30boat
N/A
Would there be any advantage in making them in Teflon?
Teflon cutless bearing
- Thread starter 30boat
- Start date
vyv_cox
Well-Known Member
Often the opposite. Pure Teflon is soft and has poor mechanical properties. Glass is added to improve these, giving the typical white appearance. The glass filler can have a dramatic effect on stainless steels, which it abrades fiercely. Specialist PTFE components, such as piston rings in reciprocating gas compressors, are glass-free for this reason, but many are very expensive.
Bobobolinsky
Well-Known Member
Nope, go with Vesconite if you want to pay for a high quality bearing.
misterg
Well-Known Member
As far as I'm aware, PTFEs are white whether or not they're glass filled (due to the crystalinity inherent in the material). FEPs are similar materials which can be transparent. (I stand to be corrected.)
Still useless for cutless bearings, whether filled or not
/Pedant
Andy
Neil_Y
Well-Known Member
Or Maritex which is non melting or softening and resists marine growth?
As Vyv sais teflon is a soft material and not suitable as a bearing material, some bearing manufacturers will face a bearing with teflon but this masks a poor bearing. The latest water lubricated shaft bearings have in built lubricants that are activated if the temperature rises and also have a surface chemistry which resists marine growth, alongside high mechanical strength and limited thermal expansion.
Brent Swain
N/A
I once used a 39 cent, gray plastic hose barb, for a direct drive bearing on a one inch shaft, turning 2500 RPM. Lasted several years. No noticeable wear in that time.
Any soft plastic will work.
Any soft plastic will work.
30boat
N/A
What about Acetal then?
Brent Swain
N/A
Acetal is a bit hard and brittle . Softer PVC works well.
stevebirch2002
Well-Known Member
What size bearing are you after Nuno? I make bearings for the Vega out of a fantastic material (Vesconite). If you can let me know the dimensions (OD & ID) then I will see what I can do.
Cheers
Steve B
Cheers
Steve B
30boat
N/A
Hi Steve
My arrangement is weird in that the P Bracket bore is imperial but the shaft is metric(25mm).The problem is that no cutless bearings (that I know) come in those sizes so the ones I've been getting are slightly undersize and have to be set in epoxy.As a result of not being pressed in the inside diameter is too large for the shaft.They don't ever last longer than a few months.I must launch on Monday so no time to fit one of yours but next time I haul out I'll measure the Pbracket bore and let you know.
Cheers
Nuno
JonJon
Well-Known Member
I thought rubbery type nitrile materials were very good at resisting erosin from gritty particles. The environment the cutlass bearing operates in is often contaminated with mud and sand -especially if you hit a sandbank or venture into shallow water and the nature of the bearing allows it to cope. Whereas a traditional material bearing would fail rapidly. In the 'awlfield they use rubberised screw type pumps to pump mud exactly for this reason.
Bobobolinsky
Well-Known Member
If you need a bearing quick
http://www.theplasticshop.co.uk/nylon-66-rod-40mm-to-60mm-diameter-1760-0.html
They send by return of post, the black is the grade for bearings, as it contains moly bisulphide, which gives it it's black colour.
Any machine shop will lathe it quick. A 250mm by 50mm rod cost me £10.50 plus postage.
http://www.theplasticshop.co.uk/nylon-66-rod-40mm-to-60mm-diameter-1760-0.html
They send by return of post, the black is the grade for bearings, as it contains moly bisulphide, which gives it it's black colour.
Any machine shop will lathe it quick. A 250mm by 50mm rod cost me £10.50 plus postage.
30boat
N/A
Thanks.I thought Nylon is not suitable for underwater bearings as it swells.
Tranona
Well-Known Member
Nothing unusual about your cutless. It is a standard size 1.5"od 25mm id fitted to many Westerlys. Available from any stern gear specialist or Trafalgar Yacht Services.
If you are getting a short life it suggests there is something else wrong. Misalignment is the obvious one, either engine to shaft or P bracket to engine centreline.
BTW if the inside diameter is too great that suggests you are using a 1" (25.4mm) bearing as cutless bearings do not compress when you fit them.
30boat
N/A
That's the thing,those bearings don't fit, they're too small which means my P Bracket is not the correct size.I've been getting my bearings from Trafalgar Yacht Services and they know their businness.Alignment is not an issue as I have an Aquadrive that's been set up very carefully.My presently fitted bearing has an internal diameter of 25mm,says so on the box,and it's still not tight on the shaft.Maybe the rubber will swell a bit under water,I don't know.
Tranona
Well-Known Member
It is not supposed to be tight on the shaft. The shaft should turn easily even when dry and it floats on water when in use. If it is wearing with an Aquadrive that suggests even more strongly that the shaft is out of line because it cannot move in relation to the engine.
If the P bracket is not the original 1.5" bore suggests it might have been replaced at some time and not properly lined up with the Aquadrive output.
If the P bracket is not the original 1.5" bore suggests it might have been replaced at some time and not properly lined up with the Aquadrive output.
Neil_Y
Well-Known Member
You have to get them sized for a clearance fit.
Nearly all the bearings we supply are for epoxy/clearance fit which has a couple of benefits over a press fit. But the ID is a different size if you insist on interference/press fit as the bearing suffers some bore closure.
Maritex is available in any ID and any OD (to 22") currently.
http://www.h4marine.com/Downloads/Maritex AQUARIUS General Calculator REV 20100519.xls
Designers and diy use this calculator to determine sizes, some are supplied blank for local machining or we can supply finished. They are Lloyds approved for water lubricated shaft bearings and are used by a number of Navies that operate in a lot of sand and silt, they are also used by Pilot boats in the UK and have been specified on the latest submarines so thay have some pedigree. They are also used in mining pumps with very abrasive slurry so they seem to cope very well with abrasives.
Nearly all the bearings we supply are for epoxy/clearance fit which has a couple of benefits over a press fit. But the ID is a different size if you insist on interference/press fit as the bearing suffers some bore closure.
Maritex is available in any ID and any OD (to 22") currently.
http://www.h4marine.com/Downloads/Maritex AQUARIUS General Calculator REV 20100519.xls
Designers and diy use this calculator to determine sizes, some are supplied blank for local machining or we can supply finished. They are Lloyds approved for water lubricated shaft bearings and are used by a number of Navies that operate in a lot of sand and silt, they are also used by Pilot boats in the UK and have been specified on the latest submarines so thay have some pedigree. They are also used in mining pumps with very abrasive slurry so they seem to cope very well with abrasives.