I trained as physicist. There was/is never a budget or availability for the parts one needs (you want an inlet port for a Nitrogen laser???). We had to make things ourselves. Which meant we had to learn how.
I was first taught machining by machinists of the Manhattan Project era (near the end of their careers). They were an amazing bunch… I miss them.
They were very concerned about safety (try machining precision molds for explosives; plutonium), fine finish (try machining…), correctness (we have to get this done quickly and correctly, there is a war on), and low waste (there is a war on).
We learned/worked on hand driven knee mills (Bridgeport, a company still in business). Learn to do it manually, then add automation (which was governor driven motors).
Things were handed down orally, student to teacher, so I do not know of a written reference. I will dig our my Machinery and see what I can find something this weekend. As a machining and CNC teacher myself I still pass along what they taught me, albeit updated for the CNC age.
In there honor, I pass along what I was taught.
A) Never, never, never put any part of your body inside the work volume when the spindle is engaged.
The end mill can cut through steel. Your hand is softer. A mistake only takes an instant.
When manually milling, always keep your weak hand behind your back (grasp your belt).
Always wear short sleeve shirts or turn up your sleeves and use a band to keep them that way.
Nothing that might catch on the machine.
B) A drill is 4 times better at plunging than cutting. An end mill is 4 times better cutting than plunging.
C) Do not cut material deeper than 1/2 the diameter of your end mill.
(Mark) Some modern end mills can do more (e.g. full diameter). Don’t get cocky. Start
conservatively and safely.
D) Plunge an end mill at 1/4 the cutting feed rate.
E) Learn to HEAR and FEEL chatter.
We would intentionally cause chatter, in different types of materials, until we could detect it
instantly. What’s known a unconscious competence.
E) When dealing with a new material and/or tool, perform tests.
Look up the chip rate (per flute) from the material vendor. Calculate the feed and speed.
(Mark) There are programs available today that take the pain out of this and get the initial
setting quite close to optimal. See G-Wizard Calculator for one of the best examples
I know of.
Start with the general guidelines above - even if the end mill vendor says differently.
Don’t depend on linear cuts to determine chatter and finish. Cut chevrons with a bend of more
than 30 degrees.
F) Never, never, never trust a feeds and speeds formula from an outside source - test it carefully.
Spindle power, lubrication, axis drive motor power, and end mill sharpness can be different.
Materials with the same specification can be slightly different from different vendors - and batch
(Mark) Feeds and speeds formulas for wood can be dangerous! Oak from Arkansas can be quite
different in hardness and density than oak from Illinois… or Spain. TEST IT CAREFULLY!
G) Diverge from the simple guidelines slowly. Get things in production quickly using the good enough
your determine from your initial tests. Use downtime to optimize.
H) Finish is a big deal. It’s not about getting the geometry (shape) cut correctly, it’s also how clean
the finish is. Finish is not only about looking good, it can be a critical requirement in some usages.
(Mark) See “try machining precision molds for explosives; plutonium”
I) Use the correct tool for the job. If you don’t know, ASK!
(Mark) Do not go for cheap end mills from unknown sources. They are crap.
Go with tools from known quality sources. Do not shy way from something like an AlTiN
coating because the end mill cost 50% more - it will last 3-5 times longer than High
Speed Steel (HSS) and cut faster!
Example: that Onsrud end mill for cutting polycarbonate that cost $30 will last nearly forever
and since it is optimized for the job will give you amazing cut speeds and fine finishes.
(Mark) My “go to” tool vendors are Niagra and Onsrud. My “go to” coating is AlTiN. YMMV.
(Mark) Carbide3D has very good end mills. I don’t buy them because I have $$$ of tools already.
(Mark) Carbide end mills are not all that same. If you’re looking for quality end mills the necessary
phrase is “solid carbide, micro (fine) carbide”. Coatings increase the life of the end mill
considerably more than the increase in cost - and they allow machining to go faster too.
If people are interested I can do a posting about how end mills (and drills) are made, how to
select/order them, and to not get lost in the coatings forrest.
J) Never waste time, resources or energy. If you’re going to have to repeat something, think about
how to use jigs and fixtures to make the work flow be efficient.
(Mark) Learning to “think in jigs/fixtures” is one of the hardest things to learn in machining. It’s really
scary to watch a master machinist machine a jig to machine a jig to machine a part and not to
see why they could see how this was necessary, instantly, from the outset. Well worth the effort!
(Mark) Safety should be the first priority.
Spindles moving at high speed and running at high revolution rates can be dangerous. A
broken end mill or a poorly fixtured part can go flying at high speeds.
An enclosure should be a very high priority item. If not, eye protection is a must.
Spindles moving at high speed and running at high revolution rates create a lot of noise.
That noise can damage your hearing. You can still damage your hearing even if the sound
doesn't seem so loud - damage is a function of intensity (loudness) and exposure time. CNC
machines often run for (very) long periods of time...
Yes, mowing the lawn is dangerous to your hearing.
An enclosure should be a very high priority item. If not, hearing protection is a must. One
of the cheapest hearing protectors are those used for shooting. Get one with at least 25
dBa of suppression.
Those wanting to design enclosures should look into profession grade noise suppression
materials. They are cheap since one does't need too much of them for an enclosure for a
small machine. I can help if anyone wants to know.
Spindles moving at high speed and running at high revolution rates create particles, not
"saw dust". The particles are extremely fine (0.3-5 microns (millionths of an inch) and these
are as or more dangerous than Asbestos.
Another reason to be concerned are (exotic) hardwoods. Many of these are "tropical" and they
contain viruses we've not be exposed to. They also contain compounds that when machined
hard generate some nasty vapors.
An enclosure should be a very high priority item. You've got a CNC machine - make one!
The enclosure should have a dust collector system. Minimally, your dust collector should
have a HEPA filter rated for 0.3 microns. Ideally, one should have a dust separator - a cyclone -
ahead of the dust collector. It will increase the life of your expensive HEPA filters dramatically.
A good, safe dust collector system doesn't have to be expensive. Yes, something like a
professional, internationally rated piece of equipment like a Festool can be used... but if
one cannot afford it, go with a good "shop vac" with a 0.3 micron rated HEPA filter and a
plastic cyclone (e.g. see Oneida). Remember to empty the cyclone and "shop vac" OUTSIDE.
Stand upwind or get a good face mask with 0.3 micron rated filters (3M makes some good
masks at a good price).