Kity 638 Planer Thicknesser Belt Being Shred Coming Off

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31 Jul 2017
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On my Kity 638 planer thicknesser I noticed that the feed rollers weren't moving so I changed the old smooth 1000 x 15mm belt that engages the thicknesser to a new one. However, within some minutes of use, I smely burning rubber and inside the machine I found the belt shredded to piece on 1 side.
I opened up the machine and noticed that on start-up the belt is moving from a central position on the pulley to 1 side as soon as a I turn the machine on.....thus causing 1 side to rub against the metal 'cage' and shred it.
I can't see any way of removing/tightening/changing the angle of the pulley. Any ideas on what's going wrong and how to fix it?

Flat belts run on pulleys with a "crowned" curve. From your photos I can see the very gentle curve on the pulley. A flat belt self centres on a crowned pulley. It shouldn't need adjusting as long as the two pulleys are in line and their axles are parallel. From the wear marks on the pulley on your photo, it looks like the old belt was running OK. A little off in the direction away from the tooth wheel next door, but nothing I would worry about.
Are you confident that the new belt is the same length and width as the old one ?
Thank you and apologies for the late response (family bereavement).

I've learnt something new as I had no idea about 'crowned curves' and ,having checked, it is indeed a crowned curve on the pulley.

I bought a new belt from a reputable manufacturer in the UK. It was 15 x 1000 and 1mm thick. It got shredded ! So, I bought another (15 x 1000mm) from Probois Machinoutils (France) and tentatively turned the machine on - and with the cover off - and immediately the belt moved across the pulley away from the machine. So, I stopped the machine to prevent it being shredded.

So, does that mean the 2 pulleys are out of line? And if so, how on earth do I fix it? Is this something I need a mechanic/engineer for?

Hi there, Is there any play at all on the pulleys. It could be a worn bearing and with the extra tension on the new belt may be pulling the pulley off alignment. It doesn't take much. Take a straight edge and with the belt on lay it across the two pulleys to see if one is being pulled out of alignment. Also without the belt turn them by hand to see if they run smoothly and also waggle from side to side to see if theres any movement at all. If there is it may need a replacement bearing. Most bearings have type size etc stamped on them and are generaly pretty cheap. I get mine online from specialist bearing companies.
I have the same machine. In addition to the good advice from Alasdair, I notice that the flat belt seems to be extremely close to the poly V belt - the flat belt is off center yet it is very close to the V belt and it shouldn't be - with the belts in their central position you should have 8mm clearance between the V belt and flat belt

The photos do not make this clear and I can't see both of the V belt pulleys.
It looks like there is something wrong with the V belt or its pulleys so they need a thorough check. I could be wrong as my view as to what may be happening is based on your photos. Take more photos to show all pulleys.
If necessary I can take a look at mine to see try and compare them - assuming the machine was fine before the trouble started, your looking for something obvious like a pulley or shaft that has come loose but is still working.
You can remove the flat belt and start the machine and you should see if the V belt assembly is running correctly.

There is a Youtube video of our machine that shows it running. It has the covers off so you can see the belts running - this might help.
Let us know how you get on.
Well, I've had another look and it seems there is play in the pulley (nearest the handle; larger of the 2 pulleys). I took the belt off and then investigated it. I noticed that when the handle (side of the machine) is in the planer mode there is no wobble/play (pic shows straight edge touching both edges of large pulley) but when the handle is moved down to engage the thicknesser mode there is wobble/play (pic shows straight edge jut touching1 edge of large pulley). I'm a little confused with this as if it was the bearings, wouldn't there be wobble/play at both positions ? But then to answer my own question, beneath the large pulley is a tiny white 'wheel' that pushes up against the pulley in the planer mode & keeping it firm, but has no involvement in the thicknesser mode as it is disengaged. So, does that mean there is play in the bearings after all? (confused here) And if so, how do I access the bearings?

I had a look at the gap between V-belt and flat belt and with the flat belt on the outer (right had side) edge of the smaller (lower) pulley the gap is 5mm. If it is centred it is down to about 3mm. I'd like to make the gap bigger - to your suggested 8mm - but I can't see how this can be altered as both the V-belt and flat belt run off the same smaller cog and the distance between them is obviously fixed. ( I did run the v-belt and handrun it and it seemed normal with no play). Interestingly the Youtube vid I watched (not sure if it's yours Chippymint) showed the same configuration but had a different pulley !!

I will have a look at the motor mounting when I've got a bit more time......

Obviously there is is something wrong. Lets go backwards. Was it working fine at one point? Have you done or did anything happen leading up to when the problem started? For example did you change anything like a belt or a setting?
What's the width (mm) of the outer belt?
I'll try and help by looking at mine to see if I can see anything different.
It was working fine, then I started having problems with the thicknesser. For some reason the feed rollers were working intermittently i.e. I could be happily thicknessing and then the piece would become stuck so I would have to drop the feed table down , take the piece out, hoover out any dust/chippings, lubricate the table & restart the operation . This became worse to the point where the only way I could thickness was the pull the piece through the machine( I did this a number of times as I needed to get a project I was working on finished) after it exited the rollers. This is when I decided to change the belt thinking it was a belt problem.
The flat belt is 15 mm thick x 1000mm long.
Ok I'll remove my cover and check to see what my set is. I'll help as mich as I can but It might be better if you PM me with your phone number so we can talk - a lot easier.
got into this at the end.....but the last photo shows the pulley's way out of line....a flat belt cant take that much misalignment....
something is very wrong / loose....
3rd and 5th photos, to my eye show the bottom motor pulley to be at an angle, motor bearings worn?
How is the motor supported at the other end, is the motor sitting "square" to the belts?

I agree with the last picture re pully on motor. Looks like the motor as said has become loose and out of alignment or the bearing in the motor has worn or failed. It looks as though the motor is bolted to the steel chassis/plate so I reckon bearings? Unlike the flat belt the ribbed belt can cope with quite a bit of out of alignment but they quite often squeek when they are. They also tend to wear on one edge.
I think from all the good advice the best thing I can do is to investigate the motor pulley and its bearings.........a job for daylight hours at the weekend !
I can then update you with how I've got on. (Chippymint - I'll PM you at the weekend as well)
Does appear that something is moving about. As I said on the older machines you can adjust the alignment of the motor to make the belt run true. On yours it looks as though the motor is being pulled out of line when you engage the roller drive, hopefully it's just loose.
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Fergie 307 - I had a look online at a Kity 636. It seems a different set-up. With the 638, the large pulley & chain & associated cogs/pulleys are redundant in planer mode (although the small white wheel is engaged with the large pulley) but are all then engaged - with the flat belt - in thicknesser mode by pulling the side handle down. I don't really know what the little white wheel does !

So, the motor is bolted solidly to the frame by 4 bolts (none of which are loose) at the pulley end. There is nothing supporting it at the other end and thus no way of laterally adjusting it as far as I can see.
When running the V-belt by hand I noticed a lot of rattling noise from the motor/pulley which I've put on the video. This doesn't sound right, so I suspect bearings.
SO, my next question is how do I remove the pulley? I unbolted the end cover and then the pulley end seems to have a metal 'wedge' on the inside by the thread - how do I get this out - do I need a gear-puller?


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The metal wedge is the key to stop the pulley turning by itself. It locks it to the drive spindle I would think you would need pullers if its tight but also be careful if the pully is really tight you can wreck alloy pulley trying to remove it. A small amount of heat on the pulley only may help. If you take the belt off the pulley is there any movement if you try and move it side to side. and also push and pulling it etc. Was the securing bolt tight as I would think the pully should be flush with the shaft unless there was a spacer washer/shims or lipped external washer holding it slightly inset as the picture. It may be the way it was aligned originally. Also turn it by hand without the belt and feel for roughness and play in the bearings.
The metal key wedge should come off with the pulley They normally just slide out with the pulley unless they are fixed in with some kind of glue etc.
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Sorry just thought if you are using a puller make sure that you protect the thread in the shaft! I usually use an old socket so the end of bar on the puller cant wreck the threads If you damage that then new motor. Another thought although temporary you may be able to insert washers as shims between the motor and frame to adjust the angle of the pulley.