My company is not satisfied with sourced wood extension slides. There have been numerous issues of warp, splits and cracks, and failure of the sliding plastic runners inside the tracks. We are looking into making our own in-house, but need advice on the following...
- Anyone know of a stable species that has the bridging capacity and strength?
- Typical engineered camber for that species? 3 piece slide 26" close - 52" open
- Finish, bought out slides were sealed, then waxed. Any suggestions? Don't want it to bind due to finish wear.
- Is fingerjointing okay, or would you avoid it when making the rails?
(Furniture Making Forum)
From contributor P:
Are you thinking of this as a mass production item, or do you just need to make a set or two? The first thing you have to keep in mind is that, compared to metal slides, these are a crude design, and usually crudely made. Slides like this have been around forever, and people didn't used to have such high expectations as to their performance. Most people don't open their tables very often, so wearing them out is rarely an issue.
I've made a few sets of these over the years and found that any reasonably stable wood will work. I have bought a few sets, and I believe they were beech - not necessarily the most stable wood. And like you, I found the slides to be poorly made. I think that a certain amount of slop is inherent in wood slides, as having them bind would be more objectionable than having them sag. The sets I bought didn't have any noticeable camber in them, probably due to the relatively crude manufacturing involved. It's possible that you could work out the proper curves and CNC them, but then it would be hard to mount the slides to the bottom of the table.
I have had better success with metal versions of this slide - Watertown Slide Company makes the ones I used, and they worked reasonably well. They may have moved their production offshore and suffered the usual decline in quality, or they may be dead already.
There are better ways to make tables open, but if you just need one or two, I would make them in house - at least you'll get good wood. I'd recommend hard maple.
As strength and smoothness and the lack of twisting when the MC does change are keys, beech is the wood of choice. It machines well and is uniform. It sounds like you may have been getting items with poor initial moisture control.
Note that the width of the slides is not as important as the height, with respect to strength. (Consider a 2x4... step on the flat side and it bends a lot; step on the edge and it is much stiffer and stronger.)
Wax is a lubricant and also seals the wood from moisture. It is applied after finishing, as if applied before, no finish will stick on the wood. Some pieces have used only wax based finishes.
Overall, my suggestion is to try a new (and better) supplier, rather than learn a new technique and have some rejects of your own.