Dicing with Delrin - A Repair Job.

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tom osselton:
I hear you I haven't used silicone from the tube since probably 1981 so after cutting the tip and ratcheting the plunger wondering when its coming out I remembered to puncture the seal :doh:

SwarfnStuff:
No such luck with mine, Tube had been used and my usual bung some plastic supermarket bag over the main nozzle then screw a new dispensing tip over. Usually works but obviously tooooo long between uses.
Kinda makes the advert for small tube sizes make sense if only a little job. More expensive per squirt but not when the remainder sets solid.
Ah well,we live and learn,"Hopefully".
John B

Pete W.:
Hi there, Tom and John B,

Thank you for your posts. That pink goo looks interesting but I don't think it's suitable for my project for two reasons.

First of all, the mould to form my part would be prohibitively complex as my part has features on faces at right angles to each other (see the photo in my first post). Remember I said that I'm working on five dominos in case of accidents along the way - I actually only need a pair of the finished items.

Second, I doubt whether it would be stiff enough to support the M2 tapped hole against the weight of the (very expensive) optic.

I elected to use Delrin because I found some of the right thickness on eBay. Since then, I've discovered that the same seller also sells HDPE in the same thickness and it's cheaper! I don't know whether that would have been a better choice but at this stage I'll persevere with what I've got and see how it turns out.

I hope to post some more photos and description of the next stage of the project in a few days' time.

Pete W.:
Well, I managed to get some shop-time, Hurrah, Hurrah!! :D :D :D

So I've made some progress with this little project.

I showed a photo of the boring fixture in my last illustrated post. Before I could use it, I had to make a bar to mount a dial indicator in my tool-post and a wobble-bar to use to centre the fixture in the four-jaw. Both wobble-bars and indicating in the four-jaw chuck are well covered in YouTube videos etc. so I haven't bothered to show those. So the first couple of photos (see end of post) show the fixture in the four-jaw. Once it was centred, I machined a recess about 1/16" deep in the face to give a relief for the boring tool(s) when they penetrated the rear face of the Delrin 'dominos'.

The next photo shows a domino mounted in the fixture ready for boring. As I'd made the mounting holes fixing screws a really snug fit on the 4 BA. screws, I didn't indicate each domino but relied in the fixture and the dominos all having been drilled using the same template (see earlier posts).

Then there's a photo of a domino after boring through and opening-up part of the bore to match the bore of the part I'm replacing. The domino has a small pilot-hole in the required place, I opened that up with a 5.5 mm end mill followed by a 12 mm slot drill (they both happened to be at hand) then continued to the required diameters and depths using a small carbide-tipped boring bar. I was pleased to find that these tools did a good job, cutting easily and producing a fine swarf. There was a slight 'paper-edge' at the junction of the through bore and the counter-bore which my de-burring tool wouldn't reach nut my trusty Swiss Army pocket-knife coped with it OK.

The next photo shows a bored domino alongside the part I'm replacing and the final photo shows a trial assembly of the domino, the optic and the bearer bar.

The next stage of the project is to bore the remaining four dominos and then to contrive a set-up to profile them to match the original mount.

Right, photos:

Spurry:
Looking good so far. :thumbup: A lot of extra work there, with not having a mill.
Pete

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