Math for home-shop machinists

HMF

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I find myself lost when it comes to the subject of the MATH required in machining. For example, calculating the correct feed and speed rates on a lathe or mill, threading MATH, and other necessary calculations. Can you guys explain some of the calculations required and how to do them, so that this thread can be a reference for the rest of us?

Thanks!



Nelson
 
GENERAL RULE FOR CUTTING SPEED:
Example. The work is 2" in diameter and it is desired to
turn it at 35 feet per minute. How many lathe revolutions
are necessary?
35 X 12
Solution.
2 X 3.1416
= 67 R.P.M.
To find the cutting speed, given diameter of the work
and lathe revolutions per minute: Multiply diameter of work
by 3.1416 and by number of lathe revolutions, then divide
by 12.
Example. The work is 2" in diameter and makes 67 revolutions
per minute in the lathe. What is the cutting speed?
Solution.
2 X 3.1416 X 67
12
35 feet.
Eight or ten speeds are possible in an engine lathe.
Place the belt on step of cone that will give the speed nearest
to that required.
LATHE CUTTING SPEEDS USING HSS CUTTER FOR ROUGHING
cast iron=60
steel or wrought iron=50
carbon steel (annealed)=40
brass=90
FINISH IS 50% TO 100% HIGHER W/SMALLER CUTS
If confused just guess, starting with low speed first!!!
I HOPE THIS HELPS,
Paul
 
Feeds are not to be less than 17 revolutions per I" tool
travel, and finishing feeds are not to be less than 90 revolutions
per I" tool travel.
If the above is exceeded, a less speed than that given in
table from other post must be used.
For large diameters, use reduced speed, as the strain on
the tool is greater.
Cutting feeds. Lathes with belt feed are limited to
three changes; lathes with gear feed are not limited.
For heavy work, coarse feed is about 17 lathe revolutions
to 1" of tool travel.
For average work, medium feed is about 38 lathe revolutions
to V of tool travel.
For average work, fine feed is about 90 lathe revolutions
to 1" of tool travel.
For tool making, a feed of 200 revolutions is often used.
Attention. A beginner may use finer feeds until he acquires
some experience; about 80 to I" for roughing and 140 to I"
for finishing.
If all else fails guess!!!
I hope this helps some,
Paul
 
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