Tuesday 11 November 2008

New Toy

The company that I have worked at for 25 years gave me a long service award recently. I could choose anything worth £500 so I chose this small lathe / drill / milling machine combo. The tiny watchmaker's lathe I have been using up to now is not really big enough for RepRap parts. This should be just about right.

A combo like this is a bit of a compromise and only recommended if, like me, you have limited space. It gives me a lathe, pillar drill and milling machine in a small footprint.

I also bought accessories with my own money, which came to about another £300 :-
  • Cutting tools - essential.
  • Compound cross slide - for cutting tapers.
  • Drill vice - to hold things on the cross slide when milling or drilling.
  • Tailstock chuck - to drill down the axis of round things.
  • 4 Jaw chuck - for turning square and irregular shapes.
  • Milling chuck and collet set - to hold milling bits.
  • Wiggler - for finding centres and edges when milling and drilling.
  • Die holder - for tapping threads.
  • Headstock centre - for turning between centres.
I have also made a couple of accessories with HydraRaptor. The first is very simple: a t-slot cleaner for removing swarf from the cross slide's t-slots.

That saved me about £2.80.

The second object is the biggest thing I have RepRapped so far. It is a cover to go over the chuck to make it easier to turn by hand when tapping. It took over 7 hours to build and weighs 77g.

Here it is installed :-

I haven't used it yet but it feels like it should work well.

Wednesday 5 November 2008

Sky Hook

I have found that the most convenient way to provide the filament feed is to throw the whole reel into a large hanging basket and suspend it over the machine with a ball bearing. The machine pulls the filament from the centre of the coil through a hole in the bottom of the basket. As it does this the basket rotates to prevent the filament being twisted.

When the basket contains a full 5lb or 2Kg coil then it does take some force to pull the filament from under the weight of it. Since I sharpened and angled my drive screw and moved to an HDPE filament guide I have not had problems with grip, so this works flawlessly.

I have even started stacking the baskets two deep to save on storage space for different colours of plastic. The top filament can be used simply by passing it through the centre of the lower basket. Obviously only one can be used at a time.

It was easy to attach a frame over HydraRaptor but harder to do over a Darwin. I decided to attach it to the ceiling instead with a "Sky Hook", as suggested by Adrian Bowyer here.

I designed a ceiling mount to hold a skate bearing. These seem to be the cheapest ball bearings to buy. My first idea was to put an M8 bolt through the bearing and attach a plastic hook, but I didn't have any bolts long enough, so I made some plastic parts instead.

The barbs just go through the centre of the bearing, but only when they are twisted over each other.

More by good luck than design, but that means that they can't be pulled out because they pull towards each other and meet in the middle before they can clear the M8 hole.

Just to make sure I made a small locking piece which slots in afterwards to keep the barbs fully splayed.

The bearing then drops into the housing and is held in place by gravity and the ceiling.

The eye and barbs are tensioned along their strong direction, so can be quite thin, but the housing is stressed in the direction where de-lamination can occur, so I made it 4mm thick. It would be tragic if it gave way and dropped a few Kg of plastic onto the machine from a height, so I tested it with a lot more weight to get some confidence.

These 13 wine bottles weigh 16.5Kg, which is 8 times more than the plastic I intend to suspend. It held up for 24 hours with no sign of stress to the parts. Using plastic ties with barbs on the end could be a useful technique for making RepRappable fasteners.

When I came to mount it on the ceiling I realised that the three screw holes were too far apart to all screw into the ceiling joists, which are only 1.25" wide, so I made a two lug version. I made this with 50% fill rather than 25% to ensure it was as strong as the three lug version.

Here you can see a trick I did to get support for the overhanging lip. I just put a one layer thick diaphragm across the hole and cut it out with a penknife afterwards.

Here it is installed : -

Tuesday 4 November 2008

Black Heart

I made this tiny heart shaped box as a little gift for my wife's birthday.

Being such a simple shape, with no extruder off moves, it came out perfect, just like my wife.