A bit more progress has been made on the body of the flail mower. I made the adjustable height skid plate with the rear roller as an assembly for over end so far. My first try will have the bottom of the roller about 25 mm below the skid.
I also got the cutter drum back from dynamic balancing. If I was still wondering (I was) about whether the cutter layout that I came up with is a good or bad idea the balancing has settled it - what I've made is a dumb idea. I'll try to explain.
I laid out the cutters with three helixes. The first starts at 0 - the second starts 120 degrees around and 50 mm along from the start of the first - the third start 120 degrees around and 50 mm along from the start of the second. This means that as far as balance goes their starting points are even around the drum at 0, 120 and 240 degrees. But they are offset along the drum by 50 and 100 mm - this is the bit that is causing my problem. The fact that they are paid out as helixes rather than straight lines doesn't help or hinder this balancing problem - it's all in the lengthways offset (apart from other minor variations in tabs, welds and blade mass).
Despite the above design issues it was able to be balanced by the second place I took it to (the first one tried but gave up).
Below is a pic of the weights that were added at one end of the drum - it's similar but diametrically opposite at the other end of the drum.
Weights added to achieve "balance" (I didn't ask what residual unbalance he was working to):
Without blades
End 1 - 166 g
End 2 - 239 g
With blades
End 1 - 392 g
End 2 - 487 g
Easier to see with a picture....it's a lot....
He showed me the cutter drum running in the balancing machine with the blades attached and I couldn't feel any vibration at the bearing mounts at either end, so I think it will be fine to use.
The large additional weights that needed to be added to rebalance the drum when the blades were added confirms the problem is caused by the lengthways offset of the three helixes. This also means that as the blades wear and become lighter the balance will deteriorate, even if the blades wear perfectly evenly. I don't know how quickly the blades will wear so I don't know how quickly it will get worse and don't really know how much worse.
My plan for now is to get it finished so I can at least test it and see how it performs in cutting our grass. Assuming the rest works ok I'll probably start thinking about another drum layout but this time I'll have balanced tabs and blades diametrically opposite rather than being offset lengthways.
It all makes perfect sense now - yet another good dose of 20/20 hindsight. I'll call it a learning experience.
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