Knife jig aid

[Jan]

Herman,
thank you for answering Ken's questions while I was sleeping. 
As a professor of physics you are certainly better qualified for it than I am. You know better what is the stumbling block for understanding the physical concepts for your people.

Ken,
I'm glad you did not hesitate to ask for an explanation.
I think Herman's answer may help also some other members to better understand this fundamental low of motion which laid the foundation for classical mechanics.

Jan

P.S.: This morning I have asked my British teacher of English if he distinguishes between the concepts of mass and weight, and his answer was no, but he admitted that he knows that they are not identical terms. 

[Jan]

m = mass
a = acceleration
g = gravity

Most people don't do dimensional analysis, but it is pretty important to keep your units straight.

Yes, you are correct. 
For insiders, it is a valuable test of consistency. I do it if I have some doubts, but I am not quite sure how easy it is for people who are already long time out of school.

Jan

[Ken S]

Thanks all for explaning the terms.

Ken

[Herman Trivilino]

This morning I have asked my British teacher of English if he distinguishes between the concepts of mass and weight, and his answer was no, but he admitted that he knows that they are not identical terms. 

But by the laws of commerce, both national and international, they are identical terms. And in the medical field, too. The Bureau of Weights and Measures (BIPM) governs this, and they started out with just two units: the kilogram and the meter. The "weight" standard was and is the kilogram; the "measure" standard was and is the meter.

The distinction of importance is that between force and mass. The term weight means different things in different contexts.

A good example of this is the astronauts aboard the ISS. They are weightless but their physicians carefully monitor their weight because loss of muscle mass is always a danger for people in a microgravity environment.

[Jan]

This morning I have asked my British teacher of English if he distinguishes between the concepts of mass and weight, and his answer was no, but he admitted that he knows that they are not identical terms. 

But by the laws of commerce, both national and international, they are identical terms. And in the medical field, too. The Bureau of Weights and Measures (BIPM) governs this, and they started out with just two units: the kilogram and the meter. The "weight" standard was and is the kilogram; the "measure" standard was and is the meter.

The distinction of importance is that between force and mass. The term weight means different things in different contexts.

A good example of this is the astronauts aboard the ISS. They are weightless but their physicians carefully monitor their weight because loss of muscle mass is always a danger for people in a microgravity environment.

Herman,

we are discussing here physical concepts of mass and weight. In physics there is only one system of units valid for the whole world – SI. In this system weight is defined as force in the following way:

"The weight of an object is defined as the force of gravity on the object and may be calculated as the mass times the acceleration of gravity, w = mg. Since the weight is a force, its SI unit is the newton."
http://hyperphysics.phy-astr.gsu.edu/hbase/mass.html

"In everyday usage, the mass of an object is often referred to as its weight, though these are in fact different concepts and quantities."
https://en.wikipedia.org/wiki/Mass_versus_weight

Jan

[wootz]

Now that I've been using the locking collar on the knife jig regularly, a few things about it.

The shaft locking collar I use was manufactured with one facet more sloping, and put on the jig with this facet facing the Universal Support, it slides better.
You can probably see this in the photo.

The collar facets were rough, and after I polished the facet facing the Universal Support, it slides smoothly.

Locking the collar must be done on the side as in the photo below, to avoid nicking the riding surfaces of the jig.

[wootz]

I've switched to an aluminium clamp style collar 12mm, advantages over the previous one are:
- perfect fit;
- lightweight, don't change the downward pressure and feel of the jig;
- doesn't nick the jig when clamped.

[Ken S]

Clever idea, Wootz....even better with your upgrade!

Ken

[Dutchman]

... Interestingly enough, the Scandinavian countries, as I understand have two separate words, one translating as the weight force and the other as the mass.

All Western European countries except UK, use the SI system of physical quantities.
In high school we learn to use the difference between weight and mass. Using SI units leads to simple calculations for energy, power etc.
It is sad that the Anglo-Saxon countries still use old-fashioned imperial units. They thereby cause major problems, not only for their school children but in all technical areas and jobs. 
NASA, as an example, has learned from a catastrophic failure of a Mars lander (Mars Climate Orbiter, 1999) due to bad usage of physical units and now uses SI units.

[Ken S]

Dutchman, sadly. I must agree. Of all the obsolete notions related to national pride, using the old Imperial measurement system seems one of the least logical. We I've in a global society. Our markets are global. Hopefully, our scientists work together globally.

We never seem to learn. Railroad track widths used to be different, supposedly for defense. In World War II we encountered difficulties because we were using sixty degree "National" threads and the British were using fifty five degree Whitworth threads. Tormek uses different motors because of different commercial power standards.

A generation ago, a movement began in the US to convert to metric. Unfortunately tradition seemed to triumph over logic.

Many products mix the two standards. The Tormek work station, made in Germany for a Swedish company, uses 5/8" x11 tpi threads for the feet. I would be curious to learn why.

Ken

[Jan]

I've switched to an aluminium clamp style collar 12mm, advantages over the previous one are:
- perfect fit;
- lightweight, don't change the downward pressure and feel of the jig;
- doesn't nick the jig when clamped.

Wootz, thanks for letting us know you have switched to an aluminium clamp style collar. 

What concerns the listed advantages, I was surprised by the lightweight of the collar. I think that the collar weight effect is very small and even more the major part of the collar's weight is supported by the universal support. 

Jan

[wootz]

Hi Jan,

I was using the locking collar to ensure straight grinding in studying the middle overgrinding problem in straight edges.
The former brass collar adds 20% to the jig weight, and I was concerned that might be worsening the middle overgrinding.
The aluminium one is free of that.

Don't laugh, but when puzzled with this problem, I even played with magnet weights added to segments of the blade and saw them affecting the straight line at as little as 30 grams, while the brass collar is 60. So i thought it would be safer to eliminate this factor.

[Jan]

Wootz,

the weight of the collar is producing torque (outside US moment of force) which is given by the product of its weight and its lever arm. The torque is small because the lever arm (distance between the USB and the collar) is short.   

The other reason for a small torque is that the collar weight does not act perpendicularly to the lever arm.

So far the Archimedes concept of torque. I hope there are no strings attached, but as Faust said: "All theory is grey, my friend. But forever green is the tree of life." . 

The torque caused by magnets attached directly to the blade is much larger because the lever arm is much longer also. In this case I have no reservations at all.  The ring is yours.

Jan

[van]

I've switched to an aluminium clamp style collar 12mm, advantages over the previous one are:
- perfect fit;
- lightweight, don't change the downward pressure and feel of the jig;
- doesn't nick the jig when clamped.

OK, but to extract it you have to remove the upper part in "plastic" of the SVM, not to mention that it can hinder the measurement of the SVM / knife blade distance. Perhaps it would be more convenient to use the same collar model but divided into two pieces.

[Ken S]

Why would we need to extract the collar? I can see needing to move the collar for kniveswith a lot of curve in the blade. I would think just loosening, sliding it out of the way, and retightening it would solve the problem. I sharpen standard kitchen knives. Using Dutchman's tables and a kenjig, plus three knife jigs, I can leave the Projection set at 139 mm and rarely have to adjust the jig.

Ken