South Bend Shaper Cutting Speeds

[Mister Ed]

Phil - I see the piece you are not connecting on. One of the same little bits that had me confused.

But to go back to the math, (and just for simplicity) if we used an RPM of 12 and a stroke length of 1" I calculate that to be 12"/minute, or 1'/min.

But, since you're only cutting on the forward stroke ... you only cut for 3/5 of that minute, and that is the key. The cutter is travelling 12" in 3/5 of a minute ... the other 2/5 of the minute it is going backwards 12".
So 1'/(3/5)min or 1.67'/min would be the actual forward speed on the cutting stroke.

If we up the speed to, (your slowest), 42 RPM, that is 3.5 times faster than 12 RPM, so now are we cutting at 3 1/2 ' per min???

So now take that 3.5 times increase (42rpm vs 12rpm) ... 3.5 X 1.67'/min = 5.85'/min. My chart above is pretty close, rounded to 6'/min.

Now, lets take your rough degree examples and see how they come out using the logic in the text that I posted the link to. If I spread the dwell degrees across the Feed and Return strokes (didn't know what else to do with them) ... your shaper is closer to 4/7 feed and 3/7 return (per revolution).

I dropped a snippet of the formula into the spreadsheet below. We will substitute the 7/4 for the 5/3 (book example was 3/5 feed 2/5 return).

For this shaper (if your protractor was accurate ) you will have a constant of .1458 (using the 3/5 number it is actually .1389 ... they rounded to .14). Doing the math then, you would presumably have a speed of 1.75'/min, on the cutting stroke ... not that far different from the 1.67'/min above.

That is how I am understanding this shaper speed business after reading all those old documents for a day.

 

[Mister Ed]

FWIW the 1967 South Bend Catalog (available here on H-M) says the range is 3 to 114 fpm.

View attachment 142450

Rich -
When I was looking at all this info the other day, that had me stumped as well. I believe they are simply taking the stroke/min and multiplying by the stroke length. (195 strokes x 7")/12 would give the 114' number on the high side. The low side would equate to about a 3/4 or so stroke length running at 42 strokes/min.

Although true, I think it is a worthless number. You can take that 114'/min and divide by 3/5 (the theoretical part of the minute we are actually cutting) and you get a cutting speed of 190'/min ... I have 191'/min on the chart above.

I did find a cutting speed chart in a 1954 article in Popular Mechanics. I am not sure, but I believe the chart is from Atlas. I am going to crunch those numbers through the formulas above to see how they match up.

 

[Mister Ed]

Here is something I found in a Feb 1954 Popular Mechanics shaper write up (I told you I had been digging). Based on the other photos, I would say this is from Atlas, but cannot confirm.

The "Forward Travel" column is what South Bend is calling Cutting Speeds in Rich's example above. I think the first footnote at the bottom sums that measure up best "net feet cut per minute" ... meaning its not really a velocity(speed).

The second column "Cutting Speed" is really what we are trying to talk about ... the speed of the cutter when it is on a forward stroke. If I take the listed RPM & stroke length and plug it into the formula above ... low and behold the calculation matches the listed cutting speed, less a percent or two.

 

[scoopydo]

Yep it's from "Know Your Shaper" in the Popular Mechanics. There is a pdf version out there too.

George