morticer - drill marking outside line of bit

[mickthetree]

Hey all

I've got a sip 1/2" morticer which I've been considering getting rid of as I dont use it much. Thought I should give it a good workout before making a decision and I've been moderately impressed.

Cuts through oak and beech and pine fairly well.

Main trouble is the bits. They cut pretty neat edges, but the drill bit marks the outside walls of the mortice. I dont want to snug the drill up any tighter into the chisel as it would be too tight and heat up and it seems to bind up with wood and stall the motor.

So how do you set the drill bit? Should it be tight but use a lubricant? or loose or is there a sweet spot you have to find?

These are cheap bits I believe, but still they can produce some reasonable results.

Could do with raising the table on it also as the chisel stops quite short.

 

[Steve Maskery]

Hi Mick
If it's any consolation mine does the same!

OK, the basic geometry is that the bit should not extend outside the boundary of the chisel. I suspect that it does, in both our cases. I also suspect that it wold be a straightforward job to grind down the bottom end of the drill a tad to solve the problem.

The good news is that it doesn't really affect the quality of the joint very much, does it?

S

 

[mickthetree]

Hi Steve

You are probably correct. It is only slight. My technique may need refining as I overlap the passes so I end up being left with a wavy wall in the mortice.

Can I ask, do you use cheap chisels or some of those fancy ones? ;-)

 

[joiner_sim]

Invest in some decent chisel sets and the problem shouldn't be there.

 

[OPJ]

There's an old trick to setting the correct clearance between hollow chisel and auger, which involves simply a 2p coin...

Set the chisel only in to the machine but wedge the coin in about, so that chisel is actually about 2mm lower than it should be. Tighten the bolt/screw to secure the chisel. Then, insert the auger up so it is touching the chisel. Tighten the chuck. Then, release the bolt holding the chisel, remove the 2p coin and push the chisel up until it stops, before securing it back in place (and checking it for square against the fence. :wink. There you go!

I think it could be down to the quality of the chisels you're using. I have a collection of Japanese ones from Axminster that don't seem to have this problem. But, the Chinese bit that came with my previous mortiser did do this - not that it affects the strength of a joint, as Steve says. I think it's only critical when you're cutting through tenons and the mortise walls would be visible from the outside.

 

[mickthetree]

Many thanks Olly, thats exactly what I needed to know.

I'll give it a go.

Cheers Sim. Thought I'd give these ones a wirl first and see how it operates. Half the fun is getting these thigns right isnt it!

 

[awkwood]

It seems to be a problem with cheaper augers.
It is possible to true the auger by holding a file tightly against the chisel while rotating the auger this will reduce the diameter of the auger slightly

 

[mickthetree]

Found thiswhich compliments just what Olly said....

 

[Eric The Viking]

It seems to be a problem with cheaper augers.
It is possible to true the auger by holding a file tightly against the chisel while rotating the auger this will reduce the diameter of the auger slightly

I've tried that with mine, well, using a diamond plate instead of a file: it didn't make a huge difference (I didn't want to go too far, so I may not have done enough).

Oddly, when I polished the outside faces of the chisel and sharpened it properly, the effect reduced a bit. The other odd thing is that measuring the auger diameter with a vernier indicates it *is* the same as the chisel flats. I assume it rotates eccentrically because of chips pushing it over, hence the arcs cut in the side of the mortice. If that's the case, there probably isn't an easy solution, as it's caused by the clearance (slop) inside the chisel.

At a guess, Olly's Japanese chisels are probably made to much better tolerances and thus don't slip sideways so easily. It's probably good not to have too great a clearance (sideways - I don't mean vertically), as that will stop chips getting wedged. Mine has a small motor and stalls occasionally in softwood, if I'm hasty.

 

[Ironballs]

I've found that you tend to get this effect when either the machine isn't set up quite right or when using smaller bits/chisels, the smaller bits seem to deflect more easily in use whereas the bigger ones tend to just chew through the wood.

As Steve says though, it's only cosmetic and on the inside of a joint

 

[Steve Maskery]

My guess is that I should buy some better chisels. One day, perhaps, I'm getting rid at the mo rather than accumulating


Olly, you've made me smile:

There's an old trick to setting the correct clearance between hollow chisel and auger, which involves simply a 2p coin...

As we've only had 2p coins since, when, 1971 was it?, and I remember old ha'pennies (indeed, farthings, though not as legal tender any more) the idea that 2p is "old" is, well, a bit _ I can't think of the right word. But it made me laugh.

Now where did I leave my zimmer frame?
S

 

[mickthetree]

Tried it last night with a 2p coin, threepenny, halfpenny and shilling (have a jar full of them) and found the 2p coin to work the best.

Seems to stop any waste accumulating now but still cuts outside the line. Oh well, untill I can afford some good bits I think I'll go back to those pig stickers. They leave a lovely smooth finish ;-)

 

[awkwood]

The other odd thing is that measuring the auger diameter with a vernier indicates it *is* the same as the chisel flats. I assume it rotates eccentrically because of chips pushing it over, hence the arcs cut in the side of the mortice. If that's the case, there probably isn't an easy solution, as it's caused by the clearance (slop) inside the chisel.

Industrial quality augers are ground to better tolerences giving less run out, are properly hardened and could also be made from a higher grade steel

 

[monkeybiter]

I reckon the point is probably not central with repect to the perimeter of the auger