There are several ways to clamp racks to a surface. Here are the ones I have made or purchased.
2 or 3 Piece Rack Clamps
A two piece rack clamp consists of two pieces (obviously).
The first is a piece of stock similar in size to the rack being clamped. In this case its a 1/2" x 1/2" piece of square tubing cut to 3"
The second is a piece of 1" x 3" x 1/8" steel flat bar. It has two holes centered and 1.5" apart.
The two piece clamp is laid out as you see here. The first piece (square tube) is used to support the flat bar is the actual clamp and it sits on top bot the the rack and square tube.
Two bolts are used to secure it to a flat surface.
The three piece rack clamp is identical to the two piece, except it has an additional flat bar.
The three piece rack clamp is used when you need to raise the rack slightly off the surface. Or where the surface is not exactly flat.
The support (square tube) and rack are sandwiched between the two flat bars, as shown here.
Here is an actual three piece rack clamp holding the rack on a CNC gantry.
The two or three piece rack clamps are very easy to make. Just use some sort of saw to cut the readily available stock to 3", then drill some holes.
Most home centers carry this steel stock.
Solid Rack Clamps
A solid piece rack clamp are clamps that are machined out of a solid piece of aluminum.
Most of what I have found are meant to be used in some sort of extruded aluminum.
This particular clamp is meant for 15 Series 8020 and cant be used anywhere else.
Here is how it holds the rack in place.
The down side to this clamp is that it can only be used with 15 series 8020. You are also stuck with using only 1/2" x 1/2" racks. Smaller or larger and you will have to use something else.
Note: You can get some of these solid rack clamps with removable pins that allow you to use them with other extrusions or even stand alone on a flat surface.
You can make these clamps your self, but you will need access to a milling machine or CNC router.
Simple mill a rabbit the thickness of your rack into a block of aluminum, then add two holes.
One Piece Rack Clamp
While this clamp can be hard to make if you dont own a plasma cutter or band saw.
I have made these manually, but prefer using a one of CNC plasma machines.
Being one piece they are extremely easy to install on about any surface.
This shown how simple it is to use.
They can also be used on any extrusion.
This shows one holding a rack onto a steel frame.
One reason I like these clamps, is that I get some wiggle room. The solid clamps are meant to hold a rack in one position only.
Every rack and pinion drive system I have seen or built has a spring tensioner. This means if you can tweak the rack or the clamp for whatever reason, it wont affect the operation of the drive train.
One last thing. You can add a flat bar under the clamp and the rack if you need to.
How I Make the Once Piece Rack Clamps
I start with my fixture. I then insert a piece of 1" x 3" angle.
My angle jig:
My rack clamp jig:
I then have the CNC plasma cut the two holes.
I Flip the angle.
I cut the short side of the angle. In this case it is cut to 5/8".
The part is ready. I will chip off any dross that is hanging on the part and clean the part with a little acetone.