Thoughts On When To Dress Magnetic Chuck

[Mcgyver]

Somewhere in one of my posts I did mention that I indicated the table before setting the chuck on it and it was almost dead flat al over. I was surprised! When I set the chuck on it it indicated almost exactly the same. I dusted the chuck off and it was perfect. That was about 20 years ago. Not lot of use since then, never used coolant so nothing has seeped under the chuck to for any corrosion that would tend to raise the chuck from the table.
So, I'm not really sure why I get a slight rise in the center of the chuck when I turn it on. I thought that my sketch of the chuck surface might help to explain this.

JL...................

not indicate it, check the fit - how complete is the contact of the bearing surfaces between table and chuck. If its not fully bearing, it could change the geometry when you turn the magnet on

[JoeLee]

maybe its in here somewhere, but I don't remember reading where you've said you've checked the fit of the chuck to the table. If there isn't good bearing all over, then you're going to change the shape of both when you engage the magnet.

As for indicators, use a Mit anti magnetic....not sure specifically how much an Interapid is effected, but the the anti magnetic is not

Somewhere in one of my posts I did mention that I indicated the table before setting the chuck on it and it was almost dead flat al over. I was surprised! When I set the chuck on it it indicated almost exactly the same. I dusted the chuck off and it was perfect. That was about 20 years ago. Not lot of use since then, never used coolant so nothing has seeped under the chuck to for any corrosion that would tend to raise the chuck from the table.
So, I'm not really sure why I get a slight rise in the center of the chuck when I turn it on. I thought that my sketch of the chuck surface might help to explain this.

JL...................

[JoeLee]

Wow. I like to see tools taken care of. I dont have a grinder but do have a giant Walker chuck I could check but I dont think I have anything that wont be affected by the mag.

I dont know how to measure it powered up what i am saying. All my tools are metal.

We need granite JR

You know those things are DC right?

It's not an electro magnetic chuck.

JL.............

[Mcgyver]

maybe its in here somewhere, but I don't remember reading where you've said you've checked the fit of the chuck to the table. If there isn't good bearing all over, then you're going to change the shape of both when you engage the magnet.

As for indicators, use a Mit anti magnetic....not sure specifically how much an Interapid is affected, but the the anti magnetic is not

[JRouche]

Lately I have been noticing some small discrepancies on parts that I have ground. Don't really notice anything on small parts under 2" wide or 2" in length but do see some thickness variation on larger parts over 3" wide and 6" long. Last time I dressed this chuck was probably 20 years ago or so. I've always kept it clean and never slid parts across it. When I did dress it I did it with the magnet engaged as directed by the mfg. So the other day I decided to indicate the surface of the chuck. What I found wasn't an alarming difference but what bothered me the most was that when I engaged the magnet the center of the chuck would rise about .0003. Usually it's the other way around I believe. Here is a diagram of my readings.
I indicated it with the magnet engaged and with the magnet off for comparison purposes. If I remember correctly the center of the chuck would pull down a couple tenths when engaged not rise.
Internal problems?? not sure. The lever moves with the same amount of force as it always did. MO means magnet off in the diagram.

Should I dust the chuck again or do I have other issues? The chuck is an older B&S 6" x 18" with the lead segments. It's a PIA to grind it.

JL.................

Wow. I like to see tools taken care of. I dont have a grinder but do have a giant Walker chuck I could check but I dont think I have anything that wont be affected by the mag.

I dont know how to measure it powered up what i am saying. All my tools are metal.

We need granite JR

You know those things are DC right?

[nickel-city-fab]

I would guess that a lot of machines end up this way unless your in the habit of traversing your table to the extreme ends of it's travel in both directions every time you grind something regardless of how small the part is. So who is in the habit of doing that?

JL..................

Actually staying in the middle of the travel would cause all the wear to stay in the middle of the travel, making the chuck look dished as the table rides up on the unworn part of the ways. . But if the wear was on the ends of the travel the chuck would look humped. So basically what I mean is, the chuck will be a verbatim reflection of the wear, one-to-one ratio. I have seen guys "cheat" minor variations by putting wet paper underneath the part. Never tried it myself though.

[JoeLee]

It does make sense to me though. If you have say .0002 of wear at the ends of the table travel then the entire table is going to drop by .0002, taking the chuck with it. This would look like a hump in the middle of the chuck. So yes it would in fact have to be rebuilt. The sole exception might be those machines that use a hydrodynamic oil film which get a pump shot of oil to the ways at every stroke. If the ways aren't getting their oil, then every little irregularity is going to show up in the chuck and the work. I can see how a test with 5 blocks would give a pretty good mapping, much like the 2-ring test piece on the lathe.

I would guess that a lot of machines end up this way unless your in the habit of traversing your table to the extreme ends of it's travel in both directions every time you grind something regardless of how small the part is. So who is in the habit of doing that?

JL..................

[epicfail48]

I don't think that your method of setting a small surface plate on the chuck would be an accurate way to indicate anything other than the surface plate is flat simply because you shimmed it to compensate for the dips in your ways and you had to move either your saddle infeed or table to do so, thus riding the dips. The thickness of any surface plate is not a critical dimension and could vary greatly.
But I do understand what you were trying to accomplish.

The five point test would be another accurate way of checking for error, but leaves a lot of open gaps between test blocks but gives an overall idea and indicating the chuck surface directly indicates the entire surface.

It's always been my understanding that dressing the surface of the chuck compensates for minor wear in the ways, infeed and table. The wheel is mounted overhead and as long as it sparks out over the entire surface of the chuck it should be flat. It may take several passes to bring any high spots (outer ends of travel) down to the lowest spot on the chuck but once that's done it should be dead flat. If I'm missing something someone please enlighten me.

Think about this...... if you developed .0002 of wear in any of the mid travel range of saddle or table ways and you couldn't compensate for that by dressing the chuck what would you have to do? rebuild the entire machine? just doesn't sound right. I'm sure there are a lot of old grinders out there with significant wear on the ways but still grind accurately. I've seen and used a couple old grinders, like war time old, mid 1940's B&S that have never been rebuilt and they grind accurately.

JL..............

Sorry, i poorly explained myself on the shims; i didnt shim across the entire plate to compensate for the dips, just at the extreme ends in either the X or Y axis, depending on which i was testing, to bring the corners into the same level, to try and compensate for the varying thickness. My theory was that if i had a noticeably amount of wear on the ends of the ways, it would show as a dip in the reading.

Im having a hard time explaining my thought process. Basically i wasnt shimming the plate to 0, more using shims on the extreme ends and having the surface plate act as a bridge between them? Kinda like what Abom is doing with the parallels here, but in reverse i guess:

https://youtu.be/3N20fttRgKM?t=1805

[nickel-city-fab]

It's always been my understanding that dressing the surface of the chuck compensates for minor wear in the ways, infeed and table. The wheel is mounted overhead and as long as it sparks out over the entire surface of the chuck it should be flat. It may take several passes to bring any high spots (outer ends of travel) down to the lowest spot on the chuck but once that's done it should be dead flat. If I'm missing something someone please enlighten me.

Think about this...... if you developed .0002 of wear in any of the mid travel range of saddle or table ways and you couldn't compensate for that by dressing the chuck what would you have to do? rebuild the entire machine?

JL..............

It does make sense to me though. If you have say .0002 of wear at the ends of the table travel then the entire table is going to drop by .0002, taking the chuck with it. This would look like a hump in the middle of the chuck. So yes it would in fact have to be rebuilt. The sole exception might be those machines that use a hydrodynamic oil film which get a pump shot of oil to the ways at every stroke. If the ways aren't getting their oil, then every little irregularity is going to show up in the chuck and the work. I can see how a test with 5 blocks would give a pretty good mapping, much like the 2-ring test piece on the lathe.

[JoeLee]

My understanding is that dressing the chuck will make it parallel to the ways, so if the ways are flat the chuck will be too, but if the ways are convex, for example, then the chuck will be ground to match that convexity.

Im going to preface this by saying i have absoutely no idea if its proper practice, a good idea or even works, but what i did when i first got my surface grinder was take a small surface plate, 9x12 in this case, put that on top of the chuck, shim where needed to get the top side reading 0 at the extreme ends, and then swept across the surface plate with an indicator. My theory was that i would be comparing the known flat reference of the surface plate against the ways, if there was a dip in the ways it would show up as movement on the indicator since the surface plate wouldnt dip in the same way, if that makes sense.

Like i said, dunno if its a good test, but it worked for me. Weighing in on how often you should dress a mag chuck, wheres the harm in redressing, so long as you arent doing it before every job? If youre only taking off a thou or two, it seems like it would take a very long time to wear down the chuck if you were to redress it quarterly. Just got done dressing mine after about 6 months actually. Admittedly thats because im a monkey with a socket wrench and had some idiot marks from not deburring my parts before putting them on the chuck, but still

I don't think that your method of setting a small surface plate on the chuck would be an accurate way to indicate anything other than the surface plate is flat simply because you shimmed it to compensate for the dips in your ways and you had to move either your saddle infeed or table to do so, thus riding the dips. The thickness of any surface plate is not a critical dimension and could vary greatly.
But I do understand what you were trying to accomplish.

The five point test would be another accurate way of checking for error, but leaves a lot of open gaps between test blocks but gives an overall idea and indicating the chuck surface directly indicates the entire surface.

It's always been my understanding that dressing the surface of the chuck compensates for minor wear in the ways, infeed and table. The wheel is mounted overhead and as long as it sparks out over the entire surface of the chuck it should be flat. It may take several passes to bring any high spots (outer ends of travel) down to the lowest spot on the chuck but once that's done it should be dead flat. If I'm missing something someone please enlighten me.

Think about this...... if you developed .0002 of wear in any of the mid travel range of saddle or table ways and you couldn't compensate for that by dressing the chuck what would you have to do? rebuild the entire machine? just doesn't sound right. I'm sure there are a lot of old grinders out there with significant wear on the ways but still grind accurately. I've seen and used a couple old grinders, like war time old, mid 1940's B&S that have never been rebuilt and they grind accurately.

JL..............

[mikey553]

That's a lot of wear. How does it grind?

JL..............

I've got this grinder at an industrial auction and was able to check the machine while still in one piece. It was smooth, but I can bet the guys operating it did not even know it was worn so much. The majority of their business was small parts manufacturing. The grinder is sitting in my garage and waiting for me to rebuild it. This is not going to happen until I retire, maybe another year...

[epicfail48]

That's an interesting thought. Somehow I was under the impression that even if the ways had some slight wear that dressing the chuck would allow it to conform to any irregularities and be perfectly flat. If I said that right !

JL...........

My understanding is that dressing the chuck will make it parallel to the ways, so if the ways are flat the chuck will be too, but if the ways are convex, for example, then the chuck will be ground to match that convexity.

Im going to preface this by saying i have absoutely no idea if its proper practice, a good idea or even works, but what i did when i first got my surface grinder was take a small surface plate, 9x12 in this case, put that on top of the chuck, shim where needed to get the top side reading 0 at the extreme ends, and then swept across the surface plate with an indicator. My theory was that i would be comparing the known flat reference of the surface plate against the ways, if there was a dip in the ways it would show up as movement on the indicator since the surface plate wouldnt dip in the same way, if that makes sense.

Like i said, dunno if its a good test, but it worked for me. Weighing in on how often you should dress a mag chuck, wheres the harm in redressing, so long as you arent doing it before every job? If youre only taking off a thou or two, it seems like it would take a very long time to wear down the chuck if you were to redress it quarterly. Just got done dressing mine after about 6 months actually. Admittedly thats because im a monkey with a socket wrench and had some idiot marks from not deburring my parts before putting them on the chuck, but still

[JoeLee]

That's a lot of wear. How does it grind?

JL..............

[mikey553]

My ways have about .010-.015" of wear. The machine was in toolroom service for 50 years.

[JoeLee]

JL,

I understand your reluctance of taking the chuck off. If you have a decent long straight edge or parallel, you can use it to check the chuck surface, but you will not get the exact measurement.

There is nothing wrong with dressing the top of the chuck, but if your ways are worn, you are just fooling yourself. After the dressing the top of the chuck will replicate the ways. If they are curved (like on my grinder), so will be the chuck. And you may indicate it on a machine all day long and not see more than .0001", but it does not mean it is flat.

Mike

That's an interesting thought. Somehow I was under the impression that even if the ways had some slight wear that dressing the chuck would allow it to conform to any irregularities and be perfectly flat. If I said that right !

JL...........