PM701 Mortising machine maximum capacity

[Brian Leach]

Hello Everyone,

I recently chopped out four 3.5 x 1.5 x 3 mortisies by hand. Looking at the plans for the rest of my project, I was discouraged at the remaining cubic inches of wood that still needed to be removed. I sadly went inside and researched a mortising machine so that my project would not sit unfinished.

I settled on the Powermatic PM701. It seems that many of the machines in this class have a max chisel shank diameter of 5/8 in. The PM701 has a max shank dia of 3/4 in.

So, I ordered a 3/4 in. chisel from Lee Valley. I went to do a test mortise in a piece of maple, but was immediately told by the machine / performance that something was not right.

The auger smoked pretty bad going in and the chisel would not further descend once the chisel encountered the wood. I do not want to force the machine as I understand that I am working at the maximum of its capacity. I could not get the chisel to move into the wood at all. I tried a few different times with the mindset of "let's try one more time, maybe I wasn't pulling down on the lever hard enough...". I don't want to break a tooth off the rack.

This is my first mortise with the machine, so there could be a variety of reasons that it isn't working. I believe that I set up the machine correctly. I believe that the chisel / auger is reasonably sharp.

I did not check to see that the chisel is perfectly square to the fence (since it is just a test piece). Is this alignment critical?

Is is just that a 3/4 in. mortise is at the maximum capacity of the machine? And the fact that the wood is hard maple means that it just isn't going to go? Should I pre-drill all of my mortises? If I were to test cut a smaller mortise (like 1/2 in.), should the smaller tool go right in cutting?

[ChrisA Edwards]

Make sure you have the chisel to auger set up properly. The auger needs to be cutting and removing material just ahead of the chisel cutting the sides.

I haven't tried any hard wood yet, but my PM719 cut 1/2" x 2" deep mortises like butter.

You do need the chisel and auger to be super sharp.


I assume you are not hitting the depth stop prematurely.

[Brian Leach]

The instructions for chisel - auger set up are not too clear (to me). The instructions say to set the chisel insertion height using the two machine-attached shims, then to set the auger as far in the chuck as it will go, and then to remove the two machine-attached shims and move the chisel all the way up and secure it.

I can run the auger / chisel down through the hole in the table with no work piece, so we are good regarding the accidental depth stop. Valid question since this is my very first time using the machine :)

[ChrisA Edwards]

Watch this, especially staring around the 10:50 mark

https://www.youtube.com/watch?v=T19ea5_phDg&t=1251s

[Frederick Skelly]

I have a PM701. The video Chris posted looks good from my spot check. A couple other thoughts for you:
1. Make sure the sides of your chisel are polished smooth. Remove all machine marks. This will make it easier (less friction, etc) for the chisel to cut. (Yes, this can be a fair bit of work but it is worth the time.)
2. Don't forget use the diamond cone to sharpen the bit before you use it.
3. Finally, if you think the 3/4" chisel is having a tough time, change to a 1/2" chisel and make a few more passes to get the width you need.

The 701 is a nice machine that will save you a lot of work, after you get the chisels and set up right.

Fred

[Mike Cutler]

Brian
Those chisels and that bit have to be more than reasonably sharp. They have to be wicked sharp.
A 3/4" chisel is greater than twice the surface area of a 1/2" chisel. It's going to take some power to push a 3/4" chisel

[William Hodge]

That's a big mortise for a small machine. It can work.
The advice on correct set up will make a big difference.
Try roughing the mortises out with as big a drill bit as you can, in a drill press. I usually rough out any mortises that tax my chisels. I like forstner bits for the bigger mortises.
If you don't have a drill press, you can put a big drill bit in a bench top mortiser. Just make sure it's a drill bit rated for the mortiser speed. A spade bit might bend, and start whipping around like a demonic fly swatter.

[Joe Jensen]

I agree that a 3/4" chisel is a lot. I have 1/4", 3/8" 1/2", and 3/4". I tried the 1/2" and it's tough. My chisels are a very premium swiss made ones from like 30 years ago and very sharp. I doubt I can use a 3/4" unless I had a lot bigger mortiser.