Machine Shop Trade Secrets. James HarveyЧитать онлайн книгу.
the right size T-nut for a piece of tooling can be frustrating when you want to keep a job moving. T-nuts are cheap. Open a catalog and buy yourself a large assortment of T-nuts to avoid getting hung up.
32.Avoid clearing your cutter to go back for another cut.
If you rough off material in steps in a conventional mill or lathe, don’t bother clearing the tool to return for the next cut. If the roughing tool rubs or grooves the part as it is returned to the starting point, so be it. This technique saves you from having to look at your dial settings all the time.
Don’t, however, take finishing cuts over a rough surface with swirls or grooves. Clear the tool when you are within finishing range so the tool cuts with even pressure over a consistent surface for finishing.
33.Don’t bother removing a built-up edge on a lathe tool when roughing.
Your cutting tools may accumulate a built-up edge when roughing. A built-up edge or BUE is a slight accumulation of material from the workpiece that adheres to the cutting edge of your tool.
A tool will still cut with a built-up edge, at least well enough to rough with.
To make smooth, precise finishing cuts, it is best to remove the built-up edge so that chips slide off the tool freely and the edge of the tool does the cutting instead of the built-up edge.
Removing it is often easier said than done. On carbide, if you attempt to just pick it off with a knife or something, you’ll likely pull off a bit of the carbide and ruin the cutting edge. If you attempt to stone or file it off, you may end up rolling the edge over, which is also no good.
You can remove a built-up edge by applying a liberal amount of cutting oil to the tool and then abruptly but intermittently hand feeding the tool into some stock. The build up edge will usually get pushed off by the resultant chip.
Figure 1–12 A deep hole can be drilled with a conventional lathe by sliding the tailstock.
34.Drill deep holes in a conventional lathe quickly by sliding the tailstock. (See Fig. 1-12)
Chip packing becomes an issue when drilling deep holes. The deeper you drill, the harder it is for chips to get out.
Instead of winding the drill bit in and out with the tailstock crank, you can manually push the tailstock in and out along the ways of the lathe.
When the drill bit packs, loosen the tailstock and pull it back to free the chips. Then push it back in until the drill bit bottoms. Re-tighten the tailstock and drill a little more using the crank. Repeat the process until you are to depth.
You’ll be surprised how fast you can drill a deep hole with a conventional lathe using this method.
Always begin drilling deep holes with a standard length drill to get the hole started straight.
Drill as deep as you can with a standard length drill before switching to a longer one.
35.Deburr rough edges with a small angle-head die grinder. (see Fig. 1-13)
Burrs and therefore the task of deburring are the unfortunate by-products of machining. There is no way to completely avoid throwing burrs when machining.
After rough cutting stock to size, you usually have to remove the resultant burr to begin machining. You can remove those and other fairly large burrs by sanding them with a small sanding disk mounted in an angle-head die grinder.
The advantage of this method is that you can do the deburring at your machine between cuts instead of having to file or walk to a disk sander.
There are a few things you can do to minimize burrs and the effort it takes to remove them. One method you can use is to climb mill into material. The use of sharp cutters also minimizes burrs.
Figure 1–13 An angle-head die grinder can be used to remove heavy burrs quickly.
36.To save a little time, avoid turning off a conventional milling machine to change parts.
Common sense is needed here. If the setup is such that you can move the cutting tool beyond the part by at least a few inches, you can usually change parts safely without turning off the spindle. If you measure the part, file the part, or do any operation other than just changing or removing the part, then it is best to turn the spindle off.
Be especially careful around cutters that rotate close to another piece of solid tooling such as a vise. That situation is potentially more dangerous than having a cutter that is just rotating out in the open.
I know of two accidents that happened when machinists did not stay clear of a cutter rotating next to a solid piece of tooling. One machinist used a milling machine to cut screw slots in some small parts with a slitting saw. When he went to change a part, he got his fingers caught in the small opening between the rotating saw blade and the holding fixture. The blade sucked three of his fingers through the small opening. Fortunately, the opening was big enough that he didn’t completely chop off his fingers. The other incident happened in a surface grinder. The rotating grinding wheel was about 1/4" above the magnetic vise when the machinist used his hand to wipe some debris off the magnet. Four of his fingers were ground down as they passed through the opening between the wheel and magnet.
37.Cut the diameter of a lathe part instead of the face to remove material quickly.
If you have a lot of material to remove from the length of a lathe part, it is faster to remove material by taking cuts off the diameter rather than the face of the part.
38.Cut arcs by hand in a conventional milling machine by using a dowel pin as a center pivot. (see Fig. 1-14)
To cut an arc around the end of a part, use a dowel pin as a center pivot and rotate the part around by hand. Mount the dowel pin in your milling machine vise with a V-block. I’ve used this method several times with good results. Be careful. Begin by cutting the protruding corners of the part first so that the cutter does not suddenly jerk the bar and break the cutter.
Figure 1–14 An arc is being machined around the end of a small part by rotating the part on a dowel pin.
39.Cut spherical shapes with a conventional lathe. (See Fig. 1-15)
These tools are easy to set up and work well for quickly and consistently cutting spherical shapes conventionally.
Figure 1–15 These tools make cutting spherical-shapes a breeze with a conventional lathe. This tool was made by Holdridge Mfg. Co.
40.Use short, stubby end mills when possible. (See Fig. 1-16)
Short, stubby end mills don’t deflect as much as longer end mills; as a result, they last longer. End mills with flute lengths about one and a half times the diameter of the end mill, or less, don’t flex much, and can be pushed harder than longer end mills. It’s hard to beat a short, stubby corncob type rougher for removing material quickly.
Figure 1–16 Stubby end mills are rigid and should be used whenever possible.
41.Use a hex cutter for deep arrow slots.
If