Sharpening Thick Morticing Chisels

[Rick Brown]

Which jig is necessary to sharpen thick bladed, straight morticing chisels? The blade is too thick for the straight chisel and plane jig. I would appreciate any thoughts. This chisel was probably originally intended for timber framing

[Ken S]

Hi, Rick.  Welcome to the forum. I sent you a PM. Please check your essages.

Ken

[Jan]

Rick, if you intend to use the square edge jig, read the topic "How to sharpen 3/4" mortise chisel" http://forum.tormek.com/index.php?topic=2295.msg11231#msg11231

In the reply no.21 you will find how I did it.

You can also use the tool rest.

Jan

[Ken S]

Rick and Jan,

One of the many things I like about this forum is the room for different opinions. Jan has devised a very lever method of reestablishing a flat bevel. While I like Jan's idea, I also think there is room for a moderate hollow grinding in the bevel. The difference may be influenced by Jan's desire for historical authenticity to honor his grandfather. For working tools, either bevel will work.

Ionut and I discussed this same issue several years ago in posts. We found that the SVH-60 jig, the predecessor to the SE-76, can accept thicker mortise chisels.

Ken

[Jan]

Rick, I fully agree with Ken.  From the functional point of view there is almost no difference between flat and hollow grinded bevel at a heavy duty mortising chisel.

Usage of a belt sander is recommendable not only for reestablishing a flat bevel, but also when you need to remove large amount of hard steel when reshaping big tools (e.g. a broken chisel) .

Jan

[Ken S]

Good point, Jan.

A belt sander is a very efficient tool for removing a lot of metal as in reshaping.

Ken

[Hatchcanyon]

In context with the sharpening / hollow grinding discussion I also used a mortising Chisel as a reference tool. Not as heavy as 3/4" but about 1/2" thick.

Due to the fact that my shop lacks a belt sander  I gave it a try to sharpen it on the T 7.

First consideration: A mortising chisel is some kind of a rough tool. As long as the edge holds the forces and the flanks are straigt it will work. By all means it is not necessary to get a consistent (whole) bevel. A short stretch behind the edge will do.

Two approaches:

1) Grind the tool on the side of the stone like the backside of any straight iron - but how to position it?


Grinding the bevel on the wheel's side

To hold the iron I use the SVS 50 with the closed seat on the universal support. Set it to the angle intended. This gives a flat bevel but grinding the whole bevel is annoying slow.

A completely flat bevel is not of much use, therefore one may grind only some millimeters behind the bevel and that can be done on the  stone's normal grinding surface. No concerns about hollow grinding! Again the question: How to hold the iron?

The SVD-186 helps. Position the iron like a like a carving gouge and measure the edge angle with a WM-200. Adjusting is done with the horizontally mounted universal support and it's fine adjusting capability.




Úsing the mortise chise with the SVD-186

Yes it's true the SVD-186 may turn but this is easily controlled as long as the stone surface is square.


Grinded edge and part of the bevel

I stopped grinding after about 8 mm of the bevel.

Rolf

[Ken S]

Well done, Rolf!

You are expanding the versatility of the Tormek. You have found paths to sharpen your mortise chisel with either a flat or hollow ground bevel.

The Tormek is burdened by many people who (still ) think in terms of dry grinding with smaller diameter and narrower grinding wheels. We need to be aware of this bias.

The agruments both for and against hollow grinding originated in the era when the typical home shop grinder had a narrower six inch (150mm) grinding wheel. The smaller wheel produced a pronounced hollow grind. This hollow made hand honing easier by providing two reference points for maintaining a consistent bevel ( the toe and heel of the bevel). This was much loved by many woodworkers, although not by the flat bevel crowd. This hollow is much more pronounced than the small hollow produced by the larger Tormek wheel.

Using the side of the grinding wheel is a universal taboo in the dry grinding wheel universe, although it is commonly practiced. The logic for this is sound. Most dry grinders turn at 3450 rpm, very high speed, and the wheels are narrow. A cracked wheel at that speed would be dangerous. This is quite a different situation than a two inch (50mm) thick Tormek wheel turning at 100 rpm, although the old dry grinding thinking still persists.

I think the using the side of the Tormek wheel is an underused technique. I also think positioning the universal support can be more versatile than is commonly practiced.

Rolf, I commend your good work, as well as your photography.

Ken

[Hatchcanyon]

Ken,

my recommendation in this case is to grind the mortise chisel like any other chisel but stop grinding after 5 - 10 mm above the edge. This gives a negligible hollow grind or better said one that does not increase the bevel angle upwards too much. What is shown in the picture above corresponds to grinding an iron of about 3,7 mm thickness.

Frankly said, grinding the whole bevel on the side of the wheel is possible but annoying.  I also fear possible tearouts not knowing how to true the sides? (Does anybody?) For a narrower tool I would not recommend to use this method. The SVD-186 works fine for me. Yesterday evening I successfully ground another mortising chisel with 6mm width only. Even this narrow tool could be worked easily.

Rolf

[Ken S]

Good point, Rolf. The very edge, in this case the edge of the secondary bevel, is what does the cutting. The rest of the bevel is just along for the ride and support.

As a forum, we need to continue discussing getting smooth edges when using the truing tool.

Ken