Hollow chissel morticer problems

[dexteria]

Hi all,

I've got a batch of doors to do in American Hard Maple. The problem I have is that my morticer isn't handling it very well. No matter how small I nibble away at the mortice the bit and chissel heat up causing scortching, smoke etc.

The chissel and bit are 1/2" Japaneese pattern and relatively new. I have sharpened both and am using a £1 coin as a spacer to give me clearance on set up. On its own the bit drills fine. I think heat is being caused by chips coming up through the chissel in the clearance between the chissel and the cutters of the bit rather than the flutted part of the bit.

Hope you can make sence of that.

Can anyone offer any suggestions to what the clearance between the chissel and bit should be or am I missing something in the set up etc?

Thanks

Mark

[dom]

A £1.00 coin is too thick for clearance Dexteria 2p or just under is better.
Which way is your clearance hole facing, it should spout to the right.

[Stree]

A 2p coin would be a better spacer...........Even then I would have it closer, I get it set by having the auger rubbing on the chisel then adjusting so its clearing it by 2 to 3 mm.
what morticer are you using? Is the speed variable?

[Stree]

Wow! Dom the synchronous ! 2p or not 2p, that is the question............

[dom]

;D ;D ;D

[dexteria]

Thanks guys,

I'll reduce the clearance in the morning and give that a go.

I'ts an Axminster floor standing morticer, unfortunately the speed is fixed. I also have an old chain/chissel morticer but it's got an external motor that needs bolting to the floor and connected via 3 belts and I haven't got round to installing it. I could fit a speed controller to it. Would this be a worthwhile feature?

Thanks

Mark

[nickw]

dom said:

... it should spout to the right...

It should spout to whichever side you have already made a hole in - to the right if you cut your motices from right to left and vice versa.

[dexteria]

I cut from left to right and have the slot on the left.

Mark

[jfc]

I also cut from left to right and have the slot on the left . Just a thought but you are overlapping each cut rather than making a seperate hole each time and then going back to clear out the rest right ?

[dexteria]

yeah I'm doing that.

Cheers

Mark

edit: overlapping that is. Also I've just realised that my spelling is crap :-)

Mortise Chisel

Doh!

[dexteria]

Hi all,

Tried reducing the clearance beween the bit and chisel but it was still burning. I had a 9/16 English pattern set in amongst the stuff I got with the old mortiser. I managed to sharpen the chisel ok. The bit was beyond me but wasn't in too bad condition anyway.

Using this set in the mortiser still produces scorching but more of a light tan colour rather than all out black.

I think I'll take the bit to my local saw doctor and also invest in a 1/2" English pattern set.


Thanks, and any further suggestions welcome.

Mark

[woodworker]

You can try this method to see whats going wrong.

Take out the mortice chisel and mount just the drill bit, then drill a hole in a scrap piece of your chosen timber and see what happens. Then remove the drill bit and mount the mortice chisel only and mortice the hole you've just drilled and............ (I suspect your all ahead of me now ;D).

You'll now know whether the drill bit or chisel, or both are causing the problem.

[nickw]

Whoa there. Most mortice chisel bits are rather thin at the core. I would be very wary of using one that is unsupported by its chisel. At best it might bend, at worst snap.

[dom]

Hi Woodworker, welcome to the forum.

Dom

[Stree]

Have to agree with Nick there, the auger and chisel are meant to work in conjunction, both spreading the workload for each other.
Is the chisel polished bright in all faces? any friction will only add to resistance and hence friction/temperature. The auger sharpenig should be straighforward enough, only like a flat bit to sharpen just remember to take material from the inside face never the outer face.
Also a drop or two of light machine oil dripped into the moving auger can ease things, let it spin a short while then clear it off by machining some scrap softwood.
Also might be worth checking that the chisel is not splayed or split. check for splay with a straightedge, perhaps a 6" metal rule, check all four faces for a split when its under load. not all four at once, or it will burn, just apply pressure and check one face, release. same for next three faces. If its split its only fit for the bin, if its splayed you might be able to flat it off again as a temporary measure, but a replacement is really the only long term option.

[woodworker]

Your hardly going to give it full throttle with just the drill bit in. A little caution is required .
You'll be able to tell straightaway if it cuts clean or is just friction cutting & causing the burning.

I've done this a fair bit over the years and imho usually it's the bit not being sharp enough or sharpened incorrectly. They are not the easiest tool to in the shop to sharpen to a good edge.

[argus]

.

If it's an Axminster CM 19 that you have, then it's the same as mine, equipped with the cheapo Axminster Chinese chisels. which I frequently use to cut 1/2" mortices - 60mm deep and up to the same in length in seasoned Oak with no problems. The depth is limited only by the available depth of chisel.

A £1 coin is about 3.2mm thick - too much for this.

Dom's right about the 2P piece - it's 2 mm thick and about right. I use a 2mm washer on a piece of string tied to the back of the mortiser because It doesn't get lost and I don't have any money.
All you need is for the smallest amount of clearance possible between the two components to avoid rubbing. If you can get away with less - all the better. If it's too great, you'll end up with debris getting lodged in there and jamming the auger.

I find that it's best to have the chisel opening on the side adjacent to the direction of the cut, avoiding spoil being sent into a freshly cut hole, but I often alternate the direction of the work to even out chisel wear. .

Reasons why It may be binding or overheating:

1 - Your auger and chisels may be blunt, causing spoil to lodge in the gaps.

2 - Rubbing. There may be crud lodged under the spurs between the chisel sides,

3 - There may be a slight bend in the auger shaft.

The solution to the first is obvious.

The second is unavoidable in this type of concentric cutter inside a chisel, but I've overcome it by using a small amount of chain-saw oil on the tip and where the auger is likely to contact the inside of the chisel.(the best oil for this was made by Oregon for the heavy duty chains and is about the consistency of treacle).

The third demands a new chisel / auger.

Tips:

1 - It's crucial to ensure that the flat side of the chisel is exactly parallel with the rear face of the fence, or you'll have a serrated edge to your slot.

2 - You may sharpen the inside cone of the chisel, but don't forget to flatten the outsides on a fine stone.

3 - For blind mortises, keep an old fashioned mortise chisel or a corner chisel handy to clean out the sides and corners at the base of the mortise, where the machine cannot give a clean right angled cut.

4 - Short overlapping cuts are best, but take the first plunge cut slowly and carefully as this is where the chisel is doing the maximum work.

My machine works fine - so I hope this helps.


.

[dexteria]

Hi,

Its the floor stading version that I have. The chisel that I'm having most trouble with is from Axminster. Its a Japaneese pattern and cost about £50. The other that I tried in the Hard Maple is an English pattern and is made bu Halifax.

I have sent the drill bits to the local saw doctor and wil have them back on Monday.

Cheers

Mark