Attaching cabinet to the inner skin

[guy99]

We had a contractor remodel the rear of our 1984 310 Limited Motorhome. He replaced the North-South twin beds with an East-West king (72x74). To do this, one of the rear closets was removed. Also opened up the bathroom by removing the wall separating it from the hallway and moving the sink/vanity/medicine cabinet against the outer wall. Well, the fellow we hired to do this job did some nice cabinet work but never finished the job, I ended up just taking the motorhome back and have been trying to finish the work myself (The whole things is actually quite a story). Here is an issue I need help:

1. The medicine cabinet sits on top of the vanity and is attached to the outside wall. It was attached to the wall with a couple of screws. On our last trip, the screws let loose and the cabinet went flying, breaking one of the mirror doors and damaging the medicine cabinet. I have replaced the door and can repair the damage to the cabinet. But I need a secure, permanent means to attach the cabinet to the wall. The weight of the cabinet actually rests on the vanity so the attachment is need just to keep it in place. It was attached with two screws running through back of the cabinets and into the inner skin of the motorhome. Two problems with this, first the screws back out with travel, and, second when the road is real bad and there is allot of flexing they tend to pull out eventually requiring that I go to a large diameter screw. I can not see anyway to use a rivet through the cabinet and into the skin.

I tried to install rivet nuts in the skin so that I could run machine screws through the cabinet and into the rivet nuts. I've had no luck getting the rivet nuts to attach solidly to the skin. I think the skin is too soft to allow the rivet nuts to be securely mounted. Current ideas are:

1) I have some fairly large t-nuts with a flange that I think is large enough to allow me to drill 1/8 holes in the flange. I could then rivet the t-nut to the skin and then run machine screws through the cabinets and into to the t-nuts.

2) I could attach t-nuts or rivet nuts to a steel or hard aluminum plate, then rivet the plate to the skin, then run the machine screws through the cabinet and into the t-nuts.

I have attached some pictures which show the wall I need to attach to and with the cabinet in place

Any suggestions for a better approach or opinions about which of these would be better?

[dmac]

Perhaps the inner skin is too thin to structurally mount anything. Are the rivnuts aluminum or steel? Perhaps using aluminum rivnuts at ribs will work? Unfortunately, this may not match up with where you need the screws to go.

[LI Pets]

that is nice woodworking

[swebster]

Overhead cabinets in the motorhome (and trailers I assume) are usually attached using a piece of angle aluminum (1 x 1 stock or heavy guage sheet stock which has been cut and bent up by the factory to fit the angle). This "bracket" is then rivited to the skin with large head rivets then the cabeint is screwed into the bracket. Many times this can be done on the inside of the cabinet so it is blind and unseen when looking at the cabinet. It is a good idea to get a couple of rivet on the rivet lines so you can pick up a structural rib, but most of my overhead lockers are simply riveted to the skin itself).

FYI - in addition to the overhead lockers, the top of the kitchen counter and the sofa and the bed are all attached to the walls this way.

You can get angle aluminum (and sheet stock) at Lowes and the rivets from Gainger. I have a box of 250 of these rivets (I needed about 50 but Grainger only sells "BIG" boxes) so PM me if you need a few.

Your pictures show a back panel to the cabinet and a top "header" which makes it look like you can't get up in there with a rivet gun or even a screw driver. Is it possible to get a picture of the back of the cabinet?

BTW - it looks terrific.

[guy99]

The relative lack of strength of the inner skin is one reason I thought of using the plate since that would allow me to spread the load over a wider area.

I was using aluminum rivet nuts.

Based on the way the screw holes look, I'd say that it not a matter of the skin being too weak to take the load, rather there is too much stress for the soft aluminum at the fastener.

[guy99]

Originally Posted by swebster

...This "bracket" is then rivited to the skin with large head rivets then the cabeint is screwed into the bracket. ...

I assume you use sheet metal screws? No problems with them loosening with time? This is how I mounted our TV, I used two lengths of square stock which I attached to the side wall with sheet metal screws into ribs. Then I attached the mounting brackets to the square stock. It seems solid but I resolved to never remove the screws holding the square stock for fear that they would loosen up.

I tried something similar on the medicine cabinet, I riveted a hardwood 'nailer' to the skin, then drove wood screws through the cabinet into the hardwood nailer. This is how we got home from New Brunswick. The problem with this approach was that the hardwood was thick enough to prevent a flush fit of the cabinet to the wall. The same problem would rule out using angle or square stock. I could use flat stock as long as it isn't too thick. How thick does it need to be to hold the screws permanently?

This is the reason I was thinking of using a 'plate' with t-nuts and machine screws. I could mount the t-nuts so their flanges were flush to the plate, with the body of the t-nut projecting into a hole in the skin and I could use lock-tite on the machine screws.

Originally Posted by swebster

Your pictures show a back panel to the cabinet and a top "header" which makes it look like you can't get up in there with a rivet gun or even a screw driver. Is it possible to get a picture of the back of the cabinet?

BTW - it looks terrific.

Thanks, I'll get some more pictures.

Guy

[swebster]

I assume you use sheet metal screws? No problems with them loosening with time?

Actually you should use large head blind rivets. They sell em with a .65" head on them....it's the same type used by the factory.

You are right in that the angle speads the load out but since the rivets use such a wide head and require a small hole (1/4") they don't "tear out".

Here is a rough image of what I mean...

[guy99]

Steve,
Your picture is very clear. In my case I will need to drive whatever fastener I use through the cabinet into whatever I mount to. Since I would be going through the cabinet and into the bar stock, I was thinking about using the sheet metal screws.

In any case I don't see how I could exactly follow your example since the cabinet follows the contour of the motorhome exactly.

Here are some pictures of the back of the cabinet and the mounting holes:

Notice how the back is pretty much flush with the contour of the sides, this leaves very little space betwen the skin and the back of the cabinet.

[swebster]

Guy,
Wow...the back panel makes mounting it through those holes pretty hard. Since it's a flush fit there is no relief at all for even the flat stock without standing the cabinet off the wall a little.

Is that trim piece at the top easily removed? I noticed the cavity in the top of the cabinet would be perfet for mounting a bracket, but you would need to screw through the face. If you counter sunk the screws into a bracket on the back of the top then you could cover them with than trim again.

[swebster]

One other idea....what about a couple of screws coming into the side of the cabinet through that bulked it sits up against? (Of course this is where you tell me the shower is on the other side of the bulkhead). Then the other screws would simply quiet the rattles instead of support all of the weight.

There are a number of cabinets in my 345 mounted like that (screws through the adjacent bulkhead)

[guy99]

Originally Posted by swebster

Guy,
Wow...the back panel makes mounting it through those holes pretty hard. Since it's a flush fit there is no relief at all for even the flat stock without standing the cabinet off the wall a little.

Is that trim piece at the top easily removed? I noticed the cavity in the top of the cabinet would be perfet for mounting a bracket, but you would need to screw through the face. If you counter sunk the screws into a bracket on the back of the top then you could cover them with than trim again.

Good idea, I'll examine what I'd have to do to R&R that trim piece. I need to replace the back panel of the cabinet to repair the damage that occured when it came loose. Also will need to touch up the finish in several spots .

[guy99]

Originally Posted by swebster

One other idea....what about a couple of screws coming into the side of the cabinet through that bulked it sits up against? (Of course this is where you tell me the shower is on the other side of the bulkhead). Then the other screws would simply quiet the rattles instead of support all of the weight.

There are a number of cabinets in my 345 mounted like that (screws through the adjacent bulkhead)

Well, no that isn't the shower wall but it is a wall put in by my contractor. I have a problem with this wall in that it won't stay attached to the ceiling and flexes for and aft at the top edge. This is another problem I need to sort out. I'll be posting on this when I figure out how to mount the medicine cabinet.

As far as holding the weight, the cabinet actually sits on the vanity counter so the mounting doesn't need to carry much weight. The problem is that as things flex and shake the screws loosen, when they come all the way out the cabinet swings away from the wall at the top and smashes itself and other things. It almost seems like I'd be better off with an attachment system that had some 'give' in it so things could flex without breaking.

[guy99]

Do you think fasteners like this would work? I could put the cabinet in place and then set them from the outside.




Has anyone ever used molly or other anchors? Does they work on the inside skin?

[Inland RV Center, In]

Originally Posted by guy99

Do you think fasteners like this would work? I could put the cabinet in place and then set them from the outside.

Attachment 28722


Has anyone ever used molly or other anchors? Does they work on the inside skin?

Those fasteners, in time, come loose because of vibration during normal towing.

Andy

[guy99]

Originally Posted by Inland RV Center, In

Those fasteners, in time, come loose because of vibration during normal towing.

Andy

Andy,
How about molly's , they seem very similar to olymic rivets in the way they function?

Got any other suggestions to solve this problem?

[Inland RV Center, In]

Originally Posted by guy99

Andy,
How about molly's , they seem very similar to olymic rivets in the way they function?

Got any other suggestions to solve this problem?

Use screws, pop rivets or olympic rivets.

Molly's come loose. Same with drive rivets.

Andy

[guy99]

Where can i find rivets with a 1" grip range ?

[swebster]

The .65" rivets I sent match those used by the factory to secure the couch to the wall. I'd say maybe eight (8) rivets in total.

the trick is to use bar or angle stock as a "nailer" (or screwer in your case)...attach it to the wall using these mondo rivets and then secure the cabinet to the bar or angle.

The best way is through the bar stock or angle and into the wood (not the other way around) but in your case you might have to consider sheet metal screws through the wood and into the metal. Perhaps even really thick metal and a tapped thread to access a machine screw with some lock tite and lock washers on it.

[Inland RV Center, In]

Originally Posted by guy99

Where can i find rivets with a 1" grip range ?

Depending on the diameter you need, McMaster-Carr has them.

Andy

[guy99]

Originally Posted by swebster

The .65" rivets I sent match those used by the factory to secure the couch to the wall. I'd say maybe eight (8) rivets in total.

the trick is to use bar or angle stock as a "nailer" (or screwer in your case)...attach it to the wall using these mondo rivets and then secure the cabinet to the bar or angle.

The best way is through the bar stock or angle and into the wood (not the other way around) but in your case you might have to consider sheet metal screws through the wood and into the metal. Perhaps even really thick metal and a tapped thread to access a machine screw with some lock tite and lock washers on it.

If I understand it the purpose of the 'nailer' is to distribute the load over several rivets - am I correct?

If so, I should be able to put at least four rivets through the cabinet into the inner skin - if i can get rivets with an adequate grip range.

Woud 4 rivets be enough if I can get them in?