Hollow Chisel Mortiser Setup

[dlamulle]

I was hoping to get some professional input. I bought a Powermatic Mortiser and the instructions advise installing the chisel with a 1/16th to 3/16 offset between the chisel and cutting spur depending on the wood being used. I have no idea on what they are meaning exactly here. Less with softwoods or hardwoods? I know it has to do with the chip extraction but maybe a little example would be a huge help. I am building a Morris Chair using Greg Paolini's instructional video and want to start off right. I know he used a router but I have the morticer and I want to practice.

Thanks,

Dave

[dvan1901]

The general rule of thumb you see people use is the width of a nickel. What they do is put the chisel in, with a nickel in between the top of the chisel and the machine, then put the bit in, lock the bit down, then raise the chisel the rest of the way and lock it in. Make sense?

[woodhack]

The general rule of thumb you see people use is the width of a nickel. What they do is put the chisel in, with a nickel in between the top of the chisel and the machine, then put the bit in, lock the bit down, then raise the chisel the rest of the way and lock it in. Make sense?

I was told by my shop teacher back in the olden days to use a nickel for soft woods and a dime for hard woods. I have conveniently forgotten the reason why, I think it had something to do with tear-out in that old piece of crap machine. dvan's method is correct though.

[Onboard]

Dave, to clarify just a little bit (I'm hoping anyway), and using dvan’s explanation (if I may), after spacing the hollow chisel with a nickel (or dime as Marty points out), you set the lower end of the drill bit so it’s flush with the tip end of the hollow chisel, lock the bit in place and then move the chisel up to close the gap held by the nickel, then lock it in place. A small board can be used to hold the bit in place while you make adjustments. This will put the end of the drill bit just below the end of the chisel which, as you have mentioned, will help in chip removal. As far as I’ve read, softwoods create larger chips so need a bigger gap spacing, and hardwoods create smaller chips so a smaller spacing.

[dlamulle]

Dave, to clarify just a little bit (I'm hoping anyway), and using dvan’s explanation (if I may), after spacing the hollow chisel with a nickel (or dime as Marty points out), you set the lower end of the drill bit so it’s flush with the tip end of the hollow chisel, lock the bit in place and then move the chisel up to close the gap held by the nickel, then lock it in place. A small board can be used to hold the bit in place while you make adjustments. This will put the end of the drill bit just below the end of the chisel which, as you have mentioned, will help in chip removal. As far as I’ve read, softwoods create larger chips so need a bigger gap spacing, and hardwoods create smaller chips so a smaller spacing.

Thanks everyone for the replies. Without sounding just plain dumb this is what I'd like to clarify now. The bottom of the chisel has points then the top edge of the arch between the points and the bit has a point then a side cutter and a bottom cutter. The side (chipper) cutter is lower than the bottom cutter but higher than the tip. Do I slide the bit inside the chisel until it won't go up any more or do I align the cutter of the bit to the tip of a point of the chisel or the upper arch. Depending on the chisel size and the point you measure from this can be 3/8" difference. Did that question make any sense? I don't want my chisels to overheat due to inadequate chip removal and perhaps I'm being overly critical but I like to have a good understanding of something before I attempt it.

Thanks all,

Dave

[Onboard]

Dave, the short answer is yes, the tip of the bit needs to be lower than the 4 pointed tips of the chisel end. However, I found this web page that will answer your question far better than I could. There’s a good video further down in the article. Please understand, I don’t have or use a hollow chisel mortiser, so I'm sharing my understanding based on what I’ve read. I hope you find the article and video helpful.

[dvan1901]

Dave, your second question really is the reason for my first answer...If you put the chisel in, with the nickel between the chisel and the machine (i.e so the chisel doesn't go all the way up) and put the bit in so it is snug to the chisel. Then, tighten the bit. Then, remove the nickel and slide the chisel the rest of the up. This will give you the necessary clearance.

When you are looking for "how deep should I set the machine?" the general rule is half the distance of the arch of the chisel. Some even go so far as the top of the arch of the chisel. I find that is a bit too far though, but that part is easy to tune.

[dlamulle]

Dave, the short answer is yes, the tip of the bit needs to be lower than the 4 pointed tips of the chisel end. However, I found this web page that will answer your question far better than I could. There’s a good video further down in the article. Please understand, I don’t have or use a hollow chisel mortiser, so I'm sharing my understanding based on what I’ve read. I hope you find the article and video helpful.

Thanks so much for this page. It really helped me visualize the correct placement of the bit in relation to the tip of the chisel and the video was an added bonus. I set it up tonight and plowed about two dozen 1/2" mortices in the legs and side panels of my Morris chair project and it worked flawlessly, 8 were through mortices and they were square to both faces and with a good backer- board I had no chip out. I also appreciate all the other wonderful and helpful replies, thanks guys and gals.

Dave

[nateswoodworks]

If you set it up allowing for the spacing between the bit and chisel like stated before you will be just fine, just listen to your tool. One thing I do since the auger bits sometimes are a little rough due to casting burr's or rough filing and such (and this is on the better ones) is to use a small file and some emery cloth and clean up and smooth it all down. By doing this it allows the chips to pass through with ease because the chips are no longer getting hooked on the birr's and plugging mortise chisel. Another tip is get a small tube of graphite powder, can get it at any auto store, a shot into the mortise chisel while it;s running sure helps it run smoother.

Nate

[dlamulle]

If you set it up allowing for the spacing between the bit and chisel like stated before you will be just fine, just listen to your tool. One thing I do since the auger bits sometimes are a little rough due to casting burr's or rough filing and such (and this is on the better ones) is to use a small file and some emery cloth and clean up and smooth it all down. By doing this it allows the chips to pass through with ease because the chips are no longer getting hooked on the birr's and plugging mortise chisel. Another tip is get a small tube of graphite powder, can get it at any auto store, a shot into the mortise chisel while it;s running sure helps it run smoother.

Nate

I was spraying some Boeshield T9 in the top of the chisel while it was running as soon as I finished using it then letting it coat well, shut it down and not using it till the next evening. Thanks for the idea of the graphite power that sounds great. Have you had any issues with it discoloring the wood?

Dave