DW788 Rebuild

Charles Lent

Charley
Corporate Member
I have found that I only needed to replace one or two the larger bearings back near the motor the last two times that I worked on my DeWalt 788.

Lubrication of all of the unsealed bearings, even the tiny bearings up near the blade was sufficient. I did rotate the sleeves from their original positions when reinstalling them, after adding the grease to the inside with a flat toothpick and before reinstalling the sleeve.. The motor shaft connection to the connecting rod bearing is small and takes the most beating, as does the other end bearing on this connecting rod. Pressing the bearings of the connecting rod in and out can deform and stretch the holes in the connecting rod. DeWalt now offers the connecting rod with it's bearings included as an assembly because of this. Make certain that the bolt that the rocking arm pivots on is in good shape and lubricated well. Bearing points that rock back and forth, and never go a full revolution don't keep their grease where it's needed, so they wear out faster than the same bearing on a full pivoting application.

I always us a synthetic instrument grease. It remains the same viscosity it's entire life and is light enough to lube my saw well, but thick enough to remain in place. Auto axle grease is far from ideal for these saws.

Charley
 

Rick_B

Rick
Corporate Member
Well its been over a year since I started with this saw and 10 months since my last update. I was frustrated enough that I walked away from it and, in turn, from the shop in general. I am now determined to either fix the machone, find someone to fix it for me or give it way/junk it.

I decided to go back to the beginning so the saw is now assembled and running - and still noisy in my view. I have a couple of videos below to demonstrate the noise. the first demonstrates the noise at discrete speed settings. I ran the saw at a given speed, recorded it, turned the saw off, selected the next speed, turned the saw on and recorded the noise.


The second video demonstrates the noise with the speed being adjusted while the machine was running


These videos were recorded with the machine blade tension set at 4, table not assembled to the machine and machine not bolted down. I'm not experienced with this machine so not sure if my expectatkions are too high- but I think it is way noisier than it should be.

It seems to me that the noise is not bad at low speeds, gets significantly worse at intermediate speeds and quiet downs at high speeds. It also seems like the noise is louder on the videos than when you are standing in front of the machine.

I'm looking for any and all help I can get - suggestions on what is causing the noise, tips to fix, someone who can fix it for me, etc. I am struggling trying to tell where the noise is coming from - all the linkages are encased in sheet metal so the noise just bounces around inside I think.

Thanks for any help you can offer

Rick
 

sawman101

Bruce Swanson
Corporate Member
Rick, a common problem with the 788 is there isn't enough tension on the rod that connects the top blade clamp to the motor drive mechanism--that rod is inside the top arm. To correct this requires disassembly of the front, upper arm assembly, and tightening 1 turn clockwise of the rod. See this video; if this doesn't work for you, shoot me a message.
 

Rick_B

Rick
Corporate Member
Rick, a common problem with the 788 is there isn't enough tension on the rod that connects the top blade clamp to the motor drive mechanism--that rod is inside the top arm. To correct this requires disassembly of the front, upper arm assembly, and tightening 1 turn clockwise of the rod. See this video; if this doesn't work for you, shoot me a message.
Well I'm finally getting back to this. I pretty sure I know the adjustment you are suggesting Bruce - its the rode that attaches to the wedge on the rear of the upper arm. I gave it one clockwise turn, reassembled and tried - seemed a little better at lower speeds but still noisy at high speeds. I repeated the adjustment two more times. After three clockwise adjustments there was a terrible knock at higher speeds so I stopped. Any other suggestions at this point?

Bruce - I think the video you linked is addressing a different adjustment - or I am totally out in left field :)

Rick
 

Berta

Berta
Corporate Member
Well I'm finally getting back to this. I pretty sure I know the adjustment you are suggesting Bruce - its the rode that attaches to the wedge on the rear of the upper arm. I gave it one clockwise turn, reassembled and tried - seemed a little better at lower speeds but still noisy at high speeds. I repeated the adjustment two more times. After three clockwise adjustments there was a terrible knock at higher speeds so I stopped. Any other suggestions at this point?

Bruce - I think the video you linked is addressing a different adjustment - or I am totally out in left field :)

Rick
That is a different adjustment, but it does address a knocking noise that could very well be your problem. At this point what do you have to loose by giving it a try?
 

Rick_B

Rick
Corporate Member
That is a different adjustment, but it does address a knocking noise that could very well be your problem. At this point what do you have to loose by giving it a try?
I agree Berta and I think I need to start over with a major disassembly

Rick
 

Charles Lent

Charley
Corporate Member
The connecting rod and it's bearings between the motor and the vertical rocking arm has larger bearings, but is a frequent source of noise as it wears. The bearings can be replaced, but DeWalt now offers the connecting rod complete with installed bearings, because it's easy to stretch and deform the aluminum connecting rod when changing the bearings. Pay close attention to the cap screw in the middle of the rocking arm too. They can get loose, even break sometimes. Mine is now stainless, and has Blue Locktite on it's threads.

Charley
 

Rick_B

Rick
Corporate Member
Thanks Charley - I previously replaced the connecting rod and bearing but I'm going to disassemble so I can check all fasteners

Rick
 

Rick_B

Rick
Corporate Member
Yesterday I spent some time with the saw...First thing I did was disassemble the left side covers and check all linkage fasteners and bearings with specific focus on the connecting rod area. All were tight with no apparent bearing issues. I should mention that I had previously disassembled all bearings, cleaned, inspected, re-greased and reassembled. I didn't find any bearing wear issues - doesn't mean there were not any just that I didn't see any.

Next was to try and get the top arm parallel with the bottom arm - this was an effort to compensate for no real spec on tension rod and wedge positioning. Following is a picture of the final wedge position.





After reading about the cover plate modification I decided to try that. I milled a bit from the underside



I put the cover plate back on and removed the assembly from the machine. If I manually manipulate the rocker arm it still contacts the underside of the cover but that may be exceeding the "normal" movement of the arm.

After these adjustments the noise was still there - better but still fairly loud at higher speeds. I also ran it with the cover plate off (an obviously no tension) and it seemed better. Actually it sounded more like the noise was coming from the bottom arm but at some point it gets difficult to tell.

Not sure what to do next - I may try adjusting the tension rod clockwise a turn or 2? Also - try to get it bolted/clamped down just to eliminate that variable. Any other suggestions?

Thanks

Rick
 

Rwe2156

DrBob
Senior User
Have you replaced all the bearings?

I don’t use mine much, but it is a lot louder than that and I just use it.

It was even worse until I found a broken screw in the upper head.

But I can see how it would be a quest.
 

Rick_B

Rick
Corporate Member
DrBob - the only bearing I replaced was the main connecting link. All others were cleaned and lubed.

Here's a link to a scroll saw village thread I have updated Dewalt 788 Noise Problem

The summary is no progress with the covert cap grinding or tension rod adjustment. Noise is much less noticeable at low speeds, bad at intermediate speeds and back to quieter at high speeds.

I have a second machine with a non working switch (It is a type 2) - I was considering inter changing parts but would like to have at least a clue where the noise is

Rick
 

Berta

Berta
Corporate Member
One question, did you do what the video I shared said to do?
Yes, I have been told that I can be annoying.
 

Rick_B

Rick
Corporate Member
Not annoying at all Berta but I can't find the video you referenced - can you share again please?
Rick
 

Rick_B

Rick
Corporate Member
Thanks Berta - I did check that connecting link adjustment - I actually replaced the entire connecting ling sub assembly.

Rick
 

Rick_B

Rick
Corporate Member
Yes I did tighten the nut when re-assembling. I also recently went back and rechecked the nut tightening

Rick
 

Charles Lent

Charley
Corporate Member
Keep in mind that a scroll saw is a reciprocating mechanism. It's nearly impossible to have an absolutely perfect fit of all of the mechanisms so as to not have some clunk noise when changing direction. There will always be some noise. It shouldn't sound like hammers hitting, but the noise will be there, and it will vary slightly with speed changes. Each joint in the mechanism emits some sound when changing direction, and the sound you hear may be a sum total of all of these. If you haven't found one specific bad bearing point, this may be the case.

Maybe it would be best to just start using the saw again at speeds that you are comfortable with. If there is truly a bad bearing or other connection, it will become very evident some time in the future, and you will likely be able to easily find it then.

Charley
 

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