Material for block sheaves

I made new sheaves for all my old blocks and mast using "acetal".
Its an engineering plastic, and is available in white and black. Use the original bushing from the center of the block, Grind a tool to give you the correct shape for the rope to sit in, and you will have them all done in no time.
 
Many good quality blocks, including Viadana and Schaefer, for instance, use DuPont's brand of acetal plastic called Delrin:

"Delrin® acetal homopolymer bridges the gap between metals and ordinary plastics with a unique combination of creep resistance, strength, stiffness, hardness, dimensional stability, toughness, fatigue resistance, solvent and fuel resistance, abrasion resistance, low wear and low friction".
 
Even Chance said:
I made new sheaves for all my old blocks and mast using "acetal".
Its an engineering plastic, and is available in white and black. Use the original bushing from the center of the block, Grind a tool to give you the correct shape for the rope to sit in, and you will have them all done in no time.
Click to expand...

As said a good material to work with, but don't make your sheave tolerances too tight as it is effected somewhat by moisture. PTFE on the other hand is not, but a softer material so wear is a factor to consider.

Acetol will be good but just allow for a little expansion on the sheave sides.

Have fun, Lathes are great to play with.
 
Nylon is cheaper, it is more difficult to machine, as it is softer and deforms, I tried using it, some of the sheaves came out wobbly.
Use very sharp tools.
I've bought odd bits of acetal on eBay.
I've also bought bits of tool steel and ground it using a bench grinder, but I find a small silicon carbide wheel in a dremel good for sharpening.
There are several 'swarf making' forums out there.
I've also rebushed a few sheaves by turning brass bushes.
It's a hobby that leads to collecting lots of bits and bobs. A proper parting tool was a good investment.
I found a couple of basic books in the library, and borrowed a couple from a mech eng chap I sail with now and then....
 
richardsnowstar said:
And also where to buy the material?
Thanks.
Click to expand...

I've bought all sorts of plastics from Direct Plastics Online. http://www.directplasticsonline.co.uk

I like the way their web site gives detailed properties for all the plastics. The last item I made was a bow roller for a club member in UHMWPE which I hadn't come across before. I'll be interested to see how this has fared after a season on a swinging mooring.

I've just remembered that they say that UHMWPE is used for pulleys in the marine industry.
 
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Bushings certainly, but I'd prefer the Acetal for the sheaves themselves (unless you sail a nice classic with beautiful blocks anyway!). My original sheaves in the mast were Aluminium. The Acetal ones are hugely better, and actually lighter as well. They run on phospher bronze bushings that I also made at the same time.

I use Acetal every day in my working life, making jigs to construct bespoke battery and power systems. Its great to machine, and is quite stable in the marine environment. My sheaves have lasted 6 years now and are still free and unworn.

I will post up a better explination of making them tomorrow.
 
VO5 said:
What about the idea of making replacement sheaves in phosphur bronze, yes / no ?
Click to expand...

I would be concerned about electrolytic corrosion if they were in contact with aluminium in the mast.
One of the sheaves I made uses a stainless ball race, sold for skateboard wheels, with an acetal rim.
 
Even Chance said:
Bushings certainly, but I'd prefer the Acetal for the sheaves themselves (unless you sail a nice classic with beautiful blocks anyway!). My original sheaves in the mast were Aluminium. The Acetal ones are hugely better, and actually lighter as well. They run on phospher bronze bushings that I also made at the same time.

I use Acetal every day in my working life, making jigs to construct bespoke battery and power systems. Its great to machine, and is quite stable in the marine environment. My sheaves have lasted 6 years now and are still free and unworn.

I will post up a better explination of making them tomorrow.
Click to expand...

Are bushes essential? One sheave is for a genoa car that is currently rivetted. I was planning to remove the rivet an replace it with threaded stainless bar with a stainless tube sleeve over the threaded bar that with also act as a bush for the acetal or UHMWPE sheave. Does this sound like na reasonable plan?
 
Bushes aren't essential when using acetal or delrin as both are used to make bearings and bushes, they do deform under load if highly loaded

Neither are effected by moisture, or at least not to any amount that you need to worry about, nylon is so avoid it unless you allow for the changes

I take it you have a small lathe if the tools are only 6mm so it would struggle cutting 14mm wide grooves in harder materials but may well be OK if you go carefully as acetal/delrin are lovely to machine, to make a 14mm groove the easy way is just to grind a rounded end tool out but as you are restricted to 6mm shank size then get something like http://www.chronos.ltd.uk/cgi-bin/sh000001.pl?WD=6%20xc39%20mm%20ref%20tool%20773851%20profiling&PN=XMAS_GIFT_IDEAS_2%2ehtml#a773851 which is a 6mm shank profiling tool which takes a 6mm round insert which will cut acetal & delrin very nicely - I have a bigger version I use for acetal / dedlrin / ally / stainless / anything and they give a really good finish

You can't realistically polish acetal/delrin after you have cut it but you can file it and sand it if you aren't too worried about the finish or better still use router bits in a holder to get a really nice finish straight off the lathe - I use 1/4" shank bearing guided round-over bits to get a nice rounded finish on the front of the torch and battery canisters I make and made a holder for router bits from an ally offcut

You can get lots of acetal / delrin offcuts from ebay - Ace Materials do short offcuts http://www.ebay.co.uk/sch/ace_materials/m.html?_nkw=&_armrs=1&_from=&_ipg=&_trksid=p3686 - I bought a load of short ends of 50mm & 60mm from them a while ago and their stock changes so worth keeping an eye on them

I buy my acetal / delrin by the meter from http://www.metals4u.co.uk/ but they do short lengths as well - if you give them a ring they are really helpful
 
DinghyMan said:
Bushes aren't essential when using acetal or delrin as both are used to make bearings and bushes, they do deform under load if highly loaded

Neither are effected by moisture, or at least not to any amount that you need to worry about, nylon is so avoid it unless you allow for the changes

I take it you have a small lathe if the tools are only 6mm so it would struggle cutting 14mm wide grooves in harder materials but may well be OK if you go carefully as acetal/delrin are lovely to machine, to make a 14mm groove the easy way is just to grind a rounded end tool out but as you are restricted to 6mm shank size then get something like http://www.chronos.ltd.uk/cgi-bin/sh000001.pl?WD=6%20xc39%20mm%20ref%20tool%20773851%20profiling&PN=XMAS_GIFT_IDEAS_2%2ehtml#a773851 which is a 6mm shank profiling tool which takes a 6mm round insert which will cut acetal & delrin very nicely - I have a bigger version I use for acetal / dedlrin / ally / stainless / anything and they give a really good finish

You can't realistically polish acetal/delrin after you have cut it but you can file it and sand it if you aren't too worried about the finish or better still use router bits in a holder to get a really nice finish straight off the lathe - I use 1/4" shank bearing guided round-over bits to get a nice rounded finish on the front of the torch and battery canisters I make and made a holder for router bits from an ally offcut

You can get lots of acetal / delrin offcuts from ebay - Ace Materials do short offcuts http://www.ebay.co.uk/sch/ace_materials/m.html?_nkw=&_armrs=1&_from=&_ipg=&_trksid=p3686 - I bought a load of short ends of 50mm & 60mm from them a while ago and their stock changes so worth keeping an eye on them

I buy my acetal / delrin by the meter from http://www.metals4u.co.uk/ but they do short lengths as well - if you give them a ring they are really helpful
Click to expand...

Thanks for all the info. Collected the lathe today (bought it on ebay) and now trying to round up the tools and materials. I am grateful for all the help on this forum.
 
Depending what you intend to do and what you get with your lathe you may need to budget about an additional 1 to 3 times the cost of the lathe for tooling, I have a mid-sized lathe and milling machine and the actual machine cost was minor compared to the tooling costs but I have specific business needs from my machines. Hopefully you should get a few cutting tools with it.

Suggested initial purchases;
1. Mixture of material off cuts to try; deltrin, acetal, nylon are nice and easy and very forgiving to play with, aluminium is not bad, steel is cheap but much less forgiving, try different materials, speeds, feeds, etc., ebay is your friend for offcuts or lathe starter packs
2. Decent turning tools, I'd suggest as a bare minimum the profiling tool I've linked to above plus then a couple of indexable tools - indexable means that the tips are replaceable and when you blunt/chip/wreck one you just turn it around or swap it out, but they are anything from a couple of quid to maybe a fiver a pop in small sizes
3. A decent cut off tool with replacement blade as you will break it a few times to start with
4. Cheap LED light from Ikea with a bendy body so that you can see what you are doing

There is a lot of argument about whether to use indexable tools or spend the time learning to grind HSS tools - if you are turning for pleasure, have restricted time, and have the budget save up and buy indexable as the time saved is well worth it, things like an indexable cut off tool can be scary prices to start with but are lovely to work with; if your toolholder will take 8mm shanks then http://www.chronos.ltd.uk/acatalog/New_Glanze_Clamp_Type_Indexable_Parting_Tool_Starter_acks. is ideal. For plastics its overkill but has the advantage of being able to part of thick pieces and is thin so the workload on the lathe is reduced, the [h=2]Small Inserted Blade Parting Tools (Ref: PTO....) or, if it will fit, Clamp Type Parting Tool (Ref: CTPT1) on http://www.chronos.ltd.uk/acatalog/Engineering_Menu_Parting_Tools_71.html are cheaper and will get you started or the first one on http://www.rdgtools.co.uk/acatalog/Parting_Sytems__High_Speed_.html[/h]
Suggested places for tools are http://www.chronos.ltd.uk and http://www.rdgtools.co.uk/ but if you start to look around their sites you can spend a fortune

Have a look at youtube for loads of how-to videos and places like http://www.modelenginemaker.com which has loads of general turning info as well as some fantastic models and engines

If you get stuck or have any qu's just ask
 
DinghyMan said:
Depending what you intend to do and what you get with your lathe you may need to budget about an additional 1 to 3 times the cost of the lathe for tooling, I have a mid-sized lathe and milling machine and the actual machine cost was minor compared to the tooling costs but I have specific business needs from my machines. Hopefully you should get a few cutting tools with it.

Suggested initial purchases;
1. Mixture of material off cuts to try; deltrin, acetal, nylon are nice and easy and very forgiving to play with, aluminium is not bad, steel is cheap but much less forgiving, try different materials, speeds, feeds, etc., ebay is your friend for offcuts or lathe starter packs
2. Decent turning tools, I'd suggest as a bare minimum the profiling tool I've linked to above plus then a couple of indexable tools - indexable means that the tips are replaceable and when you blunt/chip/wreck one you just turn it around or swap it out, but they are anything from a couple of quid to maybe a fiver a pop in small sizes
3. A decent cut off tool with replacement blade as you will break it a few times to start with
4. Cheap LED light from Ikea with a bendy body so that you can see what you are doing

There is a lot of argument about whether to use indexable tools or spend the time learning to grind HSS tools - if you are turning for pleasure, have restricted time, and have the budget save up and buy indexable as the time saved is well worth it, things like an indexable cut off tool can be scary prices to start with but are lovely to work with; if your toolholder will take 8mm shanks then http://www.chronos.ltd.uk/acatalog/New_Glanze_Clamp_Type_Indexable_Parting_Tool_Starter_acks. is ideal. For plastics its overkill but has the advantage of being able to part of thick pieces and is thin so the workload on the lathe is reduced, the [h=2]Small Inserted Blade Parting Tools (Ref: PTO....) or, if it will fit, Clamp Type Parting Tool (Ref: CTPT1) on http://www.chronos.ltd.uk/acatalog/Engineering_Menu_Parting_Tools_71.html are cheaper and will get you started or the first one on http://www.rdgtools.co.uk/acatalog/Parting_Sytems__High_Speed_.html[/h]
Suggested places for tools are http://www.chronos.ltd.uk and http://www.rdgtools.co.uk/ but if you start to look around their sites you can spend a fortune

Have a look at youtube for loads of how-to videos and places like http://www.modelenginemaker.com which has loads of general turning info as well as some fantastic models and engines

If you get stuck or have any qu's just ask
Click to expand...

Thanks for the great advice.
 
Dipper said:
I've bought all sorts of plastics from Direct Plastics Online. http://www.directplasticsonline.co.uk

I like the way their web site gives detailed properties for all the plastics. The last item I made was a bow roller for a club member in UHMWPE which I hadn't come across before. I'll be interested to see how this has fared after a season on a swinging mooring.

I've just remembered that they say that UHMWPE is used for pulleys in the marine industry.
Click to expand...

Thanks Dipper for the advice. I have gone for UHMWPE from Direct Plastics as their site has a lot of useful info on the materials. Thheir description of UHMWPE is

"UHMWPE Rod is particularly chosen for it's low co-efficient of friction which means it will produce bearings, pulleys or bushes that are very free running, low friction and long lasting. UHMWPE Rod is also very abrasive resistant, this means that UHMWPE Rod can be used in high demand environments such as grit or gravel and survive longer than other materials. UHMWPE Rod can often be used in high demand components in the food industry, this is because it has a very low moisture absorption that gives UHMWPE Rod an FDA approval and means that bearings etc will not expand due to any moisture absorption. Another reason that UHMWPE Rod is also used in the marine industry for pulleys is it's low friction and minimal moisture absorption."

Plus it is better than Acetal for UV resistance. Will update with how it machines on my lathe.
 
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