Grinding chatter issues with Sanford MG612 Surface Grinder
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  1. #1
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    Default Grinding chatter issues with Sanford MG612 Surface Grinder

    I am working out the bugs of a Sanford MG 612 surface grinder, this is the “mid-size” grinder that Sanford offered, coming in at about 600 pounds, it has a ½ HP single phase motor and a 6” x 12” Eclipse magnetic chuck. I was told it had received new spindle bearings recently and it looks like a previous shop scraped the ways reasonable well (the table has one v-way and one flat, transverse direction is two v-ways). After grinding in the chuck, I’m seeing a small persistent chatter. I’m using the wheel that came with the grinder, a Norton 5SG46-JVS. Test cuts are as light as 0.005” or as heavy as 0.002”.
    I noticed the grinder does not have a balancing hub, is this something worth looking into? On the Sopko web-site table of contents, they refer Sanford hubs to the “Standard Taper Wheel Adapter” page; which is a good start.
    There is no apparent vibration anywhere, the “old machinist’s trick” of placing a cup of water on the chuck shows absolutely no ripples in the water.
    What are some suggestions on the best direction to go? I plan on plugging away, I have a few other wheels to try. Test steel is unhardened tool steel (O6).
    There may be an art to getting chatter out once it is ground in, right? It’s like driving on a bumpy road.
    One other machine I have uses a 3-phase motor with a VFD, is variable speed worth looking into?
    If this is a Sopko hub, it looks like I need a thin-wall 11/16” socket to take the hub off, is this a custom tool?
    Thanks in advance.
    chatter1.jpg

  2. #2
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    New spindle bearings do not necessarily mean correctly installed or loaded. Or there may be looseness in the Y axis. Try the water trick while the cup is on the shield of the wheel (tape it in place so it can't spill), and observe patterns while the spindle is ramping up in speed, and then slowing down. Also, you can run the table in X and see if that sets up any ripples.

    In general a balancing hub is a good idea, but if it's not used correctly it could make things worse. Worth investigating...

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    Guess for starters.. The chuck likely would feel smooth even if the wheel head had some bounce.....does the grinder head feel smooth. has the wheel been dresses with a new facet of a turned diamond? does the wheel head feel different with the dressed wheel-on, other than wheel-off.An oil or coolant soaked wheel will feel bounce, a problem wheel will make the wheel head feel worse with wheel on. does the wheel mount face run true to .002 or less face run out?. Can you push-in and pull-out the parked wheel and see any end play? Can you push pull the parked wheel head and see any easy to move push sloop.
    Most often a clean wheel of 7" or less will run true enough to get a good finish with not having a balancer hub or a wheel balance.
    If you fresh dress then slowly pull the wheel across from the grind side .0002 per pass with long only and feed on
    the grind side(no down feed on the climb side) does it grind smooth?

    If chatter looks like a wash table..the road bounces about the same and perhaps on a common like the it could be a pulley out of concentric...you might pull the belt and check the pulleye and any bumps in the belt...how does the motor feel for bounce with the pulley off.

    Does the long travel hand wheel have a little slop..It should because the table long travel can ride on the rack and gear (pinion) rather than on the scraped oil ways. Cant remember the cross movement but that should also be heavy on the oil ways and not held above them.

    Yes just throwing out the easy stuff first..

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    Fought this on my Boyer-Schultz and most of it wasn't the grinder's fault. I have a Norton 5SG wheel, 60 or 80, and it's quite dense. I don't know about the 46, but my SG isn't worth a darn without balancing. Without, the results look similar to your photo. If you rest your hand on a handle as the machine spins up, do you feel anything? It should be quite dead. Most white wheels don't need to be balanced, what the shop guys call "sugar wheels". I did have to balance my motor, which was out a bit. If you have adjustable feet, the machine should not only be level, but you should have the same pressure on all the feet. I had the problem with the gear rack described above- the engagement was OK, but the roll pin holding the small gear protruded just enough to hit the rack on every turn. Ground it shorter and reinstalled it. I can't imagine taking off .005, even though Norton says you can. Usually 0.0015" maximum and a few tenths to finish. Or less. Don't dress the wheel too smooth, use a moderately fast feed. If you take too little too slow you'll have a wheel that loads and doesn't cut. Hard steel grinds better than soft, but you should get a chatter-free finish on anything with good technique. The thin wall socket can be made from a cheap regular socket, turned down with a carbide tool.

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    Great feedback! I wish now I had tried the water trick right on the spindle. Also, Michiganbuck advice mentioned was right on. Both pulleys were worn so bad that the belt was hitting the bottom of the groove in one spot, a source of vibration for sure! Thank you!
    Going forward, I'll look into a balancing wheel and go slow like you say Conrad. The Sanford was missing stops so I improvised one to make sure the table did not go past the rack. I have a few diamonds to play with, so lots to do.

    worn-pulleys1.jpg

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    Also. I woul never grind .005" good way to screw up things. I usually fond a dull diamond and bad dressing technique when customer says bad bearings. When you dress. Do .002 and feed across one time and stop. If you keep going back and forth you dull the wheel. Be sure to use coolant or a squirt bottle if thats all you have. Also check rack as one of the others said. Rich

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    Diamond holder need not be fancy but should have diamond set at perhaps a 15 * angle (10 – 25 fine). This so you can turn it in the holder hole perhaps .030 so a new edge it pointing to the wheel. Mild steel holder holds mag better. Long enough so you can slide and +clamp it to it in a parallel /wide enough so it does not tip over easy. Dress off the chuck starting a job because the wheel may be way out of round..but consider setting dresser to near part size to save time and the wheel only needs a tickle..
    Start a part with slow passes across coming from the grind side. You can often slow bump .050 coming that way..But come from the climb side and you can throw a part /have a wreck with .005..Parts are not flat with first touch so be careful with hitting the high side. Ring wheels wear safety glasses. I wear a simple dust mask Good to have a small flat indicator plate near the grinder for checking parts
    *Know what I am calling the grind side… Block-in tall parts high up on the part...Say a 3" high part your bump stop should bump at perhaps 2 3/4"...A stop-bar C clamped to a solid block set on the chuck is much better that a !" parallel blocking a 3' tall part. And think a clamped block-in bar will turn in the one C-clamp so make it set on something so it cant turn.

    To have most fun you need an angle plate and a v block with clamp... and perhaps a 123 block set.(bargain brand Ok for now), Two C Clamps perhaps 6" (light weight)you will find parallel clamps are better that C clamps

    QT:[After grinding in the chuck,] *I tell new grinders "Don't grind the chuck" right off the bat...That is a tough job so one should get the grinder tuned up and get a good feel for how the wheel grinds before messing with the chuck.

    Your wheel is not my favorite but is an Ok wheel for most plane grinding work. (plane grinding is just topping parts for a fair to good finish)

    Wheel speed is important so if you find/feel the wheel slowing down then take lighter cuts(feeds)..Wheel should go perhaps 3450 or so with 7" wheels..You can figure out the motor speed and the pulley ratio for close enough rpm.,

    Wet is best...and going well off parts at the ends..even giving a count off the part for time and getting hot parts..It is a bugger to get out warps so getting hot even a thicker part is never good.

    Pulleys look common so best to not grind them but buy new. Polish off the new belt joint to be smooth if having a step.
    Last edited by michiganbuck; 04-24-2018 at 12:51 PM.

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    I have a good bearing shop near by so I picked up the pulley set today. After installing them, the surface shows improvements. I tried a piece of hardened steel and the chatter was again improved. I need to spend some time at the machine, I also have some other wheels to try. Any suggestions for new wheels, I'm grinding tool steel mostly. I think new bearings are in the future but after I get some time in, Michiganbuck, thanks for the techniques, I will work at them!
    better-surface1.jpg

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    The wheel you have is Ok for hard and soft steel. A white wheel 46k or about is also good..a 60, 80, 120 for very good finish but will not take stock as fast and will grind hotter. The finer wheel also better for a tight corner(smaller radius corner. but try the wheels you have because you can waste a lot of time and money chasing wheels.
    Don't side wheel grind until you know the drill.

    Know that all finishes don't have to be a mirror finish..

    Find how to square a part to .0002/.0001 or so..

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    Surburban Tool has a lot of great surface grinding how to videos on youtube and they are worth checking out.....

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    With the chuck fresh ground get into the habit of moving jobs, to use all about the chuck..even have some set-off parallels so you don't always put jobs at on the rail at chuck center..that will make your chuck truing last for a much longer time...use a big fine stone to stone the whole chuck.
    I have see chucks with a .015 wash-out at chuck front center and all around as flat and still like new..and guys thinking the machine was bad..

    Put it back in its box and it is not for knife sharpening or part burr removal...."chuck only" with a bit of oil...
    Norton Combination Grit Abrasive Benchstone, Aluminum Oxide, 6" Length x 2" Width x 1" Height: Sharpening Stones: Amazon.com: Industrial & Scientific

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  21. #12
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    Well, with all that very good advice, this machine had a hidden problem. I put an indicator on the nose of the spindle and got over 0.007" vertical deflection with just my "armstrong force". Well, the cover came off and as you can see in the lower left of the picture, the cast iron ways is cracked, in fact, the whole bar is broken into two pieces. Looks maybe like fork truck damage. With the amount of caked up grease, it had been this way for quite a while.

    I plan on a mild steel replacement made at a good shop nearby. After this surprise, I was also surprised to see the gibs are rectangular, not 60 degree or something, is this OK in a grinder application, or just less expensive? Fortunately the gib adjustment is on the good undamaged side. I see lots of grease, but like my mill, what look like grease nipples are really for oil, right?

    crack1.jpg

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    OK, so this photo shows my "work around" until I can get a drawing out. The gibs is broken cleanly into two pieces. I found that the top piece fits on the bottom. The top piece was not damaged. This will work with a 7" wheel and up to about 2" of daylight. Again with the indicator, now I'm finding about a thou of vertical travel with my leaning on it (lifting and pushing down). That is too much, right? I'll grind something when I have a moment to see the results. Square gibs on a grinder , who would have thought?
    work-around1.jpg

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    Well, there's my "loose Y" in post #2 writ large. Perhaps a part came loose sometime previously and jammed the spindle upwards, that would be my guess on how the damage occurred. I don't think even a total idiot forklift person would have tried lifting from the spindle, but I've misjudged people's creativity before.

    Bummer...

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    Have the replacement made from cast iron, I think you'll get better performance (slip-stick, damping, wear) over mild steel. Maybe the broken part can be analyzed for hardness/composition to figure out what grade to use.

    For vertical travel, are you talking about straight up and down? Not "rocking" due to clearance in the gib to spindle interface? A small up-down is to be expected due to screw/nut/thrust bearing clearances, I'd think.

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    Yup, straight up and down, I think based on the clearances due to wear and tear with the spindle back plate and the frame. I'm actually feeling good about this all, I found the problem, I have a work-around and it is a 'simple' part. Tempted to do a 60 degree bevel set-up.....

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    Making a new gib and way section to bolt in, then scraping everything so it's right is no small job! I don't know what the used surface grinder market is in your area, but around here they are a dime a dozen! I would never even consider doing any type of major repair on a small, hand feed grinder, much easier and cheaper to just replace it. For example, last year I bought a very good condition Harig 612 for $125. They're small enough that they can be moved by a couple of guys with just an engine hoist and utility trailer, so no rigging cost either. I've seen plenty of good condition hydraulic machines in the 618 range sell for less than $1000. If I were in your position, I'd sell the good parts off the machine you have, and invest the money into a decent machine. Of course, things may be very different in your area, but worth considering.

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    Thank you for the suggestions, in general, it is more difficult to find good, used machinery in Canada (think mining and farming) than in your area, which I would consider the heartland of America’s manufacturing since Henry Ford wore short pants (OK he was from Michigan). I have a machine shop contact in the area for advice and for access to larger machinery. He previously reworked the gibs on my Deckel slotter head, the guy is a real perfectionist.

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    This is a follow-up to my previous posts regarding a Sanford surface grinder I purchased last year. I hope this information assists anyone else with their machine’s problems. It did not grind properly even after the previous owner replaced the spindle bearings and re-scrapped the V-ways. I knew this going into the purchase. The short story is that the machine was completely worn out due to improper lubrication, and it was tipped over at some point (see previous posts) with the motor/spindle assembly breaking through the cast iron ways in one location and breaking the ways in half. Note that it was found that the two remain halves of the left-hand ways were broken such that each half had three fasteners and two dowel pins. This was a major factor in the decision to repair the machine and also to not machine new ways or toss the whole thing out.
    This is the mid-size manual feed “MG” model, basically a light-duty unit that well-suits our need to grind small punches and small tool-steel assemblies It has a 6” x 12” magnetic chuck. It is very, very top-heavy; the base is just sheet metal.
    We determined to fix the machine and went ahead to look at the major issue of a chunk of iron broken from the ways. After considering welding it up, the crack was pocketed out on my Deckel FP1 and replaced with a new piece of iron. We noticed that when the pocket was milled out, the ways ‘stressed relieved’ and closed up a bit. The new insert piece was a fitted to get it back to original, it was then held in place with a row of ¼-20 cap screws and Locktite.
    The spindle back plate had major uneven wear which was repaired by chucking the spindle itself in a friends Okuma LS lathe. Since there were features on the face of the spindle, the back face (nearest the lathe chuck) was cleaned up, then the assembly was placed on riser blocks and the opposite face was cleaned up on a Reid grinder. The assy was flipped and cleaned up again on the grinder, bringing the spindle plate accuracy to maybe plus minus two tenths.
    The ways were ground to match the width of the ground spindle plate. Since there is no adjustment in this area, we had to chose a clearance to grind to. I figured one thou clearance would just bind up, so two thou was chosen. The end result with correct ‘way oil’ (Esso Vactra #2) was very good. Now that it is working, I will re-read all the kind comments of previous posts to learn how to operate this machine to its best ability.
    Attached Thumbnails Attached Thumbnails crack.jpg   repair.jpg   insert.jpg  

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    There were more issues. Wear in the main vertical frame was severe, maybe five to ten thou and uneven from left to right and top to bottom. One feature of this machine is a lack of adjustment to take up any wear in this area, there is only one set of gibs to take up play from left to right. I’m not sure why this grinder was designed this way (keep the cost down?), however wear to the main casting or ways cannot be adjusted out. The spindle will “nod” (called pitch I think if this was an airplane) if there is existing wear. The motor is cantilevered off of the spindle assembly which will certainly accelerate uneven wear, so careful lubrication is a must for this design. The existing wear on the frame was taken out with a large Charmilles grinder (the "after" picture is shown below.

    The cross-slide Acme thread and nut were very worn, again probably due to poor or no lubrication. It had a plastic Acme nut which was filled with grit, acting as a big rotary file to grind the thread down to a toothpick (I’m not sure if this plastic nut was factory). The Acme thread was a standard size, so it and the nut were replaced.
    The vertical adjustment screw was worn, but it was unfortunately not standard anything. The screw was a square profile, not Acme. Also, the pitch was not standard; I understand this is similar to some other grinders, Boyar Schultz jumps to mind. It is a 6.66 pitch per inch, single start, ½” dia. shaft. It is still usable and difficult to replace. From what I can see, the bronze nut is more heavily worn than the screw. It would make sense in future to switch to an Acme thread rather than a square profile and use a DRO.
    The 48-tooth gear on top of this shaft was missing a few teeth, so it was replaced. It had a Boston gear number on it and was ordered from the local bearing shop. There was a bit of wear/play in the gear mesh that probably contributed to the damage, so this new gear was modified to take it up.
    I don’t normally paint machines however all this activity took time and we did find some old cans of grey engine block enamel to make it look pretty again.
    Attached Thumbnails Attached Thumbnails grinder-frame.jpg  


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