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Tensioning system to improve performance in bottom corners

chain
tension

#62

In order to achieve enough reduction (mech. advantage) from the chain slack to the sled, I had to reduce by 4x. The chain slack is attached to a double pulley with some non-elastic paracord. Then, elastic 3/16 cord is anchored on the frame, then passes through the double pulley, back to a pulley mounted to the frame, then back to the double pulley, then finally through the corner pulleys and onto the sled.

I bought 25ft of paracord and 50ft of elastic cord. The pulleys need to run smoothly for the system to begin to work. I haven’t really been using the system recently though, since my cuts aren’t in the corners right now.

Hope that helps!


#63

@Dustcloud Yah I figure for the cost of some cord and pulleys its worth trying, I’m currently designing a frame to fit my shop while waiting for my kit to get sent out.

@Jacob Thanks for the guidance.

How taut did you pretension the elastic when you set yours up?

Is this the right material? Amazon: T.W . Evans Cordage SC-316-100 3/16-Inch by 100-Feet Elastic Bungee Shock Cord


#64

I ended up with about 5-8lbf on the elastic cord by the time it hits the sled.

-JCH


#66

@Robert It sounds like you’ve got an abundance of experience on pro machines, that’s something that the community is lacking a bit based on my read of the forums, I strongly encourage your continued “comparison and contrast” of experience in the forum.

The maslow is designed to be very simple mechanically, but it has a physics problem in all the >corners. the bottom corners are the worst, but you can overcome the problem two ways.

Slow the feedrates way down in these areas. I do cut a full 3/4" in one pass with my machines and the edge finish is beautiful. Just as good as the $200,000.00 machine I used before. I’m not a fan of adding mechanical complexity to a machine when I can use the machine’s personality to get what I want.

the second thing you can do is change your bit travel direction. This will add tension to the chain that can keep the sled in the desired travel position.

These 2 methods will allow the maslow to be incredibly accurate and precise. I don’t doubt the tensioner works, but it does add loading difficulty and is another maintenance item adding cost.

Along the lines of these observations, some questions to the Maslow Developer Group:

Would it be possible to have GC attempt to implement these ideas, or could they be added another way, say via post processing script Fusion360?

  1. “Feed Rate Zones”
    whereby on the outer edges of the workspace GC enforces rates of travel known to be more accurate (obv more testing needed to determine where these borders lay, and what speeds produce the best results)

  2. “Preferred Direction of Travel.”
    To be clear @Robert , I don’t think that any of the proposed tensioners have proven themselves in the real world yet. (readers, please correct me, if i’m wrong) It seems like this would be the most difficult of the 2 proposals to implement… but along the lines of the Feed Rate Zone, this would have GC enforce a ‘clockwise travel zone’ on the lower left side and a ‘counterclockwise zone’ on the lower right.

thoughts?

Also, @Robert, some video of your maslow cutting full depth and any more details you’re able to share would be greatly appreciated!

many thanks!


#67

I like the idea. Instead of trying to figure out where to slow down from the coordinates in the gcode, a “slow down” could be triggered by a chain exceeding a certain length.


#68

excellent idea Gero!


#69

Since the coordinates in the gcode are used to calculate the chain lengths, it might be simpler to use the coordinates to trigger speed zones in the workarea.
In addition to where the sled is, it matters which direction it is trying to move - for instance in a lower corner movements away from the center need to be slower than movements toward the center. So each speed zone might have different speed limits based on direction of travel.
I wonder if these adaptive speeds would cause problems for choosing the router RPM rate? Don’t want to be on fire because of a speed limit…


#70

As far as I understand things, unless you’re using a material other than plywood, there is no reason to ever go higher than the minimum speed of 10k rpm on the default router.

I’ve run the feeds and speeds #'s (through various online calculators) and we’re still pretty much pegged on the high end (ie: not moving through material fast enough) in every scenario, inc with a single flute, @ 1/4" bit diameters.

meaning, that everyone should be at the minimum RPM in nearly every situation.

Yes, we should be concerned about friction and its consequences, but there’s not much we can do about the spindle speed as the default router, by most measures is an order of magnitude more powerful than we’re able to use to our advantage.

Now, what @Robert has said about full depth cutting (ignoring the friction concerns for now) would probably put us into a use case where the full power of the (default) router will be in play.


#72

All well said, thanks for bringing your experience. Please do go on!


#73

:heavy_plus_sign::one:


#74

@Robert, very interesting information and observations, please keep sharing!

“spreadsheet template can be used to create many cutting programs”
Can you provide a sample, this is very interesting.


#77

amen brother!


#78

Making perfect sense. Are you heading toward the effect of creating tension beyond the weight of the sled?


#80

How would that apply to the ‘calibration cuts’ made during the calibration sequence? How could (or should) those be arranged to benefit from your observations? Do the lower side cuts need to have a short pull toward the center before the vertical cut to tension the opposite chain?


#81

@Robert

image


#82

What if there was *an amount of" weight that moved (in the case of the pantograph/linkage designs) in conjunction with the linkages so that the higher and closer a particular chain’s angle came to 90deg to the top beam, the weight moved more fully underneath that side’s linkage?

In the equation above, T^3 becomes a force that increasingly pulls towards the lower left as the sled moves left, increasing tension on T^2 in this example by shifting to the left side of the sled (or even off the left side of the sled).

The more that T^2 (the right side of the machine with the sled moving in the left lower corner) extends, the more inherent slack (from chain weight (T^2) and pendulum swing of nearer to vertical T^1). If T^3 were to shift the center of gravity to the lower left of the sled (and vice versa when the sled is reversed on the workspace) wouldn’t this increase stability by keeping both chains under more tension?


#83

I think i’m describing a 3rd linkage connected to the (T^3) counterweight, forming a 3rd point that remains keyed to the linkage angles.

When one pantograph arm goes ‘high’ it pulls the weight from a point below the sled out to its side of the sled.

The weight is connected at the base of a rigid 90deg V that extends from below the router out in each direction to the point that it can be linked horizontally with the lower linkage attachment points, while still clearing the router and its associated stuff (hoses,wires, z-axis, etc).


#84

@dlang your input on this possible addition to the vertical linkage design would be helpful here as would @MeticulousMaynard’s Fusion mockup of the sled. .

(Un)fortunately I’m taking my nephew and niece 1/2 way to @mooselake country for to see the wilds of north central Michigan for a good 2 weeks after tomorrow’s holiday, I’ll have forum access but no Maslow handy.


#88

I’ve been running the Maslow for 14 months with 2x4’s that have twisted and bent. The new top beam will be rock solid. For the dimensions I’m going more symmetric with the new build. I’ll just go a little up and pretty much wider (as wide as I can before toughing the walls.) Would love to see same math.
Old motor position red, new green.


#89

Edit: If I’m not wrong, it will be near the max stretch with the stock chains.