Input from people with CNC machining experience

[gene_weber]

I need some input from people with CNC machining experience. I posted something similar in my build thread, but this seems like a better place for this question.

I'm converting a PM728-VT to CNC as a hobby machine in retirement. I have zero machining experience, and I'm trying to make sure I include the things in this conversion that I'll need/want in the future. As far as my planned usage of this mill, it's possible that I could come up with some widget that I make a couple hundred of and sell, but mostly I think I'll make one to a few of the things I draw up in CAD. I'm guessing that the majority of the milling will be aluminum or steel, and actually some hardwood.

Based on that I think:
- The machine needs limit and home switches on all 3 axes.
- The machine needs CNC control of the spindle speed and direction to coordinate feed and speed during milling.
- The machine should incorporate a spindle speed encoder to coordinate low speed spindle operation and Z axis feed for threading operations.
- I think I'd like to add a fourth axis for "A" rotation about the X axis in the future.
- I don't think I'll need an automatic tool changer or automatic flood or mist coolant control.

Please let me know if you think this sounds about right based on your experience. Am I overlooking something? Is there something you often use as a hobby machinist, or dearly wish you had?

Thanks,

Gene

 

[Reddinr]

I was in the same boat when I got started, wondering just what I really needed and what I didn't. 95% of what I do isn't production work, just one or a few prototypes of something. Here are my opinions, not knowing what your high-volume widget is, it is difficult to nail down how fancy a system you might want. Take this with a grain of salt. My background is engineering, not machining. Everything I have learned came from this forum, youtube, books and breaking things myself over the years.

In general, I suggest starting simple and adding to it, unless you just need to get some production going fast.

Limit switches for sure. Home switches if you don't want to have to zero out everything at the beginning of a run. I have limits only and just 0,0,0 manually at the start and zero the Z manually for tool changes. I think my limit switches could be used for home too if I bothered. The ones I have are pretty accurate and repeatable.

Spindle speed control is nice to have and not expensive. Or you can just change gears. If you are CNC, you can thread-mill larger holes and not worry about coordination with the spindle speed. The holes I thread are generally 3/8-16 or smaller so I use a tap-matic attachment, which, for me, is a joy to use. Or, I'll thread on the lathe if the work piece allows.

Fourth axis is nice but you might want to start out with three axis until you get your feet wet. Easy to add later as long as your software and electronics supports it.

I use a spray bottle for lube/cooling. I think I would like a better system but have not gotten around to it after 15 years or so.

Tools/accessories will be a big cost. End mills, taps, cutters, measurement devices, replacement end mills, drill bits, (a good) vise, other clamping/hold-down hardware, end mill holders or collets, a good drill chuck, replacement end mills, on and on.

What I dearly wish I had would be
- a more stout mill but I probably will stick with my bench mill because it works fine If I don't go too hard and it has a good work envelope.
- better insulated shop with better heat (working on that)
- Boeing surplus store to come back.

 

[BGHansen]

Based on that I think:
- The machine needs limit and home switches on all 3 axes.
- The machine needs CNC control of the spindle speed and direction to coordinate feed and speed during milling.
- The machine should incorporate a spindle speed encoder to coordinate low speed spindle operation and Z axis feed for threading operations.
- I think I'd like to add a fourth axis for "A" rotation about the X axis in the future.
- I don't think I'll need an automatic tool changer or automatic flood or mist coolant control.

Please let me know if you think this sounds about right based on your experience. Am I overlooking something? Is there something you often use as a hobby machinist, or dearly wish you had?

Thanks,

Gene

You have a pretty nice machine described there. It should suite you well for the projects you are describing. My CNC journey . . .

My first CNC machine was a Bridgeport with a 2-axis Anilam control. I'd never used CNC when I bought the mill; bought it because I wanted a Bridgeport and it was only 30 miles away (at a reasonable price), not because it had CNC. However, WHAT A GAME CHANGER!!! After learning the controls, I coveted the 3rd axis. Instead of changing controls to a Centroid Acorn (plan A), I bought a used Tormach 1100 Series 3. My Tormach has a 4th axis, tool changer, and coolant. I have a couple of jobs that use the 4th axis, one is making a helical gear so the 4th is a must have for that part. Coolant on/off is nice too.

The Bridgeport has no spindle on/off/speed control or coolant control. I'll either blow shop air or mist coolant when needed which is all manually done. Spindle on/off is manual also. Speed control is manual which isn't a big deal since I have to manually change tools anyhow. Turning the spindle on/off would be nice as I might run a routine and walk away. I'll glance over and see the handwheels aren't turning, routine must be done, but the spindle is running the whole time. Same for the mist coolant/shop air, it runs until I shut it off. Nice choice on your part to control the spindle on/off/speed.

I made a lot of parts (look for post from me by searching under my name and "ERECTOR") on the Bridgeport, but have pretty much moved completely over to the Tormach. That's because of the spindle and coolant control (though the 3rd axis is the biggest reason).

My Tormach does not have a spindle encoding, so no rigid tapping. That would be nice, but I do it with a Tension/Compression tapping head. It's basically a spring-loaded tapping head. It has at least 1/2" of "give" so the spindle can run at a slightly different speed than the tap threads per inch.

Bruce

 

[slow-poke]

I will echo what Reddinr stated. Keep in mind I'm just a hobby guy who likes to tinker
I don't have:
- home switches
- encoder on spindle or servo control of spindle (I do have speed control and measurement)

I do have a control panel with actual buttons so I can avoid the mouse clicks and or screen touches when doing MDI stuff.

 

[BladesIIB]

The flood coolant is a very nice option as much for clearing chips and for cooling. Things build up fast and with more climb milling the chips are going everywhere, unlike manual milling where you typically stand off the the side not getting sprayed with chips. With a CNC, they tend to spray 360, so enclosed with coolant is a huge plus IMO. Good luck with your build.

 

[Boswell]

pretty much agree with all of the above. my only possible add will be that while I think Limit switches are essential, home switches are more of a nice to have when you are not doing production work. For one-off or very low quantities, you can just zero on the part and it does not mater where in the work envelope you are. My mill has home and limit switches and I can't remember the last time I "Homed" the machine. If you plan to have a setup that you return to day after day, then you can save some time by homering the machine but if you are just going to machine a feature, you can do that easily without homing first. BTW, not trying to talk you out of a nice setup just giving you can option to simply your initial build. Easy enough to add homeing switches later.