Aluminum rod in nylon bushing produce much heat?

http://howto.homedepot.com/videos/watch/1567826211001/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, 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
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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
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http://farm9.staticflickr.com/8031/7973207210_68dc44262f_z.jpg
Just in case you want to see a picture of the bushings and spacer.

http://howto.homedepot.com/videos/watch/1567826211001/Echo-GT225-Entry-Level-Trimmer.html
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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/pdflit/europe/design/L12565_7.pdf
Another problem is nylon expands in wet environments and will make your bushing loosen up.
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anorton wrote:

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

I thought that was a property of UHMW or HDPE plastic, not nylon.
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Backwards. Chemically Nylon is a protein, polyethlene is a wax.
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anorton wrote:

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

http://plastics.dupont.com/plastics/pdflit/europe/design/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
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If you would break down and buy a small lathe you wouldn't be constantly having these problems.
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On 9/10/2012 2:24 PM, John Doe wrote:

http://howto.homedepot.com/videos/watch/1567826211001/Echo-GT225-Entry-Level-Trimmer.html
Spin it fast enough then yes, of course.
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John Doe wrote:

http://howto.homedepot.com/videos/watch/1567826211001/Echo-GT225-Entry-Level-Trimmer.html
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.

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

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
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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/watch/1567826211001/Echo-GT225-Entry-Level-Trimmer.html ...
...
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

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James Waldby wrote:

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.
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http://howto.homedepot.com/videos/watch/1567826211001/Echo-GT225-Entry-Level-Trimmer.html
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.
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Cydrome Leader <presence MUNGEpanix.com> wrote:

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.
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John Doe wrote:

Good point! What do they use?
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John Doe wrote:

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

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.

--
Steve W.

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http://www.roymech.co.uk/Useful_Tables/Drive/Shaft_Critical_Speed.html
Have fun!
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