I did this before but cannot remember what slides I used. It is self-closing and the slides used were full extension BB type (1/2").

The rack ass'y even fully loaded works perfectly even though the load on slides is rotated 90.

Whose slide should I choose this time?

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If you actually made a pull out as you have that one drawn with standard side mount slides laying on the flat you must be some sort of magician because any side mount slide we've ever run on the flat (as a guide only to keep a component aligned) would droop/sag a mile when extended.

Ive never tried it so who knows but I can hold a side mount slide extended on the flat and see the droop under its own weight.

Did you honestly build pullouts this way?

I'll take a pic and post.

The heavier KV slides have a horizontal mount rating. I think it halves the capacity though.

I put a back in those, and mount both sets of slides on it. Usually the 250# KV slides

Ive done some custom roll-outs with a pair of side mounts on the bottom (as you would conventionally mount them) and a single rolled on its side on the top for a guide.

I can deflect a wide drawer left/right at full extension with light hand pressure (simulating if it were on its side vertically and lightly loaded).

I suppose it may be fine if there is a very light load but would seem a chore.. especially at full extension.

Well! I was wrong. Good thing I had access to that one I built in 2012.

The bottom slide is upright in "standard" position, mounted to a 2-1/4" rail fixed to the underside of the bottom shelf. Top slide is as I show above.

Works perfectly.

And here is an image of the arrangement, done right.

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Thats the way Ive done them in the past when we've had to. Only input from our experience is leave yourself plenty of clearance because adjustment can be a pain and I'd be carefull with tight door gaps.

This is a fridge/tall spice unit we did a long time ago that it pretty much identical to your drawing other than two slides at the base and a single at the top.

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View higher quality, full size image (4032 X 1960)

Never built any, but I've incorporated the Rev-a-Shelf models into a couple kitchens. These used a pair of slide on the bottom mounted conventionally, then a third slide on the bottom, mounted 90-deg between the other two, which gave lateral and vertical support. They were nice but I can echo sentiments of leave yourself plenty of working room. 1/8" reveals were a minimum.

Don't think I could build them cheaper than I bought, but they are easy enough to build.