Adam Block
11-01-2015, 11:46 PM
Good evening all. Something very strange happened over the last week (no, this isn't a Halloween scare story) and I would love to hear your theories.
Backstory: Back in about 2002, I bought a new Multico PM20 benchtop mortiser. I'm not sure where I got it, but as I understand it Garrett-Wade was a distributor back then so that is a possibility.
I've used the machine very little for the last few years, but I remember it working smoothly and accurately when I used it to cut mortises for a few small to midsize furniture projects.
Last year we bought a new house and I emptied my shop and moved all my tools to the house's garage. Everything sat for a year but I finally started selling off items that didn't fit in half a 2-car garage (I'm moving from separates to a combination machine to save space). Among the items I sold at a garage sale last weekend was the Multico, to a young woodworker who (like me) loved the fit, finish, features and funkiness of the British-made machine.
In the middle of the week I got a call from the buyer who said that he wanted his money back. He explained that the chisel collet didn't seat properly, which left the chisel canted towards the mortiser fence and unable to cut straight.
I had no idea what he was talking about. I'd never noticed a problem with the mortices I cut — though to be fair I didn't actually cut that many. But then he sent me a picture showing what appeared to be a repair to the machining of the chisel collet boring. It looked very weird, and I agreed to meet him back at my house this morning to evaluate what was going on.
He showed up this morning, and there is absolutely a problem. Let me pause for a second to explain the structure of the mortiser. If you already know how these machines are laid out, you can skip the next paragraph.
The mortiser motor is bolted to the top of a hollow casting with open sides. The motor shaft passes through the top of the casting and drives the mortiser bit chuck. The bottom of the casting is bored to take a collet or bushing which holds the hollow chisel. The PM20 has three different bushings for chisels of different diameters. The solid front of the casting has a threaded hole for a set screw which passes through a hole in the bushing and seats against the chisel shank (which is a tight slip fit inside the bushing), pinning both the bushing and chisel in place.
The buyer showed me that the bushing was a sloppy fit front-to-back inside the boring (side-to-side was tight). As such, when the set screw is tightened, the bushing and chisel both cant, leaving a gap between the bushing face and the bottom of the casting of perhaps 1/40", and angling the chisel towards the body of the mortiser:
324533
(Note that the chisel flares at the tip so if the bushing fit correctly, the blade of the square would hit the bottom of the chisel first.)
Here's where it gets weird.
I removed the bushing and looked at the boring in the casting into which the bushing should slip. As mentioned, the buyer had already sent a photo, but seeing it in person was ... nuts. The back half of the boring appeared to be smeared with what looked for all the world like Bondo, as if the boring process had been screwed up, and then someone had tried to fix it with filler!
324534
Here's another photo, better showing the smear of filler on the inside of the boring:
324535
What THE HECK is going on here? I bought this machine new from a respected dealer, and the manufacturer (when it existed) had a very solid reputation. Has anyone seen anything like this before? Is fixing bad machining with filler an accepted manufacturing practice? Can anyone imagine any other way this could have happened? Damage in transport that was repaired by the importer or dealer?
And perhaps more importantly: Is there any way that this can be repaired to a normal machine standard? Could the filler could be ground out and a patch welded in, then be reground? The center of the boring has to be colinear with the motor drive shaft, but I can't imagine that usable accuracy would be that hard to achieve. As it is, I can't (and wouldn't) sell the machine, but I can't use it either. I guess in the short term I can attempt to shim the bushing, but other than that am out of ideas.
I'd be much obliged for any advice or suggestions. Thanks!
/adam
Backstory: Back in about 2002, I bought a new Multico PM20 benchtop mortiser. I'm not sure where I got it, but as I understand it Garrett-Wade was a distributor back then so that is a possibility.
I've used the machine very little for the last few years, but I remember it working smoothly and accurately when I used it to cut mortises for a few small to midsize furniture projects.
Last year we bought a new house and I emptied my shop and moved all my tools to the house's garage. Everything sat for a year but I finally started selling off items that didn't fit in half a 2-car garage (I'm moving from separates to a combination machine to save space). Among the items I sold at a garage sale last weekend was the Multico, to a young woodworker who (like me) loved the fit, finish, features and funkiness of the British-made machine.
In the middle of the week I got a call from the buyer who said that he wanted his money back. He explained that the chisel collet didn't seat properly, which left the chisel canted towards the mortiser fence and unable to cut straight.
I had no idea what he was talking about. I'd never noticed a problem with the mortices I cut — though to be fair I didn't actually cut that many. But then he sent me a picture showing what appeared to be a repair to the machining of the chisel collet boring. It looked very weird, and I agreed to meet him back at my house this morning to evaluate what was going on.
He showed up this morning, and there is absolutely a problem. Let me pause for a second to explain the structure of the mortiser. If you already know how these machines are laid out, you can skip the next paragraph.
The mortiser motor is bolted to the top of a hollow casting with open sides. The motor shaft passes through the top of the casting and drives the mortiser bit chuck. The bottom of the casting is bored to take a collet or bushing which holds the hollow chisel. The PM20 has three different bushings for chisels of different diameters. The solid front of the casting has a threaded hole for a set screw which passes through a hole in the bushing and seats against the chisel shank (which is a tight slip fit inside the bushing), pinning both the bushing and chisel in place.
The buyer showed me that the bushing was a sloppy fit front-to-back inside the boring (side-to-side was tight). As such, when the set screw is tightened, the bushing and chisel both cant, leaving a gap between the bushing face and the bottom of the casting of perhaps 1/40", and angling the chisel towards the body of the mortiser:
324533
(Note that the chisel flares at the tip so if the bushing fit correctly, the blade of the square would hit the bottom of the chisel first.)
Here's where it gets weird.
I removed the bushing and looked at the boring in the casting into which the bushing should slip. As mentioned, the buyer had already sent a photo, but seeing it in person was ... nuts. The back half of the boring appeared to be smeared with what looked for all the world like Bondo, as if the boring process had been screwed up, and then someone had tried to fix it with filler!
324534
Here's another photo, better showing the smear of filler on the inside of the boring:
324535
What THE HECK is going on here? I bought this machine new from a respected dealer, and the manufacturer (when it existed) had a very solid reputation. Has anyone seen anything like this before? Is fixing bad machining with filler an accepted manufacturing practice? Can anyone imagine any other way this could have happened? Damage in transport that was repaired by the importer or dealer?
And perhaps more importantly: Is there any way that this can be repaired to a normal machine standard? Could the filler could be ground out and a patch welded in, then be reground? The center of the boring has to be colinear with the motor drive shaft, but I can't imagine that usable accuracy would be that hard to achieve. As it is, I can't (and wouldn't) sell the machine, but I can't use it either. I guess in the short term I can attempt to shim the bushing, but other than that am out of ideas.
I'd be much obliged for any advice or suggestions. Thanks!
/adam