moving over from Throwing my hat in the sled modification ring to try and keep things a little closer to sane there
This is a kit of stainless steel pantograph arms to implement the triangular kinematics.
each kit includes:
2 vertical arms
2 #25 roller chain master links
2 #25 roller chain half links
4 horizontal arms
4 1/4" x 1.5" bolts
4 1/4" nylock nuts
2 1/4" x 3" lag screws
25 1/4" washers
I will be shipping priority mail.
$40 for the US
$55 for Canada/Mexico
$35+ shipping elsewhere
send the payment to firstname.lastname@example.org and be sure to include the address to ship the kit to in the comment on the payment or via a PM
The cad model for these is at Onshape
I exported the dxf from sketch 2 and 4 and sent them to a lasercutting shop
I have made a template to help position this top pantograph - alignment drawing.zip (2.8 KB) that should simplify installation (the basic instructions below assume you do not have the paper template)
to use this kit, take one of the long arms and clamp it to the edge of a 7+inch piece of 2x4 (or 2x3 if that’s the right spacing for your weights). You want one hole close to the end, but it needs to still have strength, so ~1/2" from the end of the 2x4. The closer these holes are to the center line of the wood, the more accurate the next step will be. Then drill 1/4" holes through the metal about a 1/2" into the wood, and switch to a 5/32 or 3/16" drill and drill down as far as your drill will go to make the pilot hole for the lag screws.
Bolt the long arm onto the wood and flip it over so the metal is next to the sled. Put a pointed bit in the router (or a very small bit) and center that bit in the small hole in the arm. Mark where the wood attaches to the sled.
unbolt the metal arm and assemble the pantograph.
At this point there are two ways to do this.
The easy way is to position a long arm like a J and attach two short arms to the top of the long arm. Stack washer, long arm, washer, short arm, washer (and add a second washer if needed), nylock nut. You want things snug enough to not rattle, but loose enough to move freely.
Assemble a second set, but with the bolts facing down.
now assemble the center, arrange the to assemblies with the bolts facing towrds you and the Js facing out. using the lag screws, assemble washer, right horizontal arm, washer, left horizontal arm, washer onto the lag screw and attach into the wood.
Once you have done this for both horizontal arms, attach the hunk of 2x4 to the sled. If everything was centered on the 2x4 edge, you should be able to just attach it at the marks you made earlier (if the holes weren’t centered on the wood flipping it over will create some errors)
attach the chains to the tips of the Js with the included master links
The result should look like this (note the stacking order of the parts)
This has an offset of one chain from the other of 3/16"
If this bothers you, you can add additional washers and stack it differently. One one side make the end horizontal bar above the vertical and the middle one below, and on the other side reverse these. In the center, add washers to put 3/16 (+1 washer) between the horizontal arms that are on one lag screw. This will put the chains at exactly the same distance from the sled.