Montag, 30. März 2020

S01E07 Spindlekopf zum Leiterplatten fräsen

For the english viewers, I have translated the whole text and put it at your disposal here: Please write me a comment how you like the project and what I could do better. Here are the links to the parts: LINKS ------------------------------------------------------ PETG: Anycubic i3 Mega: Monoprice Select Mini II: Extruder: Silicon socks: EOS 200d: Videoleuchte:

XHTC S01E07 Spindle Head for PCB milling

Hello, friends,
I know you haven't heard from me in ages.
But I continued to work on the XHTC project and I have to admit that I got a bit lost ... but well, in the next few minutes I will explain to you what I have been doing in the last months and what I have done wrong ... maybe also some things right, who knows?
So what was my goal, after I had managed to design an extruder that could be changed automatically, the first step to an automatic tool change was reached.
Now I wanted to design a spindle that could produce a printed circuit board using an insulation process.
Well, and I got a little bit lost in the process ... but in order.
I needed a holder for the milling cutter and a motor to drive it, honestly I can't see and hear the topic motors anymore.
Here is a battery of all the motors I tested ... but first I had to design the holder in Fusion360, that was relatively easy.
There are several parts, 2 ball bearings as used in skateboards, a shaft with ER11 holder for the cutter and a motor that rotates the holder with a drive belt. In addition we need two pulleys from the 3D printer, the belt itself I got from Pollin and it still holds today ... and believe me, I really stressed this part :)
The motor is powered by the contact of the magnetic balls and can be controlled by the fan command.
The following points are important for the design:
1. since the cutter has a cutting surface of only 0.1mm, we need a high rotation speed, I am talking about values that should be beyond 10000 rpm, from 8000 on we should start to keep the cutting speed.
We are talking about values of 200-600 meters per minute. Just as an example, we have a diameter of 0.1mm and a speed of 10000 ... then we just reach a value of 3.14 meters per minute, that is very little. Everything below that makes our milling extremely slow and destroys the fine milling cutter.
So everything not so easy :)
2. the whole head with spindle, drive and bearing must not weigh more than 250gr, because my hypercube is not designed for bigger loads. This becomes a problem when you take a closer look at the tested motors. I could also think about giving the Hypercube 10 or 12mm rods as bearing guide, but unfortunately this has the disadvantage that the CoreXY system becomes heavier.
3. at the high speeds the vibrations have to be observed closely. Too much of it makes the milling cutter inaccurate and the whole system does not get good.
4. the run-out must not be more than 0.05, otherwise the milling is too wide and the milling cutter is only loaded on one side. This in turn has an effect on the tool life (i.e. the durability) of the milling cutter. but my dream milling cutter already costs around 10 euros.
5. the bed has to be absolutely flat and perpendicular with the XY axis, of course we will use an autoprobing, but it can't hurt because marlin here interpolates between the points.
That should be first of all enough points, which I must consider.
So let's proceed chronologically and I tell you what I had changed:
The first thing I changed... which engine do I use best?
So believe me, I have tested at least 10 engines. It must not be heavy, must reach a high speed and still be able to turn the spindle.
i can produce a transmission ratio of 2 to 1 via the drive wheels, but i have to buy this via power or speed.
First I looked at the brushed motors, clearly simply connect them to the fan output and I can control the speed. Problem with most of the motors is that they are all cheap. That means mostly no ball bearings and the shafts have some play ... does not matter but at high speeds and lateral load the motors sound very unhealthy. They are usually not designed for this, and they do not reach high speeds ... most of them stay below 10000 rpm.
Well, then I have ordered real race engines from RC model building, cool parts ... unfortunately too heavy. Such an engine weighs already loosely over 200 grams, so unfortunately also nothing.
Then I looked at my Mini Quadrocopter, they have these tiny motors with speeds of over 11000 rpm ... incredibly cool parts, I was really impressed by the performance. Unfortunately they are also a bit weak in the power range and could hardly turn the drive wheels. If you block such a small boy also while turning, the loose 2.5 Ampere pulls through these thin wires, it becomes a
Translated with (free version)