i agree on the fact that hobbs are expensive but i have about 120 hobs that came with the machine,
Any lathe has threading capabilities and you need a lathe anyways to make the disks you cut your gears out of, you wont need any heat treating of the hob since you are only cutting plastic, a good quality toolsteel will do for that
Apparantly you havent been much around machining, i really dont know where you get the 5hours from, setup of your hobber takes about 1hr max and that includes calculating your index and feed gears, the cutting process in itself is depending on the ammount of teeths on your gear and the feedrate you can run, if you use forced air cooling on delrin or PVC you can generally run a good rate so the overall time to cut is about 10minutes 30minutes the most ! i have cut gears on hobbing machines in the past helping out in my brothers shop, those were gears used in CASE harvesters and they only took about 1hr/piece to hob, keep min mind that they were much larger in size !
There is no such thing as a manual hobber either, all hobbers are automatic, after setting it up you pull a lever and the machine automatically does its thing, after the gear is cut it returns to its starting position.
On low precision gears like this you can take a rod thats several inches long and cut the teeth on it, after you get done you pack it on the lathe and cut it in the individual gears.
Chuck Harris <cfharris@...> wrote:
Bob Groschen wrote:
....
Why would you
want to hobb them?
Because it's cheaper than the alternatives? Because it's his/her
hobby? Because they want to?
Cheaper, it is not. Hobbing machines require hobbs to work. Hobbs
are very expensive to buy, and difficult to make. At a minimum, you
need a lathe with threading capability, and a milling machine. If
you are planning on making more than a couple gears, you will need
heat treating capability, and a very fancy grinder to sharpen the hobb.
Oh, and about 5-6 hours of time if you are using manual machines, and
you know what you are doing.
I rebuild test equipment because I want to. If need had anything to
do with it, my collection would be reduced to a tiny fraction of
its size.
That's great. I rebuild for need and want too.
If you recall, 5 or 6 months ago, I offered to spec all of the
8640B gears, put the detailed drawings and part numbers in the
files section of this group, for anyone to use, and to make gear
sets available, for a reasonable (read cheap) price. All I asked
in return was for someone to buy/give me an 8640B option 1,2,3...
complete, but in unknown electrical condition to use in making the
measurements.
Nobody was interested. So, not having an 8640B to work from,
I did nothing.
Apparently I'm not the only one who believes that this effort you propose
is not worth the expense in acquiring and shipping a 8640B, particularily
one with the most desirable options. If stripped of options, an 8640B
can be had for about $100- $150. Adding in those options easily doubles
the price, for a dead or cirppled one. Shipping alone would cost $60 - $75
on top of the acquisition price.
So, let's see, at the time I made this offer, there were at least a half dozen
of you guys scrabbling about for gears, or gear fixes. That works out to what
about $30 each? I have no problem giving away that many sets of gears.
An 8640B is about 50 lbs in its birthday suit and UPS is famous for
pulverizing anything this heavy. I have limited experience with FedEx and
items this heavy, but they appear to be better than UPS for a slightly
higher shipping charge.
If you pack test equipment like it is trash, then that is what you will get when
it passes through the shipping system. I have shipped numerous big items, like
141T's, and 8640B's UPS, and they have never broken even one. It really isn't
all that hard to pack this stuff properly. UPS will even tell you how to do
it.
So you propose exchanging a couple hundred dollar generator for the
info on what, a half dozen off-the-shelf gears? I'm sorry Chuck, but
for me that's a stretch. For the same effort, I could ship just the gears
to any of a half dozen mechanical engineering friends, get the same
info and still get the gears back.
Then do so. You have the gears, and the desire. What's stopping you?
I for one don't give a rat's ass for the drawings.
The drawings were for the future. HP gave you all of the HP part numbers,
but they are no longer any good. McMaster-Carr part numbers will one day
change too, but a drawing specifying the diametral pitches, tooth counts,
width, and any modifications that may be necessary to the hubs would be good
forever.
All I would need is a
generic mechanical description of the part(s). McMaster-Carr P/N's
would be nice (assuming they have them) but not necessary, as I can use
catalogs & the internet as well as the next person.
That's cool Bob, but I don't have an 8640B, and I don't particularly want one.
You apparently do, so don't be selfish, tear it apart, and spec the gears.
You won't see one dime for your effort, you might break your 8640B in the
process, but you will be making a whole bunch of guys happy.
-Chuck Harris
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