How To Process Tombstone By 5 Axis CNC Bridge Saw?

If you are working in a graveyard or memorial stone workshop, you must know that processing a tombstone is not just about cutting a rectangle shape from a granite block. The real challenge is how to make the lettering, the photo engraving, and the curved edges all in one single setup. Traditional way using hand carving or using normal bridge saw with 4 axis is too slow and not accurate enough. So many customers ask me: "How to process tombstone by 5 axis CNC bridge saw?" Today I will share the step-by-step guide based on our real factory experience, and also explain why this machine is the best solution for your production.

Tombstone processing has a long history. In the past, workers used pneumatic tools and chisel to carve the name and date by hand. This takes many hours, even days for one piece. Later, the normal 3 axis or 4 axis bridge saw come to the market, it can cut the shape but for the 3D curved surface and the deep letter engraving, it is still not enough. Because the normal machine's spindle cannot tilt and rotate freely, so you need to change the workpiece position many times, or use different machine to finish one tombstone. That cause low efficiency and high labor cost. Also the joint between different process is very obvious, not good looking. Now the 5 axis CNC bridge saw is designed exactly for solving this pain point. It can do cutting, milling, drilling, engraving, and polishing in one clamping. This is a big revolution for the tombstone industry. 

Why we say 5 axis CNC bridge saw is much higher efficiency than normal machine? Let me give you a comparison. For a standard double headstone size 600x800x80mm, with normal 4 axis bridge saw, you need to first cut the contour, then manually change the angle to cut the bevel edge, then move the stone to another engraving machine for the letter, and finally polish the edge by hand. The total time is about 4-5 hours per piece, and you need 3 workers. But with our 5 axis CNC bridge saw (model required), the same tombstone can be finished in only 1.5 hours, and only 1 worker is needed to load and unload. The machine can automatically change the spindle angle from 0 to 90 degree, and rotate 360 degree continuously. So the tool can reach any surface of the tombstone without reposition. The engraving depth is also more uniform because the tool always keep perpendicular to the curved surface. This not only save time but also save material because less breakage during processing. Many of our clients in USA and Australia told us they increased their daily output from 3 pieces to 8 pieces after using this machine. So the ROI is very short, usually within 6 months. 

Now let's go to the core question. The whole workflow is actually very simple, even your operator with basic computer knowledge can learn within one week. We have detailed training video and manual. Here are the 4 main steps:

(1)Made a design on engraving software

First you need to use a CAD/CAM engraving software, like ArtCAM, Type3, or AlphaCAM. Our machine is compatible with most popular software. You open the software and create a new file. Then you input the tombstone size, for example 700mm length, 500mm width, 90mm thickness. Then you design the layout: the cross pattern, the name text, the date of birth and death, and maybe a photo or religious image. You need to choose the font style, the letter depth (usually 2-3mm for granite), and the tool path strategy. For the photo engraving, you need to convert the image to grayscale and then use the "height map" function to generate the 3D relief. This step requires some experience but we can provide the template library to help you start quickly. Remember to set the safety height and the clearance plane to avoid collision. After design finished, you save the file.

(2)Generate G-code for the design

The next step is to generate the G-code. The software will calculate the tool path based on your design parameters. You need to select the correct post processor for our 5 axis CNC bridge saw. We will supply the post processor file together with the machine. If you use the wrong post processor, the machine may move wrong direction or have alarm. So please make sure you choose "5 axis double table" or "5 axis bridge type" from the list. Then you set the cutting parameters: feed rate for roughing is about 3000mm/min, for finishing is 1500mm/min, spindle speed is 12000RPM for granite, and stepover is 0.15mm for fine surface. The software will generate a long text file with .nc or .txt extension. This file contains all the coordinate and angle instructions for the machine. Normally the file size is between 2MB to 10MB depending on the complexity of the design. You need to check the G-code simulation before actual cutting, to make sure there is no overcut or tool collision. The simulation is very important for safety.

(3)Import the G-code to the 5 axis CNC Bridge Saw

Now you take the G-code file and copy it to a USB flash drive. Then plug the USB into the control panel of the 5 axis CNC bridge saw. Our machine uses the Syntec or Siemens control system (depending on the model). You press the "Edit" button, then "File management", then "Import", and select your file from the USB. After import, you need to check the program on the screen to confirm the tool number and the work coordinate system (G54). Also you need to set the zero point of the workpiece. The zero point is usually at the lower left corner of the tombstone surface. You use the electronic handwheel to move the spindle to that position, then press "Set zero" on the screen. Double check the Z axis zero is on the top surface, not the bottom. Otherwise the tool will cut too deep or too shallow. After all these settings, you press "Auto" mode and the machine is ready to run. But before start, please do a dry run without the tool to make sure the travel range is enough and no interference with the clamps.

(4)Start Automatic Processing

Finally, you press the green "Start" button on the control panel, and the machine will begin automatic processing. The 5 axis bridge saw will first do the rough cutting to remove the bulk material, then do the semi-finishing, and finally the finishing pass to achieve the smooth surface. During the process, the machine will automatically change the C axis rotation and A axis tilting according to the G-code. You will see the spindle head swing left and right, forward and backward, very smart. The cooling water will spray on the tool to reduce heat and dust. The processing time depends on the design complexity, but for a standard tombstone it takes about 40 minutes for cutting and 50 minutes for engraving. You can walk away and monitor from the remote control or just check periodically. When the program finish, the machine will stop and give a beep sound. Then you open the safety door, clean the stone surface with air gun, and check the quality. If there are some small burrs on the edge, you can use manual polishing pad to touch up. But usually the surface is very smooth and ready for delivery.

(5)Some extra tips for better result:

Always use diamond tools with correct specification for granite or marble. The tool diameter for roughing is normally 12mm, for finishing is 6mm, and for small letter is 3mm.

Check the tool wear every 2 hours, because dull tool will cause chipping and bad surface.

The clamping method is very important. We recommend using vacuum suction cups or mechanical clamps with rubber pad to avoid scratching the bottom surface.

If the tombstone is very large, you need to add supporting brackets to prevent vibration.

Keep the machine lubricated daily, and clean the guide rails after each shift.

For processing Marble, Granite, Porcelain, and Quartz Stone Tombstones and countertops, we provide 5+1 Axis CNC Bridge Saw. It is a precise, effective, and user-friendly machine. The operator begins processing after taking a picture of the plate by Camera and adding the drawing layout to the image. Saw blades, milling cutters, suction cups, and pressure plate cylinders will automatically generate processing steps according to the Drawing. If the blade-cutting path conflicts, the suction cup will help to move slabs automatically. For basin, Kitchen Sink, Countertop, and inner angles, the milling cutter can do excellent work with a 7.5kw Electric Spindle. Therefore, the machine is used to help install countertops without any dust.