the bungee is tight when the sled is in the home position and will loosen somewhat when it goes up, but not too much. notice the screw just to the left of the motor. If I take the chain off the motor, it hangs on that This was my first frame and it no longer exists. it took up too much space in my garage, so I made one on wheels and then I made the one now that folds down from the ceiling.
both chain configurations are under. The first setup has the bungee that I shortened and wrapped from the chain around a pulley and over back and behind the motor. It would sag when the sled was in the upper corner close to the sagging chain. It skipped one tooth only one time of the many things I cut with it. The second one has as hanging 3 lb weight. It has wrapped a chain once when at the upper center position, and if the bike is in the wrong spot it will catch on it. but other than that, seems to be fine. The second frame is s 4’x6’ cutting area, so is smaller as well. You can really do whatever as long as the chains can moved freely and maintain tension of about 3-7 lbs. Too much and when the motor switches direction, the slop in the gear lash in the motor may cause inaccuracies.
Having a constant feeding angle (B) ensures more chain-sprocket engagement and NO chain sideways or front/back oscillations - longer chain hanging in air could lead to unwanted oscillations and misalignment while feeding which will increase the chances of the chain skipping a sprocket tooth or coming off of it
The nylon roller is 11 inches from the left edge to allow enough room for the chain (A) to pivot (E) - especially when the sled is at the top corners - 1 inch from the top is ideal as it’s high enough but no to close to the top edge to splice the wood when installing it.
Putting the s-hook on the front face instead nailing the chain end on top of the beam as other set-ups keeps the entire chain in on plane - not forcing it sideways (which is not good for any chain) and not grinding the edge of the beam.
Having C & D reversed on the idler will leave the chain free hanging from the sprocket which is not ideal for the reasons aforementioned.
Counterweight is a good way to keep constant pull on the chain slack and is very easy to implement if wanted - Just keeping everything as it is, put two screw eye in the middle of the front face (top beam) then loop the cords from the idlers down and towards the back of the spoil board, then hang the weights - a couple 4 x 4in hdpe thin plastic sheets (out of a milk gallon) in between the cord and wood (where it rubs) will prevent it from ever wear out.
If it was me having this issue i would shorten the bungee cord and call it a day.
That is a great explanation. Thanks! When I first set up, I either skipped that, didn’t understand it, or it wasn’t in there. I wondered what the nylon roller was for… Now we know. The wrap around the motor sprocket makes a great deal of sense. and should help prevent chain wrap or tooth jumps.
@2cents, this went into the manual. under section general setup as the Eastbay recommended setup.
Just looking at the setup .it seems to me that you have tried to make the cut to high on the board. At that height I would have expected the sled to over balance the top of your board and cause some sort of chaos .you will also get distortion up there the same as in the bottom corners .
@Orob I don’t think it was in there. I got them too, but it was never explained where to put them and for what reason. I thing by sheer luck I have mine in about the same position (need to check the measurements), and yes, @2cents did a great job at explaining. With that pic, I have a little modification to my set up to help out.
Actually about tigethening/shortening the bungee cord, the distance between the pulleys is about 4’ 3", with a bit of slack. Per discussion, there should not be as much slack. But the question is can this be over tensed ? ( will too much tenion in the bungee cord per EBS instructions cause other probems ?)
Yes, if there is more tension on the slack side of the motor than on the sled
side, the motor will turn a bit without moving the chain (as it’s moving through
the backlash in the gearbox). for a 10’ top beam, this is at around 4-6 pounds
of force applied to the sprocket on the slack side of the chain (double the
little over 3 pounds of force on the sled in the bottom corners)
the problem with the bungee or a spring is that it’s providing the most tension
when you want the least (when the slack side is short and the sled is in the
opposite bottom corner), and the least tension when you want the most (when the
slack side is long as the sled is in the top near corner), that’s why the weight
approach works better, it provides constant tension.
No - In theory, if at any time while the machine is cutting you pull the chain from the slack side more than on the sled side, it could induce a tiny bit of backlash in the motor gears due to changing tooth face (contact plane)
In practice this does NOT occur, the cord pull will never exceed the sled weight at any position.
When the cord is stretched to its max (60in - sled on the bottom) the sled side is pulling 16lbs vs 5 lbs on cord/slack side, so NO backlash issues at all.
The bungee provided is 40in long - You can safely shorten it to 30in without risking any backlash - the pull from it will be 9lbs when stretched to 60in
You can use the EBS setup with counterweights as well if wanted.
In our tests the sled pulls a bit more than 16lbs when down in the middle - down at the corners about 6lbs which is still more than the pull on the chain slack side so NO backlash - these measures come right from the ring, you still need to add the chain weight 3/4 length ~.8lb more
Sure, will do it over the weekend and report back. Also It may be worth mentioning that the actual pull of the cord (9lbs) or spring is half (4.5lbs) because it does not pull directly on the chain but from the pulleys.
Sure, will do it over the weekend and report back.
Thanks, while the spreadsheet works even if it’s numbers are wrong (comparing
known-good configs with what you are considering), if it is giving significantly
incorrect results, it would be good to figure out why and fix it.
Also It may be worth mentioning that the actual pull of the cord (9lbs) or
spring is half (4.5lbs) because it does not pull directly on the chain but
from the pulleys.
isn’t it that the pull on the chain is half (so 8 pounds of force from the
spring/weight/cord becomes 4 pounds of pull on the chain)