Aggressive grinding

Mr. Fixit · Feb 6, 2019

This is probably a very subjective question with many variables, but I will ask anyway.

Using a 3 phase 1 hp surface grinder (Harig 612) with a 7” x 1/2” 46I or 46J wheel with and without flood coolant, what would a normal maximum grind depth be when grinding the equalivent of a 1 square inch area of HSS?

I have minimal experience with this machine and I am practicing with tool bits for my lathe and shaper.

Thank you.

michiganbuck · Feb 6, 2019

Sorry I don’t have the answer for that. I would guess/consider about 3/8 cubic inch per minuet per horse power. That might be about .040 grinding a 1 cube for a 1 hp grinder. Perhaps a 36 G or H for a 24 to 32 rms finish might be the better wheel for better time...
Grinding technique can affect grinding rate. Traditional grinding is to down feed .0002 to perhaps .015 or more and incremental cross feed perhaps .005 to .060 or more, crossing only one direction so the lead of the wheel is a rougher area and the follow is the finisher. HSS on the lower end of feed rate.

Another technique is to down feed incrementally with no cross feeding to perhaps .0002 to .020 and then leaving .0002 to.004 left for an incremental cross feeding after a dress. Yes, having a step over to accommodate the width of the wheel to cover the part before the finish pass.

The feed rate is governed by the loss or motor RPM. Slowing perhaps 10-15 % then coming back to full when off the part is OK…often the off-the part time can regulate come back RPM, and the part getting hot… a burn and warp is a huge waste of time and can permanently damage the part. Some times a feed (down or across) on the grind side only can give the come back time and heat loss time to increase stock removal rate. The grind side is the part traveling to the right on most surface grinders.. the climb side is the part traveling the the left direction.

There is little excuse to not have coolant supply even if it is a gravity hanging bucket or an aquarium pump.
Simple coolant can be washing soda and tap water. Washing soda is just for avoiding rust. With not using coolant the wait time for loss of heat expansion can be a waste of much time. Even a hand spray bottle is OK.

Heat rise can be noticed by the spark flow when grinding dry..when sparks get closer together the likeliness of a burn is greater. For high production a swing are off chuck dresser is good with setting the height perhaps .0005 to .005 higher that the finish target so after the finish dress, you know the down feed to size is .0005 or .005...yes using the down like a micrometer to make size. Eyeball to the diamond/or bump is the warning you are close to size. A spotter on the chuck is also a good high production device.. I have used a finished part with a tab of masking tape to be the warning spotter.. then a grease pencil stripe for the final .0002 or so.

IMHO

Conrad Hoffman · Feb 6, 2019

IMO, these small grinders are good for about 0.001" of down feed per pass if you do a rapid cross. I've probably ground small bosses and such slowly with 0.01 of down feed. On my Boyar Shultz it would be burning, not loss of wheel speed, that limits me, but I usually grind dry or with a brushed on layer of oil.

MR.FIXIT · Feb 6, 2019

michiganbuck said:
Sorry I don’t have the answer for that. I would guess/consider about 3/8 cubic inch per minuet per horse power. That might be about .040 grinding a 1 cube for a 1 hp grinder. Perhaps a 36 G or H for a 24 to 32 rms finish might be the better wheel for better time...
Grinding technique can affect grinding rate. Traditional grinding is to down feed .0002 to perhaps .015 or more and incremental cross feed perhaps .005 to .060 or more, crossing only one direction so the lead of the wheel is a rougher area and the follow is the finisher. HSS on the lower end of feed rate.

Another technique is to down feed incrementally with no cross feeding to perhaps .0002 to .020 and then leaving .0002 to.004 left for an incremental cross feeding after a dress. Yes, having a step over to accommodate the width of the wheel to cover the part before the finish pass.

The feed rate is governed by the loss or motor RPM. Slowing perhaps 10-15 % then coming back to full when off the part is OK…often the off-the part time can regulate come back RPM, and the part getting hot… a burn and warp is a huge waste of time and can permanently damage the part. Some times a feed (down or across) on the grind side only can give the come back time and heat loss time to increase stock removal rate. The grind side is the part traveling to the right on most surface grinders.. the climb side is the part traveling the the left direction.

There is little excuse to not have coolant supply even if it is a gravity hanging bucket or an aquarium pump.
Simple coolant can be washing soda and tap water. Washing soda is just for avoiding rust. With not using coolant the wait time for loss of heat expansion can be a waste of much time. Even a hand spray bottle is OK.

Heat rise can be noticed by the spark flow when grinding dry..when sparks get closer together the likeliness of a burn is greater. For high production a swing are off chuck dresser is good with setting the height perhaps .0005 to .005 higher that the finish target so after the finish dress, you know the down feed to size is .0005 or .005...yes using the down like a micrometer to make size. Eyeball to the diamond/or bump is the warning you are close to size. A spotter on the chuck is also a good high production device.. I have used a finished part with a tab of masking tape to be the warning spotter.. then a grease pencil stripe for the final .0002 or so.

IMHO

Wow, thank you for the tremendously detailed reply. I have gleened quite a bit here. One question though, are you saying that the best grinding method is to grind only in the one direction and not on the climb (return)? If i am understanding, this would double the time required.

Thanks again,

Steve

adama · Feb 7, 2019

For things like your lathe bits, there's a lot to be said for roughing them out with a thin cutting disc in a angle grinder free hand first. The thin grinding discs go through HSS almost as fast as they do mild steel. You can get thin cutting discs for surface grinders too and there great for precise cuts

A surface grinder is kinda really not the tool for removing cubic inches of material, hell no grinder really is.

MR.FIXIT · Feb 7, 2019

adama said:
For things like your lathe bits, there's a lot to be said for roughing them out with a thin cutting disc in a angle grinder free hand first. The thin grinding discs go through HSS almost as fast as they do mild steel. You can get thin cutting discs for surface grinders too and there great for precise cuts

A surface grinder is kinda really not the tool for removing cubic inches of material, hell no grinder really is.

I have read this elsewhere too. Sounds like a much better approach and I will avoid being so “cranky”.

Thanks.

michiganbuck · Feb 8, 2019

Normal is to feed on both sides of the part. Grind side is for chancy set-ups and when needing more cooling time. Greater step off the part at the ends is another method of gaining more cooling time for the part.

Normal and common SG grinding is to make a down feed of .0002 to ,015 (or so) when wheel is off the part and then with long travel going left and right make a cross feed at both ends when off the part, yes with the down feed staying same at the setting. Traveling cross only one way perhaps form part close side to the part far side/ then come back to the front and cross again. This allows the wheel to have a little wear at only one lead-in edge..and the follow edge to be a finisher. With a very wide wheel perhaps 3/4 or 1" one might go both ways and consider the wheel center area to be the finisher.

Hog or aggressive grinding is to not cross feed but full wheel down feed on the part with down feeds at ends and off the part to near finish size. Then often needing cool down and dress for a normal grinding skim of perhaps .0002 to .015 or so.

Hog SG grinding provides very fast stock removal and for certain work can keep up with milling.
Yes part of the SG performance is its ability to make square and close size with less effort due to closeness of the chuck and back rail and more precision feed dials and screws.

Agree one is not likely able to grind HSS steel with hog grinding on a small SG and certainly not dry grinding.

Conrad Hoffman · Feb 8, 2019

Don't forget about work-holding. The mag chuck needs some surface area to work with, lest the part go shooting off into the distance. Grinding vises are good for some things, but they can also warp many parts, defeating the purpose of grinding. If you have to remove a lot of material, a small SG is the wrong tool for the job.

michiganbuck · Feb 10, 2019

I used to tell an apprentice if you can push the work with two fingers it is a chancy job and needs being more careful grinding.
One simple trick is to bump a block-in to the go side at the top most area. An angle plate with a C clamped bar will do this chore. With the bar having the out end touching the chuck , mid section clamped to the angle plate and the close end touching the part high place, or above part's center.
A low block-in, acts like something to just trip over so might help avoid the part sliding, but gives little help to stop it from tipping over.

A square or rectangle block-in may not be a perfect right angle so might only bump the part at the lowest edge and so be a poor block-in.

gbent · Feb 10, 2019

adama said:
A surface grinder is kinda really not the tool for removing cubic inches of material, hell no grinder really is.

You need more time around Blanchards.

michiganbuck · Feb 10, 2019

I have may hours running Blanchard and agree they can really take stock ...
Still a surface grinder can hog much more than most people think.. at my first job at Cutmore Tool when the mills were full-up and we had to fill a job order we used grinders and some times would keep up with the mills.
Guys at the big shop were amassed at how fast I could knock out a job...
Yes a yard of sparks...

Yes the SG's ability to easy accuracy made part of the grinders high performance.

michiganbuck · Feb 10, 2019

The big shop almost shut down when I took vacation and a broach insert needing a step dimension taking .015 to .080 x 3/4 x 18 or 24” long (?) made of a CPM material, I think it was 14% chromium and 12% Vanadium and by carpenter or some other outfit and as hard as a rock.
It was so hard only a very hard hogging plunge would break down the wheel enough to cut. The shop bought 4 new wheels (one ceramic) trying to find a wheel that would do the job. and almost ran out of tooling while I was of the grid fishing in Canada.

Going softer only works to a point..a very hard part can break the wheel's bond with not taking any stock.

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