Indexing Blumotion Drawer Slides

Fine points of the alignment of a Blum drawer slide: Why are the screw holes not parallel with the drawer bottom? July 29, 2011

I'm getting ready to produce a project with 70 drawers. It's the first one I have done in a long time with Tandem slides. We are doing it this way because we are matching a project we did for these people ten years ago.

I moved away from undermount slides because they required too much tune up after being installed in the cabinet. Almost all of our work is flush inset and I was concerned about the longevity of any adjustments we made after weight and dynamics were added to the equation.

If you look closely at the part of the slide which mounts to the cabinet box, you will see that the installation holes are not parallel with the slide itself. In fact, the slide is designed to drop 1 mm at the back. This drop results in a drawer face that mathematically tips out at the bottom, hence the need for ratchet adjustment at back. The way the slide is designed, however, actually produces a drawer box installation where the bottom of drawer box is parallel with bottom of overall slide mechanism. If, during drawer slide installation, you index your slide parallel from the bottom of the cabinet (rather than a screw hole pattern perpendicular to front of cabinet), you do not have this drawer face shingling effect. All the facets agree with each other in a 90 relationship.

My question has to do with the Blumotion part. Blum engineered this tipping action for a reason. Was this to assist the spring/piston to close the drawer? Are there any longevity issues associated with not including this tipping action during slide installation?

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Forum Resposnes
(Cabinetmaking Forum)
From contributor K:
Interesting... I am now curious. I always install my slides parallel with the decks.

From contributor R:
There is a little lever on the back of the slides next to the hook that you can rotate and raise the back of drawer boxes to plumb the fronts.

From the original questioner:
The lever at back side is only of benefit if your slide is canted lower at backside. If you index slide installation parallel to cabinet deck, there is no gravity working on behalf of the drawer slide. The question is whether or not this gravity is an assist to the Blumotion part of the slide.

From contributor R:
Yes, the slides should slope to the back so that gravity can close them. The lever in the back allows you to compensate for the slope and plumb your fronts.

If you want better adjustment features, use the Accuride Eclipse slides.

From contributor D:
Interesting observation. It appears to me there is a corresponding amount of play/rock in the sliding members. It may depend on the slide, but the rocking/pivot point/bearings are behind the midpoint of the drawer and the front of the drawer is heavier than the back. If the mounting holes were parallel, the drawer box would sit low in the front.

From contributor L:
I have used Blum tandem for many years and have always installed them parallel to the deck without any problems and without the need for any adjustment. They always roll in fine, even without motion. Of course the cabinet would need to be plumb and level.

From contributor J:
On Blum Tandems, if you bore the holes parallel to the carcass deck, then:
- yes, the drawer slide and drawer box is canted to ensure gravity works in its favor.
- the rear ratchet levelers will need to be raised slightly to eliminate the shingling.
- this is exactly how you'd want it, so that the rear levelers have some adjustability up or down to correct for minor variations.

In practice this works out great. Bore your holes parallel to the deck - installers make sure the clips aren't raised - then a 10 second adjustment of the rear levelers and off you go. I can't fathom how longevity would be affected with boring the holes out of level or not. But then I can't fathom why anyone would go to the effort of "correcting" the gravity assist Blum engineered into the slide.

From contributor Y:
For 5 years I have installed the slides with a custom jig that squared the top of the slide with the front of my face frame. I always had problems having the drawer face sit flush with my face frames. In the last few months I have started using a Hettich undermount jig (works great with the Blum slides) and fastening the slides with a euro-screw. I swapped over to this for faster setup and instantly found out that my drawer fronts were now flush with my face frames! Didn't realize why until I read this post, got a slide and took a few measurements with the calipers.

From contributor S:
What Hettitch jig part are you referring to? Today I was putting together an order for Hettitch and I could add that on.

From contributor Y:
It's the Accura universal drilling template for runner systems. Works great for me doing face frames. Pretty sure it would do frameless also. I like the fact that I can drill all the holes before I even put the face frames on the cabinets, and the euro-screws are great (especially in the Robertson head!). Pretty expensive jig, but works great!