Adapting a radar mast

[newbie-]

I've got some ideas on how to solve for this.. But I was curious what you guys would recommend.

I have an aluminum radar arch and I originally had a (very heavy) open array radar on it. Today I removed the Raytheon R21 radar and attempted to install a new radar mast for updated radar electronics.

The bolt pattern on the radar mast doesn't match the old radar bolt pattern. Of course not, why would anything be simple?

I can't drill new holes in the aluminum arch plate because the radar mast bolt pattern perfectly overlaps some welds for the arch bottom cover. On all 4 corners. Just not an option.

I think it's important that the weight of the new radar mast is balanced well so the arch isn't under extra stress. So shifting the mast forward for clearance (while simple ) isn't a good option either.

So there's the problem. I have two metal plates with different bolt patterns that must be joined.

My idea is to fabricate an adapter plate thick enough to nest the bolts for the radar mast inside. So 3" thick or so (3 layers of plywood). Then coat it in resin to seal.

But having wood sandwiched in between two metal surfaces sounds like a bad idea. The compression, the wear, weather, ice, etc is just going to be really hard on the relatively soft wood. But I'll give it a shot.

I'm not planning to use fiberglass. It will probably be prone to cracking once I torque the assembly down.

Any simpler solutions I haven't thought of yet?

[tkeithlu]

One approach would be a single aluminum plate, perhaps 3/8" or 8mm, and use flathead screws so they can be countersunk in the plate in the two directions. That solution probably is best from a maintenance standpoint. Minimize the dissimilar metals problem with some silicone goo around the bolts.

It could be similarly done in stainless steel, but then you have large areas of dissimilar metals together and you'd discover just how much the "stainless" is an oxymoron.

I really can't recommend any wooden solution. Strength, rot, and general ugliness all come to mind.

[marcjsmith]

before wood, I look to something like starboard. if you are worried about water being trapped. you could alwaya use the starboard to make a spacer for each bolt hole. but make the spacer big enough to capture one hole from each plate. so you'd end up with four spacers and air "airgap" of sorts between the plates.

[newbie-]

Yeah I'm not happy with the outcome here. The 3x 1" plywood stack is screwed and glued together. But I felt I needed extra brackets for safety. If any of the bonds between the 3 sheets fail the entire tower is coming down on someone's head..

I don't like it. I'm going to have to redo it.

Metal is the best option here as advised.

I do see where I could possibly fit some new bolts in between the welds on both arch and mast. That would be the easiest.. I'll try that in a few weeks. Need to get on to other projects.

[DefinitelyMe]

I know you said it isn't an option, but those look like some pretty beefy welds. Would those knees be of insufficient strength if you took a chunk out of them large enough for a nut? If you could get the bolt holes to be more or less in the center of the welded triangular knees you could cut an arch in them just big enough for a nut and bolt up from below. It's what we did with the knees for our shrouds and the engineer who designed them approved the modification. Said it would not have a significant impact on the overall strength.

If not, I would lay up a thick piece of glass plate. I think your concern about cracking is not significant.