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metalmagpie
05-19-2011, 08:29 PM
I've learned many mechanical skills over the years. But one continues to elude me - sharpening a chisel. No matter what I do the thing doesn't come out right. I'm getting sick of getting sick of it, tossing dull chisels, and buying new ones. How the heck are these sharpened in the home shop anyway? I'm using a vertical belt sander with a table.

Dr Stan
05-19-2011, 08:45 PM
Cold chisels or wood chisels?

For cold chisels you really need to use a grinder rather than a belt sander. One of the key factors is to avoid over heating which will temper the chisel and make it soft. So you also need to make sure the grinding wheel is freshly dressed as a dull wheel will over heat your work faster than just about anything other than a OA torch.

When I went to the Navy's MR school we were taught to use a center gage to measure the included angle on a cold chisel as it should be 60 to 70 degrees.

Wood chisels are a different case. If you're referring to the average wood chisel a carpenter may use its OK to grind it if it has a serious chip in it, but you still need to watch out for excessive heat. Finishing up with a stone is a good idea.

For wood carving chisels they should never be subjected to a grinder. Start with a stone if necessary and then move on to a leather strop and/or buffing wheel. One can also get leather wheels for sharpening wood chisels.

lakeside53
05-19-2011, 09:05 PM
I use a Tormak (80rpm water wheel) for wood chisels. Yes, a slight hollow grind which isn't perfect, but they work well. It's EQUALLY important to flatten the back (why would you just sharpen one side of a knife?) AND to relieve the top edge to about 20 degrees, then hone it on a lather wheel. I have a neat guage for my Tormak.

For Japanese chisels, the back is relieved to make flattening easier. It can be a real pain on an "English" chisel - usually done on a water or oil stone.

You can test your edge by shaving the hair off your arm... :)

With a light touch, you can sharpen a wood chisel on a belt sander, but... the back really needs to be done by hand, as does the final honing.

You can get a number of jigs to hold the chisel for hand sharpening on a stone, and for a grinder wheel.

KEJR
05-19-2011, 09:08 PM
I don't know for sure, so take this with a grain of salt, but to do it the right way I would suspect that you might want to rough it on the sander and then do the final sharpening with a flat surface and a hard stone or 600grit paper on a surface plate or flat plate glass, etc. From what I've read is that you really want to have a jig that holds the tool to be sharpened at a fixed angle. If you can imagine, doing it by hand you could easily roll over a knife edge and not know it. Maybe there is a simpler or better way?

the other thing about the belt sander is that you might try a fixture on that and some fine grades of sandpaper. As you might imagine you will get a chainsaw finish on rough paper. Finer sandpaper might need just a few drops of water as well to keep from loading up, just be careful the paper doesn't get soaked and rip apart or something like that. It is worth a shot anyway.

KEJR

Mcgyver
05-19-2011, 09:14 PM
wood? you need to get them very sharp for maximum performance.....how do you get anything very sharp? figure out a way to maintain the angle between two surfaces as you progressively use finer abrasives. I go up to a 8000x waterstone that puts a mirror finish on and man are they sharp!

Lee Valley sells a convenient little fixture for chisels and plane blades - if you can find it amidst the gardening and giftware :D. after lapping the back edge to a mirror, it holds the blade a constant angle for doing the bevel surface. Its advantage is an eccentric that lets you change the angle a degrees or two for the final grit - a micro bevel i think they call it. Basically means you only have to work a smaller area with the finest stones.

Wouldn't take much for a man who knew metalworking to make one along the same lines if the price has become silly on them

Robin R
05-19-2011, 10:50 PM
Mcgyvers got it about right and here is a link, avoiding all the gardening and giftware. http://www.leevalley.com/US/wood/page.aspx?p=32968&cat=1,43072,45936 There are other options on their site, including better quality water stones. If I have a chisel that has a nick or other damage, I start with a white aluminum oxide wheel on the grinder. They have help with that as well, though as Mcgyver says, you could make something up yourself. http://www.leevalley.com/US/wood/page.aspx?p=45938&cat=1,43072

On edit. As you seem to be having trouble, you might do well to read up on the subject, this book by Leonard Lee covers it pretty well. http://www.leevalley.com/US/wood/page.aspx?p=32991&cat=1,46096,46107&ap=1

tyrone shewlaces
05-19-2011, 11:28 PM
Sharpening is always much harder to explain than it is to do.

Here's my tips though FWIW.

1. If the edge is nicked or chipped or anything deep, use a belt sander to re-establish the angle. The angle varies depending on the user, but usually it's fine to get something close to what it was originally.

2. You MUST do two things next. Progress through from course stones to as fine as you want (I generally just need three grits and I use "japanese" water stones, which I think are about 800, 1200 and 3000). The other thing is when honing on these stones, you MUST maintain the angle through your stroke.

The tendency is to make a slight arc, so you need to coordinate your wrist, elbow and shoulder joints so the blade stays as straight-line as you can. This applies to any kind of honing such as pocket knives, etc.

3. As you get close to "done" with each grade, meaning you've smoothed out the roughness created by the previous grade, I usually change the angle just slightly so as to make a few light strokes on just the cutting edge.

4. Also as you get "done" with each grade, make just two or three very light strokes on each side of the cutting edge similar to #3 above. This removes the burr which inevitably rolls up from the general honing. The ideal picture you have in your head for an edge is a perfect wedge and that is about what it should look like by the unaided eye, but in actuality it will be just slightly curved though it should take magnification to detect any.

On your finest grit, you may want to do this last burr-removing, both-side of the edge stroke thing a few more times. But be careful not to change the angle too much and ruin any previous good work. That's really the trick. You have to concentrate and keep that angle thing consistent from start to finish and one or two steep-angled strokes may cause you to go backward a ways.

paulsv
05-20-2011, 12:01 AM
I assume the OP is talking about wood chisels?

If so, just a few things to add. For flattening the back of the chisels, which is indeed critical, I use a half inch thick pieced of float glass that I had cut to the same size as a full sized sheet of sandpaper. A little water on the back of the paper keeps it from slipping, or you can use a very light spray of adhesive, allowed to dry to the tacky stage. Work up through the grits to at least 800 and make sure the while back is flat as possible. Takes a while the first time, but after that it is just a touch up. You can do the bevel the same way, AFTER the back is completely done, using a honing guide and very even pressure to get a perfectly flat bevel. I did it that way for years before I finally broke down and got a Tormek, which isa lot easier. Remember that a sharp edge is the arris formed by the intersection of two perfectly flat surfaces, and it should be a perfectly straight line. Both the back and the bevel should have pretty much a mirror finish when you are done. The glass and sandpaper or emery cloth method is commonly called the "Scary Sharp" method, and if you Google that, you'll find a lot of info.

I always finish by carefully forming very small secondary bevel, just a few degrees less acute than the primary bevel. This can be done by adjusting the honing guide to raise the handle of the chisel. Make it just big enough to see. I always do this by hand, not on the Tormek Then when you resharpen, all you have to do is give that secondary bevel a few slicks. Don't let wood chisels get too dull before resharpening, which will then just take a few seconds.

darryl
05-20-2011, 12:44 AM
I normally use a belt sander for cleaning up the back and the angle. It's pretty easy and fast to overheat the edge, and the comments about using fresh abrasive are right on. You need neither speed or pressure, just a well controlled contact with the moving belt, and the slower the belt the less the chance of burning the edge. I mention the speed to differentiate between the hand-held belt sander and the stand mounted belt/disc combo, which is probably quite popular in small home shops. The disc turns at some blinding speed, easily capable of burning an edge in an instant, while the belt is slower, and the hand-held is the slowest ( my experience with my machines anyway). Anything that has that graphite impregnated slipper layer under the belt has the potential to round over an edge, so you must keep that in mind. It's not often that I clamp the hand held upside down in the vise to grind something, but there are times when I resort to that. I sometimes wish I could crank the speed down on the belt/disc, just to avoid burning the edge.

Most of the sharp edged tools I sharpen get abused, and I usually stop at just the belt sanding. Where I'm keeping some aside for fine woodworking, I pretty much go with the routine others have suggested- stoning, progressively finer grits, etc.

I dislike the el cheapo angle guides, but the idea of it is good. I often use the coarse/fine/superfine diamond plates for final prep- much of the skill involved in sharpening it in keeping the angles correct and not rocking over the edge. Takes a bit of time to do it right.

A machine I'd like to make is a variable speed, table mounted vertical wide belt sander with cast backing plate, with a zirconia belt. Wide as in more than one inch- three or four would be good. I'm probably stuck with a three inch belt, since that's all I can find in zirconia, but for a tool sharpener it would be fine. I like the idea of being able to grind (sand) a flat surface on something (like a chisel) as prep for stoning, etc. Come to think of it, didn't someone here build such a machine- looked pretty solid too, with adjustable table and side angles. It's great having the machine control the angles for you, and it makes for a very consistent result, not to mention easier re-sharpening.

GKman
05-20-2011, 07:43 AM
Hardest thing for me to learn was to grind the end of a chisel or plane iron square to the bottom of any nicks. We all want to grind at about 30* back and forth making a sharp edge and continue until the nicks disappear. It's very difficult to keep from burning this sharp edge. Square first then 30* back and forth until the bevel nearly reaches the edge then switch to flat stones. Grind at an acute enough angle that there is very little metal to remove with flat stones.

I use this guide on Japanese waterstones (800, 1200, 5000) plane irons and Marples chisels or 320 oilstone if I'm in a hurry chiseling rough work. I also use a 10X magnifier and a good light. Be sure to flatten the back. Any scratches on the back translate into blunt on the cutting edge. Mine have a mirror finish on the back from the 5000 waterstone.

http://www.veritastools.com/Products/Page.aspx?p=119

Thanx to Ian Kirby for all of the above except the Veritas holder which he doesn't seem to need.

Ernie
05-20-2011, 12:20 PM
If my chisel is just dull but not knicked, I use the tool that GKman referred to. It keeps the edge at a constant angle so there is no roll-over. Plus, with the lifting knob, you can set it to put the secondary bevel on the chisel. The next time it's dull, you just need to sharpen the secondary bevel. The entire edge will only need occasional sharpening. But I don't use those stones. I place a full sheet of silicon carbide wet/dry abrasive sheet on a surface plate. Just wet the surface plate with a bit of water and the sanding sheet will not slip or slide. Make sure you roll it down so it's perfectly flat. Then wet the working surface. I work my way up to 1200 grit and find that's plenty sharp enough for the amount of woodworking I do. An assortment of grits is a lot cheaper than water stones and it gives a much bigger surface to work on. If I place it diagonaly, I can sharpen a 12 inch planer blade this way. Also, you never have to flatten stones, just change the sheet when it gets dull. Remember that even a brand new chisel needs to have the back flattened to get a straight edge when you sharpen it.
Ernie

aboard_epsilon
05-20-2011, 12:54 PM
Guidance

seems they are all pointing at the high money fancy brass and steel items

all you want is one of these

http://cgi.ebay.co.uk/Eclipse-No-36-Plane-Chisel-Sharpening-Guide-Tool-/370510567807?pt=UK_Collectable_ToolsHasdware_RL&hash=item564426997f

look out and you may pick them up for under $5

they do the job perfectly for me

heres a page with a few on

take your pick

http://shop.ebay.co.uk/i.html?_from=R40&_trksid=m570&_nkw=Eclipse+CHISEL

alkl the best.markj

Circlip
05-20-2011, 01:55 PM
Lesson one in woodwork at school, 12 years old. Hell, how we have "advanced" over the last 50 odd years.

Carbon steel cutting tools and oilstones, golden oldies but still superior to modern crap.

Regards Ian.

metalmagpie
05-20-2011, 08:47 PM
Oh jeez - NOT a wood chisel! This isn't a woodworking forum! Just plain old cold chisels, none of this 2000 grit water stone baloney please! :-)

Circlip
05-21-2011, 05:55 AM
Double posted

Circlip
05-21-2011, 05:55 AM
Oh jeez, why did it take 24Hrs after tossing the grenade to explain what you wanted to know?

One double indemnity out of 12 replies.

Woodchips surface here regularly.

Regards Ian

Dr Stan
05-21-2011, 09:57 AM
Oh jeez - NOT a wood chisel! This isn't a woodworking forum! Just plain old cold chisels, none of this 2000 grit water stone baloney please! :-)

OK then just take a look at my post on pg 1.

aboard_epsilon
05-21-2011, 10:15 AM
Oh jeez - NOT a wood chisel! This isn't a woodworking forum! Just plain old cold chisels, none of this 2000 grit water stone baloney please! :-)

what a ploker ..you should have explained it right

sharpening is for wood chisels ..thats how we read it ..

your cold chisels just need a 60 -70 degree or there abouts blunt point on them...sort of like a house roof

remember to take the mushroom off the end you hit ..or you will loose an eye

then

heat the the tips up cheery red ..and quench in oil ..if you want them to last a while.

all the best.markj

Mcgyver
05-21-2011, 10:24 AM
Oh jeez - NOT a wood chisel! This isn't a woodworking forum! Just plain old cold chisels, none of this 2000 grit water stone baloney please! :-)

its exactly the same procedure, establish the angle to the correct angle to say 5 minutes and start abrading. finish with an 8000x water stone or 5 micron diamond paste.

how to expect to cut metal if you're not producing accurate cutting surfaces?

Jpfalt
05-21-2011, 03:12 PM
You guys...... a wood chisle is just like a metal chisel except that the metal chisle doesn't spray you with hard, sharp flinders of chisle edge when you hammer it into a brick.

By far the easiest way to sharpen one is to clamp a bar across the blade back so that when it lays against the grinding wheel, you get about the bevel angle you want. Then grind from side to side until it makes a nice perfect hollow grind.

Then you put the hollow down on a hone stone and press down just behind the cutting edge so that the chisel rests on the cutting edge and the edge between the hollow and the back of the tool. Add oil and skid it around a bit.

What's so hard?