OT: Enlarging Hole In Hardened Mower Blade

[drizler]

Yea I know, go get the right ones but I can't so how do I get from 3/4 to 7/8". I put it in the drill press and attacked it with a standard bit and some good quality oil but it aint cutting much. It rather just bevels it some. Can I simply heat the entire cicumference to red a 1/4' or so and do the deed or is there a better way? There are 3 of these blades that need the treatment.

[SND]

I don't know how hard those blades may be , but have you tried grinding a small flat on each lip of the drill? ( like a drill ground to drill brass ) It usualy helps some. Just run it as slow as it goes and put plenty of oil.

[Rocky D]

I didn't think that mower blades were hardened....cause they would shatter under vibration....but it appears that they are at least harder than your drill bit. Heating the center is a good idea, to anneal it for drilling in this case. It shouldn't hurt the integrity of the blade. You don't need to go to a red...maybe just a dark red. Check your balance after drilling.

[drizler]

By my definition they are hard. The drill though it has soldiered long and hard is a Harbor Freight purchase. I have a set of good ones but they are too small. Maby I will just go by Lowes and get a nice new Cobalt for the job. That is one of those sizes that I tend to use from time to time.

[Chipmaker]

FWIW a lot of mower blades are tempered to just below what a leaf spring is. SOme are and some aren't. I would be quite leary of heating the blade to anneal it and enlarge the hole, as ther is o telling what you may take out or put back into the blade by doing so Usually other than griinding a sharp edge on a mower blade other things are kindy risky. Ever see a mower blade brak accross the mounting hole and fly out in two different directions from under the deck.....I have well I did not actually see the blade itself fly but thats what happened.

That said I am a fine one to suggest not modifying an existing blade except for resharpening. I have built up blade ends and laid on a pass or two of hard face rod as my soil is sandy and was eating blades up on every cutting, and my local John Deere dealer was charging sky high prices for replacement blades, so I took a chance and built them up and hardfaced and reground an edge. They lasted many many cuttings, but usually no one is around when I cut and at the most all it would do would take out a tire on the tractor or cut a hole in the deck if it did break.

YOur gonna have to get your rpms way way down low, and use a lot of pressure on a good drill bit. HF bits I can't say if they are up to par for this or not, and don't spare the coolant / lube. I have drilled spring steel and lea springs etc by usuing a cobalt drill bit without any problems, but if your not making any headway in making chips all your doing is further work hardening the area around the hole.

Lots of luck.

[Wheels787]

Chipmaker

I have often thought of adding a hard surface to my blades on our riding mower. Wouldn`t even think about it on a push mower, but I would like to hear more about how you applied it to yours.

Thanks Mike.

[ian]

all i would do is to take die grinder with a good carbide but and enlarge the hole.

[tigman]

ian has a good idea or you could use a masonary drill bit if you have one that big. Scott

[Terry Lingle]

die grinder and a grinding stone would be my choice . If it starts bouncing it will ruin whatever cutter you are using stones are much cheaper . Terry

[T>D>C]

What's the application?

For the price of "good" carbide drill bt you can probably buy a new blade.

If your just experimenting (and you except the repsonsibility suggested by Chipmaker), heat the blade in the area with the torch to a deep straw color and let it cool very slow, this will draw the temper (soften it). After you drill it, heat the whole blade up cherry red and quench it in oil (if you don't have a high temp quenching oil, becareful, it may catch on fire and burn you and/or your property!). After it has cooled, place it in a cold oven and turn the temp to 450 for 3 to 4 hours (I made some blades out of leaf springs and at 450 for two hours gave a rockwell hardness of 57 - 60- good for knives, bad for lawnmowers).

I would buy a new blade.

[drizler]

Made in Italy and hard as a stone. I heated them cherry around the hole, nothin. Finally chucked a small grindstone in the drill press and while it tore the stone to shreds it almost got the hole big enough. At least the drill does enough to mark the outer edges. I will have to buy a couple more stones and maby it will do the other 2. One way or another it will get done and you are right, a decent 7/8 drill bit costs more than 3 new blades. I can't kick though these blades are 8 or 9 years old.

[Chipmaker]

Originally posted by Wheels787
Chipmaker

I have often thought of adding a hard surface to my blades on our riding mower. Wouldn`t even think about it on a push mower, but I would like to hear more about how you applied it to yours.

Thanks Mike.

The first batch of blades I hardfaced I used Eutetic-Castolin rods. What number they were I culd not tell you, as I had been dragging them around for years on end, and at one time I used to use them for hardfacing the hammers in a hammermill where I had worked.

The rods IIRC required a base (cushion) bead be laid down first for best results, but other rods I have used I usually only put two beads at most down. The base metal was ground uniform and built up with a bead or two of 7018 or 7013 rod, and dressed off a bit. Then I just laid two beads of whatever hard face rod I had down. The initial HF bead has some of the base metal in it so another bead gives a harder structure as it contains more of the hardface rod and less of ther base metal material.Thats all there was to it, other than haivng to grind the edge on them. YOu do not want it overly thick as it can become more brittle. There is all kinds of rods that are great for this task though. A lot of them are impact resistant, and also abrasion resistant, and that would be my first choice. I had hardfaced a set of bush hog blades, and they went for many years and still had quite a decent edge on them.

The area on my blades I had the worst problems with were on high lift blades. They have a pretty good swept up angle on the trailing edge, and in the area that transitions from flat to upswept, it would erode away pretty quickly in my sandy soil. A single layer of hardface cured that as well. I never clamped or placed them in a jig to HF just fixed them with the edge to be welded facing up. Never had any warp. You may get fine hairline cracks, but oon some HF rods that can be expected, and usually it does not harm anything. There is one rod that work hardens, which I am going to try when I need to do a set of blades again. IIRC its made by Stoody. Should be great for mower blade applications. I know they use it a lot for building up plow shoes and shares with good results.

[Wheels787]

Thanks for the reply Chipmaker.

Our soil is not sandy, but we have flint which pops up from winter freeze and thaw. Makes for a neet show when mowing late in the day , but does nothing to keep a sharp blade. That along with the occasional trip through the gravel driveway keeps me, my angle grinder , and blades close friends!

Mike

[bobad]

Originally posted by Chipmaker
The first batch of blades I hardfaced I used Eutetic-Castolin rods.

I have always wondered what "spray weld" hardfacing would do for that erosion problem you spoke of. In my experience with oil tools, it seems ideally suited for that purpose. I bet a thin layer of sprayweld on the blade tip would prevent the blade from rounding and change the wear pattern. A thin layer on the bottom of the blade would create a "self-sharpening" effect and make the blade last 2 or 3 seasons wihtout much sharpening.

Because of all the crawfish chimneys here, my blades wear completely through in 1 season. They end up splitting, which is probably a lot more dangerous than a few grams of strategically placed hardfacing.

[Chipmaker]

I had originally wanted to use the spray process as you stated, but I did not have a spray rig yet alone an O/A setup either.....I have however applied the spray hardface on shafts etc at one time, but the company owned the torch setup and I left long before I had a need.......But I do not see any reason it would not work and work great. Some of that spray material was about borderline on even being grindable.

I have those crawfish chimneys myself, as well as lots of mounds from fireants, which I thourouoghly enjoy running over and just setting on top of blowiing those little suckers all over and in general disrupting their life much like they do mine!