Using mortiser - smoking

[LCHIEN]

I have a Jet JBM-5 mortiser, 1750 RPM (the slower speed, many turn at 3400 RPM, like the Delta).

When I make mortises with what feels like a comfortable feed rate, the wood smokes and I can both see and smell it. I try and back off the feed speed at that point...

Is that the right thing to do?

Are mortisers smoking because of excess friction between the round auger and the square chisel when it can't remove material fast enough, or is it the old feed to slow and it burns issue?

Seems like its the former but i saw some recommendations that feeding too slowly can burn. But I think that the chisel is not rotating so slow feed speed is not causing burning there, and the auger is removing material from the hole, so slow feeding will result in mostly an empty auger so nothing to burn there.

Anyone else have experience?

American Woodworker article on Mortisers says smoking is normal, esp. with higher speed machines.

[just4funsies]

I have seen smoke (a little) from mine, but the absence of burned wood tells me that this may be a metal friction thing. I do know a slower feed rate helps, and maybe less chip clogging leads to less friction. YMMV.

[kwgeorge]

Well Loring, I have the Jet also and I have run a bunch of different woods through it and I have to tell you it has never smoked or even burnt the wood. I am kind of fast when I am mortising. How dry is your wood? What kind of wood are you using? Are your bits sharp? Is the bit square to the fence? Is it possible you have a bind somewhere?

Just some thoughts.

Ken

[RayintheUK]

The problem is usually incorrect setup, having the auger too tight to the chisel. The chisel only has to follow the auger and square up the hole, it shouldn't do anything else. However, if the bit is set in the chuck so that it is too tight to the inside faces of the chisel, friction will occur. This can also result when the chuck is not fully tightened and the feed rate is a little high - forcing the auger up further into the chuck, with resultant friction.

The way to check is to CAREFULLY feel the chisel - if it's hot, settings are wrong. There is NO reason for the chisel to get hot if correctly set.

Ray.

[Tom Miller]

What Ray said, re: not having the auger too tight. Is it so hot that you're losing temper on your chisels? I sometimes use a tiny bit of lubricant where the auger contacts the chisel, but I'm not sure how much this helps -- seems like it would get wiped away pretty quickly by the chips passing through.

Regards,
Tom

[LCHIEN]

I follow the directions, insert the chisel 1/16th below the topmost position,
install the auger tight to the bottom of the chisel,
then raise the chisel the last 1/16th so that the auger has 1/16th clearance.

So I don't think the auger is binding on the chisel, spins freely enough when off.

The bit is brand new, the chisel square to the fence. I'm sure that everything is tight and not being forced into a bind when under pressure.

The wood is Brazilian Cherry - Jatoba, somewhat hard.

[just4funsies]

Jatoba is pretty hard... I've dulled up some tools myself working that stuff. Never did a mortise in it, though. Are you sure the auger bit's sharp? Does it cut OK without the chisel?

[Russianwolf]

try this. remove the chisel and just drill a half depth hole with the auger (between 1/2 and 1 inch deep, but not all the way through).

1) if it smokes, then you know its the drilling and nothing to do with the chisel/bit interface.

2) if it does, look in the hole and see if there are any indications of burning or "polished" surfaces. Not all wood will burn with black marks.

[JimD]

Loring,

Mike's test looks interesting.

Assuming it does not smoke with just the drill bit, I would try increasing and decreasing the amount that the drill bit extends below the chisel. This assumes that the smoking only occurs after you start to cut and is due to wood chips getting backed up instead of cleared. You can generally tell when the chips are not coming out as fast as they are being generated.

I keep a little can of 3 in 1 oil on my Jet mortiser (we disagree on routers but we seem to have the same mortiser). I put a piece of scrap under the chisel/drill bit and squirt a little light oil into the bit where it is exposed on the side of the chisel. It cuts down on the noise and probably also reduces the chance of burning. Most of the excess oil drips on to the scrap and then I cut my mortise. Light oil on the wood probably does not help the glue-up but by letting the excess drip off before I cut, I do not think I am hurting anything significantly.

My shock absorber thing that is supposed to keep the lever up failed early. Does yours still work? I am wondering if it is worth fixing or if the replacement would just fail quickly too.

Jim

[LCHIEN]

I'm pretty sure that the drill bit by itself is OK.
I have to press pretty hard to make the chisel penetrate, otherwise i think the tip of the auger would burn the wood just spinning. I press hard enough that I get pemnetration and the chips come ejecting out the chip slot in the side of the chisel at a good rate.

I thik the burning is inside the auger probably chips caught between the auger and chisel. The square hole is not black, but I both see smoke and smell the burning (my daughter says what's that BBQ smell?) and I can see peppery stuff mixed in the ejected chips.

I have seen some blackened chips come out of the auger after cleaning up.

I'm using a brand new auger/chisel set from my old Delta mortiser attachment - I did not use the one that came with the mosrtiser. may be i should try that one.

Jim, I did allow 1/16th clearance (as per the manual) and later tried 1/8" with no change.

And, my pneumatic cylinder is working fine.

[JimD]

Mine squeeked a lot and maybe burned some before I started lubing it with the 3 in 1 oil. Alignment of the drill bit to the chisel can affect the squeeking but when you are pressing hard enough to go into hard wood I think the chisel may move slightly. That first hole is generally a pain. I generally lube before the first hole. Sometimes I do the holes on the ends first then nibble out the middle. Sometimes I just go in a line. I do not like making the four sided holes in hardwood. It always seems to be a bit of a struggle - significant force required and then the chisel doesn't want to come back out.

I also bought a sharpening kit from Lee Valley. I haven't used it yet but I would if I was having trouble like you desribe. It was not a lot of money. The cone shaped hone is supposed to be diamond.

Jim

[Russianwolf]

Loring, to check the bit you HAVE to try without the chisel. The reason being is the chisel isn't just squaring the corners, it also slices a tad off the sides. So any burning that the bit is doing is concealed after the chisel does it's job.

Give it a shot and see.

[Tom Miller]

Loring, to check the bit you HAVE to try without the chisel.

Mike,

Do you know for sure that the auger can be used by itself? I have no idea, it just seems like they might be designed only to work in conjunction with the chisel. They may not have any cutting edge to shear the sidewall.


Regards,
Tom

[meika123]

I have been having the same problem with mine for some time. I have a budget brand mortising machine, and it cuts square mortises, but also smokes quite a bit at times. I bought a tool to sharpen the chisel, and attempted to sharpen the auger bit. It still smokes, however.

Looking forward to seeing this problem solved.

Dave in NC