I'm taking the knee apart on my CNC mill and sending out for
rebuild...

I have an extra ball screw on hand that is perfect for replacing the
Acme hand knee lift screw. I'd then put a servo motor on the knee.

I did some preliminary layout for initial design of how to do this. it
will work best to rigidly mount the ball screw and spin the ball nut
with the nut located right at the bottom of the knee sitting on a
taper bearing.

Anyway, with this layout it would be all but impossible to change out
a timing belt. You'd have to take the knee apart. (There's always a
design weakness for maintenance)

Anyway, a #35 roller chain would make for a far easier and less
expensive installation. Given that the knee will only move slowly at
tool changes and always have downward force; is this causing another
problem that I don't see?

Karl

On 2011-02-24, Karl Townsend wrote:
I'm taking the knee apart on my CNC mill and sending out for
rebuild...

I have an extra ball screw on hand that is perfect for replacing the
Acme hand knee lift screw. I'd then put a servo motor on the knee.

I did some preliminary layout for initial design of how to do this. it
will work best to rigidly mount the ball screw and spin the ball nut
with the nut located right at the bottom of the knee sitting on a
taper bearing.

Anyway, with this layout it would be all but impossible to change out
a timing belt. You'd have to take the knee apart. (There's always a
design weakness for maintenance)

Anyway, a #35 roller chain would make for a far easier and less
expensive installation. Given that the knee will only move slowly at
tool changes and always have downward force; is this causing another
problem that I don't see?

Karl

A good timing belt should last a very long time under these
conditions. I would expect the condition of the 1,000 lbs knee pushing
on the ball screw all the time, to be quite punishing for the ball
screw. If you have pneumatic support, it would help.

But please keep us posted, this sounds like a very interesting plan.

i

Ignoramus3498 wrote:

On 2011-02-24, Karl Townsend wrote:
I'm taking the knee apart on my CNC mill and sending out for
rebuild...

I have an extra ball screw on hand that is perfect for replacing the
Acme hand knee lift screw. I'd then put a servo motor on the knee.

I did some preliminary layout for initial design of how to do this. it
will work best to rigidly mount the ball screw and spin the ball nut
with the nut located right at the bottom of the knee sitting on a
taper bearing.

Anyway, with this layout it would be all but impossible to change out
a timing belt. You'd have to take the knee apart. (There's always a
design weakness for maintenance)

Anyway, a #35 roller chain would make for a far easier and less
expensive installation. Given that the knee will only move slowly at
tool changes and always have downward force; is this causing another
problem that I don't see?

Karl

A good timing belt should last a very long time under these
conditions. I would expect the condition of the 1,000 lbs knee pushing
on the ball screw all the time, to be quite punishing for the ball
screw. If you have pneumatic support, it would help.

But please keep us posted, this sounds like a very interesting plan.

i

Second the recommendation for a pneumatic or hydraulic counterbalance
and an axis brake. Pretty much all commercial CNCs with heavy Z axes
have such a counterbalance, as well as a mechanical fail-safe brake to
prevent the axis from dropping when the servo is not powered.

As for coupling the servo, I'd go with an oversized timing belt.
Something like a 2" wide belt could be reasonably expected to outlive
you as long as the pulleys are properly aligned.

On 2011-02-24, Pete C. wrote:

Ignoramus3498 wrote:

On 2011-02-24, Karl Townsend wrote:
I'm taking the knee apart on my CNC mill and sending out for
rebuild...

I have an extra ball screw on hand that is perfect for replacing the
Acme hand knee lift screw. I'd then put a servo motor on the knee.

I did some preliminary layout for initial design of how to do this. it
will work best to rigidly mount the ball screw and spin the ball nut
with the nut located right at the bottom of the knee sitting on a
taper bearing.

Anyway, with this layout it would be all but impossible to change out
a timing belt. You'd have to take the knee apart. (There's always a
design weakness for maintenance)

Anyway, a #35 roller chain would make for a far easier and less
expensive installation. Given that the knee will only move slowly at
tool changes and always have downward force; is this causing another
problem that I don't see?

Karl

A good timing belt should last a very long time under these
conditions. I would expect the condition of the 1,000 lbs knee pushing
on the ball screw all the time, to be quite punishing for the ball
screw. If you have pneumatic support, it would help.

But please keep us posted, this sounds like a very interesting plan.

i

Second the recommendation for a pneumatic or hydraulic counterbalance
and an axis brake. Pretty much all commercial CNCs with heavy Z axes
have such a counterbalance, as well as a mechanical fail-safe brake to
prevent the axis from dropping when the servo is not powered.

Mine does have a pneumatic counterbalance.

As for coupling the servo, I'd go with an oversized timing belt.
Something like a 2" wide belt could be reasonably expected to outlive
you as long as the pulleys are properly aligned.

Those timing belts live just about forever. They look like new on my
mill.

The failsafe brake should work even if the timing belt breaks,
though. (iow, it should not be on the motor). Not a big deal, but
would be preferable.

It is a great project, take some pictures and keep us posted.


i

On Thu, 24 Feb 2011 08:44:10 -0600, "Pete C."
wrote:


Ignoramus3498 wrote:

On 2011-02-24, Karl Townsend wrote:
I'm taking the knee apart on my CNC mill and sending out for
rebuild...

I have an extra ball screw on hand that is perfect for replacing the
Acme hand knee lift screw. I'd then put a servo motor on the knee.

I did some preliminary layout for initial design of how to do this. it
will work best to rigidly mount the ball screw and spin the ball nut
with the nut located right at the bottom of the knee sitting on a
taper bearing.

Anyway, with this layout it would be all but impossible to change out
a timing belt. You'd have to take the knee apart. (There's always a
design weakness for maintenance)

Anyway, a #35 roller chain would make for a far easier and less
expensive installation. Given that the knee will only move slowly at
tool changes and always have downward force; is this causing another
problem that I don't see?

Karl

A good timing belt should last a very long time under these
conditions. I would expect the condition of the 1,000 lbs knee pushing
on the ball screw all the time, to be quite punishing for the ball
screw. If you have pneumatic support, it would help.

But please keep us posted, this sounds like a very interesting plan.

i

Second the recommendation for a pneumatic or hydraulic counterbalance
and an axis brake. Pretty much all commercial CNCs with heavy Z axes
have such a counterbalance, as well as a mechanical fail-safe brake to
prevent the axis from dropping when the servo is not powered.

As for coupling the servo, I'd go with an oversized timing belt.
Something like a 2" wide belt could be reasonably expected to outlive
you as long as the pulleys are properly aligned.

A chain would be easier. I agree you should copy what everybody else
does if you can. I don't see a problem with chain but wanted a double
check.

Yes, I'll plan some sort of counterbalancing. It will have to go on
either side of the saddle below the table. My math indicates two 4"
diameter air cylinders with a 12" stroke would be perfect. Hope eBay
is my friend here. I'll design this after i find some parts cheap.

I hadn't considerred a brake. This would have to go on the drive end
of the servo after the pulley or a solenoid plunger to pulley itself.
Do you have a part suggestion?

Karl

On Feb 24, 7:28*am, Karl Townsend
wrote:
I'm taking the knee apart on my CNC mill and sending out for
rebuild...

I have an extra ball screw on hand that is perfect for replacing the
Acme hand knee lift screw. I'd then put a servo motor on the knee.

I did some preliminary layout for initial design of how to do this. it
will work best to rigidly mount the ball screw and spin the ball nut
with the nut located right at the bottom of the knee sitting on a
taper bearing.

Anyway, with this layout it would be all but impossible to change out
a timing belt. You'd have to take the knee apart. (There's always a
design weakness for maintenance)

Anyway, a #35 roller chain would make for a far easier and less
expensive installation. Given that the knee will only move slowly at
tool changes and always have downward force; is this causing another
problem that I don't see?

Karl

I'm interested in CNC, but I don't know a lot about it. Probably I'll
go down that road in a few years, but two things come to mind. It
seems that you would be worried about backlash and want to keep it at
a minimum. 1st: Could you use a tensioner on the chain to reduce it?
(Similar to the ones found on car engines.) 2nd: Since you will
probably have an encoder, doesn't the software take into account the
backlash and compensate for it (assuming that you're measuring the
movement of the table and not the servo or stepper)?

On Feb 24, 8:28*am, Karl Townsend
wrote:
...
I did some preliminary layout for initial design of how to do this. it
will work best to rigidly mount the ball screw and spin the ball nut
with the nut located right at the bottom of the knee sitting on a
taper bearing.

Anyway, with this layout it would be all but impossible to change out
a timing belt. You'd have to take the knee apart. (There's always a
design weakness for maintenance)
...
Karl

You can't block up the knee and detach the ball screw?

jsw

Karl Townsend wrote:

On Thu, 24 Feb 2011 08:44:10 -0600, "Pete C."
wrote:


Ignoramus3498 wrote:

On 2011-02-24, Karl Townsend wrote:
I'm taking the knee apart on my CNC mill and sending out for
rebuild...

I have an extra ball screw on hand that is perfect for replacing the
Acme hand knee lift screw. I'd then put a servo motor on the knee.

I did some preliminary layout for initial design of how to do this. it
will work best to rigidly mount the ball screw and spin the ball nut
with the nut located right at the bottom of the knee sitting on a
taper bearing.

Anyway, with this layout it would be all but impossible to change out
a timing belt. You'd have to take the knee apart. (There's always a
design weakness for maintenance)

Anyway, a #35 roller chain would make for a far easier and less
expensive installation. Given that the knee will only move slowly at
tool changes and always have downward force; is this causing another
problem that I don't see?

Karl

A good timing belt should last a very long time under these
conditions. I would expect the condition of the 1,000 lbs knee pushing
on the ball screw all the time, to be quite punishing for the ball
screw. If you have pneumatic support, it would help.

But please keep us posted, this sounds like a very interesting plan.

i

Second the recommendation for a pneumatic or hydraulic counterbalance
and an axis brake. Pretty much all commercial CNCs with heavy Z axes
have such a counterbalance, as well as a mechanical fail-safe brake to
prevent the axis from dropping when the servo is not powered.

As for coupling the servo, I'd go with an oversized timing belt.
Something like a 2" wide belt could be reasonably expected to outlive
you as long as the pulleys are properly aligned.

A chain would be easier. I agree you should copy what everybody else
does if you can. I don't see a problem with chain but wanted a double
check.

Yes, I'll plan some sort of counterbalancing. It will have to go on
either side of the saddle below the table. My math indicates two 4"
diameter air cylinders with a 12" stroke would be perfect. Hope eBay
is my friend here. I'll design this after i find some parts cheap.

I hadn't considerred a brake. This would have to go on the drive end
of the servo after the pulley or a solenoid plunger to pulley itself.
Do you have a part suggestion?

Karl

http://surpluscenter.com

cylinders and brakes...

Ignoramus3498 wrote:

On 2011-02-24, Pete C. wrote:

Ignoramus3498 wrote:

On 2011-02-24, Karl Townsend wrote:
I'm taking the knee apart on my CNC mill and sending out for
rebuild...

I have an extra ball screw on hand that is perfect for replacing the
Acme hand knee lift screw. I'd then put a servo motor on the knee.

I did some preliminary layout for initial design of how to do this. it
will work best to rigidly mount the ball screw and spin the ball nut
with the nut located right at the bottom of the knee sitting on a
taper bearing.

Anyway, with this layout it would be all but impossible to change out
a timing belt. You'd have to take the knee apart. (There's always a
design weakness for maintenance)

Anyway, a #35 roller chain would make for a far easier and less
expensive installation. Given that the knee will only move slowly at
tool changes and always have downward force; is this causing another
problem that I don't see?

Karl

A good timing belt should last a very long time under these
conditions. I would expect the condition of the 1,000 lbs knee pushing
on the ball screw all the time, to be quite punishing for the ball
screw. If you have pneumatic support, it would help.

But please keep us posted, this sounds like a very interesting plan.

i

Second the recommendation for a pneumatic or hydraulic counterbalance
and an axis brake. Pretty much all commercial CNCs with heavy Z axes
have such a counterbalance, as well as a mechanical fail-safe brake to
prevent the axis from dropping when the servo is not powered.

Mine does have a pneumatic counterbalance.

As for coupling the servo, I'd go with an oversized timing belt.
Something like a 2" wide belt could be reasonably expected to outlive
you as long as the pulleys are properly aligned.

Those timing belts live just about forever. They look like new on my
mill.

The failsafe brake should work even if the timing belt breaks,
though. (iow, it should not be on the motor). Not a big deal, but
would be preferable.

It is a great project, take some pictures and keep us posted.

i

Most commercial CNCs don't use timing belts to couple the servo, so the
brake is usually inline. An oversized timing belt shouldn't brake in our
lifetimes so we don't need to worry. Even if it did, the table would
lower at a moderate rate, since there are losses in back driving a
ballscrew. If you have flow restrictors on the counterbalance cylinders,
they will limit the drop rate also.

Karl Townsend wrote:
I'm taking the knee apart on my CNC mill and sending out for
rebuild...

I have an extra ball screw on hand that is perfect for replacing the
Acme hand knee lift screw. I'd then put a servo motor on the knee.

I did some preliminary layout for initial design of how to do this. it
will work best to rigidly mount the ball screw and spin the ball nut
with the nut located right at the bottom of the knee sitting on a
taper bearing.

Anyway, with this layout it would be all but impossible to change out
a timing belt. You'd have to take the knee apart. (There's always a
design weakness for maintenance)

Anyway, a #35 roller chain would make for a far easier and less
expensive installation. Given that the knee will only move slowly at
tool changes and always have downward force; is this causing another
problem that I don't see?

Karl


You will need a brake on the ballscrew or it will drop when the power
turns off.

John

I'm glad rubber timing belts weren't around 50 years ago, otherwise
there'd surely be some unusable old machinery now.

On 2011-02-24, Jordan wrote:
I'm glad rubber timing belts weren't around 50 years ago, otherwise
there'd surely be some unusable old machinery now.

I see plenty of unusable old machinery now!

i

On Fri, 25 Feb 2011 09:37:09 +1100, Jordan wrote:

I'm glad rubber timing belts weren't around 50 years ago, otherwise
there'd surely be some unusable old machinery now.

The Bridgeport J-head was introduced over 60 years ago with a timing
belt in the head. My circa 1960 LeBlond Regal has a timing belt that
drives the spindle in the highest speed range. Both machines are very
successful designs.

--
Ned Simmons

Ignoramus3498 wrote:

On 2011-02-24, Jordan wrote:
I'm glad rubber timing belts weren't around 50 years ago, otherwise
there'd surely be some unusable old machinery now.

I see plenty of unusable old machinery now!

i

Yep, and a worn out timing belt is a lot cheaper and easier to replace
than a gear with teeth broken off.

On Feb 24, 5:37*pm, Jordan wrote:
I'm glad rubber timing belts weren't around 50 years ago, otherwise
there'd surely be some unusable old machinery now.

Fortunately they used leather belts instead.

jsw

On 2011-02-24, Pete C. wrote:

Ignoramus3498 wrote:

On 2011-02-24, Jordan wrote:
I'm glad rubber timing belts weren't around 50 years ago, otherwise
there'd surely be some unusable old machinery now.

I see plenty of unusable old machinery now!

i

Yep, and a worn out timing belt is a lot cheaper and easier to replace
than a gear with teeth broken off.

And I see plenty of old machinery with timing belts, like my Clausing
lathe.

i

On 2/25/2011 9:59 AM, Pete C. wrote:

Yep, and a worn out timing belt is a lot cheaper and easier to replace
than a gear with teeth broken off.

I can make a gear, not a belt.
Some belts that were made are no longer available. I know that to be the
case because I have a sewing machine with an irreplaceable timing belt.
Unless there's a compelling reason to chose otherwise, I'm for a metal
only solution.

Jordan wrote:

On 2/25/2011 9:59 AM, Pete C. wrote:

Yep, and a worn out timing belt is a lot cheaper and easier to replace
than a gear with teeth broken off.

I can make a gear, not a belt.
Some belts that were made are no longer available. I know that to be the
case because I have a sewing machine with an irreplaceable timing belt.
Unless there's a compelling reason to chose otherwise, I'm for a metal
only solution.

Faulty logic. If you can make a gear, you can also make or rework a
pulley to match a modern timing belt.

Jordan wrote:
On 2/25/2011 9:59 AM, Pete C. wrote:

Yep, and a worn out timing belt is a lot cheaper and easier to replace
than a gear with teeth broken off.

I can make a gear, not a belt.
Some belts that were made are no longer available. I know that to be the
case because I have a sewing machine with an irreplaceable timing belt.
Unless there's a compelling reason to chose otherwise, I'm for a metal
only solution.


What is the machine with the unobtainable belt?

--
Steve W.

On 2/25/2011 2:18 PM, Pete C. wrote:


Faulty logic. If you can make a gear, you can also make or rework a
pulley to match a modern timing belt.

OK to a point, subject to accessibility, and I'd need to make two pulleys.
I've no undue beef against belts, just question why you'd choose one
over other solutions. If there's no reason to use one, why would you?
The subject under question doesn't consider noise, as it's only to move
the tool's knee. I guess, starting from scratch, a belt might be easier
and cheaper, but maybe not if using stock sprockets or gears. I like to
put in a vote for systems that are well proven, run with their guts
hanging out, and usually give warning before failure - unlike belts.

On 2/25/2011 3:18 PM, Steve W. wrote:

What is the machine with the unobtainable belt?


Czechoslovakian - do you want the brand? I'll have to check, but I think
it's Helvetia.

Karl Townsend wrote:
...
Anyway, a #35 roller chain would make for a far easier and less
expensive installation. Given that the knee will only move slowly at
tool changes and always have downward force; is this causing another
problem that I don't see?

Would the plane of the chain be horizontal? If so, chain doesn't like
to run like that - it's weight tends to run it off the sprocket unless
it's tensioned just right or has guides.

Bob

Jordan wrote:
On 2/25/2011 9:59 AM, Pete C. wrote:

Yep, and a worn out timing belt is a lot cheaper and easier to replace
than a gear with teeth broken off.

I can make a gear, not a belt.
Some belts that were made are no longer available. I know that to be the
case because I have a sewing machine with an irreplaceable timing belt.
Unless there's a compelling reason to chose otherwise, I'm for a metal
only solution.

Well, about the "irreplaceable timing belt," I pray to differ. If you
have the specifications of the original, or even the dimensions of the
pulleys, you could either have one made to order or make one yourself
if you're inclined. I know it's possible to get belt material in bulk,
and whoever sells the bulk material will also sell the means of attaching
the ends. I've seen sewing machine belts that are nothing but big O-rings,
for example.

If you really wanted to get it going and aren't too persnickety about
presentation, you could use panty hose. ;-)

Cheers!
Rich

On 2/25/2011 9:46 PM, Rich Grise wrote:


Well, about the "irreplaceable timing belt," I pray to differ. If you
have the specifications of the original, or even the dimensions of the
pulleys, you could either have one made to order or make one yourself
if you're inclined. I know it's possible to get belt material in bulk,
and whoever sells the bulk material will also sell the means of attaching
the ends. I've seen sewing machine belts that are nothing but big O-rings,
for example.

If you really wanted to get it going and aren't too persnickety about
presentation, you could use panty hose. ;-)

Cheers!
Rich



OK, I didn't know it were possible to make a timing belt at home. To be
clear, a panty hose won't do the job of a timing belt - it'd behave like
a V belt and do nothing to synchronise shafts (unless I tie regularly
spaced knots in it?).
My old Czech sewing machine (Halvena) wouldn't be worth the price of a
belt today, but when it first broke a couple of decades ago (I can't
seem to throw things away) I searched for a toothed belt with 7mm pitch
and got nowhere. I might have more luck since the advent of internet!
The point is, a rubber belt will not last the life of the rest of the
machine, and could be a nuisance to replace, unlike a chain. A new belt
may well "see you out", but what about your grandkids? Think posterity!
The clear advantages of belts - cleanliness, dryness, lightness,
simplicity, quietness - shouldn't blind us to their shortcomings. Have
you a car with a timing belt? When do you plan to do its regularly
needed replacement? Ignore that at your peril!

On Fri, 25 Feb 2011 00:05:28 -0500, Bob Engelhardt
wrote:

Karl Townsend wrote:
...
Anyway, a #35 roller chain would make for a far easier and less
expensive installation. Given that the knee will only move slowly at
tool changes and always have downward force; is this causing another
problem that I don't see?

Would the plane of the chain be horizontal? If so, chain doesn't like
to run like that - it's weight tends to run it off the sprocket unless
it's tensioned just right or has guides.

Bob

Good point. An issue I hadn't considered.

I really worked this little design problem with Autocad last night.
I'm not coming up with a good idea. Not finding a decent way to do the
pulley is only one issue. Putting two lbs. of **** in a one lb. box is
the real problem.

if someone out there would like to spend time with this, I'd actually
*pay* money. Hard for me, I know. But cheaper than building it wrong.
The person would need something like Alebre or other 3D modeling
software.

On another note, I found a Pro to come out and scrape in the ways. And
a company to send the ball screws out for rebuild.

Karl

Jordan wrote:

On 2/25/2011 2:18 PM, Pete C. wrote:


Faulty logic. If you can make a gear, you can also make or rework a
pulley to match a modern timing belt.

OK to a point, subject to accessibility, and I'd need to make two pulleys.
I've no undue beef against belts, just question why you'd choose one
over other solutions. If there's no reason to use one, why would you?
The subject under question doesn't consider noise, as it's only to move
the tool's knee. I guess, starting from scratch, a belt might be easier
and cheaper, but maybe not if using stock sprockets or gears. I like to
put in a vote for systems that are well proven, run with their guts
hanging out, and usually give warning before failure - unlike belts.

Unlike gears, belts allow any amount of separation between the two
shafts in question, and that separation distance is independent of both
drive ratio and overall pulley diameter (subject to some minimums), and
without needing a train of idler gears to fill the gap. Belts also allow
more misalignment without problems than gears do. Most belts I've seen
give plenty of warning before failure.

Jordan wrote:
On 2/25/2011 3:18 PM, Steve W. wrote:

What is the machine with the unobtainable belt?


Czechoslovakian - do you want the brand? I'll have to check, but I think
it's Helvetia.

Make and model if possible. There are a LOT of machines out there that
are rebadged. I have 4 machines here that look different outside but
under the hood they are the same machine.

--
Steve W.

Karl Townsend wrote:
On Fri, 25 Feb 2011 00:05:28 -0500, Bob Engelhardt
wrote:

Karl Townsend wrote:
...
Anyway, a #35 roller chain would make for a far easier and less
expensive installation. Given that the knee will only move slowly at
tool changes and always have downward force; is this causing another
problem that I don't see?
Would the plane of the chain be horizontal? If so, chain doesn't like
to run like that - it's weight tends to run it off the sprocket unless
it's tensioned just right or has guides.

Bob

Good point. An issue I hadn't considered.

I really worked this little design problem with Autocad last night.
I'm not coming up with a good idea. Not finding a decent way to do the
pulley is only one issue. Putting two lbs. of **** in a one lb. box is
the real problem.

if someone out there would like to spend time with this, I'd actually
*pay* money. Hard for me, I know. But cheaper than building it wrong.
The person would need something like Alebre or other 3D modeling
software.

On another note, I found a Pro to come out and scrape in the ways. And
a company to send the ball screws out for rebuild.

Karl


How about a shaft drive to a worm gearbox with the ball nut driven off
the driven gear?

--
Steve W.

Jordan wrote:
On 2/25/2011 9:59 AM, Pete C. wrote:

Yep, and a worn out timing belt is a lot cheaper and easier to replace
than a gear with teeth broken off.

I can make a gear, not a belt.
Some belts that were made are no longer available. I know that to be
the case because I have a sewing machine with an irreplaceable timing
belt.
Unless there's a compelling reason to chose otherwise, I'm for a metal
only solution.
Have a look here

http://www.arceurotrade.co.uk/projec...ive%20Mods.pdf

and maybe

http://www.cad2gcode.com/pulley/

If you have the time then maybe you can re-engineer the sewing machine
to use a belt that is available. It's not unknown for manufacturers to
have custom components made, such as belts, so you have to buy the
spares from them at an increased mark-up, A mate used to work for a farm
machinery manufacturer that did that for some V belts. At the end of the
day you can work around it but it depends what you time is worth.

Jordan wrote:
On 2/25/2011 9:46 PM, Rich Grise wrote:
...
If you really wanted to get it going and aren't too persnickety about
presentation, you could use panty hose. ;-)

OK, I didn't know it were possible to make a timing belt at home. To be
clear, a panty hose won't do the job of a timing belt - it'd behave like
a V belt and do nothing to synchronise shafts (unless I tie regularly
spaced knots in it?).

OK, it sounds like I inadvertently spoke out of turn. I neglected to
distinguish "timing belt," but that raises a question - a "timing belt"
on a sewing machine? I fear I must recuse myself then. :-)

My old Czech sewing machine (Halvena) wouldn't be worth the price of a
belt today, but when it first broke a couple of decades ago (I can't
seem to throw things away) I searched for a toothed belt with 7mm pitch
and got nowhere. I might have more luck since the advent of internet!
The point is, a rubber belt will not last the life of the rest of the
machine, and could be a nuisance to replace, unlike a chain. A new belt
may well "see you out", but what about your grandkids? Think posterity!
The clear advantages of belts - cleanliness, dryness, lightness,
simplicity, quietness - shouldn't blind us to their shortcomings. Have
you a car with a timing belt?

Aha! Yes, I have, TWICE! The first was a Ford Fairmont; I paid for the tow
and repair by barter! They fixed my car, I set up their computer. They even
threw in the tow! ;-) I'm quite proud of that little factoid.

The second was a 1975 Plymouth Gran Fury, in the early 1990's, with a
couple hundred thou on it. It was also a clearance engine, but I didn't
have cash on hand to have it fixed and I was living in an apartment that
wouldn't let you do your own car work beyond an oil change anyway.

So, yeah, I know the difference between a timing belt and a v-belt,
and as I've said, I'll be recusing myself now.

Thanks,
Rich

On 2/26/2011 12:20 AM, Pete C. wrote:



Unlike gears, belts allow any amount of separation between the two
shafts in question, and that separation distance is independent of both
drive ratio and overall pulley diameter (subject to some minimums), and
without needing a train of idler gears to fill the gap. Belts also allow
more misalignment without problems than gears do. Most belts I've seen
give plenty of warning before failure.

Pros and cons - nothing perfect in engineering.
If belts gave plenty of warning, we needn't do regular scheduled changes
for our cars' timing belts? That's a special case of course and not a
big issue for most machine tool applications, but transmission failure
in many apps is not a trivial problem. I think alignment ought to be
pretty good for wide toothed and ribbed belts, in the interests of
longevity.

On 2/26/2011 10:20 AM, Rich Grise wrote:
a "timing belt"
on a sewing machine?

Indeed. There's lots of high grade engineering in the humble sewing
machine. Timing these is very important. The oldest toothed belt I saw
was on an ancient Singer. It seemed to be made of string and wire.

Jordan wrote:
On 2/26/2011 10:20 AM, Rich Grise wrote:
a "timing belt"
on a sewing machine?

Indeed. There's lots of high grade engineering in the humble sewing
machine. Timing these is very important. The oldest toothed belt I saw
was on an ancient Singer. It seemed to be made of string and wire.

Yep, you want to see a complex machine take a look at the older machines
with multiple stitch functions done mechanically. Timing belts, cams and
gear drives galore.

--
Steve W.

On 2/26/2011 10:11 AM, David Billington wrote:


http://www.arceurotrade.co.uk/projec...ive%20Mods.pdf

and maybe

http://www.cad2gcode.com/pulley/

If you have the time then maybe you can re-engineer the sewing machine
to use a belt that is available. It's not unknown for manufacturers to
have custom components made, such as belts, so you have to buy the
spares from them at an increased mark-up, A mate used to work for a farm
machinery manufacturer that did that for some V belts. At the end of the
day you can work around it but it depends what you time is worth.

The article is about using belts to reduce vibration. That sounds like a
good application, if vibes are a problem.
For the sewing machine, I'd already sourced some possibly usable
alternative sprockets from some office equipment, but time has passed
this project by and if I were sensible, I shouldn't be doing anything
with it - old stitchers are real cheap. The real oldies are particularly
good. Until they introduced plastic gears, rubber belts and suchlike,
the domestic sewing machine was virtually everlasting.
I have an Italian motorbike with fancy "desmodromic" cams. I was pretty
chuffed, but less so when I realised that the most ordinary stitcher
also uses desmo!

On Feb 25, 6:11*pm, David Billington
wrote:
Jordan wrote:
On 2/25/2011 9:59 AM, Pete C. wrote:
...
If you have the time then maybe you can re-engineer the sewing machine
to use a belt that is available. It's not unknown for manufacturers to
have custom components made, such as belts, so you have to buy the
spares from them at an increased mark-up, A mate used to work for a farm
machinery manufacturer that did that for some V belts. At the end of the
day you can work around it but it depends what you time is worth.

Was it the type of belt where the cogs are stiff wire wound and
crimped around a plain flat belt?

jsw

On 2/26/2011 8:31 AM, Steve W. wrote:
Jordan wrote:
On 2/25/2011 3:18 PM, Steve W. wrote:

What is the machine with the unobtainable belt?


Czechoslovakian - do you want the brand? I'll have to check, but I
think it's Helvetia.

Make and model if possible. There are a LOT of machines out there that
are rebadged. I have 4 machines here that look different outside but
under the hood they are the same machine.


Halvena model 132
It's older than I thought - there's a date on it 1959.
I'd be delighted and astonished if you can find a belt for it.

Jordan wrote:
On 2/26/2011 8:31 AM, Steve W. wrote:
Jordan wrote:
On 2/25/2011 3:18 PM, Steve W. wrote:

What is the machine with the unobtainable belt?


Czechoslovakian - do you want the brand? I'll have to check, but I
think it's Helvetia.

Make and model if possible. There are a LOT of machines out there that
are rebadged. I have 4 machines here that look different outside but
under the hood they are the same machine.


Halvena model 132
It's older than I thought - there's a date on it 1959.
I'd be delighted and astonished if you can find a belt for it.


http://www.sew4less.com/category/117/Belts_by_length

Will probably have one.

http://www.sewingmachineparts.net/timing_belts.html

Guy can probably find one as well, but if you measure it first you may
as well look for it on Sew4Less

--
Steve W.

On 2/28/2011 3:31 PM, Steve W. wrote:


http://www.sew4less.com/category/117/Belts_by_length

Will probably have one.

http://www.sewingmachineparts.net/timing_belts.html

Guy can probably find one as well, but if you measure it first you may
as well look for it on Sew4Less


I tried the first website - size not listed (in fact, nothing metric).
I emailed the second some days ago - no response. I interpret that as a
"not in stock".
That's evidence that rubber transmission belts may not be available for
old machines, I think.

Karl Townsend wrote:

Anyway, with this layout it would be all but impossible to change out
a timing belt. You'd have to take the knee apart. (There's always a
design weakness for maintenance)


Will you be able to keep waylube from getting on the belt?

Wes