Poor surface finish using Myford

Hi Steve

You say “A mate suggested that the machine was not running fast enough but it is at the highest rpm that the belt system will allow”.  Therein lays the rub.  Long ago I learned a sort of rule which allows you to approximate the speed of a lathe/milling machine.  For mild steel it is speed = 288/D where D is the diameter in inches (or speed = 7315/D if your in millimetres).  If you are machining a bit of 1inch mild steel you should run at about 300 RPM or the nearest and perhaps lower speed your pulleys will give you.  For harder metals choose a slower speed.  If your tool is ‘singing or chattering’ then slow the spindle down.>>

Choose your tool shape with care. Much has been written about this almost any My Hobby store booklet on lathe work will tell you.  Make sure that your tool edge is sharp.  I ‘rub mine up on a cheapo diamond or an lace w:st="on">Indialace> stone.  I polish it on a bit of an old razor hone I scrounged from an old (h)air chopper who took off more for 1/3d than the others did for 2/-.  Set the tip of the tool at the correct centre height for the lathe.  Use a good gutting fluid and you should get a coconut every time if and over here it is a BIG IF your metal is truly homologous.  If you have to use some of the ‘Old Red Mans’ rubbish then good finishes are rare.  I always (when I can) leave the work piece over night to allow the surface stresses to come out.

Hope this helps.  If it is any comfort two weeks a co I was machining a chunk of 40mm (probably Bulgarian) steel down to make a 27mm pin for an old Hungarian tractor.  I had taken 15mm off and the work piece literally fell in half. Oink!

Good luck