Need advice on first build

[lcifers]

Hi guys,

First off thanks for all the great information on this site. It's really a staggering amount of information. I've spent quite a few hours now soaking in as much as I can.

I am getting ready to start a build. The primary use of the machine will be secondary machining operations on injection molded plastic parts. This will be done in relatively large volumes.

A secondary use will be milling plastic prototypes.

But I also want to be able to machine aluminum. I've see threads on routers that are cutting aluminum but most have been cutting thin sheet stock. I would be making aluminum molds for things like casting. I don't need to be in a hurry - I mean I can take really light cuts - but this will be billet machining not sheet stock.

Does anyone have any suggestions for an existing build to start from? I think something like 24 X 24 table will be good, although I know of nothing on my radar screen that will require anything that large.

I have a manual lathe and a Grizzly mill / drill (G1007) so I can fabricate parts. I want to build something out of aluminum and would prefer that it does not require welding.

I am using SolidWorks so if anyone has any models of motors, ball screws, rails, etc that would be awesome.

On a side note, would I be better off to convert the mill / drill? To me the machine seems hardly worth upgrading, but I'm open to thoughts on that.

Thanks in advance for any suggestions. I'm looking forward to documenting my project!

- Luther

[DonFrambach]

Hi Luther,

I just made a 14"x14" fixed gantry router out of 8020 extrusions, parts from CNCRouterParts.com, and 20 mm supported round rails. The router cuts aluminum well using a Taig spindle and small bits. I'm sure it could be built larger and retain sufficient rigidity to cut aluminum. Here's a link: http://www.cnczone.com/forums/diy-cn...ter_build.html (photo from post #84)

Don

[lcifers]

Hi Don,

Great build! I read it from start to end Looks like a very sturdy unit. A few questions:

- What model Taig spindle is that? Looks like you sometimes use a different spindle? I think I want to have something low speed for aluminum and something high speed for plastic and wood if I do any wood projects. Is the best way to have 2 different spindles?

- How does the rail / roller system compare with the linear ball bearing rail (like Hiwin) or the round guide (Thomson or Glacern)?

- What pitch ball screw did you use? For X and Y, using NEMA 23 380oz/inch motors, I wonder what max rapid I could achieve without tripping the G540? For fast rapids, should I be thinking about a different motor?

Something else I was thinking I should be more clear on. There will be two uses of my machine that require special attention to component selection and chassis design. One will be milling aluminum billets (taking my time with that) as mentioned before.

The other will be fixturing say 20 plastic parts on the table and pressing "Go" and milling some feature in all of them. Then pulling the finished parts, loading it up again, and repeating. This will be production type work, with a few thousand to do. So the machine will see a lot of cycling. I need it to run for a long time without stopping for motor or other faults.

With those things in mind, any special considerations I should make in component selection?

Thanks!

[DonFrambach]

Hi Luther,

I'm am no expert on CNC so I hope I'm giving you good advice.

For your questions:

I have a Taig ER-16 spindle that I use for bits up to 1/2" (shaft diameter) and up to 10k rpm. I use this spindle to cut aluminum and brass on my other small mill. I plan to use it occaisonally on the new router.

I have a small spindle from Wolfgang Engineering (he's on ebay) that is driven by a small AC motor at about 20k rpm. This spindle accepts 1/8" shaft bits. I plan to use this router to make detailed carvings in wood and aluminum on my new router. I have ordered an upgraded spindle driven by a DC motor from Wolfgang Engineering that has a bit more power and, I think, I will be able to run at slower speeds.

I think it is best to have a system to easily change spindles so that you can optimize the spindle for whatever cutting task you have. (That's pretty easy to implement as I did)

I am using cold rolled steel and carriages from CNCRouterParts.com for the Z axis and for the axis on the gantry. I am using a 20mm round guide system for the other axis that I purchased from Glacern. So far everything is fine so I really can't compare the two systems.

I'm using 1/2" 10pitch single start lead screws. For a 24x24 system you may want to go with 5 start lead screws. I'm using an old computer directly driving my G540 board and that limits me to 75"/min rapids. I believe that with a SmoothStepper board I could go faster but don't really want to go any faster with my small router. I think that the motors are not the limiting facter. With 5 start lead screws, the rapids would be at least 300"/min. Even faster rapids could be achieved with a rack and pinion drive system.

I really can't advise you on cutting plastic. I've cut a little acrylic with my Taig spindle with good enough results but certainly not cutting anything quickly.

Good luck.

Don

[DonFrambach]

Another thought on spindles:

Although I have no experience with this, I understand that a number of people are using small electrical routers controlled by the "Super-PID" to run at optimal rpms for their cutting task. Here's a link:
http://www.cnczone.com/forums/diy-cn...ontroller.html

If you decide to go that route, I also understand that a number of people have upgraded their collet systems to reduce run out. Here's a link for that too:
Collets, Nuts and Toolholders

[lcifers]

Thanks Don - I'll look into those spindle options.

Do you by chance have 3D models of any of those parts? I want to try to model as much as possible before I purchase any components in case things change - which they surely will... I have the 80/20. I'm particularly interested in spindles, ball screws, motors, and Glacern parts.

Thanks again for the help! I hope to have the initial concept uploaded tomorrow night. It will look pretty familiar!

[lcifers]

I'm trying to figure out the ball screws and motors I need. Probably a dumb question but how do you know stepper motor RPM? I don't see it shown on any of the motors I have looked at.

I think the right process is to:

1) Decide what rapids I would like to have
2) Select pitch of screw based on 1)
3) Select motor based on screw pitch and mass I'm moving

Am I going about that right? If not, how do I correctly select ball screw pitch and motor size?

Thanks.

[DonFrambach]

Sorry, I don't have any models. I only made a rough mock up (using Google SketchUp) as I was working out the general dimensions of my small router.

I'm not sure what the maximum rpms my steppers can do but it's pretty fast - much faster than my lead screws and delrin nuts can handle.

Your design decision process seems very reasonable to me. Hopefully someone with more knowledge than me can supply the basic information that you need. I just used what seemed like was working well for others. It seems to be working fine for me too but the pieces that I selected may not be optimal.

Don

[RomanLini]

Hi lcifers, I built a small machine designed for precise machining of plastics and long hours of use. It also does aluminium quite well but I don't like the mess.

If you wanted to do aluminium for production I would suggest a metal machine you can run vertically or at a tilt of 60' and flood coolant to wash away all the chips.

For plastic production you can run the machine flat and just use a vacuum pickup boot on your spindle.

My machine is here if you want a look;
Diy_hobby_small_plastics_mill_router.html

[lcifers]

Thanks guys.

Don, I'm sure using the same components you did would work great. The difference might be in that I need get the rapids as fast as possible for the production work. I realize I'm setting my goals well beyond my level of expertise, but am hopeful to get it all figured out I've learned a lot from reading about your build and others on this site.

Thanks Roman. Your build was the first one I read! Very nice machine! Interesting idea about evacuating aluminum chips. You have me thinking about a steel jig that I can use to flip the entire machine upside down for milling aluminum Kind of like a jig used in steel frame welding, pivoting on the center of gravity... Hmmm...

I see you used 8mm lead screws. What I've found so far are 5mm and 10mm. How do these look?

3 Anti Backlash Ballscrews RM 1610-350/800/1350mm CNC - eBay (item 250671135079 end time Jan-19-11 03:50:08 PST)

I have a lathe and can machine them down to the right length. Do they look like decent ball screws?

I also looked at the ones at Keling. Anyone have experience with those?

Thanks!

- Luther

[ger21]

Originally Posted by lcifers I'm trying to figure out the ball screws and motors I need. Probably a dumb question but how do you know stepper motor RPM? I don't see it shown on any of the motors I have looked at. I think the right process is to: 1) Decide what rapids I would like to have 2) Select pitch of screw based on 1) 3) Select motor based on screw pitch and mass I'm moving Am I going about that right? If not, how do I correctly select ball screw pitch and motor size? Thanks.

It can be a bit tricky when using steppers.
As stepper rpm's increase, the torque decreases. So, depending on several variables, such as force required, power supply voltage and gearing, usable rpm can vary greatly, depending on the application.
Because of this, be aware that as a general rule, that you need to trade resolution for speed when you want to go really fast with steppers. Also note that "really fast" is relative.


Generally, you start with how fast do you want to go.

But when you choose a screw, you'll need to know how much force you need to move your machine, and how much torque is required to generate that force.

Then, see if you can find a motor/drive combination that can give you what you want.

You'll want to look at stepper motor torque curves to see how much torque they have at any given rpm/ But be aware that these curves are very specific to the drive and power supply used, and may or may not correspond to your actual results, unless all the components used are the same.

Also, as steppers get bigger, their high speed performance decreases. If you need high rpms, smaller motors can often outperform larger ones.

Depending on how much torque you need, you'll probably find that steppers work best up to about 800 rpm, although I've heard of people using them at 1500rpm or more. But it really depends on the application.

Several manufacturers have motor sizing software, where you input al your information, and it'll tell you what motors you need.

[lcifers]

Thanks Gerry. Seems I have some more research to do regarding motors.

Any input from anyone on the ball screws from my last post? Any advice on the brand and also 10mm pitch vs 5mm?