Opening a 40-690

[jscott2]

My 40-690 (the DW788 clone) has a metallic knocking that seems to come from the back end of the saw.  It's under warranty so I called Delta and they admit there isn't much in the way of factory service locations since Delta and Dewalt separated.  He said it's something that needs to be resolved but didn't know when it would be resolved.  The 5 year warranty isn't worth much if I can't get service.

There is a Dewalt factory service centre in Montreal but service of Delta tools will be at their discretion, and mine probably will not be their top priority.

I have considered looking inside the saw to see what I can see and wondered what your experience has been with the 690 or 788.  Is it best to lay it on its side?  If so, am I correct in assuming the motor side should be down?  Are there any parts that can fall or spring out when the side is removed?  Can I turn the mechanism by hand while the side is off?  Can I turn it using the motor when the side is off - to better hear the noise?

Thanks in advance for any suggestions and hints.
Jim

[Mainewoods]

Jim, I've had my 690 apart to make some adjustments in the forward/back motion of the stroke.  I did it with mine upright, but it just might be easier with it on its side.  As for turning it by the motor (running it?) while its apart, no can do!  The arm cases hold the arm pivot supports, and once the arm cases are off, there's nothing supporting them.  You should be able to turn the motor by hand (screwdriver slot on motor end) nice and slow and that should allow you to see the mechanism working and hopefully see what's making your noise.  I've read of a screw and washer that's known to come loose inside, but haven't experienced it.  Be cautious putting it back together, as its possible to pinch the power cord in the slots where it rests and runs up to the circuit board.  Doesn't take a mechanical genius to take down and reassemble, but if you not at least a little handy when it comes to this stuff, you might want to have it looked at professionally.

Good luck,

Glen

[jscott2]

Glen, I don't mind taking it apart, it is fairly straight forward to get it apart but I was concerned that pulling the side off might release parts.  I'll be careful to watch for pinched cords when I re-assemble it.

I have been trying to adjust the rod under the tension lever  to minimize vibration and noise and was wondering how many turns will unscrew it from the "wedge block" at the back end.

I was just fiddling with the saw and learned that the knocking was reduced when I pressed gently on the side of the upper blade clamp, or on the top of the clamp, while the saw is operating.  (I know, be careful!) 

Thanks for the help,
Jim

[termite]

  jscott2  go to ricks scrollsaw & check out his site. he has a lot of info on scrollsaws including 788
he has 4 things you can try if your saw is knocking. i tried all 4 & it didnt help my saw. i ended up taking mine to a service center. my post of nov. 14, 2010 will tell you what was wrong with my saw
& what it cost. has worked fine since then. hope this helps.

[jscott2]

termite, looked at your post, once I found it (my fault, wasn't looking carefully).  I'll be sure to check those two parts if I decide to open it instead of going to the Dewalt factory service centre.

I have been careful not to lift the saw by the upper arm but, after it's first visit, and only, visit to the Dewalt service centre, it came back with the pivot bolt tight enough that the arm would stay up on its own.  Don't know if it is wise to leave the bolt tight, or should I loosen it.  Until I get an Easy Lift, or make my own, I should probably use a block to hold up the arm, or learn to bottom feed.    

Thanks,
Jim
The first trip to the service centre was before Delta and Dewalt went their separate ways.
J

[Jim Finn]

I once had a DeWalt 788 and it had that knocking sound also. I opened it up and found a nut had fallen off.  This nut connects the motor to the rest of the mechanisms.  It kept falling off as soon as I started it.  I finally put some locktite on that nut and that fixed it.  I sold that saw and bought a Hegner. 

[jscott2]

Well, I opened the saw up and nothing fell out or off.  Quite easy, actually.  All the nuts were tight, at least they didn't turn easily when I put a driver on them.  I didn't want to over-torque anything.  The metallic knocking at the rear seems to be fixed although I don't know what I did.

The lower of the two bolts that holds the bottom left arm cover (#81) to the left housing (#1) had obviously been run in or out with a power tool as the shaft was scored and some threads had been damaged.  It was still usable but I suspect it was damaged at the repair centre - not good quality work.

I found a video on Rick's scrollsaw site http://www.scrollsaws.com/ that went through opening the saw.  It can be reached from the left menu where it says "Free Scrollsaw Videos". It's a good resource that I hadn't found until now.

I'm still working on the knocking, and at the same time trying to reduce the vibration, but will first have to check the alignment - I have pulled and pushed the bottom rocker mount to reduce the back and forth movement of the blade.  I want to get that right before I start adjusting the tension rod as one may affect the other. Rick also has a video on fixing the knocking.

Thanks for the comments,
Jim