Has anyone successfully gone with a 12' beam?

Hardware
1

While waiting for my kit to come, I’ve been doing a lot of reading.

I have a few projects that ideally would go near edge to edge on a sheet of plywood and I’ve seen discussions about extending the beam to 12’ to keep slop down when at either edge.

I was wondering if there was anyone who actually went with a 12’ beam? I ordered extra chain. Should I also
raise the height of the beam above the cutting area from the stock design? Is there any drawback to extending
the beam past 10’? (aside from space considerations, my shop has 20’ ceilings and a 16’ rollup door)

I’m very familiar with traditional cnc equipment, but this triangular articulation is completely new to me.
I’m not expecting real precision, but the goal is to be as consistent as possible.

Thanks for any insights you guys can share!

-Ken

2

I was wondering if there was anyone who actually went with a 12’ beam?

Yes, there have been a couple posts this week from people who have gone with 12’
beams.

I ordered extra chain. Should I also raise the height of the beam above the
cutting area from the stock design?

Is there any drawback to extending the beam past 10’? (aside from space
considerations, my shop has 20’ ceilings and a 16’ rollup door)

extending the beam past 10’ helps cutting in the bottom corners, but it makes it
harder to cut in the top center.

Along the top, you are limited by the force the the motors can provide, the
higher the static force needed to keep you in position, the more likely you are
to run into problems

In the bottom corners, you are limited by the force that gravity can provide,
the lower the force that gravity provides, the more likely you are to run into
grief

take a look at the spreadsheets developed in the thread
Maslow Chain Geometry Spreadsheet and play
around with the numbers. you want to maximize the force in the bottom corner
while not driving the force in the top center up too high.

we know that a yoffset of ~12" or a sled weight above 30 pounds can cause
problems, which seems to imply that a force in the top center exceeding 50
pounds is

I’m very familiar with traditional cnc equipment, but this triangular articulation is completely new to me.
I’m not expecting real precision, but the goal is to be as consistent as possible.

we are seeing people with accuracy within ~ 1mm (1/32")

but all along, our repeatability has been good.

When the forces are too high/low, and the feed rate is too high, (and the
friction between the sled and the workpiece too high) the sled doesn’t follow
the desired path (wandering on downward cuts, rounded corners in the bottom
corners, and hooked cuts along the top)

It looks as if you can get a drastic improvement by going to a 12’ beam, a 30
pound sled, and keep the top tension under control by raising the beam a foot
higher than stock

but play around with the numbers, and if you can, play around with the actual
machine. The spreadsheet is only math, and math != reality

To quote Albert Einstein:

As far as the laws of mathematics refer to reality, they are not certain; and as
far as they are certain, they do not refer to reality.

David Lang

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Also, from recent testing on the angle of the machine:

a tilt of 20 degrees is too much
a tilt of 5 degrees can be too little (problems plunging into the material)

the stock frame is 15 degrees.

It looks like 10 degrees or possibly slightly less may be to your advantage
k

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4

Thanks! That’s even better than I was hoping for!

I’m planning on building a test frame first to see what needs tweaking and that spreadsheet gives me a good set of ranges to play with.

Do you know if the calibration functions (stuff like the chain drooping) are adversely affected by going out further than standard?

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5

Another question, What would be the drawback of extending the height even further?

For a ludicrous example, say the motors were 4 feet above the top the of the cutting area?

7

nope, they handle it just fine.

you may also want to play around with numbers going to a 14’ top beam (helpful,
but not as drastic a difference as the step from 10’ to 12’

8

The problem in the bottom corners is the angle of the chains getting too close
to vertical, that means that gravity is mostly pulling down on the chain and
only a small portion is available to swing the sled towards the corner.

The higher the motors, the steeper the angle.

That’s why the step from 10’ to 12’ is such a difference, you go from an angle
of 81.38 degress to 71.57 degrees. that makes a HUGE difference in the force
available (going to 14’ drops this to just over 62 degrees)

but at the same time, the top angle changes. The stock design has the angle at
the top center being 9.6 degrees, 12’ = 8.87, 14’ = 7.88.

This is why on my version of the spreadsheet, I have a block that shows the min
and max angle, and the min and max force as that summarized the strengths and
weaknesses of that configuration (again, to the extent that we think the math
applies)

I wish we had an idea of the right values for friction for a sled, that would
let us make a guess as to how much is added to the high value when trying to cut
in the top center, and how much is subtracted from the low value to see how much
force gravity can apply to actually accelerate the sled towards the corner.

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9

Interesting thought on friction… When the company I was working for in the mid 90s (Chrysler) merged with Daimler-Benz, the wacky germans introduced a method of calculating friction using people with specially built shoes and a ramp that increased in slope until the person couldn’t hold on and had to use the handrails. Apparently it works well but certainly gathered a crowd when they used it the first time. I was told the numbers generated were better than the american method of dragging blocks with a glorified fishing scale.

So would having another maslow system on the bottom with maybe a inline spring help? Might be able to remove the bricks too then…

10

I have used a 12’ top beam. I recommend increasing the height of the motors by 6-8 inches relative to the 4x8 worksheet. For mine, the top of the top beam is 26" above the top of the working (cutting) area. With this extra 6-8 inches, the force at the top-center is less than that of the default frame. The 12 foot beam means the machine will perform better in the bottom corners. I believe these modifications make the machine capable of cutting a full 4x8 sheet.

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11

I would say the minimum angle is closer to 10-12deg.

In my experience, anything below 10 degrees (with default router, default weights, vertical pantograph or ring setup) and the sled doesn’t make enough contact to stabilize the router except with the shallowest of cut depths.

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12

Thanks @Joshua, I’ll use those numbers as a default when i build my first frame.

@mrfugu Good to know, you saved me a step cause I was going to start near vertical and tilt out.

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