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Weights for chain tension

I was having problems with the elastic cord not keeping enough tension on the slack and the chains twisting as a result, I made a quick trip to home depot and got the cloathsline pullys and a couple conduit sweeps, here is the result (works much better, but I need to relocate the end of the chain to handle the full work area)

I didn’t bother relocating the metal pulleys from the old arrangement. the screw in the center is to hold the sled out of the way.

the paracord seems to have no trouble wrapping around the edge of the beam to get to the sweeps attached to the bottom of the beam.

pulley
$2.38 ea https://www.homedepot.com/p/Everbilt-2-1-2-in-Clothesline-Pulley-72692/206094288

conduit
$0.64 ea https://www.homedepot.com/p/Carlon-1-2-in-90-Degree-Schedule-40-PVC-Belled-End-Standard-Radius-Elbow-UA9ADB-CTN/100404151

8 Likes

Good idea and thanks for sharing. Glad to see some pics of your machine…no pantograph linkage?! :wink:

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Excellent set up. The conduit is genius!
How much weight are you running on the end of the para-cord?

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This is a machine I purchased for use at a local hackerspace, I’m just getting
it setup for use and trying to resist making too many changes :slight_smile:

once I get it cutting accurately, I plan to try all the triangulation kits
against each other.

I was having the slack sag badly enough that the sprocket was going below the
bottom of the beam and twisting the chain (causing it to skip), so I had to
address that.

so far I’ve only done one real test cut, I cut a horizontal line across the top
of the foam, it was 12mm from the top on the left, 19mm from the top in the
center, and 17mm from the top on the right :frowning:

with the same firmware, it moves differently from webcontrol and from the holey
triangulation ground control (so apparenetly webcontrol does change a few
values) so I need to track down the bug preventing GC from opening a .nc file so
that I can do another round of calibration with the holey triangulation GC

David Lang

4 Likes

I’m not sure, I think it’s in the 2-4 pound range (a couple scrap pieces of
metal). It’s not enough to trigger backlash near the top of the machine, I
haven’t double-checked near the bottom yet. I plan to replace the metal with a
couple gallon jugs of water at some point.

David Lang

3 Likes

Would additional pullies work in place of the sweeps?

most people who have used weights have used pulleys, but they need 3 for each
side, one to transition from horizontal to vertical, one to switch bach to
horizontal to wrap around the bottom of the top beam, and a thirs to go back to
vertical for the weights to drop down.

the sweeps are cheap, sloppy, and they work :slight_smile:

you don’t want to have the line slip off of a pully, it will either bind up (so
the weight doesn’t move) or the weight will fall freely and the line may hit
something else.

can’t happen with the line tied to pulleys that enclose the chain and then is
fed through the sweep where there is no way to come out.

now, eventually the line will wear, but that will take a lot of time.

David Lang

1 Like

I was thinking of additional pullies that could enclose them. I have had very little problem with my stock bungee solution. I love your solution because it changed so very little and I would like to have more consistent results. No matter where the sled is.
I question, sometimes, why so many people have more problem with the original than I. One theory I have is resistance on stock bearings. I specifically went to the hardware store to find just the right size washers that would allow the bearings to spin and not be mashed into the top beam by a secure screw in each. That is why my brain says “pulley” (as erroneous as it may be).
Do you think resistance at the bearing could be an issue?

I don’t think so, I’ve never seen more slack on one side of the pulley than the
other. What I’ve seen is that everything gets really loose and the chain sags a
LOT. it may be that you put more tension on it, but I would expect that to cause
a bit of inaccuracy in the bottom corners (as the tension on the slack side gets
hight)

try running the sled to a bottom corner, then try and manually move the sprocket
on the long chain to see which side of the gears it’s riding on. As long as it’s
still got more tension on the side towards the sled, you are ok.

David Lang

2 Likes

I used pullys but I only needed 2 per side. I drilled two holes in the top beam and ran rope through it. Then I needed one pully to go from horizontal through the top beam, and another on the back side of the top beam to go from horizontal to vertical. I just attached pavers to each rope and it has worked great.

You can kind’ve see it here:

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just to note, you don’t have to replace the sprockets with the pulleys, I like the pulleys because they don’t fall on the floor if you let things go.