3 1/2 horizontal bandsaw worm gear failure

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3 1/2 horizontal bandsaw worm gear failure

This topic has 5 replies, 4 voices, and was last updated 1 May 2019 at 20:34 by Martin of Wick.

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1 May 2019 at 13:46 #407336
Martin of Wick
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@martinofwick
I noticed that my 10 year old CY90 bandsaw has been leaking oil slightly via the driveshaft. On closer inspection this time, the oil was loaded with fine brassy material, so decided to open the gearbox and take a look and found it to have become mysteriously filled with 'antique gold' paint.

The pictures say it all realy… dissapointing as the machine has not been used hard in its life, the original 14t carbon steel sawband was still going strong before I dismantled it. BTW, for anyone contemplating dismantling, it was a right sod to get apart – everything seems to have been assembled using oversized shafts and tectonic forces. A bloody good 3 leg puller and a suitable hydraulic press is required.

As far as I could tell the driveshaft bearings seemed OK with no play or float and the worm appeared to be set correctly 90 degrees to the worm gear. The helix angle of worm and worm gear appear the same (approx 4.5 degrees)

I was wondering if anybody had a view as to the reason for the premature failure? How might this be prevented / mitigated in future?

I have purchased a new worm gear but as they are quite expensive, I would like to try to avoid having to replace them every few years (anticipate using the saw rather more in future).

New oil seals will be required, but as the unit is stripped down, would it be worth replacing the various shaft bearings as well?

As I have modified the saw to allow vertical use, Some fairly good sealing may be needed on the worm shaft as all the oil in the gearbox will be vertically above the drive shaft in that configuration. The present shaft bearing area will only accept one bearing oil seal as the centre portion between the fore and aft bearings has been machined undersize.

There is a thin walled tube spacer between the driveshaft bearings that I was considering replacing with something thicker, machined to accept internal and external O rings to seal both the shaft and bearing housing/spacer annulus. Just concerned that this is a fair bit of work and the o ring on the rotating shaft would wear very fast and become inefective.

Has anyone else come across these issues with this or similar bandsaws? I would certainly weclome the benefit of your eperience, ideas or solutions to these problems.

Truth is, it has been a good little saw, saves vast ammounts of effort, cuts straight and accurately and is very versatile with the usual mods and accessories.

Thanks,
Martin.
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1 May 2019 at 13:46 #13506
Martin of Wick
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@martinofwick
1 May 2019 at 14:01 #407338
Neil Wyatt
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@neilwyatt
Had it actually failed?

I discovered the same 'gold paint' effect many years ago, and though the worm was worn it was working fine.

I recall that I was able to improve the mesh of the worm and wheel and a check a few months ago showed negligible further wear (no 'gold' suspension).

I have been expecting to need to fit a replacement for years, but it just soldiers on.

Neil
1 May 2019 at 14:25 #407340
Trevorh
Participant
@trevorh
Hi Martin,

If and when you fit the new crown wheel you will need to set the end float/thrust.

This positions the worm shaft in relation to the crown wheel and is done by fitting shims to the bearings in the end caps

this dictates at what point the worm engages the crown and therefor will dictate how much force is applied when the two come together – too much and it wears prematurely – not enough and it will try to ride over the top

hope this helps

Trevor
1 May 2019 at 15:19 #407353
ega
Participant
@ega
Interesting that after ten years you are still using the same blade which suggests that the machine has been very lightly used.

Incidentally, I assume this is the Warco product.
1 May 2019 at 20:34 #407396
Martin of Wick
Participant
@martinofwick
Neil, Thanks for that.

In fairness the gear had not actually failed, but as you see, about a third of the tooth flank has been chewed away on the left side of the worm gear.

In the gearbox the worm and gear appeared to be well meshed and central (as far as I was able to tell cos you cant actually sight along the axis of the worm spindle). Looking again at the photo, I was wondering if the gear was not properly aligned on the axis of the worm? Is it just my eyes, or would you say that the low point of the impression the worm has cut in the gear is also to the left (I assume if perfectly aligned the low point the worm has 'cut' should have been dead on the centre).

So ,would you advocate replacing the same gear moved a couple of millimetres to the left in relation to the centre of the worm axis? at worst it would just grind down the right hand side of the gear to match the left before concentrating on the middle and eventually wearing that away to failure! Which as you say may take years.

Trevorh,

because the bearings are contained only in a die cast gearbox housing, the options for positioning the worm and gear in relation to each other are pretty limited. However, as intimated above, the worm gear can be moved up and down its shaft and locked into position with a grub. Just difficult to see the relation between worm and gear when fitting into the box. Some careful measurements will probably be needed to locate the gear exactly.

Of course, one assumes that when in use the worm gear shaft will not move in relation to its bearings for this to work!

ega,

I would say this saw has not had a very hard life. It has not been used that frequently, but when it has been used it has often done pretty heavy duty work for long periods without complaint.

The saw is one of Warco's offerings, but I expect however branded they are all much the same. Bought on impulse at a show for an almost infeasibly low price. Have not been disappointed until now. But as Neil says, best thing may be to just bang it back together and run it until it finally grinds the worm wheel to dust, which might be years hence!
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