Stepcraft CNC mill

[Knuckles]

Any mill updates?  : )

[Giles]

No updates as such, but I've been using it a lot. About four loco chassis including slide bars, cranks, motion etc.

 

 

And recently a 16mm live steam scale rebuild cutting a new cab from 0.036" nickel silver and buffer beams from 2.2mm brass (both using 1.6mm D cutter)

 

 

[Giles]

I also incidentally made an enclosure which cuts the noise down a lot! It's made from 18mm MDF and carpeted internally. The dalek type doors work really well for access. The Hoover I use for extractionbis the loudest aspect by far, now.

I've also given up on using Proxxons for spindles and use the FME- P Spindle.

 

 

Edited September 3, 2021 by Giles

[Giles]

Quarry Hunslet (7mm) chassis parts

 

 

 

7mm Peckett milled chassis

 

 

[PaulaDoesTrains]

That's very impressive @Giles. Can I be cheeky and ask what size end mills and what feeds and speeds you're using?

[Giles]

Not cheeky at all...... I will confirm when I'm on the computer for accuracy, but where possible I use a 1.6 dia D bit for everything I can, and that cuts at around 0.3mm per pass, and about 0.3mm per second, and where I have to go smaller, I use a 0.8mm D bit, and run it at around 0.2 per pass and about 0.25mm per second.

These are the cheap Chinese carbide tools sold for PCB work, at around £5 for 10. There is a reasonable mortality rate for the 0.8mm ones (sometimes one will last three or four weeks, other times I will break three in a day....) but the 1.6 are much more resilient.

 

They don't like the work moving! When cutting small pieces, I always program a tab to hold it in place and prevent it from breaking free - as that is guaranteed to snap a tool.

 

I generally get on less well with conventional end mills for this sort of work (non-ferrous profiling)

[Knuckles]

I find this all very inspiring.  Something I will have to learn defo.

 

So many potential possibilities and ideas to actuate.

[PaulaDoesTrains]

Thanks for the info @Giles. I've been experimenting with machining brass on my 3018 and have so far broken four 1mm 2-flute end mills. Ouch! I found a video on YouTube of someone milling brass on a 3018 with a cheap 1mm "corn on the cob" end mill and he was using a feed rate of 25mm per minute and a 0.2mm step-down. So I broke out my packet of corn end mills (one of those "they'll come in handy some day" purchases which may have actually been worthwhile) and started experimenting. Whilst my machine will cut with those parameters, I was seeing rigidity/backlash/tool deflection issues with my 4mm diameter test holes which came out anything but round. At 0.1mm step-down I'm getting decent results though so I think I'm going to be able to machine fairly simple parts although nothing approaching the quality and detail that you're producing.

 

As an aside, I was watching a YouTube video about PECO's CNC machines which they use to make all of their tooling and injection moulds. They routinely use cutters as small as 0.3mm diameter and sometimes 0.2mm!

 

[Giles]

Ah.... I posted having mis-read your speeds  - sorry about that! 

So I cut at around 15mm per minute with the 0.8mm I also run the spindle at between 16 and 20,000 rpm

 

Best

Giles

Edited September 4, 2021 by Giles

[monkeysarefun]

56 minutes ago, Giles said:

Interesting.... 25mm/sec feed? As you see, I cut brass massively slower than that (it works for me anyway!). I do cut acrylic at 30mm/second though....

 

Best

Giles

I read it as 25mm per minute..

[flubrush]

I'll just chuck in my experience when working with small cutters,  established after a very expensive start with a large pile of broken cutters.  I use carbide two flute slotting cutters for everything.  I cut a fair bit of styrene and I find that the carbide cutters are the only type that will deal with styrene and leave a good finish.   When cutting brass,  aluminium alloy or steel,  with a 1mm diameter cutter,  I use a feed rate of 50mm/min with a depth of cut of 0.1mm.  With a 0.5mm cutter I use a feed rate of 25mm/min,  again with a DOC of 0.1mm.  Both cutters are run at 6000rpm.   I know these figures are on the conservative side but I get a good long life out of the cutters and I now retire cutters when they are getting blunt rather than hear them go ping. :-)

 

The machine is a Seig KX1 and its top spindle speed is 7000rpm which is a bit of a limitation with small cutters when I should be looking at spindle speeds well into five figures.

 

Jim.

[Giles]

41 minutes ago, monkeysarefun said:

I read it as 25mm per minute..

You are absolutely right!  My mistake!

[Giles]

I've not tried cutting styrene, but I do cut acrylic (perspex and Trotec) from time to time, and I've tried a reasonable number of variations, and I only have any real success with high speed feed rates - 30mm per second 1800mm per minute - anything much slower and I get a build-up of melted plastic that wrecks the job. This gives me a nice clean cut. 

 

I would observe, generally, that I chose the Stepcraft over others because it looked to be the most rigid machine of its type - and I think that has been true. Certainly I've not regretted the choice. Like all things, there has been a learning curve, but it has been such a revolution to my modelling...

Edited September 4, 2021 by Giles

[flubrush]

I got the tip to use carbide cutters on styrene from a G1 modeller some years ago.   I think the theory is that the cutters are sharper than HSS and don't generate heat when cutting.  

 

Typical settings for me with styrene are - 5mm cutter : 500mm/min:0.2mmDOC:3000rpm;  2mm cutter : 350mm/min;0.2mmDOC;3500rpm;  1mm cutter : 240mm/min; 0.2mmDOC; 4000rpm.   I could push things harder but I find that the styrene starts flexing in front of the cutter and I don't get the finish I require.  I mostly cut styrene to make panelled coach and freight stock sides so I'm looking for a very smooth finish on the panels,  which I get at the speeds and feeds given.

 

I've occasionally had a look at the Stepcraft style of mill mainly to investigate larger table movements.  The KX1 is practically about 250mm x 100mm which can get a bit restricting with some models.   I cut the frames for a 1:32 scale tank loco and there's a join hidden behind the rear driver.  :-)

 

Jim.

[PaulaDoesTrains]

12 hours ago, Giles said:

You are absolutely right!  My mistake!

 

All these different units can be so confusing In all the stuff I watch online they universally seem to use distance per minute for feed rates so I've simply fallen into the same habit. I think we're both using similar feed rates. I suspect that the limiting factor with these small diameter cutters is their fragility rather than the machine's rigidity.

[JohnGi]

Hi,

 

I have a second hand Roland MDX-15 mill. which I've modified with a slightly more powerful motor, and a speed controller letting me run it up to 18,000 rpm.

 

Recently I've been making parts for buildings, using Palight (closed cell PVC foam aka foamex) for walls, and styrene for details such as windows and doors.

 

I find that the problem of melting the styrene is less if you use single flute cutters which are sold for cutting acrylic and other plastics. Less flutes add less heat to the work, and there is more clearance for removing chips quickly. 

 

Single flute cutters of less that 1mm can be obtained from CNC Plus in Germany https://cnc-plus.de/

 

Sizes 1 mm and up can be got in UK from Rennie Tools https://www.rennietool.co.uk  (also on ebay), or

from Highland Slate Workshop (ebay only AFAIK).

 

 

 

 

[Nimbus]

6 hours ago, JohnGi said:

I have a second hand Roland MDX-15 mill. which I've modified with a slightly more powerful motor, and a speed controller letting me run it up to 18,000 rpm.

 

Would be interested to see details of your conversion. These Roland machines are becoming affordable

secondhand, I presume because 3D printers have become commonplace.

 

The Nim.

[Gareth-Ingram]

I am glad I came across this thread, it has opened my eyes to the possibilities enabled by this Stepcraft kit!

[PaulaDoesTrains]

@JohnGiI agree with what you say about cutting plastics - single flute cutters are the way to go there combined with a high feed rate.