if you read the process I used, where the chain attachment point is positioned at the center of the sled before drilling the other to holes, that will ensure that they are exactly the correct length
actually, I’m thinking that it won’t cause errors.
if you have three holes, with 4" from the first to the middle, 6" from the second to the third, and your holes in the sled match (4" from the bit to the hole on one side, 6" from the bit to the hole on the other side), I think everything will match up and “just work”
If I am correct in thinking this, it makes life much easier (if the hole on one side is off a bit, it doesn’t matter, as long as it’s consistent between the sled and the arm), if it does actually matter, it means we need to be very precise, before we have precision tools to work with
if you think about the triangles created, if you are in the center (so both sides have the same angle, and you are near the bottom, a small error in the length of the chain doesn’t make a lot of difference to the vertical distance. But if you are near the top (where the angle is small), a small difference in the length translates to a large difference in the vertical distance.
I dont’ understand your statement that you have 3 contact points on the rotational bearings? maybe you can make another youtube video showing where there bearings are at? Why would a 1’ thick piece of steel bend with only 60 lbs of force on it? from yoru photos, it looks like you just have holes drilled through the wood arms with a bolt through it. is that what you consider a bearing?
Another way to correctly place the center pivot points on the 3-Bar Top Mount is to use one of the side arms as a gauge, with its chain pivot point A keyed to a mandrel chucked in the router collet. That places the other two holes of the arm at exactly the correct distances from the center.
sorry, my prior reply wasn’t answering the right question, I answered the non-centered hole instead of the offset mounts.
If we can do offset mounts, then it is easy to build a 45 degree 3-bar approach that doesn’t interfere with anything (look at the top 4 holes in the sled image I posted)
It is a little harder, but not very.
breaking out high school geometry (who said you would never use that stuff )
take a compass and draw a circle with a 6" radius. Draw two radial lines at ~± 45 degrees (exact angle isn’t critical, the fact that they are radial does). where this line intersects the circle, position the point of a compass set to 5" and mark where that crosses the circle. The resulting two points will be exactly perpendicular to the radial line and 9.091" apart.
See how three pieces of wood come together to make the joint. My concern is that if only two pieces of wood were used, a lot of force would be trying to bend that small bolt. In this design, the load is balanced on both ends of the bolt.
Sorry, I don’t feel like I am explaining this well.
the three holes must be exactly in line, and the chain needs room to swing. I plan to attach the chain to a metal bar (3/16" thick) by drilling a hole and then carving away a little metal to give the chain room to swing. As the sled is not rotating, it needs to be able to swing from ~10 degrees to ~80 degrees. So if this link is mounted at 45 degrees, ± 45 degrees of swing will work, so we don’t need to carve a lot away.
The identical bar could be used for the horizontal links.
I hope that 3/16 is thick enough to not flex in the vertical direction, if it’s not, then we would need to go with angle metal to start with (the horizontal bars can have the angle pointing away from the workpiece, while the vertical bars have the angle pointing towards the workpiece, so we never have to carve away part of the angle)
Thank you! It’s probably missing stuff and very well could contain errors, I made it in a hurry. And with the size of the images I decided to leave out some measurements/ratios. But if anyone wants to see bigger images it’s all vector so I can make them whatever size you want.
The test I made is a 3-Bar Balanced and it seems to work just great. Are you thinking it’s going to hit the router? I used 10" bars and it appears to have plenty of room but I am not using an official Maslow design, I just cut a circle of wood… If bar A is hitting when the sled is in its most extreme spot (low and to the side) then just lengthen B and C until it no longer hits… Once I have actual sled and router dimensions figured out I can calculate the actual minimum arm lengths then we can simply compare each design footprint to find the most compact (if that’s your goal).
I don’t think the sled would need to be bigger, the distance between anchor points (which is the length of A) only needs to be enough to clear the router when the sled is in extremes. B and C can technically stick out much wider than the sled and it will still work.
In my drawings I did keep the chain-tip-arc consistent between the last three designs, with that in mind it looks like the 3-Bar 45˚ might actually be the most compact (and we’ve already seen that working on a real Maslow!)
I am wondering if there’s an existing linkage in the world that would come at the right size with bushings already installed… something like a replacement windshield wiper linkage or something like that. Might find something cheap, precise, and pre-made… who knows?
remember, nothing says that the pivots need to be small bolts, use larger ones that have a smooth shoulder on them (they start at 1/4", but going to something larger will make the pivots stronger and last longer)
That won’t work (if you want accurate cuts). Assuming an equilateral linkage, the arc traced by any point on the “vertical” bars is always centered on a corresponding point between the pivots if the other two bars. This means your chain triangle will have a truncated point and it will suffer from the same problems of the original sled design with fixed chain attachments.
Yeah, that is where I think it fails. As I learned the actual diameter of the router is probably more like 7 inches. Draw a 7 inch diameter circle and then position a line that is 10 degrees from vertical, how far away from the circle’s center do you have to be before that line falls outside the circle. I think it is more than 12 inches, and that is assuming a line without any width, make that arm 1 inch wide and you are even farther away. The sled is only like 18 inches in diameter.
Yeah, I agree, I am skeptical that this would work. Going back to what you just taught me 30 minutes ago, doesn’t this suffer from the same problem as mis-measuring the distance to the chains?
From dead center, as the sled rises in the Y axis, the arms cause the chain mounting point to get farther and farther from the center, causing the sled to rise a greater distance than expected.
The blue dots are your chain attachments, they can be translated along their respective linkages but the center of their arcs (the red dots) will always fall on the grey dotted line. (again, this assumes a parallelogram linkage)
You want both red dots to become one single red dot that resides at the very center of your router bit.
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