4

Found this site searching for "loose arbor nut." A couple of years ago several subscribers mentioned that the arbor nut on their DeWalt jobsite saw (DWE7491) repeatedly came loose.

Unaware of this, I just bought a used one and discovered that my saw has the same problem. As a second owner there is no warranty coverage, although I was sent a replacement arbor nut. Didn't help.

So I replaced the arbor nut and also cleaned the shaft, washer, nut, and blade (blade had a little residue from resin removal), but none seemed to have oil/grease on them. Checked threads on the arbor and they looked fine (not a machinist, though, so check was just visual). Started saw a couple of times following that and nut remained tight, but didn't try to cut anything.

Did anyone find out, definitively, what causes that problem and what it takes to fix it?

Is there a response/acknowledgment from DeWalt about this problem? Dewalt rep I talked to suggested taking the saw to a service center.

FreeMan
  • 6,753
  • 22
  • 41
Dan
  • 41
  • 3
  • Welcome to StackExchange. It's not clear from the wording of your Question, did you find us doing a search for the issue, so you've seen the previous Q&A on this? And if so, none of the suggestions helped is that correct? Also, have you searched more broadly on the issue to look for a known solution to the problem generally? – Graphus Sep 28 '22 at 12:28
  • 3
    I think the question is "has DeWalt issued a fix for this?" and "Can I buy the fix since, as a 2nd owner I can't get it covered under warranty?" If that's the case, best bet is contacting DeWalt. – FreeMan Sep 28 '22 at 17:29
  • Found his site using search for "loose arbor nut." Replaced arbor nut, cleaned shaft, washer, nut, and blade (blade had a little residue from resin removal), but none seemed to have oil/grease on them. Checked threads on arbor and they looked fine (not a machinist, though, so check was just visual). Started saw a couple of times following that and nut remained tight, but didn't try to cut anything. Dewalt rep suggested taking saw to service center. Basically I am wondering what owners resorted to to fix the problem. Thanks – Dan Sep 29 '22 at 01:26
  • 2
    Bit of a bodge, but have you tried putting your other nut on and cranking it (reasonably) tight against the main nut? – Aloysius Defenestrate Sep 29 '22 at 13:22
  • Thank you for your suggestion. I had thought of that, as well as putting a lock washer between the two nuts. Also thought of tightening the single arbor nut far more than I have on other saws. In the meantime I plan to call Dewalt service centers around the country, hoping to find someone who can explain why this happens and how they fixed it. Again, thank you. – Dan Sep 29 '22 at 14:58
  • 2
    Does this answer your question? Arbor nut keeps working itself loose on my table saw. What am I doing wong? – WhatEvil Sep 29 '22 at 18:38
  • I would tend to agree, @WhatEvil, except that it's been determined that this is a known flaw in this particular model of DeWalt saw. It's really not user error, which is what the answers to that question are trying to rectify. – FreeMan Sep 30 '22 at 14:16
  • Yes that was an automated comment because I voted to close this question as a duplicate. If it's been established that it's nothing to do with the user then IMO it's not a useful question for this site. – WhatEvil Sep 30 '22 at 17:39
  • I've aware of the automated comment, @WhatEvil. Are you saying that this isn't a useful question because it's not about user error? I'm suggesting that your nominated question isn't a dupe target because that one addresses user error while this one is about a fix for a known (but not, to my knowledge, admitted by the mfgr) design flaw. – FreeMan Oct 04 '22 at 15:15
  • Since my question appears inappropriate for this site and none of the participants in the original exchange have indicated how they solved this problem (whether it is a nanufacturing defect seems to be an open question), this seems like an appropriate time to end further discussion. Thanks. – Dan Oct 05 '22 at 15:00
  • @Dan I don't think there's anything inappropriate in your question. In retrospect, the suggested duplicate does seem to be another example of the same problem, but the accepted answer there doesn't address the possibility that it's a defect (although WhatEvil's does). – Caleb Oct 13 '22 at 21:58
  • I have also had the blade come loose. (It has happened 3 times - very dangerous) I just bought this saw DW7491 as a replacement for a DW7490 that was 7 years old. I never had that problem with my old DW. I know that I have properly tightened the spindle nut after making sure everything was cleaned. I have noticed that the new model has flat sides on the arbor whereas the old saw did not. I believe that this is a mistake that DW made when upgrading the saw. I am going to contact DW and report this problem. – RL Belin Nov 25 '22 at 21:48
  • 1
    I had this same problem with the same saw. Dewalt was no help. Dewalt technicians were no help. I finally replaced the saw. The blade (in my case) loosened up because the saw uses back EMF to quickly slow the blade. I can see the brushes arcing as the blade slows down converting the motor to a brake. Good idea but poor engineering as the torque the blade has tends to unscrew the arbor nut when the motor doesn't coast to a stop. I am trying to defeat the brake so the motor coasts down naturally. Just haven't had time yet. Don't buy this saw!!! – B. Cram Jan 17 '23 at 21:17

2 Answers2

8

As you've probably found during your own search, you're not the only one to report a problem with the arbor nut on this saw. Here are a couple examples that I found in just a minute or two:

  • One user reported the blade coming off entirely while the saw was running, resulting in damage to the saw. Someone replying to that message also says that their arbor nut becomes loose after a while, and suggests retightening it periodically.

  • Another user on the same page thinks it's strange that Dewalt doesn't advertise the saw's braking feature. To me, that suggests that at least in some cases the saw may stop spinning quickly, which would explain the arbor nut coming loose. Perhaps some of these saws have bad bearings in either the arbor assembly or the motor?

  • A review on Amazon admits that the blade only comes off "sometimes."

  • At least seven different users commented on the suggested duplicate to say that they've had the same problem with the same saw.

So to answer the title question, it sounds like the problem is known to at least some users, but not admitted to by Dewalt. I don't think it matters that you're not the original owner — a table saw that's known to have a problem with the blade coming off in operation is downright dangerous, and certainly defective.

If I were in your shoes, I'd write to Dewalt explaining the problem, and I'd attach copies of the reports linked above as well as any others you may have found as evidence that there's a problem. If you have the time, you might also do some testing to quantify the problem -- maybe use a torque wrench to tighten the nut to known, repeatable setting, and then see how many times you have to start and stop the saw before the nut becomes loose. I'd also be sure to send a copy of the letter, attachments, and data to the CPSC.

Caleb
  • 9,573
  • 1
  • 18
  • 46
  • 2
    Excellent advice. It should go without saying, but I'll say it anyway - use the blade guard at all times with this saw! Especially since a user reported the blade coming completely off. – FreeMan Oct 14 '22 at 15:14
  • Bravo, what an excellent Answer. – Graphus Oct 14 '22 at 16:34
  • 1
    Thanks very much, @Graphus! I hope it helps the OP and anyone else with one of these saws. – Caleb Oct 14 '22 at 17:53
  • 1
    Thank you. So far the blade comes loose only while cutting wood, not after turning off the power. DeWalt's online support suggested calling regional service centers. My two such calls (CO, NC) have not helped, but I plan to try other locations. It would be interesting to learn at what level in the corporation DeWalt is aware of this problem. Wonderful suggestions about documenting torque and contacting CPSC (along with documentation about other users who have had similar experiences). I will do that. Again, thank you for the suggestions. Dan – Dan Oct 15 '22 at 01:55
  • 1
    @Dan Glad to help. I'm sure you notice the blade being loose when you're cutting because the wood obviously resists the blade, but I don't think that cutting is actually the cause of the blade being loose -- as others have suggested in comments, the saw has to be designed so that starting the saw or cutting wood should cause the nut to tighten. I suspect that bad bearings or some other problem is causing the unpowered motor to stop quickly while the blade wants to keep spinning due to inertia, and that's what's loosening the nut. – Caleb Oct 15 '22 at 06:01
  • I appreciate the bonus @Graphus! Thanks for that. – Caleb Oct 18 '22 at 19:16
1

A very good suggestion was made in another answer (now deleted because it was an "I'm having this problem too" type answer), so I'll repeat it here:

Try adding a second nut to the spindle to use as a jam nut.

It will require enough spindle length and taking the existing spindle nut to your favorite hardware store, identifying the diameter and thread pitch, then finding a thin nut to use. It will also likely require a second wrench to tighten the second nut.

Obviously, this should not have to be done, as there is obviously a flaw in the design of the saw, but in order to be able to use the saw safely (in light of reports of people having the blade come completely off!), this seems like a reasonable work around until DeWalt offers a full fix.

Graphus
  • 65,691
  • 3
  • 50
  • 139
FreeMan
  • 6,753
  • 22
  • 41
  • All through this I was thinking a jam nut was ruled out for some reason (space being the most likely one). FWIW a slimmer nut can be fairly easily created from a standard one by the user if necessary or expedient, meaning the second wrench might become the major stumbling block. – Graphus Jan 18 '23 at 20:02
  • Not sure how a 2nd wrench is a "stumbling block", @Graphus. My TS came with a very thin wrench for the arbor nut. That would work on the inner nut, and any wrench would work on the outer nut. If it's wider than the nut, that's fine - the excess can hang over the "outside" (away from the other nut). Although, purchasing a 2nd DeWalt arbor nut wrench or a generic thin open-end wrench of the correct size might be easier, and neither is out of the question. – FreeMan Jan 19 '23 at 15:39
  • Also, I went back & forth about 3 times on "jam" v "jamb" nut... :) – FreeMan Jan 19 '23 at 15:39
  • Re. the wrench, I meant in terms of getting one that'll fit in what I presume are tight quarters. I'm assuming one would want a second of the skinny wrenches that seem standard for TS and other tools, but I've never seen sold elsewhere. – Graphus Jan 20 '23 at 06:54