Posted By John A Wright
At a customer, in an initial PUWER assessment of a 'home-made' cutting machine, I'm going to request the engineers improve the guarding.

The machine traverses a 50%-guarded 30cm toothed circular blade across a table, cutting rigid plastic sheet.

The operator has fixed guarding in front of him, uses two-handed controls, so he can't get near the blade when it's rotating.

In it's part-completed state the cutting area of the machine still needs guarding along the traverse direction to protect any other employees from sticking their hands in, also behind the machine where the moving blade could be accessed.

The guarding might still leave small (smaller than hand) gaps at the sides and also leave wide gaps above and below the cutting area which arms can't get at.

But I'm wondering if projectiles from a disintegrating blade/teeth might make their way at speed through any remaining small gaps.

Anyone have experience of the trajectory of disintegrating saw blades, do bits fly off at a tangent from any point on the circumference, or only where it's cutting, and might metal bits bounce off the rigid material (being cut) and therefore fly out in any direction, particularly outwards or upwards or even downwards?

John W

Posted By Robert K Lewis
The guards are there to prevent contact with dangerous parts but the case law has stated that it is not there to contain flying parts from the disntegration of part of the machine.

Concentrate on the contact and not the remaining small areas - providing contact with the dangerous parts are prevented.

Bob

Posted By John A Wright
Hi,

By 'home-made' I mean their engineering dept. construct cutting machines themselves for special cutting jobs. The saw blade/guard was purchased three years ago. They construct the traversing mechanism, and a clamping mechanism that holds the sheets to be cut, and the general structure around which they fit any other necessary guarding. Their skilled electricians construct the controls, switches, e.g. the blade will only rotate if the on button is held down, the other hand operates the traverse.

One reason it's not sufficient just to spring-guard the moving blade is that the items being cut are not flat, they are usually corrugated or upside-down saucer shape. The plastic sawdust doesn't just do downwards. The rigid plastic material (which they manufacture) is high quality but a malfunction during the cutting could produce sharp splinters of plastic, hence they like to guard around the process. The process is noisy (the sheets vibrate) and guarding also aims to reduce noise. The end-result can still be >90dB so ear defenders are worn by operator and area near machine.

The chances of blade disintegration would appear to be low, they are not cutting concrete. The blade is three years old but was rarely used in a previous saw machine.


John W

Posted By CFT
Thanks John; would you say this company is the only one in it's field? As I wonder what other similar companies do for specific machinery production?

I note they manufacture the plastic, do they have all necessary certifications in place for the machinery such as harmonised standards and declaration of conformity, as they appear to manufacture that as well?

CFT