On Wed, 1 Nov 2017 09:54:42 -0700, "Bob La Londe"
wrote:



"Larry Jaques" wrote in message
news
On Tue, 31 Oct 2017 10:06:03 -0700, "Bob La Londe"
wrote:

"Larry Jaques" wrote in message
. ..

On Mon, 30 Oct 2017 14:01:19 -0700, "Bob La Londe"
wrote:

Sanding by hand is an art. Have you considered a DIY or purchased
wide drum sander?

*** It is, but I have a fair feel for the work I am doing. I'm no expert,
but I get passable results and repeat customers. I would be deathly afraid
of creating gouges or valleys with a drum sander. I sometimes use the flat
platten of a belt sander for hard parts.

I'd think the platen would be as likely to score as a drum sander.

*** the sandpaper might score the surface if I was using a coarse grit, but
the platen is hard and flat. Again, its not for material removal. A single
quick pass flat from end to end will clean up all the burrs. A round drum
may leave a valley from its round shape if there is even a slight change in
hand pressure as the work piece is passed over the drum. When I say harder
parts I mean "harder" parts. Like 4140HT or... Not more difficult parts.
Yes I do mostly low pressure aluminum molds, but I occasionally take other
jobs.

You could build it to fit your largest mold and
then it could ostensibly handle anything that size or smaller.
https://www.pinterest.com/brad2179/d...ander/?lp=true
You could use emery instead of garnet paper.

*** Yep. That was the core of my query. Finding emery cloth paper size
sheets at fair prices. IT HOLDS UP. Some of the sources I've seen just
say
coarse, medium, fine. Even though the price may be ok I have to pass on
those. I want to know the grit. Or atleast the grit I am starting with.

Often, you have to ask the mfgr, and sometimes they have to ask their
engineering dept for the micron or grit size. I use 6" x 2" diamond
hones for the most part. $30 for a once-a-lifetime purchase isn't
bad. I wonder how a DMT would work for you. Apparently, diamond
hones are used to hone aluminum bores (unlined--gasp!) in engines.

*** Now that IS a great idea if I could afford diamond hones that are paper
size or larger. When I do this I want to completely engage the entire
surface of the plate. Again its not about material removal. Its about a
quick clean up of the burrs and any really high tool marks. If I actually
remove the tool marks I sanded to hard. (Usually)

If it's denibbing, wouldn't a narrower-but-long-enough strip do? 2x8
or 3x8, maybe?


Additional question: Why do you have to wet-sand?

*** The paper doesn't clog up. I am sanding mostly aluminum. It clogs dry
paper pretty fast. Its also why I hand dress molds between tool changes.
I
do not want to significantly change any dimensions. I just want to knock
off the burrs before I place the tool height setter on the mold plate.

Yes, clogging is a nasty habit of abrasive papers. I doubt that
stearates would make much difference with aluminum, but they do with
wood dust on garnet paper. Emery sounds like your winning choice.

*** I actually start learning how to do this several years ago, and only
switched to this as my primary business last year. The first of this year I
shut down my contracting company of 23 years to focus solely on this
specialty niche of machining. Really only one market segment of the niche.

Yeah, one tiny piece can keep a person busy.


If I
ran an ATC or even ATC spindles that used tool holders I could use a tool
height table and only have to dress the mold once at the end of the job,
but
alas this is a self paying hobby that turned into a business. Every tool
pays for the next one. Decent ATC spindles cost. I'll have them sooner or
later, but for now I am still making parts.

You're going to CNC mill the surfaces? That seems a bit more serious
than a hand-sanding for burrs.

*** Often after milling a cavity there are small burrs around the edges.
If I just threw a tool height setter on them the depth could be off
(depending on the previous cutter and the aggressiveness of the cut) by a
couple thousandths. If (for example) the next cut is an air vent of only
.002 to .003 then it might not cut at all, or not deep enough. A quick
brush with a fine grit rubber block with little pressure removes those burrs
and allows me to get a good next cut. I supposed I could tie up machine
time chasing every edge with a tool, but its faster to do this in between
measure by hand. Like I said if I had ATC spindles or atleast fixed height
tool holders on my little high speed machines I could just dress the burrs
once at the end of the job, but I don't so I found something that works with
what I have. A final brush on the granite block sort of unifies the
surface.

A spare granite (broken tombstone), or your good surface plate? =


*** Some of you may recall when I started down this path nearly ten years
ago I asked for a lot of advise on this group about high speed small cutter
machining in aluminum. I got some good advise, but a lot of it was not
really specialized enough for what I was pushing for. Some of it was ok for
very limited jobs, but not ok for jobs that took days. That was faster more
efficient finished products. One person said, right here on this group,
"You may be the only one here who is an expert at what you are trying to
do." At first I took it as a slap in the face, because I was very much a
neophyte seeking advise. Then I realized that what I am doing is not a
major portion of machining as a whole. Many people here with decades more
experience than me might not have the best answers for me and the goals I
was trying to achieve. I would have to take the advise I could get,
experiment, break tools, destroy machines, and make my own best compromises.
For now, relatively cheap high speed spindles and a lot of hand finish work
is the best compromise. As the work comes in the compromises shift more
towards machinery investment with less hand finish work.

P.S. I just quoted my biggest price ticket job ever (as a mold maker)
yesterday. The customer said yes. They haven't sent me any money yet, but
if they do I'll probably be upgrading atleast one of my machines to an ATC
spindle unless I decide something else will give me a greater immediate gain
in productivity.

Congrats, if and when.


P.P.S Yes I have destroyed machines. Well maybe abused them to the point
where I had to completely rebuild them might be more accurate. Thank
goodness I started as a hack know nothing hobbiest repairing and rebuilding
my own machines or they would have been "functionally" destroyed.

Abused or just flat wore out? Maybe a combo? And almost everyone
starts out as a hack hobbyist. Time and experience temper that, if
you keep your hand in long enough and frequently enough. I swear, I
have to learn to TIG every time I turn the machine on. I just don't
use it very often, and I haven't practiced as I should to really learn
it well in the first place. That should change shortly, as I finish
the harder of the items on the gazillion page project list now that
I'm retired.


P.P.P.S Yes, I had jobs that took days to machine. No those aren't Star
Trek days. LOL. One mold I made early on took 30hrs of machine time PER
SIDE. I slept on my shop floor with the machine running. The least little
change in pitch woke me instantly. I had to cut it twice because I screwed
up on design the first time.

Oh, ouch! But at least it wasn't a crash from a screwed up line of
code and you put a spinning mill bit through your chest.


I spent a week in the shop to get that one
done. A job like that would now take me only a few hours per side. That
job was 1.3 million lines of code per side. I recently did a job that was
over 5.6 million lines of code (2.3 per side). I ran the two halves on two
machines simultaneously, and it came off the machines for hand finish work
in just under 8 hrs.

Perhaps I could ask you a couple questions once I get the Green
Monster finished and start learning/writing G code. That's a healthy
sized programming task.


I'm not bragging. Or I'm not trying to anyway. Just trying to explain
where I am coming from and how I got here.

Cool, I get that.

--
The Road to Success...is always under construction.
--anon