Need more advice on PT modification / repair (the saga continues) - Jet JPT-260

[wobblycogs]

A few weeks ago I posted a question asking about a modification I was considering making to my PT. At the end of that thread I decided to replace the chain and see if that fixed the issue. Many thanks for all your help there but now I come to actually do the job I don't think the chain is the issue. I debated just tacking this question on the end of that thread but it's a different issue so I thought it warranted it's own discussion.

I bought a chain tool and a new chain (as close a match as I could find) and set about the repair. The chain came apart easily but when I came to inspect the sprocket on the outfeed roller for damage I discovered it was nearly impossible to rotate by hand . This machine has failed similarly to this before. According to Jet it was due to overly hard bushing material and they even had a free onsite repair (that's long since ended). I replaced the bushings a couple of years ago and everything had been running fine.

When I got the replacement bushings they came pre-greased and I seem to remember reading they didn't need anything else, this seems to be wrong though and I can't find where I read that. The bushings have no oiling points built in but they pretty clearly need some lubrication. I'm convinced now that the chain is slipping on the outfeed roller because it requires excessive force to rotate. If I put a spanner on the locking nut I can rotate the shaft so it's not completely seized. It's smooth running but tight, it feels like dried up old grease is the issue.

I think I need to fit lubrication points to these bushings but this is outside my experience so I could do with some advice. At the moment I have two ideas for where to add lubrication points (please see photos attached).

Idea 1... Three of the four bushings are fairly easy to access and the fourth is do-able. I could probably add a grease fitting to the side of the bushing. The problem is the bushing wall is quite thin where I'd need to add the fitting. It's thin enough I'd probably need to remove the lead in on the thread of the nipple. I'm concerned something will fail over time.

Idea 2... On top of the bushings is a spring and grub screw to apply downward pressure on the timber. There's a flat spot on the bushing for the spring to seat on. There's not space for a grease fitting but I could drill through the bushing at this point. To lubricate the bushing I'd remove the grub screw and inject a little oil. This area isn't sealed off so oil will run out but some will make it in, the hole through the bushing will act as a tiny reservoir.

I'm favouring option 2, it's simple and I'm pretty confident it'll work. Any advice welcome.

As for what to use for lubrication, I have oil for the headstock of my wood lathe that feels like it would be perfect, just the right viscosity. I honestly have no idea what's best though.

Many thanks for any help.

 

[Spectric]

What is the bush made from? Having a grease nipple is fine but where is the grease going, is there any scroll on the shaft or in the bush? For a lube think of something with moly in it . The right solution would be for there to be a proper bush in that housing, either oilite or bronze. Another idea that depends on the hardness of the shaft is to drill the centre with one cross hole and nipple in the end.

 

[wobblycogs]

I couldn't say for sure what the bushing is made from, I would assume cast iron. Both the bushing and the shaft are smooth, there's no grooves to hold oil / grease. I could probably make shallow grooves in the shaft, I'm sure I could rig something up in the wood lathe.

I did consider trying to drill and then counter drill the shaft. I might be able to do that on the off side but the driven end would be difficult with the tools I have available due to the length of the hole needed, it would be a high aspect ratio.

Thanks for the lubricant advice.

 

[Inspector]

Have you considered oil cups? Model steam engine oil cup with Engraved screw on lid. 5BA Price each. | eBay They also come in a 90º version that might fit the awkward location. It looks like the bushing slides into the casting from the roller side which would preclude installing them on the bench. The bushings could be drilled such that the oiler was on an angle beside the pressure spring.

Before doing that though I would just make a practice of putting a couple three drops of thin oil (3in1,hydraulic etc.) on the end of the bushing and where the shaft enter on the inside. Give it a few minutes to wick in before wiping off the excess. If you do it every 10 running hours or so you should be good. Isn't that why they had Oilers on trains?

Pete

 

[wobblycogs]

I did consider oil cups, I didn't realize why made tiny ones like that though. I'll head down to the workshop just now and see if I could fit them in.

You are correct in how the bushings are fitted. The whole cutter head assembly needs to be taken apart in order to work on them which is most irritating.

I spent some time dripping in oil as you suggested last night. The infeed roller, which wasn't too bad to start with, greatly improved. The outfeed didn't improve at all. That just letting the oil wick in would be a great fix though.

 

[clogs]

as the Inspector suggests oil cups.....
two things, u must be able to get to the oil hole easily or it wont get done and drilling and tapping can be a pain esp in cast iron without proper tools but if u just drill a hole and cover it with a Neodime magnet disc ...that will keep the dust out of the hole....
I can assure it works as I've done it on my Myford lathe,,,the original oil inserts are hopeless.....
also did this to the counter shaft on my Colchester lathe....I converted some big grease nipples.....with brass screw on caps....

u need to decide which side of the bush that takes the weight/pressure then drill out on the opposite side....or the highest point....
saying all this is fine but u really need to strip the machine out to gain access......
cast iron bushings are really good but the machining of the bush and it rotating part must be superb....
pretty sure the front bearing on the VB36 lathe is of this sort...well it was when I was looking at a new one....
Gas turbines dont use roller bearings either, just oil and solid bushings....
back to realality, bronze is the go to bush material....but it does still need a little lube....although oilite bronze is self lubing....
If ur bushings are cast iron stay with em....
it's really worth the effort in the long run.....

 

[wobblycogs]

Well, what would you know. I've just popped down to the workshop to see if I could fit in oil cups and it seems the oil I dripped on the shaft yesterday has worked its way into the bushings. The infeed now rotates very freely, I can even get it to spin freely a little. The outfeed can now easily be turned by with just finger tips whereas yesterday a spanner was needed.

I've continued to drip in oil where the shaft meets the bushing and I managed to get what I assume is some old grease out (looks like used motor oil). I've been rotating the roller with a socket on a drill to help work it in there.

Now I have a dilemma. Do I strip down the cutter assembly and try to fit oil cups, which is certainly the best solution, or just make sure I drop a little oil on the ends of the bushings each time I use the machine. The latter is certainly the easier option and I'm fairly confident I'll do it regularly as I do it with the lathe religiously.

 

[clogs]

wobbly clogs
just oiling the ends is just a get u home bodge I'm afraid......
I bet if u could see inside the bush the inner edge would be dry....
U have got away with it this time but remember the cost of those shafts will write the machine off once damaged.....
it aint worth it....once they are all scored up any new replacement bush will not last.....
I understand ur dilemmer but u will sleep better at night knowing it's been done properly....
Shame it wasn't modified at the factory.....
A hole designers not understanding what they are doing...prob just out of uni in nappies......lol...

 

[okeydokey]

I guess the following rambling note shows my lack of knowledge about bushes.
So, if the bush (this is really the bearing for the shaft to rotate within) is made of cast iron then surely it needs a regular drop of oil, maybe 3 in 1 oil in the spray can with straw (pressed hard against the shaft/bush joint) turning slowly would help force it in, so it gets inside the bush. And once it's in then maybe small pump oil can with your lathe headstock bearing oil (I had some from Record Power once - good stuff) would do.
Or as some are easy to remove then as a trial take one out clean thoroughly and likewise the shaft - then generously coat with the slightly sticky headstock oil and reassemble adding more oil as you go and see how it works.
Squirt a bit more now and then.
As you have replaced the bearings, they will be the new type that Jet were using as replacements so that points me towards my above thoughts.
Hope this is helpful
cheers

 

[wobblycogs]

Thanks, touch wood the machine is currently working. I basically did as you suggested, just kept dripping oil in until the bearings ran freely. Ideally they would have some sort of oiling system but I don't use the machine anywhere near as much as I would like so for now at least it's going to have to make do with a sign on the front that says "oil before use"

I replaced the chain with the best match I could find. The new chain is significantly strong, no way that will stretch! I looks like the old chain did stretch slightly, maybe 4mm over it's length.