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 aluminum tube and a 1/4 inch diameter aluminum rod for
the driveshaft.

The rod will be rotating inside of nylon bushings. The nylon
bushings will be stuck inside of what Lowe's describes as "1/2" ID
PVC Reinforced Braided Vinyl Tubing". So that the bushings are
held snugly inside of the aluminum tube.

FWIW. Another way Lowe's describes that spacer tubing is "1/2 ID
Braided PVC Tubing". It's a flexible clear plastic tubing with
reinforcing material inside.

Question: Is the aluminum rod spinning inside of the nylon
bushings going to cause the bushings to get hot enough to melt the
plastic tubing, with everything closed inside of the aluminum tube?

Thanks.





--
Everything fits perfectly, I'm just hoping it doesn't melt.
Aluminum bushing material pickings are slim at Lowe's, so I'm
assuming that what they have is suitable for a bushing. They are
in the specialty parts drawer area.

On Sep 10, 3:25*pm, John Doe wrote:

Question: Is the aluminum rod spinning inside of the nylon
bushings going to cause the bushings to get hot enough to melt the
plastic tubing, with everything closed inside of the aluminum tube?

Thanks.

What is the rpm of the shaft? How hot is it when you are using it?
How long do you intend to use it at one time? Are you using any
lubricant? In short you do not provide enough information for someone
to answer your question.


Dan

http://farm9.staticflickr.com/8031/7...dc44262f_z.jpg

Just in case you want to see a picture of the bushings and spacer.






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 aluminum tube and a 1/4 inch diameter aluminum rod for
the driveshaft.

The rod will be rotating inside of nylon bushings. The nylon
bushings will be stuck inside of what Lowe's describes as "1/2" ID
PVC Reinforced Braided Vinyl Tubing". So that the bushings are
held snugly inside of the aluminum tube.

FWIW. Another way Lowe's describes that spacer tubing is "1/2 ID
Braided PVC Tubing". It's a flexible clear plastic tubing with
reinforcing material inside.

Question: Is the aluminum rod spinning inside of the nylon
bushings going to cause the bushings to get hot enough to melt the
plastic tubing, with everything closed inside of the aluminum tube?

Thanks.

"John Doe" wrote in message
...

Question: Is the aluminum rod spinning inside of the nylon
bushings going to cause the bushings to get hot enough to melt the
plastic tubing, with everything closed inside of the aluminum tube?

If you would break down and buy a small lathe you wouldn't be
constantly having these problems.

"John Doe" wrote in message
...
http://farm9.staticflickr.com/8031/7...dc44262f_z.jpg

Just in case you want to see a picture of the bushings and spacer.






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 aluminum tube and a 1/4 inch diameter aluminum rod for
the driveshaft.

The rod will be rotating inside of nylon bushings. The nylon
bushings will be stuck inside of what Lowe's describes as "1/2" ID
PVC Reinforced Braided Vinyl Tubing". So that the bushings are
held snugly inside of the aluminum tube.

FWIW. Another way Lowe's describes that spacer tubing is "1/2 ID
Braided PVC Tubing". It's a flexible clear plastic tubing with
reinforcing material inside.

Question: Is the aluminum rod spinning inside of the nylon
bushings going to cause the bushings to get hot enough to melt the
plastic tubing, with everything closed inside of the aluminum tube?

Thanks.



Your design is not really clear. Are there two bushings? How are the
bushings held in alignment? If they are not well aligned, the friction will
be quite large and the bushings will wear.

However Nylon is generally only used for low RPMs. You might have a problem
with a line trimmer. Here is a link that has a table of maximum speeds and
loads for Nylon and Delrin bushings
http://plastics.dupont.com/plastics/...n/L12565_7.pdf

Another problem is nylon expands in wet environments and will make your
bushing loosen up.

On 9/10/2012 2:24 PM, John Doe wrote:
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 aluminum tube and a 1/4 inch diameter aluminum rod for
the driveshaft.

The rod will be rotating inside of nylon bushings. The nylon
bushings will be stuck inside of what Lowe's describes as "1/2" ID
PVC Reinforced Braided Vinyl Tubing". So that the bushings are
held snugly inside of the aluminum tube.

FWIW. Another way Lowe's describes that spacer tubing is "1/2 ID
Braided PVC Tubing". It's a flexible clear plastic tubing with
reinforcing material inside.

Question: Is the aluminum rod spinning inside of the nylon
bushings going to cause the bushings to get hot enough to melt the
plastic tubing, with everything closed inside of the aluminum tube?

Thanks.





Spin it fast enough then yes, of course.

anorton wrote:
...
http://plastics.dupont.com/plastics/...n/L12565_7.pdf
...

quote
Soft steel or stainless steel, as well as all non-ferrous metals
do not run well with plastic bearings, even those with
a socalled ‘‘self-lubricating’’ filler. It is only a question of
load, speed and time until wear increases rapidly, leading
to premature failure
/quote

"anorton" anorton removethis.ix.netcom.com wrote:

Another problem is nylon expands in wet environments and will
make your bushing loosen up.

I thought that was a property of UHMW or HDPE plastic, not nylon.

"John Doe" wrote in message
...
"anorton" anorton removethis.ix.netcom.com wrote:

Another problem is nylon expands in wet environments and will
make your bushing loosen up.

I thought that was a property of UHMW or HDPE plastic, not nylon.


Backwards. Chemically Nylon is a protein, polyethlene is a wax.

anorton wrote:

"John Doe" wrote in message
...
http://farm9.staticflickr.com/8031/7...dc44262f_z.jpg

Just in case you want to see a picture of the bushings and spacer.






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 aluminum tube and a 1/4 inch diameter aluminum rod for
the driveshaft.

The rod will be rotating inside of nylon bushings. The nylon
bushings will be stuck inside of what Lowe's describes as "1/2" ID
PVC Reinforced Braided Vinyl Tubing". So that the bushings are
held snugly inside of the aluminum tube.

FWIW. Another way Lowe's describes that spacer tubing is "1/2 ID
Braided PVC Tubing". It's a flexible clear plastic tubing with
reinforcing material inside.

Question: Is the aluminum rod spinning inside of the nylon
bushings going to cause the bushings to get hot enough to melt the
plastic tubing, with everything closed inside of the aluminum tube?

Thanks.



Your design is not really clear. Are there two bushings? How are the
bushings held in alignment? If they are not well aligned, the friction
will be quite large and the bushings will wear.

However Nylon is generally only used for low RPMs. You might have a
problem with a line trimmer. Here is a link that has a table of
maximum speeds and loads for Nylon and Delrin bushings
http://plastics.dupont.com/plastics/...n/L12565_7.pdf

Another problem is nylon expands in wet environments and will make
your bushing loosen up.
Depend on how the nylon is constrained. The swelling due to water
absorption can tighten the bushing leading to seizure. My neighbour had
this happen on a prototype using a nylon bearing and while all was well
when installed after sitting in a damp environment over a weekend the
mechanism couldn't be moved due to swelling of the nylon.

John Doe wrote:
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 aluminum tube and a 1/4 inch diameter aluminum rod for
the driveshaft.

The rod will be rotating inside of nylon bushings. The nylon
bushings will be stuck inside of what Lowe's describes as "1/2" ID
PVC Reinforced Braided Vinyl Tubing". So that the bushings are
held snugly inside of the aluminum tube.

FWIW. Another way Lowe's describes that spacer tubing is "1/2 ID
Braided PVC Tubing". It's a flexible clear plastic tubing with
reinforcing material inside.

Question: Is the aluminum rod spinning inside of the nylon
bushings going to cause the bushings to get hot enough to melt the
plastic tubing, with everything closed inside of the aluminum tube?

Thanks.


Well if you're planning on running the rpms anything over idle the
bushings might last 10 seconds before they melt.

You would be better off using round rod and small bearings. Easy enough
to square the end with a file.


--
Steve W.

On Mon, 10 Sep 2012 13:07:21 -0700, "anorton"
wrote:

Here is a link that has a table of maximum speeds and
loads for Nylon and Delrin bushings

http://plastics.dupont.com/plastics/...n/L12565_7.pdf


Thanks!!!

Gunner

--
"Confronting Liberals with the facts of reality is very much akin to
clubbing baby seals. It gets boring after a while, but because Liberals are
so stupid it is easy work." Steven M. Barry

On Mon, 10 Sep 2012 19:24:59 +0000 (UTC), John Doe
wrote:

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 aluminum tube and a 1/4 inch diameter aluminum rod for
the driveshaft.

The rod will be rotating inside of nylon bushings. The nylon
bushings will be stuck inside of what Lowe's describes as "1/2" ID
PVC Reinforced Braided Vinyl Tubing". So that the bushings are
held snugly inside of the aluminum tube.

FWIW. Another way Lowe's describes that spacer tubing is "1/2 ID
Braided PVC Tubing". It's a flexible clear plastic tubing with
reinforcing material inside.

Question: Is the aluminum rod spinning inside of the nylon
bushings going to cause the bushings to get hot enough to melt the
plastic tubing, with everything closed inside of the aluminum tube?

Thanks.
Running aluminum in nylon without lubrication will result in very
short bushing life. Aluminum running in nylon even with lube will
still have a pretty short life. I know you are trying to keep the
weight down but for long bushing life you really need to run a hard
material against the nylon. A hard anodized aluminum shaft might work
but you're not gonna be paying to get your shaft hard anodized. Can
you use a dowell pin in place of the part of the shaft that runs in
the nylon? Frankly, I wouldn't use nylon in your application. I would
use Delrin AF. You can get sample bushings for free from some
manufacturers. Can you Loctite a hardened or even soft steel bushing
over the aluminum shaft where the shaft runs in the nylon? And are you
really stuck using nylon? That shaft is gonna be spinning about 10,000
rpm which translates to 654 feet per minute which translates to
sliding some aluminum across some nylon the length of a football field
in less than 30 seconds.
Eric

On Mon, 10 Sep 2012 19:24:59 +0000, John Doe wrote:
[re bushings for drive shaft for inline skating push stick]
http://howto.homedepot.com/videos/wa...l-Trimmer.html
....
I'm replacing the outer shaft and the inner driveshaft, with a
straight aluminum tube and a 1/4 inch diameter aluminum rod for
the driveshaft.

The rod will be rotating inside of nylon bushings. The nylon
bushings will be stuck inside of what Lowe's describes as "1/2" ID
PVC Reinforced Braided Vinyl Tubing". So that the bushings are
held snugly inside of the aluminum tube.
....
Question: Is the aluminum rod spinning inside of the nylon
bushings going to cause the bushings to get hot enough to melt the
plastic tubing, with everything closed inside of the aluminum tube?

As others said, (a) tell us the shaft RPM and (b) from following URL,
running aluminum in nylon bushings is problematic.
http://plastics.dupont.com/plastics/pdflit/europe/design/L12565_7.pdf

Also, if you have a setup to measure melting points, tell us the
melting points of your materials. From wikipedia links below,
nylon melts in a 190€“350 C range, and PVC in a 100€“260 C range,
so it might be possible to get some nylon that melts at a lower
temperature than some PVC. In any case, heat transfer through
the nylon will be slow, so I think your nylon bushing will melt
down before the PVC does, even if your PVC has a low melting point.
http://en.wikipedia.org/wiki/Polyvinyl_chloride
http://en.wikipedia.org/wiki/Nylon

Have you looked through all the sintered Oilite bushings available
at local hardware stores? Typical Ace HW and TruValue HW stores
carry assortments of dozens of different sizes of bushings like
those shown at http://www.oilitebushes.com/ and such a bushing
is worth considering if you can't get miniature ball bearings.

--
jiw

James Waldby wrote:
On Mon, 10 Sep 2012 19:24:59 +0000, John Doe wrote:
[re bushings for drive shaft for inline skating push stick]

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

...

I'm replacing the outer shaft and the inner driveshaft, with a
straight aluminum tube and a 1/4 inch diameter aluminum rod for
the driveshaft.

The rod will be rotating inside of nylon bushings. The nylon
bushings will be stuck inside of what Lowe's describes as "1/2" ID
PVC Reinforced Braided Vinyl Tubing". So that the bushings are
held snugly inside of the aluminum tube.

...

Question: Is the aluminum rod spinning inside of the nylon
bushings going to cause the bushings to get hot enough to melt the
plastic tubing, with everything closed inside of the aluminum tube?


As others said, (a) tell us the shaft RPM and (b) from following URL,
running aluminum in nylon bushings is problematic.
http://plastics.dupont.com/plastics/pdflit/europe/design/L12565_7.pdf

Also, if you have a setup to measure melting points, tell us the
melting points of your materials. From wikipedia links below,
nylon melts in a 190€“350 C range, and PVC in a 100€“260 C range,
so it might be possible to get some nylon that melts at a lower
temperature than some PVC. In any case, heat transfer through
the nylon will be slow, so I think your nylon bushing will melt
down before the PVC does, even if your PVC has a low melting point.
http://en.wikipedia.org/wiki/Polyvinyl_chloride
http://en.wikipedia.org/wiki/Nylon

Have you looked through all the sintered Oilite bushings available
at local hardware stores? Typical Ace HW and TruValue HW stores
carry assortments of dozens of different sizes of bushings like
those shown at http://www.oilitebushes.com/ and such a bushing
is worth considering if you can't get miniature ball bearings.


Could be worth looking at the Igus site
http://www.igus.co.uk/default.asp as they have a number of bearing
materials and can supply shafting in various forms in SS, anodised
aluminium, chrome plated etc. They have design info also.

John Doe wrote:
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 aluminum tube and a 1/4 inch diameter aluminum rod for
the driveshaft.

The rod will be rotating inside of nylon bushings. The nylon
bushings will be stuck inside of what Lowe's describes as "1/2" ID
PVC Reinforced Braided Vinyl Tubing". So that the bushings are
held snugly inside of the aluminum tube.

FWIW. Another way Lowe's describes that spacer tubing is "1/2 ID
Braided PVC Tubing". It's a flexible clear plastic tubing with
reinforcing material inside.

Question: Is the aluminum rod spinning inside of the nylon
bushings going to cause the bushings to get hot enough to melt the
plastic tubing, with everything closed inside of the aluminum tube?

Thanks.

those engines are rated to about 10000 rpm. I see your bushings melting or
vibrating as they wear. We're talking a screeching vibration as the shaft
rolls backwards on the bushing surface. A slender tube and rod are the
perfect setup for such this.

I'd just get some cheapo radial ball bearings and sent this into your
tube. they can handle the speeds with no problem.

Cydrome Leader presence MUNGEpanix.com wrote:

John Doe jdoe usenetlove.invalid wrote:

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 aluminum tube and a 1/4 inch diameter aluminum rod for
the driveshaft.

The rod will be rotating inside of nylon bushings. The nylon
bushings will be stuck inside of what Lowe's describes as "1/2"
ID PVC Reinforced Braided Vinyl Tubing". So that the bushings
are held snugly inside of the aluminum tube.

FWIW. Another way Lowe's describes that spacer tubing is "1/2
ID Braided PVC Tubing". It's a flexible clear plastic tubing
with reinforcing material inside.

Question: Is the aluminum rod spinning inside of the nylon
bushings going to cause the bushings to get hot enough to melt
the plastic tubing, with everything closed inside of the
aluminum tube?

those engines are rated to about 10000 rpm. I see your bushings
melting or vibrating as they wear. We're talking a screeching
vibration as the shaft rolls backwards on the bushing surface. A
slender tube and rod are the perfect setup for such this.

I'd just get some cheapo radial ball bearings and sent this into
your tube. they can handle the speeds with no problem.

Using a 1/4 inch aluminum rod driveshaft, how many ball bearings
per foot?

That sounds fine. To most people, like for production, cost of
ball bearings over some bushing material would be the main
concern? In other words... Why don't grass trimmer manufacturers
use ball bearings?

Thanks.

John Doe wrote:
... Why don't grass trimmer manufacturers use ball bearings?

Good point! What do they use?

Bob Engelhardt bobengelhardt comcast.net wrote:

John Doe wrote:

... Why don't grass trimmer manufacturers use ball bearings?

Good point! What do they use?

My curved shaft (being replaced with a straight shaft) grass
trimmer uses a continuous single piece bushing made of nylon or
whatever.

John Doe wrote:
Using a 1/4 inch aluminum rod driveshaft, how many ball bearings
per foot?

I'd plan on one every 8" or so unless the rod is alloy that is stiff.



That sounds fine. To most people, like for production, cost of
ball bearings over some bushing material would be the main
concern? In other words... Why don't grass trimmer manufacturers
use ball bearings?

That depends on who made it. The higher end commercial units do have
ball bearings and solid drive shafts.
The low end home owner stuff usually doesn't.


Thanks.


--
Steve W.

"John Doe" wrote in message
...
...
Using a 1/4 inch aluminum rod driveshaft, how many ball bearings
per foot?

http://www.roymech.co.uk/Useful_Tabl...cal_Speed.html

Have fun!

John Doe wrote:
Cydrome Leader presence MUNGEpanix.com wrote:

John Doe jdoe usenetlove.invalid wrote:

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 aluminum tube and a 1/4 inch diameter aluminum rod for
the driveshaft.

The rod will be rotating inside of nylon bushings. The nylon
bushings will be stuck inside of what Lowe's describes as "1/2"
ID PVC Reinforced Braided Vinyl Tubing". So that the bushings
are held snugly inside of the aluminum tube.

FWIW. Another way Lowe's describes that spacer tubing is "1/2
ID Braided PVC Tubing". It's a flexible clear plastic tubing
with reinforcing material inside.

Question: Is the aluminum rod spinning inside of the nylon
bushings going to cause the bushings to get hot enough to melt
the plastic tubing, with everything closed inside of the
aluminum tube?

those engines are rated to about 10000 rpm. I see your bushings
melting or vibrating as they wear. We're talking a screeching
vibration as the shaft rolls backwards on the bushing surface. A
slender tube and rod are the perfect setup for such this.

I'd just get some cheapo radial ball bearings and sent this into
your tube. they can handle the speeds with no problem.

Using a 1/4 inch aluminum rod driveshaft, how many ball bearings
per foot?

You'd really have to test that out. How flexible your shaft and tube are
will matter.

That sounds fine. To most people, like for production, cost of
ball bearings over some bushing material would be the main
concern? In other words... Why don't grass trimmer manufacturers
use ball bearings?

I checked some manuals from redmax, to look at the exploded diagrams.

here's one

http://www.redmax.com/ddoc/RMXI/RMXI...20and%20up.pdf

They don't really list what bearins are there, which is probably none, but
I'm guessing the shaft they use is sufficiently stiff to not need support
at any place other than the ends. Their typical engine has a female
spline shape cut into the clutch. Lining up bearings and shafts is a pain,
so they're probably just supporting one side of their shaft at the engine
which has a ball or roller bearing at the end, and then at their little
gearbox thing that changes angles and holts the cutting blade/string or
whatever the tool uses.

To them, the less the part count the better.