The Forestry Forum

General Forestry => Sawmills and Milling => Topic started by: DR_Buck on December 26, 2004, 06:41:42 PM

Title: WM LT40 Drive Belt Tension
Post by: DR_Buck on December 26, 2004, 06:41:42 PM
I need to adjust the drive belt tension on my LT40HDG25 and the manual calls for correct belt tension to have 7/16" deflection with 14 lbs of deflection force.   Question is: How do I accurately measure 14 lbs of deflection force?    ???
Title: Re: WM LT40 Drive Belt Tension
Post by: Tom on December 26, 2004, 06:57:39 PM
Here's my non-mechanically minded answer.

The belt has to slip when the clutch handle is released.  If it doesn't then the blade continues to turn, or it fights the brake..

If it is too loose the belt will flop and may come off of the sheave.
Procedure on my old mill:
I would set my brake so that the handle would be at the 10 oclock positin (1990 lt40)

Then I would tighten the drive belt so that the belt would be barely loose and the brake engaged when the handle was disengaged.(at the 10 oclock position)

If you aren't running, have the belt "in gear" (tightened) then 1/2 inch of play is about right. (using some Kentucky windage)  If you have ever tightened an alternator or generator belt then you can do this. :)

You wouldn't believe the amount of grip that a V belt has on its sides when riding against the V in the pulley.   Too much tension isn't really required if the belt and pulley are in good shape.

Title: Re: WM LT40 Drive Belt Tension
Post by: DR_Buck on December 26, 2004, 07:10:24 PM
Thanks Tom...   Kind of thought it was like tightening an alternator or generator belt.  

Loosen the bolt
Cuss alot
Stick the pry-bar between the alternator and the water pump
Cuss alot
Pull as hard as you can
Cuss alot
Tighten the nut again.  

Real simple
Title: Re: WM LT40 Drive Belt Tension
Post by: Bibbyman on December 26, 2004, 07:30:07 PM
JB of Wood-Mizer told me...

With engine NOT running - pull the lever to engage the drive. Then take the belt with one hand and twist it.  If it will turn about a 1/4 turn with some effort,  it's about right. It's worked for me.

I've found that when you've got wavy cuts that can't be explained by dull blade, gummed up blade, bad guides, etc.,  it'll be the drive belt too loose.  Your engine will often times sound like it’s running fine so you just keep pushing it but with a loose belt,  you’re getting some percent slippage so the harder you push the blade, the more it slips and the worse cut you’ll make.
Title: Re: WM LT40 Drive Belt Tension
Post by: sawmillsi on December 26, 2004, 08:16:28 PM
Hi guys,

Just a thought from a swinger, why not use a small fishing balance. The ones that have a hook at each end (no barb) and when you put the fish on one end and hold the other, a little needle gets pulled down against a spring and you can read the weight.

Could you put one hook at the midway point on the belt and pull on it. This would tell you the loading for the deflection.

We can buy these balances for about $3 at Kmart.

Si
Title: Re: WM LT40 Drive Belt Tension
Post by: DR_Buck on December 27, 2004, 03:51:55 AM
Bibby,

Thanks for the suggestion. Your recommendation fired off a long unused neuron in the brain.  I remember the 1/4 twist thing for v-belts from some time in the past.  Not sure how far or where in the past, but I remember.

Si,

Great idea also.  But I'm not sure a
Quote
a small fishing balance
will work.  Where I fish, 14 lbs is a large fish.  I might need a large fishing balance.


Thanks,
Dave
Title: Re: WM LT40 Drive Belt Tension
Post by: Gilman on December 27, 2004, 08:41:16 PM
Should the belt tension be enough to stall the engine, or should the belt slip before the engine stalls?  

Title: Re: WM LT40 Drive Belt Tension
Post by: Bibbyman on December 28, 2004, 05:12:42 AM
What engine do you have on your 40 Super?

I'd think on a small engine - 8-20hp, yea maybe you'd kill the engine..

But on a larger engine - 30hp+,  I think the belt would slip before you'd kill the engine.
Title: Re: WM LT40 Drive Belt Tension
Post by: VA-Sawyer on December 28, 2004, 03:29:47 PM
If the belt slips, then that means you can't use all the hp from your engine. At higher hp you can ruin a belt if it slips for only a second or two.  With recipicating engines the power curve falls off pretty quick as soon as you exceed max HP. This means that the engine should bog and die before the belt slips.
Electric motors can produce torque that far exceeds their "rated limits" for short time periods, before the excess current smokes the motor.  I seem to recall that "breakdown torque" may be  200-300% of "rated torque".  I would expect the belt may slip first in such setups.  
As an example... I would design a drive system that had a 10 hp power source by using components rated at 12-15 hp. The recipicating engine would bog and probably die, if loaded to 15 hp. The electric motor, on the other hand, may produce 20-30 hp under overloaded conditions for a short time before the current limiters blow.  I would not be suprised if a 12-15 hp drive system slipped or otherwise failed under those conditions.
VA-Sawyer
Title: Re: WM LT40 Drive Belt Tension
Post by: Fla._Deadheader on December 28, 2004, 05:24:59 PM

 We use 1 "B" Section belt, and I can stop the 24 HP Honda IN IT'S TRACKS. RAT NOW. ;D ;D ;D
Title: Re: WM LT40 Drive Belt Tension
Post by: DR_Buck on December 28, 2004, 05:39:12 PM
Tightened the drive belt today and man what a difference! :o :o

It must have been slipping for some time. I had forgot how fast I could go through logs!  It was like having a different saw.  Didn't have any blade dive or wandering like had had been recently experiencing.  I thought I might have had a batch of bad blades.  

I also got reminded of how hard the clutch arm is to operate when the belts are adjusted properly. ::) My arm is aching. :'(
Title: Re: WM LT40 Drive Belt Tension
Post by: Minnesota_boy on December 28, 2004, 05:56:35 PM
I'm with you on the arm.  This November I had to tighten my mill's belt and WHOA!!! what a difference in sawing and WOW!! does the arm ache at the end of the first couple of days after that.
Title: Re: WM LT40 Drive Belt Tension
Post by: Bibbyman on December 28, 2004, 06:37:15 PM
Now'd be a good time to check your engine's top end RPM setting - if you've got a way to do it.  Engines have a way of slowing down and even a 100 RPMs can make a BIG difference.
Title: Re: WM LT40 Drive Belt Tension
Post by: VA-Sawyer on December 28, 2004, 08:41:03 PM
That's why I put that tach on my saw. I also have a pocket tach by the same company that I could use for spot checks. I just found it too handy to have a tach in constant view. It is a lot like a "loadmeter" for me.
VA-Sawyer

P.S.  to  FDH, I can also bog and kill my 24 Onan in a second with my saw. I hit BIG tramp metal.... It sounded horrible for a second then everything was quiet. I don't want to do that again. ::)
Title: Re: WM LT40 Drive Belt Tension
Post by: sparks on January 04, 2005, 09:29:07 AM
Drive belt tension is the most forgotten adjustment. We've been indoctrinated that a belt will squeal when loose. It won't in this application. If you hear the drive belt squeal while sawing, it's definitly to loose. Glad to hear you adding to the sawdust pile again.  :)
Title: Re: WM LT40 Drive Belt Tension
Post by: pigman on January 08, 2005, 06:25:37 AM
Quote
Now'd be a good time to check your engine's top end RPM setting - if you've got a way to do it.  Engines have a way of slowing down and even a 100 RPMs can make a BIG difference.

How do you check the engine rpm of a small diesel without a built in tach. I think my Lambordina may be slowing  down a bit, but I have no way of knowing for sure. Could be I am just getting faster,. ;D
Bob the fast sawyer
Title: Re: WM LT40 Drive Belt Tension
Post by: shopteacher on January 08, 2005, 02:15:19 PM
Hi VA-Sawyer,
Was wondering what kind of tach you put on your mill and where one can be purchased?  Any idea of the price?
Thanks
Title: Re: WM LT40 Drive Belt Tension
Post by: VA-Sawyer on January 08, 2005, 02:56:16 PM
Shopteacher,

I have a small digital tach that I got from a company called Design Technology Inc. Their website is  tinytach.com. You can see a picture of it on page 4 of the "Useful Sawmill Mods" thread. This has been a really nice company for me to deal with. I origionally purchased a basic unit from them that only had RPM and Hourmeter functions. I was offered a chance to evaluate one of their new designs for free. They sent me one of their new Commerical Units to try out on my saw for a while. It had a shorted sensor lead and wouldn't work when I got it. The company was willing to send me a second unit free of charge, but I said I would try to fix the first one. I got it working with a little trickey soldering and ran it for about 50 hours so far. I really love  the extra features in the Comm. unit. It displays RPMs while the engine is running, so I can monitor how much load I'm putting on the blade. I can also cycle through an hourmeter, two countdown timers, and max RPM. I think that my 'fix' isn't holding up very well, so I'm going to order a new one from them in the next few days.  I also purchased a Pocket-Tach from them for my chainsaws and other small engines. Overall, I would have to say that I've been very happy their units. I believe that the problem I had with the Commercial unit was because it was an early unit. I don't expect to have any problems with the unit I'm going to order next week. They also make units that work on diesel engines.
If you call the company with questions, talk to Steve, he seems to know his stuff.
VA-Sawyer

Title: Re: WM LT40 Drive Belt Tension
Post by: Bibbyman on February 01, 2005, 07:55:28 AM
JB of Wood-Mizer told me...

With engine NOT running - pull the lever to engage the drive. Then take the belt with one hand and twist it.  If it will turn about a 1/4 turn with some effort,  it's about right. It's worked for me.

I have been corrected by Mr. JB that he did not give me the above advice.  He recommends using the deflection measurement documented in the book – unless you’re experienced enough to judge the deflection by hand.

Further,  he cautioned that over tightening the drive belt could cause premature failure of the motor bearings.

Thanks JB for pointing out my error.

(But somebody did tell me they used the twist method.  Maybe it was John Hicks?)   ::)