Mortiser performance


Well I borrowed a mortising machine from a guy I work with. Its the older model delta and this guy and the guy he got it from said it works great. Additionaly there was an article in last months FWW about mortiser setup. With all this I did a modest initial tune up on the mortiser to make a couple of test cuts since I have not used one before.
I guess the part I was most surprised about and was wondering if it was normal was that the sides of the mortises seem to have scalloped edges. As if the edges of the auger bit are wondering a few thousands outside the edges of the chisel. Albiet, the scallops are very small but I was expecting the walls of the mortise to be very smooth. Can anyone shed some light on this. Is this normal? Is it the bit or is there a lot of runout on the bit. Also I set the bit and chisel clearance as per the FWW article and the bit seems to get very hot. Enough to make white oak smoke. Is this right?
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Without seeing the scallops I would offer two guesses: 1.) Your chisel is not quite aligned with the fence and your stock. This will cause an enlongated "Z" pattern down the sides of the slot. 2.) Your hold-down hardware is not quite doing the job (loose, mis-aligned, etc.) My first bet would be on 1).
Also I set the bit and chisel clearance as per

Some smoke with hardwood is not terribly unusual. Your bit might be getting a little dull, but once you get shavings inside of the chisel heat builds. Hardwood cuts a little slower causing the problem to worsen. Make sure your chisel is installed to allow the shavings to escape to the side or out the front. If they build up against the fence and hold-down (rear exhaust) it will worsen the problem.
RonB
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A correction to my entry - You bit or chisel might be getting a little dull. Both will slow the time it takes to plunge into hardwood.
RonB

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"BD" wrote in message

Sharpen both. The key to success with a hollow chisel mortiser is sharp chisels and bits, and don't hog the wood.
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Thanks guys. I will make sure everything is square and sharp. These were just preliminary practice cuts so I'm sure I can tune it up a bit better. Also in the FWW article were tips on sharpening the chisel and bits so I will do that as well.
One more thing. How much deeper should the depth of the mortice be than the tenon or what part of the bit do you use to gauge the depth of the cut because I did notice that the auger obviously goes a tad deeper than the chisel but it isn't really a flat bottom.
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I try to make sure that the bottom of the gullet of the chisel cuts as deep as my tennon will go.. or a hair more.
-Steve

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C&S wrote:

Go at least a hair more. Radial or tangential shrinkage is much higher than longitudinally, and you don't want the joint to pop. This is becomes more of a concern the deeper the motise, eg. timberframing.
JP
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"BD" wrote in message

I generally shoot for a generous 1/16" deeper than the length of the tenon for the inevitable glue pool at the bottom of the mortise.
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Well these mortises are going into quadraliner posts I've constructed. The post walls are 3/4" plus a 3/4" backer I put on the inside face to recieve the tenon. What about making it a thru tenon except that the end of the tenon is on the inside of the post? Any drawbacks? I suppose that was about as clear as mud.
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BD wrote:

Welcome to the wonderful world of shitty hollow-mortising chisels. You join a long line of forum posters. (No butting.)
The problem I had with mine was corrected by shrinking the diameter of the cutting portion of the bit itself.
Notice when you rotate the bit within the chisel that the outermost part of the cutting portion of the bit protrudes beyond the sides of the chisel. Bad.
In order to correct mine, and three of the four provided with the machine were defective, I chucked the bit into a hand drill, set it to _reverse_, and with INCREDIBLY light pressure held it sideways against some taped-down emory paper. Note the above capitalization...if you put much pressure on that bit, and by 'much' I mean essentially any, you will snap it in half like a twig, only the twig is sharp and rotating at 2500 rpm. Also bad. They're just not meant to take much lateral loading at all.
I used a very low speed (not 2500 rpm), very aggressive paper, wore every piece of safety equipment I could find, including industrial-grade high-impact safety goggles, and I think I may even have been in a different room.
A safer solution would be to either have a sharpening service correct it for you, or to file it by hand.
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