Chapter 10.1 - The Computer Rack
This isn't an official chapter of Building the KRMx01 CNC Machine, but it has to be done before I can continue with the next chapter of the book. I decided that rather than place the computer on a shelf that maybe I would have a go at some sort of computer rack and drawer system (to come later as an upgrade) to maximize the space available from the CNC stand.
I also need to mention that I built this from materials on hand so can only give you general information on how it is made. I am sure you can replicate it with other materials you have available to you.
The computer rack is made from aluminum stock and pieces of cut 2" angle iron used as connectors. The aluminum stock I used was U-Channel from an old stand up rack and some 1-1/4" x 2-1/2" material with slots of sorts that was salvaged from some pharmacy fixtures. I realize that isn't the greatest description, but it was just some stuff I had on hand.
The U Defined
Before I start on the actual build of the rack it is important to know what a U is. If you look at the image to the left, you will see that the mounting holes for a computer rack are defined in to spaces called U's which the best I can tell is shorthand for units. Each U consists of three holes equally spaced on .625 (5/8"), and the distance between the U's are .5" (1/2") from center to center of the U holes. The holes are typically drilled and tapped for #12-24 or #10-32 screws. This configuration is handy for things like switches, drawers and keyboards, but when dealing with heavy items like computers and monitor trays, you will discover that the mounting holes will not work using the standard size. Most computer racks for business use use square holes of about 3/8" on the side. These holes still use the standard spacing but instead of being threaded use a square nut held inside a clip that will clip it to the hole for mounting.
Building the Rack
Again, I reiterate that I made the rack from materials on hand and you can do the same. The only thing to consider are the pieces that you use to make the uprights. You will want to make sure they are heavy enough to handle the weight and pressure of whatever you have hung inside it and that you follow the drilling schedule for the U spacing.
Use the four images above to follow along with the steps below.
I started by measuring from the front to back of the KRMx01 stand on the inside of the angle on the far left side of the stand. My stand is not perfectly square so my sizes are a little off from each other. With these measurements I deducted about 1/8" from the lengths to allow for some play.
Cut two supports to this length. I used some aluminum stock that was used for some pharmacy fixtures but you could use something like square or rectangular tube stock. The idea is that it will be rigid enough to bolt it to the stand and support the weight of the uprights and the equipment you bolt to the uprights.
Next you will need to make some sort of connectors to connect these support to your stand. I used 2" x 2" x 1/8" angle iron. I cut two pieces 1-1/4" long and two pieces at 1-3/4" long.
Next I attached the angle pieces to my supports. I started with the bottom support by placing the 1-3/4" angle iron piece on the side of the support pointing towards the center of the stand flush with the end. I drilled a 3/8" hole through both the angle Iron and the support. I used 1/4-20 bolts to bolt them together but I wanted some play so I could move the angle a little bit at both ends. The top support I done a little bit different. Because the extrusion I was using had a slot on the ends I fashioned a nut from a piece of steel that would slide in the slot. I drilled and tapped it for a 1/4-20 bolt. This would allow the angle iron bracket to slide. The 1-1/4" angle bracket is fastened to the top of the support so that the support will hang down and clear the bolts on the table top.
Next I attached the supports to the stand. I wanted my computer rack to be as far to the left side of the stand as I could get it. So to do that, I started with the bottom support and clamped it to the angle iron of the bottom of the stand and adjusted it so that its face was flush with the inside edge of the stand. The images above show what I mean. With the support clamped in position, I clamped the angle iron pieces to the front and back of the stand and tightened the bolts that held them through the support piece. Next I found the center of the angle against the front and back of the stand and center punched and step drilled a 3/8" hole through the stand and the angle iron piece on the support. These were bolted in place using a 3/8-16 x 1" bolt with a washer on each side, a lock washer and a nut.
The top support was put in place and the angles clamped to the stand and the 1/4-20 bolts holding the angle were tightened.
Next it is time to position the uprights. Since I am using parts from an old computer rack, all I have to mind is the position of the U's on the rack. My solution to this was to make the other bottom support like above and have it ready to clamp in place. To cut the upright to length, I measured the width of the bottom support to the top of the stands bottom piece of angle iron. Next, I marked the center between two U's and measured below the distance I found previously. Next, I measured from the bottom of the lower support and the top of the upper support. Using this measurement, I marked the upright to this dimension using the bottom marked line I just made on it. I cut four of these out. Next I used a rack mount drawer as a spacer and attached to two of the uprights. I placed the drawer and two uprights into the rack using a couple of 1/8" thick material to set the height of the bottom of the drawer off the stands angle iron. You can see this clearly in the first and second image above. Finally I clamped the second lower support beam in place.
Next pull the upright against the lower corner of the stand and clamp it into place. Take a level and plumb the left upright on both sides. You may have to reposition the top support to do this. When all is good, clamp everything into place.
Now take and drill a 1/4" hole through the top left upright and the support. Bolt together with 1/4-20 bolts using a washer on both sides, a lock washer and nut. With the first bolt in place remove the clamp and drill a hole for a second bolt. Add the second bolt to the upright. With the second bolt in and tight, double check that the upright is plumb. Then drill a 3/8" hole through the stand and the top support angle connector and bolt with a 3/8-16 bolt. Again using a washer on both sides, a lock washer and a nut.
Next I took a rack mounted keyboard drawer and mounted it between the other pair of uprights and put it in position between the lower supports. I placed a piece of 1/8" thick angle on the right bottom support and laid a piece of 1/8" strap across the right support and stand angle just like the drawer in the front to keep the bottom spacing correct. Next I made sure that the front of the front upright and the back of the back upright were spaced 29-3/16" inches apart on both sides and clamped them into place. With both bottoms in position, I drilled and bolted the lower right support on both the front and back. Next I made sure the right side uprights were plumb and clamped to the upper support. Next I drilled and bolted the uprights to the supports.
When all four uprights were bolted to the top supports, I moved the drawer and keyboard tray to the top of the uprights to ensure the spacing. Once they were moved to the top, I drilled and bolted the top right support both front and back.
Once all the supports were bolted in, I drilled and bolted the uprights to the supports, minding that I kept the 29-3/16" spacing from the front of the front uprights and the back of the back uprights. The uprights on the left side were drilled through the uprights, support and stand angle. The uprights on the right were just drilled and bolted to the supports.
I know that was a long drawn out description that may have been hard to follow, but if you look at the images above it will be pretty self explanatory on how the thing went together. There may be much better ways of getting a rack in the KRMx01 stand, but this is what I had on hand and worked for me. Granted, it ain't "PERTY" but I will make some trim to clean it up a bit. Besides, I need to make progress so I can get the electronics done.
The completed computer rack
Here is an image of the completed computer rack. From the top down is a Keyboard tray, a drawer to put goodies in, a slide out shelf with cable management for the PC that will control the KRMx01 machine. A couple of things to point out. If you are making your rack uprights from scratch, it may be best to just punch and pilot the U's with an 1/8" bit and leave them until you are ready to use them. This way, if you have to make larger holes for bigger mounting rack equipment you are not re-doing anything and for equipment that take multiple U's you are only setting the holes you really need to use.
Below are some more images of the computer rack with equipment installed. Additionally they show how easy it is to access stuff in the rack. Also, i want to point out that when the machine is up and running I will do some more stuff for trim and beautification. (Well at least as much as my limited abilities will allow.)
I have included another picture for you to look at. This one shows the cable / wire management in the back of the rack. As things progress, many more wires will be added and will get tidied up some more.
With the Rack completed I can move on to the next chapter, the KRMx01 Electronics. See you there.