Rotary cutter bladt tip speed?

[daTeacha]

3 inch stuff is wood stove fodder for me. It makes nice pieces to throw in the stove in the morning after an all-night burn. It lights off in a minute or two and burns quick, bringing the stove up to temperature quickly enough to allow me to add some bigger stuff before I leave for school.

 

[Bob_Young]

Don't have the info in front of me, but remember at one time studying a brush cutter brochure (probably Woods) and noticing, within a series with same gearbox HP rating, that BTS increased with mower size. In other words, the gearbox output shaft on all sizes was turning at the same speed; so BTS was determined by the length of the blade. (Though I did NOT do the math)

This makes sense as you can hardly expect a manufacturer to design gearboxes with different drive ratios for each mower size produced. What it does suggest is that:
1) There is no magic BTS for a brush cutter
2) The largest cutters in a series will generally have the highest BTS
3) The smallest cutters in a series will feed back the least shock to the tractor - thus are naturally more suitable for smaller tractors.
4) The smallest cutters are more demanding in terms of PTO RPM if they are to cut cleanly
5) The smaller cutters may never perform on a par with the largest cutter in a given series.
6) The smaller cutters may take more abuse than the larger cutters in a series.

---if my assumptions are correct.
Bob

 

[john_bud]

"For higher BTS, the damage to the equipment might be worse when you hit a buried steel pipe, large rock, stump etc. It would sure have more whacks before the clutch could be stomped or the 3pt raised. "

Johnbud - Is this true if the slipclutch is properly adjusted?

Well yes, it's technically true even with a slipclutch properly adjusted. The slip clutch limits the transfer of power from the tractor to the mower, but the mower is still full of rotational energy and will continue to bang into the object -- damage to the blade, carrier and gear box can occur. Some shock will also get back to the tractor and small additive damage occurs. Over time - breakage occurs. (Metal fatigue driven)

Now for the rest of the story. I wrote the original comment thinking about how many of the slip clutches are on infrequently used equipment -- froze hard! For all practical applications, when the slip clutch is working you're ok fine.

jb

 

[Glowplug]

I had always assumed that the higher blade tip speed the better it was for a finish job. I based this on the fact that my ZD28 mower has a BTS of about 18,000 fps. And these are small blades. Take this into account and then look at the Rhino rotary cutters. The GR84 has a BTS of only 9900 fps. But it has a cutting capacity up to 4 1/2", has a Cat II/III hitch, requires at least 60hp, weighs over 2,000 lbs., and is considered "super-duty". To compare apples to apples, the Rhino SE7 (84") has a cutting capacity of 1", weighs 1000#, and has a BTS of 14,024 fps. On the other hand the Woods BB8400 has a cutting capacity of 4" and a BTS of 16,000 fps. Clearly things are not so simple. I don't think you can look at the BTS as a stat on its own. It is something to take into account when looking at the whole picture. It may be considered, for what it's worth, when comparing rotary cutters that are nearly the same size, weight, and have the same size blades. But it doesn't tell the whole story.

I do know, however, that if you have a very heavy blade mowing very fast the kinetic energy is going to be higher and it will pulverize anything you run over! (K.E.=1/2 mv^2). So I guess if you wanted the most destruction that would be what to look for.