If lightness is a high priority, should a driveshaft be hollow?

I'd like to replace the driveshaft of a grass trimmer. Since
lightness is high priority, does a hollow tube make sense?

Thanks.

On 28/08/2012 21:38, John Doe wrote:
If lightness is a high priority, should a driveshaft be hollow?

I'd like to replace the driveshaft of a grass trimmer. Since
lightness is high priority, does a hollow tube make sense?

Thanks.


Yes

As long as it will provide the necessary torque, and not buckle.

Or you might be able to replace steel with solid aluminium, or glass
fibre, or carbon fibre.

In article om,
newshound wrote:

On 28/08/2012 21:38, John Doe wrote:
If lightness is a high priority, should a driveshaft be hollow?

I'd like to replace the driveshaft of a grass trimmer. Since
lightness is high priority, does a hollow tube make sense?

Thanks.


Yes

As long as it will provide the necessary torque, and not buckle.

Or you might be able to replace steel with solid aluminium, or glass
fibre, or carbon fibre.

As you near the limits, you can push them back by making it composite
(ie, if steel of X wall thickness will work, and steel of YX will
buckle, there will probably be some values of Y for which filling the
center with lightweight rigid foam will then not buckle.) But you are
probably not riding that hairy of an edge...

--
Cats, coffee, chocolate...vices to live by
Please don't feed the trolls. Killfile and ignore them so they will go away.

On 8/28/2012 1:38 PM, John Doe wrote:
If lightness is a high priority, should a driveshaft be hollow?

I'd like to replace the driveshaft of a grass trimmer. Since
lightness is high priority, does a hollow tube make sense?

Thanks.

The driveshaft on my 1955 Ford was hollow.
That's the most recent one I've tried to lift.

http://howto.homedepot.com/videos/wa...01/Echo-GT225-
Entry-Level-Trimmer.html

That's my two-stroke 21.2 CC grass trimmer.

I'm replacing the outer shaft and the inner driveshaft.

The outer shaft is easy enough.

The inner driveshaft will probably be either of these two...

Aluminum 6061-T6 Bare Drawn Tube
0.375" x 0.065" x 0.245"

Stainless T-304/304L Seamless Tube
0.375" x 0.065" x 0.245"

If steel should be used, should it be lighter than that?

I'm planning to use bearings in the shaft. The original flexible
driveshaft was contained within a long continuous (maybe HDPE, or
UHMW) bearing along the entire curved shaft.

John Doe fired this volley in news:k1jm5q$s22$1
@dont-email.me:

If steel should be used, should it be lighter than that?

I'm planning to use bearings in the shaft. The original flexible
driveshaft was contained within a long continuous (maybe HDPE, or
UHMW) bearing along the entire curved shaft.

Let's see, now. It's not a gear-head whacker, it's a curved shaft job.

Five feet of speedo cable is too heavy? What can it weigh... five or six
ounces? Half a pound?

You expect ordinary drawn tubing to take a near-30-degree bend at only
about 50x radius/diameter, be bent and re-bent continually as it rotates
in the bearings, and _last_? It'll part company with itself in a few
hundred revolutions.

There's a reason they use flexible shafting in those toy weed whackers.

I think you're nuts, unless you plan to go to a straight shaft, AND plan
on not whacking weeds with it anymore.

LLoyd

"Lloyd E. Sponenburgh" lloydspinsidemindspring.com wrote:

John Doe jdoe usenetlove.invalid fired

http://howto.homedepot.com/videos/wa...l-Trimmer.html

That's my two-stroke 21.2 CC grass trimmer.

I'm replacing the outer shaft and the inner driveshaft
[with a straight shaft].

The outer shaft is easy enough.

The inner driveshaft will probably be either of these two...

Aluminum 6061-T6 Bare Drawn Tube 0.375" x 0.065" x 0.245"

Stainless T-304/304L Seamless Tube 0.375" x 0.065" x 0.245"

If steel should be used, should it be lighter than that?

I'm planning to use bearings in the shaft. The original
flexible driveshaft was contained within a long continuous
(maybe HDPE, or UHMW) bearing along the entire curved shaft.

Let's see, now. It's not a gear-head whacker, it's a curved
shaft job.

My replacement shaft is straight.

Five feet of speedo cable is Half a pound?

Yes. A half a pound is significant in my application. But it needs
to be replaced for other reasons, too. And since it's being
replaced, I'd like it to be light as possible.

You expect ordinary drawn tubing to take a near-30-degree bend
at only about 50x radius/diameter, be bent and re-bent
continually as it rotates in the bearings

No. And the motor probably would not be able to turn it.

and _last_? It'll part company with itself in a few hundred
revolutions.

I probably should have made clear that the new shaft is straight,
and that the reference was mainly about the motor power.

--










There's a reason they use flexible shafting in those toy weed whackers.

I think you're nuts, unless you plan to go to a straight shaft, AND plan
on not whacking weeds with it anymore.

LLoyd

John Doe fired this volley in news:k1jp60$alf$1
@dont-email.me:


I probably should have made clear that the new shaft is straight,
and that the reference was mainly about the motor power.

Carbon fiber or hardened aluminum arrow shaft stock. It can be had to fit
bearings, too.

LLoyd

John Doe wrote:
If lightness is a high priority, should a driveshaft be hollow?

I'd like to replace the driveshaft of a grass trimmer. Since
lightness is high priority, does a hollow tube make sense?

Thanks.

Just be aware that the loads might be way
greater than you think when the blade hits
something.

"Jim Stewart" wrote in message
...


John Doe wrote:
If lightness is a high priority, should a driveshaft be hollow?

I'd like to replace the driveshaft of a grass trimmer. Since
lightness is high priority, does a hollow tube make sense?

Thanks.

Just be aware that the loads might be way
greater than you think when the blade hits
something.

This is the powered-skate guy with the short temper.

Jim Wilkins wrote:
"Jim wrote in message
...


John Doe wrote:
If lightness is a high priority, should a driveshaft be hollow?

I'd like to replace the driveshaft of a grass trimmer. Since
lightness is high priority, does a hollow tube make sense?

Thanks.

Just be aware that the loads might be way
greater than you think when the blade hits
something.

This is the powered-skate guy with the short temper.

I miss the old day where we just had to tiptoe around
Lenny the Lurker...

"Lloyd E. Sponenburgh" lloydspinsidemindspring.com wrote:

So, then, how about arrow shafting? It's hard, it's light, it
takes a (longitudinal) beating in its intended purpose.

I appreciate the suggestion. I would like to use it. But...

Besides having a budget, I have several pieces with measurements
that have to match, like inner diameter to outer diameter. Since I
don't have metal working tools, everything must be ordered parts
that fit together.

Outer shaft
Aluminum 6061-T6 Drawn Tube
0.875" x 0.777"

Inner driveshaft
Aluminum 6061-T6 Bare Drawn Tube
0.375" x 0.245"

That inner diameter matches the outer diameter of the end piece
that is plugged into the socket driven by the motor. Using the end
part of the original flex shaft. Its actual outer diameter is
about .247, with some sanding it should fit snugly (glued).

Next up, find nylon (or whatever) bushings that will fit the 3/8
inch outer diameter of the driveshaft, and fit into the .777 inner
diameter of the outer shaft.

Connections at the other end of the driveshaft, to the geared
wheel, is hopefully the last task. Before testing.

I have a vague idea of what the RPM is going to be. Wheel size is
somewhat adjustable.

--










LLoyd