Carbide inserts



Voor de site "Home Model Engine Machinist heeft één van onze leden een artikel geschreven m.b.t. de vraag of je op een hobbybank ook carbid inserts moet gebruiken en of die dan net zo scherp moeten zijn als snelstaalbeitels. Zie onderstaand het artikel ( in het Engels) Dit is de link naar deze site.

'Cutting metal is in close-up not really cutting but a discontinuous rip-off proces. The sharper the tool the finer the rip-offs, the lower the forces and the smoother the resulting surface. The cutting speed of carbide inserts is roughly up to three times the cutting speed of high speed steel HSS. And this higher speed gives a much smoother rip-off proces. Compare with plowing snow at low speed and high speed. So the sharpness of the insert will not affect the process much, and a slightly less sharp cutting edge is stronger and more wear resistant and thus allows for bigger chips, that produce higher cutting forces. For small precision parts it is however beneficial to give the insert a really sharp cutting edge using a fine diamond grinding/honing wheel.
The use of carbide inserts depends fully on those higher cutting speeds. Your lathe tu2004v has I believe a maximum spindle speed of 2500 revs. This means that you have a good carbide cutting speed for steel down to diameter 20 mm, and for brass and aluminum down to diameter 40 mm. For diameters smaller than this you would be well advised to switch to HSS tooling. The HSS cutting speed for steel is OK down to diameter 6 mm and for brass and aluminium down to diameter 12 mm. Several members of my horological society use a small second lathe capable of high revs like up to 15.000 - 20.000 revs for the small parts with diameters to be cut say from 1 mm up to 10 mm.
In my own workshop I have pampered myself with a Schaublin 102 VM lathe which goes up to 3000 rpm with a frequency controller, a Myford Super Seven of similar size which also with a frequency controller goes up to 5000 rpm and a TAIG with a DC motor and DC control that goes up to 18.000 rpm spindle speed.
Overall it is my strong believe that the hobby machinist and the hobby equipment reflect the workshop practices of 60 years ago. So it is very helpful if you have acces to a workshop engineering manual of about the 1960’s.'