevent lateral twist ..

Japanese pull saw cutting off the end of a stretcher ..


On the other hand, a Western backsaw cuts on the push. This loads up the saw and applies tension differently. Now a spine is required to avoid the blade twisting ...

Western push saw cutting off the end of a stretcher …


In short, the strength of the Knew Concepts fretsaw lies with its ability to prevent the blade losing tension. This prevents the blade moving around. That is what increases control. There is no doubt that the vintage design can do a fine job - I happily used this one for several years - however, emotions aside, it is just not as controllable as the KC fretsaw.

Last point: the comparison here was of a 5" vs a 3" frame, which favours the latter. I only have the 5" version of the KC but recommend getting the 3" size when asked which to choose. With the adjustable blade angle option, there is no need for a wider frame, and the rigidity of the frame goes up significantly more.




Regards from Perth

Derek 


December 2013