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Bottom blade grinding is driving me up the wall

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Will Sat, 12/03/2022

A little while ago I bought a grinder and a bb grinder and all has been, well, kind of ok…

Cylinders I can grind without too many issues, thanks to Hortimech and others on the forum. Bottom blades however….

Recently I was reading an article about just how critical the bb is to the cutting process. I’ve never been that happy with the results of my endeavours, probably a bit more contact (ie heavyish) than I would like in order to cut paper. And I’ve always had it in mind that’s it’s the bb part that’s not up to snuff.

Today I took out a known good mower, a Shanks Golf Deluxe 16”. Despite the cylinder and bottom blade not being in their first flush of youth this mower would cut a single sheet of paper with zero contact. I do not know what sort of magic was at play but the thing was unbelievable, the best mower I’ve ever had for the actual quality of cut. Literally like using a pair of scissors. Anyway I whipped off the bb thinking I couldn’t make it any worse, just a light freshen on the grinder, perhaps it would be even better. 
 

Well, you guessed it, it’s back together and now it won’t even cut a folded piece of paper on medium contact. Not only am I mad with myself for messing up a superb mower, I can’t fathom why this bb grinding is so blooming hard.

I’m using an A&E FH1 grinder - any help most gratefully received!

Will

Forums

wristpin Sat, 12/03/2022

 

The best bottom blade grinder is, in my opinion, the AE Anglemaster which deals with both the top and front faces of the bottom blade with a single set up.

Flat or lipped ?  I always grind with a small amount of relief. Easier to do with lipped blades than flat ones . Then the front face of the blade needs a few degrees , 3-5 of undercut. If you are refacing a previously used flat blade it’s often necessary to create quite a wide area of relief so that the cylinder blades only engage a narrow area at the front . 

 

 

Will Sat, 12/03/2022

Hi Angus, thanks for the feedback.

yes, I’ve been looking for an Anglemaster for a long time without success, they seem to be extremely thin on the ground. When you do see them they tend to be part of a set for which serious money is usually required.

This was a flat blade. I didn’t take a huge amount off, more of a touch-up, I cannot fathom how I’ve managed to mess this up.

how long should I be taking to grind the bb? Should it be done lightly with a lot of passes, or heavier and fairly quickly?

Will

Will Sat, 12/03/2022

Ps Perhaps I’ve ground it completely flat and the cylinder is now dragging the paper across the top face of the bb? I’ll have another play tomorrow and add some relief as you suggest

wristpin Sun, 13/03/2022

Light passes with a well dressed wheel. I’m not familiar with your model of AE but my BRL that can do single blade cylinder grinding, I have permanently set up  for up to 24” bottom blades, works best with light cuts . If one goes too heavy it tends to ride the high spots rather than level them. Just traverse taking the tops of the bumps, working down until you get a continuous cut. A wide felt tip marker is useful for getting a quick view of what’s going on ( age and varifocals don’t help). It could do with a coarser grit wheel for bbs, but no one seems to do one now.

Over 24” I have to switch over the big BRL that can do up to 36”  and has the option pumped coolant which was useful in the days when I was doing lots of knocked about gangs and hydraulic 5/7s; could get a shift on taking heavy cuts without burning.

Back to your issue ,and whisper this quietly, if it’s needs must to “ recover” a well scalloped flat blade, I have been known to dig a trench just back from the front edge with the angry grinder. Shifts metal quickly . Imagine a standard cut Auto Certes blade.