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Basic Surface Grinding

Discussion in 'METAL FINISHING, CUTTING & WORKING' started by Ray C, Nov 3, 2013.

  1. Ray C

    Ray C United States Moderator Staff Member Moderator

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    Hi...

    Here's a quick photo sequence of some surface grinding. The piece is a home made turret block attachment made from 4140 and heat treated to Rockwell 55C. -Pretty darn hard...

    sg1.JPG

    First thing with this piece and any other is to remove all the scale and file down any/all edge burrs. Do a good job of that as a small burr of a thou or two will prevent the piece from sitting flat on the mag table. That will not only throw the geometry of the part off, it will lead to a lot of extra time standing in front of the grinder.

    sg2.JPG

    Before putting the piece in the grinder, take a good machinist square and check all the sides for squareness. It's possible you have three good sides and one that's a little out of square. In that case, set the part face down on a good side and true-up the bad side first. If you set it down on a bad side first, the error will propagate as you flip sides -and you'll get to spend more time standing in front of the grinder. Use your best judgement when selecting the starting side. It's always wise to check first and save yourself some time. If you have a raw piece of stock, it's usually wise to mill it flat first.

    To setup the piece, with the machine powered off, I use my thumb to rotate the wheel while gradually lowering the head until it just barely makes contact. Once that is established, without the motor turning, I run the part in all directions under the piece to see if any areas are sticking up high. You may need to back-off the head if there are high spots.

    sg3.JPG

    Next, the machine is turned on and the head is lowered in this case about 0.0003" -which is a fairly deep grind. When first starting, you must push the piece into the direction of rotation. Failure to do so could loosen and unscrew the wheel and it will happen in a heartbeat. A complete pass is made first "left to right" then "right to left" back to the starting position, then, the part is moved forward by 50 thou (or so). The part is started at the back...

    sg5.JPG

    ... and moved-in about 50 thou at a time until it's completely covered. Although not shown here, the part is moved completely under the wheel. You don't stop when the front edge of the wheel reaches the edge of the part. You keep going until the backside of the wheel clears the ending edge of the part.

    sg6.JPG

    On this part, it took about 8 cycles starting from top to bottom each time lowering the head about 0.0002" until the entire surface started to flatten out. Here's the half-way point in the cycle. As you can see, there's a little slope in the part.

    sg4.JPG

    And finally, here's the finished surface. This was a 46 grit wheel and it looks OK if you ask me.

    I flipped the part over and did the other side. It went much faster than the first side and the whole surface took an even grind unlike the first side which you can see, had some slope to it.

    The best part of this is taking a micrometer and measuring afterward. This part does not have critical external dimensions yet, I intended for it to be 2.200" wide. When it was milled, I made it several thousandths oversize. After cleaning-up both sides, it came out to 2.2012" and the variance was well under a tenth everywhere you check. If so inclined, I could make successive passes and bring it down by 0.0012" -but I am not so inclined.

    Another quick note... In the summer time, parts heat up quickly and I usually use Kool Mist. Today, the shop is nice and cool (pleasantly so) and I only ran light compressed air at the surface with no liquid evaporative. The part stayed nice and cool the whole time. If it did get hot, the variance in width would have easily blown 3 ten-thous.

    Finally, it took about 40 minutes to do both sides of the part.


    sg7.JPG


    Ray

    sg1.JPG sg2.JPG sg3.JPG sg4.JPG sg5.JPG sg6.JPG sg7.JPG
     
  2. xalky

    xalky United States Global Moderator Staff Member Director

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    Nice. Cool little tutorial too. :thumbsup:
     
  3. Ray C

    Ray C United States Moderator Staff Member Moderator

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    Thanks, glad you liked it. Yes, it was primarily intended to be a tutorial because I know member "Sandia" just got a SG up and running. Figured he might appreciate this. Also wanted to demonstrate that a #46 wheel does a fine job of finishing and that 80, 100 or even 120 is overkill and would take much longer to do. In the last photo, I put my hand there so you could see the reflection. It's not a bad finish at all. Using the real fine wheels is a curse in a way... The finish would be almost like a mirror but all it takes is one little screw-up and bingo, now the only thing you can see is that tiny imperfection. It kinda takes the fun out of it... With wheels like that, it's probably best to have auto table-feed -which I wish I had because hand-operating the machine is a killer on the lower back.

    BTW, when you're doing this, I find it helpful to find ways of rotating my shoulders and back and standing in different positions to cut down on muscle fatigue and stiffness.

    Ray
     
  4. DMS

    DMS United States Active User Active Member

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    Thanks for posting this Ray. I think surface grinders are one of the least used machines in the hobby shop. I haven't used on since shop class. Lately I have been thinking one might be useful. The problem now is, where to put it?
     
  5. Ray C

    Ray C United States Moderator Staff Member Moderator

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    Yeah, and don't forget, they're not exactly light as a feather either. This ancient thing is just a hair under 1500lbs...


    Ray

     
  6. buffdan

    buffdan United States Active User H-M Supporter-Premium

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    Thanks Ray for the post.

    Do you ever use flood coolant?
    Do you have duct collector setup for this?

    Dan
     
  7. Ray C

    Ray C United States Moderator Staff Member Moderator

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    No, never tried flood coolant; seems too messy. Just the KoolMist system sometimes when it's cold in the shop just use the nozzle to blow CA.

    Absolutely, I have a dust collector. I think one of the pictures shows the 4" draw tube. BTW, that draw tube is a flexible/collapsible piece about 20' long. It's available at Lowes and/or HD. Works great. The vacuum unit is this one: http://www.harborfreight.com/13-gallon-industrial-portable-dust-collector-31810.html

    If you don't use dust collection, you'll have a metallic taste in your mouth for hours. The dust packs in your nostrils and most certainly in your lungs.


    Ray


     
  8. buffdan

    buffdan United States Active User H-M Supporter-Premium

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    That's a reasonable cost for a dust collector.
    I use my shop vac on my SG, but looking for a better solution

    Does this dust collector contain the dust in the bag, or some leakage into the air?

    I have a vacuum dust collector on my blast cabinet, but its expensive..
    Looking for more cost effective solution.

    Thanks for sharing

    Dan
     
  9. Ray C

    Ray C United States Moderator Staff Member Moderator

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    BTW, according to the serial number, that SG is about 100 years old. Originally, it did not have a motor-driven head but was factory converted at some point in it's history. It had/has a fairly known chain of ownership of two factories and one private owner who used it at the last factory before it was put out of service. He had it in his garage for a decade or so -and now it's in my garage -and will stay there! Based on it's markings and prior knowledge of the previous owner (and his father), it's been rebuilt about 5 times; on average, once every 20 years. FYI: It made Harley Davidson parts for the last 50 working years of it's life.


    Ray

    - - - Updated - - -

    That collector works just fine and is not loud at all. Matter of fact, I really like the sound it makes. The bag puffs-up big time and needs about 3' of clearance where it sits. Most of the dust never reaches the bag. In over a year, I've never emptied the bag and it's all but completely empty. Gridning dust is heavy and gets trapped in the "corrugated" folds of the draw tube. Every couple weeks or so, I drag the tube outside and 5lbs of grit falls out... It seems to make good fertilizer in the flower garden. I don't think I'd chance putting it in the vegetable garden.


    Ray


     
  10. itsme_Bernie

    itsme_Bernie United States Active User Active Member

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    I love this thread Ray!! Thank you! This lesson is right up my alley, since I am in the market for a Surface grinder, and think I found one.

    How long do you take on each pass? Silly question, but I've never seen it done. What is tiring about it compared to lathe work? Is it that fine a feed per turn? The machine I'm looking at is also manual (or I couldn't afford it :) )

    I have a woodworking dust collector, single stage. I am going to put a bucket into the system to make it closer to two stage. Do you feel it keeps the other machines in your shop pretty clean? Safe to have in the same room? When I even dress a wheel to the bench grinders it is a tasty mess hah hah

    Questions questions questions! Hah

    Bernie
     
  11. Ray C

    Ray C United States Moderator Staff Member Moderator

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    Hi Bernie...

    The passes are pretty fast. That piece is about 6" long and if I had to guess, a full pass (going from L->R then R->L) is 5 seconds. To cover the part from top to bottom (on one side) is about 5 minutes. I'm sure You Tube has some live videos.

    On a lathe, you don't do much at all. With this thing, your left arm is cranking back and forth like an organ grinder's monkey and every five seconds, the right hand makes a quarter turn on the infeed. You can easily fall into the trap of locking your body into a hunched-over and set position for a long period and before you know it, your shoulders are tight and stiff and lower back is aching.

    BTW: I really should mention that full face protection could save your vision or life. I highly recommend wearing it.

    ... Good luck with your machine. What kind and size? BTW, if ever I had to get a different one, a 6x12 instead of a 6x18 would suit me fine... Autofeed... yeah, I'd love that.


    Ray


    - - - Updated - - -

    Yes, I never really notice much airblown dust on other machines nor does it build-up on my eyeglasses (unlike with my sand blaster). The trick is to get the draw tube lined-up right on with the direction of the projecting dust.

    Ray
     
  12. churchjw

    churchjw United States Active User Active Member

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    Thanks for this post. I use my koolmist with my grinder as well. I have not set up a dust collection system yet on mine. But you are right I desperately need to. I get that caked in the nose black dust and that can't be good for ya. I was thinking of using one of the Oneida dust deputes hooked to my shopvac. I have one on my blasting cabinet and it works great. Please post more on the surface grinder this is one area I am very weak. I would like to see how you set your coolant up and more on your dust system.

    Jeff
     
  13. itsme_Bernie

    itsme_Bernie United States Active User Active Member

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    Gotcha- that was what I pictured, having just turned the handles on the one I saw.. :) ...


    Looking online at pics, it seems the one I found is a 6x12... Manual feed. I bought the lathe from this guy, and he seemed to find nice machines, and kept his machines tip top :)


    I am all over keeping myself safe and my other machines clean. I use the same vacuum setup as your grinder when I am cutting cast iron on the lathe. I just don't have a clue how much dust really goes up when finish grinding like you did there.

    I second Jeff's request for a part two of this post!!!! :)


    Bernie
     
  14. Ray C

    Ray C United States Moderator Staff Member Moderator

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    You're welcome...

    Well, assuming your grinder is nice and flat and in proper working order, the most important thing is to have a very well balanced wheel. I've shown my balancing setup many times here but if you need to see it again, here it is. That axle was specially made to fit the grinder hub and with it, the balance weights can be adjusted to statically balance the wheel. It makes a huge difference in the quality of the grind. A slightly unbalanced wheel will leave little cup-marks on the surface. Many hubs have no balancing mechanism. The ones that do cost over $600 each -so I make my own and have posted threads here on how I make them. I have no idea how anyone can do a good job w/o a balanced setup.

    BTW: In the picture of the bearing balancer, you can see the black draw tube. It's a heavy plastic that bends and stretches -and most important, does not collapse when the vacuum is switched on. You can't use the tubing from a clothes dryer vent as it will just collapse immediately. Anyhow, the vacuum system is trivial. I just connect the tube to the unit (it fits perfectly) and use a telescoping stand to position the hose inlet right in-line with the grinding dust. Simple as that. The tubing is heavy enough to not start on fire and most of the dust settles in the tube and never makes it to the bag.

    Balancer Arbor.JPG Backside Balancers.JPG

    Next thing is to surface the wheel with a diamond. They cost about 40 bucks and last a long time. It's the small rod-like thing sticking out of the holding cylinder. The actual diamond is 1/4 carat and is embedded and silver-soldered into the rod. It is purchased that way. The holding cylinder is a piece of drops with a hole drilled to hold the rod/diamond and a bolt to hold the diamond in place. With the motor off, you clamp the holding cylinder with the mag base, move it very close to the wheel (but not touching), lock the x-direction of the bed, spin the wheel by hand and lower the head juuuust until it starts to touch, move the diamond away in the Y-direction then lower the head 1/2 thou. Fnally, turn on the motor and move the diamond across the wheel slowly. Keep lowering the head 1/2 thou at a time until the wheel face is even. -Takes all of a minute or two.

    The vacuum should be on the whole time as the wheel kicks-up dust and that is aluminum or silicon oxide -not good for the lungs.

    BTW: I'm using the XYZ coordinate system as in milling -and don't know if that's the correct ordinate system traditionally used in grinding. Feel free to clarify if I'm wrong. Also, I never learned grinding prior to the last few years so, this is all coming from the school of hard knocks.

    sg8.JPG

    After that, you just do what's mentioned in the first part of this thread.

    At the surface (pun intended), it's pretty easy. In reality, many things can go wrong. Using the wrong type of wheel on a given metal, too much downfeed (good is 0.0001" for a finish pass and 0.0002 to 0.0003 is about right for rough passes), not recognizing when the wheel needs to be faced, too much infeed in one pass, heat buildup... Those are the easy things that go wrong. Then you get into the hard problems, like how to do thin pieces or holding pieces at angles... In the near future, I'll show some stuff about how I've tackled that.


    Ray

    Balancer Arbor.JPG Backside Balancers.JPG sg8.JPG
     
  15. churchjw

    churchjw United States Active User Active Member

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    I have seen your balance wheel post before but now I need to go back and read them. I have seen the cupped finish you mentioned before and never knew what caused is. Looks like a wheel balancer and hub is in my future to build.

    Jeff
     
  16. Sandia

    Sandia Active User H-M Supporter-Premium

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    Ray, thanks for the post. Very informative. Believe me, I can use all the instructions I can get. I ordered two 46 grit wheels, per your suggestion, and got them yesterday. I plan on spending some time with the grinder, hopefully this week. I am going to try to rig up a stand for my dust collector first and then look into your static wheel balancer. I will have to find that post, I know have seen it before. I will continue to follow your future post on the SG.

    PS: I will contact you on helping me set up the VFD to variable speed.

    Thanks much,
    Sandia
     
  17. Hawkeye

    Hawkeye Canada Active User H-M Supporter-Premium

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    Ray, you're not helping. I've been needing a bigger shop for some time. Now I have to find space for a surface grinder. :biggrin: And find a surface grinder. Nothing gives a finish like a grinder.

    Good post. Thanks.
     
  18. Ray C

    Ray C United States Moderator Staff Member Moderator

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    Yeah, I hear y'a... I'm fresh out of space too. Where there's a will, there's a way!

    Ray


     

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