Linkage kits are now available! 🎉

Mounting bolts, bushings, and washers are provided but the standoff blocks are not included because their length is an unknown variable that depends on sled size, router weight/brand, z-axis (or not), brick weight, etc. etc. They should be blocked out to match your system’s center of gravity. The method I used to mount them worked really well and is easy to implement, I will put a more full description with pictures in the instructions (which I am writing right this moment) but briefly:

Mark and drill 4 mounting holes in the sled.
Cut 4 blocks to your desired length.
Drill a hole through each block.
Using the provided bolts as guides, glue the blocks to the sled.
The linkages mount to the sled using through-bolts and nylock nuts (provided).

Yes, that’s exactly what they do, and they work well but they’re a little bulky visually. I’m trying to figure out a slick metal U bracket solution but so far this is the most realistic (and inexpensive) solution.

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Just picked up the last one :slight_smile:
Would it not be possible to provide an SVG for cutting a new sled (assuming the rigid router a lot of us are using?)

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That’s a great idea! I’ll try to put something together. I’ll make sure it has spots for the linkage attachments too.
I’m cutting more kits tomorrow so they’ll be available again! Thanks!

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I put together some comprehensive (hopefully) instructions for assembling the linkage kits: Linkage Instructions

I’ll edit, add, and fix things as they come up. For those of you who are curious what the kit looks like there are detailed descriptions and pictures in that link.

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Beautiful write up!

Feel free to host that type of thing on the wiki if you want. I know it’s not an ‘official’ part of the kit, but as long as it’s on it’s own page it should be fine. It’s also good where it is :grin:

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Update!
I did some stress testing tonight! I weighed down my sled with 75 pounds of weight and put the chains at 124˚ internal angle (emulating a near-top scenario). I measured (and double checked with math) 80 pounds of tension in each chain!
I used inline spring scales on the chains and got 80 pounds.
I then did the math to double check that: 75lb x 0.5/cos(124˚ x 0.5) and got 79.89lbs

There were zero breaks, cracks, or problems with the linkages! I think this proves that not only will the linkages handle the normal forces (which will max out at around 30-40 pounds per chain assuming a 20 pound sled) but that this system can handle rogue spikes in the system and that they hold up fine well past the forces the motors are even capable of (which is about 66 pounds per chain).

There are some on the forums who think the chains will regularly see 66 pounds of force, while I haven’t been able to get anyone to prove that to me this should still help alleviate fears even for them. The motors should stall long before the linkages break.

I had planned to stress the system to it’s breaking point but I was not ready for 75 pounds to come crashing to the floor. I still may break things to find their failure points but I think I will do it one component at time in a more controlled setting.

In other news, the first batch of linkage kits is in the mail! I’m waiting on some of the specialty hardware parts that should get here later this week to send out a second batch. The demand for kits was a little higher than I expected so I didn’t order enough parts the first time. Also, my wood supplier ran completely out of 1/4" baltic birch, this was the first time I had seen that happen in 5 years buying wood from them! I bought more wood yesterday but have quite a bit of laser cutting to do now. So, needless to say I am a little behind the curve but I am catching up and will get things finished and in the mail asap!

One more conclusion from the evening: I probably would have loved taking trigonometry…

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OT, but what make/power laser do you have?

Put a temporary shelf under the sled so the sled only drops a few inches, then load them to the breaking point

That’s a lot of kits if you used up your supplier’s inventory…

Would not worry about breaking, the weakest point in linkage as I see it is that you pull the splinter you have attached the chain through the hole. It’s the wear over time that worries me the most

I thought about just moving everything closer to the floor (since I’m not actually using motors yet, basically just anchors into the wall at this point). 75 pounds is a lot, I sort of ran out of ways to safely add weight too. I can easily remedy this and test to failure, I just didn’t do it last night. I think it would be best to test the system as a whole (instead of modularly) if possible.

I did not use up their wood inventory, I haven’t sold that many! I went to buy wood and they were completely out! Thankfully I had some on hand still but I’ve since burned through that. I wasn’t prepared for more than about 5-10 kits (I know, that was a very poor estimate - my wife even told me it wasn’t enough), I ended up getting orders for more than that so I’m playing catch up. I just didn’t want to end up with a couple hundred dollars of unusable hardware sitting on a shelf in my garage…

I cut most of these on a “generic” Chinese laser using a Reci 100W water cooled CO2 tube. The bed size is about 24" x 40". I also use a Full Spectrum 90W (also Reci water cooled CO2) with a 35"x47" bed. The Full Spectrum is not at my house though - I help run and manage that laser cutter at a local maker space. The Full Spectrum software is MUCH better than the “LaserDRW” software that came with the Chinese laser but the higher wattage and accessibility are really nice. There are ways to upgrade/change motherboards and in-turn software but I have not really dug into it. I believe there are even some really nice open-source software solutions now (for people who have grown frustrated trying to understand and use poorly translated Chinese software).

On the 100W I cut this 1/4" 7-ply birch at 65% power and 15mm/sec. I “etch” (they are vector paths, not rastering) the letters at 6% power and 20mm/sec. The Full Spectrum allows me to cut open paths (imagine the letter C) however the laserDRW software closes all open paths with a cut line (so the letter C looks more like an O with a flat side). This is ridiculous in my opinion and actually almost doubles the time required to cut these kits (because parts can not share a cut line). I still feel like there must be a solution but I have not been able to figure it out yet.
I know that’s more info than you asked for… sorry about that :slight_smile:
-Logan

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Are you talking about pulling the cotter pin through the hole? I definitely don’t think that will happen. I tested that piece alone and it didn’t break with 150 pounds. When I was testing it I wan’t at home and only had 150 measurable pounds to hang on it. The forces on that pin are shear, it would take a LOT to break or bend it through the hole; the tolerances there in intentionally tight. I’m pretty sure the wood will break elsewhere (maybe even motor mounts) before that pin could be pulled through the hole.

Wear could be a thing, but I think it would take a LOT of use to become a problem. And if it ever did become a problem you could adjust for it by moving the router up on the sled to account for it. Even with noticeable wear the triangulation kinematics should hold true (but the “tip of the triangle” will move up above the router bit). Remember, these linkage arms are only moving a handful of degrees, it’s not like a spinning axle. Graphite might even be an idea worth trying if someone is worried about friction wearing down surfaces… with the 7-ply plywood you have 21 alternating layers of grain direction which should help reduce wear greatly.

As usual I could be totally wrong on all of this, these are just my educated guesses/hypotheses.

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Not even close. Not to sidetrack the topic too much (the audience snickers, knowing the easily sidetracked moose), but take a look at Scorchworks Laser Whisperer for the m2nano controller. I have a cheap K40 with laserdrw, with a replacement C3D controller (Smoothieware or grbl laser) sitting there waiting to be installed among with a stack of other mods. There’s G+ groups for the K40, Cohesion 3D, and the Laserweb control software.

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It’s not that I expect the machine to hit that 66 pound load regularly, it’s the
worrier in me wanting to be sure that it has no problems even when that does
happen :slight_smile:

is there any measureable flex under that load?

David Lang

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I totally hear ya, that’s why I even did stress tests. My gut says it should be fine but my worrier says “you better test it bro” (my worrier sounds like a pushy frat-boy sometimes).

I’m going to say “maybe”, but it was really hard to tell. From the front there was nothing perceivable so I sighted down the bar that the chain attaches to; even then I couldn’t really see any flex so I pulled down hard on the sled (which already had 75 pounds) Accounting for the chain angle I probably had well over 95 pounds of force on each chain (Since I was the one adding the force I couldn’t actually measure it). Anyway, I took this picture at that moment because that’s exactly what I was looking for:


If you look closely there’s a little white line that I added, the line is perfectly straight. It’s hard to tell if the perceived flex in this image is due to the depth of field from my camera or if it’s real. I imagine that at least some of it is real. Even if it is real this is far more force than the system should ever experience (even under extreme conditions).
I personally believe that any spikes in the forces in the system will be just that, spikes. They will be extremely momentary and will happen at moments like when the sled changes directions, which means that they will not affect overall accuracy. I also agree that there probably will be spikes! Any extreme forces in the system won’t be constant though.

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A couple of assembly notes/warnings or whatever…

First off… great job! Good directions and all the parts are top notch.

But, so that maybe somebody else won’t make the same mistakes I did:

  1. Take the handles off the router… I hadn’t. It might be possible to make it all clear, but that’s a mess. Also, do that before you put the linkages in the way :slight_smile:

  2. Somehow find a place to put the linkage points on the sled that don’t cause you to drill through into your z-axis mount. I actually caught it before drill hit metal, but… I’m still struggling to get the z-axis mounted so that the linkage fits with it’s support block and still clears the router. I’m going to have to modify the support block on that side.

Part of #2 comes from the fact that I did as suggested in the instructions and used a ‘B’ linkage bar to measure from the router center point. By the time I found I had a conflict, that linkage was all glued and not nearly as accessible, so I didn’t want to remeasure it all.

My current plan is to fake all this up so that it works reasonably well and use the machine to cut a new sled. This one I cut out by hand and have been hacking on anyhow. I’ll use CAD/Maslow to re-measure this stuff so that things are clear.

Next up (sorry)… one design issue I see… the chain attachment points. Strong enough, no problem, and neat idea. But I’m afraid they are fiddly to disconnect. So far I’ve had a fair number of times I want to drop the router off the ends of the chains to do whatever. That’s easy with the stock design, not so much with this.

Please don’t take that as criticism… especially since you did this without a real unit to play with :slight_smile: - Just an observation. It may be as easy as changing to a larger/longer cotter pin so that I can reach them without pliers (just thought of that).

Anyhow, here’s a picture…

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Thank you so much for your feedback @bdillahu! This is fantastic!

I was a little worried about the ease (or lack there of ease) of removing chain attachments, I didn’t really know how often people actually remove the sled but assumed this might be a problem. (I actually found disconnecting the entire clevis by removing the barrel bolt was easier) The cotter pins I sent with the first 10-15 kits were those short ones only because I literally had them in my garage and I was having a hard time finding a good source for longer ones - I’m sorry about that. When I re-ordered hardware I found longer cotter pins; so all the kits from about #16 on have longer pins. The new pins are a little longer than an inch. Also, on that note, I designed those clevises with the intent that a longer pin could be used, that’s why they have that U shaped cutout. I even considered using a longer straight pin, like 2" long so it can be easily grabbed (A properly sized finish nail would even work…). If the fit was right there’d be little chance of it working it’s way out accidentally.

My original goal was to use a hairpin cotter pin like the ones Maslow ships with, but it needs to fit through the chain sideways so the diameter needs to be less than .098". I was just having a hard time sourcing those so far, but I have not given up! I’m sorry for any frustration those short pins have caused anyone!

Thanks again for the feedback! I will try to improve the instructions to account for the z-axis problem you ran into as well.

-Logan

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As you say, a nail may be the best solution :slight_smile:

I’m probably missing the obvious, but why can’t/shouldn’t we just use the Maslow style and have it go in the opposite direction (rotated 90deg). I’m not sure if it would fit or not (not at the machine right now), but looks like it would/could work.

Sounds good…

Looking forward to getting this dialed in and really put the thing to some use…

When I initially tested this design I found that the Maslow hairpin cotter pin inserted in the other direction would hit the crossbar when the sled was at extremes. But I then lengthened the clevises a bit and (embarrassingly) I don’t think I re-tested the clearance :flushed:! It might actually clear! A smaller pin in that direction almost certainly would clear, and would probably be much easier to add/remove than the current design.

Honestly any pin/nail/wire that doesn’t hit the crossbars will work. Feel free to experiment! Depending on where the pin goes through the chain the measurement from the bit to the chain will change by a couple mm but that’s not a problem if you measure right.

I’ll try to check that clearance when I get home tonight and report back.

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Looking at it, I think it would… or a smaller pin that direction would certainly be easier. Should have thought of that last night when I posted it, but was tired and it didn’t cross my mind :slight_smile:

If it works, might save you sourcing some pins for future kits…

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Ha! It’s okay, I should have tested it again before I committed to the cotter pin idea! I have no excuse!

I mentioned it in the other thread, but they do seem to clear. Note I turned them on their “side” instead of up and down… that allowed a little more clearance, but I think it would be fine either way.

They are certainly easier to get ahold of :slight_smile:

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