Basic Surface Grinding

Ray C

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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
 
Nice. Cool little tutorial too. :thumbsup:
 
Nice. Cool little tutorial too. :thumbsup:


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


Ray

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?
 
Thanks Ray for the post.

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

Dan
 
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


Thanks Ray for the post.

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

Dan
 
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
 
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


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
 
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
 
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