http://www.lunamachinery.com.au/index.php?page=home

Some Notes for cutting fly screen or small extrusions with a drop saw.

By Roland G Riese

Cutting small extrusions specifically mitre cuts are very often considered, by a lot of customers, as hazards.
One of the most irritating things that can happen is that small off-cuts are catapulted out of the saw and tend to reach incredible speeds.
These off-cuts can hit operators unexpectedly that work nearby or hit people that happen to go pass. In any case it is hazardous. 

These unsecured off-cuts can also damage the cutting equipment. The off-cut can get pulled into the cut and rip out teeth from the saw blade propelling them though the workshop or destroying the fence of the saw. It is a nuisance that puts the equipment out of action and can require costly repair work.

The repair costs on a Luna saw for an accident like this are almost always within reason while most of our competitors repair cost can be considered as outrageous – in some cases proving to be more economical to buy a new saw; e.g. you could get yourself a nice new Luna saw for around the same investment cost as is required to fix this on a competitors equipment! 

Well now you might ask what can be done to avoid accidents like this in the first place and there are several approaches to lower the risk.

The first thing to consider is wearing the recommended safety equipment;

-         Don’t operate a drop saw with out safety glasses. 

-         Wear reasonable working clothes with long selves and use ear muffs. 

-         Guard the saw so that bits from the saw can not hurt the operator working near by. 

These are just a few measures that limit the amount of damage that will occur if there is an accident. 

You could cut through the extrusion and then wait until the saw blade stops before pulling the saw head up. Some saws do have a saw blade brake (unfortunately the ones available with brake are not of good quality and therefore not handled by Luna); there is the option of installing a VDF with forced dynamic braking that can be used for three phase equipment. 

I mention this to touch on all the possibilities of making the equipment safe. 

The next thing is common cense. Very often we visit customers that try very hard to keep the off-cuts very small and then throw away a section of aluminium that is 300 or 400mm long. Yes, I do agree it is not always possible to keep the off-cuts longer but where possible this is an easy way to reduce the risk of having small sections flying around the workshop.

Prevention is better possible if there is an understanding what actually happens when you cut a small off cut.

On a straight cut the unclamped off-cut is pushed back to the saw fence by the rotating saw blade. If the saw is in good working order and the off-cut is larger than the gap between saw blade and saw fence and the cutting gap in the table is not too big there is usually no problem. The off-cut tends to move away from the blade due to vibration and does not get caught when the blade is pulled up.

If the saw fence centre tips (saw blade gap) are lower than the rest of the fence then the following can happen. 

If you cut a long but small extrusion the saw blade will actually produce a bending moment at the centre of the cut at on the aluminium extrusion.

If the saw blade cut reaches a specific point during cutting both sides of the extrusion will be pulled against the fence. 

The outside of the saw cut on that extrusion (the operator side) is now higher than the other inside and that causes the extrusion cut to jam the saw blade. This can damage the saw blade, the fence of the saw or just make the cut bad. Very often it also tends to jam the saw blade and cause the blade to stop if your motor is not very powerful. 

If you are cutting a small piece off with a saw fence that has a bent saw gap section then the following can happen. 

Because the fence is bent inward the off-cut is pulled to the saw blade and if the off-cut is pulled up the teeth of the saw blade, which are wider on the side, it will push the off-cut hard against the saw blade fence and jam the saw blade. If the off-cut is small enough it can rip through the fence damaging the fence, the saw blade and sometimes the saw table. Naturally it can fling also out off the saw into the workshop.

The same can happen if your saw is in good working order but you choose to make the off-cut just big enough to fit into the gap between saw blade and the centre tip of the saw fence. 

To prevent this from happening, check that your saw is in good working order:

-         No wobbly saw blade

-         Saw face centre gap tips same height as the rest of the saw fence

-         No damages to saw fence

-         The saw table insert or gap specifically in the saw fence area is not damages.

-         Always clamp the two sides of the extrusion to be cut if that is practical. 

If you do mitre cuts and you cut small pieces you will have this problem of cutting usually without fail. 

The saw blade and the fence in that setting producing an off-cut that is like a wedge. The extrusion off-cut is pulled by the rotating saw blade against the saw blade body and the fence tight. If you lift the saw blade up the saw blade teeth will wedge the off-cut into the angled gap deforming the off-cut and flinging it out the off-cut out of the saw in a random direction.   

If you use the other side of the saw with the wide angle for cutting the tip of the off-cut gets into the gap between saw fence and saw blade and this creates a similar problem. This side is also harder to clamp then the other side if you have short off-cuts. 

To overcome these problems there is really one practical way; you have to clamp the extrusion off-cuts. 

There are clamps available to clamp the off-cuts but there is more a nuisance as a benefit if you are cutting a mix of extrusions.

Most aluminium fabricators make themselves clamping aids usually from hard wood those are used in conjunction with a pneumatic material clamp that is on the saw on that side. 

You might have to make a clamping block up for every extrusion that is causing you grief, but that is in essence the best and safest way to overcome the problem.

Some customers have a mix of extrusions that allows them to produce a clamping arrangement that remains permanent on the saw. 

However, the majority of operators have loose clamping blocks that are used in conjunction with the material clamp of the saw. 

No off-cut clamp design seems to be quite the same and everybody seems to think that their specific design is the best. This might be true, though from our experience everybody operates and fabricates in a slightly different way suited to the type of product that they fabricate. 

Back to Spare Parts/Tips