The horror under the chuck

[michiganbuck]

That would be the *fourth* dresser, as I already have two over-wheel ones and one that can be clamped to the table or chuck. Isn't that enough?

Yes you have enough.
I have had an overhead, an optical form, table set block, a set pad swing arm, a slide that mounted to any fixture, a Vinco or Last Word.. Oh and diamonds the were a Specific radius, a hand held roller and a Norbide stick, and an arbor to set a wheel to a TC grinde, rolling rolls for crush wheels. how many is that?
Likely many of us think an overhead is not true enough for dressing for a chuck grind. Perhaps .0000? error angle.IMHO.
The best dresser for accuracy is off the table so could be table mounted or set pad mounted.

 

[michiganbuck]

If the set pad is not flat I would grind it with up most care and caution. A burn on the set pad could ruin the machine IMHO.
Use a 46 or even courser wheel (36?) of top quality, grind wet and pause at ends for a cool-off time.
I think a burn can put permanent damage into a machine top or a magnetic chuck and so should be avoided at any cost.
The finish is not important but flat is.

Yes I would travel it for 10 minuets before starting grind to let it warm up.

 

[TDegenhart]

That's pretty harsh statement that a burn will ruin a machine. I understand what you are getting at that is that the burn will warp the table. I might be inclined to not use the machine on a part that goes to MARS and comes back but for run of the mill grinding I don't see a problem. Just go back grind out the burn.

Tom

 

[ballen]

Dear MB,

OK, I got the point about the dresser.

If the set pad is not flat I would grind it with up most care and caution. A burn on the set pad could ruin the machine IMHO.

I'm not sure if you saw the post where I checked the set pad. It is flat but pitted, see this post.

Use a 46 or even courser wheel (36?) of top quality, grind wet and pause at ends for a cool-off time.

Ok, I got that part, and I agree. I posted some details of the 46 wheel that I have, is that suitable? See this post.

I think a burn can put permanent damage into a machine top or a magnetic chuck and so should be avoided at any cost. The finish is not important but flat is.

Yes, agreed.

Yes I would travel it for 10 minuets before starting grind to let it warm up.

Before I mapped out the geometry of the ways, I let the machine warm up (hydraulic pump circulating oil) for about half an hour.

Cheers,
Bruce

 

[michiganbuck]

Cant tell how bad the pitting in the photos. Don't think minor pitting a problem and perhaps a good smear of grease would be fine, also don't have a problem with grinding the pad if you are a grinder hand. What about Garbsen? Is it at the edge of the mountains? there still gold found near Salzhemmendorf (don't know if spelling is correct). I had a great grandfather on my mothers side who was burgermeister of Hamburg way back when.
Grease and graphite power would be much the same as Cash's mix. Just plane grease might do well for perhaps 10 years.

 

[ballen]

Hi MB,

Cant tell how bad the pitting in the photos. Don't think minor pitting a problem and perhaps a good smear of grease would be fine, also don't have a problem with grinding the pad if you are a grinder hand.

If you look at the print of the pad, you'll see that there's very little contact area left. The pitting is deep, probably up to about 0.1mm.

I'm definitely NOT a grinder hand, I'm a beginner, that's why I am going very slow here. I am sure that someone with experience would have finished this in a day or two.

What about Garbsen? Is it at the edge of the mountains?

Nope, it's about as flat as the top of the grinder table. Within 1km of where I live, the maximum height deviation is about 3m.

There still gold found near Salzhemmendorf (don't know if spelling is correct). I had a great grandfather on my mothers side who was Burgermeister of Hamburg way back when.

Salzhemmendorf is just a short drive away, Hamburg is quite a bit farther.

Grease and graphite power would be much the same as Cash's mix. Just plane grease might do well for perhaps 10 years.

Yeah, but I'm not there yet. Need to paint the peeling parts of the table, and deal with the table top and chuck bottom first.

Cheers,
Bruce

 

[michiganbuck]

Grind .004 off pad and table and chuck seems Ok IMHO s long as you don't try to rush the job.

Make a dry run to be sure to off-wheel clear both sides.

Dofner is a very good quality wheel and I could grind the chuck and pad with the 2A46 K10 VAX white aluminum oxide.

A 36k would be a safer wheel for the task. Still care need be taken to not allow heat build-up and often dress.

You might call them to ask what they recommend.

Certanly would not hurt to have three wheels.

 

[CarbideBob]

I just scrape off the rust with a carbide broach blade and do not worry.
Since we run very wet (10-20 GPM, think two garden hoses full blast) all my chucks have a sheet metal tray between them and the table which is certainly not precision mounting.
.........I like lots of water based coolant, somewhere around half the spindle HP at the pump is good in my world for getting rid of stock fast.

Found two things that hold up under long term high volume water based coolant.
One is a 50/50 mix of white lithium grease and STP. The other is a gear lube SHC-630.

Personally a table top would have to be very, very bad before I would grind it in case it distorts. If ground I'd go back and check the ways and maybe scrape.
On little small grinders the Harig manual warns you to never do this. On a rebuild one would grind top and then refit the ways.
I have never seen a chuck grow in the middle from rust but perhaps would not as we grind out dings and such on a regular basis.
Bob

 

[John Garner]

The phrase "white lithium grease" makes me almost as nervous as the word "Lubriplate", as I've found that there are a few good white greases and a number that seemingly turn into marble as they loose their oil. (In my experience, Pennzoil 705 has been the worst in this regard, but there are others.)

Beyond that, Lubriplate is a brand name, and its owner, Fiske Brothers Refining, makes and sells dozens of different lubricants under the Lubriplate brand. Trying to describe a specific type of grease as Lubriplate is, in reality, like expecting the names Exxon-Mobil, Chevron, Sunoco, BP, or Total to describe a specific type of grease.

With that out of the way, probably the most water-resistant greases I've used and found satisfactory are 1) those in Fiske Brothers' Lubriplate 100-series (Lubriplate 100, 105, 110, 115, and the higher-temperature-rated 130A and 130AA, and 2) Mystik JT-6 (Not JT-6 High Temperature).

 

[tdmidget]

I am currently on a hydro electric job and for the area undeer the facing plates ( at eitther end of the wicket gates) we are applying MolyKote 111, a thick silicone grease. If the volume of water to make 80mw at 85 ft head can't wash it out then that might be what you are looking for. Or at $19.95 for 5oz tube, maybe not.

 

[ballen]

Hi Bob,

Thanks for the advice about the grease.

Personally a table top would have to be very, very bad before I would grind it in case it distorts. If ground I'd go back and check the ways and maybe scrape. On little small grinders the Harig manual warns you to never do this. On a rebuild one would grind top and then refit the ways.

I'm worried about this.

My testing at the end of this post shows that the ways and table are accurate to a few microns (0.0001"). I put a calibrated granite surface plate, good side up, onto the table, mapped the surface-plate-to-wheelhead distance with a Heidenhain 1 micron resolution probe, then subtracted out the tilt of the surface plate.

So I really don't want to screw up the table, for example by grinding the pad in way that introduces stresses that twist it. On the other hand, the pad is pitted and has very little contact area for the chuck to sit on. You can see that earlier in the same post, where I put a blued surface plate upside down on the table top. So when the chuck is snugged down, that might also twist the table.

The question is, which is the worse, grinding the table top flat, but risking stresses in the skin of the top which might twist it? Or clamping the chuck (with a reground flat bottom) onto the existing table top, but risking that the clamping force twists the table, because it is so pitted that there won't be even contact?

I am waiting for the paint to arrive, so not doing anything, just asking for advice about the next steps, and trying to think it through carefully. The grinder is in such nice shape, I really don't want to f**k it up.

Cheers,
Bruce

 

[michiganbuck]

1. I think you would be good to grease it up and clamp the chuck on with an oil hone to both the magnet and the pad.
2. Nothing wrong with grinding the pad and the chuck bottom and top if you can do so with not burning it, hence buying the 36k would make doing that safer. Yes with rushing the job you can burn with the 36K.
Tricks to safe grinding a big job, Use suitable wheel/ well wet/ pause at ends for cooling time/ dress often/ grind only on the grind side if needed.
And Bob Bailey says balance the wheel. ( Normally I don't that on a 7" wheel and often don't on an 8" name brand wheel but there is nothing wrong with balancing every wheel.)

 

[Richard King]

Hi guys, I am sorry I have been busy and sort of forgot this thread...I will comment again but I'm about to head off to the IMTS show again today and will comment again tonight...or tomorrow morning as I have been invited to go to the Kingston Minds Jazz Club tonight....not sure I will go as I have been there when I was 40...hard for me to get up after a night of relaxing at a jazz club/bar. Rich

 

[Richard King]

Reading all the suggestions took bit and as I read them I was thinking everyone is making good points. I went back and looked at the pictures and observed a few important things everyone can think about. 1) Cash suggests grinding the table top, which I do before scraping a machine and after I am finished. But the Mattison bases are longer then the table and if the table warps a bit I don't think it will affect things like it would on a lightweight table as you have on the J&S. But if Bruce is not going to rescrape the ways on I would not kiss the table top in this case. I have found kissing a table top will grind out the hard facing and possibly warp the table. I think debating about the grease is silly, pick a good grease and use it or Vactra 2. Go with any of the old timer mixtures. They all have their favorites and they would not recommend something that doesn't work. They work for them. Pick one you like and use it.

2) Then I looked at the mag chuck, wondering if it was manual or electric. It looks electric. The centers of those chucks grow when they get hot and if the ends don't get hot the middle will grow and touch. You could do an experiment set the chuck on the granite with a thin layer or bluing, you have a photo of how the chuck looks when it is cold. Also check the hinge or swivel of the chuck, obviously it will swivel on both ends as that's what the blue now shows. Then attach the electric and turn on the power and see what happens when the chuck warms up. I suspect the center will blue up and the swivel will move into the middle.

If this happened then I would not grind the bottom of the chuck as this was probably made that way from the factory. I would dress the wheel off the magnet as I have never seen a overhead dresser work that great even on new machines. Later if you want to dink with it, do it. I would also align the back rest parallel to the table travel and kiss side wheel it.

We all come here to help each other, there are many ways to do things. You need to learn on your own also. You will never learn anything with out making a few mistakes along the way, no shame in that and when someone says they never make a mistake they are a liar.. Please do the experiment on the bottom of the chuck as this would be a good learning tool for all of us.

If that happens then let it cool down, grease or oil it tighten the left side down tight leaving the right side snug but not tight and only grind the top of the chuck with it turned on. You will want to use the 2 garden hose method of coolant (meaning the more the merrier. The 46 grit wheel is good. Rich

 

[ballen]

Dear Richard,

Thanks for weighing in on this. What you have written makes sense. There is one place where I can elaborate a bit.

Then I looked at the mag chuck, wondering if it was manual or electric. It looks electric.

You can find a lot of detail about the chuck in this other thread that I started earlier, before I even purchased the machine. The group here has been an enormous help because I don't know squat about grinders and needed a lot of advice.

The chuck and controller were made by the German company Wagner Magnete and resold/badged SAV. People I have talked to in Germany and the UK tell me that this is one of the very best in the business and very high quality.

The machine was delivered in 1986 by the German J&S distributor with that chuck and controller already installed. I have learned quite a bit about these because the electronics controller was damaged when I bought the machine and I needed to fix it. The sellers told me that this was the only part of the machine that was not working properly, as far as they knew. (Electronics is an area where I have professional training and a lifetime of hands-on experience, so fixing it was not hard. My theory is that the chuck controller failed within a year after the machine was purchased in 1986, and after that, the grinder was not used much and just gathered dust in a corner of the shop. Hence the "low miles" on the machine.)

The chuck is a model EP-200, and is called a "Permanent Electro-Magnetic Chuck". The way it works is as follows. To magnetise the chuck, the controller delivers a pulse of current (actually many short ones, 10 milliseconds long) which are (on average) 200 VDC at 10 Amps. The overall pulse only lasts about half a second. During that time, the chuck is getting 2 kilowatts of power, which is a lot, since it's all converted into heat in the chuck. But that only lasts half a second. After that, the controller turns off the current and the chuck is not heated at all. Zero.

This current pulse magnetises the chuck and it retains that magnetism until the demag cycle, which is a series of similar current pulses of alternating polarity and decreasing amplitude over about 8 seconds. So in normal use, there is no current flowing in the magnet and no heat.

The advantage of this system (according to manufacturer literature) is two-fold. First, if the power fails, then the work does not come off the magnet. Thus it's good for operator and work safety. Second, since normally no current is flowing, the magnet is dimensionally more stable because it's not being heated from inside.

This weekend I will magnetise the chuck and do the swivel tests that you suggest. It's not ideal because my surface plate is 450 x 300mm and the chuck is 450 x 150mm, but I think it will work OK anyhow.

Cheers,
Bruce

PS: I calculated how much the chuck is heated by magnetization/demag, and the effect on its shape. Here are the specifics:

Specific heat of steel is 0.5 kJ/kg K. Chuck weight is about 35 kg. I assume that most of this is steel, not copper, whose specific heat is slightly less. So the specific heat of the chuck is 0.5 kJ/kg-K x 35 kg = 18 kJ/K.

Energy delivered to magnetise the chuck: 2kW x 0.5 seconds = 2000 Joules/sec x 0.5 sec = 1000 Joules = 1kJ. 1kJ of energy will raise the temperature of the chuck by 1/18 K = 0.05 Kelvin. This is the same as raising the temperature by 0.05 Celsius or 0.1 degrees Fahrenheit

I think the demag cycle pumps in about 4 times as much energy, so that will be 0.4 Fahrenheit. So in all, a full mag/demag cycle will raise the temperature of the chuck by 0.5 Fahrenheit or 0.25 Celsius.

The effect of a 0.25 Celsius temperature change on the LENGTH of the chuck is about 1.2 x 10^-5 x 0.25 x 450mm = 1.3 microns. The effect on the height of the chuck is 0.2 microns = 200 nanometers. The effect on the width of the chuck is 0.4 microns.

 

[michiganbuck]

Agree with Richard..He and I could grind the job with the 46k. You with perhaps not having much grinding experience should be extra careful with using the 46k (my favorite starting wheel and I would use it). (Still having three wheel in the shop would not hurt perhaps 80, 46 and 36).

Perhaps one big mistake a first time chuck grinder makes is crashing into the high place of the chuck (or job). Good to map the chuck to then come in to by-hand with wheel parked (not running) to feel the high place. This to Confirm the map is good with a hand feel with wheel off and reading the dial to feel a rub only there (at the high)you Know the feed dial spot where you expect to first touch the chuck when grinding.

Not a bad idea to to pass over the whole chuck .002 away while you let the machine warm up and treat the free pass (s) like grinding with perhaps .0002 down feeds till you make the first grind..

A full wheel bump bottom into .001 (perhaps even .0005) will burn the chuck. Definitely if on the climb side.

(I know someone will say you could knock the wheel off by hand feeling the part, but if one could do that then that person should not be using a surface grinder.)

 

[Richard King]

Yes do a dry run over the whole chuck as Buck suggests the size of the chuck...especially after you have had the rust issues, better safe then sorry...many times I put a sheet of paper on the chuck and slowly feed it down until the paper flies out. Bruce you sound like you have your nuts in a row. just remember to turn on the chuck when you grind the chuck and use more coolant then you think you need. Burning the chuck sucks, in the old days when a chuck had lead instead of ceramic coils on top we would use a hand scraper and lower the lead a few thousands as it would plug the wheel.....I will shut up now and let you do your thing. Rich
PS: put a mag base on the mag and indicator on the granite so you can observe if the check grows when it heats up

 

[ballen]

Dear Richard, Dear Buck

Thank you, I am glad this has converged.

The green color-matched 2k PU paint has arrived, so that's next on the list, along with checking the chuck.

Richard I'll put my Heidenhain probe on the chuck and reference the plate as you suggest. It will be interesting to see what effect the internal stress from mag/demag has on the shape of the chuck. I am convinced that the effects of heating are minimal, but might also run through 5 or 10 mag/demag cycles to see if I can observe a micron or two of growth from internal heating. But the real question is, does magnetising the chuck then make the bottom lie in a true plane?

The grinding coolant is on order. In the end I have ordered 5 liters of Wunsch Oil KS-AB. This was what was recommended by the company after some telephone discussion. It is a transparent fully synthetic coolant intended for grinding. I'll may also need to spend some time fussing with the coolant system because there may be minor issues to fix there as well (leaks, for example).

I'll mix 3 liters of coolant with 75 liters of water to get a 4% strength solution. Should I use tap water (fairly hard where I live) or distilled water or deionized water or rain water or does it not matter? (I just saw that the manufacturer's sheet says "drinking water", perhaps I will ask them also.)

Cheers,
Bruce

 

[michiganbuck]

I am anxious to see the results of Richard’s chuck heat test. On the plate and dry will be somewhat different than on the pad and with coolant but still a very good thing to know.

In a perfect world distilled or filtered rain water would be best but doubt many do that.
My daughter’s well is so hard with lime it would not be very good.

Perhaps try to be sure all the rust removal chemical is out of the metal with a washing soda wash. But the soda will leave a fine powder so that has to be removed before painting.

 

[ballen]

Hi Buck,

I am anxious to see the results of Richard’s chuck heat test.

In my opinion the test is not about "heat" because the calculation above shows that electrical heating from the mag/demag cycle for this type of permanent electromagnetic chuck will not have a significant effect.

HOWEVER the internal forces when the chuck is magnetised are very large . The force per unit area on the surface is about 30N/cm^2 or 3kg/cm^2. Since the area is 625 cm^2, this works out to 2 tons of force. The internal forces between the magnetic poles must be comparable. So if the chuck distorts when magnetised, I think it is those internal magnetic forces that are responsible, not heating.

Perhaps try to be sure all the rust removal chemical is out of the metal with a washing soda wash.

One of the nice things about Evaporust and other chelating solutions is that after being well-rinsed (which I have done) they leave a very paint-friendly surface behind. In fact many metal-prep sprays (Hammerite metal prep, to cite one example) are a chelating agent diluted in water.

Cheers,
Bruce