Grinding wheels and HSS

This is where bits of wisdom will be stored, a frequently asked question section with answers.

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MikeC
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Post by MikeC » Tue Jan 16, 2007 12:37 am

Thanks Harold. My T&C grinder hes variable speeds (change pulleys) so I can get it humming for this 6"er. On the parting wheel.. what exactly am I looking for? Surely you don't mean a fiber reinforced zizz wheel like we use in a die grinder?

As for the exact use of this 6" wheel, it will be easier to show a picture than to try to explain it, but I'll try. This is not a deep slot, but the back angle on either side of a 2 flute center cutting endmill that forms the split point, if you will. It appears to me, just looking at it and trying to figure how it was originally made, to have been made with a rather wide large diameter wheel instead of a saw blade like cut.

Harold_V
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Post by Harold_V » Tue Jan 16, 2007 1:08 am

tornitore45 wrote:Harold, you mention that Si Carbide is not suitable for ferrous because the SiC dissolve in the steel at high temperature. What happen then?
Needless to say, I'm one of those kinds that rarely takes anyone's word for anything. I am, by nature, very curious, and have a reputation for being very hard headed. I questioned what I was taught, but I had the opportunity to experiment on a surface grinder, which was an instant AH HA moment. The information is deadly accurate.

If you're familiar with grinding, you know that wheels can fail to cut for various reasons, most of which are very apparent. However, it's not always clear when a wheel is dull, or loaded.

A silicon wheel that has been applied to steel loses its ability to grind almost instantly, and displays the same qualities of each of those conditions. What has happened is the silicon carbide has been absorbed into the steel, rounding the abrasive such that it no longer has cutting edges. Grinding wheels are, in a sense, milling cutters with a huge number of teeth. If these teeth are dulled, they cease to cut, or cut under considerable protest, with lots of heat. Such a wheel requires considerably more pressure to force the cut, if it cuts at all. All in all, the wheel experiences a total collapse in performance. You end up with a glazed surface, often heat checked, and can have a series of waves produced. That's common, considering the wheel often shits ever so slightly when it's under poor condtions.

There may or may not be harm done. I've yet to read where the material suffers any reportable changes in structure, but a wheel that is introduced to a part on a surface grinder has a serious chance of dislodging the part from the chuck from the increased pressure. That can provide some interesting moments, particularly if the part is thrown clear.

My limited experiment resulted in a wheel that left a terrible finish, and wouldn't remove much material. Repeated dressing allowed for little grinding before the same condition existed. It's actually a good thing to experience so you can see and understand the ramifications of making a bad choice.
What about using Sic for a final touch up where hardly any heat is generated.
Due to surface speed, there's almost always enough heat generated to cause dissolution. That the part doesn't heat past comfort in your hand by no means indicates that the point of contact is cool enough.

Silicon carbide is used extensively for honing, and also for lapping. In both cases, surface speed is so low that the problem doesn't exist. If you can duplicate that condition, there's absolutely no reason why you can't, or shouldn't, use silicon carbide for steel. Fact is, it will outlast aluminum oxide by a serious margin.
I usually rough my HSS with a SiO weel and then give a mirror finish with the SiC weel. Is that so bad?
In my opinion, the only thing wrong would be that if the wheel does experience dissolution, the condition encourages more heat, which encourages more dissolution. The wheel will provide the illusion of "polishing" your tool, but it likely comes with a degree of edge rounding. You really want a wheel to be free cutting, and that option is readily lost when you use the wrong wheel. I wouldn't do it, and you may be pleasantly surprised to find your tools cut better if you didn't. It might be worth a try.

If, by chance, you have a slow speed device, there's nothing wrong with your process, although I'd encourage you to do all your grinding totally free hand, without the use of guides or work rests. Watch for a post in the future that addresses the idea. I'll try to remember to explain how I was introduced to the system, under protest, long after I became a journeyman machinist.

Harold

Harold_V
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Post by Harold_V » Tue Jan 16, 2007 1:29 am

MikeC wrote:Thanks Harold. My T&C grinder hes variable speeds (change pulleys) so I can get it humming for this 6"er.
Of course! My comment was based on the use of your wheels with the typical 6" bench grinder. That would be on the slow side, although with a J wheel, they would still perform relatively well for offhand grinding of toolbits.
On the parting wheel.. what exactly am I looking for? Surely you don't mean a fiber reinforced zizz wheel like we use in a die grinder?
No-----the wheels of which I speak do not have any reinforcement, and are available in very narrow widths, for sure 1/16", and could be even narrower. They have a 1¼" bore. They are available in fairly large diameter, at least 6", perhaps larger. It may require you to check with a supplier of wheels that has a large inventory----but I know they're out there. I haven't purchased one in well over 25 years, so I have little to offer in the way of information. You should be able to find them included with other parting wheels-----just look for thin wheels that are resinoid bonded and have no reinforcement.

For your information, you can usually part a shank, 1" diameter, heat treated, in something like 15 seconds with such a wheel. The shank should be spun while being parted, which can be accomplished by hand with a small crank. These wheels are nothing short of magic.
As for the exact use of this 6" wheel, it will be easier to show a picture than to try to explain it, but I'll try. <snip balance>


The operation you spoke of is not gashing. Gashing is the process of removing the center portion of multi-toothed end mills to prepare for resharpening. They are not center cutting when so ground. That explains why I was at a loss at your wheel selection.

The grind you intend to make can be accomplished with a straight wheel, with the periphery, no wheel thinning required, but side dressing desirable. Stops should be set to control center. There is more than one way to make a setup for this operation, and your wheel is an excellent choice, regardless of which one is chosen. This operation may be an excellent opportunity for you to understand the value of hand dressing the wheel as opposed to diamond dressing.

Harold

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BadDog
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Post by BadDog » Tue Jan 16, 2007 4:19 am

Thank you Harold, I am very much interested in the upcoming posts on the matter. :D

I’m also interested in the hand grinding techniques, but lack a machine suitable to carry out the operation with much success. My shop is full to the point of bursting, far past the point of inconvenience. My total arsenal is unlikely to include more grinding fixtures than the current ChiCom 6” POS grinder that serves mostly as a wire brush platform these days (partly due to lack of power), several belt grinders of various uses, and the surface grinder.

One choice is to upgrade the ChiCom to a better/larger grinder, which is something I would like to do. But I can’t sacrifice the multi-use aspect to place only a “cutter grinder” of the common Baldor variety.

Another is to multi-use the SG. It already mounts a 7x1-1/4 wheel, and just as you suggest, offers a great variety of stones as well as the hub mount system for easy/quick changes with minimal setup/truing requited (assuming multiple hubs). It also has a balanced 3 phase motor and VFD for speed control as well as a premium spindle. Perhaps a modified guard would allow use as a standard grinder? Thought the table would be very much in the way.

I’ve also considered another custom build grinding station that would solve some of this problem, but at my current rate of progress (or lack there of) it is not worth consideration as affecting anything in the somewhat near future. <sigh>

Anyway, thanks for all your for me and all the others who are benefiting from your effort. I included this ramble just as a sort of idea where my thoughts are, feel free to comment (or not) on any foolishness or dead ends you care to flush out. I am not easily offended. :D
Russ
Master Floor Sweeper

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tornitore45
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Post by tornitore45 » Tue Jan 16, 2007 9:46 am

Re. clarifications on problems using SiC on Steel.

Harold, your answer is the kind of deep dive insight you do not find easily.
After digesting you explanations, I can relate now.
I do get a nice polish, but it does feel like there is more rubbing than grinding, particularly if dressing was not fresh.
I have a junk grinder 5" at 1750RPM which deliver perhaps 2200SFM under load.
The poor results on the SiO weel on the left, lead me to the SiC on the right to get a seemingly decent surface, it probably helped the SiC operation, that the speed is soo low. Still the plan is to get a half decent 8" grinder.

The need to reach 6000SFM also explains why I could hardly find any 5" weels on the market, no single phase induction motor could ever spin them fast enough.

Keep spreading the knowledge.

Mauro
Mauro Gaetano
in Austin TX

dirty old man
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Post by dirty old man » Tue Jan 16, 2007 10:39 am

Harold V, the post here about tool grinding should be helpful to newbies and us old farts!
The past 40+ yrs. in the trade have taught me methods only slightly different than yours for hand grinding tool bits.
I use the tool rest, in close to the wheel for safety, preventing the tool bit or your fingers from being inadvertedly pulled down into the wheel inside the guard.
But I don't rest the tool on the rest. I use the rest to steady the edge of my hand, and the fingers of that hand to hold the tool bit at the proper attitude towards the wheel, up above the rest. The fingers on the other hand serve to help hold the tool bit and apply pressure towards the wheel.
Dave

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Victor_R
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Post by Victor_R » Tue Jan 16, 2007 1:48 pm

Well, one brand new modern computer later and I'm back on line. (motherboard died) I've been doing what dirty old Dave (haha) does for years when grinding tools. I use the tool rest as a finger rest well below center. Without it I tend to shake a little. I'm also a great believer in using those little 1 inch wide belt sander/grinders for touching up things. They work great.

Harold, your written dissertations were a fun read and well done. You must have some bad weather up there that's keeping you inside at the computer. It would have taken me many long hours to write something like that. I look forward to the next one.

Thanks, Victor
The machines are gaining ground upon us; day by day we are becoming more subservient to them ~ Samuel Butler (1863)

tag
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Post by tag » Sun Jan 21, 2007 1:03 am

Harold

I just want to send a quick thanks for taking the time to write the tool grinding posts. They are especially informational to people such as myself who are just getting into this as a hobby.

Thanks again
Tom

Harold_V
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Post by Harold_V » Sun Jan 21, 2007 1:48 am

dirty old man wrote:I use the rest to steady the edge of my hand, and the fingers of that hand to hold the tool bit at the proper attitude towards the wheel, up above the rest. The fingers on the other hand serve to help hold the tool bit and apply pressure towards the wheel.
Dave
Dave,

That's the exact process I used (ten years in the trade at that point) when I was forced to using the system I now use, one without a rest. I was hired into a shop that had a solitary grinder mounted on a steel pole, one of the roof supports in the shop. The grinder was mounted about chest height. I hated it at first, but quickly came to see its benefits, which were grinding most any form without the rest getting in the way. you can grind farther down on the wheel when there's no rest in the way, so you can see what you're grinding. You quickly learn to use the wheel as a guide, which works very well if it isn't bouncing.

As to the guard, I made my grinder, specifically for this kind of grinding. While you could get caught between the guard and wheel, it's far enough down around the wheel that it's never been a problem, and I've used the grinder since '67, so it's had a good shakedown. I'm also steady as a rock when I'm grinding tools. Don't know how that's going to work as I continue to age.

This system is particularly useful in grinding chip breakers, which I've done as long as I can remember. I'll probably repeat much of this when I post on the grinder in the near future. It's valuable enough that everyone should be exposed to it. Those with talent and a yearning to grind better tools should give it a go before dismissing it. It's really that good!

Harold

Harold_V
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Post by Harold_V » Sun Jan 21, 2007 1:52 am

I'd like to extend a heartfelt thanks to all that have read and commented on my recent posts. It's nice to know it's helping those that have an interest in bettering their skills.

Frankly, I don't know what any of us would do without having the benefit of the knowledge of those that went before us passed on to us. Much of what I promote is not of my making, it was passed on to me by my peers and tutors---and has been very instrumental in my success on machines. I'm pleased to be able to pass it along to others.

Harold

Gunbuilder
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It is we who are indebted to you

Post by Gunbuilder » Sun Jan 21, 2007 12:36 pm

Harold_V wrote:I'd like to extend a heartfelt thanks to all that have read and commented on my recent posts. It's nice to know it's helping those that have an interest in bettering their skills.

Frankly, I don't know what any of us would do without having the benefit of the knowledge of those that went before us passed on to us. Much of what I promote is not of my making, it was passed on to me by my peers and tutors---and has been very instrumental in my success on machines. I'm pleased to be able to pass it along to others.

Harold
Harold, on behalf of all of us, we thank you! Thank you for sharing the knowledge and experience you have accumulated on this subject.

I too had pursued the indexable carbide tools for my 14" Southbend. The other day after reading your post on chip breakers. I carved a decent HSS tool, put it in the indexable post and was fairly pleased with the results. With more practice I might be able to keep the knowledge you passed on in your post.

Thank you once again,

Paul

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BadDog
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Post by BadDog » Sun Jan 21, 2007 2:15 pm

Thing is, it's not everyone who acquires the skills that will take the time to try to pass them on. Particularly not to (almost) complete strangers who are unlikely to be able to even return the favor. Seems like most folks these days are much more inclined to keep their "secrets" in an attempt to shore up their own weak self esteem by flaunting that they can do something better than another. Your efforts have been much appreciated by all, and at least for me, really helped bring together many things I was at least aware of, and slowly starting to understand individually, but had not quite put together effectively yet. I’ve ground bits before, but not nearly as effectively OR as confidently as I have using just what I read in your recent several posts. I eagerly await the additional installments you’ve mentioned.

Thank you...
Russ
Master Floor Sweeper

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