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Acetal Annealing?

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  • Acetal Annealing?

    I intend to cut new reversing gears for my 52" Sheldon lathe using black acetal. Several articles suggest annealing before machining which would start at 7:00 AM on day 1 and conclude at 2:00 PM on day 2. This involves hourly ascending temperature adjustments from 7:00AM to 4:00PM, then hourly descending adjustments from 9:00PM to 2:00PM the next day.
    Is it worth the effort or this this one of those things that never gets done and the parts work fine anyway?

    Don't want to make them twice.

  • #2
    I have never heard of this before. What is the theory behind it? Stabilize for less movement while machining?

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    • #3
      First time ive ever heard about annealing acetal, least without it being 3d printed, so i went googling:https://www.boedeker.com/Technical-R...ing-Guidelines

      From the link, "

      Experience has shown us that very few machined plastic parts require annealing after machining to meet dimensional or performance requirements". Link goes into more detail, but from what i gathered unless you use blunt tools or machine off a huge volume of material, you shouldnt need to worry about it

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      • #4
        Never heard of such a thing. But I suppose it could be done with a Nest type programmable thermostat, a ceramic space heater fan and a cardboard box.
        Location: Jersey City NJ USA

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        • #5
          Oh, "black acetal"? Is that like "shiny steel"? What type? Brand?

          Broadly, there is homo-polymer and co-polymer. And then there are different brands, with varying quality, and different formulations. Years ago I had some 3' x .75" acetal drops that I purchased from a machine shop. It looked fine but was awful and loaded with residual stress that caused substantial distortion after any cutting or machining. Porosity is another consideration.

          I've made consumer products for years out of Acetron-GP, where both the dimensions and "spring" are critical. Great stuff. I've had other brands substituted and they were inferior and caused headaches.

          Acetal is typically extruded, and grain orientation will also factor in distortion - flats vs. rod. How hot will your gear box get? Are the gears simple flat discs, with no side relief?

          Heating acetal beyond a certain point can result in rapid decomposition and release of formaldehyde. Review the many posts on the internet about annealing, but ultimately check with the mfgr of the exact product you are using.

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          • #6
            I've made loads of acetal gears and I never heard of it either.
            Peter - novice home machinist, modern motorcycle enthusiast.

            Denford Viceroy 280 Synchro (11 x 24)
            Herbert 0V adapted to R8 by 'Sir John'.
            Monarch 10EE 1942

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            • #7
              I've never heard of it either, but it might not be best to machine it if it is very cold, say around freezing, or when it is a very hot day.

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              • #8
                Just looked at the calendar and it's gone way past April the First ------------------------

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                • #9
                  Annealing is probably not necessary for cylindrical parts regardless of internal stresses. Distortion is only a problem when stresses are relieved unequally, such as milling one side of a piece of flat stock. Even cold-rolled can be turned without fear of distortion.
                  It's all mind over matter.
                  If you don't mind, it don't matter.

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                  • #10
                    Originally posted by gellfex View Post
                    Never heard of such a thing. But I suppose it could be done with a Nest type programmable thermostat, a ceramic space heater fan and a cardboard box.
                    350°F
                    https://plasticsintl.com/media/wysiw..._Annealing.pdf

                    Looks like the consensus is no, don't need to loose a night's sleep for this.

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                    • #11
                      I've made a lot of close tolerance parts out of Delrin and Acetal and never annealed any of them. Never had any problems with warpage.
                      Kansas City area

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                      • #12
                        I notice acetal is very heat sensitive. Dimensions change if you dont keep it cool while machining.

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                        • #13
                          I've had acetal that was very brittle, it chipped badly in machining. It was probably off-brand, cheapo, generic material. I can't be sure that annealing would have solved the issue, but it might have.

                          Back in the day it wasn't uncommon for dealers to substitute acetal when Delrin was ordered. Not so much any more.

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                          • #14
                            The 2.25" rod I have is from Online Metals.

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