Learning grinding my own please help

I have a Harig surface grinder at work. (pics to follow) We just got it hooked up coolant tank cleaned a new diamond dresser.

I am trying to learn grinding (totally green!) we really have no use for the grinder at work but it's just sitting there so we got it wired.

I tried to make some blocks 1.25x1.5x2.0 out of 17-4

I got really close on the 1.250 dim. I got 1.2501-1.2502 but I overshot the 1.5 by a few tenths.

What I want to do is make some blocks out of something I can harden. We have 4140hf annealed 4130q&t

Now for the questions!!

What should I make the blocks out of?

How big should I make them before hardening?

Does it shrink or grow at all?

Is a rough cut on the mill ok or should I grind before hardening?

What is the best way to ensure squareness? Flatness and size I understand but squareness I'm lost in how to controll or adjust for that.

I guess that's all for now


Any and all suggestions or comments are very welcome!

Thanks
Nick

I'd suggest you make your blocks out of O-1 hardened & drawn to Rc58-60.
It's fairly stable, easy to heat treat and relatively inexpensive. Mill it +.005 per surface, heat treat, and grind it in. For hot rolled stock, allow .100 per surface for decarb. If you'd rather have blocks that are only cased, your 4140 could be treated to Rc30-32, milled to size +.005 then case hardened .015 deep followed by finish grinding.

Learning surface grinding

Hi Nick:
It's a bit difficult to give you decent advice without knowing a bit more about just where you're at on the learning curve.
Have you seen a knowledgeable operator using one before?
Have you used one before or been trained on one at all?
Have you read any literature on how to operate a surface grinder?

Grinding is an art like many other subspecialties of the metalworking trades...it's not too difficult to throw a block onto the magnet and make sparks, but there's a lot more to it and a really experienced hand can make a job that's a frustrating pain in the ass for you, look totally easy.

Your best bet by far is to get some one-on-one training by a toolmaker, preferably a specialist grinder hand...you'll learn more in a day with a guy like than than you will in years of farting about on your own.
Try to find a retired guy to help you out and don't forget to pay him!

Regarding your specific questions, you can choose any good tool steel, or even have mild steel case hardened; machinistrrt's suggestions will work fine.
My personal preference for making measuring and gaging equipment is A-2 toolsteel; it's air hardening and one of the most stable toolsteels especially if it's cryo treated after tempering.
It's capable of very high hardness, has good abrasion resistance (but is still reasonable to grind) and is tough enough to tolerate being knocked about a bit.
17-4 PH is a poor choice; it doesn't get nearly hard enough for a reference block.

I typically mill my blocks 0.005" per side oversize and almost never grind before heat treat.
I glass bead the blocks after I get them back to take off the firescale (keeps the wheel from glazing over).
Rough cuts are typically 0.001" downfeed and 0.025" or so crossfeed per stroke until I'm within 0.001" of target dimension.
I dress frequently and run coolant where ever possible.
Finish passes are typically very light...0.0001" if I need good precision and a perfect surface.
I dress the wheel with a nice sharp diamond at a fast traverse rate aind a 0.0005" DOC so my wheel is nice and open and will cut cool and free.
Wheel selection is a whole 'nuther topic for a future thread.

Making parts rectilinear is most commonly done by processing them against a known master...a grinding vise, an angle plate, a mag square.
There are other ways...if you know how to measure a rectangular block for squareness, you can compensate for deviations by grinding a step in your part that will tilt the part in the direction you wish to compensate, then flipping the block so the step side is against the magnet, grinding the second side, then flipping the block again to eliminate the step.
It's all very tedious which is why toolrooms spend thousands of dollars for good quality master square devices.
To get an idea, Google for Hermann Schmidt; they make very very nice stuff specifically for this purpose, but it's also very very pricey.
Trying to get a pair of surfaces orthogonal to within 0.0001" in 6" is not easy, and the price reflects that reality.

On a last note: grinders are among the most dangerous machines you'll ever encounter in a shop.
They look so innocent but they are utterly intolerant to fuckups.
Be extraordinarily careful, get into a routine that has you turn the mag chuck on and then immediately check the block to see if you can shift it on the chuck.
Do it every time...it's got to become a habit.
Make damn sure you don't rack the wheel into the job...the friction goes up orders of magnitude with only a very small increase in DOC, and will rip the job off the chuck and usually explode the wheel too.
Never stand a tall skinny block up on the chuck and expect to kiss the top of it...it's got to be packed properly or held in a vise or clamped (securely) to an angle plate or it'll take off like a rocket.
Grinding wheel burns are really, really painful and slow to heal...don't stick your fingers where they don't belong.
Lastly wear your safety shades...always...no exceptions.
Cheers and good luck

Marcus
www.implant-mechanix.com

Thanks for responding guys!

Marcus,

Truth is I have never seen a grinder operated besides a couple quick suggestions from some of the older guys in the shop. That leads to another problem everyone I talk to at work seems to have different oppinions about how things should be done.

I have not read any books on grinding. Do you have any suggestions?

Thanks again I'll let you know how things go and I'm sure I'll have more questions!!

Actually I have another question already!!

After dressing your wheel and measuring your piece. (let's say we have .0003 to remove) How do you pick up/touch off your wheel?

When dressing your wheel how much should you remove?

reset the zero on the dial before you move it so you know where you left off, if you only need .0003" to come off allow the piece to fully "spark out" running the wheel over the piece several times till there are no more sparks and you don't hear it anymore. I touch off with the wheel spinning and traversing with blue on the piece to see where it cuts, feeding by hand carefully. you can touch off with a shim, but be careful about damaging the wheel. Dressing the wheel you only need to take a few .001" passes

Avsfan135 said:

Actually I have another question already!!

After dressing your wheel and measuring your piece. (let's say we have .0003 to remove) How do you pick up/touch off your wheel?

When dressing your wheel how much should you remove?

Click to expand...

One technique that has worked well for me is to use a piece of paper between the wheel (or cutter) and the work. As the wheel is advanced, I detect when the wheel starts to cut the paper. Then I know I am within a couple of thousands of the work. Then the wheel is very slowly advanced until the wheel touches off. Note that if the work has not yet been ground, that there may be high spots. Once I note the touch off setting, I back the wheel up several thousands and traverse the work for high spots. Failure to do this can lead to some unpleasant gouging and burning or even throwing the work off the chuck.
Tom

Suggestions to start grinding. Buy "Machine Shop Practice" volume 1,2.Read about blocking, squaring etc. a good place to start.

Tips from a self taught grinder. Dress the wheel before the final cuts, but before it is critical. say 2-3 passes before size. Do not dress before the last cut , you will always miss the size that way.

Post it notes the size of your fingernail folded over the first edge, held with spit seem to work well for touching off.

For final size, say you need to move .0004" down, Lower the wheel .005" then crank it up .0046, if you just lower the wheel .0004 and it like my half century old machine, it may move another .0001-2" by itself in use. Since my wheel is graduated in.00025" I added a 1" travel .0001" acccumative DI on a sliding bracket, really helps those final cuts.

The grinder I use is only 1/2HP, with no coolant so deep cuts are not a good idea. a .005" doc with .050 feed is near my comfortable maximum. Most cuts are .002-3 at .100 roughing cut, then reduce feed to .025 for a nice finish, with much less doc. As the grinder has no auto advance it is quite a workout to grind in the chuck at .010 feed, times 8 cranks on the travel wheel=800 cycles per inch, 6 inch chuck =4800 cranks on the travel wheel. This is why manual grinders are not that desirable in a shop that needs to make $$$.

You will need some known square 123 blocks with holes, a couple fine pole magnetic blocks. Fool around with the mag blocks, you will quickly see that positioning work on top of these is important to line up with the poles of the chuck itself. If you need to grind a washer say that is .050 thick , how to keep it from shooting off the chuck like a bullet. Position the mag blocks, so that the washer is at the rear edge of the mag block, and in the strongest part of the mag field. Now slide a 123 block with a piece of .040 stock clamped to it in such a way as it will clear the wheel travel, while preventing the washer from kicking out. You would also want to use light doc and feed for such an operation.

The grinding dust is a real PITA, make a vaccum attachement if you don't have one, coolant is best but the grinder needs to be designed for it, else a mess. my $.02

To just get an idea of set-ups find some books. Norton has a good Grinding wheel users guide.

But you as well need some visual aid as you have nobody to learn from where you are at.

Search surface grinding on you tube and you will at least get some ideas on how things are done.

Thanks again for the responses I really appreciate it!


Another question...

When making threaded holes in blocks that will be hardened do I do anything differently? If I get them back from being hardened and a screw won't pass do you just re-tap by hand?

Thanks

Nick

Hardened tapped holes

Hi Nick:
Probably the most important thing you can do is choose your steel wisely.
Most air hardening tool steels are good, and won't move enough to make a noticeable difference.
Case hardened steels, on the other hand, can swell like crazy and leave a hole so badly distorted that you cannot get a screw through it.
Trying to re-tap these with hand taps is a hopeless case if the steel is any harder than about 40 Rockwell C
Oil hardening steels are intermediate in nuisance, often it's the firescale and the burned oil residue that prevents the passage of the screw; these can usually be cleaned out by running an old tap through, but the scale will play hell on the cutting edges of the tap.
Water hardening steels distort more than oil or air hardening steels, and can be as bitchy as cased steels.
Cheers

Marcus
www.implant-mechanix.com

Thank you very much! That is very helpful

What kind of tolerances do you all think I should give myself to start with on squareness flatness parralellism dimensions?? Etc.

I do have a CMM to use for measurement.

Thanks
Nick

part tolerances:

Hi Nick:
That's another complex question cleverly disguised as a very simple one.
Obviously, if you're making a reference square, closer is better, but it can be intensely frustrating to chase tenths with an inadequate machine poorly accessorized, with a newbie operator, so without knowing all of the conditions, it's difficult to say.
But a practical way to look at it is this:
If the grinder is basically in good shape, you can expect to hold flatness and parallelism better than 0.0005" on blocks of the size range we're talking about (biggest dimension under 4", and least dimension over 1") without special effort.
That means throwing the block up on the mag chuck (recently reground of course), and whacking of 0.001" at a time with a reasonably chosen wheel in reasonable balance, properly dressed.
If you leave a cooldown interval before your last passes (which should be 0.0005" or less), or your machine has coolant with decent filtration, you can routinely work within 0.0003" in the same manner.
If you want to hit 0.0001" or better, you have to start paying MUCH more attention to details, ensuring the machine is in perfect condition, stoning the chuck and the workpiece properly, dressing and balancing a rigorously chosen wheel to a much more exacting standard, paying much closer attention to the grind direction and the state of the wheel as it deteriorates, filtering your (now mandatory) coolant etc etc.
This is where the art of it all really separates the truly experienced hands from the herd.
Note this is just for the simplest of tasks; making two surfaces flat and parallel on a block of decent proportions.
Making it square within tenths as well adds a whole new layer of attention to detail.
If the blocks have unfavourable proportions or the material is chosen poorly, your task gets way more complicated and may become impossible.
If you need to create fancy geometry, with dressed wheels, the complication factor rises again.
As an added issue, qualifying your work within tenths is also a more rigorous job...you can't simply grab the nearest beater shop mike and pretend it's dead on.
Bottom line: if you can get your block within 0.0005" of all relevant geometry; dimensions, squareness, parallelism, flatness, finish, etc etc; you've done pretty well on a general shop machine with no obvious deficiencies.
Cheers

Marcus
www.implant-mechanix.com

Exactly what I was hoping for. I figure that once I get the basics down and can stay within .0005 of my target sizes I can move on to more insane tolerances.

I do have coolant I'm using a synthetic that we use in our cnc equipment Wallover. However when I put it in it was blue and it comes out a milky green!! This is after I cleaned the tank. I'm going to clean it again obviously I didn't do a good job the first time but it brings up a good question.... What coolant do you recommend and what type of filter do you use?


Also where are you? At this point I want to just come to your shop and learn direct from the source!

Thanks again
Nick

Marcus I saw your website you do some nice work!

Here is my grinder




And a close up of the surface of the mag chuck. It's in bad shape that black spot must be .010 deep! Someone just buried the wheel.

It's also nicked and banged up. I haven't ground it yet because everyone here has a different opinion on how it should bs done. My books get here tomorrow and I'm gonna see what they say about it!

Avsfan, when you dress your chuck take off as little as possible. Touch off on an undamaged looking area and take off about .0005. Repeat until you have about 90-95& clean up. Dress and continue about .0002-.0003 at a pass. Stone it anytime there might be a scratch. Scratches can be prevented by resting parts on a piece of paper.

Thanks!!

You grind parts with paper underneath?? I like it! Seems kinda scary though!

Thin standard 80 gram writing paper works a treat, actually parts seam to be gripped far harder and with a lot more friction to resist sliding this way. Not ideal if the parts too small - your running coolant though.

As to grinding the chuck i only take enough off to get back to good geometry. As is i have reground my j&s 540 about 3 times in 9 months. There's still a low spot about 1" square on one corner but i have not needed the full chuck face yet hence just work around it. If you have any douts in grinding something that big your self just slap a chunk of steel as near to the same size on it and have a go. Im not sure what magnet chucks are made from, but hardness wise its not much better than mild steel, hence its easy to have a practice chunk and see how your wheel dress is likely to work.

opinions vary on grinding method. Some insist shallow cuts with a wide stepover are the only way to go, others say heavier cuts with a narrow step is. I tend toward narrower stepover and heavier cuts per pass in most situations. You'll find situations where your techniques change.
For a first project I'd leave a bit more than 0.005 per surface on the parts. I'd leave 0.010 just so you can feel your way into it. Shoot for a midway point, if you miss it you have another chance. If its something where you "have" to nail locations, grind the part soft to be sure its square and true before you machine the important features.
Be sure to support tall parts or you'll make a dart board out of anything down wind of the grinder.