According to :
That is why it is best to go with the strongest material I can find. A
material that will best withstand the kind of force generated(when a
3/32" wide area attermpts to shear off a 3/32", 1/8" diameter pin).
Hmm ... that depends on whether you *want* it to shear to
protect the rest of the system at some point, or whether you want it to
hold on as long as possible.
If the latter, I would suggest either a hardened dowel pin, or a
solid carbide pin.
Then having the pin stay in place would again be an issue.(And
corrosion resistance is still important).
Do you *really* need that much strength? The roll pin should be
plenty. I consider the dowel pin or the solid carbide pin to be
seriously extreme conditions.
Note that with a dowel pin, you would drill the hole through the
shaft slightly undersized, and use an undersized reamer to make it a
just *barely* undersized hole.
I don't know of a better plastic for this. Basically any of six
holes/slots of various shapes(drilled all the way through the Delrin)
would fit within a 1-1/4" area and there will be a minimum space of
3/16"-1/4" between any of them. This is one reason why I was thinking a
drill press might be the best way to go.(Rpms would be a big guess at
this point).
Remember -- the slot will be scalloped -- at least until you can
file it smooth -- assuming that you have a place to run the file to do
that.
I have a Dremel. :-)
Yes -- but I don't find a hand operated Dremel to produce that
smooth a slot.
Yes, but how would I determine when it was balanced?
Switch on the lathe spindle at a low speed, without planning to
make a cut. If the lathe doesn't try to walk off the table, keep
increasing the spindle speed to see where it does try to walk off the
table. The higher you can get the speed without things galloping
around, the better. If it does start bouncing, stop it, move the
counterweight either a bit more distant from the center or closer. Try
again. If the problem occurs at a lower speed, you moved it the wrong
way.
Do you know if I can I buy these counter weights or do I have to make
one myself?
A counterweight consists of:
1) A chunk of scrap metal of about the right weight, drilled and
tapped for a bolt.
2) A bolt which fits through a slot in the faceplate.
3) Probably, a flat washer to spread out the contact of the bolt
head to the underside of the faceplate.
Of *course* you make it yourself. Until you are set up, you
don't know how much weight you will need. If it is not too much, put a
bolt through from the back, with washers on both sides of the faceplate,
and then start adding nuts to the bolt until you have the right weight.
Since you're going to be drilling steel with only a 1/8"
diameter drill bit, you will probably want something close to the
maximum speed the lathe is capable of. (Check the SFM recommendations
for the drill bit material in the material you are drilling and compare
it to the results of calculation to determine the desired spindle speed.
SFM recommendations?
Material specification, first?
1) What material you are drilling? (IIRC, it was a stainless
steel, but don't expect me to remember which stainless steel.
2) Drill bit material? You've got the choices of Chinese or
Indian pseudo-HSS, a real US (or European) made HSS, a high
cobalt steel (and which percentage), or a solid carbide drill
for starters. Also, there are various coatings TiN, TiAlN, or
various others which affect the friction, and thus the proper
speed.
Also -- some of the better ones will have polished parabolic
flutes, which will reduce the friction even more, with or
without coatings.
Drill bit grind. There are various angles available for normal
tips, plus there are split tips, which replace the chisel point
(which sort of rubs material out of the center area) with
secondary cutting edges, which will allow you to drill with a lot
less force, and will produce less heat.
I don't know which you will opt to buy.
And which lubricant/coolant will you be using? That affects
your choices as well -- and may interact with some of the other
choices. (Speaking of lubricant/coolant -- I would suggest that
you hang something behind your lathe (between it and the wall)
to avoid a line of coolant/lubricant spray forming on the wall.
(After all, someday you will be moving out of that apartment,
and not having to pay to re-plaster the wall could be a
significant savings.
Personally, I would probably go with a cobalt steel bit, with
split point, parabolic polished flutes in screw machine length,
and would spend some time looking for the best coating to use --
*if* I were going to be making thousands of these.
If I were going to make only a few, I would pick a good drill
bit from the set which I have -- or maybe a brand new one for
drilling SS -- and just select a speed which would be safe for
the bit. (But I don't buy Chinese drill bit sets, and I *do*
have a cobalt steel set of number-sized bits in screw-machine
length and split points as one of my things ready to hand.
If it comes down to chosing the *right* SFM, I would pick up my
copy of _Machinery's Handbook_ (a recent edition), and look up
what the proper SFM would be for the combination. And I would
then probably use something a bit slower, as these are for
massive production, and are a speed selected to make the optimum
tradeoff between the time the job takes and the life of the
drill bit. And the time taken to change the bit counts for more
than the cost of the bit in this equation. You won't have
production capable machinery, so don't push it.
The chart on page 1030 of the 24th edition of _Machinery's
Handbook_, for 303 SS (among some others) suggests for HSS that
you use a SFM of 20 (Opt) or 40 (Avg), with a feed of
0.015" per revolution (Opt) or 0.007"/rev (Avg)
The other column for drilling assumes indexable insert drills,
which make no sense at the size were you are working.
I'm not sure how you are going to manage a known feed rate while
drilling in the lathe, unless you mount a drill chuck to the
toolpost and set the feed gearing to accomplish that.
Anyway, for a 1/8" drill bit, and the slower SFM listed for HSS,
I see something like 611 RPM, which you would have difficulty
hitting exactly, anyway.
There seems to be no point to checking out the right speeds for
indexable carbide insert drills, as they don't make any that
small.
By comparison, the speeds for 12L14 (and other free-machining
steels) are 365 (Opt) and 740 (Avg). The slower of those two
calculates out to about 11,153 RPM. And the 12L14 will not work
harden if you pause in the drilling for a moment, while the SS
is very likely to.
So -- make a copy of _Machinery's Handbook_ one of your
purchases. The answers to *many* of your questions can be found
there, and I will henceforth assume that you have one for such
questions.
Enjoy,
DoN.
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