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still trying to figure out where you get the hour for hobbing the gear from !
those are small parts with fairly large DP in soft material, according to some preliminary calculations based on delrin and my machine handbook it should take about 10-15minutes to hob 1gear !

The biggest challenge in casting is to get airpockets out, one way is to use a cylinder to push the epoxy into the form until the material overflows out of a second hole, or you can put the form on a vibrator to achieve this, im not an expert but i have seen some castings done and thats how they did it.

Chuck Harris <cfharris@...> wrote:
lothar baier wrote:

Some things or actually a lot of things we do for a hobby have nothing to do with logic, sometimes you just do things
for fun, i have about $350 in the hobber including all acessories, i bought it not to make money but i figured that
its a nice complement to my metal hobby shop and $350 is a ammount that i can justify spending on a hobby !

I wouldn't argue against that, I have tens of thousands of dollars
in my machine shop. But I still won't waste my time hobbing a
gear that I can buy for $2. I would rather spend my shop time on
things that would be too expensive to purchase, if I could buy
them at all.

Why would

somebody want to fix testequipment or build a ham radio rig ? it cheaper to buy especially if you put in all the time
you spend - you do it for fun and to learn something, you gain alot of valuable skills by practicing - as it says
practice makes perfect, the other reason is that you have control over your parts and even if they are not available
anymore down the road you can still make them and fix your equipment, also you can make them better by using more
advanced materials. Plastic gears normally are not hobbed except if you use delrin,

You are in luck, the HP gears are already delrin on brass hubs.

Like nylon, delrin shrinks continually. Unfortunately, the brass hubs do not, so
given time, the gear will break at one of its roots.

PVC is a pain because it leaves a

I am not sure what PVC has to do with anything proposed.

bunch of burrs that need to be removed, the other side of PVC is that it becomes brittle over the years, normally the
gears HP used were made in a very crude way - injection molding which has a high yield and is cheaper in Qty. My idea
is to either use delrin or aluminum, the forces on the flanks of those gears are not very high and the rotating speed
is very slow so by far the specs are no challenge. All you need to know to make them is the number of teeth , the
diameter and the pressure angle, height and id of the gear.

And that information is what I was going to provide to the group.

If you hobb the gears, and make them available for sale, you
will quickly discover that you have to charge something for your
time, tooling and materials. Suddenly, you will see why metal
gears are so damned expensive... custom gears even more so.

If you are using manually operated machines (at $350, I think you are),
between blanking the gears, and hobbing the teeth, you will have several
hours in each gear you make.

US microwave engineers with experience are making what these days? $90K
to $130K? That works out to $40 to $60/hour paid to the engineer. They
cost their companies 2 to 3 times that much.

I don't think the guys that hang out on this group are going to be willing
to pay you $200 per gear. If you charge $5 per gear, your wife will divorce
you. I offered several gear *sets* at the cost of one broken 8640B OPT/1/2/3.

My price exceeded what the market would bear... even though I would essentially
be working for free.

-Chuck Harris




__________________________________________________
Do You Yahoo!?
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still trying to figure out where you get the hour for hobbing the gear from !
those are small parts with fairly large DP in soft material, according to some preliminary calculations based on delrin and my machine handbook it should take about 10-15minutes to hob 1gear !

The biggest challenge in casting is to get airpockets out, one way is to use a cylinder to push the epoxy into the form until the material overflows out of a second hole, or you can put the form on a vibrator to achieve this, im not an expert but i have seen some castings done and thats how they did it.

Chuck Harris <cfharris@...> wrote:
lothar baier wrote:

Some things or actually a lot of things we do for a hobby have nothing to do with logic, sometimes you just do things
for fun, i have about $350 in the hobber including all acessories, i bought it not to make money but i figured that
its a nice complement to my metal hobby shop and $350 is a ammount that i can justify spending on a hobby !

I wouldn't argue against that, I have tens of thousands of dollars
in my machine shop. But I still won't waste my time hobbing a
gear that I can buy for $2. I would rather spend my shop time on
things that would be too expensive to purchase, if I could buy
them at all.

Why would

somebody want to fix testequipment or build a ham radio rig ? it cheaper to buy especially if you put in all the time
you spend - you do it for fun and to learn something, you gain alot of valuable skills by practicing - as it says
practice makes perfect, the other reason is that you have control over your parts and even if they are not available
anymore down the road you can still make them and fix your equipment, also you can make them better by using more
advanced materials. Plastic gears normally are not hobbed except if you use delrin,

You are in luck, the HP gears are already delrin on brass hubs.

Like nylon, delrin shrinks continually. Unfortunately, the brass hubs do not, so
given time, the gear will break at one of its roots.

PVC is a pain because it leaves a

I am not sure what PVC has to do with anything proposed.

bunch of burrs that need to be removed, the other side of PVC is that it becomes brittle over the years, normally the
gears HP used were made in a very crude way - injection molding which has a high yield and is cheaper in Qty. My idea
is to either use delrin or aluminum, the forces on the flanks of those gears are not very high and the rotating speed
is very slow so by far the specs are no challenge. All you need to know to make them is the number of teeth , the
diameter and the pressure angle, height and id of the gear.

And that information is what I was going to provide to the group.

If you hobb the gears, and make them available for sale, you
will quickly discover that you have to charge something for your
time, tooling and materials. Suddenly, you will see why metal
gears are so damned expensive... custom gears even more so.

If you are using manually operated machines (at $350, I think you are),
between blanking the gears, and hobbing the teeth, you will have several
hours in each gear you make.

US microwave engineers with experience are making what these days? $90K
to $130K? That works out to $40 to $60/hour paid to the engineer. They
cost their companies 2 to 3 times that much.

I don't think the guys that hang out on this group are going to be willing
to pay you $200 per gear. If you charge $5 per gear, your wife will divorce
you. I offered several gear *sets* at the cost of one broken 8640B OPT/1/2/3.

My price exceeded what the market would bear... even though I would essentially
be working for free.

-Chuck Harris




__________________________________________________
Do You Yahoo!?
Tired of spam? Yahoo! Mail has the best spam protection around

still trying to figure out where you get the hour for hobbing the gear from !
those are small parts with fairly large DP in soft material, according to some preliminary calculations based on delrin and my machine handbook it should take about 10-15minutes to hob 1gear !

The biggest challenge in casting is to get airpockets out, one way is to use a cylinder to push the epoxy into the form until the material overflows out of a second hole, or you can put the form on a vibrator to achieve this, im not an expert but i have seen some castings done and thats how they did it.

Chuck Harris <cfharris@...> wrote:
lothar baier wrote:

Some things or actually a lot of things we do for a hobby have nothing to do with logic, sometimes you just do things
for fun, i have about $350 in the hobber including all acessories, i bought it not to make money but i figured that
its a nice complement to my metal hobby shop and $350 is a ammount that i can justify spending on a hobby !

I wouldn't argue against that, I have tens of thousands of dollars
in my machine shop. But I still won't waste my time hobbing a
gear that I can buy for $2. I would rather spend my shop time on
things that would be too expensive to purchase, if I could buy
them at all.

Why would

somebody want to fix testequipment or build a ham radio rig ? it cheaper to buy especially if you put in all the time
you spend - you do it for fun and to learn something, you gain alot of valuable skills by practicing - as it says
practice makes perfect, the other reason is that you have control over your parts and even if they are not available
anymore down the road you can still make them and fix your equipment, also you can make them better by using more
advanced materials. Plastic gears normally are not hobbed except if you use delrin,

You are in luck, the HP gears are already delrin on brass hubs.

Like nylon, delrin shrinks continually. Unfortunately, the brass hubs do not, so
given time, the gear will break at one of its roots.

PVC is a pain because it leaves a

I am not sure what PVC has to do with anything proposed.

bunch of burrs that need to be removed, the other side of PVC is that it becomes brittle over the years, normally the
gears HP used were made in a very crude way - injection molding which has a high yield and is cheaper in Qty. My idea
is to either use delrin or aluminum, the forces on the flanks of those gears are not very high and the rotating speed
is very slow so by far the specs are no challenge. All you need to know to make them is the number of teeth , the
diameter and the pressure angle, height and id of the gear.

And that information is what I was going to provide to the group.

If you hobb the gears, and make them available for sale, you
will quickly discover that you have to charge something for your
time, tooling and materials. Suddenly, you will see why metal
gears are so damned expensive... custom gears even more so.

If you are using manually operated machines (at $350, I think you are),
between blanking the gears, and hobbing the teeth, you will have several
hours in each gear you make.

US microwave engineers with experience are making what these days? $90K
to $130K? That works out to $40 to $60/hour paid to the engineer. They
cost their companies 2 to 3 times that much.

I don't think the guys that hang out on this group are going to be willing
to pay you $200 per gear. If you charge $5 per gear, your wife will divorce
you. I offered several gear *sets* at the cost of one broken 8640B OPT/1/2/3.

My price exceeded what the market would bear... even though I would essentially
be working for free.

-Chuck Harris




__________________________________________________
Do You Yahoo!?
Tired of spam? Yahoo! Mail has the best spam protection around

still trying to figure out where you get the hour for hobbing the gear from !
those are small parts with fairly large DP in soft material, according to some preliminary calculations based on delrin and my machine handbook it should take about 10-15minutes to hob 1gear !

The biggest challenge in casting is to get airpockets out, one way is to use a cylinder to push the epoxy into the form until the material overflows out of a second hole, or you can put the form on a vibrator to achieve this, im not an expert but i have seen some castings done and thats how they did it.

Chuck Harris <cfharris@...> wrote:
lothar baier wrote:

Some things or actually a lot of things we do for a hobby have nothing to do with logic, sometimes you just do things
for fun, i have about $350 in the hobber including all acessories, i bought it not to make money but i figured that
its a nice complement to my metal hobby shop and $350 is a ammount that i can justify spending on a hobby !

I wouldn't argue against that, I have tens of thousands of dollars
in my machine shop. But I still won't waste my time hobbing a
gear that I can buy for $2. I would rather spend my shop time on
things that would be too expensive to purchase, if I could buy
them at all.

Why would

somebody want to fix testequipment or build a ham radio rig ? it cheaper to buy especially if you put in all the time
you spend - you do it for fun and to learn something, you gain alot of valuable skills by practicing - as it says
practice makes perfect, the other reason is that you have control over your parts and even if they are not available
anymore down the road you can still make them and fix your equipment, also you can make them better by using more
advanced materials. Plastic gears normally are not hobbed except if you use delrin,

You are in luck, the HP gears are already delrin on brass hubs.

Like nylon, delrin shrinks continually. Unfortunately, the brass hubs do not, so
given time, the gear will break at one of its roots.

PVC is a pain because it leaves a

I am not sure what PVC has to do with anything proposed.

bunch of burrs that need to be removed, the other side of PVC is that it becomes brittle over the years, normally the
gears HP used were made in a very crude way - injection molding which has a high yield and is cheaper in Qty. My idea
is to either use delrin or aluminum, the forces on the flanks of those gears are not very high and the rotating speed
is very slow so by far the specs are no challenge. All you need to know to make them is the number of teeth , the
diameter and the pressure angle, height and id of the gear.

And that information is what I was going to provide to the group.

If you hobb the gears, and make them available for sale, you
will quickly discover that you have to charge something for your
time, tooling and materials. Suddenly, you will see why metal
gears are so damned expensive... custom gears even more so.

If you are using manually operated machines (at $350, I think you are),
between blanking the gears, and hobbing the teeth, you will have several
hours in each gear you make.

US microwave engineers with experience are making what these days? $90K
to $130K? That works out to $40 to $60/hour paid to the engineer. They
cost their companies 2 to 3 times that much.

I don't think the guys that hang out on this group are going to be willing
to pay you $200 per gear. If you charge $5 per gear, your wife will divorce
you. I offered several gear *sets* at the cost of one broken 8640B OPT/1/2/3.

My price exceeded what the market would bear... even though I would essentially
be working for free.

-Chuck Harris




__________________________________________________
Do You Yahoo!?
Tired of spam? Yahoo! Mail has the best spam protection around

still trying to figure out where you get the hour for hobbing the gear from !
those are small parts with fairly large DP in soft material, according to some preliminary calculations based on delrin and my machine handbook it should take about 10-15minutes to hob 1gear !

The biggest challenge in casting is to get airpockets out, one way is to use a cylinder to push the epoxy into the form until the material overflows out of a second hole, or you can put the form on a vibrator to achieve this, im not an expert but i have seen some castings done and thats how they did it.

Chuck Harris <cfharris@...> wrote:
lothar baier wrote:

Some things or actually a lot of things we do for a hobby have nothing to do with logic, sometimes you just do things
for fun, i have about $350 in the hobber including all acessories, i bought it not to make money but i figured that
its a nice complement to my metal hobby shop and $350 is a ammount that i can justify spending on a hobby !

I wouldn't argue against that, I have tens of thousands of dollars
in my machine shop. But I still won't waste my time hobbing a
gear that I can buy for $2. I would rather spend my shop time on
things that would be too expensive to purchase, if I could buy
them at all.

Why would

somebody want to fix testequipment or build a ham radio rig ? it cheaper to buy especially if you put in all the time
you spend - you do it for fun and to learn something, you gain alot of valuable skills by practicing - as it says
practice makes perfect, the other reason is that you have control over your parts and even if they are not available
anymore down the road you can still make them and fix your equipment, also you can make them better by using more
advanced materials. Plastic gears normally are not hobbed except if you use delrin,

You are in luck, the HP gears are already delrin on brass hubs.

Like nylon, delrin shrinks continually. Unfortunately, the brass hubs do not, so
given time, the gear will break at one of its roots.

PVC is a pain because it leaves a

I am not sure what PVC has to do with anything proposed.

bunch of burrs that need to be removed, the other side of PVC is that it becomes brittle over the years, normally the
gears HP used were made in a very crude way - injection molding which has a high yield and is cheaper in Qty. My idea
is to either use delrin or aluminum, the forces on the flanks of those gears are not very high and the rotating speed
is very slow so by far the specs are no challenge. All you need to know to make them is the number of teeth , the
diameter and the pressure angle, height and id of the gear.

And that information is what I was going to provide to the group.

If you hobb the gears, and make them available for sale, you
will quickly discover that you have to charge something for your
time, tooling and materials. Suddenly, you will see why metal
gears are so damned expensive... custom gears even more so.

If you are using manually operated machines (at $350, I think you are),
between blanking the gears, and hobbing the teeth, you will have several
hours in each gear you make.

US microwave engineers with experience are making what these days? $90K
to $130K? That works out to $40 to $60/hour paid to the engineer. They
cost their companies 2 to 3 times that much.

I don't think the guys that hang out on this group are going to be willing
to pay you $200 per gear. If you charge $5 per gear, your wife will divorce
you. I offered several gear *sets* at the cost of one broken 8640B OPT/1/2/3.

My price exceeded what the market would bear... even though I would essentially
be working for free.

-Chuck Harris




__________________________________________________
Do You Yahoo!?
Tired of spam? Yahoo! Mail has the best spam protection around

still trying to figure out where you get the hour for hobbing the gear from !
those are small parts with fairly large DP in soft material, according to some preliminary calculations based on delrin and my machine handbook it should take about 10-15minutes to hob 1gear !

The biggest challenge in casting is to get airpockets out, one way is to use a cylinder to push the epoxy into the form until the material overflows out of a second hole, or you can put the form on a vibrator to achieve this, im not an expert but i have seen some castings done and thats how they did it.

Chuck Harris <cfharris@...> wrote:
lothar baier wrote:

Some things or actually a lot of things we do for a hobby have nothing to do with logic, sometimes you just do things
for fun, i have about $350 in the hobber including all acessories, i bought it not to make money but i figured that
its a nice complement to my metal hobby shop and $350 is a ammount that i can justify spending on a hobby !

I wouldn't argue against that, I have tens of thousands of dollars
in my machine shop. But I still won't waste my time hobbing a
gear that I can buy for $2. I would rather spend my shop time on
things that would be too expensive to purchase, if I could buy
them at all.

Why would

somebody want to fix testequipment or build a ham radio rig ? it cheaper to buy especially if you put in all the time
you spend - you do it for fun and to learn something, you gain alot of valuable skills by practicing - as it says
practice makes perfect, the other reason is that you have control over your parts and even if they are not available
anymore down the road you can still make them and fix your equipment, also you can make them better by using more
advanced materials. Plastic gears normally are not hobbed except if you use delrin,

You are in luck, the HP gears are already delrin on brass hubs.

Like nylon, delrin shrinks continually. Unfortunately, the brass hubs do not, so
given time, the gear will break at one of its roots.

PVC is a pain because it leaves a

I am not sure what PVC has to do with anything proposed.

bunch of burrs that need to be removed, the other side of PVC is that it becomes brittle over the years, normally the
gears HP used were made in a very crude way - injection molding which has a high yield and is cheaper in Qty. My idea
is to either use delrin or aluminum, the forces on the flanks of those gears are not very high and the rotating speed
is very slow so by far the specs are no challenge. All you need to know to make them is the number of teeth , the
diameter and the pressure angle, height and id of the gear.

And that information is what I was going to provide to the group.

If you hobb the gears, and make them available for sale, you
will quickly discover that you have to charge something for your
time, tooling and materials. Suddenly, you will see why metal
gears are so damned expensive... custom gears even more so.

If you are using manually operated machines (at $350, I think you are),
between blanking the gears, and hobbing the teeth, you will have several
hours in each gear you make.

US microwave engineers with experience are making what these days? $90K
to $130K? That works out to $40 to $60/hour paid to the engineer. They
cost their companies 2 to 3 times that much.

I don't think the guys that hang out on this group are going to be willing
to pay you $200 per gear. If you charge $5 per gear, your wife will divorce
you. I offered several gear *sets* at the cost of one broken 8640B OPT/1/2/3.

My price exceeded what the market would bear... even though I would essentially
be working for free.

-Chuck Harris




__________________________________________________
Do You Yahoo!?
Tired of spam? Yahoo! Mail has the best spam protection around

First off the 8640B was designed in spokane and as to my knowledge this division was disolved years ago, most engineers were send to other divisions or into early retirement.
This question would have to be answered by a ME and not a EE , most large companies have a strict separation in between system engineering, mechanical engineering and electrical engineering, then the ME who designed the gear doesnt necesarily have knowledge about who makes the gear this is normally done by purchasing.
so even the ME might not have the info you are looking for.
I doubt HP used catalog parts, HP was famous for custom parts, yes the qty was not too high for the stanbarts of running a injection molder but first of you dont have to think in today standarts but have to think 20 to 30 years back plus the 8640 was not cheap so HP could afford to pay a premium on the price.
A CNC with a CNC Dividing head could possibly do the job, you would have to slant the dividing head, the other part could be hobbed.


Chuck Harris <cfharris@...> wrote:
There are different scales of machines used for injection molding
ranging from machines that make a part every time you pull the lever
to high production machines that are fed from monster sized bins of
plastic pellets.

But I do agree that they want to set the machine up, and just let it
plug away essentially 24-7.

This is part of the reason that I don't believe that HP used any
custom made gears in this machine. Someone made that little gear
set. An HP insider that could share some of that information would
sure be handy.

-Chuck Harris

J Forster wrote:

Peter, setting up and adjusting an injection molder is a BIG job. They want
to run millions of parts, not 100.

Best,
-John


Peter Gottlieb wrote:

If the company that made the gears is still in existence they might
still have the molds and be willing to do a run. You'd need an insider
at HP to get that info and a letter from them authorizing the use of the
mold.

Peter

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I have an on site manual. It appears it was intended to be used with a set of spare modules. The book covers how to trouble shoot the 8642 using the built in test equipment (bite) down to the module level. The one I have covers the 2427A series. I might have a spare copy. I will try and look over the weekend. This book has extensive flow charts for the troubleshooting. BTW, the book is about 2" thick.

Geoff Greer

most of the time if you look in the parts list it gives the cage code or reference# of the manufacturer, the problem is getting authorization from Agilent to use the mold, they are pretty hard headed about stuff like this, i tried to get this release form one time for a transformer however they wouldnt give it altough the unit was long out of support, we worked around it by having the supplier add one additional tap to the primary windings at 100V now the transformer was not 100% identical anymore and they could make it !

Peter Gottlieb <hpnpilot@...> wrote: If the company that made the gears is still in existence they might
still have the molds and be willing to do a run. You'd need an insider
at HP to get that info and a letter from them authorizing the use of the
mold.

Peter

Chuck Harris wrote:

Casting is definitely the way I would go if I couldn't
spec that universal drive gear set.

I have made some pretty decent low speed gears using
JB Weld and a silicone mold. And there are better
casting compounds available.

-Chuck Harris

d.seiter@... <mailto:d.seiter%40comcast.net> wrote:

This probably wouldn't work due to shrinkage, but if there isn't

much load on the gears, couldn't you cast a

replacement with a very short fiber filled epoxy? Assuming you had a

set of good gears to start with.

-Dave

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i was eyeballing a EDM for a bit but unfortunatly dont have enough floorspace right now, another problem is that most EDMs require 3phase current which i dont have out here.
There are some benchtop type hansved edms on ebay every once in a while.
Another issue it that you need to have a electrode that resembles the form of the gear made of graphite or copper and usually those are CNC machined parts

Chuck Harris <cfharris@...> wrote:
Hi Pete,

That gear may be a problem. I cannot say that I have ever
noticed that one... or if I did, it probably scared me so much
that I put it out of my mind ;-)

The only economical way of making it would be to cast it out of
some plastic... probably a metal loaded epoxy would do. I'll have
to check Boston Gear and see if they by some chance have such a
gear set. I doubt that HP had it custom made.

I've been planning to add an EDM machine to my machine shop. Making
an injection mold for this gear might be reason enough.

-Chuck Harris

pdxoregonpete wrote:

I'm sorry this has gone this way, I just offered to buy
the junker and if someone lived in Reno could pick it up
strip it keep the rest of it if they wanted to,
and send someone like Chuck or a retired mechanical
engineer I know draw up a set of plans then give them to
someone with a hobber, Then post the details on mfg.com and
maybe a Chinese shop would surprise us with the cost.

There's just one gear thats not a simple one, Fig 5 near
the bottom of the page


-pete

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the first step would be to get a model made out of graphite or copper to use with a EDM to make a mold, the next step is to injection mold the gear, you could use epoxy or just a thermoplastic, problem is that EDM hours arent cheap and it takes a good bit of time to errode a form like this

Chuck Harris <cfharris@...> wrote: Casting is definitely the way I would go if I couldn't
spec that universal drive gear set.

I have made some pretty decent low speed gears using
JB Weld and a silicone mold. And there are better
casting compounds available.

-Chuck Harris

d.seiter@... wrote:

This probably wouldn't work due to shrinkage, but if there isn't much load on the gears, couldn't you cast a
replacement with a very short fiber filled epoxy? Assuming you had a set of good gears to start with.

-Dave

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i think a cnc machine could do the job

lothar baier wrote:

i was not factoring the time to make a hob since this in my view is not needed, first off i have a bunch of hobs, i
addition there are hobs on ebay on a regular base and there are several companies that trade or rent hobs fairly
inexpensive. No the hobber doesnt have a bowl feeder, my definition of automatic and yours differ, automatic in my
vocabulary means that once the machine is setup all you have to do is to change your blanks, pull a lever and use a
gauge to check your finished parts every once in awhile. I grew up and went to college in germany, the second
operation lathe is a unknown animal there, most all lathes have threading capabilities the only difference is how its
done, some usually the cheap ones require change gears while the more expensive ones have gearheads you just have to
switch some levers. Even with making blanks 5hours is far fetched, anytime i made blanks i usually ended up machining

You misunderstood what I said. 5 hours to make the *hob*, not the gear.

To hob one gear would take a couple of hours. There is an economy of scale,
but this is a small scale project. I doubt that you would make more than 10
sets in a production run.

a cylinder that was 10-12" in legth, machine it to excact diameter then put it on the gear hobber and hob the gears,
then put it back on the lathe , part the gears and do the secondary machining, next step was to grind the flanks and
induction harden the flanks( i dont remember anymore what came first the grinding or hardening) on some larger gears
the gear was packed in some toxic stuff and put into an oven for hours to harden Generally plastic always turns out
rough, over the years i have experienced two methods to reduce this,- a sharp almost razorlike cutting tool is
understood- the first method is to use a forced airstream to cool and blow away the chips, part of the problem when
machining plastic is that the material starts ro melt and then the chips "cake" together and adhere to the edges,
removing the chips and cooling are the most effective ways, another method that i actually discovered for teflon is
to use liquid nitrogen to virtually "deepfreeze" the plastic, the only disadvantage is that you have to machine
fairly quick and you have to consider the shrinkage of the material when taking measurements I know it was a lucky
purchase, i was chasing gear hobbers down for years and usually anytime i found one that was reasonable it turned out
to be without change gears, i know what a good set of change gears costs and i know the cost of a hob, new and used
as well as the cost of sharpening them, i have been involved in machine shop operations more than i wanted to but if
your brother starts a business and he doesnt have $ to hire somebody the family has to pitch in :) so altough im a
EE i know almost anything there is to know about machining

As do I. My first job in a machine shop was when I was 15 years old.
And I apprenticed under my dad until I escaped and went to college.


-Chuck Harris

There are different scales of machines used for injection molding
ranging from machines that make a part every time you pull the lever
to high production machines that are fed from monster sized bins of
plastic pellets.

But I do agree that they want to set the machine up, and just let it
plug away essentially 24-7.

This is part of the reason that I don't believe that HP used any
custom made gears in this machine. Someone made that little gear
set. An HP insider that could share some of that information would
sure be handy.

-Chuck Harris

J Forster wrote:

Peter, setting up and adjusting an injection molder is a BIG job. They want
to run millions of parts, not 100.

Best,
-John


Peter Gottlieb wrote:

IMO, that's the really hard way to do it!! I'd measure the gears and
write a simple spec and have the experts do it, or failing that, cast it
out of filled epoxy resin in a Si rubber mold. See what I just posted on
that issue. There are companies that do such castings as a business.

Best,
-John



Chuck Harris wrote:

Yes. I've been away from this sort of stuff for quite a few years, but Emerson & Cuming and others used to supply
a wide variety of casting materials. I'd try calling their engineering department.

I had a good friend who used to do this for a business... making precision cast components using various resins
and fillers. He's start with a clear liquid epoxy resin (from Dow as I remember) and then mix in fillers. He
ALWAYS used two-part fairly low viscosity epoxies (resin & hardener)

Most of the molds were made from machined aluminum masters, using GE RTV (two-part) supported in little tin cans
to maintain tolerances. He's make a number of the silicone rubber molds from one master, then mix up a batch of
the epoxy.

After mixing, the epoxy was degassed in a dessicator with mechanical pump, then poured into the molds, degassed
again, then put into an oven to set up.

Finally, the parts were machined to tolerance.

Using this technique, he made lots of parts for GR and EG&G.

Best,
-John



Chuck Harris wrote:

If the company that made the gears is still in existence they might still have the molds and be willing to do a run. You'd need an insider at HP to get that info and a letter from them authorizing the use of the mold.

Peter


Chuck Harris wrote:

Hi Pete,

That gear may be a problem. I cannot say that I have ever
noticed that one... or if I did, it probably scared me so much
that I put it out of my mind ;-)

The only economical way of making it would be to cast it out of
some plastic... probably a metal loaded epoxy would do. I'll have
to check Boston Gear and see if they by some chance have such a
gear set. I doubt that HP had it custom made.

I've been planning to add an EDM machine to my machine shop. Making
an injection mold for this gear might be reason enough.

-Chuck Harris

pdxoregonpete wrote:

i was not factoring the time to make a hob since this in my view is not needed, first off i have a bunch of hobs, i addition there are hobs on ebay on a regular base and there are several companies that trade or rent hobs fairly inexpensive.
No the hobber doesnt have a bowl feeder, my definition of automatic and yours differ, automatic in my vocabulary means that once the machine is setup all you have to do is to change your blanks, pull a lever and use a gauge to check your finished parts every once in awhile.
I grew up and went to college in germany, the second operation lathe is a unknown animal there, most all lathes have threading capabilities the only difference is how its done, some usually the cheap ones require change gears while the more expensive ones have gearheads you just have to switch some levers.
Even with making blanks 5hours is far fetched, anytime i made blanks i usually ended up machining a cylinder that was 10-12" in legth, machine it to excact diameter then put it on the gear hobber and hob the gears, then put it back on the lathe , part the gears and do the secondary machining, next step was to grind the flanks and induction harden the flanks( i dont remember anymore what came first the grinding or hardening) on some larger gears the gear was packed in some toxic stuff and put into an oven for hours to harden
Generally plastic always turns out rough, over the years i have experienced two methods to reduce this,- a sharp almost razorlike cutting tool is understood- the first method is to use a forced airstream to cool and blow away the chips, part of the problem when machining plastic is that the material starts ro melt and then the chips "cake" together and adhere to the edges, removing the chips and cooling are the most effective ways, another method that i actually discovered for teflon is to use liquid nitrogen to virtually "deepfreeze" the plastic, the only disadvantage is that you have to machine fairly quick and you have to consider the shrinkage of the material when taking measurements
I know it was a lucky purchase, i was chasing gear hobbers down for years and usually anytime i found one that was reasonable it turned out to be without change gears, i know what a good set of change gears costs and i know the cost of a hob, new and used as well as the cost of sharpening them, i have been involved in machine shop operations more than i wanted to but if your brother starts a business and he doesnt have $ to hire somebody the family has to pitch in :) so altough im a EE i know almost anything there is to know about machining

Chuck Harris <cfharris@...> wrote:
lothar baier wrote:

i agree on the fact that hobbs are expensive but i have about 120 hobs that came with the machine,

That was a very lucky purchase. The hobs alone, if they are sharp and
any good, are worth easily 10 to 50 times what you paid for your machine.

Now, do you have any 48 dp hobs in your collection? If not, you will
be making, or buying some before you finish this project.

.... Any lathe has

threading capabilities

Begging your pardon, but that is not true. Most lathes used in
industry are second operation machines, and they can only cut a
thread if you have a die already made. A hob is way out of their
league.

The only other lathes used these days are CNC lathe centers. Manual
machines show up only in small model shops, and hobby machine shops.

.... and you need a lathe anyways to make the disks you cut your gears out of,

I included that in my guesstimate of the time to make a single gear.
Did you?

.... you wont need any

heat treating of the hob since you are only cutting plastic,

Plastics, such as delrin and nylon seem soft and buttery, but they are never-the-less
abrasive when you cut them. An unhardened tool steel hob will make quite a few gears,
but the sharp edge will be gone very early on. Plastics such as nylon and delrin
cut with a very ragged edge unless the tool is scary sharp.

If you are only going to make a couple for yourself, sure, you can take short cuts.
If you are going to make them for others, you don't dare.

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,

Ever tried making a hob? I have made a few, and 5 hours is a good estimate for
one hardened and ground tool steel hob made on manual machines. If you have ten
identical hobs to make, you can take advantage of some economy of scale, but to
make one hob, will take you about 5 hours.

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,

Really now? So, you have a stock feeder that puts the new blank into
your hobber, and removes the old? You just walk away, and the bucket
gets filled with gears?

No? Then you have a manually operated hobber. Someone has to be in
attendance during the entire operation.

-Chuck Harris




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