While I was upgrading my 19" BS it wondered what the actual forces/tensions were on BS blades.
One could of course purchase an expensive blade tensometer but then it dawned on me that there might be a relatively easy way to measure the tension on the blade using a known weight and digital angle finder.
Method
Construct a small pulley to ride on the end of a piece of flatcar steel and clamp this to the BS table
Construct a simple blade clamp (a square block of steel with a slot in it that could attached to the blade with an eye bolt)
Attach Eye-bolt to a known weight using a piece of string and allow string to run over pulley so that the weight hung vertically over the side of the BS table (like this)
The measure angle of deflection of the blade from the vertical using a digital angle finder
I found I had to remove the throat plate, and not use too large a weigh otherwise the blade touched the pre guide structures under the table
The Weight used (3kg) divided by the tangent of the angle should then give the blade tension?
Maybe someone could check that that is right?
In the case above picture 3/tan(1.1º) comes out to be 156 kg of tension
Method
I systematically varied the tension setting on the BS and measured the angle so I was able to plot the tension as a function of angle/
Note this is for a carbon steel, 18 x 0.65 mm blade.
The graph shows the actual tension is linear from about setting 3 to about setting 8 and does not depart far from linearity for the other settings.
The curve looks quite smooth but is a result of multiple iterations of data collection ,
For example, just increasing or decreasing the tension and taking an angle reading gave very inconsistent results, sometimes just changing the tension did not change the angle at al.
To get around this I adjusted the tension and then manually spun the wheels by hand for at least 5 revolutions to redistribute the change in tension around the wheels. At high tension I could hear faint creaking sounds as the tensions redistributed.
Despite this there were still slight systematic differences between when increasing and decreasing the tension - the points shown on the graph are an average of going up and then down the tension scale and they seemed to have evened themselves out in the process.
Is it good for anything? I don't know, I usually just the blade flutter method to set the tension - I was just curious as to what the actual tensioning forces were.
One could go on from here to work out the MPa involved but I will leave that to those that are interested to do for themselves,
One could of course purchase an expensive blade tensometer but then it dawned on me that there might be a relatively easy way to measure the tension on the blade using a known weight and digital angle finder.
Method
Construct a small pulley to ride on the end of a piece of flatcar steel and clamp this to the BS table
Construct a simple blade clamp (a square block of steel with a slot in it that could attached to the blade with an eye bolt)
Attach Eye-bolt to a known weight using a piece of string and allow string to run over pulley so that the weight hung vertically over the side of the BS table (like this)
The measure angle of deflection of the blade from the vertical using a digital angle finder
I found I had to remove the throat plate, and not use too large a weigh otherwise the blade touched the pre guide structures under the table
The Weight used (3kg) divided by the tangent of the angle should then give the blade tension?
Maybe someone could check that that is right?
In the case above picture 3/tan(1.1º) comes out to be 156 kg of tension
Method
I systematically varied the tension setting on the BS and measured the angle so I was able to plot the tension as a function of angle/
Note this is for a carbon steel, 18 x 0.65 mm blade.
The graph shows the actual tension is linear from about setting 3 to about setting 8 and does not depart far from linearity for the other settings.
The curve looks quite smooth but is a result of multiple iterations of data collection ,
For example, just increasing or decreasing the tension and taking an angle reading gave very inconsistent results, sometimes just changing the tension did not change the angle at al.
To get around this I adjusted the tension and then manually spun the wheels by hand for at least 5 revolutions to redistribute the change in tension around the wheels. At high tension I could hear faint creaking sounds as the tensions redistributed.
Despite this there were still slight systematic differences between when increasing and decreasing the tension - the points shown on the graph are an average of going up and then down the tension scale and they seemed to have evened themselves out in the process.
Is it good for anything? I don't know, I usually just the blade flutter method to set the tension - I was just curious as to what the actual tensioning forces were.
One could go on from here to work out the MPa involved but I will leave that to those that are interested to do for themselves,
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