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I have a combined jointer and planer with three knives mounted on a rotating cylinder. Each knife is fastened using five screws. Additionally, two springs are under each knife, pushing it upwards — out of the cylinder. Once I unfasten the screws, the springs pop the knife out.

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I would like to know if these springs are there just to make removing the knives easier or if they serve a purpose when the machine is running.

I am asking because these springs are so strong that they make it difficult to set the knives properly. I really have to push with all my might to keep them in place, so minor adjustments are always a struggle. I am considering removing the springs or replacing them with weaker ones.

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Do the springs pushing at a jointer knife do anything useful when the jointer is running?

It would appear not, as according to many things I've seen and read it's not uncommon for jointers to either deliberately or unknowingly be run without some or all of the springs under the knives.

This thread, Replacement Springs for Under Knives on Old Delta Jointer, on SawMillCreek might be particularly useful because it covers so many of the possibilities in the various responses — some missing, deliberately taking them out, replacing them with both weaker and stronger springs, along with some advice on how to set the knives top-dead-centre without spring tension.

If your not to picky about tension most Hardware stores have a selection. I replaced mine with a bit more tension on the springs, it just makes a bit harder to keep the knife in the slot while your setting the height.

On Jointers I've used in the past that had springs under the knives, I always tossed them. I found they make getting a even setting difficult.

The 16" jointer that I used to have did not have springs or jack screws and it was no trouble to set the knives.

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  • So that's a "definite maybe" then, eh? :D
    – FreeMan
    Commented Jul 24, 2022 at 17:03

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