Mid range design #1

[Bernd]

Gentlemen,

I’m new to CNCzone. I’ve read through both this thread and the Hardware Design thread. Very interesting. First a bit about my background so everybody understands that I’m not just talking off the top of my head. Machine shop was my major back in high school. After high school I went to work for a machine tool company that produced gear cutting machines. There I was a two year apprentice and got to work on every kind of machine in the machine shop. Then actually worked on the machines themselves to produce master parts, plus customer training. Then I worked a very long stint on the assembly floor bringing the machines to life. Ran machines from full manual operation to 6 axis CNC machines. So after 30 years I’m retired and now have time to spend on my hobbies.

So with that said I’d like to offer my 2cents. I don’t believe you can design a machine without first knowing what it’s supposed to machine. I see no mention of what this router is supposed to cut. Is it, wood, Styrofoam, machineable wax, aluminum, brass, steel, etc. Once that’s decided then you can figure out what materials and electronic equipment you need to fulfill the job.

Obviously the harder the material machined and the faster you want the machine to cut the more you will need a rigid machine. If your just going to make Styrofoam parts rigidity and accuracy, plus a faster feed rate, does not need to be that great. If you want to make parts out of aluminum or brass for say a model airplane, model train or steam engine then you need more precision and to get that precision you will need rigidity. So it depends on what you want to do with your cnc router that will determine the materials used.

Some were in the near future I hope to build a router to make parts for my model railroad, live steam, and RC airboat hobbies.

Regards,
Bernd

[plcamp]

Guys and Gals, what happened all activity on this thread has stopped, did I miss the final design direction?

Paul

[rutman]

some ideas:
1.
forego traditional bearings - use polished steel on steel or steel-teflon-steel sandwich. All the serious xy tables I've seen seem to have large steel on steel areas.

2.
use carbon fiber over stout wood , instead of metal, for structural parts. cost comes out comparable and strength if done right may be better

any old timers have some feedback?

[dkirtley]

I just joined a few months ago, so may not qualify as an old timer but....

The only real benefit of the bearings is they offer a bit of friction reduction, sealed lubrication, and make a nice replaceable package when they wear out. HDPE, Teflon and bronze bushings are also options. Metal on metal is used in machine tools all the time. *THEY* are the tradition. Just a bit fussy to fit. They even use wood for bearings in big hydro-electric turbines. Usually lignum vitae.

Why the synthetic carbon fiber instead of natural carbon fiber (Wood)? You might be able to get a tiny bit lighter with a synthetic carbon fiber structure but the total composite of wood + carbon fiber + resin will most likely be heavier as a unit. I assume that you are not planning on getting the CNC machine airborne so it probably isn't much of an issue either way . Take a look at Matthias Wandel's home made bandsaw (Woodworking for engineers) The section of video where he hooks up his dial indicator and measures the flex hanging his weight on the arm of the saw and he gets about half the deflection with his wood framed saw compared to the cast iron saw is pretty eye opening.

Originally Posted by rutman some ideas: 1. forego traditional bearings - use polished steel on steel or steel-teflon-steel sandwich. All the serious xy tables I've seen seem to have large steel on steel areas. 2. use carbon fiber over stout wood , instead of metal, for structural parts. cost comes out comparable and strength if done right may be better any old timers have some feedback?

[rutman]

Originally Posted by dkirtley .... HDPE, Teflon and bronze bushings are also options. Metal on metal is used in machine tools all the time...

Ok thanks for the feedback.
Since writing that back in '09 I've gotten ahold of some excellent linear bearings off a CT scanner that made its way through the junkyard I've been fooling in.
2 each of 166cm, 74cm, and 4 of 50cm.
So I've designed something around those that is intended to mill aluminum and anything softer. Also for the eventuality that I can spare the money, I am leaving room for a laser head.
The mill axle is held within another concentric cylinder which travels in Z with the mill axle. This is to provide extra rigidity due to the large throw of the machine (50cm) meaning I have 0.5Nm of side-force induced torque on the mill head for every Newton of side force. I suppose I need to do the maths to see the deflection on a 50cm diameter rod under e.g. 250Nm of torque. Does anyone happen to know what side forces to expect on a mill cutting aluminum at some reasonable (nonindustrial) rate?

images at CNC - Saymoo Wiki

[dkirtley]

Glad you are still around. I felt pretty embarrassed when I noticed that I responded to thread was several years cold.

The side forces are not really that easy to calculate. It depends. Geometry of cutter, size of cutter, speed of spindle, depth of cut, feed rate of the spindle, sharpness of cutter, amount of lubrication, grade of AL. Most times it is the skill of the operator to adjust on the fly. Computers still can't adjust to circumstances as well as a human operator.

Originally Posted by rutman Ok thanks for the feedback. Since writing that back in '09 I've gotten ahold of some excellent linear bearings off a CT scanner that made its way through the junkyard I've been fooling in. 2 each of 166cm, 74cm, and 4 of 50cm. So I've designed something around those that is intended to mill aluminum and anything softer. Also for the eventuality that I can spare the money, I am leaving room for a laser head. The mill axle is held within another concentric cylinder which travels in Z with the mill axle. This is to provide extra rigidity due to the large throw of the machine (50cm) meaning I have 0.5Nm of side-force induced torque on the mill head for every Newton of side force. I suppose I need to do the maths to see the deflection on a 50cm diameter rod under e.g. 250Nm of torque. Does anyone happen to know what side forces to expect on a mill cutting aluminum at some reasonable (nonindustrial) rate? images at CNC - Saymoo Wiki