Base Assembly

Bolting T-slot extrusion together, adding brackets, squaring frame, and mounting Y axis rails to build CNCR-BASE ().

Components

Custom Parts

Purchased Parts

  • 2 x Y Axis Ball Screw Kit (1610 x 1000mm) with ball nut, BK12/BF12 mounts, and motor coupling (14mm) [DWG#41,3,4,21,22,23]
  • 2 x Y Axis Linear Rail Kit (HGR20 x 1200mm) with 2 x HGH20-CA bearings each [DWG#39]
  • 2 x Y Axis Motor (NEMA 34) [DWG#38]
  • 2 x Y Axis Homing Switch (Panasonic LS-TB-T with matching cables, 1 x CN-14A-C2 and 1 x CN-14A-C5) [DWG#24]
  • 4 x T-Slot Inside Corner Bracket (with cable tensioning mounting point) (McMaster #5537T291 or similar) [DWG#32]
  • 2 x Steel Rope with loops (48in, 400lb load) (McMaster #30645T573 or similar) [DWG#40]
  • 4 x S-Hook (10mm thick, 400lb load) (McMaster #9380T14 or similar) [DWG#20]
  • 2 x Turnbuckle (400lb load) (McMaster #30315T24 or similar) [DWG#43]
  • 1 x Y Axis Cable Chain (Igus #1500-068-100-14068-34PZA2-1166m) [DWG#5]

Hardware

See the Bill of Materials in the drawing for a full list of hardware. Hardware is referenced in this guide using the Item number from the bill of materials [DWG#XX]

Frame Assembly

Extrusion Assembly

Start by assembling the perimeter of the frame (CNCR-BASE-TSE-RM and CNCR-BASE-TSE-OM) “right side up” on a large, flat surface (so that the bottom surface of all four extrusions are co-planar). Bolt the components together with the long M8x60mm cap screws [DWG#37], tightening until snug. Use a tape measure to verify that opposite (parallel) sides of the rectangular frame are equal length:

  • Y axis length can be adjusted by loosening, moving, and re-tightening one of the joints because of the slop in the clearance holes through the -RM parts.
  • X axis length can be adjusted using shims in one or both of the joints to ensure that the distance between the inside of the two -RM parts is exactly 1440mm.

Flip the entire assembly upside down so that it is resting only on the two -OM parts. Insert and align the two -IM parts so that they rest on the same flat surface as the -OM parts (if one of the -IM parts is too long, add another shim to both of the -OM joints on one side to widen the gap). Bolt the -IM components to the frame with the same long M8x60mm cap screws, tightening until snug. Use a tape measure to verify that the distance between the outside of the -RM extrusions is identical at all four parallel mounting locations and use shims to correct as necessary.

With the assembly still upside down on a flat surface, add the blocking extrusions (CNCR-BASE-TSE-OBM, CNCR-BASE-TSE-IBM, CNCR-BASE-TSE-CBM) between the -IM and -OM extrusions where indicated. Bolt the blocking extrusions to the frame with the long M8x60mm cap screws, using shims as necessary to ensure that the -IM and -OM parts remain parallel.

To ensure a lasting fit, apply threadlocker (blue Loctite) to each of the M8x60mm cap screws from the -IM and -OM parts by removing and replacing them one at a time, tightening them to their final torque when they are reinstalled. The blocking extrusions should not be coated with a threadlocker at this time because they may be adjusted after the probing step of commissioning.

Cable Installation

Flip the frame assembly “face up” on a flat surface for the cable bracket installation.

Mount the T-Slot inside corner bracket [DWG#32] to all four corners using M8x16mm flat screws [DWG#44] and M8 T-slot nuts [DWG#33]. If using the recommended McMaster corner bracket, the locating nubs on the bottom face of the bracket must first be ground off (sub-flush) before installation. Ensure that the bottom face of the bracket is co-planar with the bottom faces of the frame extrusion before tightening, and use threadlocker to permanently secure the screws.

Optionally flip the frame assembly “face down” on a table to make installing and accessing the cables easier.

Connect an S-Hook [DWG#20] to each of the four inside corner brackets. Fully extend both turnbuckles [DWG#43] and connect them to the S-Hooks at the back of the frame. Use the looped steel cable [DWG#40] to connect each turnbuckle to the S hook on the opposite corner (diagonal) of the frame. Tighten both turnbuckles until they are snug.

Use a tape measure to read the diagonal length of both sides of the frame. Tighten the turnbuckle on the longer side until the two diagonal measurements are equal. Continue tightening both turnbuckles in equal amounts until the desired tension is achieved (200-300 pounds). Verify that the diagonal lengths of the frame still match.

Rail Mounting

Ensure that the frame is “face up” on a table. Place a long, straight, flat reference surface (like a carpenter’s level) across all of the -IM and -OM parts and butted up against the long edge of the -RM part (cable side). This surface will act as a reference for the rail installation, but the top edge of the -RM part can be used as a backup option.

Mount one of the rails [DWG#39] to the upper most outside slot of the cable-side -RM component, using the M5x20mm cap screws [DWG#27] and M5 t-slot hammer nuts [DWG#26] in every hole on the rail (it is probably easier to pre-screw the nuts and bolts together through the rail then slide the entire assembly into the slot at once). Tighten the bolts until they are barely snug, from the front to the back, using a combination square to set the top edge of the rail 10mm below the top edge of the -RM component of the frame.

Tighten the front-most rail screw fully to secure it’s position, then slide one of the rail bearings onto the front of the rail. Arrange a dial indicator on a flexible arm with a magnetic base (magnetized to the bearing) so that the dial indicator measures the height of the reference surface at the Y-axis position of the bearing. Zero the dial indicator at the front (previously tightened) screw position.

Slide the bearing back and forth along the rail while watching the dial indicator to observe any excessively high or low spots. To correct these spots loosen the nearby bolts and tug on the rail to move it into place, then re-measure with the dial indicator. Once all of the excessively high or low spots have been corrected, the fine adjustment can be made.

Moving from the front of the machine to the back of the machine, position the bearing just rearward of each untightened screw, then push or pull the rail until the gauge reads zero. Tighten the screw to secure the rail in its final position. Continue until all screws have been tightened. When completed, verify that the dial indicator reads within tolerance along the entire length of the rail (if it does not, loosen all screws rearward of failing areas and repeat the procedure).

Repeat the entire procedure on the other -RM component.

Screw and Motor Mounting

Bolt one of the CNCR-BBM () (Y12-FIXED configuration) plates to the back of the -RM extrusion on each side, and one of the CNCR-BBM () (Y12-FREE configuration) plates to the front of the -RM extrusion on each side, using M8x20mm cap screws [DWG#35] and M8 t-nuts [DWG#33]. Tighten the bolts until just barely free (final tightening will not be done until after the gantry is mounted, but the plates should be free to slide on the extrusion for now).

Bolt one of the BK12 bearing blocks [DWG#4] to each of the -FIXED plates, and one of the BF12 bearing blocks [DWG#3] to each of the -FREE plates, using M6x40mm cap screws [DWG#31]. Tighten fully and use threadlocker to ensure a permanent connection. Mount the ball screw [DWG#41] between the bearing blocks, using the nut on the BK12 block to secure the screw to the fixed end. Keep track of the retaining clip that is used on the BF12 block, which will be installed later!

Bolt the CNCR-BASE-MM () plates to the back of the -RM extrusions of the frame using M8x25mm cap screws [DWG#36], then bolt the Y axis motors [DWG#38] to the -MM plates using M6x20mm cap screws [DWG#30]. Tighten the bolts until snug (final tightening will not be done until after the gantry is mounted).

Assemble the shaft adapter [DWG#21,22,23] and use it to connect the Y axis motor to the Y axis ball screw.

Note that the front hard stop plate for the Y axis, CNCR-BASE-HS (), is not mounted until after the gantry has been mounted to the base.

Component Mounting

There are a few other components and accessories that can get mounted to the T-slot framing at this stage, although they can also be mounted much later in the assembly process without extraordinary difficulty.

Cable Chain

CNCR-BASE-TSE-ECM ()

This small piece of extrusion gets mounted to the outside of the CNCR-BASE-TSE-RM () (Cable side) using M8x60mm cap screws [DWG#37]. This little arm supports the cable chain [DWG#5] which is connected by two M6x16mm flat screws [DWG#29] and M6 t-nuts [DWG#28] (although it may be easier to mount these parts after the gantry is connected).

Homing Switches

CNCR-HSM ()

The homing switch sensors [DWG#24] are connected to a plastic adapter part [DWG#19] using two M3x12mm cap screws [DWG#25] each. The plastic adapter part mounts onto the top slot of both of the CNCR-BASE-TSE-RM () extrusions using a single M6x16mm flat screw [DWG#29] and M6 t-nut [DWG#28] each. The plastic adapter parts should be pushed all the way back until they touch their corresponding motor mount.

Zip Tie Mounts

CNCR-TSE-ZTM ()

Several plastic zip tie mounts [DWG#45] that help route cabling from the Y axis motors and homing switches can be bolted to the frame at this time. Each plastic part is mounted with an M6x16mm flat screw [DWG#29] and M6 t-nut [DWG#28]

Base Plate

CNCR-BASE-LSP ()

This large, heavy, cut steel plate adds both ballast and stiffness to the machine. It is connected to the bottom of the frame using 24 M8x12mm cap screws [DWG#34] and M8 t-nuts [DWG#33].

Rail Guard

CNCR-BASE-SG ()

These bent steel strips provide mild protection to the Y axis bearings, rails, and homing switches. They are connected using 7 M8x12mm cap screws [DWG#34] and M8 t-nuts [DWG#33] each. Bias the guards inward at this point to ensure adequate clearance when installing the gantry. After installing the gantry, the guards can be adjusted to provide maximum protection without any interference.