Why use a CNC Mill

[Heronguy]

Last summer I was fortunate enough to get good deal on a Sherline 2000 CNC mill.  As a former software developer I was intrigued with the idea of computer control but as a novice ship builder and novice wood/metal worker I thought It would be most likely that I would just use it in manual mode with the hand wheels while I learned some skills.

 

One of my 1st "projects" involved making a weaving accessory for my spouse.  That involved a simple pattern of drill holes in a board.  The CNC program was pretty trivial but it was cool to stand back and watch the machine do the work (my management credo: "I love work - I can sit and watch it for hours").

 

But what about ship modelling use.  The 2nd project was working on a "riveting Jig" based on the Syren jig defined by Chuck P.  More drilling but to tighter tolerances.  

 

This took a lot longer due to learning about milling machine backlash adjustments as I tried to debug a systematic error in the positioning of the holes in the 2nd and 3rd rows.  

 

 

 

More recently I wanted to square a section of the main mast on my Essex cross section.  This was exciting as it was an opportunity to to use the rotary table that came with the mill. This was another little job that I wanted to do precisely and, since I can lose count on the hand wheels quicker than I can turn them, I used the computer interface in manual mode (so the computer drives the CNC steppers in response to individual move instructions - basically gives you DRO capability - no need to count hand wheel turns).  I practiced the moves on a spare bit of doweling to be sure before I put the already prepared mast near the cutter.  

 

It was going well until I jogged left instead of right!  One ruined mast.  

To be fair I could have made the same mistake with the hand wheels but the damage would have been minimal.  Time, I decided, to write the CNC program to square my mast.

 

 

 I realize that all of this stuff could be done with the mill in manual mode, but as I said, I love "work watching".

 

Last week I finally came up with a need for the CNC mill that I couldn't have done otherwise.

 

The brackets to hold the stunsail booms to the yards (if I've got the correct words ) for the Essex cross-section were horrible(plywood) and making them

out of brass sheet silver soldered didn't turn out too well, so I decided to try milling them.

 I really like the result. The milling took over 40 minutes the 1st time (with a 1mm end mill I used a really low feed rate).  The 2nd 3rd and 4th ones one took 12 minutes and I ramped up fedd rate and depth of each pass. There were 2 small manual steps after milling the basis shape.  I drilled the holes for the spars rather than having the end mill do that part, and I flipped the piece over to mill the substrate off freeing the bracket from the stock.

 

 

 

 

 

[Heronguy]

Pros and cons of CNC Mill

 

The advantages obtained by CNC capability on the mill include:

 

  ability to move the cutter in any of the 4 axes simultaneously (e.g. milling an arc)

  precise control over movements

  ability to reproduce multiple identical parts

  the joy of watching the machine do the work

 

The disadvantages include:

  having to specify milling intentions in a very primitive programming language (g-code)

  learning curve of the CNC programming language (g-code)

  cost of the system

 

Things I still have to explore:

   CAM software for designing parts (I’ve played with FreeCAD and ben frustrated,  will try out Fusion360)

   Path generating software ( to take CAM model and generate the g-code to machine the part.

 

Things to be aware of:

  There is no magic in the systems at present  You still have to know how the part can be milled.  You have to specify the order things happen, the tools to use, and you have to know the capabilities and limitation of your particular mill and tools.

 

 

[Heronguy]

I'd love to hear how others on this site are using their CNC mills and lathes.  I have a lathe on order and although I debated CNC vs DRO for the lathe I eventually decided on the CNC version  since the computer interface provide the equivalent of DRO information another seem to me to be opportunities if controlling X and Z axes concurrently on the lathe (I'm thinking balusters for railings for example - I might want to produce many identical ones).

 

 

[BANYAN]

An interesting analysis Heronguy (name? - sorry I hate using avatar names but I acknowledge privacy is a personal choice also).  I went through the DRO vs CNC analysis when I purchased my Sherline also and the DRO won out mainly due to the cons you point out.  I have found that except for a very few tasks most can be achieved with a DRO with some care and patience.  The two main drivers for my choice were the amount of time I expended on learning yet another skill and, I would still end up with a number of failures etc due to not programming correctly.  I therefore went manual, with the assistance of the DRO, to do the jobs I do.  

 

When it came down to it it was simple maths and economics:

- how often in a build do I use the mill?  

- how long would it take me to set up the job (for both)?

- does the cost differential warrant this?

 

That said, if you have a CNC and mastered G-code; and even better if you can draw the 3D object and transfer/translate to G-code then it is certainly quicker and more efficient to use CNC.  Another benefit I suppose is that you could achieve outputs with CNC with far less accessories such as tilting tables, compound cutters (taper accessory) etc.

 

cheers

 

Pat

[Heronguy]

Thanks Pat,

By the way, my name, Doug, is in my signature, like yours

 

I agree that  cost/benefit analysis is valid.  I don’t assign cost to the learning and the setup phases - is a personal choice but not fair to assume for others.   

 

In in terms of benefits I don’t know how I’d have milled the bracket without  CNC.  I suppose if it wasn’t an option I’d have settled for the soldered bracket and perhaps even practiced more to do a better job.  I was pretty pumped by my milled piece though - that’s worth something for me!

[mtaylor]

If you're doing a run of the same parts, such as, say 50 cannon, then an automated system is good as it's repeatable.  For one off's then not so much.

[BANYAN]

Hi Doug - signature probably in the signature block and hidden  -  I find having the signature blocks on wastes too much screen space.  Sorry I should have thought of that.

 

Thanks for your continued feedback as I have continued to remain interested in this option (CNC).  As Mark points out, CNC could be valuable for repeated efforts, or as you point out for some of the more intricate parts.  I must admit I have wasted quite a few pieces by inadvertently (read a lack of skill) not resetting the part correctly for the next step in my manual processes.    At this stage I am still trying to learn (and relearn) too many other things than take up G Code and I am not sure my blood pressure would withstand the frustrations   I will follow your efforts with interests though.

 

cheers

 

Pat

Edited April 19, 2018 by BANYAN