flattening chisel backs

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Forum topic by malorty posted 05-31-2011 01:32 AM 4505 views 0 times favorited 9 replies Add to Favorites Watch
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5 posts in 2583 days

05-31-2011 01:32 AM

Hello all,
I just got all set up to sharpen my first set of chisels and am finding it very laborious to flatten the back. I started on a 1000 grit waterstone and after about 20 minutes I could still see machine marks at the tip of the blade so I dropped to 220 grit sandpaper on a flat surface for another 10 minutes, still wasn’t contacting the top 1/16” or so of the blade so I switched to 80 grit. It started getting a little more noticably flat but I got too tired to continue. Is this normal for brand new chisels? They aren’t the best (Craftsman) but it just seems like its taking for ever for the abrasive to even start to contact the top 1/16” of the blade. Anyone have any input?

9 replies so far

View nailbanger2's profile


1041 posts in 3165 days

#1 posted 05-31-2011 01:37 AM

You might try a belt sander turned upside down with no less than 150 grit on it. Keep a sharp eye on it so it doesn’t overheat.

-- Wish I were Norm's Nephew

View Rileysdad's profile


110 posts in 3301 days

#2 posted 05-31-2011 01:56 AM

You might try using an extra coarse diamond plate if you have more chisels to flatten. Keep in mind that you only need to do this once to each chisel.

-- Measure twice, cut once, buy extra stock.

View DLCW's profile


530 posts in 2676 days

#3 posted 05-31-2011 03:44 AM

You can start with 180 wet/dry paper on a piece of glass. Then move up to 220 wet/dry then 400 wet/dry. Then switch to your water stones (or oil stones) to hone and polish. Less expensive chisels require a lot more aggressiveness getting them tuned up. For the front of the chisel grind it so it has a concave form. Then use the sandpaper method mentioned above to sharpen, hone and polish.

I follow this method anytime I get a new chisel or plane. Makes fast work so you can get to work making chips fly.

-- Don, Diamond Lake Custom Woodworks - - "If you make something idiot proof, all they do is make a better idiot"

View crank49's profile


4032 posts in 2993 days

#4 posted 05-31-2011 03:51 AM

I don’t ever start on 1000 grit for anything. That grit is for when I’m almost done.

Unless you got some really dud chisels from Sears, you should be able to start with 150 grit silicon carbide paper, grind for about 10 minutes, step up to the next grit, about 2 to 5 minutes, then continue with progresivly finer grits and usually the times get shorter each grit.

It could take 100 hours on 1000 grit to do what could be done in 10 minutes on 150.

View yrob's profile


340 posts in 3675 days

#5 posted 05-31-2011 03:53 AM

It does take a while but you only have to do that once. If you buy good chisels, it helps are they are close to flat already. Anyhow, the way I do it is I have a granite reference plate (big, heavy very very flat) and I put automotive sandpaper (the wet/dry kind) on it. I start with 180 grit then go up the grits up to 600. I only go to water stones after it is already pretty flat. A friend of mine uses a worksharp 3000 (from woodcraft) and it is quite fast and work very well. Its designed not to heat up your chisel and ruin it.

-- Yves

View malorty's profile


5 posts in 2583 days

#6 posted 06-07-2011 07:42 AM

Back at the flattening. I have a few more questions though. So I got a piece of flat granite instead of the glass plate (a little more stable on my bench) and dropped to 100 grit wet/dry paper. It’s going a little faster but still have machine marks at the top 1/8” or more of the chisels. Should I just keep going? How many sheets of sandpaper should I need to go through? It seems like the grit is wearing down.

I did manage to flatten the 1/4” chisel today and moved on the the 1000/6000 grit waterstone. How polished should the chisel be after 6000? it seems a little cloudy and was wondering if you only obtain a mirror finish with an 8000 grit. Also should I be washing the stone off periodically through the flattening process?

I feel like I’m going crazy with this whole flattening process, I don’t know if I’m doing something wrong or if I bought cheap chisels or what!

View yrob's profile


340 posts in 3675 days

#7 posted 06-07-2011 07:52 AM

What might be happening is that you have a high spot several inches up the back of the chisel so the front never makes contact and you cant get rid of your machining marks. It is not necessary to flatten the whole back. Just the first inch or so is plenty. I usually keep an inch or so on the sandpaper and sharpen on the edge of my granite slab. Just make sure you press the chisel well so its perfectly flat on the sandpaper.

As far as waterstones, you want to develop a slurry on it. It should be wet and stay wet. You dont want it to go dry or it will not cut properly. You also dont want to rinse it all the time because you will get rid of the slurry which does most of the cutting. I have a spray bottle that I use to keep my stone wet. Before using them, let them rest in water for 15 minutes or so to saturate them with water.

-- Yves

View Loren's profile


10476 posts in 3670 days

#8 posted 06-07-2011 09:24 AM

A cheap, coarse oilstone from Harbor Fright or whatever discount store
works pretty good for grinding chisel backs. Such stones are sold as
sharpening tools, but all they are suitable for is lawnmover blades –
and flattening chisels.

Kerosene makes the best lubricant but sewing machine oil or baby
oil works good too. I’ve used dishwashing soap on as a lubricant on
oilstones as well, with good results.

I prefer waterstones, but they are a little hard to get and spendy
if you just want to grind some dumb chisels.

View hokieman's profile


185 posts in 3776 days

#9 posted 06-08-2011 04:58 AM

I was amazed how my coarse DMT diamond stone made quick work out of lapping chisels and plane irons. The you do the main bevel on the coarse stone and then hone on the water stones or scary sharp and you’ll be in business. You can get the coarse diamond stone for about 40 – 50 bucks. Here’s a link to sharpening supplies for the DMT stones.

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