Flail Mower Let's talk flail mowers

[dlmpsy]

Thanks for the recommendations. I've been thinking about the Caroni since last summer. It's about income tax time, so I'm getting ready to bite the bullet.

 

[Waratah15]

Hello All,

I originally posted this in the Build It section but think it may be more appropriate here.

Planning to build a flail mower for my ASV Skid Steer, realise you are PTO kinda guys...if it's any consolation I do have a Kubota BX1800. But reading through the forums there is an absolute wealth of knowledge here and I was hoping you may be able to help me out.

Just after some advise before I get into the 3D drawings stage, I'll be drawing it all up in Solidworks and would be more than happy to share laser cutting files etc once I get to that stage.

Plan to run a hydraulic motor something like this one
Surplus Center - 2.8 cu in CHAR-LYNN 101-1001 HYD MOTOR

This style of motor runs at about 1000rpm

I have 16.3 gpm and a 3000 psi relief pressure on my hydraulics to run the mower

Seems like flail blades need to run at around 8500 fpm, I'm guessing that the overall diameter of the main shaft and blades - cutting tip to cutting tip is about 12 inches. That means that if I run the shaft at 1:1 with the motor (via belts) @ 1000 rpm I will only be getting 1' x 3.14 x 1000 rpm = 3,140 fpm.

So my options seem to be, either 3:1 with the belts or combination of inline gearbox and upping the ratio with the belts. of course I could always increase the diameter of the cutters tip to tip but don't want to make the whole thing too massive considering its a low flow skid steer.

Maybe I need to run a motor like this, with 5000 rpm (scary!) and gear it down with the belts.

Surplus Center - About Us

Any suggestions here please?

Next question - the main shaft that the flail blades are attached too, are they solid steel? Maybe 3 or 4" diameter with the ends turned down for the bearings. That's one heavy shaft at 72 inches, couple of hundred pounds right there. I realise this assembly will need to be dynamically balanced.

Hoping I'm not wearing out my welcome here, regarding the hydraulics, if someone with some experience here could chime in I'd really appreciate it. My ASV has controls in the cabin for forward and reverse but I'm looking at what I will need on the mower deck for the circuit. Seems like I need a pressure relief valve to keep the psi in the acceptable range for the motor, is there anything else that I should be putting into this circuit in terms of flow control or cushion valves?

Some of the lower end skid steer flail mowers lack the ability to 'float' in relation to the skid steer. The Bobcat one looks really nice and seems (although I'm not exactly sure) to have a mechanism that lets it articulate up and down as well being able to rock one side higher than the other. At the very least I'd make it free in the up and down plane to follow contours more effectively.

Any thoughts/opinions/advice gladly received, thanks, Jonathan

 

[GinNB]

Why such a small diameter cuttershaft? 12" tip to tip for the blades is pretty small. The increased RPM required would probably be harder on bearings, assuming that you could keep such a small cuttershaft stiff and straight. Larger diameter tubing is much stiffer than smaller diameter or rod. I'd check a materials manual to see the amount of force required for much deflection in the center of the shaft. What happens if it hits a rock in the middle? Lose a pair of teeth and going around how many thousand times before you can stop it? Rigidity in the center of the shaft is good. Overkill is the best. I'd use a bit larger tubing to help with the needed tip speed.

Haven't checked recently, but off the top of my head I think I remember the tip speed on an Alamo SHD is in the 3500+fpm range. 3800 maybe? I was told that at a dealer ages ago but couldn't find it in print when I looked. If they were right and my memory is good, you aren't that far off.

 

[Waratah15]

Thanks GinNB, only picked 1' out of the air, trying to work out the scale of the machines I've seen on-line. Starting with clean sheet so I can do it any size I want. I got the 8 or 9000 fpm figure from the Bobcat site but I haven't been able to work out how most of the mowers powered by a 580 rpm PTO could get anywhere near that so what you are suggesting makes sense. Don't want to run anything anywhere near 5000 rpm on equipment like this.

If anyone could measure or roughly know the size of the centre shaft and the total tip to tip diameter that would be a great help.

 

[IslandTractor]

Thanks GinNB, only picked 1' out of the air, trying to work out the scale of the machines I've seen on-line. Starting with clean sheet so I can do it any size I want. I got the 8 or 9000 fpm figure from the Bobcat site but I haven't been able to work out how most of the mowers powered by a 580 rpm PTO could get anywhere near that so what you are suggesting makes sense. Don't want to run anything anywhere near 5000 rpm on equipment like this.

If anyone could measure or roughly know the size of the centre shaft and the total tip to tip diameter that would be a great help.

Do you have the capability of dynamic testing and balancing of the rotor? That is the most critical part of the fabrication as the rest is really just a PTO or hydraulic power transfer device. If you don't, perhaps it would make sense to bite the bullet and purchase a rotor from Alamo or Caroni or one of the other companies that make these mowers. You might find it cheaper in the long run to purchase a PTO flail and convert it. Depending on what duty machine you want, that might be the cheapest and fastest way to do it.

 

[Code54]

My center shaft is 9" in diameter (think the book said 3/8 wall thickness) not including the shackle or knives. It is a Bomford/Turner commercial model. The overall weight is 1258 if I remember correctly.
Hope that helps

 

[Waratah15]

Do you have the capability of dynamic testing and balancing of the rotor? That is the most critical part of the fabrication as the rest is really just a PTO or hydraulic power transfer device. If you don't, perhaps it would make sense to bite the bullet and purchase a rotor from Alamo or Caroni or one of the other companies that make these mowers. You might find it cheaper in the long run to purchase a PTO flail and convert it. Depending on what duty machine you want, that might be the cheapest and fastest way to do it.

I'll certainly have the shaft and blades balanced after construction, it's possible to buy flail mowers in Australia with the bobcat attachment but they are insanely expensive. The other option is to buy an second hand pto unit and convert that. Just love designing and making things! It's a disease I have and there doesn't seem to be a cure!

 

[Waratah15]

My center shaft is 9" in diameter (think the book said 3/8 wall thickness) not including the shackle or knives. It is a Bomford/Turner commercial model. The overall weight is 1258 if I remember correctly.
Hope that helps

Thanks Code54, that may be a little too big for my hydraulics but sounds much better than the 3" solid I was thinking of.

 

[Waratah15]

Just sourced some 6 1/4" OD 3/8" wall cold drawn seamless hydraulic cylinder tube - $300 for 72"

Can't quite work out why these units are $10,000 dollars here! I know these are excavator mount units but there are some big margins as far as I can work out.

Excavator Brush Mowers

 

[leonz]

Hello Warata,

Before you get too too far on this-

You should vistit the everything attachment site or the skid steer attachments.com and you can purchase a quick attach kit that can operate a standard PTO drive three point hitch type heavy duty flail mower with your ASV hudraulic system using a pump mounted in the quick hitch that rotates the flail mower gearbox at the rated 540 RPM using the ASV hydraulic system.

I have one question is your ASV unit a high flow unit?


Save your time and money and do it this way.:thumbsup: