Having problems w/ chatter issue on surface grinder...

[REK Knives]

So I got an old, well used surface grinder from a guy on craigslist probably 8 months ago... finally got up and around to messing with and using it but am having some sort of issue where it's leaving dimples all over the surface of whatever I am grinding. This is what I have done so far:

• Made sure the magnetic chuck is level and that the grinder is very stable
• Checked all of the moving parts (chuck, spindle arm, wheel, arbor, etc.) to make sure there was no play and nothing was loose - all was good
• I've tried 3 different wheels, and dressed .100" off of the last one in .010" passes. When I dressed the wheel I locked in the x axis as much as I could by those sliding stops in the picture below (I was only able to lock one in and then held the x axis in place against the stop w/ my leg while making the y axis passes to dress the wheel...
• When I grind I am using a Kool mist unit which is spraying right where the wheel meets the metal
• When grinding the metal I am only removing .002" per pass and going quickly and smoothly, not stopping part way through

One weird thing I've noticed is that even if I don't lower the wheel at all after I have made a pass, I can continue to make passes in the same spot on the metal and throw sparks every pass (I only counted up to 15 back and forth passes and it was still doing it slightly).

Any ideas guys? I'm at a loss...

 

[javand]

You shouldn't need to lock X when dressing, just feed in and out in Y.

10 thou per pass is extremely aggressive for your finish dress. Do final dress 1 or 2 thou max. I use a single point or multipoint nib dresser (whatever is convenient) oriented vertically (not angled) directly under the center of the wheel.


Also, to get a nice finish, you want your finishing passes to be .001 or .0005 and then spark out (keep traversing until you've got little or no sparks)


The waves you're seeing are from either too aggressive of dressing, or too aggressive feeding, or your wheel not being locked down tight enough causing it to move out of concentricity even after it's dressed, sometimes this is caused by aggressive feeding and it not being tight enough.

You should be able to do all this without coolant even. Although if you want to make multi-thou roughing passes, you need coolant, and you need to make finishing passes to clean up. Also, don't even try to take more than 1-2 thou on hardened stock, especially below 3/16 thick or so. That's just the limitation of the application.


What operation are you trying to accomplish here?

 

[Wowbagger]

Hey Josh,

Howsit ?

I'm no machinist expert, I got a nice 13" lathe but like I say no expert . . .

One weird thing I've noticed is that even if I don't lower the wheel at all after I have made a pass, I can continue to make passes in the same spot on the metal and throw sparks every pass (I only counted up to 15 back and forth passes and it was still doing it slightly).

I work with bearings a fair amount though . . . I'm thinking maybe you need to get more western with it when you are yanking it around checking for bearing play (and or put a dial indicator on it and have some one watch it while you really yank it around). The keeps making sparks thing leads me to believe the wheel rides on the surface (lifts up if you will) and then drops some after it does off the end of the work.

That's my view any way.

Also the table "ways" where the bed travels have "gibs" and those need to be adjusted for no play and lubed with way oil. I am kind of assuming this but that is the way of machine tools. Pun intended.

A third thing . . . I have no experience with this but I have read that some grinders have AIR BEARINGS. The shaf(s) turn on a layer of air from a compressor rather than have ball or needle bearings. This is to keep the grit out of the bearing surfaces (the air is constantly blowing out the sides of the bearing to some small degree). Probably not the case on yours but figured I'd mention it.

Hope you get some real help soon but this gives you something to read until that glorious moment arrives.

Cheers !
(oh . . . and I'm jealous . . . I have always eyed those in the shops and catalogs )

 

[Wowbagger]

I thought of one other thing.

This grinder has a wheel that is defective from the manufacturer



It seems to have a hard spot in it (it is a water bath wheel by the way). No matter how carefully I dress it or which of several dressers I use it still tends to go back to its old way and sounds like this : Grinnnnnnnd clunk, Grinnnnnnnd clunk, Grinnnnnnnd clunk. If I back off a little with the blade i I am grinding then it just says : clunk . . . . . ., clunk . . . . . . , clunk . . . . . . as the high / hard spot touches the blade. Others have told me that their exact same grinder does not do this. It is a very slow speed grinder like a Tormec but slower. I would get a new stone for it but it is just toooooooooo slow and so I have just given up on it.

Maybe if I hook 'er up to some 440 volt she would get going good.
just kidding.

Sooooooo that was a long round about way to suggest maybe your stone has a hard spot in one or more sectors.

 

[Drew Riley]

How did you check for play?

With your wheel spinning, and a DTI on the hub, do you see any run out for vibration? How's the spindle motor feel when its running. Do you feel any vibration there?

 

[javand]

That finish doesn't look bad for the technique described, he's simply going to hard, and dressing too aggressively for finishing.

I seriously doubt he's got spindle problems. Vibration can cause finish issues yes, and I've seen crap quality stones that couldn't get good finishes, but they were significantly worse than what his photos show.


Fine finishing is done with very light finish passes sparking out, with a stone that's been dressed with fine final passes. The bigger a dressing cut you take, the courser the grind, the more aggressively it'll cut, but the worse the finish.


I'd recommend 0.001 dressing, and .001 or less for your finish cuts. If you grind aggressively before the finishing passes, you have to re-dress for the finish usually. Yes, it's normal for you to keep cutting on subsequent passes without feeding more in Z, and if you're too aggressive the work expands from built up heat and it's exacerbated, which leads to a worse finish.


You can cut .002 per pass or significantly more depending on stock thickness, but you can't expect a good finish if you hog a bunch and quit without redressing and/or slowing down for final passes. Regardless, .010 dressing pass is extreme, and will not give a good finish, with any stone.

 

[JTknives]

Did a lot if surface grinding as a machinest and we take very little off per pass. Most passes where only .001 to .003 and finish passes was .0002-.0005 and then spark it out till no sparks left. But this was on machined parts that where already square. Then we would flip the part over and put a sheet of phone book paper between part and mag chuck.

 

[REK Knives]

You shouldn't need to lock X when dressing, just feed in and out in Y.

10 thou per pass is extremely aggressive for your finish dress. Do final dress 1 or 2 thou max. I use a single point or multipoint nib dresser (whatever is convenient) oriented vertically (not angled) directly under the center of the wheel.


Also, to get a nice finish, you want your finishing passes to be .001 or .0005 and then spark out (keep traversing until you've got little or no sparks)


The waves you're seeing are from either too aggressive of dressing, or too aggressive feeding, or your wheel not being locked down tight enough causing it to move out of concentricity even after it's dressed, sometimes this is caused by aggressive feeding and it not being tight enough.

You should be able to do all this without coolant even. Although if you want to make multi-thou roughing passes, you need coolant, and you need to make finishing passes to clean up. Also, don't even try to take more than 1-2 thou on hardened stock, especially below 3/16 thick or so. That's just the limitation of the application.


What operation are you trying to accomplish here?

Thanks for all your help and suggestions, I will give them a shot in the morning. I actually did dress the final pass only 1-2 thou so I think it too aggressive feeding. How long does it take to spark out? How many passes?

I have some scissor blades I am making, they have been water jet and ht but I need to surface grind before I grind them to make sure everything lines up.

How did you check for play?

With your wheel spinning, and a DTI on the hub, do you see any run out for vibration? How's the spindle motor feel when its running. Do you feel any vibration there?

Well I have a machinist friend who told me with a dressed wheel to set a glass of water on the chuck and see if the water rippled at all... I did this and no movement of the water whatsoever. The spindle motor and everything feels very smooth. When I turn the motor off and touch the wheel it feels very smooth.

 

[DanGraves]

All the say on how much to remove I can agree with. I have the same grinder and it has a bearing that is brass cone shape on the side closest to the stone wheel and a ball bearing on the other side. The cone shape brass is made to adjust or tighten when gets sloppy. This may be your problem. To tight and it will run hot and to loose it can do what you are talking about. On mine there is a plate on the side which explains hot to pull spindle. A bit tricky and when I did mine I also just replaced the back bearing. The system rides in an oil bath that is important to keep full with spindle oil. I cant say for sure this is your problem but it was on my machine which is the same as yours. Did you surface grind the mag chuck? Good luck.

 

[REK Knives]

All the say on how much to remove I can agree with. I have the same grinder and it has a bearing that is brass cone shape on the side closest to the stone wheel and a ball bearing on the other side. The cone shape brass is made to adjust or tighten when gets sloppy. This may be your problem. To tight and it will run hot and to loose it can do what you are talking about. On mine there is a plate on the side which explains hot to pull spindle. A bit tricky and when I did mine I also just replaced the back bearing. The system rides in an oil bath that is important to keep full with spindle oil. I cant say for sure this is your problem but it was on my machine which is the same as yours. Did you surface grind the mag chuck? Good luck.

Thanks Dan! If you get time would you mind taking a pic to show me? Otherwise I'll snap a few pics in the morning and see if you can point out what I may need to adjust. I haven't noticed what you are speaking of yet...

 

[javand]

Another thing I'll add: Make sure you're not crashing into your work on your first engagement after dressing the wheel.

You need to engage at .001 or less. The usual trick is to lay a piece of paper (typically .005 thick) on the work, feed Z down until you're just touching the paper, remove, turn on the spindle, then slowly start feeding down .001 until you engage all the way across the work.

Also, are you aware that you shouldn't be taking full wheel width passes? i.e. if you have a half in wheel, you cannot expect to take half in wide passes and get a good finish.

 

[Kosa_PL]

In my small opinion ( I using SG from short time but I have some observations.
Because of wrong feed and probably wheel, grinding forces are to big and wheel making chatter.



60 grit wheel ( now 99A60K on ceramic waiting for 59A60I [59A is a mix of AOx for tool steel] K hardness of wheel is to big)
Per pass: 0,01-0,025mm
Finish: 0,005mm -> sparkout
Wheel speed: 33m/s
Table feed: 20m/min
Cross feed: 1,8mm per pass
Wheel dressing: 2x 0,01mm or to clean state + 0,01mm on last pass.
DIY fogbuster cooling (better than KoolMist, no fog around): Silvergrind 3001 5% - 350ml/h 35psi ( Grinding need more coolantin MQL than milling/turniung)

RESULT:
http://imageshack.com/a/img921/7959/M5G9ID.jpg

Before with blunt diamond and poor dressing ( with dresser mounted above wheel, and without cooling) : that was on 0,01mm passes...
http://imageshack.com/a/img905/820/j1Znec.jpg
http://imageshack.com/a/img633/5540/bz05CI.jpg

 

[REK Knives]

alright I am uploading a video to yt right now of what I'm doing so you guys can help me figure it out... I tried dressing the final passes only .5-1 thou for a few passes and the same on the final passes/spark out of the actual piece but had no success, it's doing the same thing. But I do have a question...

When I'm moving the x axis nob and if I put my hand on the magnetic chuck I can feel a smooth type of bumpiness as the rail rides over the gears, I'm wondering if this is normal and if this may be the issue?

 

[Drew Riley]

I thought of one other thing.

This grinder has a wheel that is defective from the manufacturer



It seems to have a hard spot in it (it is a water bath wheel by the way). No matter how carefully I dress it or which of several dressers I use it still tends to go back to its old way and sounds like this : Grinnnnnnnd clunk, Grinnnnnnnd clunk, Grinnnnnnnd clunk. If I back off a little with the blade i I am grinding then it just says : clunk . . . . . ., clunk . . . . . . , clunk . . . . . . as the high / hard spot touches the blade. Others have told me that their exact same grinder does not do this. It is a very slow speed grinder like a Tormec but slower. I would get a new stone for it but it is just toooooooooo slow and so I have just given up on it.

Maybe if I hook 'er up to some 440 volt she would get going good.
just kidding.

Sooooooo that was a long round about way to suggest maybe your stone has a hard spot in one or more sectors.

You're not leaving the wheel in a water bath while it's off are you? If so, the sound you're describing may just be the balance of the wheel. Any part left in water will be heavier than the dry parts that are out of water, and you'll get a significantly imbalanced wheel.

 

[javand]

alright I am uploading a video to yt right now of what I'm doing so you guys can help me figure it out... I tried dressing the final passes only .5-1 thou for a few passes and the same on the final passes/spark out of the actual piece but had no success, it's doing the same thing. But I do have a question...

When I'm moving the x axis nob and if I put my hand on the magnetic chuck I can feel a smooth type of bumpiness as the rail rides over the gears, I'm wondering if this is normal and if this may be the issue?

I dunno bud, I'd setup an indicator and check to see if it's showing significant movement. One or two thou I'd attribute to your chuck being off and/or needing to be ground in, but if you see it jumping 10 thou at a time, there may be an issue. There may be some kind of gib that needs to be adjusted to keep your ways engaged, I'm not familiar with your grinder at all.

Do your sparks look erratic as you feed across X?


Worst case, I'll be down your way sometime in the next few weeks, I can take a look at it.

 

[REK Knives]

I dunno bud, I'd setup an indicator and check to see if it's showing significant movement. One or two thou I'd attribute to your chuck being off and/or needing to be ground in, but if you see it jumping 10 thou at a time, there may be an issue. There may be some kind of gib that needs to be adjusted to keep your ways engaged, I'm not familiar with your grinder at all.


Do your sparks look erratic as you feed across X?




Worst case, I'll be down your way sometime in the next few weeks, I can take a look at it.

Thanks dude!! I would be very appreciative of that if I can't get this issue fixed before then!

ok! This is where I'm at so far... I used the dial indicator as suggested. I don't have any variation on the magnetic chuck which is supposed to be relatively new anyway...

But when I checked the spindle I found .010" run out!

The only thing that i'm confused is to how this would cause the issue... because if the wheel is firmly attached to the spindle and the wheel is dressed this should fix all the run out issues correct?

 

[javand]

You can't test the spindle for runout where you're at. You're on the neck of a spindle adapter, not the spindle.

This is likely still a technique or tooling issue IMO. What side of Greenville are you on?

 

[REK Knives]

You can't test the spindle for runout where you're at. You're on the neck of a spindle adapter, not the spindle.

This is likely still a technique or tooling issue IMO. What side of Greenville are you on?

Ahhh yeah I'm ignorant about this stuff... I'll just admit it hehe.

I'm actually in Easley, but only about 15 min from downtown Greenville.

 

[javand]

K, that's about 1.5 hours from me, but I've got to go to Traveler's Rest sometime soon. I'll let you know when, as soon as I know.

Other than seeing a video, I dunno what's going on at this point. Does the machine seem to have any vibration when you turn it on? What wheel are you using?

 

[REK Knives]

K, that's about 1.5 hours from me, but I've got to go to Traveler's Rest sometime soon. I'll let you know when, as soon as I know.

Other than seeing a video, I dunno what's going on at this point. Does the machine seem to have any vibration when you turn it on? What wheel are you using?

Cool I'm 20 min from TR =)

No, no vibration, not so much as a ripple in a glass of water when I set it on the magnetic chuck and turn it on... very smooth. I've tried 3 different wheels, although they were from the guy I got the surface grinder from (there's no telling how old they are) they all have the same issue....

Here is the video

[video=youtube;OTvqcVN7QCs]https://www.youtube.com/watch?v=OTvqcVN7QCs[/video]