Advice needed on a possible P/T modification to prevent the chain skipping

[wobblycogs]

There's a photograph with annotations attached which probably explains it better than I can do with words!

Essentially the problem is that when under load the chain that drives the feed rollers will skip on the outfeed roller occasionally , particularly on hard timber that requires more power to feed. The P/T has an idler pully to take up slack in the chain but to my eye it's on the wrong side to be properly effective. On the side it's on it's being pulled by the drive sprocket so it's always tight. The chain on the out feed side is always very slack. It's hard to see but I'm pretty sure that the idler pulley is at maximum adjustment so I assume the chain has stretched somewhat but even when new I believe it was very close to skipping on the out feed roller.

I'm considering fitting a second idler pully on the out feed side of the chain which would give it better engagement with the out feed sprocket. Does this sound like a good idea? It seems like a reasonably easy modification assuming I can get it below the cutter drive belt, I think there's just enough space.

 

[rogxwhit]

If I follow the line of the chain with my eye behind the casing between drive and driven sprockets, it seems to be overly slack. Could you shorten it? I'm not familiar with this machine, just working on how it appears. I'd be tempted to take a couple of links (pairs) out.

This should at the same time occasion the idler to apply more tension ...

If you're a cyclist, you'll already have a link remover ...

 

[ChaiLatte]

Just to be clear, please confirm the right hand chain that leads to the drive motor goes downwards in normal use.

You are correct that the idler should be on the slack side of the drive.

Can you unhook the right hand leg of the chain from the idler/tensioner and let it run direct to the drive sprocket from the infeed sprocket. That should then create some slack so the left hand leg can be run more vertically from the drive sprocket, go over the right hand side of the idler and then run horizontally to the left onto the outfeed roller sprocket. That gives you nearly 180 degrees wrap on the outfeed.

Have you a manual that shows it is currently routed as OEM specification?

 

[clogs]

wobbly cogs.....great name by the way......lol.....

had a similar problem with my 2 post car lift...I even geared it down so I'd get a longer life from the 3 drive belts.....
in the end did this....u'll note that it's a triple belt system so used 3 bearings per idler....
the pulley was semi temp affair but it's lasted over 10 years of fairly constant use.....
I tried the manufacturers for a bigger pulley but got the cold shoulder....hence the plywood one....

if u use a roller bearing it will not mess the chain up or damage the bearing....they are not going fast enough....
depending on room it may pay to double up the bearing just to ensure the chain does get support at all times across the width...
something like a 6202 2RS would be about the right size...they are around £2 squids......
I u look on ebay they list bearing sizes....it wont take long for u to find something...
and I very much doubt the chain is worn out....might be a poor imitation of a chain tho...
I also had to repair a machine for a client, although the chain was slack when assembled it was diff to thread it around the gears as it did not have a split link....think it may have beed a DeWalt......

 

[rogxwhit]

Can you re-feed the chain with its length as is, so that its slack leg runs against the tensioner rather than its tight (drive) leg?

 

[Spectric]

but to my eye it's on the wrong side to be properly effective.

A tensioner whether belt or chain is positioned on the no load side, you will find under load one side is under tension and all the slack is on the other side, this is where the tensioner should be. You need to fix the problem rather than look at ways to overcome it so are all the teeth in good condition, if the chain is worn then replace or otherwise remove links bearing in mind you can get half links to get the slack out.

 

[deema]

As @Spectric has said, it’s almost certain that the idler has the chain wrapped around it from the wrong side. Can you look in the manual to verify how the chain is threaded. (Or give us the model number). It looks like an a SCM machine? If this machine was not new to you, it could have been tinkered with by the previous owner. I suspect the chain has been modified probably shortened and wrapped on the idler on the wrong side to give the initial infeed roller sprocket more grip of it. Looking at the sprocket it appears that the teeth are ‘too short’ and worn down considerably when comparing with the outfeed roller sprocket. If the sprockets teeth are worn down it will slip under load. I suspect you need a new chain fed around the sprockets correctly and all the sprockets replacing.

 

[wobblycogs]

Thanks everyone for the insights, to answer the questions that have been asked...

The P/T is a Jet JPT-260, it's a few years old but it's not done much work compared to what it's designed to be able to do. @deema @Spectric The sprockets are in good order, the tips of the sprockets still have their black coating so they are very hard to photograph (I've just been to the workshop to check). I've checked the manual and the chain is run correctly, this is the way it was designed. I have attached a service manual I found which shows the chain path and how to set the tension. It seems to say that that chain has to be loose to allow the feed rollers to move up during operation but the chain is far too loose on my machine.

@ChaiLatte @rogxwhit the chain does indeed go down on the right hand side. I hadn't considered the possibility of running the left hand side over the idler. The machine is set up as per the manual. I doubt the chain is long enough to go over the idler from the left but it's certainly worth keeping in mind as a possible fix.

I don't have a link remover but I think my first attempt at a fix should probably be to remove a link and see if that's enough. My concern with putting an idler on the slack side is it might prevent the feed rollers from moving as timber goes through. I suspect I'd need an idler that was spring loaded.

 

[Yojevol]

Would it be possible to turn a larger diameter jockey wheel?
Brian

 

[cowtown_eric]

I had a similar problem with my makita 2040 planer.

Makita's solution- just change the chain. They said it's virtually impossible to see the inside linkage to see wear.

The chain was inexpensive enuf, and changing it solved the problem on that occassion and some years later too!.

Your photo suggests idler wheel has reached end of travel, further indication of chain wear.

Eric in the colonies

 

[wobblycogs]

Thanks @cowtown_eric, you're probably right about the chain being worn out. I'll see if I can get a replacement. I'm surprised it's worn out already as the machine hasn't done a lot of work over it's life but it's a cheap possible solution I suppose.

I could probably turn a larger idler wheel.

 

[sawdust1]

I had a similar problem with my Axminster 15inch thicknesser where passing timber through would cause it to
judder and the chain would sort of jump as the cogs would momentarily stall.
After going through the machine the out feed rollers needed resetting, after 20 odd years of use it must have
moved, this solved the problem i was having.
Does your handbook tell you how to check the distance between out feed roller and bed, i had to make up a
spacer block as instructed and use a feeler gauge.

 

[ChaiLatte]

It seems to say that that chain has to be loose to allow the feed rollers to move up during operation but the chain is far too loose on my machine.

OK. That makes a difference. Maybe add the extra idler, but move the red circle up and to the right in your photo so it mirrors the OEM one about the vertical stiffener.

With a looser chain, the quality of drive will depend on the wrap angle on the sprockets (number of teeth engaged). With the new ider in the suggested position, the chain running to both driven sprockets will be nearly horizontal, so vertical movement of them (due to altering thickness) will have the least effect on chain tension.

 

[rogxwhit]

I suspect I'd need an idler that was spring loaded.

Ah. In order to comment earlier, I'd made an assumption that the idler was spring-loaded!

I'm sure this is solvable. Keep at it.

 

[recipio]

Have you given the mechanism a good blast of WD40 ? It's surprising how it frees up sticky bearings. Otherwise I wouldn't redesign the machine. Replace the chain as a first start.

 

[wobblycogs]

@sawdust1 I've had this machine complete in pieces as I had to change the feed roller bushings, that's where I got the technical note from. The feed rollers are spring loaded from above so they are to some extent self adjusting. There's no guidance in the manual for setting the loading but it's pretty obvious when they are set incorrectly. I'm happy this isn't the issue.

@ChaiLatte thanks, good idea regarding moving the second idler higher up. I can move the existing idler to it's minimum setting which will give me more chain to play with.

First tings first I think I'll try a new chain, that shouldn't break the bank. Failing that it'll be another idler. Thanks for your help.

 

[deema]

Now, I could be wrong, but you’ve been holding out on us! I think this is you on UTube repairing your PT when it jammed up the last time!
I was interested in seeing what the bushings are. They look like a sintered pressed material, and they and the shafts dont have any oil grooves within them. I’m guessing that either sawdust has got in, probably worn the bushings enlarging the holes allowing more sawdust in until it’s packed in and stopped the rotation, or its a repeat of the same problem. You need I believe to take it apart and determine the cause of the stiffness. I’m nit sure now much material there is in the bushes, but I’d be looking at drilling them and pressing in sintered bronze bushes into the bushes.