This post seems timely, given the recent, and ongoing, threads on stands, and the dissatisfaction many feel with whats available off the shelf. Its a bit of a long post, so bear with me.
My sliding upper tier stand is complete! Moe so inspired me that Ive been on a mission to find the perfect slides for the upper tier. I wanted to post my results as this forum has been so helpful for me, and thought maybe it might inspire some, and assist others.
I built this sliding 2nd tier onto my X stand. I, like others here, have never had a problem with it, other then wanting more room for pedals, but I can make do. The stand has served me well for many, many years, and hundreds of gigs. Its double braced, and I have the forum inspired safety strap just in case. Ive used it for a 2 and 3 tier stand, so I know it can support the weight. I've purchased 2 upper tier add ons in the past, but was never satisfied. I was able to use one of them for this design. About a year and a half ago, I ditched both pre-made second tier attachments and built a stand where the upper board sat on the lower board. Think I've posted pics of it. Problem was the upper board was too far away from me, and I was too hunched over. At the end of the gigmy back/hips were so stiff, I could hardly stand after a set, hence the reason why this sliding design was so attractive. I used a U shaped 2nd tier for this design. While it was way too high to serve well as a 2nd (or 3rd tier), it worked perfectly for this. I cut it at just the right height to be level with the top of the XK2 (should also work if I upgrade to a XK3C) to make the slide channels level. It fits into the cross bars of the X stand and secures with a tightening knob.
I thought I'd found the perfect product made by a company called Accuride. Took a week, but I finally got a response from them. Unfortunately, it's a brand new product, and they couldnt sell directly, i.e. had to go through a distributor/retail outlet. After waiting 2 more weeks, I found something comparable on eBay that looked close. I made an offer, and got them for $20 a piece. Theyre an industrial ball bearing slides, and major heavy duty. Their description is : THK FBW/FBW2560R Linear Bearing Guide Slide Rail Pack 488mm. Theres 3 mounting plates per slide that are 1 5/8"x2 5/8"x1/16. I thought Id be mounting an aluminum bar to these that would run from front to back of the keyboard, which it would sit on. Turned outI didnt need to, and that prevented the addition of another 1/4-1/4" in height. While testing things out, I put some foam pieces onto the mounting plates and put the top keyboard on it. It was really secure and slid nicely.
Here are the slides:
http://thumbs.ebaystatic.com/m/mscCdaovrPOOmrC04x2kfNg/140.jpg
Since the mounting plates are metal, I needed to secure some foam to them for padding. Again, to not add any more additional height, I used some foam underlay I had left over from doing some flooring; its this green, really tough foam/material, and is only about 1/8 high. I used contact cement to secure it, and figured Id paint it or something.
Here they are in their ugliness, but you can also see how the channel sits on the end caps of the XK2. I used the same green foam to pad the underside and protect the wood underneath:
http://i826.photobucket.com/albums/zz190/daddyg3042/IMAG0259_zpsdac7f947.jpg
I mounted the channels on a 2x2 aluminum square tube that I bought from a steel shop here in town for $10, plus $2 for end caps. I used a standard threaded bolt through the full tube to give it strength. Drilling through the slide's channels was difficult, as the metal was really hard. I dont have a drill press, so had to do it with a hand drill. Took 20 min. of continuous drilling per side, but I finally broke though.
I drilled a 1 hole in the bottom of the square aluminum tube, which accepts the top of the 2nd tier support snugly, and is a really quick and easy assembly. The 2nd tier "upgrights" can stay attached to the X stand during transport. I do need to remove the square horizontal bar for transport, but the channels both swivel back onto the square bar, making it basically one pole thats the 2nd piece of the stand now. I bought some Velcro straps to secure the pole to the X stand, so its really easily transportable.
Here's the stand with the 2nd tier uprights, horizontal bar, and slides swiveled back onto the tube:
http://i826.photobucket.com/albums/zz190/daddyg3042/IMAG0267_zps2f4606d1.jpg
And here it's ready for transport:
http://i826.photobucket.com/albums/zz190/daddyg3042/IMAG0265_zpsdaf50067.jpg
Thus far, everything was going really well, except the slides slid a little too easily. I was concerned the board would move around while playing. That worked itself out as the bottom of the top keyboard, a PC3, had rubber bumpers on it. Turns out, when theyre positioned inside the slide channel, they stop the PC3 from moving once in place, yet with some slight upward pressure the board slides nicely. Pretty easy to do in between songs, and even during them.
I bought some liquid rubber at the hardware store, and dipped just the top of the mounting plates where the green foam is cemented, and voila.its now black and grips the underside of the board even better. I did the same thing underneath so the tracks grip the wood on the XK2. I also made some end caps for the slide with this. I folded paper around the end of the channels, and wrapped them in Saran wrap, dipped, and now have some custom end caps! I did some other cosmetic things to it as well that I wont bore you with, but Ill tell youliquid rubber is da schitt!
Heres how they turned out; I sort of swirled the rubber as it was drying to give it even more grab:
http://i826.photobucket.com/albums/zz190/daddyg3042/IMAG0270_zps430e3d2c.jpg
One last thing, the X stand is not quite stable enough for two boards that are offset. In the past, I used another set of legs to prevent the board from tipping over backwards. For this design, I extended the rear feet of the X stand about 6 by simple using round tubing. I joined the X stand to the extension by using a smaller diameter 6 piece of tube inside the stand, then adding a 6 tube of the same diameter as the stand, i.e. X stand tube female to 6 tube male to 6 tube female. Very secure, and you cant even tell unless youre really looking.
Here's how far it extend out:
http://i826.photobucket.com/albums/zz190/daddyg3042/bdd19108-1dbf-4869-8d65-da887d453763_zps46145cd8.jpg
Two more shots of the boards with PC3 pushed back, and then pulled in closer. It can actually be pulled directly over the XK2 if all I'm doing is piano/epiano, etc:
http://i826.photobucket.com/albums/zz190/daddyg3042/IMAG0271_zps8aa7809e.jpg
http://i826.photobucket.com/albums/zz190/daddyg3042/IMAG0272_zps323d3c5f.jpg
And one showing the distance between the boards...it's less then 1":
http://i826.photobucket.com/albums/zz190/daddyg3042/IMAG0273_zps4512edd9.jpg
So.all told, I spent around $60, and about a day & a half of actual work. I've put both boards on it, slid it around vigorously, sort of rocked it back & forth. It's very stable. I think I finally have something that is gonna work, and I'm pretty stoked. It'll make it's maiden voyage on a gig tomorrow.
So...thanks so much for the inspiration, Moe. Sorry for being somewhat long winded as well.