Standard CNC Machine Assembly Tips [Archived]¶

What you get out of the machine is partially a function of the time and effort you put into building and calibrating it, and this guide can help you with some of those activities.

Now onto the fun stuff - putting your machine together. While the drawings for our plans contain the majority of the information you will need to assemble your machine, there are a few pointers we'd like to pass along to make the construction of your machine go more smoothly. Many thanks to our previous customers, who have provided a lot of these helpful tips.

1. General Building Tips¶

We recommend building the machine in order of the sub-assemblies:

• first the base (CRP110)
• then the gantry risers (CRP120)
• followed by the gantry (CRP130)
• and finally the Z-axis (CRP140)

Separate instructions are available for some of the components used:

• Linear Carriage Instructions
• Standard Rack and Pinion Drive Instructions

We recommend going over the plans and making sure you have all of the listed parts. Your machine should be packed by sub-assembly, which is helpful, as there are a lot of parts! If somehow you are missing parts from a sub-assembly, let us know right away, rather than robbing parts from another sub-assembly - we can get things out to you and avoid confusion as to what parts go with what.

2. Gotchas¶

There are a just a few small non-obvious things you can do to avoid frustration with your build, and these are noted below:

1. When assembling the 110 base assembly, make sure all of your connections to the cross members are flush - this will help square the frame and insure you have a good foundation to build on. A couple of pipe clamps can help to pull the side rails together before you tighten the fasteners down.

2. When assembling the CRP120 units, put the brushes on the gantry risers before mounting the units to the carriages! Otherwise, the screws for attaching these are very difficult to get to.

3. When putting the 130 gantry assembly on, make sure that the tapped holes are in the proper position for the bumpers, and that the gantry is not on upside down or backwards. If you do put it together backwards, don't take it apart -- tapping additional holes in the ends is easy (the holes are pre-formed to the proper size, so no drilling is required), but it's best to check. Note, this warning does not apply for all machines -- some machines (like the CRP2448 with short gantry) have all of the end holes tapped.

4. When putting the rack and pinion drives on, the motor pulley can be moved through quite a range on the motor shaft. Different motors have different length shafts, so before tightening the set screws on the motor pulley, check to make sure the pulley is aligned with the gear/pulley drive spindle. This position likely will not coincide with the end of the motor shaft - don't panic.

5. If you are using a NEMA 34 rack and pinion drive or our newer PRO Rack and Pinion drives, assemble your carriages with the longer 40mm bolt provided in the PRO kits tension kit before assembling the carriages to your system. See the PRO R&P Instructions.

6. Once you are able to drive your machine around, and have verified there are no mechanical interferences or other issues, we highly recommend adding Loctite to the motor set screws and re-tightening these. Slipping motor pulleys are the primary source of head-scratching positional issues on these machines.

7. When installing the gear rack on the sides of the machine, this is intended to be installed in the middle t-slot of the 1545 extrusion, with the teeth pointing down. Additionally, the gear rack should be biased towards either the front or the back of the machine. The reason for this is that when the rack and pinion drives are installed, the pinion gear that interfaces with the gear rack is not centered between the linear carriages, but is biased to one side. Which side is dependent upon whether you mount the rack and pinion (using the pivot bolt) to the front or back of the carriage. Either way is acceptable, but you want to make sure your drive pinions are biased in the same direction as the rack. In either case, you will want to fasten the rack approximately 1" off the end of the extrusion.

3. Rail Alignment and Squaring¶

The majority of your machine kit can go together easily just by aligning the edges of the components with each other during assembly. However, the rails on our linear carriage based systems do require some adjustment. It is not uncommon for the cold rolled steel to have a small amount of bow to it, and this can actually be pulled out during assembly with care. The steps to accomplish the installation of your rails are below:

1. For the CRP110 base assembly, it is best to use a 1/2" (12.7 mm) spacer and a clamp to evenly space the rail off of the extrusion the entire length of the machine. Tighten the fasteners to the extrusion as you go. Put one face of the clamp on the extrusion, with the other face on both the rail and your 1/2" spacer. If you don't have a convenient 1/2" spacer, the z-axis motor mount is 1/2" thick:
   
   This approach should insure your rails are relatively straight and parallel, and will make the rest of machine assembly significantly easier.
2. For the CRP120 assembly, it is also helpful to use clamps on either side of the riser, aligned so the clamping faces are clamping both the steel riser and the extended carriages attached to it. Only light clamping pressure is required (over tightening can crush the bearings, so use just enough pressure to get things aligned). This will minimize the need for additional squaring later on once the gantry is installed:
   
3. For the CRP130 assembly, check for square by manually driving your machine all the way to the bumpers at the back of the machine (without R&P drives engaged). If the two sides do not touch, the best place to address this is at the vertical interface between the gantry risers and the gantry. A thin shim (we recommend a piece of an aluminum can if you don't have shim stock available) can be placed at the inside interface of the gantry riser that is not touching (see picture below). A shim here provides approximately a 20:1 lever arm, so as an example, a 0.005" spacer will move the opposite riser forward approximately 0.100" once the bolts are re-tightened.
   

4. Z Axis Construction¶

The Z-axis is one of the more intimidating aspects of machine construction to most people, but it's not terribly difficult. Follow the steps below to assemble your z.

1. Adjust the extended carriages for the z so they slide nicely on your z-axis steel. It is best to do this before mounting them to the high z plate.
2. Fasten the extended carriages to the high z plate for the z axis. Do not tighten the mounting bolts all the way.
   
3. Attach your dumpster nut to the high z plate. It can be easier to install the drive screw now as well. The orientation of the drive nut doesn't matter particularly - it can be pointed up or down. Thread the screw through the nut enough so that it sticks up above the ends of the carriages.
   
4. Pre-mount your steel to the z extrusion, using the same 1/2" spacer technique you used with the CRP110 base assembly. Make the steel flush with the end of the extrusion without tapped holes. This end will be the bottom of the z axis.
5. Attach the bearing block using the supplied drop-in t-nuts and screws. Mount the bearing block with about a 3/4" (19mm) cap between the block and the edge of the steel so there is room for the shaft collar and thrust washers required below it. Do your best to make the bearing block square and flush with the sides of the extrusion - it is exactly 3" wide, so a plate or block referencing both the edge of the extrusion and the side of the bearing block can assist with this.
   
6. Assemble the shaft collar and one set of thrust bearings and washers onto the Acme screw. Tighten the shaft collar about 2.25" from the end of the screw, then add the washers and thrust bearings as shown below:
   

   

   
7. Slide the z axis extrusion and steel with the bearing block attached onto the Acme screw and into the extended carriages.
   
8. At this point, you can use a soft jaw clamp to press the extended carriages against the steel and the sides of the high z plate to get the z axis aligned and remove slop from the bearings. Once you have done this, you can tighten the bolts that hold the carriages to the high z plate.
   
9. Now back to the other side of the extrusion. Add a series of thrust washers at the top of the bearing block, followed by the shaft coupler:
   

   
10. Attach your motor mount and then your motor, tighten the clamping screws on the coupler, and your z axis is ready to go!

OK, that's it for now. If you have other questions or there are things that aren't clear, Contact Us and we'll try to provide updates. Thanks again for your interest in our kits!