Engine Pivoting for Belt Tensioning?

SineWave · April 09, 2017, 08:15:55 AM

Hey, guys,

Getting ready to build my first bandmill. Plan to use the Linn basic sawframe and a 22hp HFT engine. Was considering a centrifugal clutch, but they're more $ than I want to spend, and I don't like the options I'm seeing for pulley sizes.

So I'm debating on a different clutch system -- either an idler pulley on a lever, or a pivoting engine-mount plate to raise and lower the motor.

I see that some of you are using the pivoting engine-mount plate for a clutch.

Question: How far, up and down, should the pulley move between the "idle" positon and the "engaged" position? (I would use a 2-belt system with 2-groove pulleys.) Is 3 inches enough?

Question: How are you allowing for belt wear and stretching? It seems like as the belt wears and stretches, you're going to want to be able to raise the engine even further than you did with new belts. Are you also using an idler pulley tensioner to take up this slack ... or maybe allowing some adjustment in how high the engine pivots?

I'd love to see any pics or sketches of how you guys solved these problems...I feel like I'm trying to reinvent the wheel.

Thanks in advance for any replies.

Jeff

Kbeitz · April 09, 2017, 09:11:15 AM

Just another thought... Speedx tractors used a engine slide.
This way you would not need to worry about engine oil on a
a pivoting engine.

york · April 09, 2017, 09:32:32 AM

Slide-i agree,i plan on rebuilding the head on my old TH and it will be a slide setup for the belt tension....

Ox · April 09, 2017, 09:44:48 AM

X3 for slide. If you can rig up a heavy spring it'll really help to keep constant pressure on your drive belts so you don't have to constantly run up nuts or bolts or whatever. An old valve spring or two comes to mind.

coastlogger · April 09, 2017, 10:28:20 AM

I have the tilting engine setup it works just fine. A cam underneath the plate engine is bolted to lifts one side up(overcentre cam)The plate has oblong holes to allow for engine movement as belts wear.I added a pusher bolt to make that process go better. Dont have to adjust very often.You dont need much pulley travel at all. Im thinking an inch I can measure if you want more detailed info.

Ox · April 09, 2017, 11:38:00 AM

Don't forget to add a little bolt under the belt to hold it off the pulley so's everything stops turning eventually...

Kbeitz · April 09, 2017, 12:49:22 PM

Don't forget to have a belt guard on both pulleys or you'r belt
wont release when you tilt it back. The guards makes the belt
bow in the middle and raise off the pulleys.

warren46 · April 09, 2017, 01:49:57 PM

My Timber Harvester is set up with an over center idler pulley that tightens a 3V band. I took a bit if tinkering but now it works really well. You don't need to move 100 plus of minus of engine or motor to do it

SineWave · April 09, 2017, 03:19:01 PM

Thank you all for the great replies. I like this idea of a sliding engine better than either the pivot or the idler pulley.

Ox and KBeitz, I'm having a bit of trouble visualizing what you suggest when you say

"Don't forget to add a little bolt under the belt to hold it off the pulley so's everything stops turning eventually..."

and

"Don't forget to have a belt guard on both pulleys or you'r belt
wont release when you tilt it back. The guards makes the belt
bow in the middle and raise off the pulleys."

When I did a search of this subforum, I saw a similar suggestion to what you said here, KBeitz, but I'm a little foggy on how exactly this works. Can you explain a little more and/or show a picture? Are there arms or something inside the belt guard that move when you move the "tighten/engage" lever?

Thanks again guys, I'm glad I asked because I had not considered making the engine slide instead of tilt.

Jeff

Edit: Now that I think about it, I think I understand your suggestion, Ox -- When you move the engine to disengage the belt, the belt contacts a bolt that helps hold it away from the driving pulley, but when you move the engine to tighten the belt, the bolt no longer contacts the belt ... right? Still unclear on Kevin's suggestion, though...

Kbeitz · April 09, 2017, 04:11:08 PM

Without a guard the belt will lay in the pulley and want to keep
everything moving. With a guard the belt will be guided to help
lift the belt away from the pulley. I learned this when I was around
14 years old and took the belt guards off my old wheelhorse. I could not
get it in gear with out samming it and then the tractor would not stop.

SineWave · April 09, 2017, 04:45:47 PM

Thanks for the drawing Kevin. So I guess what happens is, the guard prevents the loose belt from falling on the lower side, and this allows there to be some slack when you loosen it, is that right? In other words, there's nothing special hidden behind the belt guard ... the key is in making the belt guard just large enough, but no larger than it needs to be...right?

On my design, I think the small driving pulley will be above the large driven pulley...in other words, your drawing would be turned about 45° clockwise ... but I guess if I make a guard that's just barely wide enough, when I loosen the belts, the sides of the belt guard will hold the belt "in" and force there to be a "sag" below and around the driven pulley, allowing it to disengage...

If I'm understanding it right, many thanks for the tip because this wouldn't be obvious to me, and I probably would have made my belt guard too big!

Kbeitz · April 09, 2017, 04:56:10 PM

Yep... You got it ... I do have the drawing backwards. You need the belt to
lift off the drive pulley. Most guards have 1/8 to 1/4 gap between the pulley
and the belt when it's tight.

On some units there is bolts inside the guards that does the work instead
of the guards.

SineWave · April 09, 2017, 05:02:05 PM

I gotcha. So on my setup with the big driven pulley below the small driving (or pulling) pulley, I would want the guard to be real tight all around the bottom driven pulley, especially directly below it, where the belt would fall due to gravity, so that when I lowered the engine to loosen the belt, the slack created would separate the belt from the driving pulley at the top.

That makes sense. Thanks again.

Kbeitz · April 09, 2017, 05:09:07 PM

Quote from: SineWave on April 09, 2017, 05:02:05 PM
I gotcha. So on my setup with the big driven pulley below the small driving (or pulling) pulley, I would want the guard to be real tight all around the bottom driven pulley, especially directly below it, where the belt would fall due to gravity, so that when I lowered the engine to loosen the belt, the slack created would separate the belt from the driving pulley at the top.

That makes sense. Thanks again.

Yep you got it....

Here is a good sample of what they do on garden tractors.
Just a cheap metal bracket to help keep the belt in place.

Magicman · April 09, 2017, 05:53:34 PM

My Wood-Mizer is designed so that the drive belt is lifted off of the pulley but still contacts it enough so that the belt still crawls. This crawling prevents the pulley from wearing a flat spot on the belt.

SineWave · April 09, 2017, 07:29:10 PM

Quote from: Magicman on April 09, 2017, 05:53:34 PM
My Wood-Mizer is designed so that the drive belt is lifted off of the pulley but still contacts it enough so that the belt still crawls. This crawling prevents the pulley from wearing a flat spot on the belt.

Interesting, and a good idea. Thank you, and thanks Kevin for that pic. That's something I could weld up fairly easily for the bottom pulley, I would think...

Larry · April 09, 2017, 09:07:29 PM

You need to research what belt you will use as some are not safe for clutching applications. I know cog belts such as AX and BX are not recommended. As I understand, they can grab in use when they are not supposed to. Regular A and B belts are safe but I don't know about any other style of belt.

I always liked over center with idler solutions. Moving motors can be hard on the shoulders.

SineWave · April 09, 2017, 10:13:28 PM

Thanks for the tip, Larry. Was planning on using double "B" v-belts...

Kbeitz · April 10, 2017, 04:31:00 AM

My experience with some of the older garden tractors is that even with
all the guards in place sometimes the clutch can be a little grabby. we
would hold a bar of cannon wax on the belt while it was turning. Doing
that would take the grappyness right out of it but it would not make the
belt slip under a pull.

SineWave · April 10, 2017, 06:57:40 AM

see below; i accidentally quoted myself instead of editing myself, and now i can't delete this post or the other one.

SineWave · April 10, 2017, 06:58:30 AM

Quote from: Kbeitz on April 10, 2017, 04:31:00 AM
My experience with some of the older garden tractors is that even with
all the guards in place sometimes the clutch can be a little grabby. we
would hold a bar of cannon wax on the belt while it was turning. Doing
that would take the grappyness right out of it but it would not make the
belt slip under a pull.

Interesting, thanks. When the alternator/waterpump belt on my inboard (Chevy 350) boat started slipping, a few people told me the same thing, suggesting a wax product that was sold for windows or doors (I forget, but I think it was called AGS "Door-Ease" stick lubricant). I couldn't find any locally so I ended up using standard belt dressing (sticky stuff sold in spray cans by Napa) so I never bought any. It sounded crazy to me that a wax product could make a belt "sticky-er" but maybe it works the same way your cannon wax works...

What's "cannon wax"? I googled it but don't see anything relevant...

SineWave · April 10, 2017, 07:54:06 AM

For those using a lever to engage an idler pulley or raise/pivot/slide the engine to tighten/loosen the belts:

Are you also rigging your throttle cable to your belt-tightening lever so that when you engage the belts, you also throttle up ... and when you disengage the belts, you also throttle down? Seems like it wouldn't be too tricky to rig...

Kbeitz · April 10, 2017, 08:12:08 AM

Quote from: SineWave on April 10, 2017, 07:54:06 AM
For those using a lever to engage an idler pulley or raise/pivot/slide the engine to tighten/loosen the belts:

Are you also rigging your throttle cable to your belt-tightening lever so that when you engage the belts, you also throttle up ... and when you disengage the belts, you also throttle down? Seems like it wouldn't be too tricky to rig...

Ha ha... I had to go back to see what i typed.

canning wax.... Sorry for my mistake...

SineWave · April 10, 2017, 08:40:26 AM

That ought to be cheaper than "Door-Ease" ... thank you sir!

Clover · April 10, 2017, 09:15:01 AM

SineWave, I built my mill with the sliding plate motor mount and if I were to do it over I'd use a tilting motor mount. It's just less complicated and you don't need to move it much to declutch. I would go with a 5" pully at the motor again I started with a 3" but had the belts slip a bit on larger logs. I'm now using a five inch and experience no slipping. If your facing your drive shaft of your motor and the belts go to the right to the driven pully then you need a bolt or bracket to hold your belts UP and ON the left bottom of your pully. This will release the top of the tension side of the belt off of the pully when you declutch. It doesn't hold it tight just enough to keep the belt off of the top of the pully. Mine doesn't move while declutched and I have no extra wear either. I will shut down if I have an extended period of idling.
You can see four bolt holes around your drive shaft. You would use the bottom left one if belts go right and bottom right hole is belts go left. This may take a bit of trial and error to position it properly. I use a 1" piece of angle iron to hold my belts off of the pully.