Sicklebar mower draft

[Tim Harrigan]

The draft requirement for mowers is the sum of a rolling resistance, a mechanical resistance, and a functional resistance related to crop or material flow. Rolling resistance is the force needed to keep a wheeled implement moving at a constant speed while deflecting rubber tires, compressing soil, and overcoming wheel and axle-bearing friction. Mechanical resistance is the power absorbed by the implement under no-load conditions to overcome the friction of moving parts. The functional resistance is related to crop cutting which varies with crop yield, crop moisture and other factors.

In draft measurement work at Tillers International in Scotts, MI we measured the draft components of two ground-driven McCormick-Deering #7 sicklebar mowers. One had a 5-foot cutterbar and weighed 850 pounds. The other had a 6-foot cutterbar and used a hard rubber caster wheel (12×3) to support the front of the mower. The 6-foot mower weighed 900 pounds. Each mower had steel wheels (32×5½). Gearing was such that each rotation of the drive wheels provided twenty-five rotations of the flywheel (fifty cutting strokes).

Draft measurements were made with the 6-foot mower in early June in an alfalfa-grass hay crop yielding about 2½ tons per acre of dry hay. Draft of both mowers was measured in the same field in mid-July in a crop yielding about 1½ tons per acre. At about the same time a friend in Germany, Peter Herold, was making similar tests with a 4.25 ft cutterbar in a 2nd cutting grass-clover crop yielding 1.7 ton/acre.

The average travel speed in each trial was 3mph. Assuming no wheel slip, this travel speed provided about 1,640 cutting strokes per minute. An average draft ranged from 63 to 69 lbf per foot of cutterbar length. Total draft was about 400 lbf for the 6-foot mower, 320 lbf for the 5-ft and 272 lbf for the 4.25 ft mower.

We evaluated the rolling resistance by measuring the pulling force of the mower without cutting. The sum of the rolling resistance and mechanical resistance was measured as the pulling force with the cutterbar engaged but without cutting any hay. The functional or crop resistance was measured as the total draft while mowing minus the rolling and mechanical components.

At Tillers, rolling resistance contributed 94 to 123 lbf (pounds-force) to the mower draft, a load equal to 30% of the total draft. Mechanical resistance added 74 to 93 lbf and accounted for 23% of the total draft. This was the power absorbed by the mower with the cutterbar engaged under no-load to overcome the friction of moving parts. Crop resistance from cutting the hay crop accounted for 47% of the total draft load, adding an average of 152 lbf to the 5-foot mower and as much as 200 lbf to the 6-foot mower. In Germany, Peter evaluated total draft but not the individual draft components.

Based on the results of our work, an average draft of about 65 lbf per foot of cutterbar length is a good estimate of the pulling force needed for mowing. The total draft would be perhaps 50 lbf less with pneumatic rather than steel tires. The caster wheel added to the rolling resistance of the 6-foot mower but reduced the neck load carried by the team. Proper mower adjustment and lubrication will help minimize mechanical resistance and draft. Problems that will increase crop resistance and draft include loose or misaligned guards, dull or loose knife sections and loose guard ledger plates.

Mowing is a challenging task because the weather is often hot, the team needs to maintain a good speed for good mower functioning, and it is best if you do not have to stop part way through a swath. A pulling force for a sled or stoneboat on hay ground equivalent to the pulling force needed for mowing would be a sled loaded to about 700 lbs GVW for the 4.25 ft mower, 800 lbs for the 5 ft mower and 1000 lbs for the 6 ft mower.

[blue80]

fantastic Tim, thanks for your (plural, including those you work with) work and excellent explanations!

Kevin

[Marshall]

So put in laymans terms, how many acres of hay can I cut with a No.7 5 foot cutter bar and a pair of average size haflingers?

[Tim Harrigan]

What kind of shape are they in? How much hay do you have? How do you plan to rake and bale or gather it? How far do you have to haul it? Anybody helping you? Is your mower in good operating condition? How may hours a day do you have for mowing? Got rocks? Got hills? How hot is it? Mow in lands or around the field? Got any point rows?

[Marshall]

They have been used some but are not is great shape yet. The mower has just been totally rebuilt by a fella that knows what he is doing(not me). I have seven acres of grass hay with few rocks. I may rake with them but not the same day. I would use the tractor to bale and haul to the barn. This is pretty much a solo operation. The grass is not real thick either(topic for another discussion).

[Tim Harrigan]

Knock down one acre per day and see how it goes. You will have days when you have to mow, rake and bale on the same day and you are going to have to work around the weather.

[Marshall]

Tim, are you really able to cut and bale grass hay all in the same day? I am about 45 miles east of Bay City. Not really that far from you. I have always grown alfalfa and it took forever to dry. This is my first year with the grass hay. It is a mixture of orchard grass and perennial rye grass.

[Tim Harrigan]

No, not in one day. First day you cut and start drying, second day cut more and start drying, third day cut and then rake what was cut on day one, next day cut, rake what was cut on day two, bale what was cut on one. That would be ideal, probably take even longer for cut 1 to dry, just depends on the weather. You do not want to be caught with too much hay on the ground if it rains and those days when you have to cut, rake, bale, haul, unload and stack are going to be long days.

[Marshall]

Ok. Makes sense now. I don’t think I would be able to do it that way with working out full time. If I ever get the produce farm going full time so I can be home I will give it a try. The more I can do with the horses the better.

[near horse]

Hi Tim,

Out of curiousity, how does the mower draft etc relate to plowing drafts (I know there are lots of variables there as well but just ballpark) – seems the mower would be a little easier for a team than say a 12″ 1 btm sulky, even in good ground. What do you think?

[Tim Harrigan]

Yes, I generally expect plow draft at 600 to 800 lbf compared to 400 for the 6 ft mower. Plow draft will be a lot more variable. Draft in the same field can easily double throughout the year as the soil changes from moist and friable to dry and consolidated. I think I showed the results of plow draft measurements somewhere in this working with draft animals category. If your team is conditioned for plowing they should be ready for mowing.

[Does’ Leap]

Tim:

Thanks for this information. How does field slope affect overall draft? Were your measurements done on flat land? We mow with a 6 foot bar on a Vermont hill farm. I consider our horses in pretty good shape, but haying is tough work for them, especially first cut. When mowing is over, we tedd and rake with the same team. Luckily for them, we bale with a tractor. We hope to hook our halflinger with our team during tedding and raking to make things easier. We are debating between hooking 3 abreast or switching the halflinger in and hooking her with just one, giving the other a rest. Any thoughts on what would be more restful?

This picture was taken in late May of last year and gives a sense of the slope and hay density.

George

[Tim Harrigan]

Beautiful place you have there.

Mowing is quite a challenge in a number of ways. Probably one of the biggest challenges is that the team has to maintain a speed suitable for mowing and in our experience that is about 3 mph. In our plowing work, the travel speed was less than 2 mph. So while the pulling force for mowing is not generally as great as for plowing, the power demand (force per unit of time) is not much different. For instance, a 700 lbf plow draft at 1.8 mph requires about 3.3 hp. A 400 lbf mowing draft at 3 mph requires 3.2 hp. And it is usually hotter when mowing which puts even more stress on the team.

I have a simple rule-of-thumb for pulling uphill that considers the implement draft, the % slope and the weight of the implement. I guess your mower with rider weighs about 1000 lbs, similar to ours. You probably have some 10% slopes, 1 ft rise for every 10 ft of run. Let’s say your mower draft on level ground is 400 lbf. My rule-of-thumb for mowing up the 10% slope is you are lifting 10% of the weight of the mower for every foot you pull it. So add 10% of the weight of the mower to the normal draft on level ground. So 400 lbf level plus 10% of 1000 lb (100 lbf) equals 500 lbf draft on the uphill pull. A 25% increase in draft. So now, if you hold the 3 mph travel speed, the power requirement jumps to 4 hp. That is a lot of work for a team of two. That’s why I like the 5 ft bar. My friend Peter Herold from Germany was quite surprised at the length of bar we used, I think the 4.25 ft bar is more common over there. That could be because the hilly terrain is pretty common over there as well.

Tedding and raking do not require as much power (draft or speed) with a bar-type side delivery rake/tedder as does mowing. I would tend to go with two and give one a rest with that type of tedder but your team might tell you differently. Their opinion counts more than mine.;) If you are using a rotary tedder they require quite a bit more effort and three might be best.

OK, here is a picture I took of a rotary tedder at HPD 2004 I think. These rotary tedders and rakes have a much greater power requirement than the bar rakes and tedders. Notice that the these rotary tedders are engine powered from the forecart.

[jac]

This is great info.. Tying this to Kevins question about night time working and mowing.. Somewhere on this forum I saw a mention of sugar levels dropping in hay. Is sugar higher or lower at night ? I remember grandfather saying he was in the field by half 4 in the morning and done mowing by 10 before it got really hot. This gave the horses an easier day and he said the dew lubed the knife as well..and this was in the 30s when temps were considered hot in the high 70s Was the sugar down at that time in the morning ?.. Would Kevins idea of night working be a way to mow hay and still get a quality result and ease the horses also ??..
John

[mitchmaine]

nice photos. i’m getting the itch to drop some hay. we run a 9′ rotary rake and a 4x tedder with a ground drive fore cart with three horses, and i don’t think they work any harder than two mowing. the side rake moves much easier, and two pull it handy, but the rotary rake sweeps a better job, i think. i think i might use three horses rather than rest one. the horse that didn’t get rested has a long day. mitch

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