This document presents a simple method for determining the angle of a doctor blade on any roll using two templates. Template A is placed with one corner touching the roll and doctor blade, while Template B is placed with one corner also touching the roll and doctor blade. The overlap angle between the templates indicates the doctor blade angle. For smaller rolls, there is a minor error that can be corrected using a scaling on Template B or a calculated error angle formula based on template length and roll diameter. Measuring the angle using this method provides a starting point, and the supplier's guidelines should be checked to ensure the correct doctor blade angle.

1. Determination of Doctor Angle
By:
D K Singhal
deveshksinghal@gmail.com

2. Importance of Angle Measurement
Doctor angle plays a significant role in
getting proper doctoring results. Too
steep an angle can damage the roll surface
and/or doctor blade itself, while too little
an angle may result in inadequate cleaning
of roll surface.
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Determination of Doctor Angle
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3. A Simple Approach
The objective of this presentation is to
show a simple, very simple tool to
determine angle of doctor blade on any
roll.
However, it is always recommended to
get a proper doctor angle measuring
device from some good supplier.
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Determination of Doctor Angle
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4. Items Required
Two templates similar to these indicated.
(You may use two identical visiting cards for this.)
Scissors.
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5. Step One
Cut these along dotted lines.
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Determination of Doctor Angle
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6. Step Two
You will get shapes as under-
Template A
Template B
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Determination of Doctor Angle
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7. Template A Position
Hold template A in such a way that its one
corner touches the desired roll at the
point of doctor blade, and the line
indicated in red color in aligns the doctor
blade.
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Determination of Doctor Angle
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8. Template B Position
Hold template B in such a way that its
one corner touches the desired roll at
the point of doctor blade, and the
other corner touches the roll.
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Determination of Doctor Angle
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9. Measurement
Place both templates as shown in the
figure, and measure overlap angle on
template B. The overlap angle is the
doctor angle (almost) for larger size rolls.
However, there would be a minor error
for smaller rolls which needs to be
corrected as shown in next slides.
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Determination of Doctor Angle
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10. Scaling of Template B
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25 24 23 22 21 20 19
For ease, the top side of template B can be
scaled as shown in figure above.
Whenever you need to measure angle of
any doctor blade, just measure directly from
these, compensate for correction factor, and
get the correct angle immediately.
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11. Determination of Error Angle
Error Angle
It can be shown that the error angle is
A function of roll diameter and template
Length.
It can be given as e’ = Sin-1(L/D)
Where,
L is template length and
D is roll diameter.
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12. Error Due to Template B
The error caused by the limitations in
design of Template B decreases with
increase in roll diameter. Some typical
values are as indicated for template length
of 75mm◦
◦
◦
◦
Roll Dia.
750mm
1500mm
4250mm
Error
5.7˚
2.9˚
1.0˚
February 2014
Example
Press Roll
Dryer
14’ Yankee
Determination of Doctor Angle
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13. Correction of Error
The error, though it is a minute one, can
be added to the measured angle value to
get the correct doctor blade angle.
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14. Measured Angle
Doctor angle can be expressed in two
ways.
◦ With reference to radial line (BSI), and
◦ With reference to tangential line (ASTM)
This method gives angle along tangential
line.
To get angle along radial line, just subtract
the angle computed from 90˚.
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Determination of Doctor Angle
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15. Angle Measured
After you have got the running doctor
blade angle, you may check with the
supplier guidelines whether it is correct
or needs to be altered.
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16. Happy Doctoring!
Please send your comments and feedback to:
D K Singhal
deveshksinghal@gmail.com
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