Am I understanding correctly that the bars could be curved? That would let you get around the router a lot easier (especially for a router with handles, etc. that stick out more)…
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Yes, there is nothing special about straight bars, it’s the distances between points (and their relationships to each other) that matter.
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I don’t think there’s actually a need for a mounting point below the router! Below is a quickly butchered version of your drawing to illustrate. This could eliminate any clearance issues, and be extremely easy to make & mount.
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Are both pantographs necessry? I think I remember that dlang showed that Bar’s pulley and ring traveller would work with one side fixed. Is it possible this would as well?
@pillageTHENburn, and now I see the light! thank you! That is a cool idea, and could potentially still have an adjustable chain attachment height on the arms as well.
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Oh snap! YES! This idea was tickling the back of my brain but I couldn’t figure it out! (I was envisioning windshield wipers or camera cranes…)
You nailed it! The only difference I can see mechanically is that in this design two of the “horizontal” bars are in tension and two are in compression. In the other design they are all in tension. I don’t think this would actually affect anything though. Perhaps it would change the balance of the sled by being anchored above the router/CG? Gosh, this is a great idea. We must try these at once! Ha!
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@bar Awesome! and it looks great to boot.
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Is that mentally or physically?
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I tested out the angles of the chains at what I think is the maximum points on the stock setup.
It was 15 degrees from vertical and 10 degrees from horizontal, below are the photos of the positions.
I also not that the router diameter is about 4.74 inches in the best case scenario, but there are quite a few protrusions and such.
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I assume (sorry, they physics/geometry of these I don’t totally grok) that the length of the arms isn’t overly important except for potentially the leverage applied (and them being equal where needed)?
Thinking having them not extend much beyond the sled would make sled storage (and dealing with it in general) easier.
Thanks SOOOO much for these drawings guys… these I can understand 
Both! Near Au Train.
Having the links alternate between tension and compression is not good
for precision because the pivots will undoubtedly have play in them,
which will create errors upon transition from tension to compression or
vice versa (just like gear backlash creates error upon torque
reversal…this was why @bar designed the bricks into the Maslow in the
first place: to avoid torque reversal on the motor sprockets hence avoid
backlash errors).
pillageTHENburn[1]
August 25
Oh snap! YES! This idea was tickling the back of my brain but I
couldn’t figure it out! (I was envisioning windshield wipers or camera
cranes…)> You nailed it! The only difference I can see mechanically is that in
this design two of the “horizontal” bars are in tension and two are
in compression. In the other design they are all in tension. I don’t
think this would actually affect anything though. Perhaps it would
change the balance of the sled by being anchored above the router/CG?
Gosh, this is a great idea. We must try these at once! Ha!>
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In Reply To
ImpetuousWombat[3]
August 25
I don’t think there’s actually a need for a mounting point below the
router! Below is a quickly butchered version of your drawing to
illustrate. This could eliminate any clearance issues, and be
extremely easy to make & mount. [image][4]>
Visit Topic[5] or reply to this email to respond.
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- https://canada1.discourse-cdn.com/flex031/uploads/maslowcnc/original/1X/3623cc4ece4ad4b41125ad276790f6d771826b5a.jpg
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It shouldn’t alternate between tension and compression. The top bar will always be under compression and the bottom one will always be under tension. (This is regarding the design where they are both attached above the router)
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Good grief, that above-the-router-six-bar-dual-half-pantograph is brilliant! The linkage I was investigating will never be as good as that.
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Even with a COG in the middle, cords and vacuum hoses might affect the angle a little. I think if the pantographs work cheaply and well enough we’re better off with the bricks on the bottom and two pantographs.
Thanks for the research!!
You’re right, the length of the arms shouldn’t affect the angles as long as they’re the right proportions. Size might affect the leverage on the parts and how much slop we can get away with, but otherwise it shouldn’t matter. I’m not sure if shorter or longer is better as far as slop, but my guess is shorter arms would be more tolerant.
As far as storage, even long arms may be able to be folded down near the bricks and stay out of the way 
Yup. We can play around and see where we have room for slop and where we don’t. Worst case, a small handful of cheap (fidget spinner level) sealed bearings could be used if rotational tolerances are tight. This should still be much cheaper and easier than a perfectly round, rigid ring and higher quality grooved bearings, and I bet we can cut the bars with the Maslow. Installing and aligning the bars should be pretty simple. Clamping the bars together when drilling holes will ensure that the distance between points is consistent. Alignment of the top mount on the sled would just be a matter of measuring from the router center up, at the same distance as the outside bar’s holes.
It’s so fun nerding out on this stuff with you guys! The inventiveness and collaboration of this community is amazing.
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As @pillageTHENburn states, the individual bars don’t flip from compression to tension. Nevertheless, @ihabfahmy raises a good point. The main reason why you don’t see many linkages in mechanical systems is that they are tricky to get right (well, also they get heavy quickly, but that’s not a big issue here). The key is making sure that there is very little play in the system. You will want a decent bearing that doesn’t have much play, then have the two parts of the bearing securely attached to their respective bars. I’m thinking press fit for the bar connected to the outer ring and clamped by a close-fitting machine screw for the bar connected to the inner ring. You also want bars that won’t flex or stretch.
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One of the side arms, with a pin temporarily secured in the chain pivot point and chucked into the router collet, could be made to accurately position the mounting locations for the pivots on the sled. Or if there were a third, middle arm, identical to the side arms but flipped, it could be attached to the sled after its attachment location was marked with a pin in the collet.
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catching up on this topic
the weight is only to add tension to the chains, not to lower the CG, balance the sled or anything else.
if the sled is heavier, the motors cannot lift it as high, and won’t be able to move it as fast. This isn’t a big deal as you can just move the motors higher and accept lower speeds.
The other issue I see is the need for accuracy in building the pantograph, the base maslow design works well if everything is built and measured precisely, the problems happen when you are off by a few mm in your measurements and it causes larger errors. A pantograph will also have this problem, along with the bars needing to be straight.
more links result in more things that have to be done precisely.
top far angle is 9.7
top near angle is 59.7
spread is 110.6
bottom far angle is 31.4
bottom near angle is 80.7
spread is 67.8
top center angle is 17.2
spread is 145.6
so the narrowest angle needed is ~67.8 degrees and the widest 145.2 so the chains need to move ~77.8 degrees