Lawnmower blade inflation ?

Once I had a date with a Dutch girl who wore inflatable footwear.

When I sought a second date, unfortunately I learned that she had popped her clogs.

Easy enough to sharpen mower blades. What slightly annoys me is the blades in my Bosch shredder, which are induction hardened giving a relatively thin hard layer right at the edge, the life is very short if you re-sharpen them. (I have not got round to trying to re-harden them after sharpening although I might have a go now that I have a little propane-fired "tube-oven")

Were you considering hardening the steel yourself?

Is that just a rotary one then? At least its not one of those new fangled plastic sacrificial ones where you use up about ten for one lawn. Brian

So why don't they harden it all the way through then? Brian

GOV.UK shows RPI as 245 (Jan 2013) and 295(2021)

So that means 20% official inflation since 2013.

It was down to $1.11 briefly on 23/3/2020 and bumped around $1.25 until September 2020.

If those parts were imported when the pound was so low then this would have a big impact on prices.

Probably because mower blades are likely to hit hard objects from time to time, and hence need to be very tough. A fully hardened blade might tend to shatter, and send shards of steel flying out toward the operator.

Cheap eBay ones are probably just mild steel. Ive been using the same blade on my Hayter 56 for 20+ years. As it wears down I just rebuild with weld and sharpen.

Mike

No, it is already a carbon steel so I would just take the whole thing up to bright red heat and quench either in water or oil. The final bit of edge should go glass hard because of its narrow section, the cooling rate of the main part (about 50x6mm) should be slow enough to give it a reasonable ductility. Given the geometry, I don't believe you could get an accurate temper with a gas torch (in the way you might temper a wood chisel, say).

Because this way is the cheapest. Also, if you did through-harden the whole thing up to the "glass-hard" which presumably gets the best cutting edge it would be very brittle, and you would not want it fracturing at the stress concentration where the drive spindle goes.

I've no doubt they could be engineered for longer life in various ways (at a price), but this method gives them sales on consumables.

If you watch the USA TV show "Forged in Fire" quenching in water for something with a cutting edge is not recommended as it usually results in micro cracking within the metal.

What they don't tend to show during that program is tempering after the heat treatment to harden - heat again to a lower temperature and let it cool in ambient air - repeat if necessary.

Whilst it is easy enough to sharpen them, if you hit one big thing that damages the blade sufficiently that you end up removing quite a bit of material (and near the end), I wonder if we should put some effort into keeping the balance along with a reasonable edge?

I built a motorcycle wheel balancing spindle (turned a couple of ally cones and fitted bearings on the ends of the shaft) that allows for (at least) a reasonable static balance and when daughter was running her gardencare business, she could get through quite a few blades (/pa) and thought of making something similar.

I was going to turn (or 3D print) a hub with a couple of light bearings in to fit the hole in the centre of the blade and compare the level of (static) balance accuracy on a new compared with a used / post sharpened one (and tweak as necessary). [1]

As long as you only remove material over the same range at both ends of the blade then it shouldn't impact the dynamic balance very much?

Cheers, T i m

I don't think that will matter as much in a shredder as it would for (say) a proper woodworking chisel or a lathe tool. Since my dead blades just go into my scrap metal bin I'll start with the simplest possible heat treatment, when I get around to it. I don't know that TV show, do they suggest oil-quenching for cutting edges?

"3D" balancing for a crankshaft driving rods and pistons is quite an art. I suspect that for a typical flymo blade balancing across a knife edge (centred on the hole, and perpendicular to the blade of course) might be sufficient. But your route would be good if you were doing a lot of them.

I think mower blades are pretty non-critical from the balance point of view. They don't rotate all that fast. I just grind some sort of edge on the leading side of the blade (when I can be bothered) and leave it at that. I've never noticed much change in the level of vibration and I've owned a few metal bladed rotary mowers over the years:-

Atco push along Kubota T1600 diesel Wessex topping mower on three point hitch Stiga 'out front' mower

I've found that it's the general level of crud stuck on the underside of the mower deck that has much more effect on how well it mows. A good clean-up with a pressure washer can be a revelation! :-)

They oil quench the whole blade (not tang) sometime using clay to "protect" the bit that doesn't need to be hardened as much. It is a timed competition so some of the steps in making a "quality" blade may be omitted. However shown in the few programs is quenching in water or too hot before quenching in oil produces visible cracks in the metal. During testing of the blades (knives, swords and hacking items) that poor heat treatment to harden edges often results in the blade snapping in a spectacular way.

The format of the program is 4 contestants forge a (knife) blade in 3 hours and then add a handle in a few more hours. Two contestants are eliminated and other two are given 4 to 5 days in their own forge to make the same edged weapon which is then tested back in the studio.

I always check balance on mine after sharpening .. and adjust until balance is true. Simple as putting a nail in a vice so its parallel with floor and put hole in centre of blade on it.

Have you not done that and noticed any difference?

But the hole is normally bigger than most nails so I'm wondering how sensitive it (not) might be?

That was why I wanted to check the balance on a new blade and then compare that after it was used and again after being sharpened to see how they compare.

Cheers, T i m