Blind Bolt, yet again!

[Plomong]

I need to fix a 20 x 12 cm white metacrylate panel to a bulkhead to which there is no rear access once the panel is in place.

The panel must be removable for future access to the rear of the panel, which will carry a Wind instrument (ST50). Before fixing, there is a 70mm diam. hole in the bulkhead, which the panel is designed to cover. The hole could be enlarged to the panel size minus panel / bulkhead overlap of, lets say, 12 mm minimum all round.

The first idea was to stick 4 nuts on the rear of the bulkhead, coinciding with boltholes drilled through the bulkhead and the panel. However, tests on some scrap pieces using some available loctite were not successful -- the nut to glassfibre bond was fragile. If there is any chance that the nut could come loose, making future panel removal impossible, the solution is not acceptable.

Searching the web, I found the following:
ecrou en cage

that would be perfect. However, stainless A4 grade steel would be required.

Does anyone have any idea where I could source such a SS fixing, M4 or M6?

Or have some other ideas on how to blind-bolt the panel to the bulkhead?

 

[Guest]

Do you mean pronged Tee nuts

http://www.avonstainlessfasteners.co.uk/products2.htm

 

[bigwow]

rivit nuts would be the answer me thinks

 

[2Tizwoz]

Countersunk self tappers covered by the wind instrument too simple?

They could be covered with caps like these on this American site. or available easily from screwfix

 

[fisherman]

If m4 or m6 is big enough, can you not screw a hardwood strip on the back, countersunk screws flush with the b/h, then s/s wood screws to hold the instrument?

 

[fibz99]

Use self tapping screws instead ?

 

[Plomong]

Wind instrument has studs that pass through panel and fastened with small nuts. The panel then needs fixing to the bulkhead, with visible bolt-heads alonside the instrument, not possible to have them behind it. I'll use decorative dome-head bolts -- didn't look bad on an earlier job I did for a friend 12 years ago, but that had access to the rear of the bulkhead.

Problem created by boat dealer who stuck the instrument to the bulkhead with sika. Removal for repair under warranty damaged the bulkhead -- hence need to have a removable panel for future access.

 

[Plomong]

These appear to be for wood. Would the sink into glassfibre far enough to not come loose on undoing the bolts??

 

[savageseadog]

Rivnut Nutcert or Avdel

 

[Guest]

Can't read, sorry. Pictured a internal wooden bulkhead.

For fibreglass bulkheads, just tap them like metal.

If it is too thin epoxy rounds of 5mm thick Tufnol to the back.

Else epoxy 2 ply strips to the back and use the wood idea.

How do you plan to seal it from water?

 

[Plomong]

Have contacted Bollhoff about these -- asking for suggestions. Will see what they come up with.

 

[Plomong]

[ QUOTE ]
How do you plan to seal it from water?

[/ QUOTE ]

By careful application of Sikaflex sealant, as I did last time on another boat, 12 years ago. No leak since!!! But in that case I had rear access to the bulkhead. The problem then was covering a bloody big hole to fit an instrument smaller than the hole in which the previous, defunct, instrument had been mounted.

The dealer in this present case stuck the instrument with some type of mastic glue that really stuck it on!!! But he had to remove it -- it didn't work!!! Dead on arrival!!! Now I don't want to let him stick it back on when it comes back from repair -- I want a better solution, which means DIY !! Hence the questions.

[ QUOTE ]
For fibreglass bulkheads, just tap them like metal.


[/ QUOTE ]

I have never done this. Is it really effective?? Is it a strong fastening?? You never know when someone falls against the instrument pushing it downwards, maybe, with his or her weight on it.

Will think about this solution.

 

[Plomong]

savageseadog -- will look these up tomorrow night. It is late here now, and time to sign off.

 

[Guest]

Tapping fibreglass is quite easy. What is the bulkhead thickness? You need at least a nut thickness. Always use a slightly undersized pilot hole.

I asked about sealing it because I thought from the earlier posts you did not like the permanent nature of Sikaflex. For water proof you just need some of that very soft stick on foam rubber they use on the back of instruments.

Some cooking oils and Sikaflex do not like each other if you ever have to remove some thing else. Takes a while.

 

[oldsaltoz]

Have you considered hinging panel?

 

[simonfraser]

why not get a tacktick wind and an nmea interface, flush fitting, no wires ?

 

[andy_wilson]

Your problem is using loctite. Clean / grind it off thoroughly and epoxy the nuts in place.

Better still epoxy some bolts in place. You can get special blind fasteners designed to laminate in. They consist of a threaded portion and insted of a bolt head they have a wide flange with holes designed to be bonded into place or laminated over.

Bed onto some epoxy and fasten firmly with nuts on the outside (check alignment is good), then add more epoxy to encapsulate. Once set, remove the nuts and you have 4 secure studs ready to take your panel.

 

[fisherman]

Some of the Sika products are designed to 'let go' for dismantling.

 

[kds]

Can you fix the panel with sika and then fit instruments to that ?
Ken

 

[Guest]

Alloy expander bolts ..... no need for anything else.