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Blacksmithing and metalworking questions answered.

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Drill and Cutting Coolant/Lubricant:

Keeping drills, taps and cutters cool and sharp

Cutting fluids or coolants greatly increase the life of drill bits, taps, lathe and milling cutters as well as saw blades.

The standard cutting fluid was a dark sulphurized oil. Today water soluble oils are used in recirculating systems and mist systems. There are also simple shop recipes, make do's and localized cutter lubricants.

These products all do a number of things:
  • Cool the cutting edge
  • Lubricate the non-cutting surfaces and chips
  • Wash away fine chips
For light duty work I use WD-40 because it is handy as I keep several cans in the shop at all times. The spray cans are convenient dispensers and work well on moving parts. The residue that does not evaporate helps protect the machine.

For production drilling I have used kerosene mixed with motor oil. The kerosene boils and evaporates at the cutting edge cooling where it is most important. This can be a smokey way to drill and can be a fire hazard.

On machines with pump systems including lathes, mills, saws and grinders you use water soluble oil. This makes a milky white liquid that cools and lubricates. It washes off easily and carries other oils to the tank. These are know an "tramp" oils and there are systems for removing them from the tank. Most water based coolants have an anti-microbial agent to prevent them from going stale. Bacteria growing in the coolant can be a health hazzard and often stinks.

Pumped systems can be messy on saws and drills. Some production drill presses are equiped tables with a large gutter and drain as well as no holes for coolant to leak through. Saws tend to be messy even when designed for coolant.

Mist systems also use water based soluable oil coolants. These systems use a small container of the coolant and and air powered atomizer to spray the coolant on the work. These are handy for machines that do not have drain pans or aprons to catch fluid from a pumped system. Care must be taken as to what type of coolant is used as mists are inhaled by workers and can be a serious health hazzard. Oil mists are particularly hazardous and should be avoided.

For taping the same coolants are commonly used especially when a machine has a pump or mist system. However there are special tapping compounds that cool better and lubricate better under the high pressures of taping.

One of the best taping agents was "Tap Free" a non-flamable solvent based product. It had a low boiling point and you could hear it "sizzling" at the cutting edge. It was amazing stuff but has been taken off the market.

Currently there are a number of taping fluids on the market and they all do a fairly good job. Machinists often use them on difficult to machine materials on lathes and milling machines as well as for tapping.


I've used my el-cheapo Taiwan vertical/horizontal metal cutting band wet and dry. I used the same high carbon blades for both procedures. Cutting higher carbon steel, there was a definited difference, with wet cutting being both faster and with a longer blade life. I did not use a regular "cutting oil", I used Tap Magic, which I happened to have on hand.

Paw Paw - Wednesday, 12/11/02 02:56:55 GMT

I started buying taps made for my CNC machine from J&L and find they are great for hand tapping as well. With good taps you can feel the difference.

Cutting oil?
Another area where you can feel the difference. Some of the better ones like Rapid-tap and tap-EZ have had to change their formula, guess they can't use florinated hydrocarbons anymore, but they still work better than regular oil. The old black sulferized lard oils are still great too.

- grant - Saturday, 11/08/03 12:11:43 EST

Tap Lube:
I often use a stick lube for machine or power tapping. (My favorite is Tapmatic Edge Lube) Far less messy than the oils but a little more critical in application. Don't jam a bunch into the flutes just let the tap rub against the stick to pick up a little bit. After the tap is warmed from the first hole it melts on very quickly. Particularly good in Aluminum operations and works for sawing also.

SGensh - Saturday, 11/08/03 13:07:29 EST

This product was waste dry cleaning fluid with a little beeswax and perfume (to cover the laundry stink). It was trichlorethlene I think. ABSOLUTELY the best. Reduced taping force by four to one or more. Tap life increased to 10:1. Life was good.

You could hear it sizzle at the cutting edge when you turned the tap. This cooling at the cut was what made it work so well. This required a thin liquid and a low boiling point.

It stated, DO NOT USE in automatic cooling systems and as cutting fluid. . . Well, people did it anyway. Bad fumes when used normally and much worse when abused. The abuse is what ended it. . .

The replacements are not nearly as good but are much better than nothing.

- guru - Saturday, 11/08/03 13:30:28 EST

Tapping experience: Practice, practice, practice. It's a touchy, feely sort of thing.

Most of my experience is with A-36, 1018, and annealed 4140.

Sharp taps don't stay that way very long. As Grant said, you can feel good cutting. Pushing a less than sharp tap "to get one more hole" or to just "finish the hole" is a recipe for disaster. Always keep new taps in stock specifically to avoid the "one more hole" error.

Don't worry about using a slightly bigger than recommended pilot hole, but definitely avoid using a smaller than recommended bit. A good wall chart of metric, alphabetical, numbered, and fractional bit sizes in decimal diameter are a good help here for quick decision making.

The spiral flutes are my best choice taps (the ones that look a bit like drill bits), and I try to use those that are 1/2" to 3/4" long in the cutting zone. Most of the shards/cuttings/shavings (whatever they're called--Paul, Jr. on American Chopper calls them stringy things) just come out the top like gangbusters. I do have to stop once in a while to use a magnetic tipped scribe to extract crap from blind holes.

I use power tapping a lot with 3/8" and 1/2" NC taps. A magnetic drill with a Jacobs chuck tightened as much by hand as possible. I keep my fingers on the switch and turn it on only momentarily. I pilot drill blind holes deeply to avoid bottoming taps. Handheld drills are conducive to breaking taps by an unsteady hand. I admire Steve's ability, but I can't do it.

Junk in the relief grooves of a tap or drill bit will cause jamming and breakage. In and out, in and out, like you know what, is the best way to ensure a well done hole.

I have found the only way to keep concentricity as I go from small to larger bits and then the tap is to keep the mag drill locked into one position. It is tedious to unchuck and then rechuck, but concentricity is VITAL to good power tapping.

It is surely best to use a tapping head if using the drill press so that forward and reverse actions are quick and controllable. In a mag drill there isn't enough room to mount one. Dexterity and focused concentration are needed.

There are taps of different materials for tapping different materials. My machine shop supplier brought this to my attention, and it pays off in tap life to use the right combo. Reading the print in a voluminous catalog like MSC's ought to accomplish the same advice. I haven't checked Machinery Handbook, but I bet it is loaded with knowhow.

Tapping fluids vary enormously in productivity. I'd love to have some TapFree. I keep experimenting with brands and don't remember the name of the best stuff I've found--it is in a green and white aerosol can. Come to think of it, I'm on my last can so I gotta try to find some more. This stuff came out of an auction, so might be pretty old. Not as good as the guru says TapFree was.

With big diameter taps I use my mill and use a bit holder that allows the tap to determine feed conditions. Again, concentricity is vital. On the mill, one steady downfeed movement is all that's ever needed with spiral groove taps. I don't do much of this big stuff, so my advocacy is cautious. Your mileage may vary.

- John Larson - Saturday, 11/08/03 19:59:45 EST

Cutting fluid:

Haven't worked in a steel shop in about three years, but when I did we used something to lube the mag-drill called "Hawg-Wash". It was a Milwaukee product made specifically for drill coolant and we used it in Milwaukee rotobroach or button drills. Vegetable based compound that came in a small bottle that was mixed with water. Worked very well in all applications I tried. Wonder if any of you guys have any experience with it and would it make a suitable tapping fluid?

- Larry - Saturday, 11/08/03 21:46:10 EST

Drilling and tapping lubes. From many years experience with power tapping and internal and external die chasing of threads I can offer the following: For the common steels, almost nothing beats a HIGH QUALITY sulfurized oil. This means a name brand like Rigid etc. We found several off brands that were very bad, and also caused derimitis in the employees. The ratio of fat to oil and sulfur in these oils is critical, and if the fat is too high, bad results!

Another good choice, that beats every other oil we tried, especially in screw machines was a MASTER CHEMICAL product, OM303. This oil was exceptional in carbon and stainless steels for all screw machine operations, and I now use it in roll splining. Harder to find for the small shop but a gallon or two will last a long time.

On Tap Free and the other trichlor products, good riddance! life is too short to spend any of it dead, injuried or in jail. These products did work somewhat, but a good tapping oil will also do the job, and not give off fumes that ARE dangerous.

For tapping aluminum, stick tallow is very good, especially with roll taps. In a pinch kerosene will work, but is not nearly as good.

On all tapping fluids. To recycle, insure good filtration. Under serious study, we found that a 10 micron filtration prior to reuse improved tool life by about 20%, reduced dermititisis, and improved the thread finish. A simple bag filter rated to 10 microns will work for the small shop.

ptree - Sunday, 11/09/03 09:39:12 EST

Even good taps break. We EDM them out on parts that are worth it. Actually, we thread mill much of the production stuff now. Better threads and virtually no damaged holes. I really like roll tapped holes, but getting roll tapping right can be a trick. Coolant, TiN coating, and correct tap drill size are essential. When buying taps, make sure you understand what H limits are. There are classes of tapped hole size. Different H-limit taps produce different pitch diameter threads. Tight or loose. Cheap (even name brand from a hardware store) taps can be all over the map from an H-limit standpoint so may not be consistent from tap to tap. Machinery's Handbook has info. MSC catalog might discuss it.

Sulphur cutting oil is good. LPS makes a green water based cutting fluid that works well too. I can't remember the name. But it's sticky when it dries.

I like tapping holes in a lathe when I can and it's lathe work anyway. Rotating the part with the tap centered and started with a center in the tailstock. Tap drilling done in the same chucking.

Tapping heads in radial drills are sweet too! Seems like cheating almost. Grin John!

I agree that cheap taps and dies are a complete waste of time and money. I bought one cheap set from Whorbor fright one time. I let kids wreck them on inconsequential work so they learn.

- Tony - Sunday, 11/09/03 18:10:27 EST

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