- Joined
- Sep 5, 2013
- Messages
- 3,784
A while back I bought a second-hand Mitutoyo micrometer off our local Used listings. The mic itself is in perfect condition but the same could not be said for the case. It was missing a pretty substantial chunk off one corner and I hemmed and hawed about what to do with it until I eventually got after it this weekend (well, my weekend anyway).
Rather than making a new box I decided I’d try to fix the existing one, and I wanted to see if I could do it with a plastic dutchman. There’s a critical misjudgement that occurred here but we’ll get to that later. For now I figured I had a shot at heat-forming a piece of Sintra board (expanded PVC) thereby avoiding any complex joinery and shaping. I’d bent Sinta lots of times before but never in a compound shape so this was the challenge.
I made a female form of MDF and a male plug to fit inside. The plan was to heat the Sintra until floppy, quickly position it over the female mould, then jam the plug into place and hold it until cool. And, weirdly enough, this worked! I enlisted the shop press to hold the assembly while the plastic cooled and that bought me lots of time without having to fuss with free clamps and things.
Once the moulded blank was off the form I trimmed the flash from the edges and set to fitting it to the box. There was a bit of back and forth with files and test fitting, but really it didn’t take that long and I got a pretty decent fit. And here’s where my error reared it’s head — I had assumed (erroneously) all along that the case was PVC, hence my choice for Sintra so I could cement the patch into place. But in fitting it sure didn’t feel like PVC anymore and, well, it’s not. I’m not exactly sure what it’s made of but it’s a lot like nylon or polyethylene, and nothing sticks to it. Dang! Oh well, I was too far in to give up now so I bent up a couple little reinforcements out of sheet steel and peppered them into place with pop rivets. I was going to go back to the milling machine to clean up the final height and cut the small rebate around the edge but it was actually faster to just cut it in by hand.
All in all I’m still pretty happy with the fix. I did goof on one corner and ended up with an obscenely large gap but I left it. What the heck, it looks little like Frankenstein’s monster anyway so what’s one more scar? I think I’ll put some thin polyethylene foam lining but that’s for another day. For now, this case is closed....
Thanks for looking.
-frank
Rather than making a new box I decided I’d try to fix the existing one, and I wanted to see if I could do it with a plastic dutchman. There’s a critical misjudgement that occurred here but we’ll get to that later. For now I figured I had a shot at heat-forming a piece of Sintra board (expanded PVC) thereby avoiding any complex joinery and shaping. I’d bent Sinta lots of times before but never in a compound shape so this was the challenge.
I made a female form of MDF and a male plug to fit inside. The plan was to heat the Sintra until floppy, quickly position it over the female mould, then jam the plug into place and hold it until cool. And, weirdly enough, this worked! I enlisted the shop press to hold the assembly while the plastic cooled and that bought me lots of time without having to fuss with free clamps and things.
Once the moulded blank was off the form I trimmed the flash from the edges and set to fitting it to the box. There was a bit of back and forth with files and test fitting, but really it didn’t take that long and I got a pretty decent fit. And here’s where my error reared it’s head — I had assumed (erroneously) all along that the case was PVC, hence my choice for Sintra so I could cement the patch into place. But in fitting it sure didn’t feel like PVC anymore and, well, it’s not. I’m not exactly sure what it’s made of but it’s a lot like nylon or polyethylene, and nothing sticks to it. Dang! Oh well, I was too far in to give up now so I bent up a couple little reinforcements out of sheet steel and peppered them into place with pop rivets. I was going to go back to the milling machine to clean up the final height and cut the small rebate around the edge but it was actually faster to just cut it in by hand.
All in all I’m still pretty happy with the fix. I did goof on one corner and ended up with an obscenely large gap but I left it. What the heck, it looks little like Frankenstein’s monster anyway so what’s one more scar? I think I’ll put some thin polyethylene foam lining but that’s for another day. For now, this case is closed....
Thanks for looking.
-frank
