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Bob UK
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Posted on Friday, 20 March, 2015 - 08:51:   Edit PostDelete PostView Post/Check IP

The cutting speed is the speed that the cutting edge moves relative to the material being cut.
In a milling machine the tool moves, in a lathe the workpiece moves.

Example 1" dia steel bar in a lathe. Look in tables for steel then the tool material
For HSS tooling and EN1a steel the table will say 80 to 100 ft/min.

So 1" times pi = 3" per rpm.

or 0.25 ft per rpm.

80 ft divided by 0.25ft equals 320 rpm.

So rpm of lathe should be 320 to 400 rpm. The same calculation is used for drills and mills, use tool dia.

Because most machine gearboxes have a fixed range of gears. The exact speed is impossible. So I use 3 as pie and go say 90% of best gear.

Brake Drums.
Today I done 4 drums for a Vauxhall Wyvern. These were 8 inches dia. So because the cutting speed for drums is about 80. 300 rpm is ok for 1 inch then 75rpm for 8" using HSS Tooling. The tool I use is a left-hand cranked point 1mm radius tungsten carbide. So I can run faster at 100 rpm.

The auto feed is set to 5 thou per rev. The drum is 1.5" deep. 1.5 decided by 0.005 is 300 revs so at 100rpm it takes 3 mins.

To set up is 5 mins
to load drum is 30 seconds and then 3 mins to skim. 4 drums takes less than 30mins. Sometimes a second pass is needed. One 10 thou skim often is enough. A quick emery sanding of the open end chamfer.

Due to health reasons I took over an hour.

The drums cleaned up with a 10 skim 20 thou on diameter.

7.50 per drum. Lathe is now left in drum mode ready for the next drums.

Money for old rope.

(Message approved by david_gore)

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