Motor spring question

[whonea]

Old faithful (1980's vintage MArk V) ate a drive belt the other day and in the process of installing a new belt I found that the motor driven pulley assembly was not adjusting to maintain tension at the highest speed setting. The sheaves would close until the belt rode about 3/16 deep in the pulley, then stop. A light tap would close it all the way and it appeared to hold the tension under load but slowing the speed and moving back up would again stop short of full closure. Looking more closely, the sheave was "hunting" around that point. I took the sheaves apart, cleaned and oiled them - with no belt, the assembly moved easily over the full range of the shaft and at full close the sheaves were close enough that the drive belt stood a good 1/8 inch proud of the sheaves, so there is plenty of travel and it's free. Being and old engineer, the hunting would seem to indicate that the motor spring is not exerting enough force to maintain belt tension when extended. Is it common or likely that the spring has fatigued of the last 25 years or so and that replacing it would solve the problem?

The spring is cheap enough, but I'd hate to fight that mother off and back on if a new one won't solve the problem. Any thoughts or experience with this?

[dusty]

I am waiting for the experts to weigh in on this one. It sounds to me as though you have already done what I would have thought would correct your problem. My very first thought was - lubricate. Clean and lubricate.

Good Luck and I'll be watching to see what the experts have to say.

[beeg]

My MarkV is about the same age and the spring is fine. Check the documentation you got with the belt. The new belts they had to go with have a different adjust point. There is a sawdust session that might help you.

http://www.shopsmithacademy.com/SS_Arch ... _Index.htm

[billmayo]

If you have no difficultly pulling the floating sheave toward you, then the spring does need replacing. Just do not let the floating sheave loose when it is pulled back as it will compact the sheave spacer causing clearance problems. I find that the set in the belt will cause the motor sheave to be "hunting". Even a new belt will take a set if left in the sleeve? I store all my belts inside out and without the sleeve. I find putting a load (SPT) on the headstock will help settle the sheave hunting down and the headstock will continue to function. I find switching to a cog and link belt helps prevents this "hunting" of the floating sheave.

I normally find the floating sheave sticking from crud on the motor shaft. I find using Kroil on the motor shaft will quickly loosen any crud and allow the floating sheave to function again. Quick, down and dirty solution.

Old faithful (1980's vintage MArk V) ate a drive belt the other day and in the process of installing a new belt I found that the motor driven pulley assembly was not adjusting to maintain tension at the highest speed setting. The sheaves would close until the belt rode about 3/16 deep in the pulley, then stop. A light tap would close it all the way and it appeared to hold the tension under load but slowing the speed and moving back up would again stop short of full closure. Looking more closely, the sheave was "hunting" around that point. I took the sheaves apart, cleaned and oiled them - with no belt, the assembly moved easily over the full range of the shaft and at full close the sheaves were close enough that the drive belt stood a good 1/8 inch proud of the sheaves, so there is plenty of travel and it's free. Being and old engineer, the hunting would seem to indicate that the motor spring is not exerting enough force to maintain belt tension when extended. Is it common or likely that the spring has fatigued of the last 25 years or so and that replacing it would solve the problem?

The spring is cheap enough, but I'd hate to fight that mother off and back on if a new one won't solve the problem. Any thoughts or experience with this?

[charlese]

... The sheaves would close until the belt rode about 3/16 deep in the pulley, then stop. A light tap would close it all the way and it appeared to hold the tension under load but slowing the speed and moving back up would again stop short of full closure. Looking more closely, the sheave was "hunting" around that point. I took the sheaves apart, cleaned and oiled them - with no belt, the assembly moved easily over the full range of the shaft and at full close the sheaves were close enough that the drive belt stood a good 1/8 inch proud of the sheaves, so there is plenty of travel and it's free. Being and old engineer, the hunting would seem to indicate that the motor spring is not exerting enough force to maintain belt tension when extended. Is it common or likely that the spring has fatigued of the last 25 years or so and that replacing it would solve the problem?

The spring is cheap enough, but I'd hate to fight that mother off and back on if a new one won't solve the problem. Any thoughts or experience with this?

I hesitate to step into the exchange between you two engineers, but I'm used to that as my son and one grandson are also those creatures. Sometimes my suggestions work. Sometimes not!

Let me take on the weak spring question first. - Reading your assessment of "...fighting that mother off and back on"... my guess is the spring is strong enough. Also I feel confident the motor shaft, key and keyway are clean and lubricated.

Although I'm not clear on the meaning of "hunting", but imagine it means the two sheaves are varying in their distance from each other. Hmmm, what could cause that? It is my guess your problem may lay in the upper idler shaft/control sheave system, rather than the motor shaft/sheaves. If the upper control/idler shaft is worn and there is wobble there, it may be the distance between these sheaves could vary, causing belt tension changes.

As I said this is a guess, but as long as you have the headstock apart, it deserves a look. The control sheave should slide smoothly with no twist. A close inspection of the keyway and "short key" (which is actually quite long - over 3" as remembered) is worthwhile.

[whonea]

Thanks for the input - I rechecked everything and the system is as tight and smooth as I could hope for. Even cleaned the whole mess with brake cleaner and a hot spray but got no satisfaction there so I tried the Kentucky windage method - drove some shims behind the spring. Bingo - 3/16 inch shim restored full high speed travel so looks like it's time for a new spring. I think I can guess at the cause, BTW. The saw sat unused for about 3 years and my son was the last to use it before the vacation. He left the speed set at dead slow which fully compresses the spring - ideal conditions to let the spring take a set. I know some manuals say to always shut down at slow speed, but from a materials standpoint that's not the best strategy for long term storage. For less than $5 (plus shipping) it will be a cheap fix.

[charlese]

whonea- Thanks for your last post. I had thought that a long storage at slow speed position might compress a spring, but have read of many machines stored for long periods, without mentioning this as an issue.

Could you tell us what part of the World you call home? Do you think the storage location had anything to do with the spring weakening? Do you have an idea if climate would tend to affect the spring tension?

I read an article in a woodworking magazine lately that addressed coil springs in bandsaws (blade tension springs) If I remember right, these coil springs rarely lose compression strength. Other parts of the saw get worn to spring compression strength is no longer a strong as it once was. (I hope that's accurate!)

[shydragon]

My SS was in storage for 14 years at one of the sawing positions. By chance, I happened on this forum before I ever turned in on and followed all the instructions from everyone here, before ever turning it on.