Here's a diagram of a crank driven by a gearbox.
The existing arrangement is on the left:
http://i53.tinypic.com/21eap7l.jpg

The crank pushes a half ton weight backwards and forwards a distance
of three inches, five times per second.
After a few years the bolt keeps loosening or breaking, and the
bearing surround is cracking. Is that a surprise?

The gearbox and shaft and mandrel cannot be altered.
I propose bolting a steel pipe around the mandrel and welding that to
a plate with an offset shaft, and using a much bigger roller bearing.

Or if there was some existing product that would do the job, I'd
consider that. Any other brilliant ideas?

On Fri, 22 Jul 2011 17:59:48 -0700, Matty F wrote:

Here's a diagram of a crank driven by a gearbox. The existing
arrangement is on the left: http://i53.tinypic.com/21eap7l.jpg

The crank pushes a half ton weight backwards and forwards a distance of
three inches, five times per second. After a few years the bolt keeps
loosening or breaking, and the bearing surround is cracking. Is that a
surprise?

The gearbox and shaft and mandrel cannot be altered. I propose bolting a
steel pipe around the mandrel and welding that to a plate with an offset
shaft, and using a much bigger roller bearing.

Or if there was some existing product that would do the job, I'd
consider that. Any other brilliant ideas?

I always look forward to your questions :-) What you propose should
work, I'd think - although I'd question whether bolting the pipe to the
mandrel falls foul of "The gearbox and shaft and mandrel cannot be
altered"? Or are there convenient bolt-holes in the perimeter of the
mandrel already?

Presumably there's enough clearance between the crank and the mandrel for
the plate that you mention to fit without needing to offset* the crank
somehow? My only other suggestion - assuming you'd not be making use of
existing holes in the mandrel - would be to bolt the plate to the face of
the mandrel and forget about the welding and steel tubing, but that does
assume there's enough space to work with (given that you'd have the
combined width of the steel plate and mounting bolts to deal with, rather
than just the plate in your version)

* or are you planning on this? I note it's not on the list of things
which can't be altered :-)

cheers

Jules

On Jul 23, 1:27 pm, Jules Richardson
wrote:
On Fri, 22 Jul 2011 17:59:48 -0700, Matty F wrote:
Here's a diagram of a crank driven by a gearbox. The existing
arrangement is on the left:http://i53.tinypic.com/21eap7l.jpg

The crank pushes a half ton weight backwards and forwards a distance of
three inches, five times per second. After a few years the bolt keeps
loosening or breaking, and the bearing surround is cracking. Is that a
surprise?

The gearbox and shaft and mandrel cannot be altered. I propose bolting a
steel pipe around the mandrel and welding that to a plate with an offset
shaft, and using a much bigger roller bearing.

Or if there was some existing product that would do the job, I'd
consider that. Any other brilliant ideas?

I always look forward to your questions :-) What you propose should
work, I'd think - although I'd question whether bolting the pipe to the
mandrel falls foul of "The gearbox and shaft and mandrel cannot be
altered"? Or are there convenient bolt-holes in the perimeter of the
mandrel already?

The mandrel is immovably attached to the shaft and the gearbox and
motor are too huge to lift and take into the workshop.
I can drill and tap into the mandrel. There are already a number of
holes in it (and broken bolts) from failed repair attempts.

Presumably there's enough clearance between the crank and the mandrel for
the plate that you mention to fit without needing to offset* the crank
somehow? My only other suggestion - assuming you'd not be making use of
existing holes in the mandrel - would be to bolt the plate to the face of
the mandrel and forget about the welding and steel tubing, but that does
assume there's enough space to work with (given that you'd have the
combined width of the steel plate and mounting bolts to deal with, rather
than just the plate in your version)

There's plenty of room. The face of the mandrel doesn't have a lot of
space on it, what with the large shaft going through it and a couple
of holes with damaged thread.
I'll make the pipe a tight fit and put three or four bolts through to
the side of the mandrel.
At the moment there are two set screws going against the thread of the
old bolt to stop it turning. That's horrible!

The crank pushes a half ton weight backwards and forwards a distance
of three inches, five times per second.
After a few years the bolt keeps loosening or breaking, and the
bearing surround is cracking. Is that a surprise?


Another idiot boy question but if I don't ask.....

Is it possible that the bolt/bearing acts as a "damper" for vibration
transmitted through the crank which might otherwise do some harm to the
shaft/mandrel/gearbox with a more rigid coupling?

--
Robin
PM may be sent to rbw0{at}hotmail{dot}com

"Matty F" wrote in message
...
Here's a diagram of a crank driven by a gearbox.
The existing arrangement is on the left:
http://i53.tinypic.com/21eap7l.jpg

The crank pushes a half ton weight backwards and forwards a distance
of three inches, five times per second.
After a few years the bolt keeps loosening or breaking, and the
bearing surround is cracking. Is that a surprise?

The gearbox and shaft and mandrel cannot be altered.
I propose bolting a steel pipe around the mandrel and welding that
to
a plate with an offset shaft, and using a much bigger roller
bearing.

Or if there was some existing product that would do the job, I'd
consider that. Any other brilliant ideas?




Is it not a case of the crank pin (bolt) being under specified? Is the
weight guided in any way or only by the crank pin? If so maybe the
alignment is not perfect. I'd want the bolt to be replaced by one
significantly fatter and made from a good medium carbon or alloy
steel, with good provision for lubrication. could the bearing be
replaced by a spherical self aligning one?

AWEM

On Jul 23, 7:51 pm, "Robin" wrote:
The crank pushes a half ton weight backwards and forwards a distance
of three inches, five times per second.
After a few years the bolt keeps loosening or breaking, and the
bearing surround is cracking. Is that a surprise?

Another idiot boy question but if I don't ask.....

Is it possible that the bolt/bearing acts as a "damper" for vibration
transmitted through the crank which might otherwise do some harm to the
shaft/mandrel/gearbox with a more rigid coupling?

Well, I suppose I could add a spring to the crank.
But it otherwise has been running OK for some 40 years. Just the bolt
needs replacing often, and the hole it is screwed to in the mandrel.

On Jul 23, 7:57 pm, "Andrew Mawson"
wrote:
"Matty F" wrote in message

...



Here's a diagram of a crank driven by a gearbox.
The existing arrangement is on the left:
http://i53.tinypic.com/21eap7l.jpg

The crank pushes a half ton weight backwards and forwards a distance
of three inches, five times per second.
After a few years the bolt keeps loosening or breaking, and the
bearing surround is cracking. Is that a surprise?

The gearbox and shaft and mandrel cannot be altered.
I propose bolting a steel pipe around the mandrel and welding that
to
a plate with an offset shaft, and using a much bigger roller
bearing.

Or if there was some existing product that would do the job, I'd
consider that. Any other brilliant ideas?

Is it not a case of the crank pin (bolt) being under specified? Is the
weight guided in any way or only by the crank pin? If so maybe the
alignment is not perfect. I'd want the bolt to be replaced by one
significantly fatter and made from a good medium carbon or alloy
steel, with good provision for lubrication. could the bearing be
replaced by a spherical self aligning one?

Yes the bolt is vastly under specified even though the bolt that has
been put in is high tensile. There's no room in the mandrel for a
fatter bolt. And the roller bearing is way too small.
I thought someone would have asked by now, but the crank is pushing a
whole room full of people and furniture backwards and forwards around
five times per second! I think it's mounted on roller bearings.

On Sat, 23 Jul 2011 01:59:48 +0100, Matty F wrote:

Here's a diagram of a crank driven by a gearbox.
The existing arrangement is on the left:
http://i53.tinypic.com/21eap7l.jpg

The crank pushes a half ton weight backwards and forwards a distance
of three inches, five times per second.
After a few years the bolt keeps loosening or breaking, and the
bearing surround is cracking. Is that a surprise?

The gearbox and shaft and mandrel cannot be altered.
I propose bolting a steel pipe around the mandrel and welding that to
a plate with an offset shaft, and using a much bigger roller bearing.

Or if there was some existing product that would do the job, I'd
consider that. Any other brilliant ideas?




Is it a figment of my imagination? Or the drawing? Or your proposal?

But the distance from mandrel to crank shaft appears shorter in the
proposal. And that is in fact one of the things that sprang to mind. The
shorter that is the less leverage applied to the bolt where it enters the
mandrel.

I think part of the advantage of your proposal is the reduction in
effective length of the bolt. But I'd also take on board the other
comments here about acting as a shock absorber. If that is the case, maybe
some absorbent material inside the new pipe and plate would be
advantageous?

Rod

On Jul 23, 8:31 pm, polygonum wrote:
On Sat, 23 Jul 2011 01:59:48 +0100, Matty F wrote:
Here's a diagram of a crank driven by a gearbox.
The existing arrangement is on the left:
http://i53.tinypic.com/21eap7l.jpg

Is it a figment of my imagination? Or the drawing? Or your proposal?

But the distance from mandrel to crank shaft appears shorter in the
proposal. And that is in fact one of the things that sprang to mind. The
shorter that is the less leverage applied to the bolt where it enters the
mandrel.

The sideways cranking distance is supposed to be the same.
But it's just a sketch made from memory.

I think part of the advantage of your proposal is the reduction in
effective length of the bolt. But I'd also take on board the other
comments here about acting as a shock absorber. If that is the case, maybe
some absorbent material inside the new pipe and plate would be
advantageous?

I don't think a shock absorber is necessary. But I'll find out if it
breaks!

In message
,
Matty F writes
I thought someone would have asked by now, but the crank is pushing a
whole room full of people and furniture backwards and forwards around
five times per second! I think it's mounted on roller bearings.

Ah! The earthquake machine!

The purpose of the *pipe* seems to be to transfer the reciprocating load
from the bolted pivot to the outside of the mandrel. An alternative
might be to locate and support the spigot plate with plain pins and use
recessed cap head screws to secure it to the mandrel. Presumably you are
anxious to minimise the thickness of the plate.

A thought on the bearing.... SKF must still have a technical dept.
within the sales group who could advise on a suitable bearing.
Self-aligning roller sounds likely. The sort you see on rail wagons:-)

regards

--
Tim Lamb

On Jul 23, 9:08 pm, Tim Lamb wrote:
In message
,
Matty F writes

I thought someone would have asked by now, but the crank is pushing a
whole room full of people and furniture backwards and forwards around
five times per second! I think it's mounted on roller bearings.

Ah! The earthquake machine!

The purpose of the *pipe* seems to be to transfer the reciprocating load
from the bolted pivot to the outside of the mandrel. An alternative
might be to locate and support the spigot plate with plain pins and use
recessed cap head screws to secure it to the mandrel.

The flat end of the mandrel does not have enough space on it as there
are already holes in it with broken bolts inside.
The side of the mandrel is in good condition.

Presumably you are
anxious to minimise the thickness of the plate.

I don't think the size of the plate matters. It's going round at a
constant speed like a flywheel. If I had a block of steel big enough I
would dispense with the pipe and make the whole thing in one piece.
That's my specialty, and welding isn't.

A thought on the bearing.... SKF must still have a technical dept.
within the sales group who could advise on a suitable bearing.
Self-aligning roller sounds likely. The sort you see on rail wagons:-)

The first job is to find a suitable roller bearing lying around, free
of course! The bearings on each end of 50 HP tram motors are a good
size.

On Sat, 23 Jul 2011 01:24:04 -0700 (PDT), Matty F
wrote:

I thought someone would have asked by now, but the crank is pushing a
whole room full of people and furniture backwards and forwards around
five times per second! I think it's mounted on roller bearings.

Earthquake simulator?

I'd try to lose the thing marked "bolt" on the repair, and just go with the
things marked "bolts". "bolt" is just held in with setscrews, and will cause
trouble aligning the cap thing...

Thomas Prufer

On Jul 23, 9:28 pm, Thomas Prufer prufer.pub...@mnet-
online.de.invalid wrote:
On Sat, 23 Jul 2011 01:24:04 -0700 (PDT), Matty F
wrote:

I thought someone would have asked by now, but the crank is pushing a
whole room full of people and furniture backwards and forwards around
five times per second! I think it's mounted on roller bearings.

Earthquake simulator?

I'd try to lose the thing marked "bolt" on the repair, and just go with the
things marked "bolts". "bolt" is just held in with setscrews, and will cause
trouble aligning the cap thing...

Yes maybe. I suspect that the thread in the hole is stuffed anyway.
But I though I would need to put washers on each side of the bearing
to hold it on.
Whatever I do would be stronger than what's there.

In message
,
Matty F writes

A thought on the bearing.... SKF must still have a technical dept.
within the sales group who could advise on a suitable bearing.
Self-aligning roller sounds likely. The sort you see on rail wagons:-)

The first job is to find a suitable roller bearing lying around, free
of course! The bearings on each end of 50 HP tram motors are a good
size.

E -mail doesn't cost and you can ask what are the common applications as
an indication where to start looking. You can estimate the mass of the
room + furniture + people and you already know the rotational speed and
crank throw.


They were very helpful people when I worked there nearly 30 years
back:-)

regards

--
Tim Lamb

In message , Robin
writes
The crank pushes a half ton weight backwards and forwards a distance
of three inches, five times per second.
After a few years the bolt keeps loosening or breaking, and the
bearing surround is cracking. Is that a surprise?


Another idiot boy question but if I don't ask.....

Is it possible that the bolt/bearing acts as a "damper" for vibration
transmitted through the crank which might otherwise do some harm to the
shaft/mandrel/gearbox with a more rigid coupling?

I think it's more a matter of force = mass x acceleration

the bolt isn't up to the task

What's the bolt made of, steel?

Maybe splash out on a bit of titanium or summat

.... summat's good

--
geoff

In message
,
Matty F writes
On Jul 23, 7:57 pm, "Andrew Mawson"
wrote:
"Matty F" wrote in message

...



Here's a diagram of a crank driven by a gearbox.
The existing arrangement is on the left:
http://i53.tinypic.com/21eap7l.jpg

The crank pushes a half ton weight backwards and forwards a distance
of three inches, five times per second.
After a few years the bolt keeps loosening or breaking, and the
bearing surround is cracking. Is that a surprise?

The gearbox and shaft and mandrel cannot be altered.
I propose bolting a steel pipe around the mandrel and welding that
to
a plate with an offset shaft, and using a much bigger roller
bearing.

Or if there was some existing product that would do the job, I'd
consider that. Any other brilliant ideas?

Is it not a case of the crank pin (bolt) being under specified? Is the
weight guided in any way or only by the crank pin? If so maybe the
alignment is not perfect. I'd want the bolt to be replaced by one
significantly fatter and made from a good medium carbon or alloy
steel, with good provision for lubrication. could the bearing be
replaced by a spherical self aligning one?

Yes the bolt is vastly under specified even though the bolt that has
been put in is high tensile. There's no room in the mandrel for a
fatter bolt. And the roller bearing is way too small.
I thought someone would have asked by now, but the crank is pushing a
whole room full of people and furniture backwards and forwards around
five times per second! I think it's mounted on roller bearings.


Smaller earthquake or ...

Atkins diet all round

--
geoff

"Matty F" wrote in message
...
Here's a diagram of a crank driven by a gearbox.
The existing arrangement is on the left:
http://i53.tinypic.com/21eap7l.jpg

The crank pushes a half ton weight backwards and forwards a distance
of three inches, five times per second.
After a few years the bolt keeps loosening or breaking, and the
bearing surround is cracking. Is that a surprise?

The gearbox and shaft and mandrel cannot be altered.
I propose bolting a steel pipe around the mandrel and welding that to
a plate with an offset shaft, and using a much bigger roller bearing.

Or if there was some existing product that would do the job, I'd
consider that. Any other brilliant ideas?

The plan looks good to me. The big improvement will come from the designed
reduction in the gap between mandrel and bearing combined with the
increased diameter of the shaft that goes through the bearing over that of
the bolt alone.
I assume the black area surrounding the original bolt is a piece of thick
walled tube which will be welded to the backplate of the big piece of tube
as well as having the bolt through it. It would be a good idea to either
have that thick walled tube machined, or weld on a washer to prevent the
bearing moving sideways, with a second large washer under the head of the
bolt.

I would also use more than one bolt through the wall of the big tube to
clamp it onto the mandrel. Welding nuts on the outside will give greater
depth of thread than just tapping the tube.

Please post picture of the before and after.

Mike

Making a crank stronger

Don't use a crank. Switch it to an eccentric. You avoid the overhung
crankpin and bearing and you can also use a much bigger eccentric
sheave. The downside is thatyou have a much bigger bearing surface in
the eccentric sheave, so you probably need to source a scrap-price
large ball race before commencing.


Otherwise don't make a crank, use an existing one. Take a small
scrapyard engine (light diesel for preference) and recycle 1/4(ish) of
the block, with the crankshaft, one con-rod and one piston as a
crosshead.

If you do this with a wet liner engine (a Rover K is ideal, as it has
a main bearing ladder) you can even throw away most of the block and
just weld brackets to hold the wet liner (which is now a cylindrical
trunk guide) in position with the crank bearings.

In article
s.com, Matty F scribeth thus
On Jul 23, 7:51 pm, "Robin" wrote:
The crank pushes a half ton weight backwards and forwards a distance
of three inches, five times per second.
After a few years the bolt keeps loosening or breaking, and the
bearing surround is cracking. Is that a surprise?

Another idiot boy question but if I don't ask.....

Is it possible that the bolt/bearing acts as a "damper" for vibration
transmitted through the crank which might otherwise do some harm to the
shaft/mandrel/gearbox with a more rigid coupling?

Well, I suppose I could add a spring to the crank.
But it otherwise has been running OK for some 40 years. Just the bolt
needs replacing often, and the hole it is screwed to in the mandrel.


'Com on Matty fess up!, witch bit of engineering is it this time?..
--
Tony Sayer

Andy Dingley wrote:

Don't use a crank. Switch it to an eccentric. Â*You avoid the overhung
crankpin and bearing and you can also use a much bigger eccentric
sheave.

Isn't it likely to be a fatigue problem from the bending stress?

What about an outrigger bearing on the opposite side with the crank
mirrored. The bearing could be a self aligning plumber block.

AJH

On Jul 24, 12:51 am, "MuddyMike" wrote:

I assume the black area surrounding the original bolt is a piece of thick
walled tube which will be welded to the backplate of the big piece of tube
as well as having the bolt through it. It would be a good idea to either
have that thick walled tube machined, or weld on a washer to prevent the
bearing moving sideways, with a second large washer under the head of the
bolt.

I was thinking of making the black bit out of solid steel. It all
depends on what bearing I can find. There used to be a couple of very
large bearings that I will look for.

I would also use more than one bolt through the wall of the big tube to
clamp it onto the mandrel. Welding nuts on the outside will give greater
depth of thread than just tapping the tube.

I think I'll be using pipe with about 6mm wall.

Please post picture of the before and after.

On Jul 24, 1:40 am, Andy Dingley wrote:
Making a crank stronger

Don't use a crank. Switch it to an eccentric. You avoid the overhung
crankpin and bearing and you can also use a much bigger eccentric
sheave. The downside is thatyou have a much bigger bearing surface in
the eccentric sheave, so you probably need to source a scrap-price
large ball race before commencing.

Yes that was the first idea I thought of. It all depends if I can find
a bearing bigger than the existing mandrel.

Otherwise don't make a crank, use an existing one.

The existing setup works OK for about a year, so my improvement should
do the job. But I'll see what the motor guys have lying around.
I did think of having a large weight spinning around at 300 rpm but
that could go horribly wrong.

On Jul 24, 2:39 am, tony sayer wrote:

'Com on Matty fess up!, witch bit of engineering is it this time?..

Well it's either a steam engine converted to run with an electric
motor, or it's an earthquake house. But why would we want artificial
earthquakes when we have thousands of real ones? (Because those are a
long way away!)

"Matty F" wrote in message
...
On Jul 24, 1:40 am, Andy Dingley wrote:
Making a crank stronger

Don't use a crank. Switch it to an eccentric. You avoid the overhung
crankpin and bearing and you can also use a much bigger eccentric
sheave. The downside is thatyou have a much bigger bearing surface in
the eccentric sheave, so you probably need to source a scrap-price
large ball race before commencing.

Yes that was the first idea I thought of. It all depends if I can find
a bearing bigger than the existing mandrel.

Otherwise don't make a crank, use an existing one.

The existing setup works OK for about a year, so my improvement should
do the job. But I'll see what the motor guys have lying around.
I did think of having a large weight spinning around at 300 rpm but
that could go horribly wrong.

I dont have the tech knowledge of the guys that have replied, but.. At the
moment you appear to have an easy fix (replacing the bolts)
if you stiffen the mechanism and this transfers the `damage` elsewhere then
that could be a much more complicated and costly fix.
Some mechanisms have a `weaker` part to protect the whole. could the bolt be
likened to a fuse in a plug?
Anyhow thats my non technical input.

"Matty F" wrote in message
...
On Jul 24, 2:39 am, tony sayer wrote:

'Com on Matty fess up!, witch bit of engineering is it this time?..

Well it's either a steam engine converted to run with an electric
motor, or it's an earthquake house. But why would we want artificial
earthquakes when we have thousands of real ones? (Because those are a
long way away!)

What you need is an eccentric like they use on steam engines.

A big bearing with a central disk bolted to the shaft with a few bolts
offset by half the required stroke and an even bigger disk around the
outside connected to the rod. It depends on if you have a big enough
bearing.