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I need to change the blade on my Dewalt DCS391 circular saw for the first time. The blade clamping screw is for an hex key left-hand threads, but I can't unfreeze it no matter how much lever of pressure I put on it, I'm starting to eat the screw head.

Dewalt DCS391

I'm following instructions from the manual with no luck.

Suggestions?

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  • Are you using a simple L-bend allen key or a ratchet and socket? The amount and quality of force you can apply depends greatly on using the right tool. Get a 3/8" drive allen socket and a ratchet and keep everything aligned well and I bet it'll pop loose.
    – isherwood
    Mar 20, 2018 at 17:36
  • I'm using an L-bend allen key, it's good idea, I'll get a good Hex Bit Socket Set and try with it.
    – Maxime Poulin
    Mar 20, 2018 at 17:47
  • Yeah, you're lucky to get 20 lbs-ft of torque with that. You could also grip the hex key you have with a locking pliers or an adjustable wrench.
    – isherwood
    Mar 20, 2018 at 17:58
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    When you do get it out you should consider replacing it with a new fastener because it sounds like you may have damaged it a little. A new fastener costs a lot less than this frustration next time!
    – Matthew
    Apr 22, 2018 at 21:30
  • @Matthew indeed I bought a new one :)
    – Maxime Poulin
    Aug 11, 2018 at 15:09

4 Answers 4

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Following up on how I've resolved this and what was the issue. At the time of this post I've tried everything that was suggested and the clamping screw did not bulge at all. However, I did not had access to was pneumatic tools in my shop at home, so I went to a local tool store and they dislodged the clamping screw for me.

They explained to me my mistake and why I had such a hard time removing it. The issue was that I've inverted the washers (r, s) and they were not in the correct position.

Here's a picture of the circular saw once it was correctly assembled with the r and s washers in the correct position.

correct assambly of DCS391

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  • A) Thanks for coming back to post your answer! B) Wow! After pointing that out, yeah, it's pretty obvious that the blade clamp washer was missing from the OP. Bet that's a mistake you won't make again. :D
    – FreeMan
    Jun 28, 2020 at 16:07
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From the manual:

  1. Thread blade clamping screw (H) into saw spindle by hand (screw has left-hand threads and must be turned counterclockwise to
    tighten).

This matches your posting. Can you confirm that you are turning it clockwise to loosen it?

If you are, one method of releasing a tightly stuck fastener is to strike it sharply with a mallet. You would obviously want to ensure that the blade will not rotate and that the saw assembly will not be dislodged. Perhaps clamp the base plate to a bench and provide support for the hex key axis that passes into the fastener.

Use eye protection, as the result should be that the key flies into the air after the blow, but causing the hex bolt to release.

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  • Indeed, i'm turning it clockwise to loosen it like the instructuctions indicates. Already tried the same with a mallet with no luck, I'll try with an 3/8" drive allen socket and a ratchet, maybe I'll have better luck and will be able to apply a Iever if needed.
    – Maxime Poulin
    Mar 20, 2018 at 17:49
  • Some type of impact wrench might be nice as well.
    – JPhi1618
    Mar 20, 2018 at 18:52
  • I have used a block of wood to keep the blade from turning, placing the saw on a table with the plate flat, or even clamped to a table, then I always use a 6 or 12-point socket, whichever I grab first from the toolbox.
    – Jeff Cates
    Mar 21, 2018 at 19:06
  • I use the impact method all the time put pressure on the Allen key until it flexes then strike with a small hammer.+
    – Ed Beal
    Jun 28, 2018 at 15:46
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I had the same issue..wrecking the screw head using the Allen key supplied with my dewalt ..it's just not beefy enough for the job..after countless attempts I went big and got my multi tool on it and cut a groove into the top of the head, I then sat the saw blade between my black and Decker workbench clamps and nipped it up tight so the saw couldnt move and gave it a hefty clout (remember - clockwise to loosen)!! with my bolster chisel and lump hammer..job done!! I had already purchased a new screw and clamp for just over a tenner on fleabay..I'm chuffed I have now got my dewalt back in working order after struggling with my corded one..it's just not the same!..cheers guys

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I would apply a penetrating oil such as wd-40 or if its rusty then pb blaster. not a lot, and let it sink in the threads for 10 min. Then try again with your tool.

If you say you are using an allen key, you could put something on the end like a section of small pipe (or the cylinder from a metal pen?), to make it longer and gain leverage. Secure the drill so it doesnt move if you can while doing this.

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    WD-40 is not penetrating oil. It’s for polishing your missile. Seriously, look it up. They have really good marketers who make you think it’s for everything but it’s actually pretty bad at most jobs. Kroil, PB Blaster or Liquid Wrench are good penetrating oils.
    – Harper - Reinstate Monica
    Jun 28, 2020 at 18:24

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