How to translate Logan 820 Feeds chart

tmenyc

H-M Supporter - Gold Member
H-M Supporter Gold Member
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I've been trying to understand the feeds chart on my Logan. Its spindle speeds using the direct gears are limited to 179, 334,620,420,780, and 1450 rpm. I've certainly read everything I could find, and the classic example of 100 SFM being a good feed rate for 12L14 makes sense, from 420 rpm x 1"/3.82= 110. But how do I connect, algebraically, the 110 to a feed rate in the chart? What are the units on the chart? What am I missing here?

Many thanks,
Tim

Logan feeds chart.jpeg
 
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Cutting speed is spindle rpm *PI *diameter of material being cut.

All the feed charts tell you how much the carriage or cross feed advances PER revolution of the spindle.
 
The units in your chart is in inches per revolution. I think you are trying to determine which feed rate to use for a given material, no? The answer depends on a number of factors - RPM, material, size, depth of cut, etc. Simplest answer is to look up the recommended feed rate for your material in a chart and set feed for that. For example, most charts will tell you to rough 12L14 at 0.006" per rev so you set your lever to 24D to cut at 0.006"/rev.

With that said, all the charts are for industrial applications. Basically, the recommended feed rates are to enable maximum metal removal rates. Some, not all, charts take into account the HP of the lathe. Rigidity of the lathe is NOT considered but is assumed to be adequate to handle feed at the rate they recommend. I will tell you now that your lathe does not fall into that category.

What I do is look at the chart for a baseline setting in IPR for the material you have and set it, then do test cuts. My lathe is only an 11" but it is very rigid for its size and has a 2HP motor. I try the cut at the DOC I want and at the speed I chose and see how the lathe handles that feed while roughing and finishing. I then alter the feed depending on how the lathe responds to the cut and it is almost always different than the recommended feed rate. Once I figure out what works best for that material using a particular cutter set for DOC-X at RPM-Y, I make note of it for future reference. Over time, you will build up a list that is actually useful for you because the charts are usually not useful.
 
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Mikey,
somehow it always makes sense when you respond. Now I see that the relationship is not a couple of steps of simple algebra, and should use the table, but starting with the 24D for now. Many thanks.
Tim
 
You should know that feed rates for both HSS and carbide are the same in the charts but are not at the lathe. When using HSS, drop your feed rates down unless you are taking light passes
 
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