Belt sander for flattening and grinding?

[J_SAMa]

Hi,

I work almost exclusive with hand tools and have never even taken any of my tools to a grinder. But some of my old, lightly pitted chisels and plane blades really need a lot of flattening... Sandpaper on granite works okay but I always get a slight bit of rounding over no matter how tight the sandpaper is clamped or how much liquid I use to stick it down. Also I don't like the mess it makes.
Has anyone tried flattening on a belt sander? Does it also round over the tool? I don't have one so I've never tried. How well does it double as a grinder for grinding bevels? Or am I better off sticking with sandpaper on granite?

And please, if you know of a cheap (under 60 pounds), handheld or bench belt sander, please recommend.
What about those bench grinder/belt sander combo machines?

Thanks in advance,

Sam

 

[Jacob]

Brilliant for bevels, hopeless for flattening.
I wouldn't bother flattening chisels anyway, nor plane blades except for a few mm from the edge to under the cap iron

 

[AndyT]

There is a special metalworking belt sander. I've seen MrPete / Tubalcain use one on some of his excellent YouTube videos. It would have the advantage of not containing any flammable sawdust, waiting to be ignited by a spark... Probably over £60 though!

 

[JohnPW]

I've got quite a lot of old chisels with convex backs and I also seem to get rounding over if I try to flatten with sandpaper on a flat surface. I've also tried using a coarse oil stone but that's either too slow and/or rounds over as well.

Yes I know I could just put the first 20mm of the back on a stone when removing the burr but that would only make the convexity worse over time, and it is nice to have a flat or slightly concave back, if possible.

I've never tried a belt sander but I have tried a Tormek. Trouble is it leaves the back with shallow ridges that needs further work on a stone. It does get rid of pitting very easily.

Another idea is to use an engineers scraper, like scraping a plane sole, but I'm not sure how well that would work on hardened steel.

Ideally you would want a very coarse and fast cutting stone with a slightly convex top. I've seen very coarse diamond stones on online shops but they are very expensive, like more than £100!

 

[bugbear]

Another idea is to use an engineers scraper, like scraping a plane sole, but I'm not sure how well that would work on hardened steel.

Very poorly. Even mild steel isn't very nice to scrape.

BugBear

 

[RKrush]

No way use a belt sander for flattening. You will round edges, unless you are really, really careful. For grinding bevels belt sanders are great. I use wheels and belts, but far prefer belts for chisels and plane irons. Note, I would always finish on fine stone or strop.

Most chisels that are not already flat when new, are concave on the back.These are simpler to flatten without rounding edges. If the back is convex then it is easy to unintentionally make it worse.

To flatten chisels and irons I use sand paper and a small surface plate. Thick plates are essential; tiles or float glass are too prone to flexing, unless they are mounted perfectly. Ensure the paper as no lifts off the surface using water or low-tack spray adhesive. To apply pressure properly I use a hot glue gun and bond on a scarp of wood to the back of the tool to give a good hold. I can add an image if it is of use?

If the back is convex then concentrate some sanding on the centre. Then flatten as above.

 

[J_SAMa]

Brilliant for bevels, hopeless for flattening.
I wouldn't bother flattening chisels anyway, nor plane blades except for a few mm from the edge to under the cap iron

Yes I have tried just flattening the first half an inch or so on a 250 grit diamond stone. It worked for the chisels but not the plane blades.
Now, I can easily put a slight back bevel on plane blades and even work with convex chisels but it's the PITTING I'm worried about. I'm trying to find a way to not just flatten but also grind past the pitting to expose fresh steel. We all know a pitted edge is worthless...

 

[J_SAMa]

Any of you know how the hollows on Japanese blades are made? Maybe if I did the same I could then just use my diamond stone to fish off. I tried hollow a few chisels with a drill powered small grinding stick and it didn't work that well... It was much slower than I thought...

 

[Jacob]

Not worthless. If pitting is a prob the simplest is to either ignore it and put up with lines when you plane (or chisel), which can then be sanded or scraped off, or to apply a bit of back bevel. If these are unacceptable then just bin it - blades and chisels are cheap and not worth hours of work.

 

[bugbear]

Any of you know how the hollows on Japanese blades are made?

Forged in at time of manufacture.

BugBear

 

[matthewwh]

Most plane irons can be shaped by cold working. Carbon steel ones are only hardened from the slot down, so by putting the sharp end in a vice and doinking the top lightly you can put a few thou of bend into it - enough to present the underside of the cutting edge to the stone so that the pitting will be easier to remove.

For chisel backs use the roller of the belt sander or linisher rather than the platen and work the chisel forwards and back. If you let it rest in one spot you will get a groove very quickly.

 

[JohnPW]

I managed to put a slight hollow on a chisel back using a Tormek, BUT the stone had uneven wear and should have been flattened. I noted where the hump on the stone was and placed the chisel on it and moved it forwards and backwards. Top chisel in this pic:

Dark areas are the flat bits, light areas are very slightly hollow, except for the very bright bit in the middle of each chisel which is a reflection.

The middle and bottom ones were done when the tormek stone was flat or nearly flat.

 

[matthewwh]

Good, it looks like you have got the bulk of any bumps out of the way.

If you now lay the chisel across the width of a coarse aggressive stone and work it forward and back (just drifting the underside of the cutting edge onto the stone every few strokes) you should get a reasonably even surface and a nice shallow concavity in the length (you are not looking for a concavity in the width).