Dewalt 788 Noise Problem

[rick_b]

Good morning folks - I just joined your group based on a recommendation from an acquaintance.  He thought maybe you folks could give me some guidance in resolving a scroll saw noise problem.

I bought a used Dealt 788 scroll size that had some noise.  I went through the Bob Brokaw videos and did a tear down to inspect bearings and sleeves - all seemed OK so I cleaned and re-greased.  I did replace the large connecting link on the motor shaft.  After putting everything back together the noise was no better - maybe a little worse.  I read were a common problem was the tension rod so I adjusted that several times in both directions (CW and CCW).  No improvement!  I ended up walking away from it in frustration for over a year.  Now I am back at it.

Below are links to youtube videos of the noise level.  I the first video I ran it ona set speed, shut it off, chnaged the speed level and started it back up.  In the second I simply adjusted the speed while the machine was running.

i adjusted the tension rod again CW three turns.  The noise improved at low speeds but develop a real bang at higher speeds.  I think I have noticed that the noise has always been speed dependant.

So I'm looking for any help in diagnosing this problem

Thanks

Rick

[Joe W.]

Hmmm . . . 
Not the same noise mine was making when I joined the group a couple years ago.
Replacing the connecting rod solved my problem.
Here's a thought - if you are confident the bearings/sleeves are good and adjusting the tension rod isn't making a significant difference, perhaps the problem is farther back.  I'm thinking the motor shaft itself that connects to the connecting rod.
Only other thought that comes to mind is perhaps the long (upper and lower) horizontal rods might be bent.
Good luck with it.
If it cuts OK, and I say this with tongue in cheek, the solution is hearing protection.  

[Scrappile]

Seems I remember a reading some where where there can be a place where the some part can hit something and it was an easy fix.  What I just wrote does not help you buy may trigger someones memory.  Maybe @kmmcrafts remembers.

[JustLarry]

It could be the upper arm  is hitting the bottom of the cover plate (Lid part#80). It could be the tension rod is hitting the cover plate (Lid part#80).  Rick's Scrollsaw        https://scrollsaws.com/        gives information on fixing this:     

Scroll down in the left column to Dewalt Tune-up.  Then in new screen scroll down past the parts diagram and picture of blade and table hole and you will see pictures for removal and repair of the lid.  This did correct knocking on my saw.

Larry

 

 

 

Edited November 8, 2022 by JustLarry

[rick_b]

So I have read that the tension rod should go clockwise and counter clockwise.  I have done both to no avail.  Is there some spec or dimension that indicates approximately where the tension rod should be?

Rick

[kmmcrafts]

Hard to say what it is without actually being there to see what's going on, but my first thought was.. I see it's not really bolted down.. having a saw just sitting on a bench not securely bolted down can make a lot of noise and vibration.. though the sound I hear really doesn't sound like a unbolted saw but I feel like I'm hearing several different levels of noise which may hinder the diagnose process.. sometimes microphones can pick up sounds and play back in video that otherwise might not really be heard too.

When I took my saw apart for rebuild I think when I put the rod and tension assembly back together I adjusted it until I had tension on the tension adjuster lever then i think I gave it another 1-2 turns is all.. I never had any noise.. but I did have that kind of tight.. Now that I've taken several saws apart.. I'm thinking that maybe it is important to have it adjusted somewhat properly.. It's been 10 years since I worked on a DeWalt but I would think you want the upper arm to be Parallel to the table front of saw to the back or very close.. I would think too tight might make the upper arm not come down far enough and too loose would come down too far? Gosh it's been a long time since I mess with the DW saws.. 

Did you take any bearings apart at the front of the saw or just inside the saw at the back by the motor? For me I had issues with the fine sawdust getting into the bearings etc. at the front lower ( sawdust drops down onto the lower bearings ) and absorbs the moisture that's in the grease creating a dried / caked up bearing.. If you haven't taken the front portion apart.. I might check there if adjusting that rod doesn't do anything.. It to me doesn't sound like that classic rob hitting the metal covers. Sounds like a bad bearing somewhere to me.. but again.. not being bolted down might be noises I'm hearing too.

[OCtoolguy]

Go to scrollsaws.com and read about filing the cover plate that comes in contact with the rod. Especially if the rod is too loose. There is a sweet spot for the rod once it's adjusted correctly but it can still hit the cover plate. It's a simple matter of filing or sanding off the offending area of the plate. Very simple fix. 

[rick_b]

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

[Joe W.]

31 minutes ago, rick_b said:

Any other suggestions?

Try using a stethoscope or piece of rubber tubing to home in on the area creating the type of noise you are hearing.

That has worked for isolating car motor noises and may help with this gremlin. 

[OCtoolguy]

2 hours ago, rick_b said:

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

Grind some more off the cover plate. I had to take enough off that there was no cover left in the end of it. It won't hurt it to take more off. The rod is still hitting the plate. It's not the rocker arm that's hitting the plate, it's the rod.

Edited November 7, 2022 by OCtoolguy

[rick_b]

4 hours ago, OCtoolguy said:

Grind some more off the cover plate. I had to take enough off that there was no cover left in the end of it. It won't hurt it to take more off. The rod is still hitting the plate. It's not the rocker arm that's hitting the plate, it's the rod.

I'm confused - the tension rod fits on the other (top) side of the cover.  Not sure how the rod is hitting on the underside of the cover?  I' m sure there is something obvious I am missing

Rick

Edited November 7, 2022 by rick_b

[OCtoolguy]

2 hours ago, rick_b said:

I'm confused - the tension rod fits on the other (top) side of the cover.  Not sure how the rod is hitting on the underside of the cover?  I' m sure there is something obvious I am missing

Rick

You know, it's been a few years since I did mine. Maybe you are right. But I kept removing material until the knocking stopped. I'm old an confused. Dang!

Edit: After writing the above, I went to that site and looked at this pic. It shows the rod running under the plate. If that is the case, you can see where relieving the area in question and tightening up the rod would make the noise go away. 

 

Edited November 8, 2022 by OCtoolguy

[rick_b]

That's a very deceptive picture.  I don't believe there is any way the tension rod can be assembled under the cover but I'm going to take a second look in the morning

Rick

[Scrappile]

Have you gone to youtube and search dewalt knocking or something similar there are several videos about it   maybe one would help.

[JustLarry]

The tension rod sits under the cover plate as the picture shows. The tension rod sits on the cover plate.  Here is copy of instruction for adjusting tension rod.  Note instruction shows when part #80 is removed you will see the tension rod and a small bearing sleeve.....

1) Tension Rod Adjustment. Referring to #24 (Rod, Draw), it threads into the Wedge #23. Typically, it needs one or two more turns (clockwise) to enable sufficient tension with the tension lever.  In order to get to the rod (it is pretty easy, just takes a couple of minutes) Take off the plastic cover (#71) by taking out the 4 screws (#44). Just loosen the whole assembly and move it out of the way. Remove part #26 and part #80. You will see the tension rod and a small bearing sleeve on the "L" end of the tension rod. Set the sleeve aside. The rod is flexible enough to turn it without removing anything else. I suggest one CLOCKWISE turn, partially reassemble, test the tension and take up another turn only if necessary. I set mine to get proper tension at a 3 to 3-1/2 setting on the tension lever gage.

Edited November 8, 2022 by JustLarry
Corrected wrong information.

[rick_b]

Folks - please don't take this as argumentative but I absolutely don't see how the tension rod can go under the cover plate.  The cover plate (part 80) only has one hole and it is threaded for the bolt thatv attaches part 26 to the cover plate.  Part 26 has a cam surface that the L in the tension rod fits in and provides the tensioning function.  If the tensioning rod is under the cover how does the L go through the cover and into the part 26 cam surface?  I'm sure we are having some vocabulary issues with over/under, etc

Rick

[rick_b]

So here are a few pictures of How I think the cover plate is assembled.  Please feel free to point out if I don't have this right

 

 

If we agree this is correct then the grinding of the leading edge of the bottom side of the cover plate (as shown above) doesn't seem to have anything to do with the tension rod - at least directly.  I have seen this grinding operation recommended in several places but never have seen a why?

Rick

[JustLarry]

Rick,  You are correct.  The picture in parts breakdown is deceptive and information I posted is wrong. Just got through looking at my 40-690 which is same a the 788. 

Larry

Now to make corrections to my posts above.

[rick_b]

No problem Larry - I think we are now on the same page.  Now to figure out where to go

Rick

[JustLarry]

After reading info at Rick's Scrollsaw, I found that the upper arm can be hitting against the bottom of the plate.  That is where removing some of the plate bottom can help.

 

Larry

[OCtoolguy]

Try to picture me eating crow. You are right and that drawing is wrong. So relieving the bottom of the plate is so that the upper arm CONNECTING ROD doesn't come in contact with the plate. Bottom line here is, take as much material off the underside of that plate as necessary. I'm not sure how adjusting the tension rod has anything to do with the knocking unless having it too sloppy might cause a rattle. So it's two separate things entirely. MY BAD!

[rick_b]

Thanks Ray - I appreciate the feedbck

 

Rick

[OCtoolguy]

1 hour ago, rick_b said:

Thanks Ray - I appreciate the feedbck

 

Rick

Sorry about the bad advice. First time I've ever been wrong. 

[JustLarry]

19 hours ago, OCtoolguy said:

Try to picture me eating crow.

Ray, I had my crow well done, heavy on the hot sauce to get a good sting out of it.

Larry

[rick_b]

I've been fooling with this for several days.  Did a little more grinding on the underside side of the cover cap - no improvement.  adjusted the tension rod 2 turns clockwise - no improvement maybe a little worse.  Couldn't get tension beyond #3.  Adjusted the tension rod 4 turns counter clockwise (2 back to starting point then 2 more).  No noticeable improvement - could adjust tension up beyond #3.

I'm at a point where it sounds like the noise is coming from everywhere so I stopped.  I should note that the knocking is hardly noticeable at low speeds (1,2,3) much louder at mid range and then quiet again at higher speeds.

I feel like I'm really chasing a ghost - I'm going to have an objective third party (LOML) listen later today and get her opinion.

I'm pretty close to offering this free to a good home.

I do have a second DW788 with a non - working switch so I'm not sure how it performs from a noise perspective but I could start inter changing parts - the 2nd machine is a type 2 but I don't think there are major parts differences.

Suggestions welcome

Rick