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  • Weird project

    I have made some odd things over the years. This one is no exception. 12” diameter 14” long MDF Messy dusty project. Ugh.
    Made as a favour for my neighbour. To be used as a mold for a fibreglass cover housing remote environmental sensors or something. A bit hush hush on particulars. Some sort of new venture.
    First and last for me I hope.
    Click image for larger version

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    Chimera, schor and 2 others like this.
    Cheers
    Randy
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  • #2

    Re: Weird project

    Yummy. I remember back in the day when I was venturing to make ply wood drum shells using mdf. it looked like a negative version of what you made.

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    • #3

      Re: Weird project

      Beautiful grain on that wood.
      beachburl likes this.
      • “The greatest lesson in life is to know that even fools are right sometimes.”Winston Churchill

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      • #4

        Re: Weird project

        What measures will be taken to make the fiberglass release from the MDF, there are special paints made one is durapox but I think that is for use with epoxy resin and glass, I have wrapped moulds in plastic tape but the polyester resins effect the tape glue and make hell of a mess I guess a brush on coat of pva glue would work then 7 waxes, it would be interesting to know what is used.

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        • #5

          Re: Weird project

          Originally posted by Randy in Calgary View Post
          I have made some odd things over the years. This one is no exception. 12” diameter 14” long MDF Messy dusty project. Ugh.
          Made as a favour for my neighbour. To be used as a mold for a fibreglass cover housing remote environmental sensors or something. A bit hush hush on particulars. Some sort of new venture.
          First and last for me I hope.
          Click image for larger version  Name:	B4677E0B-FE52-4618-AF32-8566AF4DB6F3.jpeg Views:	102 Size:	37.7 KB ID:	1290220
          I hope you have got some taper on it otherwise the fiberglass will shrink onto it and you will be chopping the plug out in bits, it would be better made in 2 halves with a flange that could be fixed together later.
          There are other ways maybe split the whole thing in half and form a big wedge that could be withdrawn then remove the 2 halves.
          I have seen a few molds destroyed because not enough thought was given to how to extract them.
          Last edited by bkrits; 07-14-2020, 04:54 AM. Reason: added nore

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          • #6

            Re: Weird project

            Originally posted by bkrits View Post
            What measures will be taken to make the fiberglass release from the MDF, there are special paints made one is durapox but I think that is for use with epoxy resin and glass, I have wrapped moulds in plastic tape but the polyester resins effect the tape glue and make hell of a mess I guess a brush on coat of pva glue would work then 7 waxes, it would be interesting to know what is used.
            I don't know. I will let the fibreglass guys sweat that one. I know that my neighbour did mention that they would "finish" it before applying the fiberglass.
            Cheers
            Randy

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            • #7

              Re: Weird project

              Originally posted by bkrits View Post

              I hope you have got some taper on it otherwise the fiberglass will shrink onto it and you will be chopping the plug out in bits, it would be better made in 2 halves with a flange that could be fixed together later.
              There are other ways maybe split the whole thing in half and form a big wedge that could be withdrawn then remove the 2 halves.
              I have seen a few molds destroyed because not enough thought was given to how to extract them.
              Well I am not responsible for the whole process, I just did what I was told. I hope they figure out a way to make it work. I suppose they could wrap some tape over the back end to slightly increase the diameter and create a taper.
              Cheers
              Randy

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              • #8

                Re: Weird project

                Turning and sanding MDF is a very messy job! Good work on that one Randy. Epoxy/glass does not shrink as it cures and I have seen no evidence that polyester/glass does either. When I have made epoxy glass wing tubes using the Al spar for a mandrel, it is common practice to wrap the mould with a thin Teflon tape to provide a slip fit after the cure is done else-wise, it is impossible to fit back together again but taper isn't required in any case.

                Sounds like an interesting project.

                Ken

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                • #9

                  Re: Weird project

                  What a "fun" turning that must have been, Randy!
                  All the best,

                  Marty

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                  Secretary of Kingston Wood Artisans Inc. https://kwoodartca.wordpress.com/

                  Master Mistake Fixer (because I've made them all... at least once)

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                  • #10

                    Re: Weird project

                    Originally posted by KenL View Post
                    Turning and sanding MDF is a very messy job! Good work on that one Randy. Epoxy/glass does not shrink as it cures and I have seen no evidence that polyester/glass does either. When I have made epoxy glass wing tubes using the Al spar for a mandrel, it is common practice to wrap the mould with a thin Teflon tape to provide a slip fit after the cure is done else-wise, it is impossible to fit back together again but taper isn't required in any case.

                    Sounds like an interesting project.

                    Ken
                    Polyester glass shrinks at approx 6 percent, epoxy 2 percent
                    https://www.researchgate.net/post/Ep...curing_process
                    Google it there is so much information.
                    As for the taper on a mold it should be about 5 degrees the more the easier to to release https://www.ecfibreglasssupplies.co....c/makingmoulds

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                    • #11

                      Re: Weird project

                      That is inconsistent with the research done for the CF and USAF by NRC and it is not what I found in personal experience where, among many other applications, we formed sockets for tubes using the tube itself as a mandrel. The 2024Al tubing was not tapered ergo the mandrel was not tapered either! Both materials may shrink somewhat with aging since they do out-gas a bit but once the cross-linking is complete; they are stable. Bonded patches on Al structures would not work at 2% shrinkage. If you read the responses carefully on the citation, you will see that shrinkage depends on the polymer composition. Resins intended for laminating are designed to do just that and they are stable once cured; the same for those intended for use in bonded composite repairs. I cannot speak about the cheap stuff found at the local hardware stockist; Lord knows what it is.

                      I don't feel a burning need to use Google to inform myself on a technology that I used in the aerospace industry for over 4 decades. But thanks anyway!

                      Ken

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                      • #12

                        Re: Weird project

                        So I chatted with my neighbour and his fibreglass guy said that for small things they go for a 1% taper, but since this is so big he is going to do it in two halves, then glue the halves together. This will result in a seam but this is apparently not a concern. He thought the mold was just fine for what they are doing. Great Success!
                        Cheers
                        Randy

                        Comment


                        • #13

                          Re: Weird project

                          Originally posted by MartyFromKingston View Post
                          What a "fun" turning that must have been, Randy!
                          Though I was very satisfied with how it turned out (pun intended), the process was hideous. Now I have to spend a day cleaning the shop, in spite of having the air cleaner going, all the DC vents open and the DC running, garage door open, etc.
                          One learning was that the spur centre was unable to hold against the MDF. Any amount of torque would result in it tearing into the end of the piece. I glued a couple of pieces of 1/2" maple to each end to rectify that. You can see the remnants of it on top of the rounded end.

                          Another problem was how to get it a consistent diameter. I do not have a set of calipers that big. I tried making one from fibreboard, but it was too flexible to be accurate. What I did was use a laser level. I stacked several pieces of MDF on the lathe bed behind the tailstock so that the vertical laser line was beamed across the centerline of the cylinder. I checked that the laser was in the same plane as the lathe bed using my Wixey Tilt Box, and it was zero relative angle compared to the bed. Any low spots would be in shadow and the line would not be visible. Then I just shaved away at the bright spots until I had a visible line all along the length of the cylinder. Worked pretty well. Not machinist exact, but close enough for this project.
                          Last edited by Randy in Calgary; 07-15-2020, 09:59 AM.
                          Cheers
                          Randy

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                          • #14

                            Re: Weird project

                            Another issue of note. This piece has a lot of inertia. I would give it a spin before dialing up the speed and it accelerated to the 300-400 rpm I used for the turning no problem. In fact, it would accelerate from stopped on its own. The issue arose when slowing it down. If I dialed the speed back too fast, the lathe would trip. I would have to wait about 5 minutes before I could get the green light back. It seems the lathe electronics has some sensitivity to back emf or something. Maybe an electronic brake that senses that the piece is not slowing down enough?
                            Anyone else have this problem?

                            It is a General International 25-300.

                            I will re-post this issue as a separate topic in the turning section as well.

                            Thanks
                            Cheers
                            Randy

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                            • #15

                              Re: Weird project

                              Your piece was overpowering the electronic braking, you have to give it more time or turn the braking off, this can happen to all lathes that have electronic braking, the other thing that can happen is that the chuck will or could turn right off of the spindle, lock the chuck onto the spindle if you can.

                              Have fun and take care
                              Leo Van Der Loo

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