DW 788 Chatter

[powrguy]

I picked up a used DW 788, with the stand and worklight, and am having an issue with some "knocking" if I advance the speed past about 1/2 way on the dial.  I also can get the noise when I advance the tension beyond about 3.5, leaving the speed at the mid-setting.

I took off the switch/cover, and did the "fix" where you slightly file the underside "hump" on the tension rod cover.  I also did the suggested adjustment of the tension rod, by rotating it one turn counterclockwise, then, when that did not fix the issue, I did another 1 turn.  Still have the "knocking" noise and before I tear it apart, I wondered what I need to look for next.

The blade was the only one that came with it, which appears to be about a No. 3, reverse tooth, and whoever had the saw knew about lightly scuffing the blade ends, as they were obviously done that way.  I have an assortment of Flying Dutchman blades on the way, but the "knocking" is not gonna be fixed by new blades.  I bought a foot switch, and the saw cut fine, although in 1/2" baltic birch, I could tell the blade has seen quite a bit of use.

Any other help/tips are appreciated.  I'm a novice at this scrollsawing.

[JTTHECLOCKMAN]

Is it  a type#1 or type #2??  Should say on the label. Do you know how many hours are on the saw??  Knocking is not a good thing but can be overcome. There are videos on how and what to look for. It was posted here not long ago. Will have to look for that.  It is a 4 part series and shows everything about that saw.

http://www.bing.com/videos/search?q=video+of+how+to+take+a+Dewalt+788+saw+apart&docid=607991385635949302&mid=3B91AE534679124A612E3B91AE534679124A612E&view=detail&FORM=VIREH

Edited December 29, 2018 by JTTHECLOCKMAN

[kmmcrafts]

Looks to me as though it's had a replacement motor at some point in its life.. the replacement motors don't come with a identification tag sticker from DeWalt to decipher the model and type or serial number.. 

Where does the noise seem like it's coming from? back of the saw or up front? I'm betting since it looks as though maybe the motor had been changed.. makes me wonder if they put it back together and made sure to get everything nice and tight back there.. Watch the video's JT posted a link to.. they might help you better understand the inside of the saw and will certainly give you some pointers on what to look for.. I might suggest getting some solvent to clean out the old grease and repack the bearings ( provided they are in good shape ) with some good synthetic grease if you end up opening it up.. 

[JTTHECLOCKMAN]

Good eye Kevin. You really must know what you are looking at when buying a second hand saw plus need to run it through its paces unless it is a ridiculously low price. Same with any tool with motors and moving parts. 

[OCtoolguy]

I had a similar knocking noise on my used Dewalt too. I found a very loose bolt at the main connecting rod inside the saw. The drive rod was good and snug on the motor shaft but at the other end where it connects to the vertical drive arm, that bolt was loose. And, it had been replaced at some point with the wrong bolt. Once that was fixed the saw became very quiet. I did the full service like shown in the 4 part video that Gwinnett/Bob Brokaw produced. That video was fantastic. I ended up downloading all 4 parts and creating a movie with them. I refer back to it every once in a while. In my estimation, once tuned properly, the Dewalt is one of the best saws on the market. Especially for the price.

[powrguy]

I think it may have had the replacement motor, as mentioned, since there's no ID label on it.  I only paid $250 for the setup, so I would like to make it quiet and not do additional damage if it has parts that are failing, by replacing them.  I'm a little squeamish about dis-assembling the thing, and I have watched every video I can find, including all the Bob Brokaw videos that show how to service the saw.  I tried the tensioning rod adjustment trick, and turned the rod 1 turn at a time, CCW looking from the FRONT of the saw.  Didn't seem to make any difference, so I left it that way.  I'm not having a rattle at speeds in the lower 1/2 of the scale, and the blade at tension as I "ping" it.  If the speed is increased, it starts to rattle.  Maybe I will have to bite the bullet, and try my hand at servicing and at least inspecting all the bearings, and making sure everything inside is properly tightened?

[OCtoolguy]

Something has occurred to me before and it just happened again. When we refer to the front or the back of the saw, I take it to mean that the front of the saw is the part where we do the cutting and the rear of the saw is the opposite end. Is that the correct thinking?

 

[OCtoolguy]

6 hours ago, powrguy said:

I think it may have had the replacement motor, as mentioned, since there's no ID label on it.  I only paid $250 for the setup, so I would like to make it quiet and not do additional damage if it has parts that are failing, by replacing them.  I'm a little squeamish about dis-assembling the thing, and I have watched every video I can find, including all the Bob Brokaw videos that show how to service the saw.  I tried the tensioning rod adjustment trick, and turned the rod 1 turn at a time, CCW looking from the FRONT of the saw.  Didn't seem to make any difference, so I left it that way.  I'm not having a rattle at speeds in the lower 1/2 of the scale, and the blade at tension as I "ping" it.  If the speed is increased, it starts to rattle.  Maybe I will have to bite the bullet, and try my hand at servicing and at least inspecting all the bearings, and making sure everything inside is properly tightened?

I feel pretty strongly that your knocking noise is from the tension rod assembly. You said you did the file trick on the rod adjuster cover. You may not have taken it down enough. And, the tension rod itself may still be rattling. On my saw, the knocking/rattling sound was pretty much throughout the entire speed range but got worse as I increased the speed. I did all the same stuff that you have done and I even experimented with the rod by turning it the other way until it knocked. I then backed it off until it stopped. I filed quite a bit off the cover too. I think your problem is something not too serious but I would still strongly recommend that you take it all apart and clean and grease all the bearings and sleeves. If I lived close enough to you, I'd be happy to help you.