Improved chain tensioning for top beam configuration

Joining the party: today I added a 30 inch bungee from Harbor Freight. Moved nail higher up to a block to get out of way. Added middle block with long hook to keep tension cable outwards, which helps keep outfeed chain in alignment with infeed chain. Co-planar for the win! Will put in some hours and report back here.

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The 26 inch HF bungee (not measuring hooks) idled at 38 inches and was pulled to whopping 58 inches at the farthest point - bottom middle. I wore safety goggles and face mask because this is past safe operating conditions, so I will replace with something else soon. However this bungee and moving chains to be co-planar resolved my issue. Two failed cuts in same area with chain bunching and wrapping. But this third cut was great! The top right gear “rode up” a little, but the chain never jumped. I just used a “pitch and angle locator” device and measured left to be 14, right to be 18. So my top beam is likely twisted. I feel like I should go buy a new one, and a 4x4 at that. Thoughts?

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Here is the result: All the red circles were failures. Right side circles was chain bunching. After bungee, instant fix and perfect square cut. Love it!

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For the price of a 10 foot 4x4 you could get a 10 foot piece of unistrut (or the big box store equivalent). No worries about twisting, much lighter weight.

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Yeah I guess that makes the most sense. Looked at a few of the uni strut designs on here. Appears easy to mount motors with bolts and washers as most people have it in a configuration with slots on the top and bottom.

But I didn’t see any wooden frames (let alone Bar’s Bolt together) with just a metal top beam. If you have seen pictures of any on here please share. Otherwise I may just have to hash this out with a bunch of L brackets

You can check out mine here

It’s wall mounted, but it would certainly be easy enough to adapt to have legs

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What I am planning to do is to use a pair of 2484 bracket attached to the legs
with short (1’ or less) lengths of unistrut across the top of these, with the
unistrut top beam attached to the short lengths.

This will let me eaily adjust how far out from the frame the top beam is to
handle different material thicknesses (I want to be able to work on both sheets
of aluminum, and the edges of 2x4s)

https://www.globalindustrial.com/p/storage/struts-and-framing/unistrut/unistrut-1-58-90-gusseted-fitting-p2484eg-7-hole-electro-galvanized?infoParam.campaignId=T9F&gclid=EAIaIQobChMI-oPhk9WN2wIVh4qzCh2JXQIlEAYYASABEgKKNfD_BwE

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You guys are much further along than me, so thank you for sharing and giving direction. I used a washer to shim up my right motor. Checked both motors and sled angles, all measure 15 degrees. No noticeable chain Riding or Skipping when moving. Sidebar: Previously cut circle on top left measured 13 3/8 by 12 3/4. Today’s circle cut in bottom middle measured 13 1/4 by 13 1/4 :slight_smile:

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You sir, are a genius. That is exactly what I needed to fix the flex issue on my top beam. I ran out this morning and picked up a length and installed it.

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You are so right. Cutting in the very top middle, my ~30" bungee that resolved lower issue was now not tight enough to keep tension. Not sure if @bar is still using new paracord so I will be switching this maslow to pulleys and weights like our other maslow, except routing behind in middle.

I am still using the new thicker cord. I haven’t had any issues, but I will keep a closer eye on it at the top center

ChuckC, If you are still looking for a timber frame with unistrut top bar, check this out,
I copied it and it works really well, Handy to have some sheet storage behind!

https://www.summet.com/blog/2018/03/03/long-board-sheet-storage-maslow-cnc-frame/

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Used a bit of bungee, cut and just zip tied to length.
And a couple of idle cogs.

No chain skip.

Works perfect (for now) ha

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for those people using weights, how heavy do you need to go to get the chain under control?

you really don’t want to have to go heavier than the tension on the chain (around 3 pounds), is that enough to keep the chain under control?

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@dlang if chains are in perfect condition, pulleys spin freely, rope not dragging on anything to cause friction, not using too many pulleys: about 5lbs for each chain. If any links have imperfection and “stick” sometimes, increasing weight to 9lbs completely eliminates problem.

I have about 20 cutting hours on current counter weight setup with our wood Maslow, not 1 skip. Happy to report it has worked so well, we started adding same system to our metal Maslow :smiley:


(Only outstanding issue is bottom corners, work in progress)

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hmm, since the tension on a stock system is only just over 3 pounds, this means
that you are going through 0 tension and backlash comes into play in the bottom
corners.

going to a 12’ beam increases this minimum force to 6.4 pounds so the 5 pound
weight would work and avoid this problem.

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Hey Bar,

What is the length of the new 3/16" bungee you are using?

Thanks!

adamdj

I believe that they are 145cm

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Has anyone modified the bolt through design for a unistrut top beam yet? I need to do it relatively soon, and I just wanted to check and see if anyone has a hardware list.

For those using the plastic spacer on the motor mount to keep the chain tight to the sprocket can you tell me what length of scew bolt you used to attach the spacer to the motor through the motor mount. Thanks if you can.

@Cbolt360