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Micromaster 510 Surface Finish and Vibration

Safarir

Plastic
Joined
Jul 21, 2013
Location
Qc, Canada
Hi all,

I recently got my hand on my first surface grinder, a Brown & Sharp 510. After doing some initial testing, I was really unhappy with the surface finish I was getting: I am getting a lot of "wave" in line with the Y axis. After reading a lot on around the internet and on this post, I decided that the best first step is probably to balance my wheel. To do so, I made a simple wheel lock nut and used a microphone taped to the spindle and a spectrometer app on my phone to measure the vibration. I then used the 4 run technique to find the appropriate balancing weight.

out1.jpg
The result was a lot better but not fantastic. To make sure that the problem come from vibration and not the table roller, I made this test cut:

out2.jpg
On this block, the top part mark (with a M mark) was cut at a medium feed speed, the center part was cut at a slow feed speed and the lower part at a fast feed speed. My conclusion from this test is that since the line spacing depend on the feed speed, the vibration must be coming from the wheel/spindle/head and not the table.

This is when I went down a rabbit hole: I decided to play with some vibration analysis. What I did is mount a cheap adxl345 accelerometer to the spindle housing and connect it to a esp32 which allow me to log data remotely.

out2.jpg

I did some signal processing with python. I am running the capture at 400hz which give me a 200hz bandwidth once I do a dft analysis. Here are some of the results:

out.png
This first plot is the vibration with additional screw added to my balancing adapter. You can clearly see the spike at 47.5hz cause by the imbalance on the wheel, running at 2850rpm. One interesting thing is that the vibration seem way stronger along the height and not so much side to side.

out.png
This second graph is after I balanced the wheel. You can see it is quite a bit better around 47.5hz. One interesting fact is the spike around 112 moved to around 105, I still have not explanation about that.

At this point, you probably noticed the giant spike at 60hz. Fun fact, the vibration is actually totally off the scale at around 12, I had to chop it down a bit so we can see the rest of the graph. I think this is actually cause by the motor, running at 3600rpm. I decided to do some more testing and remove the o-ring that drive the spindle to test the vibration caused by the motor itself.

out.png
In this test, I did not move the sensor at all from the previous test. The really interesting part is that the entire noise floor dropped significantly ! I am really surprise how much vibration across all frequency range is coming from the spindle. The 60hz component is still there which to me mean my motor need some balancing.

Where am I going with all of this ? No idea ... I just thought this was quite interesting and wanted to share my finding. My next step is to remove the motor from the machine and test it by itself. I would really like to get rid of this 60hz vibration before doing more testing. I will check the bearings and might try to balance the motor.
 
It does look like most of your vibration is coming from the motor. It may or may not help to get that balanced. Quick question, how fast were you running the table? And what about wheel grit and hardness?
 
It does look like most of your vibration is coming from the motor. It may or may not help to get that balanced. Quick question, how fast were you running the table? And what about wheel grit and hardness?
It is hard to say exactly how fast I am running the table. The best I can say is: about what seem average from the youtube videos I watched.

I have a old linear scale laying around somewhere, I might try to hook it up the the setup later on to see if I can measure the speed.
 
Thanks for sharing your testing.
As fast as you can hand crank long travel and as slow with taking a light cut should be OK. You should feel not much more than a hum putting your hand on the motor or the wheel head. Hog grinding a fast long travel feed can mess up the finish.
Long travel slow often gives the best finish but can make out-of-balance waves easier to see.
A one-hand push-pull on the wheel head under an indicator can be a good idea,

The wheel should as tight as using two hands, one on a 6 to 7" long wrench and the other on the wheel. I tighten my wheels a tad tighter than that.
And the diamond set to a new facet.
This is a good surface finish video, and diamond use/angle at the end. Note that he says going a certain way/direction with the cross will make a better dress, *a certain cross direction also can make a better surface finish so it is good to test a machine for the best cross direction and use that when needing the best finish.

 
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I went ahead and remove the motor. Running it by itself, I was not happy the amount of vibration coming out of it and the noise it was making. At first, I thought it might just be all the gunk in the fan, but removing the fan did not change anything.

out2.jpg

out1.jpg

I now have the motor fully apart and will change the bearing as soon as I have time. I am also thinking about adding some balancing hole at the end of the pulley to be able to balance it like I do with the wheel.
 
I've been interested in balancing for a while and especially my SG. Warning- if you balance the motor you have to machine a special key and tape it in the slot. Can't remember, but I think it's half thickness and the same length as what you'll ultimately use.

You've probably seen it, but here's my page on balancing my SG- http://www.conradhoffman.com/grindbalance.htm

Though not mentioned there, I did pull my motor and balance it.
 
FWIW my B&S 510 has a GE 3ph motor with a "resilient mount" that isolates vibration. Not sure what frame type your motor has. Probably worth addressing the bearings, maybe motor balance, and some sort of vibration isolation.

And if you have a big 60hz signature on the motor itself and it is single phase, perhaps that suggests the capacitor setup is not ideal.
 
I've been interested in balancing for a while and especially my SG. Warning- if you balance the motor you have to machine a special key and tape it in the slot. Can't remember, but I think it's half thickness and the same length as what you'll ultimately use.

You've probably seen it, but here's my page on balancing my SG- http://www.conradhoffman.com/grindbalance.htm

Though not mentioned there, I did pull my motor and balance it.
Hi Conrad,

Yes, I saw your page, this was my main inspiration on how to balance the wheel. Thank you for this amazing write up !

My plan to balance the motor is to balance it with the pulley installed as a single unit. I would really like to do a 2-plane balance job but I don't really have the knowledge for that yet. I am planing to do a simple single plane balancing with the exact same technique as the wheel. Do you thing that would work ?

FWIW my B&S 510 has a GE 3ph motor with a "resilient mount" that isolates vibration. Not sure what frame type your motor has. Probably worth addressing the bearings, maybe motor balance, and some sort of vibration isolation.

And if you have a big 60hz signature on the motor itself and it is single phase, perhaps that suggests the capacitor setup is not ideal.
I think we have the exact same motor:

PXL_20220716_222735885.MP (1).jpg

In this picture, you can see the rubber mount and the clamp that goes around it.
 
Hi Conrad,

Yes, I saw your page, this was my main inspiration on how to balance the wheel. Thank you for this amazing write up !

My plan to balance the motor is to balance it with the pulley installed as a single unit. I would really like to do a 2-plane balance job but I don't really have the knowledge for that yet. I am planing to do a simple single plane balancing with the exact same technique as the wheel. Do you thing that would work ?


I think we have the exact same motor:

View attachment 369116

In this picture, you can see the rubber mount and the clamp that goes around it.

I don’t recall if I just cleaned or replaced the bearings on mine, but is very quiet and smooth running.

In your video yours sounds like is definitely needs help!
 
2-plane balancing isn't much different than 1-plane. Support the armature at two places and measure at those same places. Apply corrections at the first plane to get it balanced, then do the other. Rinse and repeat, as it probably won't come out perfect the first time. I rigged up the frame below to support my armature on the bearings. Most of the correction was at the front since that's where most of the mass is, so it turned out to be single plane anyway. The frame is solidly supported and can pivot on the rod ends in the plane of the rubber band. The left side sits on a spring so the armature can basically wobble at the front. The design is similar to some balancing stands I saw in early vibration textbooks. Have to see if I can find one of those.
BalanceFrame.jpg
 
2-plane balancing isn't much different than 1-plane. Support the armature at two places and measure at those same places. Apply corrections at the first plane to get it balanced, then do the other. Rinse and repeat, as it probably won't come out perfect the first time. I rigged up the frame below to support my armature on the bearings. Most of the correction was at the front since that's where most of the mass is, so it turned out to be single plane anyway. The frame is solidly supported and can pivot on the rod ends in the plane of the rubber band. The left side sits on a spring so the armature can basically wobble at the front. The design is similar to some balancing stands I saw in early vibration textbooks. Have to see if I can find one of those.
View attachment 369123
This is awesome! What are those sensor you are using ?
 
Those are some surplus sensors from PCB Piezotronics. They cost a lot new, but sometimes show up on eBay. Today I'd just use the cheap and sensitive MEMs sensors. No doubt Digikey has them but the cool kids buy 'em from SparkFun Electronics or Ladyada at Adafruit.
 
I finally had time to make more progress:

PXL_20220729_180741448 (2).jpg
The motor was re-assembled with some new bearing, it now sound way better


Here is the vibration without the pulley

nopulley.png
And with the pulley

pulley.png
I am quite concern by this 190hz peak, which actually have a value over 180. If someone have any insight as to where this could come from, I would am really interested in hearing your opinion.
 
I'm assuming the motor spins at 3600 RPM, so the frequency of interest is 60 Hz. I filter heavily to keep everything else out, lest it skew the balancing operation. That said, no idea where the high frequency is coming from, but the first question to ask is, "is it real?" That is, is it mechanical or some electrical thing that the sensor is picking up? At that frequency and amplitude, you should be able to hear it. Tap the pulley and such to see if you can excite anything similar. It could be a harmonic of 60 that's really 180- no idea how accurate the frequency scale is. In that case it might be normal.
 
Good for you on learning about balancing and sharing your knowledge. When faced with a wavy finish, the first thing to check is the wheel dressing. Dress the face of the wheel and dress up the sides to the blotter. Make sure the wheel is tight enough so it can't accidentally rotate or it will throw everything out. As always, after dressing touch the sharp corners with a dressing stone and also drag a board lightly over the face of the wheel to knock off any "hangers".

Then try grinding. Only then if there are still problems, should you try balancing.

Also, you might be interested in making a pair of autobalancing washers. I covered how I did it here:

http://www.nwnative.us/Grant/shop articles/sharpTable/balancing/
 
Good for you on learning about balancing and sharing your knowledge. When faced with a wavy finish, the first thing to check is the wheel dressing. Dress the face of the wheel and dress up the sides to the blotter. Make sure the wheel is tight enough so it can't accidentally rotate or it will throw everything out. As always, after dressing touch the sharp corners with a dressing stone and also drag a board lightly over the face of the wheel to knock off any "hangers".

Then try grinding. Only then if there are still problems, should you try balancing.

Also, you might be interested in making a pair of autobalancing washers. I covered how I did it here:

http://www.nwnative.us/Grant/shop articles/sharpTable/balancing/
I will definitively take the time to read this, it sound really interesting !

So I went ahead and drilled some holes in the pulley to try to balance it. I knew the unbalance would be mostly cause by the keyway so I went with a simple 3 holes at 120 design. It look pretty ugly because I don't have any setscrew with me and I had to file a washer until I got the correct weight.

PXL_20220801_204230446_50.jpg

Here is the result unbalanced:

base.png
And balanced
balanced.png

Quite a bit better ! But the motor still seem to vibrate quite a bit, enough to tickle to tips of my finger when I get close to it. I really don't think this 190hz component is imaginary. To prove it, I decided to try tightening the anti-vibration mount to see if it would affect it. Here is the result with the mount loose and tight:
loose.png
tight.png
I am really confuse as to where this vibration come from, at 190hz to 192hz, it really does not seem to be a harmonic of 60hz. I am starting to think that maybe the cheap Chinese bearing I used might be the cause. I am not really sure how to verify that.

Other interesting fact: when I run my fingers along the motor, it really seem like the vibration is worst at each end and there is a point in the middle where there is nearly no vibration.
 








 
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