Can the spreadsheet be modified to calculate the tension forces in the middle area of the worksheet
As said, I find this an interesting topic.
However having a financial background/profession is not really helping. 2 questions, after playing around with the spreadsheet:
- Does the angle of the frame have impact on the output? smaller angle, more gravity
- Iām going to replace the bungee with counterweights. If I understand it correctly, the counterweight should weigh less in lb/kg than the āmin forceā in the spreadsheet. Right?
Thanks in advance.
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- Does the angle of the frame have impact on the output? smaller angle, more gravity
no effect on the spreadsheet, the force available has to overcome friction,
there is less friction at steeper angles.
yes, there is some difference between gravity pulling vertically vs pulling at
the angle of the frame, but I donāt think itās that much of a difference, and if
you are comparing frames at the same angle, it really doesnāt matter.
- Iām going to replace the bungee with counterweights. If I understand it
correctly, the counterweight should weigh less in lb/kg than the āmin forceā
in the spreadsheet. Right?
actually, if you have the chain doubled, it needs to weigh less than 2x āmin
forceā
As a test, make a series of cuts from the center bottom to the outside edge
bottom (say every couple of inches), and measure the distance between them with
calipers. Iāll bet that with standard bungee cords, you will find that at some
point along the series you get a set of cuts that are noticably closer to each
other than the rest of the series. That would be where the tension and pull of
the bungee are matching and the backlash is being used instead of moving the
sled.
With a suitable coutnerweight, that will not happen.
David Lang
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Itās already there, but sinde thatās not the limiting factor, itās not
highlighted.
Itās the first line of calculations in each setup.
David Lang
the default sled is more like 23 to 24 lbs, with 10 lb router, not 20 lbs like the spreadsheet says. top center force increases to over 40 lb.ft vs 33.7 with the correct weight of the sled.
I liked the graph that someone did on a second page showing force vs top beam height, so I added a section and graph at the bottom that will graph that automatically (and allow you to set the lowest height to check)
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I can tell a lot of time has been put into this. What I canāt tell is where we actually want to be in all of this, the ideal range. Is there a thread Iāve missed that identifies ideal outputs for these values? I have no engineering knowledge so this all might as well be in Greek. Below is my current configuration. Are there any issues/areas of improvement that should be addressed?
itās less a matter of āan ideal rangeā than it is a matter of āthe higher the
min tension the better, the lower the max tension the betterā
the stock machine is ok at the max tension (top center), and iffy at the min
tension (bottom corner), so the biggest win is to increase the min tension
without raising the max tension too much (which a 12ā top beam does well)
I give examples on the bottom right of some known systems (including some bad
ones)
In your case, you have increased the min tension ~50% and decreased the max
tension, so you will be better than a stock maslow frame, but possibly not quite
as good as a 12ā top beam frame (min tension 5.2 vs 7.4)
remember, people are getting good work done with the stock frame, the increased
min tension just makes you able to go faster and be less likely to stick.
David Lang
Okay. think I get it. So if we look at my setup cutting a 4x8 sheet centered in my wasteboard Iām set pretty well.
I could even bump my sled weight up a touch.
yep.
feedback is good, experiment and let us know the results
one thing that this calculator does not try to take into account is the lean-back angle of the frame. When we were designing the top-beam type frame, @bar misunderstood my directions and built a frame that ended up at ~20 degrees, and it just didnāt work because the sled wouldnāt slide well enough. We had someone try a frame at 5 degrees, and they had a problem with the sled pushing away from the workpiece when they tried to plunge down into it. The default is 15 degrees (which is the number that bar started with when he built the first one), but nobody has done any real testing on this.
note that as you tweak angles, it may affect the calibration accuracy, again, no testing, just be aware of the possibility and report if it does or not.
Hello, Iām new here. I wanted to ask if you shortened the top beam from 120 inches to 100 inches, how will those numbers look?
if you donāt narrow the workpiece size, the min force will be very, very low.
if your workpiece is 96" wide and your motors are 100" apart, there is only 2"
between the edge of the workpiece and the motor (actually, the spreadsheet wonāt
show how bad this is, as it doesnāt take into account the sprocket size, which
reduces this still further.
pick up something with a 5-6 ft long power cord and hold it in the air, then see
how much force you need to apply to move it 2" to the side, you will find itās
almost zero
now, if you narrow your workpiece, you can improve the minimum force, just like
extending the top beam.
if you go down to a 6ā wide workpiece, with a 8ā wide top beam, the min force
will be very similar to a 8ā wide workpiece with a 10ā wide top beam
But the reason the spreadsheet was created (and my enhanced two-config version
created) was so that you can go in and tinker with it to see what the results of
different configurations are.
feel free to copy the entire sheet to your account to tinker if you want
David Lang
Thanks, David!