On 11/14/2023 10:41 AM, MitchAlsup wrote:
> BGB wrote:
>
>> On 11/13/2023 8:06 PM, MitchAlsup wrote:
>>> BGB wrote:
>>>
>>>> On 11/13/2023 4:00 PM, Stephen Fuld wrote:
>>>>> On 11/12/2023 11:19 AM, MitchAlsup wrote:
>>>>>
>>>>>> <
>>>>>> If I buy a Lathe, I can use it forever.
>>>>>> If I buy a SW license, I cannot use it forever.
>>>>>> See the problem here.
>>>>>
>>>>> Well, there are differences.  First of all, for many sw licenses,
>>>>> you *can* use the software "forever" (i.e. lots of people are still
>>>>> running Windows XP), although if it is licensed to a particular
>>>>> hardware system, that system's life may limit your use, and you may
>>>>> not get vendor support.
>>>>>
>>>
>>>>> But I think the problem you are referring to is the limit on the
>>>>> number of copies you can make, or simultaneous users you can have.
>>>>> Of course, this is due to the obvious difference that, as opposed
>>>>> to a lathe, it is trivial to make an arbitrary number of copies, or
>>>>> have multiple different users use it simultaneously.  This
>>>>> difference accounts for the different licensing terms.  It makes
>>>>> things better for the software vendor, which, at least in theory,
>>>>> allows for more software to be created.
>>>>>
>>>
>>>> Yeah, this is a fundamental difference...
>>>
>>>> To copy a lathe would require the time and expense both to buy all
>>>> of the materials and machine all the parts.
>>> Yes
>>>> Then one may find that it ends up costing more than it would have
>>>> cost just to buy another one.
>>> Invariably
>>>> And, despite the lathes and mills typically costing $k, one is
>>>> hard-pressed to make something of comparable quality for cheaper.
>>> Yes
>>>
>>>
>>>> For stability, one needs things like a lot of weight, and the OEM
>>>> has the advantage that they can cost-effectively sand-cast big
>>>> chunks of cast iron (where cheaply making big cast iron parts is a
>>>> technology mostly out of reach of home shops).
>>>
>>>> Other alternatives are things like:
>>>>    Abrasive sand (such as garnet sand or slag) mixed with epoxy:
>>>>      Not cheap;
>>>>    Concrete: Not very good;
>>>>      Needs to be encased in metal or epoxy to not suck;
>>>>      One may still need garnet sand or slag for the needed density;
>>>>      Silica sand is cheaper, but not really dense enough.
>>>
>>>> If the machine is too light, then it would rattle or vibrate
>>>> excessively during cuts (AKA: chatter) which would ruin the quality
>>>> of the machined parts.
>>> <
>>> It is not weight per seé, it is stiffness between the piece holding
>>> the part
>>> and the spindle applying forces to remove chips from the part.
>>> <
>
>> Or, some combination of machine stiffness, inertia, and having enough
>> weight+inertia to keep the thing firmly anchored in place on the floor.
>
>
>> Like, when I tried at one point to mill steel with a 1" ballnose
>> endmill on a CNC converted G0704, I quickly stopped this as, as soon
>> as the endmill started cutting the steel, it seemed like the whole
>> thing was going to rattle itself apart...
>
>
>>>> Though, I guess if a person had access to a waterjet, they could cut
>>>> the parts out of a bunch of steel plate as layers, and then braze
>>>> all the layers together. Labor would likely still cost more than
>>>> being able to pour cast iron though.
>>>
>>>
>>>> For other parts, having machines purpose built to make one specific
>>>> part will make those parts cheaper than using more general purpose
>>>> machines to make all the parts.
>>>
>>>> ....
>>>
>>>
>>>> So, say, I don't really fault Grizzly or Tormach for the cost of
>>>> their machines, it is unlikely they could make them for all that
>>>> much cheaper and still make a profit.
>>>
>>>
>>>> Though, now having one of the Tormach CNC machines, limits can still
>>>> be noted:
>>>>    Tries to use a 1/2 inch drill on some stainless steel:
>>>>      Say, to enlarge a hole from 3/8 to 1/2 inch.
>>>>    Starts to drill, eats into steel a little, spindle: "NOPE!",
>>>>      Spindle stalls and machine goes into a faulted state.
>>>>    So, one needs to go: 1/4" (OK), 3/8" (Also OK), to 7/16".
>>>>      And then mill the hole the rest of the way via an endmill.
>>>
>>>> Say, because 1.5 kW at 10k RPM (in high range), doesn't mean it can
>>>> drill a 1/2" hole at 700 RPM. Granted, this works out to around 1
>>>> lb-ft or 192 oz-in of torque (so, not very much torque even by
>>>> cordless drill standards).
>>>
>>>> Well, or one can put it into low range by manually moving a belt,
>>>> but this kinda sucks as well, as then one has the torque to run the
>>>> drill, but not really enough RPM range for the endmill, ... (too
>>>> bad, say, they couldn't have put a CVT or similar in the thing).
>>>
>>>
>>>> So, say, vs a CNC converted Bridgeport:
>>>>     Tormach:
>>>>       + Tighter tolerances
>>>>         Holds +/- 0.005 easily
>>>>         Smaller is still hard (+/- 0.002 is still pushing it)
>>>>       + Has flood coolant;
>>>>       + Has tool changer;
>>>>       + Can dynamically change RPM.
>>>>       - Less travel.
>>>>         + Though, still more than my G0704 (at least in Y and Z).
>>>>       + Faster
>>>>           Can make quick work of aluminum and similar, ...
>>>>       - Not so much torque.
>>>>           Works fine if mostly using 1/8, 3/16, and 1/4 inch endmills.
>>>>           7/16 and 5/8 (*2), don't get too aggressive here with cuts.
>>>>           3/4: Only if you are milling plastic...
>>>>     Bridgeport:
>>>>       - Maybe gets +/- 0.005 if you are feeling lucky
>>>>          +/- 0.015 mostly OK.
>>>>       + More powerful spindle;
>>>>           Not much issue drilling holes in steel.
>>>>       + More X/Y/Z travel;
>>>>       - No coolant;
>>>>       - RPM is controlled by moving V belts.
>>>>       - Using R8 collets and drawbar sucks.
>>>>       - The software is buggy and likes to crash frequently, ...
>>> <
>>> The difference between 0.005 and 0.001 on a Bridgeport is metrology and
>>> care. If you can't measure something you cannot compensate for
>>> it--this goes double during setup where you sweep the clamped part to
>>> determine
>>> that it is held flat in the vise and normal to the milling direction.
>>> <
>
>
>> The Bridgeport in this case was modified to use ballscrews, with
>> NEMA34 steppers (IIRC, 1740 oz-in) connected to the leadscrews via
>> timing belts and pulleys (similar setup on my G0704; just using 470
>> oz-in NEMA23 motors).
>
>> Both machines can get "in the area" of 0.005", but don't seem to get
>> this with much repeatability (say, one cuts the same hole, and one
>> time it might be 0.004 over, or 0.004 under, or, ...).
>
>> Things like rotating a feature, changing the feedrate, etc, may also
>> effect what size it cuts.
>
>
>> This seems to be less of an issue on the Tormach machine (1100MX),
>> which seems to usually get +/- 0.001, but for parts asking for this,
>> this is more of a problem.
>
>
>> Though, have noted that feedrate does effect accuracy (it seems to cut
>> a little oversize if using faster feedrates or deeper cuts).
>
>> Some settings I had found that seem to work fairly well (on the Tormach):
>>    Aluminum with 3/16 endmill:
>>      RPM: 6500
>>      Feed: 17.0  inch/minute
>>      Depth: 0.015
>>    Aluminum with 1/8 endmill:
>>      RPM: 8500
>>      Feed: 19.0
>>      Depth: 0.010
>>    ...
>
>> For the Bridgeport, was generally using (for 1/8 and 3/16):
>>    RPM: ~ 3000
>>    Feed: 6.5 inch/minute
>>    Depth: 0.010
>
>> The G0704 is hard-pressed to go much over around 1500 RPM, so ~ 3.0
>> inch/minute.
> <
> I rarely use my C07300 with a spindle speed above 500 RPM, and mostly
> use 270 RPMs for milling.
>

Well, mostly it is "more RPM, more cutting", at least up to a certain
point (if RPM is too fast, the mill no longer cuts effectively).

So, if RPM is slower, feedrate needs to be slower, which means it takes
longer to make the part, ...

Well, and material, say, steel needs to be cut slower than aluminum or
brass, and stainless (or hardened steel) slower than normal steel.

Probably a majority of the parts being made were aluminum (mostly 6061,
sometimes 7075, or various other alloys).

Sometimes steel, brass, stainless, ...

Sometimes plastic, phenolic (fiberglass+resin, similar to circuit board
material, but much thicker), fiberglass or carbon-fiber composite, or
other weirder materials (often composites of various sorts).

Then, there are materials like graphite, that will crumble if one looks
at them funny, or ones that will melt into goo if they get wet (like PVA
or PVA based composites, *), ...

*: Say, when someone decides it is a good idea to make gears out of a
composite of compressed cotton fiber and PVA. But, then one has to avoid
any contact with water or coolant, as the material will melt (and then
the "chips" left in the machine later absorb coolant and turn into a
sort of sticky goo that is stuck on everything, or form a layer of slime
in the chip-tray).

Usually, "whatever shows up" and needs to be milled (someone else is
mostly dealing with sourcing the jobs and materials).

Mostly, from what I can gather, it is a lot of the stuff that either the
other shops in the area refuse to do, or would charge considerably more
to do so.

Like, say, other shops don't really want to try to hold 0.005 on
PVA+Cotton either, and then one is left to wonder how asking 0.005 even
makes sense on the material (since it is slightly compressible and will
shrink/expand based on humidity), ...

But, yeah, for a 7/16 endmill at aluminum, this would be around 4500 RPM
or so. But, depends on the machine.

So, as noted, my G0704 doesn't go much over 1500, and the Bridgeport
doesn't go much over 3000. Which, in turn, is fairly limiting for
aluminum, but mostly OK for steel.

RPM limits do somewhat limit feedrate for smaller endmills though, like
1/8 and 3/16, which are used a lot (but, it gets kind of annoying if
someone wants a feature smaller than what can be done with a 1/8
endmill; or, say, a pocket with a corner radius less than 0.063, ...).

But, say, smaller endmills, like 5/64, or 3/64, are not used as often as
they have sort of a habit of breaking if one looks at them funny. Well,
and for related reasons, a perfectly square-edged pocket isn't going to
happen (well, at least short of using a file or similar, and then
probably wrecking the tolerance and surface finish in the process, ...).

....