I didn’t want to use plain steel because we aren’t going to be able to paint the
result, and I don’t want the arms to rust when the machines sit idle for lengthy
times (as is going to be common for hobbiest machines)
from what this shop has told me about the costs, the material cost is only ~1/4
of the total cost, so going from stainless to something cheeper doesn’t help
that much. This is ~180 sq in of 3/16" plate (depending on nesting)
I’ll e-mail that guy and see what they will charge for this (and remember,
everything I’ve posted in onshape is available to the public, so anyone can grab
my design and get it made locally for them)
for anyone who cares, this is being ordered through Industrial Metal Supply in
southern california. They suggested laser cutting to handle the small (2mm) hole
for the chain master link.
Yes, this is just for the six arms as I showed in Throwing my hat in the sled modification ring - #332 by dlang These would get bolted to the edge of a 2x4 with holes 6" apart (the lower hole 3" from the center of the sled, so the outer hole is on the very edge of the sled and you may want to slightly enlarge the sled there, but remember, the hole on the top where the arms attach doesn’t have to go all the way through). This means that almost all the chain forces act only against this 2x4. If we find that I’m wrong, I’d see about getting a piece of square tube and get holes cut in it to mate up with the arms.
I am not planning to make metal sleds, I wouldn’t trust them not to mark up the wood.
I love the creativity of these different designs but I cannot help but wonder if the metal ring is Occam’s solution - simpler is probably the better approach.
I just got my permanent frame pieces cut and sanded, once it’s together and I’m consistently running parts I’m going to swing by SailRite and pick up a ring and some blocks. I’d like to try the ring method too.
I wouldn’t think beveled (file or hand grinder) edge stainless would cause a marking problem, but also don’t think it’s worth the effort.
2x4 steel tubing’s pretty easy to find in the local welding shop’s scrap bin but also likely overkill. Is there any advantage to doubling up any of the arms to combat twisting?
As a random thought, shoulder bolts might do it if they’re available in the right length. Had an expensive nyloc nut failure on a Bobcat and avoid those. Jam nuts could work, but they’re finicky to adjust right
with a balanced sled, neither design resists rotation, they both depend on the weights at the bottom of the sled to keep it from rotating.
I still haven’t cleaned out my garage enough to build my machine (and I wreaked a truck a week ago, so I have more stuff to store now as I part it out), but I would still love to have someone try a balanced sled with one fixed and one flexible chain. If that works, it would make things much easier and cheaper.
I would check with multiple vendors! We take over 100 dollars per hour in our workshop and come below the price with 20x5mm flat bar AISI 304, precision drilled and rounded ends
Sorry I sort of disappeared for a sec. Life has been pretty hectic recently.
I have further refined my files for the laser-cut wood kit that I designed and I think I solved the chain connection bracket issue (I plan to test it tomorrow) and I hope to have them available this week! After prototyping I’ve simplified things a little too, they seem super solid and quite accurate. I can’t wait to get some kits into the hands of people with running machines to see how they perform in real life!
Thank you @dlang for all the awesome work you’re putting into this!
In my wooden tests of the top-mounted version I found that there was reduced torsion on the joints and overall less (detectable) slop when I added a second bar to the horizontal members. I know it adds cost in parts and cut time (especially for metal versions) but the benefits might outweigh those costs. I’ve been pouring most of my time into designing and sourcing cheap parts for the 45˚ version I’m making but I’ve also been messing with some re-designs of both the top-mounted version (with shaped bars) and a sort of hybrid version that might be a great solution if it works. The 45˚ design has been proven to work on a real Maslow with a ridgid router, Z-axis control, and dust collection so I focused my attention there first so people can have something to use asap. After I get these available to whoever wants them I’ll continue tweaking and making things better
horizontal bars are easy, two holes at the same distance (~5.5 in apart), that are a snug fit to 1/4" bolt shoulders. I think the 20mm bar will work.
vertical bars have two 1/4" holes 6" apart, and then a 3/32" hole 3" further down. around the 3/32" hole the metal has to be cut to a 3mm radius,and there needs to be a notch up towards the other holes that allows the chain to angle up to only 10 degrees from the line of the holes. 5mm is just a little two thick, so it will need to be ground down about 1/4mm for a radius of 4mm around the hole… you probably want to start out with stock 25-30mm wide so that the notch doesn’t weaken the bar too much.
yes can do if desired. will look into costs. I work as an industry tool maker so have access to everything possible of machining equipment just lacking time to do all I want after work
Yes, as long as the compression and tension members (the “horizontal” parts) can handle the forces this is a very good solution. If the spacing provides room for the chain to move and not bind this solves the difficult chain attachment problem. I made one like this from wood and I like it, but with 1/4" thick plywood I’m not convinced that the single-ply compression member will not twist or flex (it can be laminated with more layers, which solves the flexing problems). I still think it’s a totally great option!
I like your drawing!
-Logan
That could work, I would be a little nervous that it makes things more sensitive to chain alignment, but if you used thick enough material to give the chain lots of room, it could work. you would probably need a half inch or more between them (minimum 10mm to clear the links, more to handle anything else)
the parts would have to be cut precisely to make sure the tiny holes line up without error.
part of me hates the idea of depending on a 2mm bolt over that sort of distance. It is in double shear, but there is going to be a bit of space between the arms and the chain that’s filled with spacers (2-4mm per side)
it’s worth looking into to see if the increased material cost is made up for by a decreased manufacturing cost. If the parts are laser cut, the notch doesn’t add much to the manufacturing costs.
Jakrro[1]
September 16
better with 4 arms on each side instead of notch? for strength wear
and production costs> Pantograph
Visit Topic[2] or reply to this email to respond.
In Reply To
dlang[3]
September 16
here are the dxf files for the arms I’m having made. pantograph.zip[4]
(16.9 KB)>
Visit Topic[5] or reply to this email to respond.
Each link in the chain itself depends on a pin!
Just use a sled attachment pin of the same or greater strength
(material, diameter, heat treatment, etc…) as the lonk pins and there
should be no pin strength worries since if the attachment pin shears,
then the pins holding the chain links together would also shear.
That is exactly the approach that I have been taking. The metal of the bar is
just the right thickness to use a master link to connect the chain to the bar.
But if you don’t do that, and instead want the chain to be inbetween two bars,
you now have to have a longer pin to span the gap between the chain and the bar.
Instead of the pin just being between two pieces of metal that are against each
other, it needs to span a 2-4mm gap between the metal of the chain and the metal
of the bar. Because of this, the bolt actually needs to be stronger than the
normal pins.
Bolts that you get are not going to be hardened, and they aren’t going to be
smooth in the middle where the chain is rubbing them. This will eventually
wearthe chain or the bolt, but probably not fast enough to be a problem
(especially compared to a wood/nylon version ).
).