But the flip side of this is that one can be skilled and adept at grinding tools by hand, and still have *zero* experience or skills at NC programming. I had pretty much zero there when I first went to work at that night production job.
Most of the guys there didn't even know you *could* make cutting tools by hand! But they knew G-code stuff inside and out. I learned enough in my couple of years there to keep me from being a menace to myself!
Jim
If they have segmented pieces that spin, that's what they are. Jim likes 'em, and even ol' teenut used to extol their virtues, but I'll put my grinding experience up against their opinions any time anyone wants to have a discussion. As I said, there is no better way to prepare a wheel for cutting. By their nature, they leave very sharp grain when properly applied. Problem is, it's hard to get a wheel running true. In order for them to function properly, they require a given load, otherwise all you do is grind away the components. They dress by hammering the wheel, breaking it into fine particles. Assuming you can get the wheel running dead true, you can then bear down adequately for the dresser to do a good job, but you can waste a lot of wheel getting there, and it's not all that hard to get the wheel to start bouncing again while you're using it. As I said, I avoid them totally. Don't even own one, nor do I care to. If I had a large 3 phase grinder for grinding on weldments, I'd likely have a different attitude. They're great for that application.
That's the tool I thought I'd have to explain to you.
You can't bear down with them if you want a wheel to come true. If you have a work rest, this is one place where it can pay benefits. You place the dressing stick on the rest, picking a sharp corner, lightly touching the grinding wheel, which should be at operating speed. The highs only will make contact with the stick and slowly be lowered until you finally have full contact all around. If you crowd the dressing, you tend to encourage the wheel to shrink, but not get corrected. From this you should understand that it takes a light hand. You can't horse getting the wheel running true. Once it is running true you can aggressively remove more wheel with reasonable results, though. Remember: A light touch.
Assuming your wheel is out a considerable amount, and you'd like to true it up with a diamond first, that works fine, too, but you have to use the same principle, lightly applying the diamond so only the highs get removed. As quickly as you have the wheel running true, you should change to your dressing stick. Diamond dressed wheels don't lend themselves well at all to offhand grinding because the surface is way too smooth. Exactly the opposite from what a star dresser does. A light touchup with a dressing stick will usually prepare the wheel for quite good grinding performance. Avoid the use of the little dressing sticks that are 1/4" x 1/2" x 3" in size, and are one solid piece. They are boron carbide, and while they're even harder than the silicon carbide dressing sticks, unless they are very sharp, they tend to dull the grain excessively, so your wheel cuts quite hot----very similar to a wheel prepared with a diamond, in fact.
You may see some real strange conditions as wheels spin up and down. Don't worry too much about that, just make sure that when your wheel is up to speed, it runs true. Often the imbalance of larger wheels will cause some vibration that makes them look like they're running out a lot more than they really are. If you find your wheels vibrate excessively, it's not impossible to have ended up with wheels that are not well balanced. Precision grinders have provisions for balancing the wheels, but pedestal grinders usually do not.
I trust you know to use the proper flanges, and to always run the blotters. You risk fracturing wheels when you mount them without. Hopefully you also understand how to "ring" a wheel to insure it's not cracked when you mount it.
As I said, there's nothing wrong with the concept, but it requires a light touch to be effective. Assuming you still have the diamond at your disposal, you might try again, making sure the nuts on the spindles are well snugged. I failed to mention the possibility of your wheels moving about on the arbor. You want the nuts tight, but not excessively. It's desirable to learn to use a little less pressure when tightening fasteners on grinding equipment. Unless something goes very wrong, there's usually not all that much pressure involved in grinding.
Hopefully something I've said will be useful. Why don't you give it a go, then let us know.
You don't have to say anything to convince me. I'm the first to say that a grinding wheel that doesn't run true is worthless.
I think so, although I'm really surprised that you aren't experiencing success. Are the bearings good in the motor?
I hope you realize that what the problem could be might jump right out at me, or others, but you may not recognize it, so you could have overlooked something that might be important. That's why I asked for you to describe what you're doing, and how you're going about doing it.
Harold
Yep, that sounds like a star dresser to me.
I've never had a wheel that ran out, right from the box, so I can't say how poorly they would true one. They are pretty good for getting the wheel opened up again, and they're pretty good at getting a flat surface once it gets grooved or marked.
I've tried the SiC dresser stick that you suggested. I may have been using too hard a touch on it, given your comments above.
As I said, I've never had a wheel that did not serve for at least reasonable grinding, right out of the box. What are the chances that there's just something wrong with the wheel(s) he mounted?
Jim
New wheels come with cheap plastic centers so its difficult to get them mounted concentric in the first place. Might not be a problem with small wheels but it doesn't take much on a 10 inch wheel to make the whole grinder vibrate. I think that lead use to be the prefered material for adapting the large hole in the grinding wheel to the smaller grinder shaft. Should I replace the cheap plastic spacers with something better?
I am using the standard flanges and blotters supplied with the wheels. I did not tighten the wheels very hard because they ususally tighten themselves up pretty tight. A 1.5HP motor accelerates pretty rapidly and the 10 inch wheels have a lot of mass so I suspect the motor tightened them up very tight by now.
I suspect I'm using too much pressure on the dressers and not the light touch that harold recommends.
This grinder was purchased used and the original 10 inch wheels were worn down to about 7 inchs. It ran fine with the old wheels.
Perhaps I should remove one wheel to reduce the vibration and dress the remaining wheel. After I get it running smoothly I can then add the second wheel and dress it.
chuck
I'd be the last person to discount the possibility, even with today's relatively good quality control. Weird things have been known to happen, soft sections, irregular thicknesses, none of which you'd expect. I've experienced wheels that ran terribly when installed, but turned out fine by simply dressing properly. One may have to go so far as to dress the sides to remove unwanted variations.
Harold
If you find the plastic permits the wheel to move about too much, that wouldn't be a bad idea, but use good sense. There are issues with the spacers that are critical, which explains why they're sloppy. They may not work perfectly that way, but they're safe. If you make your spacers too tight, and the bore of the wheel isn't at a perfect right angle to the wheel face, it's possible to fracture the wheel when you tighten the nuts. The snug fit would limit the wheel's ability to square with the flanges, which it will do, either by cracking the wheel, or compressing what ever is in the way.
On the outside chance that isn't happening, check how tightly they are held. If the nut had crud in the threads, it's possible it's not turning freely, so it feels tight but it isn't. Long shot, yes, but worth a look. Be certain that the nut runs freely, all the way until it hits the flange, otherwise you have no clue if you're tightening the wheel, or fighting the dirty thread. Your flanges should be imprinting the blotters. If you see signs of the wheel sliding about, with smudges on the blotters instead of imprints, you're not tight enough. The blotter should appear clean, but compressed.
It has been my experience that once a wheel starts bouncing, it encourages itself. Especially if you have no fixed reference, when you try to reduce the runout, all you do is make the wheel smaller. If you think you can simply hold the dresser of choice against the wheel and improve it, you'll be disappointed endlessly. You have to work smart at reducing the runout, which means to take it off a little at a time, such that the bounce of the wheel isn't transmitted into the dressing device. A light touch usually solves that riddle, along with taking a narrow approach. Don't use the flat face of a dressing stick, but a corner instead, where the amount in contact is minimized. Once you get a spot running true, you can usually move out and improve the immediate areas. It's not rocket science, but it does require a little thought. Surely you've already noticed how the bouncing wheel sets up a pattern that tends to repeat. You have to break the cycle.
Unless you ended up with some very poor quality wheels, there's no reason to not expect new wheels to run smoothly once dressed. If that's what it takes, then that's what you should do. Just be certain that all your efforts are when the wheels are at operating speed, and don't discount the possibility that the wheel sides may not be parallel. That would certainly yield a heavy side, and would be corrected only by dressing the sides of the wheel. I often dress the sides with a diamond, strictly for balance, right down to the blotter. It often improves how a wheel runs.
Harold
Well. I made long, stringy chips and did some experimentation with chip breaker grooves. Not much, though. A very light shallow groove worked quite well for most of what I was doing, so I didn't bother going any deeper. Once I have an better supply of tool steel I'll get a little more adventurous with my grinding. But a funny thing happened that'll let me try another strategy for manufacturing my flywheel. Previously, I was considering simply restarting the flywheel even though it would mean a hit to my grade. And today some folks were in the shop filming students engaged in hot, sweaty, unadulterated learning. At one point they asked me to swap places with another guy since I was short and he was tall. OK, I leave him with a simple command: don't move or cut anything; just look pretty. Of course, since he was one of the guys who almost never shows up he can't follow simple instructions; when I got back the hub was gone from my wheel--he also took the whole 1/8" in a single pass. At 1500 RPM. Cool! I get to restart it and try a better way of making it, I have free reign to mock the annoying twit, and I'm on TV! But the downside is that he savagely molested my carefully ground tool. (not the one I described in the other post--this is another tool that was prescribed by the teacher for this project. Looks like a grooving tool about 3/16" wide) I ground the tool back about 1/8" to get the evil off then let the teacher know I was starting over and it wasn't my fault. To face the piece I found that going from front to back with my tool (fancy one, with the rake angles and chip breaker stuff) didn't work too well. Came out nasty and teary and looked like hell and got hot. But I was smart (at least I thought I was smart) and rearranged my tooling. Instead of the normal mounting, I had the tool parallel with the axis of the lathe, ran the lathe backwards, and moved the cross feed from back to front. So, from the bit's POV, it was moving from right to left across the face of the part. Near-mirror finish and I could go a lot faster. First time in this class I've turned something to size +/-0.000 and perfectly flat all across. Stayed cool, too. Yay! Now I'm tempted to make the ass-end of that toolbit for left-to-right cutting so I can use a similar setup without having to run the lathe backwards--just in case I'm stuck with one that can't. So far for the wheel I've faced my piece to length and drilled and reamed a hole. Before the end of class I got part way through making a mandrel to hold it. It was a piece of scrap someone else left that was a disc with a tit poking out of the center on one side. I faced the wheel flat and turned that tit to my final size + about 0.030" so I'll be able to center it up next class. I still plan to drill, tap and split the tit for an expander screw. If I wind up having to remove the holder before I finish we have a four-jaw chuck on one lathe, so I can recenter it. I probably need to learn how to do that anyway. This is getting to be scarily fun--I was actually happy when I found out I had to do the wheel again. Damnit, I wish I could fit a lathe in my apartment.
[ ... ]
The simple way to do this is to grip both wheels, and try (without too much force) to advance one beyond the other, and then the other way. Too much force, and you wind up actually loosening the nut on whichever side is moving forwards, but light pressure should tell you whether one is slipping.
And also -- some flanges are rather poor shapes. Your machine ran well with the older wheels, so this probably is not the problem, but if it is, use your lathe to turn up a pair of flanges which are true on both sides. Be sure to relieve the face except for perhaps 1/4" or so at the outside diameter, which is where you want it to grip.
What I've done to true a wheel is to put a stop sleeve on a long-handled diamond dresser, (assuming that the tool rest has a clean outer edge), and adjust so it just barely takes something off the wheel, pass it back and forth until it stops spitting, then adjust it just a little deeper and repeat, until you get a clean wheel the whole way around. Repeat with the other wheel, and once both are balanced, you can then use your dressing stone to open up the wheels which are too smooth thanks to the diamond.
I've done this using parallel machinists' clamps, but I really should take the time to make a collar on the lathe for the task. It could even be a two-piece one which would let you make fine adjustments as to depth once you started truing.
Hmm ... to be sure that you get it all -- perhaps you could roll a well-inked stamp pad on the wheel's surface, and use that as a visual indication as to when it is all removed?
Then the flanges are probably good -- unless someone took time to try different orientations for the flanges until they got the best running?
Proably a good idea.
Another thing which can throw a wheel well off balance is if it was soaking in water or oil at one side or the other. This should not be the case with new wheels, but who knows what may have happened. If this is the case, the balance will slowly change as they dry out.
Good Luck, DoN.
Not sure I could do that with the big CI guards installed. Removing the guard would provide access to the outside, but still not sure about the inside. One wheel does have a bit of runout side to side.
chuck
You can. I started with a sherline and its about as portable as it gets. The 7x10 and 7x12 import lathes are popular too.
chuck
You'd have done yourself a service to have mentioned this early on. That's a guarantee of vibration. There are ways to dress the wheel, including turning it over to gain access to the opposite side if necessary. It's unlikely you'll get the wheel to run smoothly as long as it is not parallel.
Before you do any dressing, locate the wheel such that the inside runs in the best condition, so it may not need dressing. In a situation like this I like the internal flange to be integral with the arbor, so it causes the wheel to run true on one face. It makes correcting wheels much easier.
Get creative----with the side guard removed, use a piece of stock and a clamp of sorts to build a temporary work guide along the side of the wheel, adequate to support a diamond. Using a light touch, remove the highs from the wheel side. If it improves the operation, it will become noticeable as you dress, running smoother and smoother as you remove the thicker portion of the wheel.
Harold
PolyTech Forum website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.