My RF 31 and I haven't done too much damage to each other, and your advice has helped me to build some useful items. In particular, the D-shell panel from hell is ready to enter service. I currently have some mounting brackets taking up space in my shop, and hope to move on from them to a small transducer fixture.
One of the mounts brought my flycutter out of "retirement" and I decided to try one of the import brazed carbide bits that I bought a while back. With a properly "ground" tool, I was suddenly able to take a lot more metal in one cut than my own efforts allowed.
I have been reading some old threads and a couple of books, but sometimes wonder whether I am getting tricked by lathe-specific instructions?? Are there any good beginner resources on grinding flycutter tools?
One thought is to use HSS blanks and my $40 grinder (yell if I need something better) to try to make a good copy of the carbide tipped wonder. Some older threads suggest that one should expect to apply some pressure when grinding HSS. It sounds as though some of you hand-hold bits for grinding. Being a little cautious, I would prefer a vise grip, which I have also seen mentioned. Other recommendations are most welcome should anyone disagree.
What kinds of wheels do you suggest I buy? What should I get to dress them?
My first attempt at grinding a flycutter tool was to make it like a lathe tool. My second attempt to make it like what I *thought* a flycutter tool should look like. Both were miserable failures. Then I asked an old retired machinist how to grind one.... No more problems.
I handhold it after I wrap 3-4 turns of 3M high temperature electrical tape on one end for a handle.
A drill is an endmill is a lathe turning tool is a boring tool is a facing tool, etc.
You have clearance angles and rake angles. Together they make a wedge angle.
Clearance angles prevent the tool from rubbing the work. As your feed increases, so must your clearance angles. This is tied to the tensile strength of the material - softer materials have lower strength which means your tool and feed heavier without breaking. Your edge strength is reduced as your clearance increases.
Rake is ultimately material specific, but will impact the strength of your cutting tool as well. Steel ranges from slightly positive to slightly negative (including neutral). Aluminum would be slightly positive to very positive.
Tensile strength of steel is reasonably high (sometimes quite high), so you don't want too much clearance. You can't feed hard enough to make use of lots of clearance anyway. Rake is roughly neutral. Wedge angle will be kinda near, but not quite 90=BA. It will get closer to 90=BA for tough tool steels, and quite a bit smaller than 90=BA for mild steel.
Tensile strength of alumium is low, so use lots of clearance (high feeds). Rake is quite positive. Wedge angle will be quite "pointy".
Soft cast iron and brass are low/medium tensile, so a fair amount of clearnace, but not like aluminum. Rake is neutral, if not positive. Wedge angle will be between steel and aluminum.
Simple, but the above applies to all machining operations, regardless of the format. Aluminum drills have fast spirals for maximum rake. You can grind your own agressive clearnace. Drills for brass have very slow spirals for nearly neutral rake. Same for endmills, same for indexable tooling.
Nope! Not for offhand grinding, It makes the chore far too difficult, although the wheel will run very smoothly. Diamond dressing and offhand grinding to not go well together. The smooth surface cuts hot and slow, and does not serve the user well at all. As much as I don't like star type dressers, that's the best surface you can possibly achieve for such grinding, but you can achieve a surface that is very close by using a sintered silicon carbide dressing stick. I highly recommend one.
OK---more comments from me, this time not in haste.
Robin, who is working in the industry, has given you some very good guidelines on grinding toolbits. Truth is, there's very little difference between a lathe tool and a fly cutting tool, aside from front clearance. Because the tool rotates in a relatively small circle, front clearance must be extreme. Rake can be adjusted by grinding proper chip breakers, a very useful thing to know and understand.
When using a fly cutter, you have options of how the tool can be mounted. The cutting edge should be on center, even if you have to run the cutter in reverse. If you don't observe that rule, the front clearance on your tool will always be wrong for the application unless you grind it accordingly.
Yep, that's true, but it need not be excessive. And yes, your $40 grinder will work, but it likely has a terrible wheel for the purpose. I already commented earlier about dressing your wheel with diamond. DON'T DO IT! Diamond dressed wheels for offhand grinding are a bad idea. The exceedingly smooth wheel will not cut well, and will cut very hot, burning your tool instead of removing metal. Buy yourself a sintered silicon carbide dressing stick from one of the tool supply houses and learn to use it. They're cheap, less than $5, and will last you a life time in the hobby shop. The wheel so dressed will come close to rivaling the surface of a diamond dressed wheel in smoothness, yet still cut quite well. I mentioned earlier that the wheel will cut very best if dressed with a star dresser, but they aren't the easiest thing to use without wasting a lot of wheel, and putting a lot of dust in the air in your shop. They work by fracturing the grains by hammering, leaving dead sharp grain behind to do the grinding. It doesn't get better than that. I hate the damned things and don't even own one.
Unless you have a cutter grinder at your disposal, there IS NO OTHER WAY! You will never learn to grind toolbits if you use devices that limit your control. That may not make sense when you strike out, but it will when you try to hold sizes. Fact is, even a tool rest is a mistake, but it takes considerable experience before you can free-hand grind toolbits that way. I grind HSS toolbits exactly as I say-----and can grind pretty much any kind of configuration imaginable, including gear forms, and chip breakers. These, of course, are all single point tools, not multiple toothed cutters.
Dressing them has already been addressed, above. The wheels that will serve you best are aluminum oxide wheels, with a grit spread of 46 to 60. Don't go finer, although an 80 does a remarkable job of leaving a great finish. Problem is, they cut hot and slow. My personal choice is a Norton 38A60K8VBE. I don't necessarily stick to that designation----going harder (L or M) or even softer (H, I , or J), depending on what's on hand, and what the job demands. Soft wheels break down quicker, but cut faster and cooler. You'll eventually come to understand where you get the best performance for your personal grinding style. It's not the same for everyone.
Don't alter course on the bond. Vitrified wheels are the only choice for offhand grinding. You'll get the very best selection if you'll go out of your way to make an adapter with proper flanges that will accommodate wheels that run on surface grinders. Such wheels are 7" (or 8") x 1/2" x 1-1/4" arbor size. Observe all safety rules---ring the wheels before mounting them, and don't overdrive them. Don't stand in front of them when you spool up the grinder. Give it a few moments of top speed operation before trusting it. That rule applies every time you turn it, or ANY grinder, on. Also, don't under-drive the wheels.. Slow wheels behave soft and slough away quickly. They are rated at a given hardness at the proper speed, not below. Well worn wheels that are reduced in diameter run soft, but will firm right up if you can get the surface speed back up.
There's more, but this should give you some basics from which you can start.
Probably the easiest way to avoid burning fingertips while hand grinding HSS, is to grind numerous blanks, laying them down on a plate of steel (or uhlumium, loonimun) when they get uncomfortable to hold, then picking up a cool one and doing some grinding on that one until it gets extra-warm (not scorching). The room temperature plate will sink heat away from the blanks fairly quickly.
I don't care for the visegrip method because the jaws aren't really gripping the tool blank, since the jaws and the blank are both hardened materials. The jaws will hold fairly well in one direction, but not too well when rotated 90 degrees. The plier shape isn't symmetrical and is not inline with the blank's axis, and obtaining different grinding angles is a bit tedious and awkward.
A long while ago, I posted a link to one of my old webpages (gone now), a fairly easy method of making a broached holder for square HSS blanks. A section of round stock is machined to resemble a deep broach to accept the square HSS blank. I haven't seen any commercially-made tools/holders that are made for this purpose, so they would need to be made by the user AFAIK.
These holders have served me well for "grinding the hell" outta tool blanks, into the brown heat range without stopping to let them cool. A good 36 grit wheel will rip that shape down faster than you'd imagine, compared to holding the blanks with your fingers or other improvised method. The hloder makes it easy to keep the pressure on, while vigorously traversing the face of the wheel. The handle is always in line with the tool blank's axis, and makes handling of the holder easy at any single or compound angle.
The details that Harold describes will make stock removal nearly effortless. I have and use a diamond dressers, and also the dressing "stone" for cleaning/refacing the wheel face at regular intervals.
The basic steps of machining the holder are
Use 1/2" round stock 8-12" long for 5/16" blanks, 5/8" for 3/8" blanks
With a lathe or mill, cut a flat along the stock, creating a sort-of D shape, a little longer than the length of new tool blanks. Plan your cuts to keep the square in the center of the diameter.
Cut into the flat face with an endmill (lathe or mill), to create the broached recess, the same square dimension of the tool blank.. 5/16",
3/8" etc (and the length of the recess about 1/2" longer than the length of new tool blanks). Remove a little more in depth than the top of the tool blank's top side will be.
Replace the metal that was cut away to produce the flat with a section of flat stock and weld in place at both ends, but just the ends.
Rough-in the round shape of the round stock (with a grinder and/or file), then finish turning the welded-in section round, to match the round stock's diameter. Cut off the weld at the open end.
This results in a deep broach in a round handle, with one side of the broach being the piece that was welded in to replace the material that was milled away.
The trick was to keep a small gap (about .004") between the flat that was milled away and the flat stock that was added, so that the tool blank can be securely clamped in the broach with as much of the blank as you would want sticking out. Picture a collet for holding square stock, but only one side slitted and floating. The way I attained the small gap was to place pieces of shim stock between the flat piece of added stock and the machined flat, for the welding step.
A locking shaft collar can be slid over the end of broach area for clamping, or a square block that has been drilled and slitted (with provisions for a clamping screw). The square block works well when used on the grinder's tool rest, since the flat bottom side keeps a reference while the tool blank is ground, allowing for fine rotational adjustments to be made (to adjust grinding angles in relatively fine increments while referencing the tool rest).
When you become proficient at grinding cutting tools (not bits), you will have earned the right to refer to yourself as a Grindor
No self-respecting operator would call himself a grinder..
A note about sharpening cutting tools on belt sander/grinders. The cloth-backed belt will create a crown in the ground area, creating a false angle (an arc instad of a flat facet). If you're good at visualization, sharpen the tool upside-down, so the arc isn't in the immediate area of the cutting edges. Otherwise, build a belt grinder that runs the belt backwards, to sharpen them right-side up. Protect yourself from the sparks and debris.
bill, why spend the time and effort making your own flycutter inserts when they are so readily available and cheap! i use AR5 replaceable carbide tipped fly-cutter arms and have found them to work really well, and only around $10 a piece.
I've regenerated the webpage contents (pichers 'n stuff) if anyone was interested in making a holder for grinding cutting tools, but just didn't feel like saying WTF are ya talkin about?
That's certainly a possibility, and it was an even cheaper brazed carbide toolbit that showed me what I was missing. However, the gang here tells me (and they have a very good track record) that there is an advantage to being able to customize angles/shape for a given job. There is also the opportunity to grind/sharpen tools from $1 blanks vs. being stuck if something more elaborate breaks.
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