DRO For moving the head

mickri

H-M Supporter - Diamond Member
H-M Lifetime Diamond Member
Joined
Oct 31, 2016
Messages
2,637
I was replying to another thread about realigning the head of a round column mill/drill when I thought why couldn't a DRO be set up to measure the rotation of the head. Never having used a DRO my best guess is that there is a fixed in place sensor that measures the movement of another sensor. Did a little research on how DRO's work. It seems like it could be made to work. One sensor would be permanently attached to the head. The other sensor on the column would be moved to line up with the head sensor until the DRO read zero and then clamped to the column. Move the head, change the tooling and then move the head back to zero. Probably wouldn't even need a digital read out. A simple light that came on when the two sensors were lined up.

Another one of my wild ideas. Seems like it could work. Shouldn't be expensive to make and people with round column mill/drills would line up to buy one.
 
there may be slight deviations in angle, but the concept is a good one!!!
 
I would imagin it could be done using a rotary encoder and an Arduino board or something similar. A timing belt wrapped around the head to about a 1" pulley on the encoder would give my mill around a 25 : 1 ratio, should be pretty accurate. Of course if I did this I would have to also do the other 2 axis that the head can be moved. The other 2 axis on my mill would end up around a 12 : 1 to the encoder.
 
Some considerations re: use of encoder. The spindle on my RF30 clone is about 10" from the column axis. The encoder on my lathe has a resolution of 4,000 ppr. One pulse would be 2π/4000 or .00157 radians. At 10" this would be .015" of movement as the minimum detectable.
Add to that, the head moves vertically as well as rotating so whatever mechanism is used to couple the encoder to the head must be able to accommodate that motion while maintaining a minimum of free play.
 
I was not thinking that you needed to somehow keep track of where the head got moved to. Only that you would bring the head back to line up the two sensors. If a DRO can detect movement to .001 or even .0001 that same technology should be able to determine when two sensors are lined up within .0001. Sensors may be the wrong terminology. Quick sketch of a round column mill/drill showing one sensor under the head and the other sensor clamped to the column.

milldrill DRO.jpg
 
The problem I see is that you are trying to measure 2 variables with one number. The head position is related to the z-axis position as well as rotation. How would your sensor idea account for z-axis movement?
There is this:
ands this:

Robert
 
Last edited:
I am not trying to measure two things. All I am trying to do is realign the head. Everybody seems to be hung up on measuring how much the head is moved. Not trying to measure that. Doesn't matter how much the head is moved to change tooling. All I am looking for is to realign the head back to its position before the head was moved. I do that now with a dial indicator on a magnetic base.

IMG_3922.JPG

DRO's work by shining several lights through glass that is marked with lines a known distance apart. I have no idea how they actually get a measurement from that. By using the same technology you should be able to tell when the head moves back into its original position. I don't think that this is rocket science.
 
Sorry, I wasn't thinking you would be bringing the head back to the same Z. Your idea would should work in that setting. I have no idea where you could get a circular glass or magnetic scale though. And RJ raises a good point about resolution.
Robert
 
Last edited:
if you wish, you could use a proximity sensor to get you close.
the proximity sensor could be coupled to a simple indicator light circuit, or as others have suggested to an optical encoder/ motor driver circuit
 
I have been reading about encoders. Rotary, linear, absolute, incremental and on it goes. For someone who knows nothing about these gadgets your head spins rather quickly. The bottom line is that encoders shine a light through glass that has transparent and opaque sections in known positions with a light sensor on the other side of the glass. As the light source moves the sensors pick up the movement and somehow calculate how far the light has moved. Most interesting to me was that absolute encoders can tell when you are back to the starting point. It seems like someone should be able to make one of these things that can tell when the light source is lined up with the light sensor. Should be easier than trying to calculate how far the light has moved.

Looks to me that this would work. Someone just has to make it.
 
Back
Top