Custom rotary cutter ideas, suggestions...?

[/pine]

I've been looking for a used 4' rotary cutter without much success...I don't really have a typical need for a bush hog...no large areas to cut etc...just some stretches of wide road shoulders...so I really don't want to put that much out of pocket cash into a cutter...

I'll continue looking for a used one...but in the mean time I am considering making a custom cutter...I have a few questions...

Looking at the gear boxes at Surplus Center...they say input RPM 540/1000...I thought a majority of compact tractors generally have 540 rpm PTOs??...how do these gear boxes perform at only 540 RPMs ?? Surplus Center

Can I get a stump jumper that will fit one of these gear boxes?

I have some 1/4" diamond plate to make the deck etc...

Also have a wild idea to weld 4 brackets to the top of the deck so it could be clamped/bolted to a set of 3ph pallet forks...rather than messing with a typical 3ph A-frame...any thoughts on this?

One more question about new cutters...of the three lower end cutters 'J-bar', Frontier and Kodiak...anyone have experience with any of these ?

 

[quicksandfarmer]

I replaced the stump jumper on my cutter a few years ago and I found they are pretty standardized. The two key dimensions are the output shaft on the gearbox and the bolt holes for the blades. The most common gearbox output is the 12-spline.

The surplus center gearbox has a 1:1.47 stepup. With an input of 540 RPM the output is at 793 RPM. With a 4' diameter the blade travels 12.5 feet per revolution, with 793 RPM that is 9960 feet per minute or 113 mph. That's a good blade speed.

You want your cutter to float so that it can follow the contour of the ground and rise if it encounters an obstacle. Typically the top link has a pivot attachment so that the top link is not under strain when the cutter is in cutting position and the tail can go up and down freely. I'm not sure you can do that with forks.

 

[/pine]

I replaced the stump jumper on my cutter a few years ago and I found they are pretty standardized. The two key dimensions are the output shaft on the gearbox and the bolt holes for the blades. The most common gearbox output is the 12-spline.

The surplus center gearbox has a 1:1.47 stepup. With an input of 540 RPM the output is at 793 RPM. With a 4' diameter the blade travels 12.5 feet per revolution, with 793 RPM that is 9960 feet per minute or 113 mph. That's a good blade speed.

You want your cutter to float so that it can follow the contour of the ground and rise if it encounters an obstacle. Typically the top link has a pivot attachment so that the top link is not under strain when the cutter is in cutting position and the tail can go up and down freely. I'm not sure you can do that with forks.

Thanks for the input...
Honestly I know nothing about rotary cutters other than what I see on the net and from the road...never really looked at one closely...but I have gathered enough that I think I could make one fairly easily?? (I have in the past over estimated my on hand tools/abilities etc.)...

I currently have a hyd. toplink w/ check valve but I'd have no problem with making a custom top link to use with a cutter...can easily make up any combination of hyd.,chain, turnbuckle etc.,etc...

 

[quicksandfarmer]

My honest opinion is that it's something you can buy for less than the cost of the parts. You can get a basic one from Northern Tool for $800. Considering around $125 for the gearbox, $125 for the stumpjumper, $70 for the blades, $120 for the PTO driveshaft, plus all the little bits and pieces, the steel, the paint, etc., there's no way you're building that for $800 even if your time is free. Plus you get a proven design.

Start with that, and then modify it.

 

[aarolar]

Where are you located I have a 4' deck you can have

 

[Jim Timber]

My honest opinion is that it's something you can buy for less than the cost of the parts. You can get a basic one from Northern Tool for $800. Considering around $125 for the gearbox, $125 for the stumpjumper, $70 for the blades, $120 for the PTO driveshaft, plus all the little bits and pieces, the steel, the paint, etc., there's no way you're building that for $800 even if your time is free. Plus you get a proven design.

Start with that, and then modify it.

The gearbox, pto shaft, and blades are the only parts I agree with in your assessment. You'll also need a tailwheel.

Stump jumper can be made as long as you can machine the hub hole and accurately locate the blade mounts.


I've been toying with the idea of a 7 or 8' twin disk mower (4-5' deep instead of 9). If you can stitch smaller panels togeter, or get stuff laser cut, it's easy to save some bucks and wind up with a better mower than $800 will buy out of China or India.

 

[/pine]

My honest opinion is that it's something you can buy for less than the cost of the parts. You can get a basic one from Northern Tool for $800. Considering around $125 for the gearbox, $125 for the stumpjumper, $70 for the blades, $120 for the PTO driveshaft, plus all the little bits and pieces, the steel, the paint, etc., there's no way you're building that for $800 even if your time is free. Plus you get a proven design. Start with that, and then modify it.

Considering what I would actually have to buy and excluding fabrication/labor time...I should be able to do it for $400+/-...especially if I don't have to make a 3ph attachment frame by using forks...?? BTW...I don't particularly care for NT...there are much better sources if I went the retail route...AND proven designs are easy to copy...(I don't plan on mass producing them )

Where are you located I have a 4' deck you can have

Thanks...I'll remember to check if I get down that way (3hours south) before one or the other of us changes their minds...:thumbsup:

The gearbox, pto shaft, and blades are the only parts I agree with in your assessment. You'll also need a tailwheel.

Stump jumper can be made as long as you can machine the hub hole and accurately locate the blade mounts....

I have some other shafts I can most likely adapt without sacrificing any original application components etc...( have a tiller shaft w/slip clutch, sickle bar shaft, and lots of PTO accessory shafts, u-joints etc., etc...).

I have several different depth and adjustable, heavy duty wheel yokes...

Observations, questions in general context of the thread...:

Like I said...I know very little about rotary cutters...

Is a typical stump-jumper sized to the size of the cutter or will a s-j from a 5' cutter work on a 4' deck as long as the hubs/shafts are compatible??

Can the blade for a 5' cutter be cut down to work on a 4' cutter?

That is...5' and 6' cutters are much more common meaning more salvage parts available if I could use them...??

My tractor (B 1700) only reports 14 HP at the PTO so even with a just a 4' cutter I am pushing the window on HP...but I have read lots of post of operators with even less PTO hp running 4'-5' cutters...

Again I will keep looking for a used 4' cutter and have had a few opportunities...but travel time (when someone is expecting you) is dedicated (usually business hours) time...there is a big difference when it comes to spending free time fabricating a deck etc...I'm in no rush...

Other than building up a boss where the gear box bolts to the deck...it seems like a rotary cutter would be a rather easy project...

Oh and BTW...just to prove I've learned from previous mistakes...I will run a "WANTED" ad in the most local papers....just so the week after I order a gearbox etc...someone down the road does not list exactly what I want FOR SALE...!!!

 

[quicksandfarmer]

You're right that there's not much to a rotary mower -- the moving parts are the driveshaft, gearbox, stumpjumper and blades, plus a wheel on the back so it can float. Gearboxes are sized for the input HP and the stumpjumper goes with the gearbox. So the difference in moving parts between a 4' and 5' is the length of the blades, assuming the same HP rating. I suppose you could cut the blades, but they are very hard steel and they have to be balanced so it might be difficult to keep them the same weight.

 

[Jim Timber]

I suppose you could cut the blades, but they are very hard steel and they have to be balanced so it might be difficult to keep them the same weight.

An abrasive wheel will cut them easily. As for balance - shouldn't be overly critical considering the abuse they're made to take. I'd be curious just how close to balanced any mower was when new, much less after years of service.

 

[silvertramp]

An abrasive wheel will cut them easily. As for balance - shouldn't be overly critical considering the abuse they're made to take. I'd be curious just how close to balanced any mower was when new, much less after years of service.

I cut a replacement blade down. I didn't have any balance issues.