One of the most common issues we see with diamond cutting is swarf causing problems, whether it's dropping and sticking to the blank, balling up behind the stylus, or blocking the vacuum tubing. This guide covers the potential causes and shows you how to diagnose the issue methodically.
With lathe cutting, there are many factors, mechanical, electrical, and environmental that can prevent swarf from being taken properly. Here's a list of the main culprits:
- Groove depth
- Stylus heat
- Damaged styli
- Not enough suction
- Static
- Blanks
- The weather
- Cutterhead suspension
Below we'll go through each one with a quick analysis of what you need to check. The list above is actually arranged in methodical troubleshooting order, so work through them in sequence for the most efficient diagnosis.
1. Groove Depth
Start here because groove depth directly determines whether you're forming proper swarf at all. If you're cutting too shallow say under 50 microns on an unmodulated groove you're not getting a clean chip formation. The stylus then creates very fine swarf which will have more problems like sticking to the blank.
Check your actual cutting depth with a microscope, don't assume weights are fine, the aim is always the correct groove depth. The ideal depth for plastic diamond cutting is typically 50-70 microns on an unmodulated groove. At this depth you get a consistent ribbon of swarf that curls away from the cutting point and can be easily taken by your vacuum system.
2. Stylus Heat
If you use too much stylus heat, this can created sticky swarf, which will usually react as balling behind the diamond. Test without heat when diagnosing swarf issues.
3. Damaged Styli
A damaged or worn stylus won't cut cleanly regardless of what else is right in your system. Pull your stylus and inspect it under magnification, you're looking for chips, cracks, wear or plastic residue on the cutting edge. Even a microscopic chip will cause the stylus to tear material rather than shear it cleanly.
A damaged stylus creates irregular swarf that doesn't leave properly and often produces audible distortion in the cut as well, you'll hear it as surface noise in the playback. Also check that the stylus is seated correctly in the holder. If it's misaligned, you won't get consistent cutting geometry and swarf formation will be erratic.
If you have a spare stylus to check, this is a good option to try as microscopic damage isn’t always visible on entry level microscopes. Remember to clean your diamonds if there is debris stuck to the tip.
4. Not Enough Suction
With cutting fundamentals confirmed, now check whether the swarf is actually being removed from the cutting point. Your vacuum system needs adequate suction to pull the swarf ribbon away as it's formed and transport it through the tube to your collection jar.
First, check suction at the source, at the vacuum pump itself. If suction feels weak or irregular at the pump outlet, you've got a pump problem, this is common with household vacuums that have motors that overheat, unlike side channel blowers or pond pumps designed for long continuous work.
Next, check for blockages in your collection jar. If the jar is full or has swarf packed against the filter, airflow is restricted. Empty it and clean the filter. Then trace the vacuum line from the cutting point back to the pump. Any kinks or restrictions in the tubing will reduce your suction. Check all connections, loose fittings leak air and reduce vacuum.
Finally, position of the vacuum nozzle really matters. It should be a few millimetres from both the stylus and the blank surface, positioned slightly behind the cutting point so it catches the swarf as it curls away. Too far and you don't capture the swarf. Too close and you can create turbulence that interferes with cutting.
Experiment with positioning while making test cuts, you should see the swarf being pulled cleanly into the nozzle as a continuous ribbon without adding any noise to your cuts.
5. Static
If your suction is adequate but swarf still isn't clearing properly, particularly if it's sticking to the blank, wrapping around the stylus, or clinging to the inside of your vacuum tube, static could likely be the problem. Plastic generates significant static electricity during cutting, and this can cause swarf to behave erratically.
In humid conditions static is less of an issue, but in dry environments or during winter when indoor humidity drops, it becomes a major problem. Always make sure you use anti-static liquid before your cut. The talc powder trick also works well, put a small pinch of talcum powder into your vacuum tube every few hours of cutting, but make sure your chip jar has swarf inside, as if using a side channel blower or pond pump, you do not want the talc going right through the system, it will cling to the swarf in your chip jar.
Using too much heat from a heat lamp can also cause static, they create dry air, and if using our blanks, they are fine to cut without the heat lamp on, and always worth testing this way.
You can also try anti-static guns such as the Misty Zero Stat or ionizing air blowers positioned near the cutting point if needed in certain conditions. The simplest, most effective solution for most setups is the good anti-static liquid, the talc method combined with maintaining reasonable humidity in your cutting room, aim for 40-50% minimum relative humidity if you can control it.
6. Blanks
Material inconsistencies in your blanks can significantly affect swarf formation and removal. Also different blank materials, and even colours can too. For example we use PETG, and colour blanks will hold more heat than say transparent, this will make the material act differently. Generally, we advise less heat, or even no heat on our colour blanks. They have a Shore D hardness rating of 40 so they are smooth to cut regardless and usually need less heat than plastics with a Shore D rating of 70-80, which is pretty average when you check their specifications.
Another blanks issue is directly related to groove depth, if your blanks are not flat, it can cause inconsistent groove depth, so if you are on the lighter side already, and bumps in the road, along with vertical modulation combined can cause very shallow grooves which means the swarf may drop rot the disc.
7. The Weather
Environmental conditions affect both static buildup and PETG cutting characteristics, though it's a slower changing variable than the others. Temperature and humidity in your workshop have real effects on cutting performance.
Low humidity (below 30-35%) dramatically increases static electricity. You'll notice this more in winter when heating systems dry out the air. Swarf becomes clingy and difficult to evacuate, and you'll see more of it sticking to blanks and accumulating in your vacuum system. If you're in a very dry climate or cutting during winter, consider running a humidifier in your workspace. Even bringing humidity up to 40-45% makes a noticeable difference.
Also, remember that lathes are mechanical, using lubrication on many points, make sure the machine is well maintained as a hot day versus a cold day can make lubricants act differently. This is rare, but always make sure to keep on top of it.
8. Cutterhead Suspension
This is last because if swarf formation and removal were working previously and you haven't adjusted or disturbed the cutterhead mounting, suspension is unlikely to suddenly become the issue. But, never say never, especially with lathes which can be untameable beasts at times. Triple check groove depth, rake angle, dashpot and all suspension points just to be sure. Finally, always make sure your cutterhead lowers smoothly, if it drops too fast the initial groove can be totally off, this is usually indicated by initial swarf dropping to the disc, which can then be brushed and taken up the tube for the rest of the cut.