Thanks Dan.
Sofa-bed continued:
Need to replace my home made sliders with heavy duty drawer hardware. I'm using Schock Metal 037 Series, 350mm (13.78") full extension drawer slide. $25.61 a pair.
Schock Metal web site

They are rated at 209lbs. Since the Seat Platform is fully supported in the center I believe that they should be sufficient.
I'm going to make some modifications to the slides. To make it easier for me to explain I've taken a diagram from the company website and given names to the three main parts of the drawer slide.

In my build the Base Plate will be attached to one of the end pieces. The Inner Slider will be attached, via a metal angle, to the Seat Platform. The reason I wanted to make modifications was because I wanted to increase the number, size and position of the mounting hardware. I'm not an engineer and have no way to validate my changes. I just felt the hardware should be a bit sturdier.
Start with the base plate. It comes with four mounting holes. More apt to say two pairs of mounting holes since they are so close together.

This metal dimple in the Middle Slider restricts the size of the attachment hardware.

The head of a #10 machine screw is the largest that will pass under the dimple.

I want to increase this from a #10 (0.19" diameter) screw to a 1/4" bolt.
To do this I first need to remove the "stop" at the end of the Base Plate.

Flip the slide over. The "stop" is hold on by a rivet. Drill down on the rivet head to weaken it.

Then knock it out with a punch.

With the "stop" out of the way you can now over-extend the Middle Slider. I've over-extended the slider and placed the dimple on top of one jaw of my bench vise.

Using the vice like an anvil I pound down the dimple with hammer and punch until it's as flat as I can make it. Now the head's of a 1/4" bolt will pass beneath it.


Now to add a couple more mounting holes. Between the Base Plate and the Middle Slider is a ball-bearing slider. There is a separate ball-bearing slider between the Middle and Inner Sliders. The 1/4" bolt won't fit under this ball-bearing slider. See where the ball-bearing slider sits when the slide is in the closed position and mark that spot. The bolt must be mounted to the left of this position.

Use that mark as a guide for where to drill a hole along the center-line of the Base Plate. Also add a mark for a hole near the left end.

The ball bearing tracks are greased and when you start drilling the Base Plate the filings can get into the tracks and cause problems. I found this works to keep the filings out. Get a round magnet with a hole in the center. Then center the magnet over where you're going to add a hole. Slowly drill through the center of the magnet.

All the filings stick to either the drill bit or the magnet.

Wipe the filings off the drill bit. To get the filings off the magnet just push a small screw through the hole in the magnet. Most all the filings will jump from the magnet to the screw. Then just tap the screw on the inside of the trash can and the filings fall right off. Do that a couple times and the magnet will be mostly clear. The few filings left on the magnet can be easily dusted off into the trash. Don't tap the magnet to loosen filings. Banging on a magnet weakens it.

The Base Plate can now be mounted with four 1/4" bolts.

Next up the Inner Slider.
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