"Bob La Londe" wrote in message news:tjeavs$svc$
1@gioia.aioe.org...
On 10/27/2022 4:40 AM, Jim Wilkins wrote:
"Bob La Londe" wrote in message news:tjbprv$64h$1@gioia.aioe.org...
I run D1-5 back plates on my primary lathe so removing chucks is fairly
quick and easy. I would have to get creative in order to mount them on
the mill table, an indexer, or a spacer or rotab.
For part one I tried a couple processes and concluded it was fastest to machine the hex and flat in a six sided collet block on the mill first.
Since I started with nominal size stock this left me to turn a single
radius on the part before parting it off and facing to length.
----------------------
You could chuck the hex collet block on the lathe.
In general I'm looking for ways to hold work that allow removing it to
check the fit with another, then replacing it sufficiently in registration
to continue cutting a thread. The need is more for repair or modification than for making all the parts to planned dimension.
The recent job was mounting a sink spray hose on a garden sprayer, which makes it serve as a quick response brush fire extinguisher in summer or
hot water supply for taking a shower with stove-heated water during a
winter power outage. The spray hose outlet gland nut leaked until I
replaced its O rings with a short length of rubber tubing. I also threaded
a snug-fitting knurled aluminum cap over the plastic to keep it from cracking.
I do some repair work, but generally I try to think of order of
operations that require as few setups as possible. For turning I will sometimes sacrifice order of operations convenience for being able to
machine all concentric surfaces in one operation.
For example the ID and OD of a tool holder. I use TTS tool holders on
the Tormach mill. Generally they are cheap enough I just buy them from
Tormach if they make the one I need. Sometimes I need a special one
outside the range they think is "safe" or perhaps with low enough demand
its not worth it to make for them. A piece of 1144 will make a tool
holder that will hold up for hundreds of operations. I will turn the
shank OD, recess, and tool size bore in one setup from the rear of the
holder. All the critical dimensions are done in the first setup.
Important concentricity is established. Then I'll flip the part and
shape the nose of the holder. Not so critical, and since the top RPM on
the 1100S3 is just 5120 balance is not a huge deal either. I wouldn't
make a tool holder for a 24K ISO20 spindle this way, but its perfectly
adequate for most machines running under 6K. I'll refrain at this point
from getting into my knowledge and ignorance for tool balancing.
The main chuck I use on the 1440 lathe is a Set-Tru 6 jaw with 2 piece
jaws. I can setup the chuck for a particular diameter with sub .0005" repeatability, and if I machine soft jaws turned to size I can get under .0003". The set tru feature is a bit fiddly and I haven't done it
enough to be good at it though. It takes me 15-20 minutes. When I can
I prefer to use setup and order of operations to make more important
surfaces concentric. For general use it tends to be better than any
other scroll chuck I have used anyway.
In this case the part is very non critical and it was designed that way.
The hex is very low speed intended to be used by hand with a wrench. (anything faster would be catastrophic) As long as it doesn't "feel" off
its good enough. The flat is just for a set screw for a locking collar,
and the locking collar has already been deemed redundant. There are two
radii that could be the "bearing" surface and it doesn't matter which
one for how the tool works. Since cold rolled stainless (what I keep on
hand) tends to be within a thousandth of dimension (usually 304 is
pretty close and 303 is slightly under from my experience) the nominal
OD of the stock is the planned bearing surface. The secondary OD is
turned under size and floats. Its just there so the part can pass
through the other part, and not fall out. The only "critical"
dimensions are the as shipped nominal major OD, and the length of that
first section. Basically it just needs to be .003-005 shorter then the
depth to the shoulder it rests on. The whole thing was designed to be
non critical.
I also do have a 16C lathe chuck I picked up a while back. The plan was
to set it tru on a back plate, but the 6 jaw set tru is good enough I
have not needed to play with it. Besides I like having my spindle bore
clear. Maybe if I was doing more production work on the lathe, but most
of the production or semi production stuff I do is fast and loose
tolerance. I also picked up a Taiwanese turret lathe with a 5C spindle
a while back, but its still resting on the furniture movers. There are
a few parts I make that I could do very fast on it, but the demand has
not has been high enough to get the machine off its rollers and setup.
Anyway, I try to make critical dimensions all in one setup if possible.
Even if its not as convenient otherwise for things like work holding.
In this case nothing is really critical. Maybe less than a couple
thousandths slop of the round part in the hole.
Where I can run into issues is with clocking. In this case not really
an issue, but there are parts where clocking is very important. I have
an array of tools for that from adjustable parallels to a machinist
level. I definitely do not have a fast "good enough" process dialed in
for clocking. Generally I try to avoid it being an issue by choice of
order of operations, but well sometimes I'm not as smart as I think I am
and I find myself screaming at the top of my lungs in the shop where
nobody can hear me because I realize I just spent all day designing and building something to go in the bit bucket. I'm not talking about
simple clocking where you stick the part in a spindex or rotab and do everything. I'm talking about moving a part from machine to machine and
back. Usually I think about it and realize if I had chosen a different
order of operations it would not have been an issue.
Wow! What a ramble. LOL.
So do you know what it is yet?
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I'd guess a jig or fixture latch but I don't know enough about mold making
to recognize the specifics. Some of the custom tooling I've machined makes
no sense unless seen in action, such as a collet draw-in cap with a 1/2"
hole to center an S&D drill bit shank, to sharpen it on the surface grinder
in an end mill fixture. The angles are close enough.
I have a Sanou 6" 6-jaw bookmarked on my shopping list for whenever I might decide to spend the money, though it just lost out to a 100 tooth gear for
the metric change set. When I bought the gears I was doing laser optics and
a 120 tooth gear gave more fine lens thread sizes. My 4" 6-jaw on the 5C
mount is quite useful for stock that doesn't fit a collet but it's of
limited capacity.
Where/why would you use 1144 versus 4140HT?
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