Metal strength advice

[Ringel05]

If it were my build, I would put a plate behind the fender as well

plate ---- fender --- standoff --- plate

with an appropriate sized carriage bolt through the standoffs.

In this way, the holes in the fender aren't taking the entire strain.

The fender supports are integral to the fender and designed to be used the way I'll be setting it up so no extra back support needed. Not only that it would take major mods to fit extra support inside the fender. The fender supports are part of the main bike frame. The bolts go through the holes in the fender and screw into the nut inset welded in the fender frame. They're not gonna go anywhere once attached and neither is the fender.

 

[Sunni Man]

I picked up some new Viking Bags for my bike, have the one side drilled and mounted but it mounts through the rear fender trim. The problem is the trim (which is easily removable) is really not conducive to bolt mounting the bags. What I'm thinking is remover the trim and replace it with a 1/8" x 10" X 4" aluminum plate mounted to the fender with spacers.
What my question is is 1/8" aluminum strong enough to stand up to wind weight and vibration? Each bag's max recommended load is 11 pounds.

1/8" sounds a little too thin to me.
have you considered 3/16" ?
Visually it wouldn't be noticeable but way stronger.

 

[Ringel05]

1/8" sounds a little too thin to me.
have you considered 3/16"

The flat plate is more to give the bag mounting brackets something to mount flush on and the contact points on the bracket are only about an inch and a half tall and an inch wide. The bracket stress points will go through the plate and attach to the fender frame and in reality will not be putting that much stress on the plate. If I was only mounting the bags to the plate and not the fender frame then I would probably use stainless steel instead of aluminum.

 

[Sunni Man]

The flat plate is more to give the bag mounting brackets something to mount flush on and the contact points on the bracket are only about an inch and a half tall and an inch wide. The bracket stress points will go through the plate and attach to the fender frame and in reality will not be putting that much stress on the plate. If I was only mounting the bags to the plate and not the fender frame then I would probably use stainless steel instead of aluminum.

Oh....OK, got it. ...

 

[westwall]

I'm trying to not go with steel to keep the weight down.

If you use 6061 T6 aluminium you should be fine.

 

[HereWeGoAgain]

I picked up some new Viking Bags for my bike, have the one side drilled and mounted but it mounts through the rear fender trim. The problem is the trim (which is easily removable) is really not conducive to bolt mounting the bags. What I'm thinking is remover the trim and replace it with a 1/8" x 10" X 4" aluminum plate mounted to the fender with spacers.
What my question is is 1/8" aluminum strong enough to stand up to wind weight and vibration? Each bag's max recommended load is 11 pounds.

It should be plenty strong assuming the widest part of the plate is vertical.
I'd use 6061,it's tough and easy to work with.

You'll be fine using 1/8 aluminum.
I was a machinist for just shy of 30 years and I've cut pretty much every metal known to man.

 

[mudwhistle]

It should be plenty strong assuming the widest part of the plate is vertical.
I'd use 6061,it's tough and easy to work with.

You'll be fine using 1/8 aluminum.
I was a machinist for just shy of 30 years and I've cut pretty much every metal known to man.

Have you cut Transparent Aluminum?

 

[HereWeGoAgain]

Have you cut Transparent Aluminum?

I was retired by the time it came out.

 

[Ringel05]

It should be plenty strong assuming the widest part of the plate is vertical.
I'd use 6061,it's tough and easy to work with.

You'll be fine using 1/8 aluminum.
I was a machinist for just shy of 30 years and I've cut pretty much every metal known to man.

No it's going horizontal but I'm really mounting through it. It's primarily a flat plain to square up my bag mount.

 

[HereWeGoAgain]

No it's going horizontal but I'm really mounting through it. It's primarily a flat plain to square up my bag mount.

I cant picture it in my mind.
Are the bags going to sit on it?

 

[Ringel05]

I cant picture it in my mind.
Are the bags going to sit on it?

As I posted in a previous post the mounting bolt will go through the mounting bracket, through the flat plate, though the spacers into the fender frame. The flat plate is more for squaring up the bag install. If the plate was mounted to the fender frame then the bags mounted separately to the flat plate then I would use steel instead. The bags are not heavy and the recommended load per bag is only 11 pounds.

 

[HereWeGoAgain]

As I posted in a previous post the mounting bolt will go through the mounting bracket, through the flat plate, though the spacers into the fender frame. The flat plate is more for squaring up the bag install. If the plate was mounted to the fender frame then the bags mounted separately to the flat plate then I would use steel instead. The bags are not heavy and the recommended load per bag is only 11 pounds.

Still dont see it.
I keep seeing the plates in a vertical position with the bolts going through the fenders with the spacers in between.

 

[Ringel05]

Still dont see it.
I keep seeing the plates in a vertical position with the bolts going through the fenders with the spacers in between.

Okay, I think I see where our disconnect is (maybe). The plate will be 1/8" x 4" x 12", by vertical I thought you meant the long aspect (12" length) up and down, the 12" will be horizontal with the 1/8 pointing up and down, the 4" width will be facing the side (the bag and the bike).
Imagine mounting a flat kick plate on a door, that's the way this will be but with only the two (existing) mounting points.

 

[Ringel05]

Still dont see it.
I keep seeing the plates in a vertical position with the bolts going through the fenders with the spacers in between.

This might help. Note that none of this is to scale.

 

[HereWeGoAgain]

This might help. Note that none of this is to scale.

View attachment 665278

Gotcha....1/8 aluminum is plenty strong for your application.

 

[para bellum]

Will 1/8" thick aluminum plate be strong enough for what I want to do?

So you don't actually have bag mounts that are made for those bags?

I would not use 1/8", or aluminum. For 100% holding strength in aluminum, your threads need to be 2x nominal fastener diameter.

A 10-32 screw is .189" dia. I don't think you want to use anything smaller than that for bags. That means 3/8" thickness for aluminum (if you don't want to pull the threads out).

The bag should sandwich the fender, clearance holes in everything. The threaded part should be a steel or stainless steel backing inside the fender with a thickness at least 1x the fastener dia. Torque to spec and use loctite. You'll want stainless fasteners too, never put a stainless screw in a stainless part without anti-sieze or loctite- SS on SS loves to gall.

The trim is probably a formed piece of sheet metal, a filler piece between the fender and trim could be made so you don't crush the trim piece. Then just put clearance holes thru everything. Bag, trim, fender all are sized for clearance. The only tapped part should be the steel backing inside the fender.

The fender alone, or the fender plus 1/8" of aluminum isn't really enough to do the job. Use the fine thread fastener, whatever size you go with. They are stronger and give you more flank area on the threads. Don't go less than 1x diameter and use steel or stainless steel- if weight is really an issue use titanium.

If you absolutely positively must have aluminum, use 7075- at least it approaches the tensile strength of mild steel.

 

[para bellum]

Okay, more detail was posted while I was typing.

As long as the plate is just s flat place to locate the bags, 1/8" Aluminum is fine. As long as the weight is supported by the steel fender mounts welded to the frame, no issues.

If you want to keep the trim, you could fill the backside with JB weld to prevent deformation at the fasteners. Replacing it with the spacers is fine mechanically, if it's okay with you cosmetically.

 

[Brick Gold]

I am doing this for someone else.

 

[Brick Gold]

Someone not in the band featured.

 

[Brick Gold]

I am giving this man my support despite what was purported about him.