This one is definitely a 'past mistake'... help please

[bucephalus]

Hi everyone I am hoping you can help me out because I have no idea what to do next with this problem.

I have a floor standing 6x48 inch belt and 12 inch disc sander that I believe is made by Kufo. I bought it second hand. Everything was fine until my clumsy brother somehow (I still don't know how) managed to tip it over onto the concrete floor of my workshop. It landed on the end of the belt sander and sheared straight through the part holding the non-driven pulley (is that the right term for this sort of thing?) on the right hand side - see pics below...

Now I am not technically minded when it comes to this sort of mechanical thing (I can however build you a secure Linux webserver) and I am almost at the limit of my ability after drifting out the pin on the broken side, which amazingly I managed to do without mishap... what confused me then was that the pin/bolt/shaft that runs through the pulley (or I suppose it is a roller?) and secures it is actually all one part. I thought it was going to be two 'bolts' and I could use the unbroken side to source a replacement, but now I am at a loss... when you turn the unbroken side the broken end turns too... it does not come out... any suggestions most gratefully received about what I should do to fix this or where I might be able to source a replacement part.
Thanks in anticipation
Gavin

 

[Droogs]

could it be a tight friction fit and perhaps you need to use a hydraulic press to fit/remove

 

[MattRoberts]

I think you have a few options:

1 - find a replacement part
2 - see if the piece that snapped can be welded back (unlikely due to size)
3 - remove the shaft from the cylinder, cut a slot in it and insert a new flat bar

I'd personally try option 3

 

[Eric The Viking]

Interesting problem.

If I understand your pictures, The shaft through the roller has a flat at each end, and that fits a similar-diameter peg that goes into the stand, to support the roller and either adjust the height or the belt tension (or both). One of the flats has sheared off, leaving a stubby end just outside the roller.

I think (this is an educated guess based on the shape and colour of the ends) your roller is actually aluminium tube, with the shaft and bearings potted inside it with resin. Either that or it is solid and there's a recess at each end to take the bearings, and they're secured in place with the dark grey resin I think I can see. The end looks like resin rather than paint. How they avoided gumming up the shaft and bearings I don't know.

It ought to be repairable, or you could probably get a new one made up from solid bar instead (the whole thing, rather than just the axle). I'd expect the bearings are positioned on the shaft either by friction or by circlips that you can't see, all inside the potting. If it's friction, you might drive the shaft out, as long as there's no rust close to the bearings (but you can't see that!). Then all you need to do is replace that bit of shaft (through the roller), which, assuming it's a standard diameter) is really easy to make and you might do it with hand tools (and some care). The issue is doing this without damaging the bearings inside, which you cannot see.

Matt's option three is the way to go, with option 4: make a new shaft.

It should be a straight bar, with flats at either end with a hole drilled. Try tapping the broken bar out by thumping the broken end (support the other end of the roller, but don't grip it sideways in a vice, to avoid damaging the roller surface, or crushing it, if it's hollow). Use something narrow and soft to tap with - copper or brass ideally - as you don't want to deform the broken end by steel-on-steel contact (in the way a cold chisel rounds over in use). I wouldn't try anything bigger than a copper/hide Thor mallet (or a big claw hammer), as it shouldn't need it, and you want to avoid doing further damage.

Apply gently increasing blows - don't hit it as hard as possible first go. You'll be putting sideways pressure on bearings that aren't intended for that, so you want to use the minimum force.

If it doesn't want to budge, and it is resin, you'll have to excavate carefully to find uut how things are held together. There may be circlips, if so, take a moment to curse the designer loudly and profanely (did I really say that out loud?). At that point it gets trully messy, as you can only get at the outer circlips without damging the bearings - you'll probably need to find a nice man with patience and a lathe to help you clean up the recesses

Of course, it may be that you've also damaged at least one bearing in the accident. In which case, excavation will be necessary, and you can afford to be a bit more heavy-handed, as the bearings will have to be replaced in any event.

 

[bucephalus]

Progress!

Thanks for your replies gentlemen, they are appreciated and really helped.

I think (this is an educated guess based on the shape and colour of the ends) your roller is actually aluminium tube, with the shaft and bearings potted inside it with resin...

I'd expect the bearings are positioned on the shaft either by friction or by circlips that you can't see, all inside the potting. If it's friction, you might drive the shaft out, as long as there's no rust close to the bearings (but you can't see that!). Then all you need to do is replace that bit of shaft (through the roller), which, assuming it's a standard diameter) is really easy to make and you might do it with hand tools (and some care). The issue is doing this without damaging the bearings inside, which you cannot see.

I tried tapping the cylinder down on the broken end of the shaft as suggested, and the end cap came off! (up until I read the post I hadn't end realised it could be a hollow cylinder )

Looking online it seems like I need some 'circlip pliers' to remove the circlip? I believe there are different types (e.g. internal circlip pliers, external circlip pliers, straight and bent nose pliers)..?

Having discovered that the non-driven end was hollow it finally occurred to me to look at the driven end - and then I saw this #-o

Which is a bit of a clue if I had been switched on enough to look

I also need a bit more advice about what to do next after (assuming I do) managing to remove the circlip..?

Thanks again

Gavin

 

[Eric The Viking]

I tried tapping the cylinder down on the broken end of the shaft as suggested, and the end cap came off!
View attachment 20160915
Looking online it seems like I need some 'circlip pliers' to remove the circlip? I believe there are different types (e.g. internal circlip pliers, external circlip pliers, straight and bent nose pliers)..?
View attachment 20160915

Now you're cooking!

You need external circlip pliers (for avoidance of doubt, the pins move further apart when you squeeze). You might need to file the pins down (VERY carefully - keep 'em parallel), but they're usually really cheap and useful to have both sorts to tackle everything. I have a "universal" pair that are supposed to do both internal and external (one handle changes position WRT the pins), but they're horrible to use. In frustration I got a really cheap set of external ones for about two quid (in a "reduced to clear" bin in a tool shop), and they're my go-to set now. Whatever you get, they have to be held alongside the end of the shaft, so the jaws need to taper over a longish distance (or the pins need to be bent slightly, otherwise they slip out of those little holes in the circlip too easily. If you have electronics pliers, they can be used in extremis!

Just gently open the circlip and work it off the end of the shaft, then gently drift the shaft out (for a quiet life, I'd push the broken end through, but make sure it doesn't have any torn metal sticking out to jam in the bearings. Circlips do distort if you are too enthusiastic with the pliers, so only use enough squeeze to just release them.

I expect the bearings are OK - they are dust-sealed and look decent quality. If not they also look replaceable, if necessary (you can probably use a narrow drift to tap them out from t'other end, but don't do it unless you're sure they're gone, as you'll probably damage them in the process). The size is usually marked around the rim of the bearing (or on the metal cover, if it;s sealed only on one side)

Once you have the damaged piece out, personally I'd see if you can get a replacement shaft made up - relatively simple job for any machine shop, and it'll be peace of mind. You only need the piece that runs through the roller - flats at either end and grooves for the circlips. The 'hinge' at each end is a 'roll pin' as manufactured, but It's probably not crucial that it's done that way, so, for example, you might replace them with same-diameter bolts and Nyloc nuts (ideally proper bolts, not machine screws). that would allow for easier dismantling probably, although it looks as though it was designed to pivot, either for tracking the belt or so you can clean around the bearings inside and/or replace them if needed.

Find a nice small machine shop, show them the problem and take their advice.

The whole thing looks well made - worth making the effort, I'd say. You'll have it back running sweetly in no time!

E.

PS: one word of caution: it must have been quite a bump, as the shaft shouldn't be brittle. Check carefully around the end that hit the floor, in case there's a cracked casting or similar damage that you haven't yet spotted. Also check that the roller itself hasn't been badly knocked out of shape. Again none of that would be irreparable, but you won't be able to run it usefully if it's significantly weakened or the roller isn't true.

 

[bucephalus]

Dropped it off at a local engineering firm, they said it shouldn't be a problem but they are going to call me after they've got it apart. Hopefully should be sorted soon.
Thanks again
Gavin

 

[bucephalus]

So, it's taken a few days but I now have the roller back, complete with a brand new shaft, fully assembled. The engineering guys did a great job.

Now I should preface this next part by saying that on this machine changing the belt has always been a struggle. It was only possible to get the adjustable roller to move in just about far enough to get the new belt part of the way across the roller, and then I had to 'persuade' the belt on by pushing it across and turning the roller by hand, and gradually re-tension the roller until the belt was running true. I have never thought about this too much, and just assumed I was being a bit cack-handed and making a harder job of it than it should have been. The guy I bought it from had told me that he hadn't used it much - only just remembered that now...

Well, trying to install the newly repaired roller changed my mind. It wouldn't fit. #-o

Or rather, it sort of fit - and given that the adjustment had always been a nightmare I thought it was right, but after about an hour of trying I just couldn't get the roller to move far enough 'into' the machine to fit a belt. The two black bolts/screws/arms that are on either end of the shaft have to go into two parallel holes in the machine body. If the shaft is too long the arms would not be able to stay parallel as they are wound closer into the body and the whole thing binds up. This was clearly what was happening here (or so I thought...). So after a bit of cursing and sweating I got the roller back off and drifted the pin out of one of the black bolts/screws/arms with the idea of elongating the hole in the shaft to in effect make it a bit shorter. Probably not a good idea but desperation was kicking in by this stage... and then I noticed something.

The slots in the end of the black bolts/screws/arms were not centred - i.e. they were not symmetrical. They were only off by a very small amount but it was clearly visible when you looked properly. Closer inspection showed that the hole for the drift pin was also slightly off centre. This meant that depending on which way round you mounted the arm it sat further in or out on the shaft (and a bit higher or lower). I therefore mounted the black/bolt/screw/arm I had removed the other way around - and hey presto, just like that the whole thing slotted smoothly into the machine to the fullest extent, something it had never done before.

I could wind the roller in fully, and the belt slipped on like a dream, and I had to wind the roller out considerably to tension the belt. The knurled adjustment nuts turned smoothly and easily rather than being stiff and a nightmare like previously. I can only think that it must have come from the factory set up incorrectly... the repair guys had mounted them both the same way on the new shaft, but with one the other way it fits perfectly, much better than it ever did before it was broken and thankfully it works like a dream now. The tiny bit of height difference between the ends does not seem to affect the running of the belt (and it was only a tiny difference).

You can see from the photos that there is some damage to the edge of the roller as Eric suggested there might be but it seems secure, it looks worse than it is in these photos and the roller runs smoothly.

So - got there in the end, a result. Thanks again to everyone for their advice. Now I just need to fabricate a replacement guard/stop for the end of the belt as the machine didn't have one when I bought it...

Cheers

Gavin

 

[Fitzroy]

Silver linings!

 

[graduate_owner]

May I make a rather obvious suggestion? Bolt the machine to the floor!!! Just in case it happens again, perhaps with someone's feet in the way next time.

K

 

[bucephalus]

May I make a rather obvious suggestion? Bolt the machine to the floor!!! Just in case it happens again, perhaps with someone's feet in the way next time.

K

That is a very sensible suggestion that I will be following.

 

[Eric The Viking]

Well done. Really pleased for you, and slightly jealous too

E.!

 

[lee celtic]

Nice bit of kit.. I have one on my wish list with an end feed so I can fish mouth tubing against the end roller.

And it's good to see a nice bit of kit being saved instead of replaced . 8) Good work Sir.