Cabinet Weight Capacities, Ways to Increase?

[Lisa Starr]

My husband is upgrading his Benchtop Mill and has asked me to construct a new set of lower cabinetry that it will sit on. My concern is the mill weights around 850 lbs. The top will be constructed like a work bench with the individual boards on edge and be approx 3.5" thick. He wants "kitchen cabinets" under this top. I know normal kitchen cabinetry is rated for 600 lbs. I expect to use 3/4" plywood, and my usual method is dowels, glue and pocket screws to hold it together. What can I do to handle the extra weight?

[Maurice Mcmurry]

I have had 1 inch Plywood for a few projects it is an amazingly sturdy product.

[Kevin Jenness]

Use a substantial face frame and well fastened back to prevent racking and make sure the load is transmitted directly to the floor through the uprights. If you want some extra assurance double up the upright thickness. What does "rated for 600 lbs" mean? Per lineal foot? Per average cabinet? A 3 1/2" wood top will transfer the mill load to any flanking cabinets.

[Lisa Starr]

Kevin, from what I gather, cabinet makers "certify" that their cabinets support 600 lbs. There are no mentions of per sq ft, lineal ft or otherwise. Also no mention of materials. Pretty vague to me.

[Brian Runau]

Have you considered a metal frame, with cabinets under. No weight on The cabinets this way.

[Ron Selzer]

I would build with 3/4 plywood for sides, bottom, fixed shelves and back. Top securely fastened to cabinet to avoid racking. Good 4/4 hardwood face frame

[John Kananis]

I would not make the cabinets bear the weight of a 3.5 inch top AND a mill AND whatever is being milled, what's sitting on the bench, etc.

Use appropriate lumber and make a substantial base for the bench top. Then build cabinetry and install it within the base.

[Thomas McCurnin]

What John says, and you can beef up an ordinary cabinet with some 2x4s and joist hangers.

[Jason Roehl]

What overall length is the 3.5” top going to be?

[Lisa Starr]

The top will be approx. 30 x 72". The cabinet will be drawer stacks and unfortunately, he'd prefer framelessm as it matches the other cabinets in his shop.

I'll try to take a look at building a base and installing cabinetry within.

[Carl Beckett]

If you simply double up on your vertical pieces, and keep the span down, it will be quite strong. Double wall 3/4 plywood on the sides (and vertical divider), and under 24" between supports. I have a workbench built this way - it is solid. (I would not try to build frame/braces from 2x4, it quickly becomes cludgey)

You can frame this like faceless

$.02

[Kevin Jenness]

The top will be approx. 30 x 72". The cabinet will be drawer stacks and unfortunately, he'd prefer framelessm as it matches the other cabinets in his shop.

I'll try to take a look at building a base and installing cabinetry within.

With overlay drawer fronts you can build the box with or without a face frame or with doubled up standards and the look will be the same. Doors can be mounted with surface mount Euro hinges. A substantial face frame would add some racking resistance but the fact is a normally built frameless cabinet let's say 6' wide with 3 bays and a solidly attached back, fastened to the wall, with a thick top to spread out the weight, will function just fine in this situation. The only way it could fail is if the uprights buckled in compression, the load was not supported directly under them (as with adjustable feet) or the cabinet racked (very unlikely, but if concerned attach one end to a wall or add a face frame or doubled standards). Horizontal stretchers at mid height between drawers could be used to stiffen the uprights. If you accept the contention that a single "standard" cabinet will support 600# then several ganged together should not be a problem.

If the top is solidly attached to the boxes (with slotted screws at the front to allow for movement) and the boxes attached to the wall even standard frameless boxes are not going to rack at the front. An additional framework would be extra unnecessary work in my opinion.

[Lee Schierer]

From an engineering standpoint you want to have vertical supports close to directly under the load to transfer the weight to the floor. Of course, this implies that the floor will also be able to handle the concentrated load. With an 800 pound mill you could easily have another 800 pounds of tooling and cabinet sitting on a small area of floor.

[Steve Rozmiarek]

Just to put some perspective on the engineering, a single hem fir 2x4's compressive strength is around 1000# psi. Around 5 1/4 sq inches of vertical cross section in a 2x4, so a single one can theoretically support something like 6x the required dead load you are working with. It follows that a 1"x1" of hem fir is theoretically able to support the compressive dead load you require. A 30x72 frameless cabinet built with 3/4 ply, with 2 full depth dividers has 144 sq inches of vertical cross section. Plywood has a higher compressive strength than a 2x4, not knowing what product you'd use exactly, I won't speculate, but all that I see are higher. You can extrapolate then that your basic cabinet, is potentially 144x stronger than necessary to support the dead load of the mill.

A machine is not dead load however, there are vibrations, potential dynamic forces of the stock being milled, etc. The cross sectional compressive load is far more than adequate assuming that it stays vertical. Keeping the load bearing components of a cabinet vertical while handling dynamic variables is something to consider. Common cabinet building techniques are likely adequate, but as compressive strength and ability to handle dynamic loads are dependant on the sides, dividers and back staying vertical, a mechanical joint like dados instead of the normal butt joint could be used. Commercial cabinets are generally built as light as possible to meet the normal required loads.

Honestly, you could set the mill on three 24", 1/2" case sides with 1/4" back commercially available bases and be perfectly fine. I've set far heavier countertops on islands. The only problems I've ever come across on loading cabinets was a failed plastic leveler, and a cabinet back that must have been damaged in shipping letting go and allowing the cabinet to lose stability. However as most of us like to over engineer, just make the cabinet joinery a bit better for peace of mind.

No, I'm not an engineer, but math is math.

[roger wiegand]

I'm with Steve. A well constructed cabinet made with decent 3/4" plywood will hold a *lot* of weight. Using something like MDO instead of plywood from the Borg will ensure void-free, strong material, baltic birch if you have a stock of material lying around-- but that's overkill. Not sure I'd do 72" as a clear span but with sides and at least one internal divider that goes all the way to the floor that would seem like plenty. A back made from 3/4", perhaps with some reinforcement will prevent racking, the biggest danger. I'd do the construction with glued dados, not pocket screws or butt joints-- but that's how I make my cabinets anyway. A glued in place internal shelf would further add to the strength.