Cutting foam sheets... with a needle!

[Michael9865]

Could anyone remind me why such a design is infeasible for a needle cutter?

Some quick thoughts are mentioned below.
This design has a lot of metal on metal wear points and friction points. The metal on metal points cause heat, friction, and energy loss. The spinning shaft does not have ball bearings at the points where it goes through the housing. The washers and pins are another friction point, The way it was made how could you get a good balance on the shaft to eliminate it from shaking and wearing. The piece that holds the blade and slides up and down has multiple friction points as it slides metal on metal.
The weight of the design would create issues with moving it with stepper motors and not encounter momentum slop.
A jig saw blade could create binding issues or ripping the foam as you try to turn corners.

 

[Tench745]

Some quick thoughts are mentioned below.
This design has a lot of metal on metal wear points and friction points. The metal on metal points cause heat, friction, and energy loss. The spinning shaft does not have ball bearings at the points where it goes through the housing. The washers and pins are another friction point, The way it was made how could you get a good balance on the shaft to eliminate it from shaking and wearing. The piece that holds the blade and slides up and down has multiple friction points as it slides metal on metal.
The weight of the design would create issues with moving it with stepper motors and not encounter momentum slop.
A jig saw blade could create binding issues or ripping the foam as you try to turn corners.

I believe the poster's intent was using a variation of this reciprocation mecanisim to replace the more common flywheel mechanism, which can impose unwanted bending loads on the needle. Not using a saw blade or this heavy-duty assembly, specifically.

 

[Michael9865]

I believe the poster's intent was using a variation of this reciprocation mecanisim to replace the more common flywheel mechanism, which can impose unwanted bending loads on the needle. Not using a saw blade or this heavy-duty assembly, specifically.

Ahh

 

[john ferguson]

The advantage of a .025 inch needle cutting foamboard at 8,000 strokes/minute and advancing at 20 inches per minute is that the finish of the cut is near perfect, and the smallest curve or corner can be matched. The creator of the saber saw version has made a very nice saw, but do you really want all of the weight of the saw and the drill supported on a probably light XYZ Axis CNC driven frame? Servos would have to be large.

Frankly, I cannot see why he went to the trouble of building it. Maybe someone else can.

 

[dkj4linux]

I believe the poster's intent was using a variation of this reciprocation mecanisim to replace the more common flywheel mechanism, which can impose unwanted bending loads on the needle.

I really think this is a misconception. Music/piano wire is hardened spring steel... and made to bend. My needle cutter's bending loads were always intentional... and wanted.

Seriously, I've never had a needle break due to bending unless it was forced to bend sharply against an edge... and then friction heat to failure. But, by far, most needle failures are due to stress risers formed when fabbing the needle's loops or bends with pliers with sharp-edged jaws. I used round-jaw needle nose pliers when forming loops or bends for that reason. And never, ever, straighten or adjust a bend once formed... it's a guaranteed point of failure.

-- David

 

[john ferguson]

Hi David, the round-jaw needle nose pliers seem a good solution. I went with the drilled brass stand-off which means that the piano-wire needle doesn't have to be bent at all. I suspect that drilling this small hole would be impossible without a small drill press. I have a drill press attachment for my Proxxon which made it easy for me.

I'd intended to replace my 3d printed rotor with an aluminum one, but since it is working so well, I may just print a couple of spares and forget about the aluminum - which because aligning the bearings in front and back for the wire crank is tricky to do ois a bit of a time sink.

and once again, it is such a delight to have this wonderful machine, which I never would have thought of myself.

john

 

[john ferguson]

I finished the vacuum table. The base machine for my foamcutter is a Chinese 6040 CNC Router, which is just fine for my work. I glued two 5/8 MDF boards together - i needed the stiffness because the end has to cantilever out past the end of the router bed. I cut the pattern in the upper board with a 1/4 inch bit in the router including the header and the opening for the 3D PETG printed manifold which the suction hose attaches to. I set-up the needle cutter attachment and cut the perforations in the 5mm foamboard which will become the wasteboard in use.

Still on my first music-wire needle.