Blog for the RepRap project at www.reprap.org - a project to create an open-source self-copying 3D printer. To get all the early posts on this blog with all the images as a single PDF visit this page.
Pages
▼
Monday, August 18, 2008
Milling plastic with a Reprap machine?
It might not be impractical after all... read more
I have quite a bit of experience making high speed spindles-- I run them on my mill to make PCBs.
For milling you need very good runout and high speed. dremels typically have pretty bad runout, that tend to break small tools. ( Small defined as diameter 1/32" or smaller ).
I use a custom-made air turbine spindle, which turns about 40-50k rpm and runs from a vacuumcleaner. It makes pcbs quite nicely.
the big problem i ran into with small highspeed spindles was the resolution: even a tiny bit ( like 0.03125 diamter ) does not have the resolution as a reprap. plus, there are major restrictions on the geometry you can make because the depth of cut ( even with many passes ) is very limited on the tool. IE, you get into the "subtractive machining takes a lot more work than additive machining" problem.
I think that the point is to be able to do, more or less, what a laser cutter is doing, not what a really good CNC machine can do.
Obviously, the diameter of the cutter head is going to be quite large. In the case I have at the moment, it amounts to 1/8 inch. That's quite adequate, however, to make something like a Mk II extruder.
The design is made from pvc plumbing fittings, skate bearings, and a cpu cooling fan from a PC video card.
The spindle is a piece of 3/8" drill rod, turned to fit into the bearings, with threads to load the bearings onto each other.
I use a basic set screw to hold a 1/8" diameter tool.
The skate bearings are fit into an inner tube ( aluminum ), which is mounted inside of the outer sleeve. Air is sucked into the turbine , sucking in dust as well as turning the spindle.
The fan diameter is about 1.5", which seemed to be a good tradeoff of torque vs speed.
Here is a photoset: http://www.flickr.com/photos/bluedirt/sets/72157604473595262/
There are two sets of pics in there: the ones that dont have the white PVC are an early version with a 1" diameter fan-- it turns about 90k rpm but has less torque than i wanted.
Both designs are basically the same, though-- the main difference is the size of the fans.
SOrry i dont have an exploded view-- i dont want to take it apart right now because alignment is kind of a pain.
Dave, this is really cool! Why don't you blog this in detail in the Builder's blog? This is just the kind of stuff that Reprap needs to really take off!
yep, good call, that's probably appropriate. I had a similar challenge when i was talking with Zach, who ultimately sold me on posting extruder progress on the builder blog.
i'll make a sep. blog and go that way. thanks for the interest!
For micro-milling purposes the Dremels have better runout for the money than anything else by a wide margin--.001" or better.
However, it is not unusual for the front bearing to become loose in the housing, leading to really awful runout. A wrap of electric or pipe tape to take up any slack can fix this.
Hi, Forrest:
ReplyDeleteI have quite a bit of experience making high speed spindles-- I run them on my mill to make PCBs.
For milling you need very good runout and high speed. dremels typically have pretty bad runout, that tend to break small tools. ( Small defined as diameter 1/32" or smaller ).
I use a custom-made air turbine spindle, which turns about 40-50k rpm and runs from a vacuumcleaner. It makes pcbs quite nicely.
the big problem i ran into with small highspeed spindles was the resolution: even a tiny bit ( like 0.03125 diamter ) does not have the resolution as a reprap. plus, there are major restrictions on the geometry you can make because the depth of cut ( even with many passes ) is very limited on the tool. IE, you get into the "subtractive machining takes a lot more work than additive machining" problem.
Dave,
ReplyDeleteI think that the point is to be able to do, more or less, what a laser cutter is doing, not what a really good CNC machine can do.
Obviously, the diameter of the cutter head is going to be quite large. In the case I have at the moment, it amounts to 1/8 inch. That's quite adequate, however, to make something like a Mk II extruder.
True, staying in essentially 2.5 D mode,flat stock, and +/- 1/32" tolderance is do-able for sure.
ReplyDelete"feeds and speeds" are tricky with plastics to avoid melting using a rotary tool. you'll need very high rpm.
I think that you may end up needing more speed/torque than a dremel tool.
Good luck with your project! I'm sure that you'll be able to get something going, looking at your progress so far.
"I use a custom-made air turbine spindle, which turns about 40-50k rpm and runs from a vacuumcleaner."
ReplyDeleteIs it possible that you could blog a bit about your air turbine spindle? It sounds fascinating! :-)
Sure:
ReplyDeleteThe design is made from pvc plumbing fittings, skate bearings, and a cpu cooling fan from a PC video card.
The spindle is a piece of 3/8" drill rod, turned to fit into the bearings, with threads to load the bearings onto each other.
I use a basic set screw to hold a 1/8" diameter tool.
The skate bearings are fit into an inner tube ( aluminum ), which is mounted inside of the outer sleeve. Air is sucked into the turbine , sucking in dust as well as turning the spindle.
The fan diameter is about 1.5", which seemed to be a good tradeoff of torque vs speed.
Here is a photoset:
http://www.flickr.com/photos/bluedirt/sets/72157604473595262/
There are two sets of pics in there: the ones that dont have the white PVC are an early version with a 1" diameter fan-- it turns about 90k rpm but has less torque than i wanted.
Both designs are basically the same, though-- the main difference is the size of the fans.
SOrry i dont have an exploded view-- i dont want to take it apart right now because alignment is kind of a pain.
Dave, this is really cool! Why don't you blog this in detail in the Builder's blog? This is just the kind of stuff that Reprap needs to really take off!
ReplyDeleteI have typically resisted posting my "cnc" material here because it seems a bit off topic.
ReplyDeleteMy goals are very much "make an extruder head for a cnc machine", and thus i don't care as much about contraints like "run from 12V source, etc"...
If you think its of value, though, perhaps i'll make a separate blog so that i dont clutter the main RR blog with off-topic stuff.
You might do what I do and just publish a teaser line in the blog and a link to your specialist blog.
ReplyDeleteyep, good call, that's probably appropriate. I had a similar challenge when i was talking with Zach, who ultimately sold me on posting extruder progress on the builder blog.
ReplyDeletei'll make a sep. blog and go that way. thanks for the interest!
For micro-milling purposes the Dremels have better runout for the money than anything else by a wide margin--.001" or better.
ReplyDeleteHowever, it is not unusual for the front bearing to become loose in the housing, leading to really awful runout. A wrap of electric or pipe tape to take up any slack can fix this.