Position of hollow chisel for mortisers
Riverwood1 | Posted in General Discussion on
I am a joinery instructor at a boatbuilding college in Suffolk in the United Kingdom. I recently had a student ask me which was the correct position for the waste slot in a hollow chisel for a mortising machine – facing the front or to the side? He saw me set one up facing the front and thought it odd because all the photo’s he had seen were shown with it facing the side, iether to the left or to the right.
I have always set it up with the slot facing me for the simple fact that you can see the drill bit moving, especially if you are in a noisy shop and are wearing ear defenders. You can pick up immediately if it jams with too many chips.
Does anyone know the correct position and give the reason(s) why I would be most grateful!
Replies
Hello Chipmunk. I don't know for a fact that it is the correct way, but I have my opening to the side. I do this so the chips have somewhere to go. It makes no difference until you have at least one hole established, but after that I definately think it makes a difference in the chip ejection. Peter
Peter,
I understand your thinking. However, I was taught to punch a series of spaced holes with the chisel first, as this reduces sideways thrust (and wear) on the bit. Then connect the first series of holes with another set, again balancing the stress on the bit.
The shavings will eject from the opening in the chisel, just higher up on the slot. Unless, of course, you are burying the thing up to the hilt. In that case, I'd punch the hole in two or three strokes, allowing time for the chips to be ejected, before making the final stroke.
Personally, I prefer to have the chips come out the front, as they are more likely to jam up under the hold-down if spit out sideways. Have worked in shops with preferences both ways, however.
Regards,
Ray
Can you explain in a little more detail what you mean by punch the holes first. I have been having problems getting my mortises straight with the 3/8 bit, and have been looking to improve my technique. Mark
Mark,
What I was referring to, is a technique where you punch your first hole with the mortising chisel at one end of the mortise. Then slide the stock over and leave a space, slightly less than the width of the chisel, before punching the next hole. If you are using a 3/8" bit, you will leave about 1/4"- 5/16" between the initial holes. Make a series of these 3/8" square holes, with 5/16" webs of untouched wood between, til you reach the other end of the mortise. Then go back and mortise out the intervening webs of wood to finish up the mortise.
Nibbling the wood away by gradually lengthening the mortise tends to spring the chisel towards the opening you already have. I'm sure you've noticed the tendency for the chisel to walk towards the open end of the mortise as you push it down. Since the bit and chisel are supported on all 4 sides in the initial cuts, there is less stress on them, and that results in a more accurate cut.
Regards,
Ray
I believe Multico (the British machine) recommends the slot to the side after the first plunge and, as I recall, toward the uncut direction.
I run mine to the side, mainly because I have a vacumn hose that grabs everything from the side.
Alan & Lynette Mikkelsen, Mountain View Farm, est. 1934, Gardens & Fine Woodworking, St. Ignatius, MT
Like Alan, I orient the slot towards the chip collection. However, since my chip collection is in front of the machine (a vac house taped into the "fork" of the hold-down), the slot faces forward.
I have Stanley Lister's booklet "Boring, Mortising and Tenoning" (UK publication...Volume 4 of Manual o Machine Woodworking). The pictures show the slot in the front but haven't found any explanation of why. http://www.stobartdavies.com great UK booksite. Highly recommend...MACHINE WOODWORKING TECHNOLOGY
For Hand Woodworkers
F E Sherlock
ISBN: 0-85542-041-X
For the first plunge, it makes no difference. But after that, I have found it cuts far better if the slot faces the previous cut - because the chips eject much better. With oak and, especially, ash, this really makes a big difference.
What I generally do is make a single full-depth cut at each end of the mortise, then work from one end to the other. Those first cuts have to go real slow and pull the chisel out frequently to prevent jamming. After that, with the slot facing an open hole, I can usually make full depth plunges and cut pretty fast.
I almost always go back through the entire mortise after cleaning out all the chips, to clean up the sides. The chisel will shave the sides clean, which improves the fit a great deal. This is really fast and well worthwhile.
"Everything should be made as simple as possible, but no simpler." A. Einstein
http://www.albionworks.net
I had heard the facing the opening towards the front is preferred, then the chips do not fall into the mortise. Like many things in life there seems to be several preferred techniques
Having tried it both ways, I can assure you that facing the slot toward the previous cut makes it a LOT easier. It depends on the wood of course, but some woods (especially Ash) don't clear the chisel very well, and having the slot facing an opening makes a huge difference. It does result in filling the mortise with chips, but I can't see why that is bad. Just pick it up and knock them out.
"Everything should be made as simple as possible, but no simpler." A. Einstein
http://www.albionworks.net
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