Is there a front mount flail/brush mower for CUT's?

[brandoro]

Great idea, stump grinder teeth on the blades!

You built what I was asking about. I was thinking of a flail mower on the fel arms. I have never used a flail mower but it seemed like the best choice for the job. Looks like your mower with the stump grinder teeth will work as well or maybe better.

Did you have any problems/concerns with balance when you put the stump grinder teeth on the blades?

 

[Farmerford]

Thanks for the compliments, PB and Patrick G.

Brandoro, the "g" factor at the end of a blade 24" from the center (ie, 48" mower) at 1000 rpm is about 700 (I am just guessing from memory). That is, one ounce of metal (treating mass and weight as the same for this example) at the end of the blade produces 700 ounces of centripetal force. In pounds, one pound of unbalance produces 700 pounds of unbalanced force. I guessed that about 70# of unbalanced force would produce unaccepable vibration. To produce a 70# imbalance would require 0.10# of steel at the end of one blade not balanced by the same amount at the other end. At 0.283#/ci, it would take about 0.40 ci of steel to weigh 0.10#. 0.40 ci of steel is a piece 3/8" thick and one inch square. The teeth are virtually the same size, because they have to be to avoid vibration on stump grinders, and even if not perfectly matched, it is inconceivable they could be different by the equivalent of a 3/8x1x1 chunk.

That leaves uneven placement. I forgot the calculation, but I recall that I needed to have the locations of the teeth different between the two blades by around one inch to get the equivalent of a 0.10# imbalance. Just using a pull rule and marking real carefully I got them within about 1/32".

So the short answer is that I worried a lot about unbalance, but it turned out not to be a problem if one measured reasonably carefully with common tools.

Since the arrangement in the picture, I actually welded extensions on the bladeholding arms and moved the pivot points out 5''. That let me shorten the blades so that they would not strike each other if they both swung through center when striking an obstacle. I will take a picture of that arrangement this weekend and post it for anyone who decides to try my idea. It works better than the first arrangement if you are clearing brush in the 2 to 4" diameter range.

 

[patrick_g]

Thanks for the compliments, PB and Patrick G.
That is, one ounce of metal (treating mass and weight as the same for this example) at the end of the blade produces 700 ounces of centripetal force. .

...and for the easily confused try to understand the difference between centrifugal and centripetal force and which are real and which fictitious in which instances and frames of reference (although useful in an explanatory way)

Not to stir the pot (much!) but can you consider the force that the carbide teeth place on the blade to be centrifugal and the blade structure to supply an equal centripetal force to balance it. Also to aid you in developing a headache is the need to separate centripetal and centrifugal accelerations from the centrifugal and centripetal forces they generate and so on and so forth till you reach for the Excedrin.

Pat (Sorry but the devil made me do it.)

 

[Farmerford]

Pat:

Skip the Excedrin, cause I made an "A" in Shaky Mech. The prof had been a railroad engineer (slide rule, not Johnson bar, type) and we learned all about balancing the drivers on steam locomotives (the last of which had been manufactured 20 years earlier).

(the devil made me do it)

 

[brandoro]

Generally not easily confused but I could feel a headache coming on
Not an engineer myself (either type) but often work with some, mostly I find them to be interesting people.
If I were to mount things on mower blades, my plan would be to be careful that the pieces used were as close to the same size/weight as possible and measure carefully before drilling holes to mount them.
Good to know that some knowledge and calculations were put to use. Makes me much more confident that I can replicate your installation without worrying too much about the bolts/torque being sufficient.

 

[patrick_g]

Pat:

Skip the Excedrin, cause I made an "A" in Shaky Mech. The prof had been a railroad engineer (slide rule, not Johnson bar, type) and we learned all about balancing the drivers on steam locomotives (the last of which had been manufactured 20 years earlier).

(the devil made me do it)

Please understand my confusion comment was NOT intended for you. Shaky Mech huh? Old locomotives... I lived for a time in Lima, Ohio the location of the Lima Baldwin Hamilton locomotive works.

I put on a new pair of blades for a friend and his brush hog really was then unbalanced, terribly so at some speeds. I pulled them both back off and lacking a handy weighing device picked up a scrap of PVC pipe and wedged it in a Wally World chair and parked another dusty chair near the end of the out thrust pipe. I hung the blades on the pipe at the same distance out one at a time and noted the location of the end of the pipe on the second chair.

The owner was none to confident in the impromptu scale so I showed him the same blade bent the pipe the same amount as closely as could be seen on close inspection several times in a row but that the two blades bent it a different amount, not a HUGE difference but very easily noticed. I attacked the end of the heavy blade with an angle grinder and after considerable grinding got the blades to a close match. I didn't grind the blade shorter but took off some thickness near the end where weight change would make a larger difference. The grinding location was a guess and luckily it was a good one as when the blades were reinstalled the mower was silky smooth throughout all the RPM ranges we tested (idle to PTO +)

For students taking notes to study for the final:

By not exceeding the elastic limit of the pipe and not loading it for sufficient time to permit a slow long term deformation ("cold flow") the repeatability of the deformation (bending) of the pipe was quite good and more than adequate for the task at hand.

Pat

 

[Farmerford]

Pat:

You are a hoot! I would love to have seen the Lima works when they were in full swing. I am always amazed at the size of their machinery, such as the wheel lathes for drivers and vertical mills with a rotary table for boring those steel tires they heated and slipped on the drivers.

Unbalance blades, huh? Depending on how long ago, I may have made them. From 1970-1972 I was chief engineer/plant manager for Columbus Iron Works. We were a glorified blacksmith shop with a few drop hammers, upsetters, and forging presses that made OEM cutter blades and blade bolts for Bush Hog (located a couple hours away in Selma, Alabama), Servis, Woods, Howse, Brown, and others, as well as replacement blades.

The blades started as steel bar cut to length on an 1890's shear with open gears and a flat belt driven flywheel the size of a small backyard pool spinning merrily, unshielded, a few inches from the operator. Occasionally (usually on Mondays) we might not get all the lengths the same.

After a couple years of that I changed my calling to law. It pays better, but its not nearly as much fun.

 

[patrick_g]

Pat:

You are a hoot!
Unbalance blades, huh? Depending on how long ago, I may have made them.
After a couple years of that I changed my calling to law. It pays better, but its not nearly as much fun.

Farmerford, It was last year so unless they were NOS you will not be named in the action.

Couldn't hang with real work huh, went and got a plush indoors sit behind a desk job. What will you reveal next, you wear ties???

I have been in a number of fairly widely varying jobs, enough to cause folks to think either I have a short attention span, can't keep a job, or are versatile. (Maybe more than one of them.)

Actually I came close to getting sucked into law via an interest in intellectual property law related to facets of my background and experience but turned down the scholarship I was offered as I was more than a tad burned out having just completed YAD (yet another degree) in evening classes while working full time. I think it was the second best educational opportunity refusal I ever made, the other being Harvard language school to study Chinese during the little fracas called Viet Nam (I was in USAF.)

Pat

 

[Farmerford]

Pat:

USAF in Viet Nam, huh?

In late 1969 (I think) I was an infantry platoon leader in the Hobo Woods north of Cu Chi. I called for close air support and the pilot apparently thought we wanted him to drop his napalm and fire his cannon ON the purple smoke rather than 200 meters NORTH of it. I didn't get a good look at the pilot (though he was close enough for it), but his callsign was "Rattler", and he had a big light grey plane, with "USAF" on each wing. Was that you?

 

[patrick_g]

Pat:

USAF in Viet Nam, huh?

In late 1969 (I think) I was an infantry platoon leader in the Hobo Woods north of Cu Chi. I called for close air support and the pilot apparently thought we wanted him to drop his napalm and fire his cannon ON the purple smoke rather than 200 meters NORTH of it. I didn't get a good look at the pilot (though he was close enough for it), but his callsign was "Rattler", and he had a big light grey plane, with "USAF" on each wing. Was that you?

I am very sorry for the friendly fire incident, but not all jet jocks are rocket scientists. I got out in late '67. I served during the Viet Nam fracas in support of it much of the time but was not permitted to leave the continental US due to security considerations. I still have security restrictions but am not at liberty to discuss the details. I can say that my rights under the US constitution have been permanently abridged and can never be restored.

I was not directly involved at any time with fighter forces but supported the B-52 bombers and KC-135 tankers and certain other aircraft but not fighters. I had a hand in team training issues for the B-52 combat aircrews. Now if one of the BUF (Big Ugly uh... err ahh. FELLOWS) was off target and dumped a load on you by mistake I would feel really bad as I was a party to their training. Kind of like when the guided missile cruiser USS Vincennes shot down the Iranian Airbus. People who knew my involvement with the warfighting systems onboard that were used gave me a poke in the ribs and asked where I went wrong. My comment was that I had nothing whatsoever to do with the decisions that led to using the system and firing on the target. My part was involved with how well they performed. My part worked, they hit it didn't they.

Pat