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Burners 101


Mikey98118

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No sweat Frosty.

Anyway, it has opened up the discussion; and that may give me a better handle on the issue than I have at present. The Greeks had it right about the nature of truth. Nevertheless, I keep reaching for it. Thankfully, this is only a hobby :rolleyes:

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Sanding drums (can be the fast way to enlarge inside diameters): they are also called “bands” and “sleeves.” Sanding drums can work faster than solid grinding stones, but 1/4” diameter drums often slip on their rubber headed mandrels; a dab of gasket seal or thread-locker might ease this problem. So, why do some 1/4” sleeves slip; are some of better quality than others?  Obviously, but the problem is that some mandrels are better than others. The smaller the sleeve diameter, the harder it is to find a good enough mandrel for it; one answer for this problem is nut lock drum mandrels, which can apply a lot more force against the sleeve than screw top mandrels: most of them, but not all, have ¼” shanks.

A set of lock nut sanding mandrels with 1/8” shanks, along with aluminum oxide sleeves are available from Homedepot:     

 

Nearly all sanding drums, whether sold in accessories kits, individually, or along with a rotary tool, are sandpaper that is covered with aluminum oxide. Sleeves meant for use on ferrous metals are a harder form of aluminum oxide (usually charcoal grey), on cloth, but some are zirconia, or even harder synthetic ceramic oxide grit). You aren’t likely to find them in accessories kits. but finish off the cheaper drums before buying the more expensive variety as replacements. When you’re ready for the good stuff, forget about looking all over the Net for them. Go straight to McMaster-Carr, and input “sanding sleeves” in their search engine. Google searches will give different results when you input their various names:

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Chainsaw rotary stones come is 5/32”, 3/16” diameters (the 7/32” size are too large to be much use), with 7/8” long heads; these are quite handy for grinding inside of ¼” burner tubes, and cleaning up air opening cuts. The smaller a rotary stone’s diameter the easier it is to break; especially in a rotary tool with run-out. If you can’t deal with that, there are tungsten carbide burrs that won’t break so easily; of, course a tool that is heavily vibrating from a run-out problem will fling them about dangerously, but at least it will point out that the stones weren’t the problem :rolleyes:

 

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Solid tungsten carbide versus diamond coated rotary burrs

1/8” Solid carbide rotary burrs used to be quite expensive, but are bargains these days; why? Because diamond coated burrs are even lower priced. Diamond coated accessories are almost as fast acting as double cut tungsten carbide, but are much smoother to use; for half the price, or less. The larger the accessory’s head diameter the greater the advantage diamond coating enjoys over solid carbide; which still leaves real advantage with solid carbide burrs around 1/8” diameter. However, carbide burrs fling needle sharp debris everywhere (the larger the burr, the faster their speed, so the nastier the problem gets); diamond coated burrs just fling ordinary dust particles.

    Tungsten carbide burrs are more likely to create kickback than resin bonded stones or diamond coated burrs, of the same diameters; which is why solid carbide burrs tend to leave uneven surfaces behind. As the burr diameter increases, so does this tendency, along with the likelihood of kickback violently flinging the tool about.

    “Solid Tungsten carbide” includes the shank in 1/8” size; this precludes all manner of problems that cheaper carbide burrs, that are silver brazed to a steel shank, are prone to; like cutting heads that were brazed out of true axial alignment with the shank; this causes a dangerous wobble. The shanks themselves may bend easily, or shatter if the choice of their steel alloy or tempering is wrong.

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Tungsten carbide rotary tool burrs

Tungsten carbide is 9 on the Mohs scale, but is much tougher than any crystal, including diamond. 1/8” Solid carbide rotary burrs used to be quite expensive, but are bargains these days; why? Because diamond coated burrs are even lower priced. Diamond coated accessories are are considerably slower than double cut tungsten carbide, but are much smoother to use, for half the price, or less. The larger the accessory’s head diameter the greater the advantage diamond coating enjoys over solid carbide; which still leaves real advantage with solid carbide burrs around 1/8” diameter. However, carbide burrs fling needle sharp debris everywhere (the larger the burr, the faster their speed, so the nastier the problem gets); diamond coated burrs just fling ordinary dust particles.

    Double cut carbide burrs are far more likely to create kickback than resin bonded stones or diamond coated burrs, of the same diameters; which is why solid carbide burrs tend to leave uneven surfaces behind. As the burr diameter increases, so does this tendency, along with the likelihood of kickback violently flinging the tool about.

    “Solid Tungsten carbide” includes the shank in 1/8” size; this precludes all manner of problems that cheaper carbide burrs, that are silver brazed to such small diameter shanks, are prone to; like cutting heads that were brazed out of true axial alignment with the shank; this causes a dangerous wobble. The shanks themselves may bend easily, or shatter if the choice of their steel alloy or tempering is wrong.

    Single cut carbide burrs come in two types; large grooves (for use on brass and aluminum), and narrow grooves (for use on ferrous metals); these are slower working then double cut burrs, but far less inclined to kickback, and smoother acting. While not so quick as double cut, single groove carbide burrs also work faster than abrasive stones or diamond coated burrs, but are much more controllable than double cut burrs; which are the fastest acting, but easiest to get into trouble with.

 

Note: Ads that start out claiming their single or double cut burrs to be tungsten carbide, and then shift to describing them as “tungsten steel” are actually selling regular high speed steel burrs; they are no good on stainless steel parts. With some ads, you have to look in the product description pop-up, to find out the truth.

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Rubber cushioned abrasive burrs and wheels are filled with aluminum oxide/silicon carbide, or with emery, grit—never diamond grit; they do a better job of smoothing contours and corners than sanding bands, but are faster and simpler to use than polishing compounds. Take care not to accidentally purchase straight rubber burrs, which require polishing compound for use.  Red, pink, or brown colored rubber burrs use 80 grit; green have 240 grit; blue have 600 grit; black is usually straight rubber, without grit (meant for use with polishing compounds). There are a few exceptions, where black is used to denote a different grit size; this is found in some rubber cushioned wheels, and in kits with a combination of wheels and cylinders, which are mounted on separate mandrels. The wheels are 22mm (7/8”) diameters; they should be spun between 8,000 to 15,000 RPM; 15,000 RPM for the cylinders.

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Surface Cutting

 

If you stop the disc during a plunge cut, or a chop saw blade before the cut is finished, more often than not, doing so will cause kickback. The opposite is true when surface cutting through sheet metal products, like pipe and tubing.

    Those OEMs (like Dremel Tools) who bother with thorough safety tips in their rotary tool instruction manuals, all advise the operator to run the cutoff disc back and forth on the part surface, gradually deepening a groove at the cut line, until the disc begins to break through the groove, which is then called the “kerf.” Unlike chop sawing or plunge cutting through thick parts, the operator is supposed to bring the disc to a halt before exiting the kerf; it is dissimilar to other processes, because your disc isn’t deeply buried in the part. There is very little material for the disc to “walk up,” creating an opportunity for kickback, as the disc stops. Also, the numerous tiny grit edges don’t have anything like the tendency to grab unto stock that the teeth of circular blades do. Most kickback from resin bonded cutting discs come from the sides of their discs binding against the kerf. So, surface cutting creates a unique situation, where stopping the disc before removing it from the kerf is safer than removing the disc while it is still in motion.

    Die grinders are treated the same as rotary tools for surface cutting (my own description for the technique).

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(  Try to only move the disc counter to the direction that friction inclines it to “walk” along the part, while cutting in the kerf; this is to help prevent you allowing the disc to bump against the end of your kerf; always ease into metal contact, to prevent kickbacks.

    After you finish all cuts and remove unwanted sections, then start grinding back to the scribed or inked lines with a small stone wheel, or diamond disc.

    Do not use fiberglass reinforced cutoff discs for grinding; it dangerously weakens them; then, the same fiberglass reinforcement that helps protect against torsional forces, ensures that flung sections will be larger, and will therefore hit harder!

    On the other hand, small (22mm; 7/8” or less) diameter diamond coated discs (which are slower cutting than resin bonded discs) excel at grinding tasks. Once your coated disc loses the diamond grit from its narrow edge, keep it around for grinding; such as sharpening high-speed steel, tungsten carbide, and silicon carbide surfaces. Diamond coated cutoff discs excel at sharpening drill bits and saw teeth; they are perfect for reshaping and reducing silicon carbide grinding wheels.

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    After you finish all cuts and remove unwanted sections, then start grinding back to the scribe lines or inked lines with a small stone wheel, or diamond disc.

    Do not use fiberglass reinforced cutoff discs for grinding; it dangerously weakens them; then, the same fiberglass reinforcement that helps protect against torsional forces, ensures that flung sections will be larger, and will therefore hit harder!

    On the other hand, small (22mm; 7/8” or less) diameter diamond coated discs (which are slower cutting than resin bonded discs) excel at grinding tasks. Once your coated disc loses the diamond grit from its narrow edge, keep it around for grinding; such as sharpening high-speed steel, tungsten carbide, and silicon carbide surfaces. Diamond coated cutoff discs excel at sharpening drill bits and saw teeth; they are perfect for reshaping and reducing silicon carbide grinding wheels.

EZ lock mandrel and cutoff disks are the safest way for a beginner to surface cut on curved surfaces, with a rotary tool; they are more expensive than generic cutoff discs, which run in standard mandrels, but considerably easier for a newbie to deal with, for the work needed to build a couple of burners. By the time you use up the disks in one their mandrel and disk kits, you should be well enough acquainted with rotary cutting to take advantage of the more economic offers for regular discs and mandrels. You will still find yourself reverting to the EZ lock system for tricky cutting jobs. The special discs that come with this system are 1-1/2” diameters. It is wise to save the last 1” of each disc, rather than wearing them down completely. The smaller discs are very handy for making interior cuts in small parts.

    Begin by inserting the EZ lock mandrel all the way into the collet nut on the tool’s spindle, and then tighten the nut. To mount a disk, push the plastic part of the head down against its spring, dropping a disk past the mandrel’s bow tie shaped end piece, and then turning it ninety degrees, to lock it in place.

    You can buy the discs and mandrel in kit form online, and from most large hardware stores. The spring and locking mechanism are what makes this system unique. It eliminates the usual locking screw, so that grinding and sanding wheels can be used nearly parallel to part surfaces, without interference from a protruding screw head. The disc is positively locked, because there is no screw to loosen from vibration, allowing the disc to spin on the mandrel. But most important of all, the spring allows the disc to move out of alignment with the kerf, without creating kickbacks, by nearly eliminating torsional forces; you can order them online, and they are available from numerous hardware stores.

 

Separating discs are standard jeweler’s thin (0.025” thick) 1” and smaller diameter friction cutoff discs, which come as part of most accessory kits. They are too brittle to be practical for most steel cutting tasks, but they are a safer and surer way to cut through the last 1/8” next to a corner hole, than using a larger disc. Do not be discouraged when several of them shatter, one after another; they are helping with your learning curve; at the small loss of accessories of little value to anyone but a jeweler.

 

Dremel #420 Cut-off discs are 15/16 " (23.8 mm) diameter, by 0.040" (1.0 mm) thickness, and are rated to 35,000 RPM; they are sold in twenty discs kits for $4.97 through Amazon.com; they are not fiberglass reinforced, but are much more durable in steel cutting than standard 0.025" (0.617 mm) thick jewelers’ discs; they have added safety over fiberglass reinforced discs during kickback, and enhanced control when cutting next to inside corners. These discs are meant for cutting metals; do not use their sides for grinding. The smaller the air opening the handier these discs become; they are as safe as you can get, and one kit should easily provide enough discs for even a novice to build two burners.

 

Disc mandrels: You don’t want to employ just any disc mandrel for steel cutting. The standard jeweler’s mandrel, which only has a 1/16” standard machine-screw head, was designed for making very short cuts in soft alloys, using 1” and smaller discs; not for making extended cuts in steel with 1-1/4” to 1-1/2” discs. There are special mandrels with 1/16”screws that have oversize screw heads, threading into oversize mandrel faces, and similar mandrels for 1/8” and 1/4” arbor holes; these far outperform the minimal screw head variety; you can find them offered through eBay, Amazon.com, and through most jeweler’s supply houses ( input “SEINC rotary tool mandrel” to find them quickly); these mandrels are excellent for spinning the 1-1/4” diameter fiberglass reinforced aluminum oxide cutoff discs, which are handiest for cutting out rectangular air openings on most tube burners.

 

Note: Poorly finished mandrels, provided along with some cutting discs in some ads, can cause cutoff discs and grinding wheels to wobble. This is a common problem that is seldom correctly diagnosed, because customer complaints incorrectly blame the discs. But what is actually happening is that the mandrel’s forward edge is out of true right angles to the shank’s axial center. Or, one (or both) of the flat washers provided with cheap mandrels aren’t perfectly flat. Circular motion on fine sandpaper can flatten washer surfaces, and the mandrel can be spun in your rotary tool, while its forward face is quickly trued up with a silicon carbide dressing stone, or diamond coated cutoff disc.

 

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On 10/4/2021 at 12:44 PM, Mikey98118 said:

Note: Ads that start out claiming their single or double cut burrs to be tungsten carbide, and then shift to describing them as “tungsten steel” are actually selling regular high speed steel burrs; they are no good on stainless steel parts. With some ads, you have to look in the product description pop-up, to find out the truth.

Well, now I get to eat these words. It turns out that tungsten steel is better than high speed steel for micro drill bits and rotary burrs.

Tungsten Steel: Ads that start out claiming their single or double cut burrs to be tungsten carbide, and then shift to describing them as “tungsten steel” are actually selling something better high speed steel burrs; they are aren’t as good as tungsten carbide on stainless steel parts. Unlike high speed steel, tungsten steel will keep its temper up to 932 F; not as good as cobalt’s red hardness, but not bad. Solid tungsten carbide rotary burrs only come in 1/8” diameter cutting surfaces. Larger diameter cutting surfaces are only available with brazed heads on steel shanks; these often have run-out. You can get solid tungsten steel burrs with head sections larger than 1/8” diameter; making an end run around run-out problems. Tungsten steel is also tougher than high speed steel. All things considered, they are worthwhile, if for from wonderful.

That was meant to read "...if far from wonderful."

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Layout Tools and Techniques

 

Side air entrances on high-speed tube burners should consist of three equally spaced rectangular openings cut into their mixing tubes. Each opening has two longitudinal sides, so you will need six equally spaced lines for three air openings. Hex head bolts can be found down at your local hardware store, with the right size to match up with your pipe or tube’s outside diameter. A buildup of electrical tape allows the bolt to be centered snugly within the cylinder.

    ½” by ½” metal angle can be purchased from online metal providers, becoming perfect layout tools to extend ink dots at cylinder’s end (next to the bolt’s hex points), into perfect longitudinal lines. Sliding choke sleeves become layout tools for the circular lines at the forward and rear edges of the air entrances.

    While ink lines are sufficient for those who are practiced at surface cutting into cylindrical surfaces, small drilled holes just inside of each inside corner helps to keep your cutting work tidy. Scribe lines are better than inked lines, and bluing improves the view of scribed lines on stainless steel surfaces, even more. How much care you want to put into the layout is up to you, but I recommend at least drilling holes next to the inside corners, as starting and stopping points, even after you get to feeling comfortable with this task. I’ve been making this burner design for more than twenty years, and they still help me.

    Getting those holes placed where you want them, starts with your choice of punch. Larger drill bits require center punches, but even then, the center punch follows a single blow from a prick punch, if you want accuracy. Never use more than a single blow with either type of punch, as their very hard points may shatter, if more than one blow is delivered. A single blow from a center punch can safely follow a single blow from a prick punch, only because of their differing point geometry.

    The micro holes in small burners only need a prick punch, but you still have choices to make. First, what kind of punch: manual or automatic? Automatic punches are easiest to place and keep exactly where you want them, while indenting a point for your drill bit. Unfortunately, no matter how much you’re prepared to pay for them, you can’t buy a reliable automatic punch;

great idea, but poor follow through. If you pay for the best manual punch you can buy, and if you treat it carefully (single blows only), it will perform reliably; that’s as good as things get.

    The difference between a center punch and a prick punch isn’t a matter of size. Center punches have ninety-degree points. Prick punches have sixty-degree points. Which brings us right back to size. The smaller your punch the better, because the smaller the punch the easier it is to see where its point is resting.  A Starrett 816A prick punch (4" long, with a 5/64" base diameter on its tapered point) is more than adequate for this work.  

 

 

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Below are some examples of rotary tools that are still worth what you must pay for them, despite all the price gouging going on this year

The Black and Decker RTX-6 three speed rotary tool is smaller and more ergonomic than most others, but has a 240-watt brushless motor. Most rotary tools only have 160-watt motors (Dremel’s very expensive “top of the line” models are an underwhelming 175 watts. The RTX-6 is quieter and smoother running than most of the rest, with more torque and less heat build-up than brushed motors; its speed can be switched between twelve thousand, twenty-four thousand, and thirty thousand RPM.

    The spindle on this tool is offset toward the housing’s bottom side, rather than centrally, providing cutoff discs better access on flat surfaces. The plastic housing is also deliberately sculpted around it neck area, to more easily accommodate holding this tool in the pen-style position for engraving, carving, and drilling work. The power switch’s sliding lever is located top and forward on the tool’s neck; it has an especially smooth action (most of them are stiff). This tool’s spindle lock should be handled carefully; if you break it, the tool must be sent to Black and Decker for repair (have fun with that).

   Look around for the best prices (usually on Amazon.com) for this tool; there’s some spread.

    While these are high quality tools in general, their speed control circuits are vulnerable; don’t employ them unless you like buying the same tool frequently. Why would the speed control burn out so easily on high quality equipment? Because the RTX-6 draws more amps than weaker tools, so there is more energy available to fry that poor defenseless little circuit. But brushless motors have less heat build-up in the first place, right? That is a separate issue from over stressing a speed control circuit; it is no more a part of the motor than the power switch is.

    Be sure that the external speed controller you choose really is meant for brushless motors. Why put up with the need to deal with a brushless speed controller? This tool is more powerful than the rest of the pack precisely because of what kind of motor it has; also, BLDC motors last longer than brushed motors, and don’t need to have carbon brushes replaced. So, are brushless motors really all that superior? The best (as in big $$$) battery operated rotary tools are now coming out with brushless motors, to help solve their infamous lack of power.

 

Chicago Electric markets a low-priced rotary tool (model #68696) with a few accessories (that don’ t get kindly reviews); it’s louder than I like, and larger than the Black and Decker; it only produces average torque, with variable speeds from 8,000 to 35,000 RPM from its 160-watt brushed motor. This is a generous speed range in the low end, which is important for micro drilling. My tool has held up pretty well, with occasional use; some of them don’t. Heavy vibration is typical in this tool; they are sold through Harbor Freight Tools stores, and online.

    The power switch is a rocker type, located on the bottom rear of its housing, in the pistol grip. You can sand down the rear section of its plastic collar, where it surrounds the rocker switch. No doubt its collar helps physically support it, and is also meant to help prevent the switch from being accidentally turned on (if the tool is laid down on table clutter); but it interferes with smooth stops, which are desirable for safe surface cutting operations.

    If the plastic collar’s top is sanded or filed away on a slope, starting from its center, and increasing toward the rear of the switch (its “off” side), the collar can still mostly serve its function. But there will be far less interference to quick stops, using the fourth finger. You are marginally increasing the risk of accidentally turning the tool on, for added speed in emergency stops, with reduced risk of jarring a running tool, at a critical moment during surface cutting operations. The tiny risk is further reduced by the plastic body’s shape; the pistol grip tends to force the tool onto one side or the other; further sheltering the switch.    

    Harbor Freight Tools has an excellent return policy, which altering the tool will void; make sure your tool isn’t a lemon before touching that collar.

    If the speed control circuit on one of the best rotary tool is its Achilles heel, how long would you expect this one to last? Employ a router speed controller, or leave the tool on its maximum setting.

    So, why not discuss other cheap rotary tools? Harbor Freight’s return policy and numerous physical stores to take a reject back to is why. A drop shipper is likely to have nothing more than an ad site on the Net, and behave like a black hole, when you have a complaint.

    Why not give up endless shopping and “just buy a Dremel”? Well, the oldest models still available in the Dremel lineup (their #100 and #200) still mostly get excellent reviews; the others? Not so much; compare their prices versus the amount of critical costumer reviews, and Harbor Freight starts looking like a lot better deal than you might have thought. Dremel became famous for the solid quality of their rotary tools, back when grandpa was a kid. On the other hand, their accessories are still first rate.

    Am I saying that Dremel power tools are no good? No; I’m suggesting that you forget blind brand loyalty; this isn’t your grandad’s world. I despise the Black and Decker brand, and have still bought three of their RTX rotary tools, starting with an RTX-3; my third is an RTX-6; personal animosity hasn’t prevented careful consideration of their products. Why three of them, if they’re so great? I burned out the speed control circuit on the first one, and having no clue about what went wrong, or how to fix it, threw the tool away. The second is still running fine, and the third one is pure tool greed.

    Keep reading costumer reviews, and forget brand names; they’re increasingly irrelevant. Do we all wish this wasn’t so? Sure, but it is; so, deal.

 

The Dremel #100 single-speed, and #200 two-speed rotary tools both have a 108 watt (.9 amp) brushed motor: this is a plus for cutting small air openings in burners. This is the weakest motor in the smallest package you can find in a high-quality rotary tool. The #100 and #200 are the oldest models left in Dremel’s product line; they have stayed popular this long because of their dependability; they are lighter, and smaller than other rotary tools (making them easier to grip and use).

    The #100 runs at 35,000 RPM, but becomes variable speed when plugged into a router speed controller. The #200 has two speeds; 15,000 and 35,000 RPM. Dremel’s product manual states that “use of an external speed control will damage variable/two speed electronics.” No problem; just buy a #100. If you already have a #200, remember that the only difference between them is their control witches, which are low priced, interchangeable, and plug in (not soldered in place); you can buy either switch online, and change them back and forth at your convenience.

    These tools have plenty of air vents that are properly positioned; their prices are high ($50 for the #200, and $40 for the #100. But the percentage of critical reviews is very low. On/off and high/low speeds are controlled by a single switch near the tool’s rear on the #200; with an on/off switch located in the same place on the #100. Most people find this convenient. I like more safety when cutting, but this is a weak enough tool to overlook that shortcoming; especially if you only mount the thicker 15/16” Dremel #420 discs (safest), or standard 1-1/4” fiberglass reinforced cutoff discs (acceptable) for surface cutting.

    The #100 and #200 are available through Amazon.com. The #200 is also available at Homedepot, Lowe’s, and Ace hardware stores. Unlike the bulk of rotary tools, both of these have parts available online; even the armature. You will also find diagrams, and repair videos for them online; the other reason people put up with sticker shock.

    Thread size for the plastic housing cap on most rotary tool’s plastic bodies, match up with Dremel’s. You can change flexible drives and other attachments between most of them. Collet nuts can be a different story. Most rotary tools have interchangeable collet nuts. Spindles on the #100 and #200 models are smaller, so collet nuts from other rotary tools, will not fit them, and some threaded accessories, like their fan will fit these, but don’t fit other tools. Yet, their variable chuck will fit on most other spindles’ but not these (go figure). For fine detail work, these two rotary tools are very hard to beat.

    Adding a handle will not improve safety much on these tools, because the switch type and location make the practice of stopping a cutting disc, before removing it from the kerf, impractical; with or without a handle. Mounting a handle will still improve stability while you are cutting, and therefore, the quality of your work.

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/what you see is what you get

Twenty years ago, 2” angle grinders like Proxxon’s Long Neck Angle Grinder, or the Merlin 2 from King Arthur Tools, were the only power tools that could easily make straight cuts in small burner parts; they were designed for inline motion, and had steel safety guards. A rotary tool with a safety handle mounted can now do a better job, more safely, for a small fraction of their prices.

    What has changed, to make this possible? See-through safety guards didn’t exist back then; they do now. When cutting along an ink or scribe line, it is tempting to bend over the tool, to provide the best view; a very bad habit, unless the tool has a safety guard; it’s also frustrating to try to see the cut adequately with steel guards. But you can place your disc beyond the cut line, and work in safety and comfort, when you can see the line by looking through the guard.

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Abrasive stones versus wheels: Stones have advantages in working inside small tubes and pipes. Wheels grind faster than stones, because their larger diameters create higher surface speeds, if the pipe or tube is large enough for their use; of course, a dressing stone can make the wheel fit. All of these products consist of grit bonded together by resin. But stones are also glued onto their steel shanks, creating a major failure point. Wheels have arbor holes that accept rotary mandrels, so wheels are far more durable than stones.

Silicon carbide grit is harder than and sharper than aluminum oxide. But more brittle; it is also available in stones and wheels. Silicon carbide stones have been much more expensive than the wheels (their prices are falling now). Silicon carbide stones and wheels usually come in light blue, (and occasionally) green colors; very seldom in charcoal grey. Remember to only use abrasive colors as general clues about what the abrasive material actually is. Make sure that the advertisement specifies exactly what material, before purchase.

    There are several superior materials becoming available in abrasive products, such as manufactured ceramic abrasives, and zirconium abrasives. The last place you can expect to find them is in rotary tool accessories, but you will find advertisements suggesting that ‘bargain’ stones are made with them. Just remember that you never get more than you pay for. Also, these sites do everything they can to keep you from reading their critical customer reviews.

    So, how can you balance, shape, or reduce the diameters of silicon carbide stones and wheels? With diamond coated dressing stones (or cheap imported small diameter diamond coated cutoff discs).

Zirconia Alumina (ZTA) is zirconia toughened fused alumina; it is one of the new abrasive materials available in flap discs; it may eventually become available in stones and wheels. Just because the grit is a superior material doesn’t guarantee the stone will be. Remember that factory seconds aren’t thrown out in Asia; they just get sold to drop shippers with no reputation to protect. If a deal looks too good to be true, it probably is:

CBN (cubic boron nitride) abrasive products last about twenty times longer than aluminum oxide products; it also grinds and cuts faster, because the grit is nearly as hard as diamond, but is more thermally resistant; it is just becoming available in cutoff discs.

Titanium dioxide is a new ceramic abrasive grit that is available in flap discs. From a domestic manufacturer the term “ceramic abrasive” denotes one of several advanced synthetic grits; from a drop shipper it can mean anything, or nothing whatsoever.

“Corundum sand” should denote aluminum oxide crystals in trigonal form (ex. Ruby and sapphire), but can also be used as a basically meaningless term, by drop shippers. Aluminum oxide (Al 203) comes in several forms, both synthetic (fused alumina) and as crushed natural minerals; it can simply be crushed garnet, which is 7 to 8 on the Mohs scale, or as low as 6 and as high as 8.5, depending on what source you consult; fine for sanding wood, but a poor choice on steel); or it can be corundum crystal, which is the hardest crystal form of aluminum oxide (9 on the Mohs scale). Corundum crystal comes in every color, and from opaque to gem quality translucent. One of the tricks you need to watch out for is drop shipper advertisements that start out describing abrasive accessories as silicon carbide, etc., and then go on to describe them as corundum sand. You may rest assured that they are at worst, no higher grade than the garnet found on sandpaper, or at best fused aluminum oxide: with blue are green die added to their bonding resin.

 

Note: Die colors used in various sanding and grinding products have been used for decades by abrasive stone manufacturers to denote grit particle sizes. This practice has always been a sales aid, only. There isn’t any code governing colors. Different manufactures do not necessarily use the same colors to denote particle size, and drop shippers are more than willing to use false impressions to help sell lesser products to the unwary. Blue-green to green die has been used by American manufacturers to denote silicon carbide grinding stones for over half a century. Surprise, surprise; drop shipper products favorite color for abrasive stones they are trying to pass off as something more than aluminum oxide is blue-green to green.

 

One ad also described the shank diameter of a set of these same abrasive stones both as 3mm and as 1/8" (which is 3.2mm; 0.125”); Not that it matters, since the shanks were actually 2.9mm (0.113”), which would probably be flung out of a rotary tool, with a 1/8" collet; but will work fine in a Dremel 4486 keyless chuck. Two genuine Dremel silicon carbide stones will probably last as long as ten of these ‘bargain’ stones; if you can’t find the size or shape you want in a high-quality stone, the bargain stones are the only game in town. Tiny stones are handy for working on ¼” (and smaller) burners. There were five tapered (bullet shaped) stones with diameters of 0.15”; 0.19”; 0.23”; 0.31”; and 0.39”; with five cylinders in the same diameters. This set of stones has many sellers on Amazon.com. and on eBay; the blue colored stones are #80 grit, and the yellow (#240) grit. Some offers have fine white stones (grit number unknown).

 

The best offer for these stones is a 36-piece set in a plastic box; there are blue (course grit), pink (medium grit) and white (fine grit) stones; half of them are bullet shaped, and half are cylinders; head diameters are of 0.15”; 0.19”; 0.23”; 0.31”; 0.39”; and 0.472”;

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    About keyed chucks

Ever wonder why so many drill presses in steel shops have keyless chucks? No, it isn’t because the keys get lost; it’s due to the moron factor. Some gorilla uses a hammer to tighten the original keyed chuck, instead of using the key to tighten it gradually, by using all three holes in turn: 1, 2, 3, 1, 2, 3…until the bit is tight. Just a little bit of such pounding will destroy any keyed chuck. Then the owner replaces it with a keyless chuck—because it’s too inconvenient to fire all the shop’s gorillas. And so, second rate keyless chucks have become popular, and chaos wins another victory.

    New chucks of either kind, need tender loving care; oil them and baby them over sticking spots until they wear in a little bit. Open the chuck completely and put a drop of oil on one of the ways. Then, use the motor to completely close and open the jaws a few times, to spread the oil over moving parts; repeat this procedure occasionally, to lubricate internal surfaces and protect against rust.

 

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