By Graham Bland
NOTE: Directly fits the 3018 PROVer only, not the Pro or 3020 PRO Max. The spacing of the mounting holes for the bed are different!
A vacuum bed uses air pressure to push the stock down onto the bed by pumping out the air from underneath, creating a partial vacuum. The resulting difference in air pressure applies a significant clamping force evenly over the stock. Using the suggested vacuum pump (sold separately), a clamping force of approximately 12 lbs is exerted over every square inch of the surface. 85 kPA is also approximately 0.9 kg per cm². Let’s just say the stock is not moving unless you turn off the pump.
What You Get
- Solid Aluminium Vacuum bed (300mm x 180mm x 15mm)
- Silicon Sealant strip (4mm x 2m)
- Pneumatic connectors
- Bed connector (6mm OD tubing)
- Converter (6mm OD to 10mm OD)
- All mounting bolts and washers
- Allen Keys
- Edge guides
- Connecting tubing (6mm OD x 15cm)
- Assembly and Instruction Manual
Vacuum Pump
This is the recommended pump unit; it’s simply a motor driving a pump with separate air inlet and outlet ports. (SHOP NOW)
- Rated voltage: 24V
- Vacuum: -85KPA (-12.3 psi)
- Rated power: 42W
- Air flow: 40L/min
- Inlet and Outlets: 8mm ID tubing
- Start-up current ~5A
- Steady Current < 2A
What You Get
Pump only; no power supply or wiring is supplied.
The pump needs to be secured as it vibrates. There are mounting holes on the side of the case, and it can be mounted in any position. However, do not secure it to the router frame, as that would transmit vibrations to the router.
Parts Needed
To make this work correctly, you will need some extra parts. I am assuming the SainSmart Vacuum pump is being used. The wiring and tubing lengths will depend on where you place the pump and how it is electrically connected. The values I quote are for the pump at the back of a 3018 PROVer with the 3040 extension kit fitted.
- Plastic tubing
- 6mm OD (75cm) - connects the bed to the pump coupler
- 10mm OD/8mm ID (~10cm) - connects pump coupler to pump inlet
- Power supply and connectors. This depends on the power supply you will be using and how you connect it
- 24V 2A+ power supply, must be able to cope with the motor start-up current draw.
- Motor spade connectors and suitable wiring (the motor uses 4.8mm spade connectors)
- Optional: An Inrush Current Limiter (MF72 4D13 or similar), which will reduce the start-up current draw to under 2A, allowing a lower-rated power supply to be used.
Putting It Together
Follow the assembly manual, but basically the steps are:
- Remove the existing bed by taking out the bolts from the underside.
- Install the vacuum bed using the bolts and washers supplied with the vacuum bed (they are different).
- Connect the bed vacuum coupler to the vacuum pump inlet and the vacuum pump to the power supply.
Assembly Hints
Layout
The bed mountings are symmetrical, so it can be installed with the air connection to the back of the router. Decide what is best based on your work layout. Ensure that the air tubing will not jam between the edge of the bed and the router frame as the bed moves, as it may need some support.
Re-aligning the Y Axis Movement
After fixing the bed, repeat the Y axis guide rod alignment steps to ensure it moves freely without any binding.
- Loosen the bolts holding the Y axis guide rods.
- Manually move the bed to the front by turning the leadscrew, then tighten the front bolts holding the Y axis lead rods.
- Manually move the bed to the back by turning the leadscrew, then tighten the back bolts holding the Y axis lead rods.
Bed Alignment
Aligning the bed to the spindle's movement so that it is at the same height over all parts of the bed is essential. With a normal bed, variations in height can be removed by mounting and facing a spoilboard. You cannot mount a spoilboard on a vacuum bed, and I do not recommend trying to surface the Aluminium bed!
To perform the alignment, measure the bed height above the four Y axis guide rod mountings. From the center of the bed (the air outlet), these are at the corners of a square 150mm x 90mm. The Z height is measured using the router machine coordinates recorded above each bed mounting point. Check the Z height above the bed at the Y axis mounting points using your normal method (I used the Z Probe); these should all be the same.
You are unlikely to get the differences all as zero, and it depends on what sort of work you are doing. Engraving with a depth of cut of 0.1mm needs the stock surface to be much more level than V Carving with a depth of cut of 5mm.
Alignment Process
- Set the XY zero over the air outlet in the center of the bed.
- Set the Z zero position and record the machine coordinates of the Z axis position. This does not have to be with the bit touching the bed; it can be the position after the probe cycle as long as it is consistent across all points.
- Jog to the front left corner (G90 G0 X-75 Y-45).
- Reset the Z zero position and record the machine coordinates at Z zero.
- Repeat for the other corners.
- Find the maximum Z height.
- The adjustment needed at each corner is the maximum Z height minus the Z height at that corner.
If there is a ‘tilt’ across the X axis, the gantry can be adjusted by loosening the gantry mounting bolts on one side and pushing the gantry down a bit or pulling it up as appropriate. Retighten and recheck.
For other errors, loosen the bolts holding the bed down and apply shims between the mounts and the bed to raise the low points (pieces of Aluminium kitchen foil make good cheap thin shims).
After moving the gantry or applying shims, repeat the level checking process. This is usually a trial-and-error process, but it’s worth doing, and you should only need to do it once.
My Results
After fitting the bed, I performed the leveling test as outlined above using the Z-Probe. The readings in the center and at each of the corners showed that the Y axis is pretty much level, and the bed itself seems very flat, with no signs of warping.
| Raw M/C Z Readings | ||
| -20.83 | -20.45 | |
| -20.68 | ||
| -20.81 | -20.41 | |
The Y axis seems to be level, and there are no signs of warping in the bed.
| Z Difference from Highest | ||
| -0.42 | -0.04 | |
| -0.27 | ||
| -0.40 | 0.00 | |
Taking the difference from the highest point, I can see the left side of the bed is roughly 0.4mm too low, or the right side is roughly 0.4mm too high!
Making It Better
In my case, the Y axis is level, so I can adjust the X differences by changing the gantry height, either by lowering the right gantry by ~0.4mm or raising the left gantry by ~0.4mm, or a combination of both. Alternatively, I could add shims of ~0.4mm under the mounts on the left side and ~0.25mm in the center. If that works, then I would have a level bed.
To adjust the X axis tilt, loosen the gantry bolts on the right side, push down slightly, and re-tighten while holding the gantry down. Any use of a small rubber mallet on the top of the gantry side will be denied! These results are after my third attempt, which involved raising the left side of the gantry slightly as well; there are limits on how far the bolts will move!
| Raw M/C Z Readings | ||
| -20.66 | -20.61 | |
| -20.64 | ||
| -20.68 | -20.58 | |
The Y axis is unchanged and is still pretty level.
| Z Difference from Highest | ||
| -0.08 | -0.03 | |
| -0.06 | ||
| -0.10 | 0.00 | |
Maybe attempt 4 would be better, but that’s good enough for me!
If you use shims, make sure to add them under the center mount as well and check
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