setting a blade angle using projection

[mickthetree]

Hi all

I got a 5/8ths" OBMC delivered and cleaned it up.

I now just need to grind a new primary bevel (30 degrees I think).

Is there a method I can use to work out how much the blade should project from my eclipse guide to get said angle?

Does it matter the thickness of the blade? and is this part of the equation?

Sorry if this has been discussed before, but I couldnt find anything. Maybe using the wrong term.

I was just going to set the guide from my other OBMC which has a bevel that cuts nicely, but wanted to see if there is a method for working this out.

Cheers!!

 

[woodbloke]

I now just need to grind a new primary bevel (30 degrees I think).


Cheers!!

If it's the primary bevel, then 30deg is too steep. They should be ground at 25deg...I grind mine on the Tormek at 23deg - Rob

 

[mickthetree]

Cheers Rob

Just found a reference to mortice chisels and they also recommended 25 degrees, with a possible secondary bevel of 30 degrees for softwood (which I'm using in this case)

On the side of my eclipse style jig it says "Chisels - 30 degrees = projection 3cm. But its too darn steep.

I might just set it from my other chisel which works well, but I'd like to understand how this works for future reference.

 

[dunbarhamlin]

Isn't 25° a bit obtuse for an OBMC primary?
Mine are around 20° primary with a small secondary of about 40° (freehand, so angles approximated)

Re projection, provided the back/face/non-bevel-side is used for registration (as with Kell, Veritas, modified Eclipse,) the thickness is not a factor.

Though especially for something brutal like a large OBMC, why not freehand it? You're not trying to sneak up on the minimum bevel the steel will handle, so precision or even repeatability not important. Also, an OBMC will commonly be larger than a guide can comfortably accomodate.

When commissioning my OBMCs, I just used a guide to square the bezels.

(I also 'break' the primary bevel - which lends itself to Jacob's infamous convex bezel technique)

Cheers
Steve

 

[Paul Chapman]

which lends itself to Jacob's infamous convex bezel technique

Blimey, Steve, be careful - you'll set him off again :shock: :shock:

Cheers :wink:

Paul

 

[woodbloke]

which lends itself to Jacob's infamous convex bezel technique

Blimey, Steve, be careful - you'll set him off again :shock: :shock:

Cheers :wink:

Paul

...not on here, thankfully [-o< - Rob

 

[mickthetree]

ah so thats why some of the old chisels I've picked up have convex bevels!

Didnt think of freehanding as its so bloomin big! bit unweildy, but I'll give it a go.

A wedge cut to the right profile should help me I think. nice tip.

It has a VERY high angle on it at the mo and only dents the wood. Very big chisel so lots of material to remove. Although I was very surprised how fast my old oil stone reground an old, nicked plane blade.

Thanks for all the pointers! Appreciate it.

 

[woodbloke]

ah so thats why some of the old chisels I've picked up have convex bevels!

If you bought them anywhere near Matlock, that's the reason! :lol: - Rob

 

[Ironballs]

Dunbar makes a good point, you whack a mortice chisel dead hard with a mallet and then clean up with another chisel after, so angles don't have to be that precise. Just remember to not try and take all the waste out in one and chip away at it

 

[dunbarhamlin]

If you bought them anywhere near Matlock, that's the reason! :lol: - Rob

:lol:
Re freehanding it's such an enormous bezel on a 5/8" that it is very easy to register, just like a router cutter. And, as like as not it'll be a laminated blade, so reshaping the primary will go quickly and it will naturally tend towards more acute as the face/cutting edge is much harder.

 

[bugbear]

Is there a method I can use to work out how much the blade should project from my eclipse guide to get said angle?

I'm far from convinced the Eclipse (which I own) would be up to "managing" such a beast, even if you did work out a suitable projection distance.

I would freehand it (and I'm normally a big fan of honing guides).

BugBear

 

[Jeff Gorman]

I got a 5/8ths" OBMC delivered and cleaned it up.

Wazzat den?

Jeff

 

[PeterBassett]

I got a 5/8ths" OBMC delivered and cleaned it up.

Wazzat den?

Jeff

Oval Bolster Mortise Chisel. Pig-sticker. Dirty great lump of iron.

 

[Tony Spear]

which lends itself to Jacob's infamous convex bezel technique

Blimey, Steve, be careful - you'll set him off again :shock: :shock:

Cheers :wink:

Paul

Too late mate!

He's been at it again for the last few days in here:

http://www.woodworkuk.co.uk/forum/viewt ... f=4&t=3608

:roll:

 

[promhandicam]

I use one of these for getting the angle right for sharpening blades.

HTH

Steve






:wink:

 

[PeterBassett]

:wink:

:lol: I've got two, just to be sure!

 

[promhandicam]

:lol: I've got two, just to be sure!

Yes but what do you calibrate them against? I got myself one of these to check my workshop measure against. I don't usually use it on site but as it is a bit bulky.

Steve