开云体育

Brian asking about printing directly on the build platform gives me the opportunity to talk about printers.

Suggesting I print on the build platform suggests he is thinking of an FDM printer. FDM stands for Fused Depositin Modelling and is more easily described as "the sort of printer that melts a filament and squirts it out of a nozzle. They typically look like this.

These do print directly on to the, typically, heated bed and squirt PLA plastic in layers to build up the model. Its the bed and the extruder on the gantry that do all the gyrating around. Whilst these can produce useful stuff its not usually fine enough for model purposes with the layering quite visible.? [ I started with one of these but since I have had my new printer I haven't touched it]

There is a technology that i have had stuff printed by commercially - this is what CW rail use - that I will mention as it explains a progression. In this sort of machine you start a set of prints with a tank filled with resin. The controlling software places items to be printed at various locations in this tank shaped space. It can stack them, add items inside other items and there isn't a visible support mechanism for stacked items. The reason for this is that you start with a tank full of resin and the lasers then operate to cure the resin. The process is costly because it turns the tank of resin in "stuff" or "scrap" there is no reuse of that resin. The uncured stuff has the consistency of, well, that tablet of soap you left in a puddle on the sink. Its not solid and its not really liquid. After the process it washes off with a pressure wash leaving your model.

The motivation with this sort of printer is to pack as much stuff in a print run as you can and minimise the scrap. This partly explains why when you order a model from the likes of Shapeways one time it comes out printed the way up you wanted and the layers don't really show but the next time its done a different way up and looks horrible. At a certain level they don't care about your model, their profitability relies on them packin stuff in.

My new printer is a resin printer but it works in a different way

This is a Formlabs Form 2. All the laser stuff is in the base of this machine and the build platform is on the Z axis which moves up and down.

On top of the base is what they call a tank but its more of a tray really. It has a photoreacitve that the laser works up through. On the right you can see a black arm that stirs the resin and just off the end of it you can see a slope under a black mass. The black mass is the resin cartridge. In the top of the shot you can see some prints hanging from the build platform

This is looking up at the print with the build platform elevated to its finished position.

When you set the machine up the tanks come a virgin clean tanks and you can put any one of 28 differen resin cartridges in the machine. They are all chipped and the contol software moniters them. When you put a virgin tank on for the first time and then add the resin cartridge it then pairs that sort of resin to that tank. You can change the cartridge for another of the same material but it won't let you mix them.
When you start a print this happens

1. The machine checks the tank and cartridge to check they are paired or pairs them if they are new
2. lets resin in to a fill level
3. starts to heat the resin to 31'
4. stirs it occasionally whilst it heat.
5. Lowers the build platfrom into the resin
6. Cures the first layer
7. raises the platform
8. stirs the resin
9. lowers the platform
10. cures the next layer.
11. repeats until done, topping up the resin in the tray

As you can see your stuff prints upside down dangling like a stalactite and surplus resin drains off. When you set up your prints you have to consider this draining. Flat horizontal surface tend to pool resin which cures by association leaving a bobbly surface. The set up software tries to prevent this. As an example in the Townsend Hook loco body kit the reason the tank fillers are a seperate item is so that there is a hole for the tanks to drain of resin and these sleepers, which are hollow backed rather than solid have holes in them under where the rail goes.

I think thats enough of 3D printing for tonight

Paul