Hello welcome to Enote engineering I'm Alan
Today I am looking at calibration of DRO and that is
just because you fitted some DRO scales and a readout to your machine
It doesn't mean to say that the reading you're getting is correct
there could be a deviation in that reading and to check that you need to check is against a standard
now by a standard I mean you may have some slip gauges or block gauges
and you can use the block gauges as a standard to check against your DRO
let's say you've got a set of imperial block gauges
and you could build up with those gauges a 10 inch length to check your DRO
so you build up your 10 inch length of block gauges
and use the calibration chart that came with the gauges to determine the actual length
of those blocks because each block may be a small amount undersized
if you add it all together it will tell you the actual length that you've built
so it might be 0.0005" less than 10 inches
next thing you need to do set the blocks up on the machine
and then take a reading from one end of the block to the other end of the block
and compare what your digital scale says the reading is
now if it's correct and it's exactly the same
then you don't need to alter anything but if it's over or under you may need
to alter and calculate a compensation factor that will put the scale reading correct
so that's what we're doing in today's video
so let's go to the workshop and see how we do it
today I'm just checking my digital readouts
to see that the display value is the same as the actual movement
and to do that you need to set a reference piece to the table
So what I have here a couple of parallel strips in the slot that's so I can put
the gauge block in push it up against the parallel strips and I know it's parallel to the table
on this end I have a small gauge block just to give me the
height for this one so I can touch a dial indicator on the front face move
back to this face and get the length on the digital readout
so this block underneath is lightly clamped
then I've pushed this block up against it which is a four inch gauge block
and I've just lightly clamped it
so this is not moving backwards and forwards or sliding
so now I've got my reference piece set up
and then later I can add extra blocks to this to see what the readout over a distance is
on the milling head I've put a leaver type Indicator to give me a reference
now there's some things I'm not happy with
the lever indicator only goes to 0.01mm
then you will also have error on your gauge blocks
because most gauge blocks are slightly under the size that they say
but you need to refer to your calibration chart for your gauge blocks to see
the more you build up how much deviation is from a standard size
the other thing as well is temperature
today it's fairly cold in the workshop so I fitted these blocks to the table
I've left them on the table for a good hour so they can adjust and become the
same temperature as the table
so I'm trying to normalize the temperatures as best as I can
now if you're holding the gauge block in your hand for 10 minutes it warm up
so the reading you get will have an error compared to these gauge blocks that are on a cold table
another thing I should point out is if your linear scales are in metric
I would try and use metric as the measuring standard
if they're imperial I would use imperial because you don't want your display
calculating something and putting more error into the reading
although this gauge block is in imperial I'm doing all my measurements in metric
it's just an aluminium clamping piece and all it's doing is holding down the gauge block
that's underneath lightly and then stopping this gauge block on the top here from moving backwards
so when I've pushed this 4" gauge block up against that it's level with the face
so what I'm doing now is moving the dial indicator forward
or moving the table until I can get a zero reading the dial indicator
That looks about zero now I will zero my X-axis scale
so this is in absolute, zero and it's metric
and on my z axis I will zero my Z axis to give me the position of the dial indicator
and the next thing to do is move the table to the end
lower the dial indicator down
and bring it back to zero
now we'll take a look at the readout for that
there's the reading 101. 605 now a 4 inch gauge block is 101.6
so I'm point 0.005mm longer
now that could be the dial indicator I don't know or it could be the scale
so what I'll do next is add another gauge block to the
table and we'll take it to the next length
I've just pushed a three inch gauge block on there
I've just zero the dial indicator at the start of the gauge blocks zero my X
then go back to the other end of the blocks
I think that's right the result is 228.945 and it should actually read 228.6
this is the correction coefficient formula
for working out the figure that you must enter into
your display to correct the error this applies to this digital readout but
should be in your manual
so after you've worked out the calculation
you press X then mm/inch that's it compensation X
so you enter the number in 1.50918
Entre
that should have put the scale correct
Now let's see if the compensation makes any difference
come back onto the dial indicator
and the reading for the length of the gauge block
is 226.600mm and nine inch length should be 228.600
so I've reset that to give the correct reading over nine inches
now we'll move on to the Z axis
I've changed too my plunger dial indicator
which is in 0.0001" so it's easier to see
we'll just lower this down to zero it
call that zero,
zero my Z axis on the scale then lower this down until I get Zero
now the reading I've got there is 101.570
and four inch should be 101.6
so it's just under
so this is the formula to calculate the correction factor you need
S =( L- L 1)/ ( L/1000)
where L is the length in millimeters
and then this is the displayed length
so you've have the Length that you're measuring and the actual displayed length
this is the calculation that we did
so we've got four inch gauge block which is 101.6mm
so we have 101.6
which is the length that we were measuring
and it gave us 101.57
so that works out 101.6 -101.57= 0.03
then we have on this side 101.6
divided by 1000
so then we've have 0.03 / 0.1016
it comes out at 0.2952755
now we need to put that into the z axis as the correction coefficient
so we're looking at the Z axis
so what you need to do is zero Z
And then Z (input) mm/inch
now once you get compensation of Z
we put the figure in here from the calculation
Which is 0.2952755
enter so we've have Z at zero
so if you re measure the gauge block hopefully it
should come to the right size
so I will remove the block and go down to the table
round to zero there
101 600 smack on
It takes it's a bit fiddly I don't know why sometimes it works and sometimes it doesn't
but as you can see that's altered the 4" reading before was 101.570
now it's changed it to 101.6 which is
dead-on four inches
so that's two axes converted
so all I need to do now is look at my Y axis
okay the setup for the y-axis once more
I'm just holding this gauge block lightly move this square across and now
I can push the gauge block to get it Square to the table just put a bit of
load onto the back of that to stop this moving
we just move that round to zero just there
now I'll zero my Y axis thats zero
lift up
move across lowered it down so that the tip of the indicator is just
above the slip gauge move it along to until it zeros
there that's saying 101.610
so that's 0.010 microns out and what I'll do just a double check
zero that there and do it backwards 101.61
so we want to enter the correction figure we're only 0.01 out on the reading
so I'll see whether I can get down to zero
so to do that again we zero Y
enter the value and put metric
it should come up with compensation of Y which it has and the reading was
I've tried a few times and that's the best I can get the y-axis to
it should be 101.6 but it's 101.605 which is actually one division of the scale
oh well that's it for today hope that's useful I'll put
the chart up again with the calculations on hope you found that interesting and
we'll see you next time on Enots engineering