Mowing Violent start of rotary cutter

[robert thomas]

Although what you say may work, it is not how a slip clutch is designed to work. If I start the mower at 1/2-2/3 throttle and allow the slip clutch to slip, to get the mower going, how is the slip clutch going to perform at full throttle under a heavy load? It will slip excessively and burn out the clutch. I think the reason it works for your customers, is because they mow relatively light duty grass/weeds and don't make the clutch slip at full pto speed. I would guess, the hardest the mower ever works is on start up for your clients. I have several attachments with slip clutches for CUTs and Ag tractors and would never allow a slip clutch to be so loose to slip on start up.

i have a heavey duty lands pride i bought with my dk45. when the dealer brought out i ask him about it and he smiled and said hey its under warrenty start slow and it will be just fine. It's a tractor not a B.M/W.:laughing:ive been mowing so many rocks and hidden stumps lately that it dosent bother me any more:ashamed:

 

[jda1961]

i had a dk55 and a bush hog 305 heavyduty rough cut mower, that tractor destroyed that cutter, twisted the pto 3 times and it never broke, replaced that with a modern shaft and slipclutch. the thing alway engaged hard, thats the major flaw in all kiotis with the electro engagement of the pto. pushing in the clutch should in my opinion over ride all driveline systems. i never really did get use to that part of it, even at idle its still a jolt. i sold mine and don't think i'd buy another one just for that reason, to many good used tractors out there for that.

 

[Grrrr]

I'm a bit late joining in on this one.

But I will echo the comments that a slip clutch does solve this problem to a large extent.

Your all missing the point so far re the slip clutch

The slip clutch should not be so loose so as it slips for more than a second on startup.

When the blades are stationary, they are folded in funny positions out of balance, and there is a massive amount of torque required to get that initial bit of spin on them. That first jolt to get them to spin and throw the tips out is what starts the machine vibrating.

If you have a slip clutch, as the PTO bangs in, the clutch will absorb the first half a second or so of it, and start the blade spinning and get the tips flung out. Only just so as the blade is moving - and then it will be tight again and the blades will get up to speed.

You can prove this concept by starting the PTO, turning the PTO off, waiting for the blades to almost stop, and then start the PTO up again. It will be much smoother even with a very small level of pre-rotation.

This concept is well known in the full size ag machines, we run two big square balers making bales 3 foot x 3 foot by 7 foot long, with a great big plunger that shoves the grass back through the chamber.

The manual specifies that everytime the plunger goes to the end of it's stroke, the slip clutch should move about 1/3rd of a turn, and you can observe this happening. It takes some of the shock out of the driveline.

When you start the baler up the slip clutch will slip for the first few turns and then catch up with itself as it all starts turning.


Most big tractor nowadays do indeed have a slow start, taking about 3 seconds from very slow to ramping up. Just a matter of filling the clutch packs up slower.

But some machines still manage to stall the tractor the resistance to start turning is just so great. Two solutions we use to help this, one is to let the clutch out in a high gear just as you are about to engage the PTO to nearly stall the tractor which drags the RPMs down, and then engage the PTO. Only works with gear tractors though.

The second method is to be lifting the loader or the three point linkage at the same time. The oil needs to be flowing into a cylinder so as it can't fill up the clutch packs so quickly. Dead heading it against a cylinder as mentioned in this thread already won't do much (no different to having the valve shut in terms of oil flow).

 

[joe48]

The cutter blades are getting crossed when it is stopped and when you restart, it takes a while to throw the blades out to operating position. Always start slowly at lower RPM and with the cutter slightly off the ground. Sounds like the tractor PTO is kicking in very abruptly. Ken Sweet

Ditto; same on my 4' KK hog, it is the blade stuck at an angle and until centrifugal force straightens it out it'll vibrate the fillings out of your back teeth!