Pros and cons of a double belt arrangement for a 1340gt?

D

diamond

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I know the subject of the PM 1340gt belt has been discussed ad nauseam however I didn't find this question.

When I got the lathe 8 mo a go I immediately put a Gates notched belt on it. I run a VFD and use a the high range pulley arrangement and have found I have no need for the low range. I can go 70rpm up to 1800rpm with the VFD and it works fine for my use. Below 140 the motor sings a bit but I only go down that low for light parting and drilling work. In fact most of my work is light duty stuff. Mostly hobby gunsmithing.

I found the Gates notched belt has a big problem with memory. I've taken it back off and put the stock belt on. I don't know if it will last but I did notice it ran a bit quieter. That's got me thinking of going to a link belt.

Now that I'm researching link belts I'm wondering, has anyone done a double belt upgrade and what are the pro's cons of doing that? For a link belt I'd be running a A profile belt (most of these pulleys are fine with either A or B profile it seems). Maybe a double belt just adds more noise? Or would it in fact run smoother? Less potential for slip I'm sure but I don't do a lot of really heavy work. VFD gives a soft start so that isn't really a concern.

I have read all the comments about running in reverse. I do but not under any load. Mostly just running the carriage back when threading and the nut is engaged.

Have a 10% off coupon and considering these before it expires:
5/8" x 3" double pulley for headstock shaft
3/4" x 3" double pulley for motor shaft
And the 5' x 1/2" link belt from HF that I can get for $28 with the 20% off coupon. Don't know if I could make 2 belts out of 5' but even if I had to buy two of them the whole mod would be less than $90.

What does the wisdom of the forum say? Is this a dumb idea? Just go with single link belt & stock pulleys? Thanks!!!

-dave
 
Only reason for a double or triple belt is to transmit more power, which is not needed. You also have more issues with equal length belts and harmonics between belts, so short answer is stick with a single belt no matter what you do. I would just flip the motor pulley end and run the larger motor pulley to the larger headstock pulley. Less likely to take a set with a larger diameter pulleys, gives a better speed range of power vs. high speed position, it needs something like a BX27. As far as the Gates, I am really surprised that it is taking a set, I used them on my 1340GT and on my ERL-1340 and have not had any issues. One problem with belts is if they are old, they will get stiff. I bought some "new" Gates belts off of Amazon and they were really old and not as pliable as the new belts I previously purchased from Royal Supply. If you are having a problem with the Gates, give them a call and see what they say/recommend.
 
My Gates belt takes a set, too. I got it from Amazon so maybe I should buy one I know is new.
 
Thanks Mark. You're confirming my suspicion about double belts. I don't need it and will introduce other headaches. Right now my pulley arrangement is the 3.5" size on both motor and headstock shaft. the stock "A" configuration I think it is. I might try that suggestion to flip. Might have to up the frequency limit on my VFD. I can get to 1800rpm now in the 1:1 configuration of the two 3.5" pulleys, or a tad more, easily without going over 60hz much. If my math is right (assuming 3.5":5" pulley ratio) I'll need an upper frequency of 85hz to still get 1800rpm. Just have to see how the stock motor likes that. I think you told me it can handle even 90hz.

Regarding the Gates taking a set it may also be that I had too much tension, causing the set (and maybe the noise too). I did have it cranked down pretty tight, thinking that was best but I've picked up on both in reading up on the other belt threads that real tight is not a good idea. Couple other factors, my shop is not heated unless I'm in it so it got cold this winter but a bigger factor is my machine sits with the belt stationary for a while at a time when I'm on travel. Several weeks maybe. Perhaps I should loosen it or even take the belt off during those away times.

Thanks again for the help!
 
I also got mine off Amazon. Perhaps there's a theme here.
 
Another reason for a double belt, is you do not need to keep the setup as tight, lessening the load on the bearings. I thought it was crazy that my Fosdick drill press has 4 belts, but when you look at them, there is not much tension on the pulleys, so also not much load on the bearings.
 
I have a 1340, run a green link belt, and build/modify pistols and a little bit of rifle work. On a whim I put a 'real' belt on and experienced memory issues and some slight vibration at certain speeds.

I went back to my link belt. YMMV. :)
 
Do NOT run it too tight, you will get more vibration and it will take a set. You just need enough to transmit the power and the notched belts do a better job of gripping. Had another individual with a 1340GT and had vibration, traced it to the belt being too tight. I use the weight of the motor plus some light pressure on it. Another good reason for having the belt tension not too tight is if something crashes the motor will hopefully slip on the belt. I do not agree two belts are better, lots of problems on the G4003G with belt vibrations of two belts. They need to be matched and the alignment of the pulleys spot on, so a bit more difficult and poor belts will mismatch just slightly as too length and position on the pulley. I would also consider a fresh belt, my last set for my ERL-1340 came from Amazon, they are not as pliable. If I recall there is a new version of the Tri-Power which is the II series. Amazon is cheap sometimes, but often you are not sure what you are getting. Just my opinion, YMMV.

Run your stock motor to 90 Hz, it does just fine and power is more optimum in the 60-90 Hz speed range. With the motor pulley flipped and running the larger headstock pulley, the top speed should be about the same at 90 Hz.
 
I'm now quite sure too tight was/is my issue. I was cranking down on it, a lot. Now I have just the weight of the motor. That is seeming to be just fine after running a bit and letting the belt "warm and settle" then loosen and again retighten with just the weight of the motor. Did that about 3 times until I couldn't see the motor drop when loosened.

I am going to flip the motor pulley this evening. The pulley ratios when flipped (having measured to confirm) are 3.5:5.25 and the math says exactly 90hz for 1800rpm so you're spot on Mark. I did also pick up a link belt just to play with it. I'll report on that with some A/B comparison tests.
 
I had more vibration when I used the weight of the motor to tension the belt. I have to raise the motor a bit to reduce vibration.
 
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