Backing Plates

[jimbouy]

When renewing various deck fixtures what is the rec. material for the backing plates.

Stainless steel... obviously but what thickness.

What I 'm getting at I guess is can you cut and drill the stuff yourself easily or in general do you need to get them made up.

Secondly when fitting what "sealing" material goes behindthe plate... sealant ....nothing or a mix of epoxy and chopped glass.


Jim

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[Guest]

Will talk in mrning .....

Hope all went well ..... still waiting that e-mail !!

Cheers

<hr width=100% size=1>Nigel ... and of course Yahoo groups :
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[Mudplugger]

Jim, it depends on what the likely loads on the fittings are going to be, and the area that you can spread the load over.... Have used 10mm Ally, 8mm Mild Steel and 6mm s/steel in the past and bedded them all on P40...and never had any problems... tend to be guilty of over engineering for my own peace of mind, Hope this helps...Tony W.

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[kingfisher]

Depends on the kind of loads you are going to stress tha plates with. Also, when you drill though the deck, you have to drill out the core (usually balsa wood). Let's say you want an extra eye pad on your deck.
1) Drill through the four holes where the bolts will go through.
2) With a bent needle, pry out as much of the core material as you can. For larger surfaces, such as for a winch, you will have to drill larger holes from the inside out.
3) Fill the void with resin, mixed wit fibres. This can be bought ready-mixed.
4) re-drill the holes
5) Seal between the padeye and the deck by using COPIOUS amounts of sealant (eg sikaflex or 3M, NOT silicone).
5) place the padeye, thread through the bolts, place the backing, use large washers.
6) Tighten the bolts, so that the sealant is squeesed from underneath the padeye. Do not tighten them completely
7) Allow the sealent to harden, tighten the nuts completely.

Make sure that no moisture can get to the core.

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[oldsaltoz]

G'day Jimbouy,

I use S/Steel mostly for backing plates, the thickness and size will depend on what I'm backing, but 6 mm is fine for most jobs on deck fittings.

You can drill it yourself, just use a cutting compound and keep plenty of pressure at a low speed on the drill and you should be ok. It's a good practice to remove any corners from the plate I normally bevel the bottom edge as well.

Bedding in of plates: I use a mix of resin and Micro Fibres make sure you wipe away any excess when you nip the plate up, as it's not easy to sand off.

Any S/Steel should be treated after cutting or drilling to prevent rust staining later, pickling paste is freely available in most welding shop outlets.

Do the plate up firm but not tight, let the resin cure overnight and nip it up tight the next day.

I hope this helps.

Avagoodweeknd........



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[Guest]

Backing plates / pads can in any material you choose - but obviously there are advantage materials for respective jobs.

Smaller and highly stressed jobs would warrant stainless steel - as then it would not crush or split

Lower loaded and larger areas can be backed with hardwood or even marine ply. these would be suitably glassed in of course to prevent water damage in end grains etc.

On very light loaded items that really are needing the deck / structure secured - rigid plastic has been used at times .....

Knowing you Jim .... you will want the feeling of security and strength that St. Seel gives ...... just take note of the weight and over-engineering that can be applied with this material. In most cases with even high loads 6mm is probably enough, and in general loads 4mm could be enough .....

I always find that drilling st.steel a pain .... even when done slow with plenty lub ..... impatience probably.

Now onto an excellent material that is totally corrosion proof and is light in the bargain .... immensely strong as well. Duraluminium ...... they make all sorts of plane bits out this stuff. I came across this stuff when I used to build model boats /planes etc. We used it for engine mounts and wing braces / undercarraige mounitings ..... its so light its literally not much more than ally, but strength is incredible and it resists all bending to a very high degree. Wher to get it ? find Radio Control Model shop ... ask for Dural plate. I would use this for all small / med. size backing - but may prove difficult to get in big enough sheets for larger items.

Check with WOA and the guy who checked over the boat as to where you may have core in the deck ... I got a feeling that you will not have trouble with this ... but best to be sure as I am not totally sure of where you'll be fitting stuff !!
Filler between backing pad and GRP - can be Sikaflex or the good ol' resin and Microballoons .... or ready mixed resin and chopped strands. If you use polyester with the micro-balloons then it is sandable - well its easier than epoxy based. But best is to epoxy base the filler. As others have said bolt up till it squeezes out - wipe away excess, let it set and then bolt up tight.

For those silly little things that need backing .... there's nothing better than a range of large penny washers in st.steel. Of if there is possibility to bridge bolts ... say in a double bolt cleat etc. - a small st. steel plate that traps both in one .......

Tip - if you find that you cannot insert a bolt from under etc. as in a toe-rail ..... drop a st. steel stud bar down from above far enough to put washers / nuts one etc. and then draw it back up so that all beds up in the toe-rail .... nuts on outside and wind her up. Cut off excess and bobs the proverbial.

Cheers - talk later ??


<hr width=100% size=1>Nigel ... and of course Yahoo groups :
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[Benbow]

You have plenty of good advice here. I would add that it is important that the load is applied evenly throught the plate. Round off corners otherwise you can get big load concentrations through to the deck here. This is as important than sheer size or thickness, so for really critical applications I would use a pyramid of plates each smaller than the last. For lighter loads it is common to do this with glass mat and resin, glass in one big piece of matt, over that put a smaller one, and so on. Gives even transfer of load over the whole area.

That is also why good bedding-in of a metal plate is important.

HTH

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[jimbouy]

Thanks to all

<hr width=100% size=1> "It is a pleasure to give advice, humiliating to need it, normal to ignore it"

 

[Avocet]

If it helps, I've been quite impressed with some "extra cobalt" HSS drill from Screwfix for drilling stainless. They do seem to keep their edge a bit better than ordinary HSS drills!

http://www.screwfix.com/app/sfd/cat/pro.jsp?ts=03118&id=10842



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[jimbouy]

Now that's a good hint.

<hr width=100% size=1> "It is a pleasure to give advice, humiliating to need it, normal to ignore it"