Chain tensioning spool

that is a super clean setup. did you weight the cords on the back side of the stand or is the sling on the top bungee to move when the sled is in the lower corners?

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Cool idea using the measuring tapes. If you live in the US and you have a Harbor Freight nearby, they often (of course, not now, it never fails…) have 25 foot tapes as freebies if you buy anything. If you ever shop there check out https://www.hfqpdb.com/ before you go and there is almost always a 20% off coupon and a freebie to be had.

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Matthew,

I wish there were freebies like this where I live, but no - I had to pay 10 euro in cold, hard cash for each tape. Sometimes they have them on sale for 5 euro apiece.

I would warn against 25 ft (7.6 meter) tape though. I started experimenting with a single spring from one of those, and it was too weak. I ended up using two springs from a 33 ft (10 meter) tapes that are 25 mm (1 in) wide. There are wider 1 1/2 inch by 33 feet tapes available, so if you can have them cheap, maybe even better candidates.

Ultimately I’d like to find a cheap single spring with sufficient power and number of rotations it can deliver. For my design, 10 rotations are needed to wind the full length of the chain (14 feet), and a few more to pre-tension the device. Springs from retractable cords and garden hoses look promising, but I haven’t had a chance to get one of these.

If we find a good spring, the spring assembly of the winder can be made even more compact.

Emil

increasing the diameter of the winder will reduce the number of turns needed. A
small increase in diameter may have a significant change in the number of turns
needed (as the inner windings hold far less chain than the outer ones.

I’ll also note that you may be able to get away with only one side of the chain
holder, the chain should nest on itself fairly easily (although it will be a
very ugly tangle if you let it get out of control)

ho many turns of tension do you get from a 25 and 33’ tape measure spool?

David Lang

David,

Correct, it is possible to play with the internal diameter, and the current one (78 millimeter - not 70 as I said in the video) is coincidental. But rather a lucky coincidence, because:

  • make it smaller, and you will need more turns, and have less space for the inside chain end pin;
  • make it larger, and you will have to slightly increase the outer size of the spool, and (more importantly) you get less pull because of the increased leverage.

[One side chain holder will most likely require a bearing sitting in a thicker material, because the chain spool is heavy and will tend to tilt the axle. Currently the shaft is sitting on two points sufficiently far apart to counterbalance - will not have this in a narrower design. - whoops, realized you meant something different. I wouldn’t risk winding the chain on a spool without support on both sides.]

I was getting about 10 usable (that is, without the spring screeching at the limit) turns from a 25’ tape spring, and about 18 from 33’. Must note that partly the difference comes from an improved catch for the inside end of the spring - I reduced the diameter of the catch for the 33’ version, shown on the video, which resulted in the spring winding better onto the shaft.

Not saying it’s impossible to build with 25’ tape measure springs, but definitely easier to get it right at the first attempt with larger 33’ ones.

Emil

what about a lawnmower or trimmer pull-cord retracter spring?

Will not work. I ordered a few hoping I can use them. Can get maybe just 5 turns from such spring, which means much larger spool. And when you increase the spool diameter, you lose the force of the pull.

It is not surprising though. With the lawnmower cord, it needs to retract just 5 feet or so.

If you compare the springs, the tape measure spring has 40 turns of 0.15 millimeter thick spring, while the pull-cord spring has about 10 turns of much thicker one.

Garden hoses and retractable power cords (e.g. vacuum cleaners) are my bet.

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Perhaps we can find something here?

Expensive…

I’d look around here (not endorsing this particular one, just as an example):

Looking at how narrow these springs are, may need a pair.

This is another reason why open source projects are so much fun to read about, VJSV fantastic idea/proof of concept build. really enjoyed looking at your work.

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Hello there, would it be ok to share some plans and measure please ?

I do like the concept so much and I want to try it with a custom made flat coil spring.
a Custom made spring can even be cheaper than buying 4 quality measure tapes… with a lifecycle of 25000.

Here are the measures I understood so far :
Spool dimensions : inside 78mm
Spool dimensions : outise ?? mm
target : 5 to 6m of effective winding.
fatigue life cycle of the springs : 25000
spring dimensions = ???
Why going with 2 springs when you can go with only 1, thicker, stronger, longer ?

Here are the data I have no clue on what to choose from :
Spring Force : about 22 to 26N = overkill ? I took the same values as “counter-weights” which are a LOT more than a measure tape spring can deliver…or even a retractable power cord… but again I have no clues… and I hope the clever guys will help lol.

I found those ones, with so much choice I am just lost.
https://www.asraymond.com/constant-force-spring/CF0550583.
Maybe It is better to order several value to play around and check.

Also, I one of you guys can come up with a hand drawing of th general principle,
where and how to place the pins, etc… Also thinking on mounting the spool around a needle bearing can help to “smooth” operations.

If forces from the router+sled gravity weight and springs are “about” the same/equal, will motors perform quicker and better with less stress/load ?

Great! Let me find time to post some measurements and comments. Fingers crossed, will do over the weekend.

That’s very cool !
Thumbs up !

Hi olbe, sorry for being a week late. Would these 80’s-style photocopies work for you? I’m too inept to produce proper mechanical drawings. Happy to answer questions.

Emil

VJSV Maslow chain spool v1 base.pdf (1.0 MB)

VJSV Maslow chain spool v1 spool and center.pdf (1.7 MB) VJSV Maslow chain spool v1 spool and fixings.pdf (1.8 MB)

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