Generating safer paths?

Hi

My scenario is as follows. I'm trying to machine some parts on 20mm perspex, using a 3.2mm end mill and have added an extra 1.6 mm for CutWidth (so 3.2+1.6=4.8). When it completes the final depth and retracts, the tool rubs onto the side of the perspex. Without going into the details of my poorly designed CNC machine, it has caused my Dremel took to smoke up, because the Dremel tool lifts the entire table up with the perspex on it and the whole thing ends up getting stuck. This problem won't be an issue in the one I'm planning to build. But in the meantime I need to use this CNC to make parts for the new one.

So short story out of the way, how do I go about generating safer paths so that the tool moves a bit into the middle of the groove that was set by CutWidth, before retracting? That way the end mill is not touching anything on the side. Can I simply draw a line and tell it to move along it?

Thanks,
Nghia

Thanks

Hello Nghia,

Sorry for taking so long to get back to you on this one.

What you really need is a lead-out move. CamBam supports lead in moves, but lead out moves are currently still on my todo list, but should hopefully appear soon.

I had a go at trying to do this manually with mixed success. As you suggest, I used another drawing object so that when the toolpath finished a circuit of the main object, it then moves to the other object which leads the toolpath away from the main surface.

There are a few things to consider though.
The extra shape needs to be big enough to generate the same number of cutwidths as the main shape.
It needs to be positioned near the starting point of the main shape - this is indicated by the position of the direction arrows on the toolpath.
LevelFirst CutOrdering must be selected.

I have attached a file to illustrate this. Hopefully it will do what you need.

The melting plastic does sound a bit worrying though. You might try turning your spindle speed down as slow as it will go and increasing your feedrate as fast as it will go and use light passes.
Another thing I found very good for cutting plastics with fast spindles, is single tooth TCT wood router bits. I got them mail order from screwfix and they were very cheap.

Good luck with Mk II !

Thanks for the suggestion. I did not consider adding an extra shape. This would be safer, albeit more time consuming, than trying to *sneak* in between the CutWidth path (which was what I originally had in mind).

Btw the plastic isn't melting, what actually melted was the Dremel (and also a Proxxon), very costly mistakes :), because the motors stalled. This time I'm keeping a watch over the machine at all times until I finish building a fuse box.

After some experimenting with 20mm perspex and using double sided tape to keep it attached to the table, I found that using two 2.5D cutting profiles seems to have solved my current problem. The first cut would cut to 18mm, with CutWidth set appropriately. The second cut would cut to the final 20mm depth without CutWidth set. I have observed previously that with a single 2.5D profile on the final depth cut it would cut the outer shape and caused the perspex to rely solely on the double sided tape to keep it attached. Most of the time, the milling bit's upward force is greater than the tape and would cause the piece to detach and jam the machine up.