Model Boat Mayhem
Technical, Techniques, Hints, and Tips => Engineering Techniques and Materials. => Topic started by: rayna on September 03, 2018, 04:19:52 am
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Hi Folks
I have made up shafts and bearings for years now but I now have another two pair sets to make so I thought i would ask the teams opinion on which is best material.
Shafts are usually stainless and tubes are brass (K&S) and previously I have made the bearings out of acrylic, nylon, uhwmpe and acetal. All have worked but what plastic do you guys find best, or should I stick with brass??
Look forward to your replies.
Rayna
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Rayna.......[from my own <*< experiences]
1. synthetic materials are excellent when used in the intended application...........
2. many synthetic materials adsorb water to their micro structure which can alter their dimensional reference
3. a heat increase within a synthetic material bush can also alter their dimensional reference
Bronze or brass family of metals when machined to bushes can tinned & soft soldered into the toleranced K&S brass tubing
The actual prop shaft can be used as the alignment former during this relatively low temperature soldering by sweating procedure
This also provides an accurate alignment between the 3 elements :-))
I would always recommend to use the brass or bronze bushes in the brass K&S tube with a stainless shaft......adding an oiler tube of course .......
Derek
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I only use bronze to make my bushes would not use anything else and as Derek does, fit an oiler
I solder my oilers onto the tube using plumbers solder, it's harder and stronger than soft solder.
John
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Stick with brass or better, bronze.
I've used 'nylon' a couple of times, the steel wears a lot more than the nylon! :o
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An awful lot of multi racers are using PEEK for bushes at the prop end, and if it's good enough for 8 horsepower at 28,000rpm, it's good enough for something electric...
I know Ian Folkson is selling genuine PEEK in suitable sizes for bushes, see http://www.iansboats.co.uk (http://www.iansboats.co.uk)
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Abstract
Polyether ether ketone (PEEK) with its high glass transition temperature, low friction coefficient, high heat resistance and good machinability is a promising material to meet the growing demand for lightweight, durable components.
In this study, radial PEEK bearings were produced by lathe machining and their rolling contact fatigue behavior under dry condition was investigated. Under low (<80 N) and high (>100 N) radial loads PEEK bearings failed under 5×105 cycles by adhesion and seizure, respectively, however under medium loads, the bearings achieved relatively long lives, as well as a unique feature of self-lubrication. An optimum load range to assure the longest possible service life of PEEK components was established.
Highlights
► For this research we produced PEEK (polyether ether ketone) polymer radial bearing by lathe machining.
► We performed rolling contact fatigue tests under dry conditions.
► We found that PEEK self-lubrication occurs during bearing work in contact with alumina balls.
► PEEK bearings achieved long bearing life through self-lubrication.
► We managed to determine the optimal load range for PEEK polymer radial bearing work.
https://www.sciencedirect.com/science/article/pii/S0301679X11003586
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I've had no experience with PEEK so I can't comment on it, but I always use bronze for prop shaft bearings, with 4 mm stainless steel shafts.
Peter.
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Martin - that test was for very high radial loads, of which in a propshaft application there should be very little to none.
(https://s.hswstatic.com/gif/bearing-radial.jpg)
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I always use PTFE in my A frames. Being water lubricated I have no bother. nemesis
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Mattie....when Noah built his Ark....... Adzes & Hammers & bolts & nuts made from Bronze were used ....he even used them for Stern Gland bushes for the propeller shafts
PEEK & PTFE >>:-( weren't even invented then
If Bronze was good enough for Noah...should be good enough for you & me
Derek
PS....Andyn......8 horsepower at 28,000rpm being transmitted against an 50x75 two blade X profile propeller will create a substantial radial load against the shaft bush O0
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We specify PEEK and PTFE for some valve seals at work as they have excellent sealing capacities with some chemicals.
but...
I have made up shafts and bearings for years now but I now have another two pair sets to make so I thought i would ask the teams opinion on which is best material.
...what was wrong with them before you feel you need to change now? One of those questions you might ask 10 different people and get 10 different answers before anyone even asks what you were doing wrong before and felt to change in the first place?
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Well I am always interested in PROGRESS if it is backed by experience and I appreciate the Forums wide experience based knowledge.
Hope that answers that thought.
PEEK is not new to me but I do not think it is available in small bits out here.
I do like he plastics for easy machining, bronze is exorbitant price wise but brass is fine so I have plenty of choices still.
thanks to all.
Rayna
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Raboesch use Delrin (acetal)... I've machined bushings from Delrin stock, it machines marvelously.
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Anyone’s interested, firm I work for operates a bar end policy, lot of the bar ends are 10” long, bronze, brass, peek, ptfe, delrin,acetal, all for about£5-£30 a length, plus post, Or collect from shaw, near Oldham,
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A nice offer. Thanks for posting that Alan.