Pallmann Cobra 09/Classic Belt Floor Sander
Maintenance and Problem Avoidance Tutorial
By Simon Gallaway June 2023
So, you have a Pallmann Cobra 09 or Cobra Classic. You want to know how to get the best out of it, produce a superlative floor finish that will leave your clients in no doubt that they chose well when they found you, earn an enviable reputation, prevent it from becoming broken on site, and speed up your work for time and cost efficiency?
This could be a helpful and easy-going read for you.
The reader may also like to study this Pallmann Manual for the 09 Cobra
https://uk.pallmann.net/fileadmin/MAM/99214/PALLMANN_manual_COBRA_GB_2014-03.pdf
or this one for the Pallmann Cobra Classic Manual
Contents:
- The perils of transport
- The dust fire waiting to happen
- The daylight test for drum alignment
- Handle height adjustment (09 only)
- Tensioner test and its importance to performance
If the ground is rough and bumpy, the jolts can fracture the arm on one side. I’ve seen it happen on at least two Cobras after an aggressive bump. It doesn’t make a sound and its appearance doesn’t really change, so you wouldn’t notice it at the time, and the trader could blissfully still take it to a job without knowing that it wasn’t going to work properly. Most traders wouldn’t want to undertake the job of repairing it, so it would have to go to a repair shop and be out of action.
When starting the next job, the symptoms of the fracture are noticeable by the Cobra cutting much deeper into the floor on one side, and no amount of adjusting that knob underneath (Cobra 09), or the wheel eccentricity (Cobra Classic) will do anything to correct it.
If the Cobra has to be wheeled across the ground, I would at least recommend taking off the motor to reduce the stress on the aluminium arm, and if the ground is bumpy, go very slowly over each bump. Ideally, put the cobra on some sort of trolley for transportation, and have the Cobra resting on the drum.
It is still recommended to leave a Cobra stored with the drum up, resting on the wheels, for fear that if it rests on the drum for long periods of time, the soft rubber might take on a permanent set and produce undesirable effects when sanding a floor.
2. Bags of sawdust are a fire hazard. The concentration of fuel and oxygen is just right for a fire to get going. If there are any nails or staples in the floor when an abrasive strikes them at speed, it usually produces a spark, a source of ignition, and the spark is then carried along with sawdust through your extraction system.
Fires caused by this means can take hours to get going, by which time the operator might have left the machine unattended, or stored the sawdust bag in the van, or the lock-up, or the client’s house if it’s more than a one-day job.
By the time anyone knows there is a fire in progress, it may be too big to contain it from its surroundings.
Best to empty the dust bag into a fire-proof bin outside the building before leaving it unattended, and hammer down or remove any metal fixings from the floor before you start sanding.
3. Ideally, the drum should be parallel with the floor, so that the belt doesn’t cut deeper on one side and light on the other, leaving saw-tooth steps across the floor which would then have to be sanded out with a rotary machine later.
True, it is said that a belt sander can never be a finishing machine, but the more even you can get the belt sander to cut, the less time and effort it costs to finish it with a rotary machine afterwards.
In the tool kit that comes with every Cobra 09 there is a special tool for gauging the correct height of the wheel that is adjustable (only one of the side wheels is adjustable – the other is fixed), but this can’t be used on the Cobra Classics, and only works on the 09 Cobra if the drum is still truly cylindrical. I have seen drum rubber that wears on one side, making it very slightly cone like, and in this case if the wheel gauge were used, the drum would still not be parallel to the floor.
However, there is a very quick and easy way to gauge how well the wheel is adjusted. First you need a small piece of flat floor, or flat surface on which to sit the Cobra. Next you need a light source, like the one on your smart phone. Set up the phone, or light source, so that it points closely towards the front of the Cobra, at floor or surface level. You’re aiming to get the light to shine underneath the Cobra from front to back. Next you go round to the back of the Cobra and get down on the floor with the side of your head on the floor so that your eye nearest the floor can see all the way under the Cobra, and of course you will see the light source when the drum is lifted up. Use the clutch lever to lift and lower the drum repeatedly slowly. If the drum is parallel to the floor, you will see that the light disappears just as the drum touches the floor. But if it’s not parallel, you will notice that the light starts to disappear first on one side of the drum, and then progressively as you finish lowering the drum all the way. This is the tell-tale test. It is very easy to do and surprisingly effective. If it does this, you will need to adjust the adjustable wheel to make the drum parallel with the floor. Cameron has produced a Youtube video on our channel to adjust Cobra wheel and drum height here.
https://www.youtube.com/watch?v=gKgiYDQrAE8
4. It is possible to adjust the height of the handle on the 09 Cobras to suit users of different heights and preferences. However, I would also suggest paying attention to good posture when considering this, as it will cumulatively make you more uncomfortable with time, if the height of the handle induces a poor posture.
Images 1, 2 & 3: The metal rod that does the lifting and lowering of the drum from the control levers is split in the middle and the spigot on the end of the upper half can be located into any of the five holes in the lower half.
The lifting and lowering arm level on the handle must be positioned to allow the drum to rest on the floor before any of this can be done, because when the drum is lifted, the bar is under tension and cannot be separated into its two halves. The handle itself has a lever at the back which when slackened can allow the handle to slide up or down, but there is also a sprung loaded knob nearer the top which must be held pulled out before the handle will actually slide. When the desired height is reached, it’s imperative to allow the knob to spring back into the nearest adjuster hole. It won’t work if the knob is stuck in between two holes; the drum won’t lift or lower properly. Once a numbered hole in the handle shaft is selected, it should be obvious that the same numbered hole on the lifting bar lower half should be used to locate the spigot on the lifting bar upper half.
Some Cobras have a different number of holes, so if you own multiple Cobras of different ages, it’s important not to mix the handles with different machines even though they will appear initially to fit, otherwise you might find a handle with five holes and a machine bar with nine holes. And you might find that the motor connectors are incompatible anyway.
5. The one thing that all Cobras suffer most frequently is a stiff abrasive belt tensioner. They pivot on a solid polished metal pivot and don’t have bearings. That’s ok because they don’t wizz round at silly mph (or radians per second for the physicists), they’re only required to rock a short distance intermittantly when you change the belt.
But, here’s the rub. Very fine dust and atmosheric condensation gets into the tiny gap between the pivot and the aluminium arm that rocks. They congeal together, making the rocker arm stiff or even seized. When that happens, the tensioner spring can no longer rock the arm until the abrasive belt is suitably tensioned, and all manner of undesirable effects can happen.
It’s very easy to test for a sticky tensioner. Simply take off the abrasive belt, and move the tensioner handle to the tensioned position again. Then, with the palm of your hand, push down on the tensioner arm to move it down, and let go as fast as you can. The tensioner arm should spring back up as fast as you can move your hand away. If it doesn’t, or worse still if it gets stuck part way along its travel in the slot where the tension roller spindle passes through the machine chassis, it’s not doing its job and needs to have the yucky stuff cleaned out of it.
There isn’t really space within this blog to explain how to do this, but I have worked with our manager, Cameron, to produce a 12-minute video for anyone who is happy to follow a few simple instructions on how to do this. This is the link to our YouTube channel and specifically this video.
https://www.youtube.com/watch?v=UaX3QzlD5GQ