Machine Shop Trade Secrets. James Harvey
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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 usually more involved and time consuming when stacking parts.
If you have to move a stack in order to do other machining operations, try to keep the parts clamped together so they move as one block. In other words, when you can, try to avoid moving the parts in relation to one another.
Figure–19 Stack milling is an effective way to save time. The tradeoff is that setups take more time and tolerances are usually more difficult to hold.
27.Stack parts on edge for drilling and tapping. (See Figure 1-10)
Drilling and tapping a stack of parts on edge can save you time. However, you have to be careful how you do it so that you don’t accumulate error.
Let’s say you have a stack of twenty 1/4" plates that need to be drilled and tapped in the center of their edges. After clamping the stack in the vise, you next have to measure the width of the stack. Then divide that measurement by 20 to get the distance you should move between holes.
Say your overall stack measures 4.94". The real distance between the centers of the plates is 4.94 divided by 20, or .247". That’s how far you would have to move each time to keep the holes centered in the plates. If you moved over .250" each time, your holes would become increasingly off center as you advanced.
Figure 1–10 A stack of parts is drilled and tapped on edge.
28.Consider buying pre-squared blocks for high quantity runs.
There are vendors that specialize in supplying material squared to size so that you don’t have to do the squaring. Having blocks prepared this way is a great way to get a job off to a fast start
29.Use an end mill in the lathe to rough out a flat bottom hole. (See Fig. 1-11)
Using an end mill in a conventional or CNC lathe allows you to rough out a flat bottom hole very close to depth with a square corner.
Any subsequent boring you do to complete the hole will take less cutting than if you used a standard drill bit to rough out the hole. You can hold an end mill in the tailstock chuck.
An end mill fed in with the tailstock will usually cut a hole a little larger than the end mill diameter; be careful that you don’t cut an oversize hole. An end mill used this way will cut with less pressure if you drill a pilot hole first. Use the “tan chip rule” for setting spindle speed.
Figure 1–11 An end mill is used in the tailstock to rough out a counter bore.
30.Keep a box of loose drill bits handy.
If you need to drill an approximate size hold—such as a pilot hole—there is nothing faster than just grabbing and using an approximate size drill from a box of loose bits.
Sample Catalogs for T-nuts
McMaster-Carr
Travers Tool Company
Rutland Tool & Supply
ENCO
31.Keep a large assortment of T-nuts on hand.
Angle plates, rotary tables, drill presses, and other machines and fixtures around the shop are going to have different