Monday, 26 January 2009

Worm Gear Filament Feed Test Bed

Here's the Worm Gear Filament Feed test bed. Constructed from laser cut acrylic.

The bracket on the right is a spare and the one on the left shows the test bed with gears, axles, O ring springs and an M3 machine screw to test the operation.

The O rings are used in place of springs and are common 16mm ID by 2.5mm. They provide the worm gears with more grip than springs and are both readily available and cheaper. They ideally need to be fitted to pulley wheels or at least collars that keep the axles square to the brackets.

This is something to be sorted that wasn't apparent until I assembled it all. I guess this is why prototyping and testing is useful.

Saturday, 10 January 2009

Feeding ABS with Worm Gears and Threaded Rod

Here's a method (inspired by all the other folk experimenting with alternative filament feeds) of feeding filament using Worm Gears and 3mm Studding.

Next job is to design the holder to mount it all to a RepRap extruder and a feed motor assembly.

The pitch of the M3 is 0.5mm per turn giving a feed rate of 0.5mm per turn of the drive shaft.

The tooth pattern cut into the gears is aprox 1mm deep so 0.33 of the diameter of a nominal 3mm plastic filament.

Whilst it all feels to grip prety well I will need to actually make an assembly and do some measurements to see how well it works really.

Worm Gear, Blank, Filament and drive shaft

Here's a picture of a worm gear, a gear blank, the drive shaft (a piece of M3 studding) and a piece of the 3mm plastic welding rod/filament that the assembly is expected to feed.

Cutting worm gears on a Lathe

Here is the finished worm gear holder with a worm gear blank in the holder and a finished worm gear on top for comparison. The cutter is a standard M3 Tap.

Note the 1.5mm PTFE disk under the worm gear blank (3mm thick) this is to centre the blank to the cutter and to support the gear during cutting whilst helping the gear to turn on the pin.

The pin is just a piece of axle with a coupling sleeve on to stop it falling through the gear holder.

I marked a line on each blank to show when it had done a full turn and with the RPM of the lathe set to about 200, advanced the gear holder into the cutter 0.05 mm per turn of the gear.

It could probably have been done quicker but I was'nt in a rush, the job worked perfectly and the cutter never broke.

Milling a Worm Gear Holder on a Lathe

I needed to mill out a slot on a holder that I was making to hold worm gear blanks whilst I cut the worm pattern into the gear. Not having a milling machine I used my mini lathe to mill a slot into the holder whilst it was mounted in the lathes tool post.

The picture above shows the milling bit in the lathe's chuck and the milled gear holder.

The milling bit was 6mm diameter and the worm gear blanks were 3mm thick. Milling the holder in the lathe it would be used in ensured that the slot was centred to the axis of the chuck.

Friday, 9 January 2009

Sanguino PlyRap

Here's a picture of the tweaked Sanguino being connected to the rest of the PlyRap electronics.

You can see in the picture a TTL to RS232 board I threw together so I could use a USB to RS232 cable I already had lying around.

Sanguino Connections

For the RepRap construction work that I am doing as a parallel thread I purchased a Sanguino to control the machinery. A quick look at how many connections I needed to make (and perhaps remake) as I experimented meant that the on board 0.1" solder pads would be quickly used up or put beyond re-use.

The solution above was to find some 0.1" pitch screw terminals (and as I am using a re-purposed ATX PSU, a floppy drive power connector) and bring out the connections to these. I mounted the connectors onto strip board made the neccesary connections for the power connector and soldered the Sanguino to the board using 0.1" pitch SIL header pins.

Automata Project

Here's the Automata project completed and ready for hand-in.

Press fit hubs for Acrylic Components

Just recently there was a need to make some custom laser cut snail cams for an automata project. I wanted to use the press fit brass hubs available from Commotion but there is a problem press fitting parts into acrylic, in that it invariably cracks or shatters.

A solution is to take the grub screws out of the hubs and then heat the hubs in a domestic oven to about 220 or 230 degrees C.

The hubs can then be press fitted into the acrylic parts initially by hand then finished using a vice to make good the alignment.

The technique worked so well that I went on to laser cut some drive sprockets for wire chain and fit hubs to them the same way.

The picture above shows the hubs fitted, the snail cams are two layers of 3mm Laser Cut Acrylic laminated together with Dichloromethane.

Long time no write

It has been a while since I have had enough time to make much let alone write about it. Over the coming weekend though I will have enough to cover some of the latest items i have been working on.

The Xilinx controler board is on hold as there are more promising not to mention cost effective FPGA's just coming onto the market and I want to see if their pricing stabilises at something sensible.