If it is recycled it ia almost certainly thermoplastic and may melt. Nothing wrong with using normal metal cutting coolant or minimum concentation soluble coolant. No more risk to mill than cutting metal. Fast feed rates help too.

If you have lot to do it might be worth making a jig with stops for a circular saw. A custom "table saw" with 3 ganged cutters on a spindle might be worth considering as you have a lot to do.

Robert G8RPI

For milling thermoplastics I use sharp cutters with high rake angles and modest speeds, around 100ft/min. But I use high chip loads, 10 to 20 thou per tooth is not unusual. For side and face cutters I might drop the chip load a bit due to low rake angles. I have never used coolant when machining plastics. Most plastics have poor thermal conductivity so coolant isn't go to do much at the cutting edge. Better to keep the speed down and chip load up.

Andrew

You should be able to clamp a bunch of them along the mill table and do them quite quickly, if you have power feed that will be nice then just 3 changes of position per batch. I'd go with a high helix cutter meant for aluminium though a sharp 3-flute HSS would be almost as good. Or find a member with a CNC, I've put mine to use doing batches of upto 30 mortice and tennon joints so a few housing joints will be easy.

If you do go for Roberts ganged table saw method which I was surprised at given his posts about electrical safety do check the saws built in electronic braking can handle the extra momentum and it should go without saying rig up some form of guard to go over the exposed crown of the blades. All this assuming the arbor is long enough for more than one blade. Sliding compound or RAS with trenching stop would be a safer saw method but a lot more moving about of the work to get the width of slot

Edited By JasonB on 15/12/2021 08:03:03

It might be possible to get the width of slot in one pass using a dado head.

If it needs to be said, the cutters need to be sharp.

A blunt cutter will tend to rub rather than cut so that the plastic melts with the hear, leaving lots of "rags" to be removed by hand afterwards.

Howard

My attempt at making little drawer knobs from black plastic rod worked well, I was amazed at the type of swarf it produced and it piled up like giant Brillo pads all over the place

I wonder what the effects of sunlight on the sleepers would be if the tracks are outdoors? Some plastic can get brittle with exposure.