Cabinet questions

[Jack Sparrow]

I'm planning a tweed-style cabinet in hardwood with no covering material. I'd like to avoid exposed hardware holding the chassis in place. I'm thinking that 1/2" long threaded inserts screwed into the underside of the top might work.



Then I can use a 1/4-20 threaded rod through the chassis and into the insert with a nut on the bottom. Inserts like this are very secure but I'm not sure about using them in an overhead configuration holding the weight of a loaded amp chassis. Thoughts? Other ideas on how to do this without drilling holes through the top of the cabinet?

I was all set to cut cabinet panels at right angles when I saw some plans that suggest the front is actually angled upward slightly. Is that the way the original cabinets were built or is that a modern improvement on the original design? I've never noticed the angle in the pictures I've seen of vintage Fenders.

I've only once ever seen a Fender finger jointed cabinet without it's covering and I thought the fingers were 1/4" thick. I've also seen some clone cabinets with 1/2" fingers. In the interest of keeping as much of the original flavor as possible, did the original cabinets have 1/4" or 1/2" fingers or something else entirely?

Thanks!

How thick are the back covers? 1/4" ply would probably be fine if I were covering it with Tolex, but 1/4" solid wood might not hold up well. For the record, what's the thickness of an original 5E7 back?

[Chuck H]

Brilliant. I've never seen it done, but that's how "I" would do it. Not sure why it's important to you. I think the clunky screws look cool. But that's JMHO. I might consider using using some sort of adhesive for the inserts since having them come loose during chassis removal (after, what, maybe fifteen or twenty years) would be a real drag. Careful work for the look. But the benefits are unprecedented. And that's pretty cool.

EDIT: Another way to hide the mount screws would be with T-nuts inserted on the underside of a cabinet. The T-nuts would be installed and then another washer could be screwed in place over the T-nut so it couldn't back out of it's mount. This seems to be the most secure method since the T-nut (mounted in this fasion) couldn't possibly become loostened like an insert might.

JM2C

[Tom Phillips]

… I was all set to cut cabinet panels at right angles when I saw some plans that suggest the front is actually angled upward slightly. Is that the way the original cabinets were built or is that a modern improvement on the original design?

The originals were built with the angled front.

… seen some clone cabinets with 1/2" fingers. In the interest of keeping as much of the original flavor as possible, did the original cabinets have 1/4" or 1/2" fingers or something else entirely?

All the originals I have seen used 1/4" finger joints

How thick are the back covers? 1/4" ply would probably be fine if I were covering it with Tolex, but 1/4" solid wood might not hold up well. For the record, what's the thickness of an original 5E7 back?

There were slight tolerance variations in the old plywood used but for all practical purposes the old backs were made from 1/4" ply. My favorite replacement material to use is high quality birch plywood. It is usually 5 ply, void free and very strong. The top surface would also be attractive next to your solid pine.


Keep in mind that there is considerable torque on the two chassis screws. To prevent damage to your inserts you may want to consider a third attachment point similar to the method Fender used on the Tweed Bassman. This was done by mounting an “L” bracket on the top of the power transformer. It was held in place by the long transformer bolt. The other side of the “L” bracket was held to the cabinet top with a third chassis bolt. An alternate third attachment point is the side of the chassis. (Not “vintage correct” but a better solution) That would be easier to implement and easier to access for chassis removal. You can see a nice chassis bracket for this purpose on the Mission Amps page at Mission Amps Hardware Page

Regards,
Tom

[loudthud]

You might consider a second mounting point on the transformer end of the chassis. Bruce used to sell a bracket that IIRC used the transformer bolts to hold it to the chassis.

[Jack Sparrow]

Good ideas on the additional mounting points. Something I'd also considered was cutting the cleats (to which the back panels get screwed) short so the chassis rests on top of them. That eliminates some of the mounting area for the upper back panel, though. That would also presume that the chassis is almost as long as the inside width of the cabinet (about 20"-21".) If the back were at least 1/2" thick, I could use a pin and socket arrangement along the top edge and just have screws at the lower sides.

I saw a black face Princeton done like this in hardwood. The builder has each end of the chassis rest on two 3/4" x 3/4" horizontal cleats with a pair of screws to push up on the top piece from the bottom and jam the chassis against the top of the cabinet. I'd be afraid of holding the chassis by friction alone like that, but it is another approach.

Maybe do both. Let the bolts hold the chassis as I'd planned but also install a short length of angle steel horizontally to the side of the cabinet about 1/4" below the bottom of the chassis. Then thread a bolt through the steel up against the bottom of the chassis. Kinda like the Princeton mount. Sort of a belt and suspenders kind of thing.

[Jack Sparrow]

The originals were built with the angled front.


All the originals I have seen used 1/4" finger joints


There were slight tolerance variations in the old plywood used but for all practical purposes the old backs were made from 1/4" ply. My favorite replacement material to use is high quality birch plywood. It is usually 5 ply, void free and very strong. The top surface would also be attractive next to your solid pine.


Keep in mind that there is considerable torque on the two chassis screws. To prevent damage to your inserts you may want to consider a third attachment point similar to the method Fender used on the Tweed Bassman. This was done by mounting an “L” bracket on the top of the power transformer. It was held in place by the long transformer bolt. The other side of the “L” bracket was held to the cabinet top with a third chassis bolt. An alternate third attachment point is the side of the chassis. (Not “vintage correct” but a better solution) That would be easier to implement and easier to access for chassis removal. You can see a nice chassis bracket for this purpose on the Mission Amps page at Mission Amps Hardware Page

Regards,
Tom

Thanks, Tom.

The plans I have show a 9-1/2" deep top and a 10-1/4" deep bottom, so a 3/4" difference over almost 2' of height. Not a severe angle and probably why I wouldn't notice it in photographs .

I'm hoping to build the cabinet out of something like mahogany but weight and price may change my mind on that. I'm looking for a cross between a vintage Fender amp (size) and an old radio. Something certain other folks won't have a problem with in the living room, if you know what I mean. I only plan to use this at home. In fact, I'm debating whether it really needs a handle if it's more like a piece of furniture.

I'll check out the Mission Amps page shortly.

[Jack Sparrow]

Keep in mind that there is considerable torque on the two chassis screws. To prevent damage to your inserts you may want to consider a third attachment point similar to the method Fender used on the Tweed Bassman. This was done by mounting an “L” bracket on the top of the power transformer. It was held in place by the long transformer bolt. The other side of the “L” bracket was held to the cabinet top with a third chassis bolt. An alternate third attachment point is the side of the chassis. (Not “vintage correct” but a better solution) That would be easier to implement and easier to access for chassis removal. You can see a nice chassis bracket for this purpose on the Mission Amps page at Mission Amps Hardware Page

Regards,
Tom

I don't think that bracket will help in my case. It assumes another hole in the top of the cabinet (it comes with a #10 screw and nut), or, in my situation, a wood screw through the plate and into the top. A better implementation for me is to make a bracket the size of the end of the chassis that extends down from the chassis by an inch or two. Weld or bolt that to each end of the chassis and it would give me space to put two screws through the extended portion of the bracket into the cabinet sides. The chassis would have to be very close to the full inside width of the cabinet or the bracket could be bent to reach the sides of the cabinet. In fact, if I use inserts there, I could use machine screws. The advantage is that the weight of the chassis is on the side of the bolt/screw and not trying to rip out screws from the top of the cabinet. (Those inserts are little more than big wood screws, anyway.) It would take a significant amount of force for the chassis to shear off a 1/4" bolt. Here's a quick sketch of my idea:

[Tom Phillips]

Understood.
Since you are planning to do a lot of custom work you could also consider making a chassis with ears the extend outward from the ends of the chassis and then fasten the chassis rack mount equipment style to cleats on the side of the cabinet. All the mounting hardware would be hidden under the back panel.
There are lots of options for improvements when you don't need to use the lowest cost production methods or make exact copies of vintage designs.