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Table Saw Belts

3K views 19 replies 12 participants last post by  unbob 
#1 · (Edited by Moderator)
I've got an old unisaw with three belts. It was sitting for a long time before I got it, and the belts are stretched so that when you turn the blade by hand, it always returns to the same place where the belts want it to go. I never thought this was an issue as I had good cuts with my full kerf Forrest blade (which is very dull).

I got a Freud 1080 thin kerf blade, which is really well reviewed and it produced horrible cuts. I returned it for another blade, and I have the same issues. I can't believe that I could have got two bad ones in a row, I have never seen a bad review period.

Is it possible the belts are causing the problem? If so, why doesn't it affect the full kerf blade?
 
#2 ·
If there was a problem with the blade in manufacturing, it's very possible to get two defective blades if they were from the same run. If purchased from the same store, it's very likely that they're from the same run, so it's possibility.
 
#3 · (Edited by Moderator)
There are a lot of issue,s who can cause a bad sawing result, but believe me it isn,t mostly the blade. The tolerance of most well made sawblade,s are very high.
But thin blades need a very precise machine. What is the diameter of the flanks (For good working mostly this has to be at least a 1/4 of the blade diameter, in your case 2,5" but 1/3 is better, especially by thin blades), Are the flanks flat and are they clean. The max swinging of the flanks has to less than 0,01 mm. What is the sawblade speed (revolutions per minute). When this is all oke it is a lot more diffecult to find the problem, but I would search the problem in the machine and not in the blade. Also it is important to know how many teeth the blade has and your wood thickness
It's worth to mention that a full blade has less wobble. The same as by wood, how thinner how more instable. And yes also bad belts can cause fibration with lead to bad sawing results.
 
#6 ·
The set in the belts isn't helping…..but I'm doubtful they are causing the problem. Is possible that when you first changed the blades a piece of something got onto the inner arbor washer (cause blade wobble)? If you put the dull Forrest back on does it still cut relatively well? I suppose the set in the belts can cause a thinner blade to vibrate more than the full kerf…...but that really seems like a stretch.
 
#7 ·
I have a 1947 Unisaw that set up for many years before I got it. I shifted the belts so the set on each belt was in a different position. I don't know if it affected the cut, but it was not as noisy. I did end up replacing the belts with a matched set.

I don't have a clue about what's going on with the full-kerf versus thin-kerf blades. I would try ruling out Fred Hargis' suggestion about the arbor washer though.
 
#9 ·
I've tried putting the old blade back on and it still works fine. The arbor washers are clean and in good shape. I think I will replace the belts and return the blade for a full kerf one instead.
 
#10 ·
Get what works for you, but I can't imagine it is the "thin" in the thin kerf blade that causes that kind of problem. Maybe there was a bad run . . .
 
#12 · (Edited by Moderator)
Are you sure the nut on the arbor is not too tight? Over-tightening the nut can cause a thin kerf blade to become "dished".
As far as belts are concerned, all three belts should be matched. That is, the amount of stretch between individual belts should be in accordance with the Rubber Manufacturers' Association (RMA). Gates, series V80 belts meet and exceed the standard and are highly recommended. Don't use the link belt type. They will not maintain even tension. They are only good for single belt use, not multi-belt.
 
#14 ·
Following up on Mr. Ron's point: The blade flange on the Unisaw is dished (that is, has a slightly raised rim). The arbor washer must also be dished, with the hollowed out part facing the blade. I had a similar problem to yours (lost washer, of course), when I tried using a flat washer. Tightening the nut distorted the blade. So I made my own hollow washer buy cutting one of the right diameter with a hole saw (same D as the arbor flange), and hollowing it with an angle grinder. Held the washer in a vise, of course. The steel was 3/16". Eliminated the problem. Those washers and left hand threaded nuts are very hard to find nowadays, especially from Delta.

I agree a TK blade would distort much easier than a FK.
 
#15 ·
A 20+y/o belt on my Rockwell Contractors saw sat for too long and the belt took a set. I could hear the lopeing sound and the saw was noisy. On a suggestion from a LJ buddy, I switched to a link belt. Problem solved. Noise level dropped in half and the saw cut like new. That was the best money I have ever spent on up grading a machine. Woodcraft, Rockler, Amazon and others have the belts
They ain't cheap but worth twice the price.
 
#17 · (Edited by Moderator)
I have bought several machines with multi belt set ups and although none of them were saws mostly woodworking lathes, and sanders, they worked great.Could you tell us why they don't work on saws? From what I have read over many years , changing to linked type belts seems to be a very large win, win, situation albeit they aint cheap. However they seem to save money and worry in the long run, also cutting down the noise levels is a big plus as there is nothing that drives me more crazy than working with a wailing screeching Irish Banshee of a machine LOL have safe fun, and I hope belt changing brings you the desired effect you seek. Alistair
 
#18 · (Edited by Moderator)
Handle Motor vehicle Fixture Wood Gas


My experience with link belts is limited. I did install the Green HF link belt on my 70s Rockwell contractors saw with much improved performance-I recommend that for sure.
This shaper had a pair of the Red ones already installed. I did purchase a set of Gates Vextra V belts for this machine, but, the pair of link belts run noticeable smoother, so, I re-installed them.
I think the link belts are to run in one direction only, if I need to run the machine in reverse, I will need to use the standard V belts, or turn these around.
The pair on this shaper have worked themselves to equal tension. I have seen these installed on table saws with multiple belts, but many advise otherwise.

I have seen in saw manuals "Unisaw" where it is advised not to over tension the belts, stating, the weight of the motor will over tension the belts.
I found if the belts are too tight-the saw cabinet will rumble-too loose-the belts will slap. Both conditions cause vibration. Sort of a fine point of between too tight or too loose probably should be found.
 

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#19 ·
The belts on my Unisaw were badly set after sitting for 5 or so years before I got it. Given the short length and robust trunions and spindle support, it didn't affect the cut quality at all. I did shift them and retention the belts and the only thing that changed was the noise. I did eventually replace all three with new cogged belts and it is smoother. You might check the blade runout to see if it's running true. You mentioned arbor washer(s), the Unisaw should only have one washer opposite the arbor flange on the other side of the blade. If running more than one washer, you could be creating a problem.
 
#20 · (Edited by Moderator)
My guy at the industrial supply gave me this tip.
My main saw uses 4 belts. When the saw is run for a periods of time, the belts heat up. When shut down, the belts cool down and take a set. After the belts cool down, rotate the arbor until it wont spring back. That way the worst set is relieved. Takes less run time for the belts to smooth out. And, if the machine is not used for a period of time, rotate the arbor now and then.
Another tip, when belts heat up, they get tighter due to more expansion in cross section then length. Best to fine adjust with warmed up belts.
 
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