# South Bend Shaper Cutting Speeds



## Mister Ed (Dec 28, 2016)

I have had a SB shaper for a couple years now. I only use it once in a while when I need to make something flat. I want to change that, so recently I have been doing a bunch of reading through some old literature. I had always wondered about the cutting speeds on the shaper and really had an "aha moment" with the relationship of strokes/min and stroke length ... as they relate to cutting speed.

So, I made up the following chart and laminated it to keep at the shaper. The center section should be avg surface feet per minute, left section are the 4 different SB belt settings, and the top is stroke length in inches.
	

		
			
		

		
	







Hopefully this helps someone else. Its funny that they really do not talk much about this in their literature.


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## ndnchf (Dec 29, 2016)

Nice - I
I'm mathematically challenged ;-)  How did you calculate the SFPM?  I'd like to make one for my 7" AMMCO.


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## 12bolts (Dec 29, 2016)

Not knocking your idea. I like it and I think I will print 1 up for my shaper too. But I would be interested in the math formula used because I am coming up with a different set of numbers 

Cheers Phil


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## Mister Ed (Dec 29, 2016)

Well, I think I have it correct, maybe not. I also rounded. I will try and dig up the couple items I was reading when the light bulb came on in my noggin. What I was not getting before was that for every revolution of the crank arm you have both a cutting stroke and a return stroke ... easy enough. But since the return stroke is faster than the cutting stroke, things get complicated. The documentation that I was reading stated that as a general rule (for a crank shaper) 3/5 of the revolution was the cutting stroke and the other 2/5 would be the return stroke. So, in the formula below the 7 (or .14=1/7) is really 3/5 x 12. The 12 is simply converting inches to feet.

I used this formula:
SFPM= (stroke per min) x (stroke in inches) x .14   [ This is the same as (stroke per min) x (stroke in inches)/7]

Or to get stroke/min for a particular SFPM:
stroke per min = (SFPM x 7) / stroke length


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## Mister Ed (Dec 29, 2016)

Here is the one publication that I used. This is from the New York Education Dept and over on the NEME site:
http://www.neme-s.org/Shaper Books/Shaper Work/Section 18 Description of Speeds and Feeds.pdf

This section starts on page 293. Take a look at page 295 and the top of 296. Then page 299 to page 303.

I wondered about the 3/5 - 2/5 rule on the strokes and if this was brand specific. But I did see this used in a couple more places as well ... so I figure it must be close enough. It is at least better than what I had before ... nothing, LOL.


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## ndnchf (Dec 29, 2016)

Thanks - I'm making my AMMCO table now.


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## ndnchf (Dec 29, 2016)

Thanks a lot Mr. Ed.  I made one using your formula (and rounding) for my AMMCO 7" shaper.


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## Mister Ed (Dec 29, 2016)

There you go! If you get a chance read those pages of the link I posted (that is where the formula came from). Even if you skip the gory details, the overall topic helped me with the understanding.

I have made it a goal this year to pay more attention to speeds on all my machines.


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## 12bolts (Dec 29, 2016)

M.E.
I just went out and cranked my shaper by hand, and (without resorting to an indicator or protractor for testing), I get, (on the bull wheel), cut stroke starting at 270° to 100° (about 53%) of a revolution, dwell time 100° to 120°, return stroke starting at 120° to 260° (about 39% of a revolution, or close enough to 2/5 ) and dwell time again 260° to 270°.
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. 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??? Even if we factor in a fudge amount for 53% of the revolution, you might get to 4SFM. Or am I just oversimplifying the math? Happy to be wrong

Cheers Phil


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## CluelessNewB (Dec 29, 2016)

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


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## Mister Ed (Dec 29, 2016)

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


12bolts said:


> 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.



12bolts said:


> 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.


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## Mister Ed (Dec 29, 2016)

CluelessNewB said:


> 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.


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## Mister Ed (Dec 29, 2016)

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.


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## scoopydo (Jan 1, 2017)

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

George


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