CNC questions

[kvom]

I've been reading a number of threads about members that either have CNC setups or are building them for home use. I am wondering about the motivations for doing so. The school I'm attending to learn manual machining has a series of CNC courses and large Haas VMC/HMC machines, so I could elect to continue on to learn the principles.

What my instructor tells me is that in general the "break-even" point for machining a CNC part is three or more copies; any less it's quicker or more economical to machine manually.

I do understand that there are some parts that are difficult to produce manually, or would be tedious (e.g., drilling 100s of holes).

Interested in members' opinions.

 

[Tin Falcon]

Here are some random thoughts from someone Mid build of a CNC mill
Most of the adapter hardware is machined the electronics are on the way I need to order order supply and ball screws.
1)overcome personal fear. I have operated cnc but have been apprehensive of diving in and really learning it.
2) Learn a new aspect of machining.
3) There are some jobs that are easier with cnc
for instance bolt circles.
4) CNC opens new possibilities like engraving.
5) Would love to have a DRO but spending a bit extra on full cnc makes more sense.
Tin

 

[ksouers]

Well, I'm not really sure what you want an opinion on; whether or not you should take the courses or head off into CNC for the home.

Right up front I'm going to admit a bias, I don't have a desire to do CNC at home for a hobby. I like manual machining. That does NOT mean I'm anti-CNC. If I was in business to make parts I'd be doing it the CNC way in half a heartbeat.

I think taking the courses for the sake of knowledge would be a plus. I would bet there are techniques learned in CNC that could be applied to manual machining. Obviously they would be more complex requiring multiple set-ups, but could be done. But then that's the advantage of CNC, stick a lump of stock in the machine and whittle out a complex profile in one set-up.

I also see many advantages to having a small CNC router table in the home shop. Anyone can be an expert engraver and making patterns for casting is easy. They also do a fine job of making small parts.

I think taking at least one course would be an interesting experience.


Kevin

 

[Kermit]

I have an observation for you from the outsiders perspective.

The guys at work running the CNC machines are all young and the other room full of manual lathes and mills is run by two guys older than me and one guy my age from Yugoslavia (or whatever it is called now )

Obviously from an outsiders perspective, the manual trade requires an extensive knowledge that comes from years of practice to achieve the same exacting tolerances that can be secured from CNC machining.

Second, there is a dire shortage of young men who understand or are learning manual machining due to the proliferation of CNC machines.

This means in the not to distant future there will arise a huge need for people that can manually machine and there will be none in this country. Which "could" translate into large wage increases for this particular skill.

I'd love to hear I was wrong,
Kermit

 

[Cedge]

Having met Kvom and knowing he's no spring chicken, I suspect his interest is not in the line of going back to work, at least not full time....(grin)

I too have a bit of curiosity on the CNC front and would probably consider the class on that basis, alone. Since no knowledge is ever wasted, and access to the machines is a golden opportunity, I'd say go for it. What's to lose?

Kermit
I hope your take on things comes to be. Nearly every shop I've been in, either had or was run by someone who was proficient in manual machining. Usually it's an older guy who has saved them enough over the years to be treated with respect and allowed quite a bit of personal leeway. These old guys can't live forever and they are being lost at an alarming rate. Few younger guys are willing to take the time or effort to learn the secrets these fellows will carry to the grave with them.

As these skills become more rare, I too hope their value increases.

Steve

 

[mklotz]

It's important to separate the pro/con CNC arguments into commercial and hobbyist applications.

In the commercial environment time, accuracy and repeatibility equate to profit and, as a result, CNC will continue to grow in that environment.

For the hobbyist the profit motive is, by definition, moot so the major attractions become:

learning a new skill
simplifying the manufacture of complex parts
removing the tedium from making a number of identical parts (visualize building a nine cylinder radial engine)
etc.

Some of us, myself included, have worked/fought with computers all our lives and enjoy manual machining because it gives us a chance to develop our manual skills and hone our craftsmanship. Our satisfaction comes from solving the setup and machining problems and learning the heritage techniques.

This means in the not to distant future there will arise a huge need for people that can manually machine and there will be none in this country. Which "could" translate into large wage increases for this particular skill.

I've read this thought many times on the various machinist boards. I don't believe it's true.

Certainly there will always be a market for people who have the skills to repair machinery too expensive to replace. That work may require machining one-off replacement parts.

However, we're only on the leading edge of NC machining. Computers and software will continue to grow more capable, more powerful and more user-friendly. (Just contrast the CNC machines of today with the dinosaurs of a few decades ago.) Moreover, the technology advance will accelerate, not just improve at constant speed, and it will get cheaper as well.

I expect that, when that machinist of the future needs a one-off repair part, he'll find it far easier to describe it to a computer and have the machine spit it out than set up his aging Hardinge and laboriously fashion it himself.

 

[shred]

I'd learn the CNC while it's available. Mix in some manual machining knowledge and you have a very powerful skill set if you want to go 'pro', and G-code is more or less G-code from a tiny machine to a big one.

I was talking to a HAAS technical rep the other day. He said he had a customer complaining about repeatability to whatever miniscule fractions of an inch they want. He goes and looks at their G-code. They're basically zigging and zagging all over the table and expecting everything to be spot on. The big machines with ball screws and servos are pretty darn good, but not perfect.

He asked them 'remember how we did precision tolerances on the old manual machines?'
They look at him blankly.. not old-school are these people.
He says "you'd always come at all the hole from the same direction.. take up any slack in the system".
They kinda went 'wha?'
He tweaked their code to stop rapid moving a little before the hole and sneak up on each one the same way. Problem solved.



We had a discussion a while back at a club meeting about hobby CNC versus manual. The consensus amongst those with both seemed to be that complex parts (especially with curves), hole patterns (especially if they had to meet up with other holes) and plate cutout work (plates with pockets, holes, chamfered corners, etc) and multiple-parts were where we preferred to use CNC, and the rest of the time we preferred to go at parts with the manual machines. Different people had different criteria for each, but generally it was some sort of personal effort-to-reward equation.

Taking a look at my Loco project, I CNC-ed the baseplate, frame-rails and cab-- the baseplate had a few angles/curves on it and a lot of holes to be in the right places; the side-rails needed to be identical, had angles and there were two of them. The cab had curves and inside windows I could draw up on the PC then cut it all from one sheet and fold it up. All of those are doable on a manual machine, but they failed my personal 'effort-to-reward' bar of manually machining them.

 

[RonGinger]

I have been tinkering with home shop CNC for at least 8 or 9 years. In the last couple years it has really become my hobby, making models has become secondary, although I am changing that this winter as Im working on a Rider Erickson pumping engine.

To me its mostly been the learning part- I was an electrical engineer, I like mechanical stuff, its a great thrill to watch a machine I built run and make useful parts.

Production has nothing to do with it. The original comment about 3 parts being break-even is nonsense. I just made a keel mold for a friend to cast lead keels for sailboat models- The code was 10 or 12 thousand lines long, it cut for about 2 hours. You cannot hand-crank that part in any amount of time.

I also just cut a 3" pipe thread into a throttle casting for a locomotive. I used my CNC mill to thread mill it, that ran 2 hour 26 minutes, I made 300 steps per rotation, 10 threads.

So CNC lets you make parts you simply could not do by manual methods.

Another argument often used by guys is that CNC is a no-skill thing- you just load the program and watch the part come out. This is also nonsense- to make a CNC part I need to know all the same stuff a manual operator does- like material selection, tool selection, work holding, speed/feed, etc. The I must additionally learn all the machine programming and operation stuff.

In industry there are simple CNC operators- but someone makes all the decisions about the job, maybe the operator does just load stock and push buttons, then call for help if something breaks.

So CNC is just another aspect of this hobby that some of us find very interesting to develop. If you like making models by old methods, have a ball, this is a hobby after all, do whatever you think is fun.

 

[Brass_Machine]

For me there are a couple of different reasons why I am going to CNC in my shop. First, please note that all my machines at this point will be capable of manual or CNC. None of them will be CNC only unless there is a manual machine to use as well.

My hobbies extend beyond model engines. Way beyond, so there are things that I would like to make/build that CNC would prove to be beneficial. But as far as model engines go, while it is nice to manually mill a steam engine or a hit n miss... I would like to someday build a multi cylinder IC engine. Such as a scale V8.

I also make parts on the side for other things and the CNC would help with that.

Eric

 

[BobWarfield]

First, I would not want to undertake CNC unless:

- I had a decent knowledge of manual machining. How to measure, what the cutting should sound like, how to judge if I'm going too fast and so on. You lose all "touch" with CNC and have to be able to rely on your experience more IMHO. As a home machinist, you can’t just be the “button presser” on your CNC. You are the designer, the one who comes up with the fixtures, and all the rest. Solid manual machining experience is a good background for that. This is RonGinger's point.

- I was comfortable with computers being a lot bigger part of my shop experience. This is inescapable when you go to CNC. In particular, you will have to deal with CAD, perhaps some CAM, certainly the machine control (Mach3, for example), and possibly CAM software or g-code programming.

- I was comfortable poking and prodding my way through making the electricals work. There are a lot of electricals with CNC, and if you have a hard time changing a light bulb, you don't want to be dealing with the frustrations of a CNC system. This doesn't mean you need to be able to do component-level diagnosis of circuit boards, but you should be handy with a voltmeter and reading a circuit diagram. Like any machine, the CNC will break sooner or later and you'll have to fix it.

Second, I don't buy the instructor's notion that CNC doesn't "break even" until you need to make several copies of a part. There are a lot of advantages of CNC that are apparent very quickly if you have even a little bit of proficiency:

- It requires less tooling. By the time you pay for a nice DRO and power feeds on all three axes you can just about pay for CNC. Not quite, but close. Add up all the other tooling you may have that is no longer required for CNC and CNC will be cheaper. But, you'd need to pay that bill up front, so it may not matter. Also, to take full advantage, you may need to buy a CAM program so you don't have to g-code it all by hand. That gets REALLY expensive and will eliminate most of the cost savings if not all.

- You can do things that just aren't possible or would be very hard with manual machining. Complex flowing curves and engraving are two examples. We have ball turners for lathes, but profiling such shapes and much more complex ones is trivial with CNC. Also, there are operations that a really talented manual machinist can do that I can't do manually, but can easily do with CNC. There is less of a burden on you, the machinist, to develop that fine art, but you will be called on to develop other fine arts.

- CNC can be faster. The CNC can whip out operations a lot faster than I can, at any rate. A big part of my impetus is this productivity. I simply can't build everything I want to build in my shop fast enough eith the hours available to me. If I invest some of those hours up front in a CNC conversion, I can get more projects done later. The complexity and speed issues are well addressed with shred's "personal effort/reward" idea, which I like a lot.

- Surface finish and precision can go way up with CNC. Did you experience an immediate improvement in surface finish when you got a power feed for your mill? I did. Can you hand feed on your lathe and get as good a finish as with the power feed? It's really hard for me, and the results are not always reliable. Now imagine if you could dial in the perfect speeds and feeds for every operation via CNC. In fact, through features like CSS, the machine will even vary the lathe spindle speed as you move towards the axis to ensure that perfect cutting speed.

Let’s end this by considering some photos. Here is a set of CNC’d pulleys hot of the machine:

Note the surface finish: it's right off the machine with no further polish or other work. How easily can you get that manually? Sure, some part of it is the radically better rigidity of the machine used, but some part is also the perfect feeds and speeds concept I mentioned.

Now consider a more typical HSM project, an upright marine style multiple expansion steam engine. This one was done in a home shop with CNC by jimmibondi (Frank) that won the HMEM November Engine of the Month:

I will venture to say that it wouldn't take me three copies of it for this masterpiece to get done a lot faster and better with CNC than manual machining. Not that you couldn't do it manually (not sure I'd have the patience), and not that it didn't require incredible craftsmanship to do with CNC, but it would just take a lot longer manually.

With all that said, manual machining is tremendous fun and CNC is not for everyone. It's a hobby, do what you like!

 

[John S]

Read this, It has a UK slant on it but you will follow it.

http://www.arceurotrade.co.uk/projects/Why_CNC/whycnc.html

.

 

[Maryak]

Read this, It has a UK slant on it but you will follow it.

http://www.arceurotrade.co.uk/projects/Why_CNC/whycnc.html

.

John,

That is a masterpiece of literature :bow:

Best Regards
Bob

 

[GailInNM]

I am an old coot who has been building model engines for over 50 years. For the first 25 years it was all manual machining as there was no reasonable way for a hobbiest to get into CNC machining. I bought a Bridgeport CNC milling machine in 1983 and about 5 years later I bought a CNC lathe. I still have and use both. I also have amanual milling machine and manual toolroom lathe. They all compliment each other, although I seldom use the manual milling machine.

For me the CNC makes it possible to make parts that have features that I want in a reasonable amount of time. I would be rare that I could not make a part manually, but it is often that I would not do so. A base plate with rounded corners and a radiused edge is an example. I could make the part with a rotary table and lots of time, or with a beltsander and a file. But, I would not do so. The time required to make four or more setups on the rotary table is more time expense than I would want to put into the part, so it would have square corners. And, I would never get the look I want using a beltsander and file. I know my limitations.

CNC also lets me accomplish more. Today, I plan to round the bottom of the crankcase of a model aircraft type engine with beam mounts. Now , I can do that on the lathe by racking the carriage in a couple of hours, or I can write a parametirc program in G code in less than 10 minutes and the run time will be less than 15 minutes. I would take me longer to do that than to set the job up on the faceplate of the lathe. Fixturing on the mill will mean clamping in the vice. Now, while the CNC is cutting the crankcase, I will have time to finish lapping the piston and matching it to the cylinder on the manual lathe.

Because of failing eyesight I probably only have a few more years that I will be able to build toys. CNC will make it possible for me to build a lot more toys in those few years.

Putting in other terms. I learned to cook using a coal fired cook stove. After building the fire, I adjusted the temperature of the skillet by sliding it to a different part of the stove top and adjusting the fire with more coal or less air. Now with my modern range, I turn the knob to what ever heat I want. And for baking I had to monitor the oven temperature and adjust the oven damper. Did it make the bacon and eggs taste better because I spent the extra time with the coal stove. Not in the least. Now with my CNC controlled oven and CNC microwave, I can get on to the more pleasurable aspect of the kitchen duties, eating.

Gail in NM,USA


Gail in NM,USA

 

[steamboatmodel]

I think all the others have explained it very well. As an retired CNC programmer/Operator, my experience was that those who knew Manual Machining always did best on the CNC. As for the break evan point on parts a lot depended on the part, I have a buddy still working at a shop and they have one customer who orders one copy of a part every year. The machining of that part takes 48 hours on a six axes machine.
Regards,
Gerald.

 

[John S]

Some observations I have found in dealing with CNC machines and beginners over the last couple of years.

Mills and lathes are totally different in the way they are used. Because mills use professionally made cutter of an exact size it's possible to cut a job first time. Lathes, because you have to take trial cuts to determine sizes and how you cut also depends on finished size means you may have to do a couple of parts to dial it in correctly.

The result is CNC lathes don't lend them selves to one off's like a mill can.

because software and programming has got better in recent ears it's now possible to code a part in a very short time, sometimes even minutes. Adding programming time to machining time means you are very often quicker than manually machining even a simple part.

The whole idea of CNC is to press go and do something else, however it's that fascinating you have to stand and watch it 8)

Accuracy and repeatability is another plus point.

Less time spent making jigs. Classic example here is the camshaft machining thread and the jigs / setting up needed for a cam shaft.
Using a 4th axis on a mill and it can do all the lobes in one setting and then it's next job could be radial slots on another part still with the same 4th axis setup.

Is it the journey or the reward ?
Double sided coin, for some it's the doing, for others it's the finished part, for the latter it's a plus, the former wouldn't be using CNC anyway.

Making use of the time available.

There are other reasons but it's a bit of a lotto, choose any 3 from 7.

JS.

 

[Kermit]

Just so everyone knows.

I wouldn't start with CNC for myself.
It's ALL about the doing it with my own hands and as soon as I turn it all over to the computer I would lose interest.

My reason for learning to machine metal are most likely different from yours,
Kermit

Great thread so far! Let's hear from everyone.

 

[scoop]

cnc v manual is always going to be a matter of personal choice.I have spent so long working cnc mills and lathes that to go back to manual and being able to work at my own pace is a luxury.I build slowly and do it when and if I want to.I feel no need to rush through one model just to start another.This does mean of course that I have to choose my projects carefully.but now that I am no longer in the production machining trade I can afford to go slowly(I'm not against the clock now).
There will always be room for both methods of manufacture and I have no intention of putting one method ahead of another,but for me I hope my days of watching a row of numbers on a screen are behind me regardless of how much faster it is.
I do agree with the chaps about the need for less tooling,being able to interpolate odd size radii instead of having to use a fixed cutter size is one of my only gripes with manual,I do miss my G 02 and G 03 codes.
Maybe the need for an old boy with old skills could rear its ugly head one day.

happy coding or winding handles,as is your choice.

Best Regards Steve C.

 

[Holescreek]

I'm not sure what my real interests are but I spend a disproportional amount of time building machines and making tooling. I built a CNC mill for no other reason than that I had an "extra" mill that I inherited, and I wanted to learn everything involved with designing, fabricating, building and running the mill. BobWarfield said just about everything that matters from the rational standpoint. I went so far as to make a 4th axis for mine which gets more use than one would have thought. Now that I have it I can make any gear I want with 15 minutes of programming and have time to sweep up. -Mike

 

[artrans]

In reading through this thread I had a thought may be some one can shed some light on taking out the production end of cnc which is where cnc really shines. can every job be done by hand machines or are there cnc only parts. and by that I mean to the point of being reasonable for example you can do it by hand and a week later your done or lets say cnc is one hour and by hand a day. cutting a cam lobe with cnc it would be easier to do. By hand you have to make a fixture just wondering I am interested in cnc very much and I am working on one as we speak and it is kicking my a** right now and every body that can help local it seems g code is a think of the past and now its conversational which is a little easier but the machine I understand is still using gcode it just you don't have to no it the machine software no's it. do I have any of right

 

[artrans]

sorry forgot something it also seems like cnc goes hand in hand with cad /cam or is that not true. I have been trying cnc for some time and it a steep learing curve going it alone. i typed in the gcode for measurements I made by hand and it duff and a simple part takes many line of code to produce that part. But Iam thinking we or most would problemly make he part less
fancy doing it by hand where I think cnc you could make the part more fancy in a shorter time.