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Old Delta Unisaw belt tension - one good, two loose

6911 Views 6 Replies 5 Participants Last post by rick1955, Jul 3, 2015

gthomson

Discussion Starter · Jul 3, 2015 (Edited by Moderator)

I have an old Delta Unisaw from 1955.
The belts have seen better days.
I got around to replacing them today - three of them.
I just bought replacements from an auto parts store - regular V belts - all the same belts supposedly (same part #.)

I put them on and fired it up tonight.
Sounds good, seems to run smooth - I did the nickel test (nickel on edge) and it gets very little noticeable vibration.

Tried a few cuts - no noticeable problems on how those looked.

But…
One belt, the one closest to the motor, seems like tension is about right.
The other two belts seem like they are flapping around a lot more, and not so great on the tension compared to the first belt.

I know the belts haven't been replaced in a very long time.
Here's a picture of the belts that came out -

While they all are pretty hard and crusty, the top one with the cracks that is the worst is also the one that was closest of the three to the motor.
I don't know why that would have anything to do with the belt in that position now being the only one tight, though. If the bad belt wore down the pully over time, then the first belt position would seem like it would be the loose one instead.

Does it make sense to just use one belt that is tensioned good, and leave off two that are not tensioned good?

I hadn't thought of this before, but just did now… maybe makes sense to swap the belts around and see what happens with the tension of all three then - problem stays with the position, or stays with the belt?

If there were some kind of bearing, bushing, arbor, trunion misalignment or problem, I'd assume that would result in a lot of vibration, which I'm not seeing?

Might it just take a bit of running time, and then re-adjustment?

Greg

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MrUnix

· #2 · Jul 3, 2015 (Edited by Moderator)

Delta used to recommend and sell a matched set of belts for that very reason. However, most quality belts these days are manufactured to such precision that it's usually not necessary. Even so, it is generally recommended that you physically verify they are the same diameter at purchase time, and mix-n-match until you find three that are the same. What brand of belts did you get? Goodyear is usually the most recommended, but many have had success with other manufacturers. If you wind up replacing them, you can get a matched set for about $15 (Jason Unimatch), or go with the Delta branded set (which is about 4 times the price).

Cheers,
Brad

PS: That link is for a Unisaw with the 3.25" motor pulley, which applies to most built after 1951 IIRC.

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gthomson

Discussion Starter · #3 · Jul 3, 2015

The belts I got were Gates 6829 -
https://www.amazon.com/gp/product/B000BQS1RC?*Version*=1&*entries*=0

I got from a local auto parts store, and had to go to three - they only had one each

But it sounds like, from what you're saying, that I should re-arrange them, and see if a different position then becomes the one with the best tension. That could help show if there are slight differences in the sizes in them, and where a matched set might then help.

I did see on another forum a guy replaced with a VX belt - sounded like he only then used one belt.
But the autoparts stores I went to gave me some pretty blank stares when I asked for a VX belt with the notches going perpendicular to the belt. And the woodworking store sent me to the autoparts stores and/or a sewing machine shop down the street.
The sewing machine shop guy was nice about it, but I could tell he was thinking 'why are you thinking I'd have a belt like this in a sewing machine repair shop?'.

I'll swap around the belts this weekend, and if the tension is still good on that first belt, and not the other two, regardless of the switch, matched sets won't help then, right?

Greg

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rustfever

· #4 · Jul 3, 2015 (Edited by Moderator)

You need to ONLY use matched belts.

Better V-belts are made in batches. Each belt of a single batch will have an identifier code printed upon them. Better dealers will keep all belts of a single batch separated. The 'same-size' belts from different batches will be slightly different, thus one or two tight belts and the others loose.

If you try to use multiple belts, you need to make sure they are from the same batch.

Forget purchasing from the Auto Parts store and get to a specialty dealer and purchase the matching belts.
I personally deal with Gates, one such manufacturer. The have matched belts in their 'Industrial' line. Don't worry about the cost as their prices are fair and not excessive.

Do your homework so you do not waste your time and money.

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gthomson

Discussion Starter · #5 · Jul 3, 2015

Doing some homework tonight…

And I'm learning some good lessons.

I moved the belts around.
The belt that had good tension before, still has good tension in another position.
And the other two still don't.

So that's a pretty good indication that the belt sizes are different.

Will start looking at the options for matched belts mentioned - I think that's my next step.

And thanks all for the input, I think I'm understanding what's next for me on this, and I'll go with that and learn some more

Greg

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Nubsnstubs

· #6 · Jul 3, 2015

I bought a matched set from Rockwell once. One was tight, and the other 2 was loose. They worked for years until I change the motor to 5 hp which had a 7/8" arbor. It now has only 1 belt, and have had no problems with it for 15 years…... Jerry (in Tucson)

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rick1955

· #7 · Jul 3, 2015 (Edited by Moderator)

Just because it has a triple pulley doesn't mean it needs three belts. The Unisaw was over built and if they designed with modern standards people would think they are cheapening it. Powermatic went to 2 belts on the 66. If you could see all the Euro saws who run one with 9 hp motors. We had a Griggio 4' slider, 10mm belt (3/8") and could fit a 20" blade and never lacked power.

I've been to plenty of shops where didn't know any belts were broken until the third one broke.

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Old Delta Unisaw belt tension - one good, two loose

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