Clutch problem

[Neil_B]

Well my centrifigal clutch gave out on me with 91 hours on the machine. Took it apart and the springs were broken due to there being no friction pads on the blocks. Luckily it's only costing me another $90 for the kit :.

Question is though, why would it wear so quickly? I did have 2 burnouts on it when the blade snubbed but is that enough to wear the pads down? Is there something else that I should be looking for that could be causing this?

I do start and stop the blade for each cut but this is supposed to be a heavy duty clutch so I would expect it to stand up to that or could that be cause for the early wear.

What do others with the clutch do while sawing?

Neil

[Tom]

I attributed my clutch wear to big logs and feed speed.  Even then I was looking at 2000 hours.  I had a couple of "burnouts" too when the blade became jammed in the swollen butt of a log.  This didn't help it I'm sure.  The internals of my clutch are aluminum and heat eventually melted it and seized the inside of the clutch up.

I am more cognizant of my feed speed now and have slowed it way down.  While I know that the blade will cut faster, I don't think that the mill will stand it.  If you cut big logs then you may want to slow down some too.

[D._Frederick]

New-Sawyer,
It could be that your clutch is too light duty for the way you are sawing. Maybe, you should think about getting a clutch that is rated for more horsepower. Could be that the mfg. cut corners, and put a lighter duty clutch on to reduce costs.

[Neil_B]

Tom,
As it stands now, I don't feed all that fast and I cut alot of small diameter logs. the odd big one comes on but none that were over 18". We don't seem to have too many around here bigger than that :(. My clutch looks to be all steel and the housing is holding out well but the pads sure didn't last.

D_F
Could be that the mfg. cut corners, and put a lighter duty clutch on to reduce costs.  

thought that more than likely that was the case but according to the clutch specs this is for heavy duty use. It listed this model  for the 40Hp and 3000 rpm range which is where I stand now.
 I'm wondering if they installed a used clutch assembly. : Could be the reason I've never really got it sawing at full capacity yet. (where ever that is).

I've got the new one on now as well as one of the one piece dual V belt. It seems to have a whole different sound to it now, as if the blade is running faster.   Will get to try it out this afternoon to see if it is much different.

[D._Frederick]

New-Sawyer,
Sounds like the clutch is correct one, are you running the engine at the correct rpm? Could there be a problem with the engine since it is new? Maybe the timing is incorrect reducing the engine torque.

[Neil_B]

I'll have to dig up the specs for the motor. I'm currently running at 3200 rpm and certainly have room now to drop down now. It seems to run so much smoother.
The motor is a Kubota 36hp (42 peak) diesal with a top rpm of 3200 but I don't know where the optimum rpm is for the torque. I'll just try dropping back to 3000 or maybe even 2800 and see how things work out. Will soon have to try the hardwoods again to see if it's making a difference or not.

[Russ]

Can't help with you're clutch problems but I have some Questions of my own. What companys manufacture clutches ?
I have a 20 hp briggs motor and I have no idear who makes the clutch and how to get parts for it. What kind of service should a clutch get ? I would think it should  be inspected every so many hours and some kind of lubrication or shoe replacement.

Rusty's Band Sawmill

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[Tom]

Check this out:

http://www.blm-cm.com/etoc.htm

[Russ]

Thanks Tom, that was quick.

[Neil_B]

Russ,
I'll call the dealer and find out what the company's name is. I had to search around the housing and found a stamped part number on it. Took the worn parts to the local bearing supplier and they found the parts I was looking for. There is no manufacturer name on the bill.  Looks like an occasional clutch kit would be all that's needed with this clutch ($90 Can) and it comes with just the new blocks, pads and springs. I'm hoping this one will last me more than 90 hours though ???

Tom,
I forgot to ask if you start and stop your mill with each cut or do you fire up and saw 'till you are done the log?

[Jason_WI]

New_Sawyer,

I wouldn't reduce the RPM. It is a centrifugal clutch and the less RPM, the less force that is applied by the clutch shoes which will increase the slippage and the heat. IF anything you could somehow add weight to each shoe so that more force is applied to the clutch bell. It may change your engagement RPM but at least it wont smoke as easily.

I smoked the clutch on my Norwood mill. I found the specs on the net for the clutch that was used and it is only rated for 8 HP and they used it on a 20HP Honda >:( ??? :-/

If you have the specs for your clutch then there should be a torque curve vs RPM plot. You should then be able to tell where the sweet spot is.

Comet makes clutch also.

http://www.lotus-equip.com/pulley_clutches.htm

Jason

[chet]

Jason are you still running yours direct or did you replace the clutch?

[Tom]

Starting and stopping the blade each cut is a Wood Mizere thing.  I don't know of any other manufacturer that recommends doing it.   Even WM doesn't do it all the time.

The Mill I use that has a clutch hasn't even the capabilities of stopping the blade each cut.  If I power it down then the blade coasts to a halt.  It takes several minutes.

I have wished sometimes that I could stop the blade quickly but it just won't do it.  Even if I devised a brake, it would have to stop 500 pounds of band wheels.

[Jason_WI]

Chet,

I am still running it direct. So far I have cut more than 7000 bf with it direct. I find that there are less wavy spots because of the constant blade speed. I used to see more dips by large hard knots. I would also notice that the blade would slow down when it hit these hard spots with the clutch on. Now when I hit these large hard knots with it direct the motor RPM is pulled down slightly.

If I can find the right clutch without having to do too many modifications then I will probably go back to a clutch for safety reasons.

Jason

Jason

[Neil_B]

Tom
Sounds like maybe I'm going to have to do some more tweaking.  ??? If I leave the mill running full tilt all the time, the carraige returns so fast that it almost jumps off the rails. I almost had it come off the end of the mill once when the solenoid stuck open and it hit the stops so hard it bent the brackets that touch the stops at the end. I tried once already to close off the flow control for the return but I didn't get much of a result out of it.

Jason,
I will see if I can get some specs for the clutch.

[Tom]

I like the "high speed gig-back" I have manual valves and feather the valve to slow the return. That's a must when pulling boards back. The manufacturer installed a heavy spring for a bumber on the "off-side" of the mill to protect the wheels and to help keep the mill from doing what you describe.  There was once one on the side that the off-bearer uses but they removed it.  It made a "pinch point" and could have taken someone's hand off.  

You might look at welding a spring bumper on your mill.

[Neil_B]

Is it just a bumper on the top side of the rail at the end of travel? Got a pic of it?

I had contemplated installing micro switches at both ends of the mill to automatically stop it if I was preoccupied ;). 'Course that wouldn't do much if the solenoid stuck open again.  

Anyway, I tinkered around this morning with the flow control valves. Reason I couldn't get any change out of them before was due to more metal in there so I cleaned, readjusted, cranked up the mill and threw her in reverse. Now it's controlling it slower so I can leave it revving.
I think I was probably wearing out the clutch from the torque of starting up so frequent. Will see how it holds up now.

Thanks guys

[Tom]

Yep! just a bumper on the top side. Yep, got a picture. :D


It's only on the return and not on the off-bearer side.
Think Safety!

[D._Frederick]

New sawyer,
With the torque of your diesel, the clutch probably does not have enough contact area for the shoes under heavy load. Instead of having a 40hp engine using a clutch rated for a maximum of 40hp, you should have a clutch rated for say-  40 to 60hp. I would say that the MFG short changed you, and that you will be spending a lot of $90. I would get back to your mill mfg and complain.

[Neil_B]

I would say that the MFG short changed you, and that you will be spending a lot of $90. I would get back to your mill mfg and complain.

I won't go there D_F, :P but I will check into other clutch paks and see what I have to choose from. If this kit lasts as long as the first one I will upgrade to a heavier model when it wears out.

Tom, thanks for the pic. Here are mine, circled, not very sturdy looking. The back ones are actually bent now from the last time it took off on me
I like the idea behind yours but would also worry about pinch points because of the layout of my controls. Something to think about though.

[oldsaw]

If the clutch smoked for any length of time, the pad surface can glaze over and slip more easily, especially when under a good load.  This will increase heat buildup, which increases wear from slippage, weakens spring tension, which increases slippage, which starts the whole cycle over again.

You may want to sand the new pads and maybe touch up the inside of the drum with some 220 grit.  Try 100 on pads, just rough up surface.

They are cool when they work.

Mark

[Neil_B]

Mark, thanks for the tip. I did go over the housing with sandpaper to clean it up but didn't do it with the new pads. If I do happen to burn out again, I'll take it apart and give it a going over.

[oldsaw]

Shouldn't be a big problem unless they looked kind of shiney.  They will eventually, I've just been more successful with brakes and clutches if I've taken that approach.  Everything just seems to seat in better, and trouble just doesn't seem to happen nearly as often.

Mark

[Neil_B]

Looks like I'm going to be looking for a larger clutch pak.
I've got about 50 hours since changing the last set of pads and the other day I took apart to check em.
Half worn already  :(

Currently it's a 4 pad clutch and I'm going to look at a 6 pad one. I very rarely start and stop the engine anymore so it must be just not taking the torque or something. I haven't even had any burn outs, OK maybe one  :.
 Still, doesn't look like it's going to hold up.

One thing I do wonder is with installing a smaller driven pulley it would make it harder to get the bands turning therefore putting more stress on the clutch, correct?
Also the engine itself doesn't increase it's speed slowly when I hit the actuator so with it going to full rpm quickly I may be putting more strain on the pads.

As D. Frederick mentioned earlier, I may go to a higher HP rated clutch and may look at a slightly lower rpm range one.
More input would be welcomed as usual.