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DRO Shaking

Tomc938

Tomc938

Ultra Member
So I installed the X-axis of my new DRO on my King 30 milling machine. This is the setup I used. There is a aluminum spacer behind the bolts holding the plate the the sensor unit is mounted on.

When I run the mill in Imperil, the 100s and 1000s flash erratically. The machine does have vibration when it is on.

Anyone have any ideas on eliminating the shake? Otherwise it looks like I have to shut the machine off to make any measurements.

IMG_3828.JPG
 
What happens if you lock the X axis only, Y axis only and then both axis? Some flip in 0.000X is common, can't say I have ever seen 0.00X bounce around. If your DRO supports a shake (filter display value) function try turning it on.

Gibs tight?
 
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Is you reader head correctly positioned relative to the scale? they usually come with an orange plastic shim. also you can try limiting the resolution in the DRO to tenths. This is important if you have 5-10 micron scales but have the DRO set to 1 micron.
 
All of my DRO's do that - unless you take relatively light cut or take medium cut and really lock the sucker up. Otherwise its standard. The tenths move around. Only when not properly locked, dull endmill and heavy cut or heavy drilling operation I may see thousands move around.

Its not uncommon to forget to lock things up, use somewhat dull endmill and during heavy cut... do one not exactly straight - like say off to one side by 1/100 of an inch or more. DRO will show this movement.

Drilling with a dull drill bit over 1" can get the x axis table to "dance" if not locked up - i.e. whole x axis will visibly move left to right. And I guess y as well.
 
Do you think the DRO is measuring reality? is there a way to maybe program the gain down so its not sampling every nanosecond?
 
I have not finished mounting mine so I have zero experience with your issue. But I'm watching this with keen interest for rather obvious reasons. Some comments and questions for you to ponder.

I confess that thousandths jitter doesn't surprise me. Hundredths does.

In my ignorance, I would think that machine shake would not matter much if the shake happens on the reader head and scale simultaneously. However, if either one is mounted with some flexibility relative to the other, any movement is gunna show up. So I'd be looking to see which one can move how much.

If you turn off the machine and press on the system components, you might be able to zero in on what is moving where.

Acceleration and force usually bend things WAY more than is obvious. Put a dial indicator almost anyplace on big stuff and watch the needle move as you lean on things. Stress and strain are ALWAYS present no matter how big something is.

There doesn't appear to be any strain relief on your cable. If it is shaking, it will shake the reader head. Try constraining the cable.

Your description of how your system is mounted isn't clear to me nor are the photos. Can you take a few more photos and/or add a drawing?

More specifically, the size and length and resistance to motion and force of the mounting brackets in various axis would be a concern of mine. I see lots of pictures on the web of people mounting things on long thin brackets. Maybe they have to do that, but I'd avoid it if possible.

Other generally speaking things to consider:

Twice the thickness = 1/2 the movement.

1/2 the length = 1/2 the movement

1/2 the suspended mass = 1/2 the movement

When you are talking about steel or aluminium, and mere thousands of an inch, it's hard to visualize movement. Try imagining the components and brackets to be made of rubber and take a critical look at them again.

Also, consider harmonics. What happens when you run the machine at different speeds?

Edit - Apparently aligning the bar code on the scale and the bar code of the reader is also important. If they are not aligned, the last set of digits are more likely to flicker.
 
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YYCHM said:
Are you supposed to leave those things in place? I thought they were a shipping lock and removed mine.
Click to expand...

I thought those were a gap gauge. On the magnetic scales, the gap between the reader head and the scale is important so they provide a strip of plastic to set the gap with. It is sort of like a spark plug gap tool.
 
PeterT said:
Do you think the DRO is measuring reality? is there a way to maybe program the gain down so its not sampling every nanosecond?
Click to expand...

I bet it is.

The sampling filter on mine is a bit of a mystery to me. I have not been able to easily see how it works. The Chinese English in the manual is horrible. For the time being, it seems more like a time lock that essentially freezes the display for a few seconds at a time. Sort of a low speed "update".

But the manual does suggest that it is there to help smooth out the readings in machines with heavy vibrations. That implies measurement averaging or some other form of mathematical smoothing. None of which would thrill me. I don't like it when programmers who have no clue about real world machines start adding their programming genius to how things work. It doesn't usually end well. Rant over.

If I assume they actually do know how the machine works, I'd sure like to know what the smoothing function really does and how it really works.
 
I'm waiting to receive mine...
About the ground connection, if i remember, there is no ground pin on the plug ?? si, no need to the ground wire from the dro to the head...
What do you guys think about that?
 
Blouin55 said:
I'm waiting to receive mine...
About the ground connection, if i remember, there is no ground pin on the plug ?? si, no need to the ground wire from the dro to the head...
What do you guys think about that?
Click to expand...
I i was talking about the pdm30 plug...
 
Blouin55 said:
I'm waiting to receive mine...
About the ground connection, if i remember, there is no ground pin on the plug ?? si, no need to the ground wire from the dro to the head...
What do you guys think about that?
Click to expand...
The reader head is grounded to the display unit through the connected wiring. I believe @Darren is talking about proper grounding of the power wiring and the display unit (which is probably connected through the mounting hardware. Just make sure everything is properly connected and not insulated. For example, the factory mount on my system has low friction nylon washers in it for smooth movement. But if you are not careful, these washers can also act as insulators. The system should have a good three prong power cord and the chassis should also be grounded to the mill.
 
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@Tomc938 - the flat bar that the sensor is mounted to looks thin, could it be vibrating and affecting the readings? I think something thicker and stronger (angle or rectangular tube) would be more rigid.
 
YYCHM said:
What happens if you lock the X axis only, Y axis only and then both axis? Some flip in 0.000X is common, can't say I have ever seen 0.00X bounce around. If your DRO supports a shake (filter display value) function try turning it on.

Gibs tight?
Click to expand...
Well do I ever feel silly. Something as simple as tightening the gibs eliminated all flickering! Didn't even need to lock it.

I'll sleep better tonight!
 
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