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Understanding blum undermount Drawer Slides

by Lorenz Prem
published on October 27 2012 5:24 pm

Undermount drawer slides are a mark of quality in kitchens today. They offer an effortless feel of motion when opening and closing drawers no other system on the market can match. Cabinet makers love them for their forgiving nature. Undermount drawer slides are much easier to install than their traditional forbearers.

One of the largest, most well-known makers of undermount drawer slides is the Austrian company blum. Over the years their Tandem drawer system has built a reputation for quality and ease of installation. Let's take a look at what makes blum undermount slides so great.

The final product just work

First and foremost a set of good drawer slides must function properly. Users notice the ease with which a drawer opens. A good drawer should be easy to move; as if it was floating on air. The engineers at blum designed their slides to feel just right.

A drawer on blum slides will slide in and out of a cabinet supported by rollers directly under the drawer. The hardware supports the weight of the drawer for below. This allows the drawer to slide freely even when loaded down with a lot of weight.

For added user excitement blum offers a soft close mechanism called "blu-motion". The system is built into the drawer slide. There are not additional installation steps required. Should the blu-motion device break, it can be removed and replaced. Existing tandem drawer slides can be retrofitted with the blu-motion device.

Adjustability is built in

On of the strongest, most useful feature of the Tandem system is the adjustability of all their components. The engineers at blum understand that a cabinet is rarely, truly square and straight. Small mistakes are common, especially in non-CNC based cabinet shops.

The blum Tandem system allows drawers to run freely even if the drawer itself is not square, or the cabinet is misaligned. Fine adjustments on just about all components of the system make this possible.

For example, a depth adjustment screw on the locking device can be used to dial in the projection of the drawer front. If the drawer slide is installed too far in the cabinet, the screw can be used to bring the drawer forward without having to reinstall the slide.

Off course there is a limit to what the adjustment system can do. It cannot compensate for large errors, but mistakes in the order of 1/16"-1/8" are nothing to worry about. As a result installation of blum undermount drawer slides is fast and easy.

Installing the slides

There are several ways to install the slides in the cabinet. The slides themselves have mounting holes at the front and the back. The easiest way to install the slides is to attach them to the cabinet with screws. Correct alignment of the slides is paramount. For the drawer to slide freely, the slides must be installed as straight as possible.

Blum sells a number of mounting brackets that allow the drawer to be installed in a variety of ways. Mounting the slides to the back or the sides of the cabinet is particularly popular. The Tandem brochure contains all the devices available.

Preparing the drawer

There are three requirements for a drawer to be compatible with the tandem system.

First, the drawer must have a rim around the bottom. The arm of the drawer slide mounts to this rim using a locking device and a locking pin in the back.

Second, there must be a gap in the rear of the drawer to allow the arm of the drawer slide to pass through. The instruction manual details the exact size and location of the gap.

Thirdly, a small hole must be drilled into the back of the drawer near the gap for the slide arm. This hole accepts a locking pin mounted on the pack of slide arm. This locks the drawer in place at the back of the slide. Blum sells a drilling jig for locating this hole quickly and accurately. The layout jig is a strongly recommended accessory. It makes building drawers faster and more accurate.

The locking device

The slides are connected to the drawer with locking devices at the front of the arm. This locking device uses a big red/orange lever to attach the drawer to the slide arm. To remove a drawer the user simply has to press the unlock lever. The drawer disengages from the slides and can be lifted out.

A locking device must be installed in both front corners of the drawer. It attaches to the rim of the drawer with screws. The blum drilling jig can be used to perfectly locate the screw holes for the locking device.

Blum sells several different types of locking device. They all function the same, but differ in the way they attach to the drawer and how they can be adjusted.

The basic locking device with the height adjustment feature should be your default choice. The height adjustment feature comes in handy on drawers with flush drawer fronts. It makes aligning the gap around the drawer front fast and easy. The depth adjustment feature is useful for inset drawers where perfect depth alignment is necessary.

Measuring and layout

There are layout guides for all of the different products blum sells on their website. The guides contain technical drawings for all installation scenarios.

Drawer design can be a bit complicated at times. The Hingmy drawer calculator simplifies the design process. Simply enter the size of the cabinet opening and the calculator will return the size of the drawer that fits your slides and opening.

Installation guides can be found on blum's website. Make sure you choose the right guide for your drawer slides. The measurements differ from model to model.


The blum Tandem undermount drawer slide system is a very good choice for custom cabinets. The slides are easy to install, adjustable in every direction, and create a feel of quality that is second to none. The system is incredibly forgiving allowing for out of square drawers and cabinets that would make other types of slides bind.

Overall the Tandem system is the perfect choice for woodworkers and professional cabinet shops alike. Tandem equipped cabinets are of the highest quality at comparatively minimal effort. A product that allows me to make mistakes and still functions perfectly is a winner in my shop.

About the Author
"Lorenz is the founder of Hingmy. When he is not reviewing power tools or improving the site, he is building things in his workshop or playing hockey."