To CNC or not to CNC – that is the question.

[GoCreateParticipant @gocreate]

Hi

I recently added a small cnc facility to my workshop, while I prefer conventional methods which are much more interesting and challenging the CNC adds some options for parts that I can’t do other wise.

In this respect I limit my CNC to a) Parts that need engraving/etching b) parts that would otherwise be expensive or long delivey castings c) parts that would require alot of fabrication and silversoldering. Here are a few examples.

 

 

Above is a water lifter in 2 halves to be silver soldered together and finished by conventional machining and by hand. Left is one half finished on the inside only, on the right the matching half complete inside and out.

 

Above is a steam header just off the cnc and ready for conventional turning/drilling and finishing. This would otherwise be a casting or fabrication.

 

Above are brackets ready for hand finishing. Could be done by conventional machining but I think most modellers would prefer a casting.

 

Above is a name plate ready for finishing and infill painting. This would otherwise probably be a casting or maybe etched.

 

For me the cnc adds some conveinience and control over buying castings. While I can fabricate I don’t like fabrication involving alot of parts, my preferance here would be to cnc what I can.

 

Nigel

PS sorry for any bad spelling, I wish this forum had a spell check.

 

[Anonymous]

Posted by blowlamp on 12/01/2012 10:11:53:

 

Those are good examples of pieces that can be nicely hand machined, given by Andrew and Terry.

 

 

Hi Martin,

 

Err, actually I machined the parts using a CNC mill? I did take the slot in the expansion link to final size by draw filing and referencing to a Hoffman roller, and then draw filed the die block to fit the slot, but the majority of the machining was CNC. The outer profile as shown is as it came off the mill. Since I was making the link for somebody else I figured he could draw file it to obtain the finish he wanted!

 

Regards,

 

Andrew

 

Edited By Andrew Johnston on 12/01/2012 19:13:48

[Sub MandrelParticipant @submandrel]

David,

 

That’s an excellent description of how to learn assembly language – but it does take a certain type of mind to be able to do it.

 

I must say that Nigel’s latest pictures are making me think again about the desirability of CNC – as does the two days machining these by hand (photo only shows one semi-finished wheel):

 

t might not have been a lot quicker, but I bet the end results would have been better and (compounded with DIY and PS2) set off my carpal tunnel problem again!

 

Neil.

[blowlampParticipant @blowlamp]

Posted by Andrew Johnston on 12/01/2012 19:13:36:

Posted by blowlamp on 12/01/2012 10:11:53:

 

Those are good examples of pieces that can be nicely hand machined, given by Andrew and Terry.

 

Hi Martin,

Err, actually I machined the parts using a CNC mill? I did take the slot in the expansion link to final size by draw filing and referencing to a Hoffman roller, and then draw filed the die block to fit the slot, but the majority of the machining was CNC. The outer profile as shown is as it came off the mill. Since I was making the link for somebody else I figured he could draw file it to obtain the finish he wanted!

Regards,

Andrew

Edited By Andrew Johnston on 12/01/2012 19:13:48

Hi Andrew.

 

Yes, I did see that you’d CNC’d it, I was just making the point that it could have been hand done with some effort, whereas that thing of mine would never have been made by me without CNC.

 

 

Martin.

[John Stevenson 1Participant @johnstevenson1]

OK long post go get a coffee.

First off let me make it clear that I don’t push CNC at the expense of all else, my main job is emergency repairs. If it gets broken I have to fix it and that mainly means manual milling turning, welding etc. In fact my large CNC hasn’t turned a wheel in 5 or 6 weeks.

What I do want to do though is burst some of the incorrectly conceived bubbles that a lot of people who actually have no knowledge and are just repeating, want to shout out.

Thinks like CNC are only good for production runs. This is rubbish given that a complex part can be programmed and cut in far less time than getting a pattern made or fabricating then machining.

You need to learn G-Code before you can run one. Again rubbish, modern computer programs do all that for you. As an example of this I recently did a morning training secession at ARC’s Leicester store on an introduction to CNC. Due to space and getting enough training the course was limited to 4 people and I asked before hand what each persons conception was and two people said this was a limitation for them.

I asked the two people to nominate one of themselves and a guy stepped forward.
I then handed running the course over to him ! Basically I told him what to do, he did it hands on and we all watched.

Started off with a pre drawn DXF file of a con rod, basically pre drawn because it was not a lesson on CAD drawing and also no two people will use the same program anyway, end result is whatever program you use needs to output DXF and I know of no ‘proper’ CAD programs that don’t.

BTW ignore Terry’s reference to Parametric CAD made earlier, not having a stab at Terry but Parametric CAD [ usually expensive ] is where you change one dimension and it updates the whole drawing, whilst very nice it is not a pre – requisite. My take is if you draw it right you don’t have to update it <bg>

 

I know many people who have spent a lifetime CAD drawing without the help of parametric s.

So the DXF file was imported into Cut2D a cheap CAM program from Vectric which has one of the shortest learning curves I have seen. For each part of the shape the contour was selected, tool selected which also had feeds and speeds allocated to it. 6 contours were generated, pocket, small end boss, big end boss, small end bore, big end bore and outside.
To save time in programming the same tool was chosen to do all these contours and the part saves and the part was then post processed.

A word about post processors, all these consist of is a conversion file that reads the geometry on screen and convert’s it into way point co-ordinates with the correct G_code in front of it.
Each post is special to a particular machine and when correctly written means there is no editing to do.

Our trusty helper who we will call Fred as I can’t remember his name, sorry Fred <g> was then instructed to fasten the blank in a vise on the machine and set up origin point and tool length offset. I then deleted these and made one of the other guys set it up just to prove they hadn’t nodded off.

Before the G-Code was loaded into the machine I took a small piece of paper and some sellotape and covered the G_Code window up on screen, the code was loaded and Fred was told to press start.

25 minutes later we had a con rod, complete and on size. another 25 minutes later we could have had it’s mate if needed or even one half the size if we had entered 0.5 on the scaling box wihout having to redraw or reprogram it.

At this point we had a finished con rod and no one, including myself had seen ANY G-Code at all because of the piece of paper.

What actually happens is that as you use a CNC and see the code you learn it by osmosis, one day it will suddenly hit you “I can read this ” and then the bubble bursts and you think to yourself, what a sad ba$tard <bg>

CNC is just another tool, if you can make use of it then go for it.
Terry mentions using the word amateur and I can’t agree more with him. Taking the amateur status for some it’s the making of the part, for others it the finished part. Many have workshops not to build models but to support another hobby like vintage cars and bikes.
For them it’s getting the needed part as good and quickly as possible.

Time is also of a premium nowadays, gone are the days of disappearing into the workshop 6 nights a week. CNC can help here in that you can do more on the workshop nights than could could do manually but you get extra nights sat inside doing a bit of programming and planning.

One thing that people say that CNC is good for I do disagree with though.
They say that you can be doing something else whilst the machine is making the part.
That’s total rubbish – it’s that fascinating you have to stand there and watch it !!

John S.

[Steve WithnellParticipant @stevewithnell34426]

But I think that’s the point Martin, if blended curves are a drudge, use CNC, if you enjoy producng the blended curves by hand, then enjoy doing it by hand. I think it’s just a case of choosing the right tool for what you want to achieve.

 

 

[Anonymous]

Hi Martin,

 

No problem, I was just a bit worried I hadn’t explained myself properly. After all I’m an engineer, so English isn’t my forte.

 

Regards,

 

Andrew

[Alex gibsonParticipant @alexgibson50133]

Hi John S,

I suspect you’ve heard this question a million times but here goes again. If i convert my X3 mill to cnc would i still have some form of manual control for quick one off jobs for example when i want to use it as a drilling machine? I already have a pc in the workshop which just by chance is parked next to my X3 and I’ve seen kits advertised on the web to convert this mill to cnc but I’m still fond of twiddling the handles. So my real question is; Will I be able to switch between manual and cnc?

 

regards

alex

 

 

[John Stevenson 1Participant @johnstevenson1]

Alex,

Depends on the kit. X and Y, the table movements are easy, just fit a double ended motor and stick a hand wheel on the end.

 

Z, head movement is a problem in that AFAIK, no one does a kit where you can fit a handwheel to the Z .

 

When we used to do the kit for the X3 the Z was driven internally inside the column by a 2:1 belt reduction and supported in a top bearing.

It could be possible to fit a hand wheel to an extension at the top but whether it would be reachable or not is another problem.

 

Alternative is to use the Z under CNC as a rise and fall and use the quill as the manual feed.

 

John S.

[Alex gibsonParticipant @alexgibson50133]

Hi John S,

thanks for that, It was the X & Y i was worried about. I didn’t realise it was as simple as using a double ended motor with a hand wheel attached. As to the Z, am I right in thinking that the stepper is mounted at the top of the column and if so would the normal Z hand wheel still be operational?

 

sorry if that was another stupid question but I’m struggling to get my head around the physical aspects of converting my machine. I’ve read most of the articles in mew with great interest however i can’t seem to grasp the relationship between size of motors, driver boards and power supplies.

 

thanks again

regards

alex

[GoCreateParticipant @gocreate]

Just to concur with John S comment about learning G code.

 

Reference to my post above, each part was programmed in 5 to 10 minutes without any knowledege of G code. The post processors used were Vectric 2D and Meshcam. 30 minutes is enough to learn how to use these programmes and start producing G code for real parts.

 

Getting started was not without problems, this and other forums provided fantastic support.

 

 

Nigel

[SpringbokParticipant @springbok]

Hi Terry

Would not let your mate see the light bulb comment

Ouch duck quick

 

Bob

[Christopher KnightParticipant @christopherknight]

Nigel, those are some very impressive bits and your comments on using CNC as an alternative to casting etc. certainly give pause for thought. John, thanks for the great post on your training session.

 

I am not bothered about the computing aspects of CNC, I have tweaked enough code in various languages to feel comfortable with yet another. Probably the most relevant was writing some routines to use a daisy wheel printer as a graph plotter for curves I needed to draw in my work – only two axes but a bit like driving a CNC machine in a way. These days, I use mainly Sketchup and TurboCad in support of my woodworking.

 

The idea of starting manually then converting or trading up to CNC is starting to gel in my mind now.

Chris

 

 

[Roderick JenkinsParticipant @roderickjenkins93242]

I don’t think anybody has yet mentioned the relative costs. Minimum price to set yourself up for milling is of the order of £1,000 including some tooling. I guess you will need to add about £3,000 to this price to buy a CNC mill, PC and the sort of software required to manufacture the items described above.

Or am I being too pessimistic about CNC costs?

cheers,

Rod

[John Stevenson 1Participant @johnstevenson1]

If you do and buy everything for yourself it can be done for sub £1000 including software.

A suitable CAD program for generating DXF’s like Draftsight is free. Cut 2D or Cambam is around £120 – £150.

DXF2GCode is free but a bit clunky – enough to get you started so you can actually get started on legally free software.

 

Mach license is about £100 – £120 EMC is free but you need to be very conversant with computers and linux to use it.

 

[Edit]

Just realised this is to convert a suitable existing machine , not buy new.

 

New prices for a KX1 are £2591 inc VAT

A KX3 is £3691 inc VAT

 

All that is needed to run these is an old computer and a copy of Draftsight [ free ] everything else is supplied.

 

John S.

[Roderick JenkinsParticipant @roderickjenkins93242]

John,

 

I’d love to have a CNC milling option and Nigel makes an excellent case with his valve body. Can you get CAM software to do that sort of job for less than ~£500?

 

Rod

[blowlampParticipant @blowlamp]

Posted by Roderick Jenkins on 13/01/2012 09:33:48:

I don’t think anybody has yet mentioned the relative costs. Minimum price to set yourself up for milling is of the order of £1,000 including some tooling. I guess you will need to add about £3,000 to this price to buy a CNC mill, PC and the sort of software required to manufacture the items described above.

Or am I being too pessimistic about CNC costs?

cheers,

Rod

 

 

 

The cheapest route would be to buy a manual mill and convert it to CNC in the future and use it to make some of the parts for the conversion in between times.

 

Second hand Computer £80 – £100 ish

Mach3 controller $175 or EMC2 for free

ViaCAD CAD software 2d/3d $99

CamBam 2d/3d CAM software $149

 

Plus:

3x stepper motors ~ £45 each

3x stepper drivers ~ £65 each

3x ball screws and nuts ~ average £80 ish each

1x powersupply ~ £60

1x interface board ~ £60

 

As well as pulleys and belts, wire, fixings and a contingency fund for everything I’ve forgotten.

 

Probably do-able for say £1200 – £1400? Much cheaper with care I would think.

 

Martin.

Edited By blowlamp on 13/01/2012 10:42:22

Edited By blowlamp on 13/01/2012 10:42:38

[GoCreateParticipant @gocreate]

Hi John

I am only scratching the surface with what I am doing, there is lots of free and very cheap stuff.

For 2D I use Draftsight and Vectric 2D, John S gave details above.

 

For 3d like the valve body I currently have the luxury of autodesk inventor which is very expensive. However, there are many other options that I am sure others can advise on one being Alibre for 199 pounds. I have used this and its OK. This will allow you to create your 3D model which you save as an stl file format. Vectric do do a 3d post processor but I use Meshcam for which I paid around 90 pounds.

 

You create your model in 3d software (Alibre), save as stl and load this into the post processor (Meshcam) which gives you the g code which you then load into your cam software (I use mach3 from Artsoft) The valve body was about 30 minutes form starting the 3d model to loading gcode into mach3.

 

The 3D modelling software does have a bit of a learning curve but online tutorials are great. If you can dedicate some time you will crack it in a coupole of days. The post processors Vectric and meshcam are dead easy, by short learning curve.

 

There are many more options.

 

FYI

I am only using a small shirline mill I bought for 200 pounds on ebay. Adding the controller and stepper motors cost about another 300 pounds.

 

I am not using ball screws, on the Shirline you can adjust backlash to below 0.1mm which I find Ok even when down milling, it does leave a witness mark when the feed changes direction but as I do the final finishing by hand it no problem. (You can see the witness mark on the inside valve body as the Z axis has changed from down to up) I don’t use milling cutters bigger than 6mm, mostly 4mm and smaller.

 

Nigel

Edited By tractionengine42 on 13/01/2012 11:07:08

[John HaineParticipant @johnhaine32865]

Having converted my S7 to CNC a couple of years ago I was in the process of converting an X1 mill but got a bit bogged down. So then I was on eBay and came across a Denford Novamill, minus its controller, which I bagged for just over £600. It is a beautifully British made machine, vastly better than any Chinese import at the same price and about the same size as the X1 in real machining terms. Break-out board and 3 stepper drives came from eBay as a package at just under £100 for the same drives that are available in the UK at about £40 each! (And they were delivered in under a week!) 36v 11amp PSU again off eBay for about £40. Then a lot of metal bashing and wiring to put the controller together (being an electronics engineer by trade the controller side isn’t a problem, but really you don’t have to do much more than connect wires to screw terminals). So if you shop around I reckon you can have an excellent machine for well under £1000 for the hardware.

 

If I was starting in this hobby again I personally would go straight for CNC for all the reasons that John S gives. CNC is the default mode for doing engineering these days, we don’t need to preserve methods of manufacture that were traditional even in 1945 (IMHO)!

 

[Another JohnSParticipant @anotherjohns]

For those in Canada/USA:

 

My KX1 came from http://www.novakon.net – they still advertise 1 as in stock. It is a KX1 with a difference:

 

– $2495 instead of $4299 quoted from another nearby distributor for a “of the container ship” kx1;

 

– it did not come with the computer interface nor power supply for the interface/steppers.

 

Anyone who wants to pick it up, please feel free to ask for my document (my notes) on how I put a Gecko G540 Stepper Driver board in it. The document is large, as the pictures are big and many.

 

Lots of good help on the Internet is available, including some great stuff from people on this forum.

 

So, I have a KX1 mill (which is a great mill, despite what some people say) for a good price, and I know how it works!

 

Another JohnS.

 

 

 

Edited By John Stewart 1 on 13/01/2012 14:54:56

[Sub MandrelParticipant @submandrel]

Get thee behind me!!!

 

This is getting all to realistic an aspiration…

 

Neil

[John Stevenson 1Participant @johnstevenson1]

Posted by John Haine on 13/01/2012 11:24:09:

 

If I was starting in this hobby again I personally would go straight for CNC for all the reasons that John S gives. CNC is the default mode for doing engineering these days, we don’t need to preserve methods of manufacture that were traditional even in 1945 (IMHO)!

 

 

This quote by John made me smile as I came across an example of this only this year.

 

At the post Myford sale I was standing outside the fitting shop with 3 of Myfords fitters watching as all the jigs and fixtures were thrown into skips and dragged off to be scrapped.

 

The fitters were nearly in tears with remarks like, “They will never make them the same again ” which on reflection is true.

 

Their time served way for say doing a headstock would have been to machine a reference face and probably an edge then this casting would have moved from jig to jig and machine to machine with hopefully inspection stages in between followed by hand fitting whent coming to assemble the machine.

 

If this identical casting would be required today it would go onto a five axis CNC and the whole operation done at the one setting with only a final inspection and due to all the previous various jig operations being omitted the hand fitting part will not be required.

 

Years ago car engines were hand assembled, today they are assembled with robots and are the better for it.

 

John S.

[John HaineParticipant @johnhaine32865]

And the thing that struck me when I did my S7 CNC conversion was how much extraneous mechanism there is in that, very excellent, machine that could be eliminated by judicious use of electronics. Simple headstock drive by brushless DC motor; no changewheels or gearbox for screwcutting or fine feed; all threads available; metric and imperial on all feeds; PXF as standard; the list goes on and on. If anyone did think of resurrecting the Myford range (RDG?) I hope they would seriously consider some investment not just in modern manufacturing but also in updating the design.

[blowlampParticipant @blowlamp]

Posted by John Haine on 14/01/2012 10:16:44:
And the thing that struck me when I did my S7 CNC conversion was how much extraneous mechanism there is in that, very excellent, machine that could be eliminated by judicious use of electronics. Simple headstock drive by brushless DC motor; no changewheels or gearbox for screwcutting or fine feed; all threads available; metric and imperial on all feeds; PXF as standard; the list goes on and on. If anyone did think of resurrecting the Myford range (RDG?) I hope they would seriously consider some investment not just in modern manufacturing but also in updating the design.

 

 

Unfortunately they can only resurrect the Myford lathe in name only now the original workforce and factory have gone.

 

To me, anything else is just a copy and is a real loss for manufacturing in England.

 

 

 

Martin.

[Roderick JenkinsParticipant @roderickjenkins93242]

Posted by blowlamp on 14/01/2012 19:37:46:

 

Unfortunately they can only resurrect the Myford lathe in name only now the original workforce and factory have gone.

 

To me, anything else is just a copy and is a real loss for manufacturing in England.

Martin.

 

I beg to differ. It’s the design that makes the Super 7 so eminently suitable for model engineering. How it’s made is irrelevant. If the accuracy and “feel” are there then it is still a Super 7. The Moore’s couldn’t manufacture it at an economic price, perhaps somebody else can. I hope so.

 

cheers,

 

Rod

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