Creating a spoilboard for the CNC 3018 router, including a CAD model.
Introduction
The CNC 3018 router has an aluminium bed. Should a tool pass through the workpiece it will hit this bed and damage it and/or the tool. Thus, it is common to place a sacrificial piece of soft material between the workpiece and the bed called a spoilboard. If the tool passes through the workpiece it merely cuts the spoilboard with no real damage done. Once the spoilboard has been cut up too much it can be either refaced or replaced.
This article discusses a design I created for such a spoilboard made out of 18 mm MDF. It features:
- Bolted down to the base with 6x recessed 6mm bolts.
- Provides a grid of 6mm threaded holes to bolt workpieces to the table.
- Includes a GCODE path to surface the spoilboard with a 1" facing bit.
The CNC 3018 router has an aluminium bed. Should a tool pass through the workpiece it will hit this bed and damage it and/or the tool. Thus, it is common to place a sacrificial piece of soft material between the workpiece and the bed called a spoilboard. If the tool passes through the workpiece it merely cuts the spoilboard with no real damage done. Once the spoilboard has been cut up too much it can be either refaced or replaced.
This article discusses a design I created for such a spoilboard made out of 18 mm MDF. It features:
- Bolted down to the base with 6x recessed 6mm bolts.
- Provides a grid of 6mm threaded holes to bolt workpieces to the table.
- Includes a GCODE path to surface the spoilboard with a 1" facing bit.
The main aim of this article is to explain how I designed this, and to provide the CAD model I designed in Fusion360.
Spoilboard Material
The spoilboard should be made out of an inexpensive material that can be easily worked. In this case I used MDF as it is cheap, easy to work with, and flat. However, MDF can cause issues as it can absorb liquids, like cutting fluid, and expand. Perhaps spraying the surfaced MDF with lacquer might protect it from liquids a little. An alternative could be to use a plastic like HDPE.
The CNC 3018 has a working area of 300mm x 180mm.
As such it can only place the spindle within this area.
However, when surfacing, I used a 1" (25.4 mm) surfacing bit.
When the spindle with this bit is placed at the extremities of the CNC’s work area, the bit will cover an area more than 10mm beyond the spindle location.
Thus, it is possible to surface a board that is slightly larger than the workplace.
In this design, I have chosen a board dimensioned 310mm x 190mm x 18mm.
CAD
The following CAD files were used to create the spoilboard in Fusion 360:
Note
Note: these CAD files are slightly different to the ones used to create the spoilboard in the photographs and video. The new CAD files are designed for a board slightly larger than the CNC 3018 work area as discussed in the Spoilboard Material section above. It also creates markings showing the extremities of the router’s work are.Warning
These CAD files have not yet been tested and may contain errors. Since I have not needed to make a new spoilboard since I created my original one, the modifications I introduced into the CAD files to match this article have not yet been used.Fixing to Table
The spoilboard is bolted to the bed to provide a firm attachment.
Six M6 x 16mm hex bolts are inserted into recessed holes on the top of the spoilboard. Inside these recessed holes the head of the bolt lies against an M6 washer. The bolts screw into M6 T-slot nuts slid into the bed’s upper slots.
The spoilboard is bolted to the bed to provide a firm attachment.
Six M6 x 16mm hex bolts are inserted into recessed holes on the top of the spoilboard. Inside these recessed holes the head of the bolt lies against an M6 washer. The bolts screw into M6 T-slot nuts slid into the bed’s upper slots.
The following figure shows the location of these recessed fixing bolt holes in the spoilboard design file.
The required holes on the spoilboard were milled using a 3.175mm flat end mill from the top. For the milling operation I stuck the spoilboard onto some hardboard of the same size using double sided tape. This hardboard was in turn stuck to the router’s base for the duration of top surface milling.
Warning
I attach the board to the bed with stainless steel hex bolts. The top of these sit about 6 mm below the top of the spoilboard. If you mill below this depth, or surface the board to this depth, then there is a danger the end mill will collide with a bolt head and cause damage. This could be alleviated by using nylon M6 bolts. As MDF is cheap, my plan is just to replace the spoilboard before it wears down anywhere near this level.Workpiece Anchors
The spoilboard has a grid of holes, each with an M6 thread. These serve as anchoring points for a workpiece. Workpiece fixings can just be screwed into these holes.
The threads in these anchoring holes was provided by M6 T-nuts hammered into recesses on the underside of the board.
The spoilboard has a grid of holes, each with an M6 thread. These serve as anchoring points for a workpiece. Workpiece fixings can just be screwed into these holes.
The threads in these anchoring holes was provided by M6 T-nuts hammered into recesses on the underside of the board.
The following figure shows the these recessed anchor holes in the spoilboard design file.
The required holes on the spoilboard were milled using a 3.175mm flat end mill from the bottom.
For the milling operation I stuck the spoilboard onto some hardboard of the same size using double sided tape.
I ensured that hardboard had holes at the locations of the fixing points milled above.
I then bolted the spoilboard, upside down to the base through the hardboard using the M6 bolts, as can be seen in the video below.
Once the holes were milled, I hammered in, from the bottom, a T-nut into each recess.
Surfacing
Once the spoilboard has been bolted onto the router’s bed, its top face needs to be surfaced to ensure it is parallel to the X and Y axis. To do this reasonably quickly, I employed a 1" (25.4mm) surfacing bit.
The bit I used was a Whiteside 6210.
Once the spoilboard has been bolted onto the router’s bed, its top face needs to be surfaced to ensure it is parallel to the X and Y axis. To do this reasonably quickly, I employed a 1" (25.4mm) surfacing bit.
The bit I used was a Whiteside 6210.
When routing I want the surfacing bit to stay within the limits of the router (300mm x 180mm) whilst covering the slightly oversized spoilboard. Since my surfacing bit is 25.4mm, I should be able to mill an area within (325.4mm x 205.4mm). To provide a little margin, I limit the clearing range to 320mm x 200mm. This should provide sufficient coverage of the actual spoilboard size of 310mm x 190mm.
In the CAD design I created a new body that was slightly larger than the area to be surfaced (body = 330mm x 210mm).
I then created a pocket in this that was the size of the actual spoilboard area to be milled (320mm x 200mm) and 0.5mm deep.
Next I created a tool path to mill this pocket using the 25.4mm surfacing bit.
This should get the spoilboard bit to cover all of the actual board.
Each time this surfacing tool path is run it should mill 0.5mm of the current surface.
Surface Lines
After surfacing the spoilboard, I like to then engrave some markings onto the surface for alignment purposes. These markings:
- Show the workarea limits of the router (actually milled a little bit smaller to ensure the engraving bit stays within the router limits). This is set to 378mm x 178mm.
- Show the router origin position (Arrow)
- Show the centre of the workspace (Cross).
- Provide a grid to help align workpieces with the router axis.
In the CAD design I created a sketch with these markings placed on the top of the spoilboard body.
These are shown in the figure below in blue.
I then created a tool path with a small end mill to cut the lines in the sketch into the spoilboard.
Video
The following video shows
- The CAD model in Fusion 360 being used to create the tool paths.
- The subsequent GCODE files for the tool paths was then used to mill a board previously cut to the overall board dimensions.
- T-nuts were hammered into the base.
- The board was bolted to the router base.
- The board was then surfaced.
- Finally the surface markings were engraved with a small end mill.