in all the surfaces, then finishing all the surfaces, or else you’ll make many moves and setups twice—it can’t always be done. On parts that warp easily—such as thin or hogged out parts—you may have to rough in all the surfaces first. When you go back to finish the part, you then cut out any warp that may have occurred during the roughing operations.
18.Use air mist to prolong the life of your cutter and increase stock removal rates. (See Fig. 1-7)
A little air/water mist helps cool and preserve cutters. Many machinists use air/mist sprayers. I usually don’t simply because I find them to be too much hassle. If you follow the tan chip rule mentioned in suggestion #10, a mist sprayer is not necessary.
Figure 1–7 A mist sprayer keeps the end mill cool.
19.Go as fast as you dare in aluminum and other easily machined materials.
It is difficult to wear out a cutter in aluminum, especially with a conventional machine.
Machining aluminum is like driving on the autobahn. You can basically go as fast as safety and common sense dictate. But don’t go so fast that you end up crashing. When conditions warrant (e.g., you have a rigid setup and a lot of stock to remove), you can put the pedal to the metal.
You can even use the rapid traverse feature on your conventional mill to increase the feed rate. The rapid traverse rate on the mill I use is somewhere around 60 inches a minute. Make sure you run the spindle fast enough to maintain a reasonable chip load in the .010" to .015" range.
In a CNC machine, you can literally fly through aluminum if your setup is rigid and you have a lot of stock to remove.
If you’re not using a fast feed, there is no advantage to running a spindle at warp speed. In fact, it is usually a disadvantage because there is a tendency for things to start chattering when spindle speeds are too high.
I’ve used a 500-inch per minute feed rate with a 1-inch diameter 3- flute end mill turning at 10,000 RPM. That’s as fast as the machine would go. If you do the math, you’ll see those parameters produce a chip load of about .016". But there is no reason to run that fast if there is little stock to remove and your cuts are short.
20.Bore holes with a mill like you would with a lathe.
For some reason, many machinists use very slow spindle speeds when boring holes with a boring head. They look like they’re stirring taffy.
There is usually no need to run a boring head at such slow spindle speeds unless the boring bar is flimsy and prone to chatter. You can usually use the “tan chip rule” for setting feeds and speeds, just like you would if you were boring a part in a lathe.
Use short, stout boring bars when you can. A short, stout boring bar will help eliminate chatter and won’t spring away as easily as a long thin boring bar. It is difficult to hold size with a thin, springy boring bar.
As far as I’m concerned, you can never have too many boring bars. You’ll need a variety of different size boring bars to match the different hole diameters and depths you’ll encounter.
21.Power tap blind holes that are drilled deep enough.
Do it under the right conditions or chances are you’ll be digging out of a broken tap. Many instructors would just say “never power tap blind holes.”
If you drill a tap size hole at least one and a half times as deep as the threads you need, chips will have a place to go and won’t cause binding. Use a spiral point tap so chips get pushed ahead of the tap. A spiral point won’t bind like a plug tap or hand tap. As long as you use a sharp tap with some cutting oil and give the chips a place to go, the tap should cut freely.
If the part design is such that you don’t have enough material to drill a hole at least 1.5 times as deep as the thread, then it is safer either to hand tap to final depth or to use a tap that pulls chips out the top.
By hand tapping, you can gauge the amount of torque you put on the tap. With this approach, you can also clean the chips out as you go.
I’ve had good results with Shark-Line® high performance taps for tapping tough materials. Use Shark-Line® taps with Hangsterfer’s Hard Cut® tapping fluids for best results.
Spiral fluted taps that pull chips out of the tops of holes are weaker than other taps and are best used in aluminum and other easily machined materials.
22.Saw your raw stock about a tenth of an inch larger than finished size.
It’s certainly possible to saw closer than .1", but for me it’s not worth the extra effort. Most saws are not high precision machines. Blades are often in less than ideal condition.
A tenth of an inch gives you a little breathing room if the saw blade runs off a little bit or if your stock isn’t held square to the blade for some reason.
If I have many small parts to make, I’ll try to saw a little closer than .1", maybe to within about 1/16" of finish size. You can usually get away with cutting small parts closer because the saw blade has less chance to run off.
Figure 1–8 Cold cut saws work great for cutting off bar stock. This machine was made by Doringer Mft. Co.
23.Use a cold cut saw for cutting off bar stock. (See Fig. 1-8)
You can really make hay with these saws. They’re especially useful for cutting off bar stock. Yet they have not gained the popularity they deserve, probably because those in charge of purchasing equipment aren’t familiar with them.
Advantages over horizontal band saws are that the blade is rigid and durable, enabling them to cut stock cleanly and close to size. They are also compact and easy to operate.
Although similar in design, these saws work on a different principal than abrasive cutoff saws. Cold cut saw blades turn relatively slowly and cut heavy chip loads, unlike abrasive cutoff saws.
24.When running multiple parts, do one operation at a time in a tool room lathe.
This applies mostly to small parts held in collets. Don’t run a tool room lathe like a turret lathe.
With the collet closer, it’s faster and easier to change parts doing one operation at a time than it is to change tools and settings.
25.Change small lathe parts when using a collet closer without turning off the spindle.
26.Stack parts when you can. (See Figure 1-9)
Stacking parts and machining them all at once can save a substantial amount of time.
However, it can be a double-edged sword. It is more difficult to hold tight tolerances with stacked parts.
Furthermore, setups are
