Reply To: Brushless foam cutter



Something to consider… the inflation needle guide can get pretty hot when the foam cutter is run at high speed (8000-10000 rpm?) for the time it takes to cut a sheet of foam board. If it gets hot enough it will soften the guide needle “threads” in the PLA and allow the needle point to drift away from where it should be.

To be honest, I normally run with no lubrication at all on the needle or in the guide. The high-quality spring steel of the music-wire needle and the brass(?) guide needle seem suited to the task, especially at lower rpms. At any rate, I consider the needle a “consumable” as it is easily fabricated and replaced. Though I’ve not had a music-wire needle work-harden and break to date, I have had a needle guide start “wallowing” in its plastic threads. It could be that a proper lubricant would help…but everything I’ve tried so far — light machine oil, vaseline — either blackened and crusted up and/or migrated down the needle and stained the work piece. Possibly white lithium grease or other non-migrating lube might be a better choice?

A better approach IMO is to “heat sink” the guide needle and spread/lessen the heat build-up so that it doesn’t soften the PLA plastic. Two approaches I’ve considered so far…

1) a 8mm BW tube motor mount can be mounted directly under the 5/16″ hole through the foam cutter platform and the guide needle then simply mounted in the motor mount with setscrews… or better (if you have a metal lathe and suitable tiny drill bits),

2) a 5/16″ x 2″ carriage bolt can be bored through its center — very similar to a 3d printer nozzle. I start with a 0.040″-0.050″ hole bored through the head for a depth of 1/2″ or so, then flip the bolt end-for-end and center-drill to form a conical opening, followed by a 3/16″ bore through the center of the bolt, to finally meet the “nozzle” hole bored through the bolt head.

I recognize the carriage bolt approach is not something many are likely to take on but I suspect a “poor man’s approach” to accomplishing a similar result is to simply purchase a real all-metal 3d printer hot-end and enlarge the nozzle opening to 0.040″ or so (~1 mm).