good morning good afternoon or good evening everybody and thank you very
much for joining today's webinar this webinar is on slope and DFTC
DFTP and the DFTFand we'll explain what those are in a few minutes, it's based around the Talyrond
instruments from Taylor Hobson and also the Form Talysurf instruments from Taylor Hobson
and analysis is typically done in associated software called metrology
4.0 software so again thank you for joining and let's press ahead now with the webinar
in this webinar we're going to take a look at a few types of analysis
on Taylor Hobson's Talyrond and formally serve systems
in particular slope analysis and departure from true circle or departure from a true plane
and that's what DFTC and DFTP mean we'll also have a look at departure from true form or DFTF
we'll make us
we'll make a start with slope analysis
and looking now at slope analysis if we look at the diagram on the left we can see a profile
a roundness profile from a typical bearing assembly for example and on it we can see one
very prominent feature there and the simulation of a ball in a ball and a bearing race
encountering that obstacle and in this case the peak to valley
of the roundness is is in accordance with its specification it's in specification
for a manufacturer of bearings for example certain harmonics are undesirable not only is
the roundness critical in these cases but also the slope of the surface at certain harmonics
as the size or the amplitude of the harmonics increase this increases the slope
of the surface and as the frequency of the harmonics increase this also increases
the slope of the surface so slope analysis is directly linked to harmonic analysis
back to the diagram there on the left the roundness
tolerance may have been passed as we mentioned
but because all of the error is in one position problems will occur during the parts function
so considering a bearing with a number of balls not just one passing around an inner race the
deviation shown may cause deterioration and wear and affect the function of the bearing assembly
and we can see what happens here on the left we can see a slope
upwards and downwards and we see deceleration as the balls move up the slope and acceleration as
the balls move down the slope and this would be on a typical bearing race we've shown it
in a straight line there but if we consider a bearing race it's the same thing that happens
as the the balls will move towards and away from the center of the bearing and so on the right
what's happening here where we've got many more undulations
the many ball bearings in the bearings bearing the race will change in velocity and the balls will
collide as they collide they will cause excessive wear to the bearing so we clearly need to quantify
the value of slope if we had a perfectly circular profile then there would be no collisions
so how do we look at the value of slope on the left here is shown the method that we use
to calculate the maximum and average slope values of an analyzed profile and what we can see here is
the blue dot with the red line red circle around it indicates the current point and typically in a
profile like this we might have 3600 data points 18 000 data points or even 72 000 data points
and we're considering each data point around the profile but we're also considering
three points either side of that ref of that point that we're considering
so the calculations are made within an operator selected window specified in degrees
and the slope for each data point within a window is calculated
by using that data point and the three data points either side so a line is drawn through those
to indicate the slope that applies to that data point
we then move on to the next data point and three points
either side of that are also taken and the average slope is calculated
so the average value for all of these these data points are calculated and stored
the maximum slope is the maximum of these stored averages and it will occur at a particular
position on the profile the average slope is the average of the stored average slopes
the units are microns that's radially per degree and that's as we go around the part
so we're dealing in microns per degree for slope values
so the slope is the rate of change of the radius with respect to angle
in a bearing race for example the angle of a window chosen for calculation
is usually related to the number of ball bearings in that race
knowing the number of ball bearings and the size of the race
it's possible to calculate the relevant harmonic and hence the critical slope angle
the contact area of the ball will enable the designer to specify the angle
at which two largest slope is critical and so the parameters we deal with in slope analysis are
maximum slope where we've specified a slope and where we specified a slope window
that maximum slope will occur at a particular position so in the example shown here we can
see that the maximum slope is 0.929 microns per degree and it occurs it's
been analyzed using this slope window here of 10 degrees and the position of that maximum slope is
at 54.3 degrees this is the zero degree position 10 20 30 40 50 54.3 degrees starts here and the
average slope of all the data points all the way around the profile is 0.419 microns per degree
when we're not considering circular bearings with considering bearing surfaces which may be flat
the same thing applies and ball bearings will decelerate upslopes and accelerate downslopes
but in this case instead of dealing with the angle we're dealing with a height and so
the slope values are calculated based on the rate of change of height with respect to length
and again there are an associated set of parameters so we have the mean least squares slope
and there is an associated window with that and we have the maximum slope and there is an
associated window and this occurs at a particular position just as it did with the circular slope
so this is linear the previous one was circular
let's have a look now at departure from true circle and departure from true plane
on a roundness instrument in this case Taylor Hobson's talyrond systems
so dftc as we've mentioned means departure from a true circle over the full 360 degrees it's
the same thing as roundness so this is if you like local roundness but why would that matter
well we might have a situation where we've got a fuel pipe such as in the picture here where
if there is a an error that occurs particularly at one point
then that's where the leakage may occur so we might have a specification over the whole
of the circle of the whole of the round part which passes but we might also have a separate
specification relevant to a particular area where we're looking at leakage so DFTC can be
used to specify departures from a true circle at an angular position on a roundness profile
so for example the cylinder bore needs to be round to set a tolerance however it
wouldn't function well as in the case here if all the roundness error was in one spot
so the local error may cause compression fuel and oil problems for example due to a poor seal
so how do we capture these errors what happens is the operator can
specify an angular window and we'll have a look at that in a minute and use this angular window
to check if the departure within that window is within a specified tolerance all around the part
so in the example here we're looking at departure from true circle
and the roundness value is 2.29 microns that's all around the part from the highest peak which
is probably here to the lowest valley which looks as if it's about there but the departure from
true circle is analyzed over this in this case a window of 30 degrees and here is that window
and that window has been moved around data point by data point until it finds the position where
it it has the maximum value and so associated with that 30 degree window is an angle of 249.1 degrees
again 0 90 180 from 90 200 to 10 to 22 32 40 to 49.1 and that's where that window starts
and so in this particular case, we might find we would possibly find that the
leakage would occur at this point
as well as having departure from true circle we have departure from true plane
and this is done for flatness measurements rather than in the vertical direction rather than for
roundness measurements but the parameters are very similar
let's have a look now at departure from true form
previously we looked at an area where leakage may occur circumferentially
if we consider a shaft and a seal we may find that leakage will occur along the length of the shaft
as well so we're interested in form variations along the shaft and so we would measure this
for example on a form talisev instrument or actually on the talirand but we would
measure it in a linear direction rather than circumference circumferentially
so DFTF departure from true form can be used to specify departures from the profile
over a specified window in just the same way that we saw on the roundness profile so for example
a bearing surface may need to have a low form error to set a tolerance and again however
it would not function well if all of that error occurred in one spot
the DFTF window is the operator selected segment within which the departures from the true form are
calculated so instead of moving uh similar to on the roundness profile, we move one data point
by data point along the profile until we find the maximum position and in this case the the
ftf window is half half a millimeter that's that distance and the form value found is 0.2 microns
that's from there to there and the position is at 168.165 and that's where that window starts
there
so in summary we've looked at slope analysis we've had a look at departure from a true circle
and departure from true plane and we've had a brief look at departure from true to true form
and that brings me to the end of this very short webinar please do take a look at our bearings
application brochure and at other information on our website at www.taylor.hobson.com
this is part of a series of bearing on me of bearing solutions webinars
again on the website you can go and have a look at any of these and many more
thank you for listening don't think there are any questions today
so i'm going to close the webinar and say goodbye
you