I’m looking forward to your test results. The theory is that things should be very good except near the bottom corners (where things may end up off by up to 1mm due to chain sag)
But in theory, theory and practice are the same, in practice they are not
so I am very eager to see your results.
So unfortunately I didn’t get very good results. I think I know why and I believe I can fix much of my issues. I’ll let the video do the talking:
My takeaway from this is that I need to add weight to the sled. I have not weighed my sled yet but even by my calculations its at 21lbs, which is the same as the stock sled with only 1 brick. I made my weight system so I can easily add weight, I just need to make a few more bars. I am fairly confident that will take a lot of slop out of the chains. I may also modify my riser setup so that the linkage nuts don’t bind at the lowest corners of the bed.
Right now I have >0.5mm tolerance in the center 2’x2’ of the bed. Out to 4’ left to right its closer to >1mm. The top and out to 6’ is somewhere around 2mm, and beyond that its useless. You can actually see in the farthest out tests that the cut “drifts” towards the slack chain, making me think this is an issue with weight. So I have about a 3’x4’ area in the center of the bed where my cuts are acceptable. For my current projects, that is okay, but I will be improving this. I would like to get 4’x6’ if that’s possible. I also haven’t tried to cut too close to the fence, as it’s a 2x4 and it sits proud of a 3/4" sheet of plywood. I need to make a plywood fence to fix that.
Loosing 8" of motor spacing isn’t helping either. I really wish I had more space for the machine, I would extend the motors as far out as possible to get better results across the entire bed.
As usual, the to-do list grows. At least I enjoy doing the work 
that does look like too little tension on the chain, so adding weight should
help (tilting to closer to vertical may help as well)
I didn’t quite get the question you were asking as you rotated the sled.
David Lang
"i would extend the motors as far out as possible to get better results across the entire bed. " Wouldn’t that increase the chain sag near the edges as the chain would have to be longer? The best option for optimal results seems to be repositioning the work piece near the center
It would mean that there is more chain on the slack side, which would increase
sag, but it also means that the chain on the other side is not as close to
vertical, which means that more of the weight of the sled is available available
to apply force to the slack side and that makes FAR more of a difference than
the added length.
David Lang
The nylock nuts on the back side of the linkage are colliding with my plywood risers. I was wondering if that’s because my machine is smaller or not, but it’s something I will be fixing by changing my riser setup to add in some clearance for the nuts.
Right now positioning all my cuts in the center of the bed until i can correct the chain sag issue. The results are good enough for my needs:
However, when I move and have more space for the machine, I will increase the distance between the motors. That will be me better results across the entire bed as @dlang mentioned above.
ahh, I was expecting a much narrower riser (a 2x4 on edge), I didn’t think about
that.
David Lang
It fits the Maslow very well that M-shaped linkage.
To me it looks like the sled touched the wooden beam at the bottom where the cut went wonky
Got some more tests done last weekend.
I added 20lbs worth of steel weights to the sled. I can now get a good triceps workout every time I attach the sled 
The added weight has helped immensly.
I sacrificed a sheet of CDX to a rigorous tolerance test to see where distortion was the worst:
I numbered each of the squares and listed their tolerances below:
My conclusions:
I need to work on the accuracy at the top of the bed. The chain actually jumped on me during testing and I’ve been revisiting my risers a little. Apparently I had quite a pitch to my chains, and never noticed because I was never in the top left corner of the machine. The squares on this particular test were too high up and the sled also tilted (after it jumped a chain link). I decided to abort the top row and investigate the results I got on the bottom half.
I’m actually pretty okay with the results I saw across the bed. I still haven’t gotten the X-Y calibration right with the linkages, so I’m out somewhere about 1mm consistently, with the X being longer than the Y. On the far right and left squares at 1m out, I expected that I would start seeing distortion on X-Y because of my motor spacing. I can see some of that distortion creeping into the 750mm and even some of the 500mm squares, which really limits me to about 600mm (~12") off center for good accuracy. The Square tolerances reflect that distortion that is happening.
I have also been upgrading the sled:
I replaced the stack o’ washers with Derlin spacers, and also used 1" spacers to clear the nylocks above the now solitary riser panel.
So once I fix the sled toppling over the top of a sheet with a second fence, I should have 1200mm x 1200mm (~4’x4’) of reliable accuracy.
Still working on a video. Editing takes a lot of time.
looks good. I think things will improve significantly once you get the
calibration dialed in.
Please keep posting details.
David Lang
I’ll be honest, I’m not sure I am going about the calibration process correctly. I fiddled with the rotation radius until the X direction was within overall tolerance, ±.5mm from 100mm. I also was trying to get the X-Y tolerance dialed in, but it only seemed to get it close, not perfect. I think at best I had about a 1mm difference. I also tried changing the motor spacing, which got me dialed into .8mm at best. For both of these adjustments, I was making small, incremental changes. I went at about .5mm each time, both above and below the original value to see what would get me close. I’m not at my machine now or I would post my current settings.
I had noticed that the last time I was calibrating, adjusting the distance between mounts value for quadrilateral kinematics actually did have an effect, even though GC is set to triangular kinematics. Is this a method I could use again or would this mess me up even further?
Sorry, thought I had responded to your post in my last reply. It does kinda look that way, doesn’t it? I don’t believe it actually did touch it, however. I set the zero distance so that the edge of the sled was about an inch away from the fence, so the program wouldn’t have moved it any closer than that. Also, the deformation of the test shape would have been the same at the bottom right of the shape as it was at the bottom left.
I’ll be honest, I’m not sure I am going about the calibration process correctly. I fiddled with the rotation radius until the X direction was within overall tolerance, ±.5mm from 100mm. I also was trying to get the X-Y tolerance dialed in, but it only seemed to get it close, not perfect. I think at best I had about a 1mm difference. I also tried changing the motor spacing, which got me dialed into .8mm at best. For both of these adjustments, I was making small, incremental changes. I went at about .5mm each time, both above and below the original value to see what would get me close. I’m not at my machine now or I would post my current settings.
I had noticed that the last time I was calibrating, adjusting the distance between mounts value for quadrilateral kinematics actually did have an effect, even though GC is set to triangular kinematics. Is this a method I could use again or would this mess me up even further?
that sounds like a bug, if those values change something, it’s wrong.
Sorry, thought I had responded to your post in my last reply. It does kinda look that way, doesn’t it? I don’t believe it actually did touch it, however. I set the zero distance so that the edge of the sled was about an inch away from the fence, so the program wouldn’t have moved it any closer than that. Also, the deformation of the test shape would have been the same at the bottom right of the shape as it was at the bottom left.
your motors may not quite be parallel to the bottom rail, that would account for
it hitting on one side and not the other.
I updated the first post of the thread to make it more useful at this point.
I created a paper template to assist in assembling this, could the people who have built these please take a glance and tell me if they think it helps?
top pantograph - alignment drawing.zip (2.8 KB)
In the next few kits I will be including spacers to use between the arms in the center (I need to check how much they are costing me to decide if it’s worth it or not)
My version for bulky routers is in transit and I can’t wait to have it in hand. I am attempting to have a new sled ready before the parcel arrives. Since both mounting holes can not be on the sled, I’ve added 2 alignment holes in the spacer-block. That gave me the idea to search for a quick release system, where the chains remain on the kit and the spacer block is detached, if I need to take the sled off. Any ideas of precision quick release systems? Once I have it in mounted I might try wing-nuts, if they don’t interfere with the movement, or need to sink them down enough.
These work, though I replaced the clevis pin with a piece of wire bent into a keeper pin. You’ll need a master link with each.
Thanks, I was unclear with my description. I attempt to leave the chains on the kit and am looking for quick release bolts for the 2 middle holes (pic) in the spacer-block so I can detach the block from the sled.
I’m now starting to include half links, and I ordered (but didn’t receive in
time to get out in this order) smaller versions of the clips that come with the
maslow that can go through the half links (similar to
https://www.mscdirect.com/product/details/67984922 )
If I was providing the chain, I’d drive out the pin for one link and not use the
master link or half link.
On the top kit, the bolts that the linkages use to connect to the spacer block
do not need to match the fasteners that attach the spacer block to the sled, so
the fact that one of the bolts would be right on the edge of a standard sled
doesn’t really matter much (or you can make a small bump-out on the sled to ease
the attachment)
you don’t really want one bolt going all the way through, as you want the block
to sled to be clamped tightly, while you want the linkage connection to be loose
enough to move.
I didn’t get the pins in time to ship out with the 4 'just before christmas’
kits, but I am worried that the half links may need to be drilled out to make
the pins fit.
the half links I purchased have a smaller hole on one side, and the pin that
comes with the half link has a shoulder on it, so the hole in the half link is
smaller on one side than on the other.
hmm, that’s a harder problem.
you need something that doesn’t allow a lot of motion when locked.
I would look at using pins like
https://www.mscdirect.com/product/details/67931881 through the block
there should be no vertical forces on the linkages, so the fact that there will
be vertical slop should not matter
