OutdoorKing Repair Forum Forums Repairs and Maintenance Questions on Walk Behind Lawn Mower Frames Reel Lawn Mowers, Atco & Villiers etc. Rear Roller/Bedknife/ Front Roller Alignment

Hey all,

I rescued a Qualcast Super 14" from the bin at work and I have spent a bit of time giving her some TLC. I have had the reel and bedknife sharpened, both seem in good order.

My question is; If there is run-out in the rear roller will this effect the cut? I am trying to get the bedknife, reel and the rollers all parallel, but I seems I am chasing my tail as the rear roller has a small dent in it and overall radial run-out.

Or does the bedknife to front roller only matter with parallelism?

Or am I just wasting my time as pretty much no lawn will be perfectly true anyway and an element of undulation is inevitable.

Thoughts?

Nothing ever runs precisely true, so the key question is how much runout you have. If you were trying to make the grass milling-machine-flat, you would be trying for a runout of much less than 0.001" Total Indicator Reading. Realistically, the ground won't be that flat, and if it were, it wouldn't stay that way for long.

A bowling green that is used for competitions will be flatter than a putting green. A putting green usually won't be flat at all, because that would make the job way too easy for the golfers - but it will have smooth curves with no bumps or undulations. Most people would like to have their lawn look smooth, though usually not flat. They expect it to feel smooth as they run the mower over it: no bumps, and all of the smooth curves fitting into a context with the rest of the curves. If it pleases the eye, and it looks and feels smooth, it's good.

The issue with an out of true roller, is that it will cause undulations rather than bumps or uneven slopes and curves. The eye can pick up undulations because they repeat: if you suspect you see one, you bend down, look along the top of the grass, and see if it is in waves. If it is, unless it is your lawn, you feel superior to the homeowner (unless yours is wavy too, of course).

There are two ways you can address your out of true roller issue. The first is the way a mower manufacturer would do it. You would measure how much runout there is, and if it is more than say 0.010"-0.020" Total Indicator Reading, you'd say it looks like it was made in a barn with blunt tools, and you'd fix it. The second way is like a critical home-owner. In that case you would look at the newly mown lawn, with your eye down close to the grass, and see if you could detect undulation. If you could, you'd take the mower back where you got it and demand your money back.

Remember, the mower cuts tracks across the lawn, and usually successive tracks are mown in opposite directions to get that striped look. Any undulations will not be synchronised from stripe to stripe, so if they are visible they will detract from the lawn's appearance.

Hey Grumpy,

Thanks for the reply. You have pretty much confirmed what I already thought to be the case; yes it has the potential to cause an issue with the quality of cut, but it is rather dependent on how affected the rear roller is.

Without having immediate access to a dial indicator and just using various tools around the house I would best estimate the rear roller would cause the bed-knife to have around 0.5-1mm of movement away from zero as it rotates. I used a straight edge and various drill bits of known diameter to come to this gestimation. I guess my thought process was if I was cutting at 10mm, a 1mm tolerance equates to a 10% movement of the bed-knife away from center.

Might be a case of suck it and see I think

Let's say it is 0.7 mm of runout measured on the outside of the roller. For the moment I'll guess it is uniform across the width of the roller. That is equivalent to 0.028" TIR. I'd say that Qualcast would, or at least should, be thoroughly ashamed of that. However note that the cutting reel is halfway along the wheelbase of the mower, so the bedknife only moves vertically by half the amount of the rear roller runout. I expect that the resulting grass height undulations of about a third of a mm peak-to-peak would not disturb anyone but a bowling green supervisor.

In other words, I agree with you: try it for a while to verify that it is pretty much undetectable in terms of grass surface-evenness quality.