My autopilot support bracket has cracked ...

[Plomong]

As can be seen, the action of sun, rain and cold has caused the autopilot support bridge to crack. It appears to be made of nylon or PTFE and is 50 mm high and 20 mm thick. It is attached using 2 short screws through the fibreglass on each side, accessible from the cockpit locker.

Can anyone suggest a suitable replacement material that a bodger like me can easily work, and that will last years, not months ??

I considered wood but am fearful that expansion and contraction due to moisture take-up and loss make that impractical.

Any suggestions ???

Plomong

 

[prv]

Another block of nylon or acetal? Should be easy enough to saw and drill.

Pete

 

[BERT T]

Acetal block available here; http://www.ebay.co.uk/itm/ACETAL-BLACK-PLATE-SHEET-OFFCUT-115mm-x-50mm-x-20mm-THICK-/121560100827
or PTFE here; http://www.ebay.co.uk/itm/PTFE-PLATE-SHEET-OFFCUT-100mm-x-75mm-X-20mm-THICK-/121471658778

 

[Boo2]

Another block of nylon or acetal? Should be easy enough to saw and drill.

+1. Acetal sheet is available on eBay and I'd take out the existing part, measure the thickness (in the constant thickness direction) and contact some of the eBay sellers to see if they can let you have an offcut. Acetal is rather easy to cut with a hacksaw and it machines well too if you know someone with the facilities.

Boo2

 

[LadyInBed]

Only the socket is from A/H, the rest is DIY.
Make another block from similar material or hardwood, I would put a brass or ss faceplate on it to protect it from uv.

 

[TQA]

A bit of Delrin will also do the job.

 

[alahol2]

Tufnol:... http://www.ebay.co.uk/itm/CARP-SRBF-TUFNOL-Sheet-25-mm-thickness-various-sizes-/361245570752?pt=LH_DefaultDomain_3&var=&hash=item541be9f6c0

 

[Tranona]

View attachment 51415


I considered wood but am fearful that expansion and contraction due to moisture take-up and loss make that impractical.

Any suggestions ???

Plomong

No problem with wood if you use a durable hardwood, which you can paint or varnish if you wish. My autopilot socket has been in a wooden coaming for best part of 25 years and is still there.

 

[Fantasie 19]

There was a chap on the Mobo forum with a 3D printer offering to do small parts at request??

 

[Plomong]

Another block of nylon or acetal? Should be easy enough to saw and drill.

Pete

Acetal doen't seem to be UV resistant at all. The bridge will be lying in the sun all year round here in the less-sunny part of the Iberian Peninsula.

Any comments ?

Plomong

 

[Plomong]

Only the socket is from A/H, the rest is DIY.

I know, and I know the bodger who made the existing piece.

Plomong

 

[Boo2]

Acetal doen't seem to be UV resistant at all. The bridge will be lying in the sun all year round here in the less-sunny part of the Iberian Peninsula.

Any comments ?

Good point, though how much direct sunlight it will get down in that crevise is anyone's guess. As Tranona said, a small piece of mahogany, teak or marine ply would work fine and be both easier to get hold of and make the part from...

Boo2

 

[prof pat pending]

There are grades of acetal that are UV stabilised, they tend to be filled with glass or carbon fiber and black, although there are white ones.
Nylon probably isn't a good choice as they absorb moisture for some time, this can cause issues with dimensional stability and stiffness

Something like HDPE (high density polyethylene) might me a good choice. Think milk cartons and chopping boards.
The downside is that you will need a specialist adhesive to bond it in place, but as your application is screwed this shouldn't be a problem.

 

[DinghyMan]

There are grades of acetal that are UV stabilised, they tend to be filled with glass or carbon fiber and black, although there are white ones.
Nylon probably isn't a good choice as they absorb moisture for some time, this can cause issues with dimensional stability and stiffness

Something like HDPE (high density polyethylene) might me a good choice. Think milk cartons and chopping boards.
The downside is that you will need a specialist adhesive to bond it in place, but as your application is screwed this shouldn't be a problem.

Good luck trying to glue HDPE, its almost impossible to stick it to itself let alone to a different material.

PTFE tends to have little structural strength and can be brittle, and its pricey compare to other plastics, it works easily though.

Small price of black acetal/delrin would last a good while and be very easy to machine or work by hand. Use a decent sharp wood plane and you can get a good finish, don't attempt to sand it. Alternatively PM me the dimensions and I'll have a dig in the "bits that may come in useful" box

 

[prof pat pending]

Good luck trying to glue HDPE, its almost impossible to stick it to itself let alone to a different material.

Things move on

http://www.tapplastics.com/product/repair_products/plastic_adhesives/tap_poly_weld_adhesive/435

 

[30boat]

I think any sort of plastic is a poor choice for this application.I would build up a block in glass and resin,polyester or epoxy, and stick in place with epoxy and some sort of mechanical fastener.For UV protection I'd paint it in black with a good single or two pack paint.
Even hardwood is better than plastic I'd think.

 

[DinghyMan]

Things move on

http://www.tapplastics.com/product/repair_products/plastic_adhesives/tap_poly_weld_adhesive/435

Last time I wanted some glue for HDPE I think it was over two hundred quid for something like 50ml so I gave it up as a bad job and went with mechanical fixings...

I have used glues for Acetal & Delrin but they are fairly sensible at around £35 per 25ml but don't have much strength, useful to hold things in place for assembly or machining though.

 

[prof pat pending]

Last time I wanted some glue for HDPE I think it was over two hundred quid for something like 50ml

Last time I did it I paid around 20 quid for one of the double barreled syringes

 

[Plomong]

Good point, though how much direct sunlight it will get down in that crevise is anyone's guess. As Tranona said, a small piece of mahogany, teak or marine ply would work fine and be both easier to get hold of and make the part from...

Boo2

That piece will receive direct sunlight over 150 days of the year. It faces SSW, and the sun here is 10 degrees higher in the sky than what you are used to in the southern part of the UK.

I'm thinking more about a wooden solution now, most Acetal on the market is not UV resistant, or the resistant grades hard to source. The links given by earlier posters lead to Acetal / Delrin that is not UV resistant.

Teak would be good.

Anyone know where I could source it in the UK by online order ??? I tried around these parts a few years ago but the local suppliers only carry teak substitutes, none of which are for exterior use in exposed locations -- only on semi-protected terrazas, etc. Remember getting cross-grain dowel pieces somewhere in the Midlands to cover countersunk screws on seat slats (10 years ago). (Edit: Remembered name of supplier: KJHowells)

Plomong

 

[Plomong]

Alternatively PM me the dimensions and I'll have a dig in the "bits that may come in useful" box

Thanks for your kind offer. If you find a suitable offcut I can send you my details by PM.

The piece is 50 mm high and 40 mm wide at the top, 28 mm at the bottom. The thickness is 20 mm, but that needs to be beefed up a bit as the wall thickness across the metal insert was just 3 mm, so 25 or 30 mm would be recommended.

The piece probably cracked due to stress concentration as, on closer inspection today, the metal insert was an interference fit, not glued in place.

Plomong