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 it, creating a partial vacuum. The resulting difference in air pressure applies a quite large clamping force evenly over the stock. Using the suggested vacuum pump (sold separately) a clamping force of ~12 lbs is exerted over every square inch of the surface. 85 kPA is also ~0.9kg 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 is going to need securing to something as it does vibrate. There are mounting holes on the side of the case and it can be mounted on its side, in any position actually. I would not secure it to the router frame as that would transmit any vibrations to the router.

Parts needed

To make this work correctly you are going to need some extra parts. I am assuming here that the SainSmart Vacuum pump is being used. The wiring and tubing lengths will depend on where you are going to put 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 are going to 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 depending on the power supply, an Inrush Current Limiter (MF72 4D13 or similar), this 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 removing 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 just as easily be installed with the air connection to the back of the router, decide on what is best based on your work layout. I have mine installed with the coupler at the back, it is imperative that the air tubing will not jam between the edge of the bed and the router frame as the bed moves so it may need some support.

Re Aligning the Y axis movement

After fixing the bed repeat the Y axis guide rod alignment steps to make sure it moves freely without any binding on the Y axis.

• Slacken the bolts holding the Y axis guide bolts
• Manually move the bed to the front by turning the leadscrew, tighten front bolts holding the Y axis lead rods
• Manually move the bed to the back by turning the leadscrew, tighten back bolts holding the Y axis lead rods

Bed Alignment

Aligning the bed to the movement of the spindle 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 definitely do not recommend trying to surface the Aluminium bed!!

To perform the alignment you need to measure the bed height above the 4 Y axis guide rod mountings. From the centre of the bed (the air outlet) these are at the corners of a square X 150mm x Y 90mm. The Z height is measured using the router Machine coordinates recorded above each bed mounting point. Put a bit into the spindle and 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 never going to get the differences all as zero and it depends on what sort of work you are going to be 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 centre 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 just as long as it is consistent across all the points, its only the differences that will be used.
• 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 the previous two steps substituting X75 Y-45 then X75 Y45 then X-75 Y45 for the other corners
• Find the maximum Z height.
• The adjustment needed at each corner is the maximum Z height less the Z height at that corner.

If there is a ‘tilt’ across the x axis then the gantry can be adjusted by slackening the gantry mounting bolts on one side then push the gantry down a bit or pull it up as appropriate, retighten and recheck.

For other errors slacken the bolts holding the bed down and apply shims between the mounts and the bed to raise the low points (I find pieces of Aluminium kitchen foil make good cheap thin shims).

After moving the gantry or applying shims between the mounts and the bed repeat the level checking process. This is normally a trial-and-error process! It’s a trial and there will be lots of errors. But it is worth doing and you should only have to do it once.

My results

After fitting the bed I performed the levelling test as outlined above using the Z-Probe.

These were the Z height(mm) readings in the centre, checking the centre height gives an extra check for a warped bed, but the chances of that with this bed are very very slim, and at each of the corners. The router position is not accurate to 1/1000 of a mm but it gets close, I would say allowing for everything maybe 0.002mm but have you ever set a depth of cut of 0.002mm? As such I am rounding these to 0.01mm It’s a hobby machine, 1/100mm is beyond any practical expectations when cutting. (For anyone using inches 0.01mm is ~0.0004”) Also if you use the Z probe at the same point a few times you will get slight variations in the readings, so I have rounded the machine coordinates to 2 decimal places.

My home position is set at the top right back of the machine, as the Z axis goes down it works in negative coordinates -5.00 would mean it is 5mm lower than the home position, -6.00 means it is 6mm lower than the home position.

The Y axis seems to be pretty much level, certainly nothing I would try and improve. The bed itself seems to be very flat, no signs of any warping are shown.

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 the X differences can be adjusted 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. OR I could add shims of ~0.4mm under the mounts on the left hand side and ~0.25mm in the centre. If that works then I would have a level bed.

To adjust the X axis tilt the Gantry bolts loosened on the right hand side, pushed down a little, 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! Also these results are after my third attempt which involved raising the left hand side of the gantry slightly as well, there are limits on how far the bolts will move!

The Y axis is unchanged so is still pretty level.

Maybe attempt 4 would be better BUT that’s good enough for me!

If you use shims then make sure to add them under the centre mount as well and check the Y axis movement is free and does not bind after retightening the mounts.

Installing the bed coupler

Screw in the coupler to the bed by hand. Insert the long end of the 2.5mm Allen key all the way into the coupler, the key locates at the very back of the coupler, and tighten. Do not use a larger Allen key in the front body of the coupler, this will destroy it.

Installing the tubing

The couplers have an outer ring which when pressed in releases the clamps around the tubing, when released the clamps extend and hold the tube in place. To insert or remove tubing first press in the outer ring, insert fully or remove the tube, then release the outer ring.

I am using a long length of 6mm OD flexible plastic tubing to connect the bed coupler to the reducing union connector, then a short length of 10mm OD / 8mm ID plastic tubing to connect the reducing union connector to the pump. The 8mm ID tube just pushes over the pump inlet connection. The lengths you will need depend on where and how you are going to mount the vacuum pump.

Wiring the Vacuum Pump

You will need a 24V 50W (2A+) power supply, these in the UK (at the time of writing) are available for around £12 including mains power lead and delivery. The power supply also needs to be able of supplying the peak start-up current for the pump motor. This is ~5.25 Amps.

This start-up current can be reduced by wiring an inrush current limiter (such as the MF72 4D13, cost ~ £1.50, there are a number of variants supporting different currents and initial resistances. This one has a 4Ω resistance and is rated at 5A) in one of the power lines. The initial resistance limits the start-up current but as the current flow warms it up (1-2 seconds) the resistance reduces to zero allowing the motor to run at full speed. With this fitted the start-up current is reduced to under 2A.

I am using a spare 24V 4.7A router power supply with a 5.5/2.5mm barrel connector, your power supply may have different connections so I am using a screw terminal barrel socket to connect to the power supply. The motor has 4.8mm spade connections.

Rough dB readings for noise (measured at around 1m distance using a phone app) are 63dB running free and 58dB when maintaining a vacuum.

Limitations

• The stock you are using must have a flat and even base otherwise air gaps will occur between the bottom of the stock and the sealing strips on the bed. The surface does not have to be mirror perfect but it has to make contact with the beading all the way round.
• The minimum size of the stock is 33x33mm, this is determined by the smallest possible placement of the beading around the central air hole. If it’s smaller than this on either dimension it will not make a good contact with the beading.
• The stock must not be porous, using cloth will not work well nor will any stock that already has holes inside the vacuum area.
• The stock must be thick enough to remain flat, Leather for example is not porous so will stay down but the bed surface is not flat, it has holes and ridges into which a flexible stock can be pulled into so depending on the thickness….
• You cannot cut through the stock, cutting through the stock will create a hole which will let air in and release the stock. Even outside the edges of the vacuum area there is nothing between the stock and the bed so you will potentially damage the bed and the bit if you try and cut through.

NOTE: For jobs where you want to cut through there is nothing to stop you from mounting the stock onto say a piece of MDF spoilboard using tape and then holding the spoilboard to the bed by vacuum, this removes the need to change the bed back and forth.

What it’s best for

It is so easy to use, especially for repetitive jobs. The full surface of the stock is available, there are no clamps to get in the way.

Repeated Engraving and carving jobs become simple. Once set up, which is not difficult, the stock can be replaced with a new one in seconds rather than having to unclamp/untape and reclamp/retape which takes much longer.

I have a project to make a 50mm cube with lettering on each side. Using the vacuum table means I can set up the beading and guides, then fix and unfix the cube to engrave on a different face in seconds with the same XYZ position. With a standard bed I would not be able to use clamps as I need access to the entire face so I would have to use double sided tape, then reset the XYZ zero position each time I changed the face to be engraved, then remove the tape and re-apply tape on another face, re-align and set the XYZ Zero positions.

Setting up a job

I am referring to the vacuum area as the shape defined by the closed area made by the beading on the bed.

The centre air hole must be within the vacuum area. The other holes are for the guide plates and do not provide any suction.

The vacuum area is outlined using the silicon bead pushed into the grooves on the bed. This area does not have to be a rectangle. Just think of Tetris! But the stock must cover and slightly overlap the entire area made by the outside of the silicon bead. The smallest possible stock size is the centre 4 squares on the bed including the bead or 33mm x 33mm (1.3” x 1.3”).

The bed slots and the bead must be clean, free of swarf and dust before placing the bead to get the best seal.

The tension used when pressing the bead into the slots must be uniform, just enough to keep the bead straight with no kinks. Changing the tension can result in unevenness due to the bead becoming thinner or not being under a little tension as it is pressed in. It doesn’t take a lot of practice to get this right, but give it a couple of tries.

The bead must be continuous with minimal gaps. Normally one piece should be used for the entire outline leaving only one possible place for an air gap where it ‘joins’ normally by a T junction. You can use smaller lengths of beading but you will get a better seal by making a T junction and lead the rest of the bead away from the vacuum area where it can just be left lying on the bed. Hint: put the unused part in a ziplock bag this will help keep any swarf, dust…. off the unused bead.  This also leaves the full length intact for different jobs with a larger vacuum area although enough is supplied to go round the outside of the bed twice. Extra silicon beading is readily and cheaply available from Ebay, Amazon…. (4mm Silicon sponge bead)

All the pictures below show errors in applying the beading:

Ideally when the stock is placed on the beading and the vacuum pump is turned on the bead will compress just enough for the base of the stock to touch the top of the bed all the way around. Especially when I started, I used a thick (10mm) piece of clear acrylic so I could see the level of the beading and how it compresses as the vacuum is applied. Even with small gaps and bumps the stock may still be pulled down, but the bumps may put the stock out of level, especially on thinner stock, and gaps in the beading will reduce the vacuum pressure holding it down less firmly.

Before starting a job make sure that the stock is firmly held. If there are any significant air gaps the sound of the vacuum motor will be different.

This sequence shows the beading applied without any obvious errors, then with a 10mm thick acrylic stock placed on top, and lastly with the Vacuum turned on.

The placing of the stock on the top of the beading (middle) should not show any high spots which may be slightly compressed, when the vacuum pump is turned on the bead should compress as the stock is sucked down (right).

The suction should also pull the bottom of the stock to the top of the bed as shown below.

Guide plates

There are 6 pairs of threaded holes on the bed, for smaller jobs the guide plates can be attached to these to provide a fixed X and Y position at the edges of the stock. These are not clamps! they are placed flat on the bed and just provide a fixed point for the X and Y positions of the stock. Useful if you are repeating a small job, you can just position the stock touching the edges of the guide plates then turn on the pump to have an accurately repeatable position.

Height Maps

As the Vacuum bed is ideal for making such things as PCBs where the Z height is critical for quality. I thought I would mention it. A height map is where you use the Gcode sender such as Candle, UGS… to measure the surface heights at a variety of positions in a grid and then adjust the Z heights in the Gcode to match the surface before the Gcode is sent to the router.

Please see the tutorials for the Gcode sender you are using for full details, in Candle this is a height map, in UGS it is auto-levelling…

Mounting on other routers

Even though this fits the 3018PROVer there is nothing to stop this bed being fixed to the top of another router bed, either by tape or clamps depending on the host router size. It weighs 1.9kg so check any acceleration settings on your router if the router moves the bed around rather than just moving the spindle motor.