Replies

1. 
   SgianDubh | Oct 05, 2002 04:47am | #1

   In theory, a dedicated hollow chisel mortiser with a good clamping system and a bottom backing piece of something nice and hard, such as maple, oak, etc., will allow you to plunge right through leaving a clean exit. In practice it doesn't happen more than 40%- 50% of the time, so it's best, in my experience, to price the job with a time allowance for flipping every piece and plunging from both sides. However, you might also consider that if you plunge from the exit side, then in theory any spelch at the far side will be hidden by the shoulders on the tenon. This depends on how much of a shoulder you are talking about. A cosmetic shoulder of about 2- 3 mm will almost certainly be disfigured by spelch in about 60% of cases, but this might be disguised by a groove worked for a panel.

   Therefore, all things considered, I find it's best to allow time for the aforementioned flipping of every piece. In any case, if you find you can plunge from only one side successfully, and it saves a bit of time, this will make up for a part of the job that you hopelessly underestimated for. Slainte, RJ.

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1. 
   UncleDunc | Oct 05, 2002 06:05am | #3

   >> spelch

   Cool word. I'm not sure it's any more descriptive than tearout or blowout, but it is certainly more suggestive of the vileness of the phenomenon.

2. 
   JeffKurtz | Oct 05, 2002 03:50pm | #5

   Sgian,

   Checked  both Word Web and the Oxford English Dictionary (unabridged), and guess what, no listing for spelch.  I'm not sure if you should get it patented or copywrited, but I do like it.  Sounds gritty, yet not so much as blow out.  Good word.

   Jeff

1. 
   UncleDunc | Oct 05, 2002 04:03pm | #6

   Too late. Google returned five references to spelch as blowout, four in wood, one in stone.

   Also, look up spelder and spelding.

   Edited 10/5/2002 9:36:39 AM ET by Uncle Dunc

1. 
   JeffKurtz | Oct 05, 2002 04:18pm | #7

   And I thought we had a genuine inventor or poet in our midst.

   Jeff

1. 
   UncleDunc | Oct 05, 2002 04:25pm | #8

   You may be right. The note on spelched stone was posted by "Richard, USA".

2. 
   SgianDubh | Oct 05, 2002 05:24pm | #9

   Not me Unc. It's early doors for me, and I'm still bleary eyed and on my first cup of coffee. So I'm not planning to look it up in any of my woodwoorking books-- all six or seven of them, ha, ha, but I certainly didn't invent the word. I guess it's just a British'ism in common usage amongst us. It's like another term I use, where I'll say, "Remove the arrises prior to polishing."  Americans would probably phrase it, "Round off the corners prior to polishing." There are plenty of other examples. I work with 'rods'. Americans call them 'story sticks'. I tend to 'cramp' stuff up, and Americans 'clamp' it, although I use the latter term too. Slainte, RJ.

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   Edited 10/5/2002 10:30:05 AM ET by Sgian Dubh

2. 
   RW | Oct 05, 2002 05:57am | #2

   Agreed. Experienced some rather dramatic blowout on oak. Oops. Flip em and be happy. If you haven't bought one yet, ask your local guy about what speed the models run at. Your average benchtop mortiser comes in 2 speeds. Slow & cool, faster and more prone to burning. I lean on slow. The fast ones just spin fast, you still don't sink the chisel that much quicker. Decided I liked having the nozzle of the shop vac just to the side of the cut too. Keeps the debris away, lets you see, and maybe all that air helps the chisel stay cooler longer.

3. 
   wamara | Oct 05, 2002 06:43am | #4

   One possibility to consider is to through mortise the work in stock that is 1/4" thicker than finished, then reduce the stock to finished thickness. This of course will only be possible if the piece is such to allow this approach. I have used this method both with chopping through mortises as well as the dedicated mortiser. By the way I use a Jet and am reasonably satisfied with it. The hold-down could be beefier, but I don't try to bottom out on the first stab so it doesn't create much of an issue for me.

   Wayne

4. 
   IronDog | Oct 05, 2002 05:52pm | #10

   Hi John,

   If your budget can afford it I would stay away from the type of mortisers that have the square chisel with internal bit and look like a drill press. My experience with them is they are not very clean cutting and hard to maintain the chisel and bit.

   I have the mortiser sold by TechMark and is the Rojek brand made in Europe. It is very well made and has a movable table and spiral bit. Very clean cutting. It is limited to the length of the spiral bit however.

   http://www.tech-mark.com/vda316.htm

   But whichever mortiser you buy, you could try this method for through mortises. Set the depth to stop just shy of breaking through the other side ( the less wood you leave the better).

   Then cut through the remainder from the other side with a sharp chisel.

   Good luck with your decision and I hope you get the job!

   Tom