Cheapo CNC Milling

Discussion in 'Workbenches, including workshop techniques.' started by simond, 3 October 2020.

  1. simond

    simond Western Thunderer

    Quite a while ago, I impulse-purchased a very basis CNC milling machine to see if I could use it to make bits of model, and, as an aside, to help my understanding of G-Code, which is (in various dialects) pretty much the standard “language” by which commands are passed to the baby machine’s big brothers & sisters in industry.

    The machine is very similar to this one; https://www.amazon.co.uk/VEVOR-Engraver-Engraving-160X100X40mm-Material/dp/B07VTZXW6D/ref=sr_1_11?crid=36T994MK8NQWL&dchild=1&keywords=vevor+engraving+machine&qid=1601733261&sprefix=VEVOr+engra,aps,147&sr=8-11

    And cost around £140 from memory, it appears that they are still similarly priced, and it was cheaper than buying an adaptor kit, steppers, controller, etc., for my baby Proxxon Miller. For a few quid more you can now get a solid state laser that fits on the same gantry to interchange with the motor. (There are a couple of DIY laser threads on RMWeb if anybody’s interested. I’d not be running any kind of laser without some guarding!)

    The miller comprises a fairly chunky 12V motor mounted in a 3-D printed holder, which forms part of the Z (vertical) axis. This slides on the X (side to side) axis which comprise a pair of 10mm ground steel rods mounted on the frame. The table on mine is 100 x 160mm. It is an aluminium extrusion, mounted on well made 3D printed bearing carriers, with sealed bearings, again on 10mm steel rods, which are also mounted to the chassis frame. The table moved fore & aft, giving the Y axis.

    As supplied, there are 3 steppers and an Arduino based control board. It needs a decent 12V supply, and a usb connection to a laptop running any of the freeware control programs. There were no limit switches included, so I made my own. Optional, but difficult to use without.

    Does it work?

    well, yes, undoubtedly, it does what the Amazon advert says, but it has some weaknesses, which probably, nay undoubtedly, go with the price.
    It cuts plastic quite well, and I guess would also cut wood, though I’ve not tried.

    It seems pretty repeatable, but there is no position feedback, so if you overload an axis, it won’t necessarily stop and could lose steps, thus it’s position.
    The motor mount is not rigid enough and mine cracked when I got ambitious tightening it. It now sports an old G cramp stopping the motor moving relative to its cradle, until I can make something better.
    Cutting brass requires some patience.
    The whole structure needs stiffening and I have a cunning plan...

    I have finally convinced it to make some buffer spacing plates for my Garratt, and it is cutting at around 0.2 mm/ sec, with a depth of cut of around 0.17mm, on 1.1mm thick brass.


    The plates are 7mm square so I turned some washers with a 4mm hole and 10.7mm OD to the required thickness, and mounted each one on a post as the photo shows. The G-code I wrote is also attached, it goes to the centre of the post, switches to incremental control, offsets to beyond the corner of the plate, then executes a “square spiral” with radiussed corners to produce the plate. It takes 26minutes and 20 seconds to run. I have no doubt whatsoever that squaring up a bit of bar in my milling machine, and then turning it in the 4-jaw would have been quicker and far less hassle, but I’d not have had all the fun (or learning).

    image.jpg

    And here are some I made earlier, bad, and good...


    image.jpg



    Robin / Boy Blunder & I had a pm-chat a couple of months ago on the subject, and he purchased a newer version, so I hope he will add his experiences to the thread. If anyone else has a micro CNC mill or is pondering, please also join in.

    Couple of other thoughts, I’m currently using “grblControl” to drive the machine, I tend to generate 2D cad on TurboCad because I’ve got it and have used it for at least 30 years. If / when I get into 3D milling, I’ll use Solidworks, which we have at work, and which I can remote-desktop to when required. There are lots of DXF - to - Gcode programs available which I have started to investigate. You can write & edit Gcode in notepad, or any other text editor, and there are lots of guides online.

    Gcode - main commands are
    G0 (that’s a zero) followed by an X, Y, and/or Z coordinate - the tool will go by the shortest route from current coordinates to those specified.
    G1 as above but at a specified feed rate
    G2 as above with extra coordinates will give a clockwise radius
    G3 as G2 but anti-clockwise

    F and a value for feed rate

    M3 clockwise spindle (can also specify speed)
    M5 spindle stop

    loads more - Wikipedia provides a good list to start with.


    Atb

    Simon
     
    Last edited: 3 October 2020
  2. Giles

    Giles Western Thunderer

    Fascinating........

    As you know, I have a Stepcraft which is also not intended for metalwork but I regularly use it for such. The software I have does all the G Code stuff for me so I don't have that complication - however, learning what the machine will or won't do is fascinating. Both with the Stepcraft and the Emblazer laser, it has been an education as to what the machines can do if you talk to them nicely..........

    [​IMG]CNC cylinder end cover by giles favell, on Flickr
     
  3. Boyblunder

    Boyblunder Western Thunderer

    Thanks for starting this Simon, it was your experience with the Woodpecker Mill and Giles’ previous post showing what he had done with the Stepcraft that prompted me to treat myself to a 3018 CNC milling machine for my birthday in July. After the initial flurry of activity in July I haven’t made any progress because other outdoor activities have taken up my time. As a complete novice when it comes to CNC machining and milling in general I was starting from scratch and haven’t got anywhere near re-producing Giles’ work. So far I have learnt:
    • The machine I bought was more expensive than Simons and isn’t listed now, the one in the following link looks identical and is £20 less than the price I paid in July (grizzle): https://www.amazon.co.uk/Protected-...ro&qid=1601798335&sprefix=3018,aps,159&sr=8-6
    • Would I buy it again? No, I would spend more money and buy this one: https://www.amazon.co.uk/SainSmart-...keywords=Sainsmart+3018&qid=1601798817&sr=8-3
    • Why? Because having spent hours reading web pages and watching Youtube videos I think Sainsmart offer much better documentation & product support. More importantly this machine has limit switches which I now realise are necessary if you are going to use the machine a lot.
    • Can the cheapo 3018 driven by me approach the standards reached by Giles with the Stepcraft or Tim Watson using his very elegant Stevens manually operated machine? Probably not.
    • Can it do what the adverts say? Definitely, it is very capable of producing accurate and quite complex shapes in wood and plasticard.
    • Although I bought the machine just out of curiosity and to see if I could learn how to program in G-code I also hoped it could profile cut parts in brass sheet to save me using a piercing saw, an activity which sets off my carpel tunnel syndrome like no other. So far it hasn’t really succeeded but I haven’t given up hope. Using pointed D cutters it will cut straight and curved lines very slowly (and accurately). The cutters tend to break when turning sharp corners so I gave up trying. I think there are 2 main reasons for this,
    1. The spindle motor on the standard 3018 doesn’t rotate fast enough for very small cutters. Its supposed to do 9,200 rpm but my laser rev counter says mine is flat out at 8,600. I think Giles’ Stepcraft is probably approaching 20,000 rpm? Motor upgrades are available and I think Simon has one, although they don’t appear to run much faster. I have wondered about fitting a Dremel motor, not done any research yet.
    2. I started using Turbocad and a free G-code generator called Carbide Create which is very easy to use. Unfortunately I soon found CC which is designed for driving large woodworking mills has a couple of serious glitches for my purpose and is too simple for machining metal; when it comes to a 90* corner it just turns the corner with no adjustment to speed, depth of cut etc and that is when the bits snap. Writing G-code manually worked better. I have since been learning Fusion 360 and the built in G-code creator in the software appears to produce lead in and lead out ramps etc. Not tried it yet.
    There are some really useful tutorials on Youtube and the best tip I have found so far is to use blue 14-day masking tape Professional UV Resistant 14 Day Masking Tape 25mm x 50m and 2-part mitre adhesive Mitre Adhesive Kit 50g + 200ml for holding flat things on the bed. The idea is you stick a layer of masking tape to the top of the machine bed and another layer to the bottom of the target material, then glue the 2 non-sticky layers of tape together with the very quick setting mitre adhesive. The machined item is held to the bed very firmly yet is quite easy to remove from its layer of blue tape when finished Since trying it on the 3018 I’ve used the idea for quite a few other projects.

    Photo is my machine set up on the kitchen table to machine the cab floor for a J50 out of plasticard. It would have been much quicker to do it by hand but it was more fun with the machine!
    Robin

    3018 J50 Floor.JPG
     
  4. Giles

    Giles Western Thunderer

    Indeed - for small cutters (0.8mm) I run at about 20,000rpm using a Proxxon IBS-E, or it's longer nosed cousin, which is the same but sometimes found cheaper. I have destroyed one of these so far (it is very hard on a drill, not designed for long continuous cutting, particularly with side loads.....)

    For holding brass or nickel silver down, I use double sided tape Tesa 4939, as recommended by Roy Link, and thus far it has served me well.......

    Now I've mostly got feed and depth rates sorted (mostly....!) The most common cause of breakage for me is the job moving at the end of the cut, or similar. The V-carve program I use allows me to place tabs to hold the pieces, and this certainly helps..... I still get breakage though. I build-up of chips can also be a problem, so I've rigged up a vacuum system which sorts that. Previously I chased it round with a brush or vacuum....
     
    Dog Star and 3 LINK like this.
  5. eastsidepilot

    eastsidepilot Western Thunderer

    For holding sheet metal down for milling on my pantograph miller I also use double sided tape and stick it down to a sacrificial board. I have found that the plastic coated cork dining table place matts are ideal.
    When it comes to releasing the work piece I use an old hairdryer or a hot air paint stripper at a sensible distance then wash the residue off in a metal tray with some white spirit and a brush.

    With regards to cutter breakages obviously speed/feed rate is important and as Giles mentions above it's at the end of the cut. With my miller being a old manual Taylor Hobson I have the ability to stop short of the final cut and raise the cutter and plunge cut the final cut if need be.

    Col.
     
    AdeMoore likes this.
  6. simond

    simond Western Thunderer

    Thanks both.

    it appears that the two Models that Robin linked are from the same school of design as mine, at least they have those same Z-axis & motor assembly, which seems to me to be a weak area. I’m thinking of how to improve mine (which as I mentioned, has a crack) and hope the fix will be useful for anyone else with the same unit.

    I’ve no idea how fast mine goes, speed control seems to be off, dead slow, a bit quicker, flat out. Pretty sure it’s nowhere near 20k. Probably same as Robin’s.

    I fell into the trap of googling Stepcraft.

    Cheapo...? No.

    I think their approach is 100% brilliant. A modular 3/4 axis system that you can fit loads of different end effectors (milling, 3D print, hot point for pyrogravure, laser, etc.) onto, and use the same chassis for loads of stuff. Having just bought a fairly large toy (see hairy bikers thread) that’s not happening anytime soon!

    Robin, I can post the details of the limit switches I’ve fitted if it would help. It certainly made my life easier.

    Atb
    Simon
     
    AdeMoore likes this.
  7. michl080

    michl080 Western Thunderer

    Robin,

    many years ago I had a training at milling machines and learned that you always need to work against the direction of the turning cutter. I believe the correct English technical term would be "upcut milling", in German it is "Gegenlauffräsen". This might be another reason for breaking cutters in corners.

    Michael
     
    AdeMoore likes this.
  8. simond

    simond Western Thunderer

    It’s interesting, with my manual mill (an aged Dore Westbury) I would certainly do that, but the advice our supplier gives for the large (expensive, rigid) CNC machines at work is the opposite. Given the lack of rigidity of these little machines, I’d probably go for conventional.

    Useful explanation here;

    Down milling vs. up milling

    Atb
    Simon
     
    AdeMoore and michl080 like this.
  9. Boyblunder

    Boyblunder Western Thunderer

    Thanks for all the advice guys. I have ordered some Tesa 4939 tape to compare and would like info on how you fitted the limit switches please Simon. The control board on my machine does have input pins for the limit switches and I have the kit to make the plugs for them but I haven't got the switches or worked out how to fit them yet.

    Michael's info on the direction of milling is very interesting, as a novice I didn't know the difference. I'm not sure it applies to what I have been failing to do, my tiny brain is struggling to figure it out. The spindle motor rotates clockwise like a conventional drill and I have been using the V cutters shown in attached photo to plough through 0.4mm (15 thou") or 0.28mm (for a smokebox wrapper) brass sheet in an attempt to replicate an etching pattern so whichever direction it travels it is cutting Up on one side, Down on the other side and ? in the centre - I think.

    The V cutters that came with the machine are supposed to be 1/8" shaft 20 degree 0.1mm tips and it also came with a set of small conventional end mills that work very well in wood, not tried in brass. Eastsidepilot directed me to a better quality 0.8mm 2 flute end mill for machining solid brass, not tried it as I don't have confidence in my programming ability yet. The V cutters are cheap as chips so I bought a pack of 10 Genmitsu replacements. As you can see from the photo they are almost but not quite identical to the originals although my efforts at measuring with an Aldi vernier suggest both types have a smallest diameter of 0.2mm, not the 0.1 stated. Several people have suggested I need CZ120 brass for machining but it doesn't seem to be available as thin as 0.4 mm. Do you think I'm attempting the impossible?
    Robin
    V cutters sml.jpg
     
    AdeMoore likes this.
  10. Giles

    Giles Western Thunderer

    If you are Profiling as opposed to engraving, I suggest you use 'D' bits - also available from Chinese suppliers. I had no real luck with conventional milling cutters for the work I was doing (frames, coupling rods, cylinder end covers etc. From brass and nickel silver), but have had consistency with 'D' cutters - including breakage of course! I confess I also tend to use whatever brass or N/S I have to hand, rather than searching out the correct grades - but that's just me....

    The smallest I use is 0.8, and I most regularly use 1.6mm, and of course the 'D' cutters are parallel sided for 5mm or so, allowing decent side profiles.

    I would have thought these would have no trouble cutting through your brass if you use light enough settings (say 0.4mm per second, 0.2mm depth)


    10Pcs 3.175X0.8mm Parallel Carbide CNC/PCB Milling Cutter Bits CEL | eBay
     
    Last edited: 5 October 2020
  11. simond

    simond Western Thunderer

    Giles

    thanks for the heads-up on the D-bits, I've not tried them, but will do so.

    Robin

    will post some pix later in the day. I used very small microswitches, and fitted them with 10BA screws. I think the switches were something like these:

    upload_2020-10-5_13-16-47.png

    I think mine have the pivoted lever but given the vibration, you might be better with the sprung lever.

    atb
    Simon
     
    AdeMoore and Boyblunder like this.
  12. eastsidepilot

    eastsidepilot Western Thunderer

    Robin,
    I'm cutting most types of brass and nickel for locomotive parts at 18,000 rpm with straight 2 flute coated cutters of 1.0-1.5mm dia. some times smaller, but this is on a manual machine. Not had many breakages which is normally when the cutter has turned blunt.

    Tapered or v cutters wont give you a square edge. As regards direction of cut it's anti-clock for outside a component and clock-wise in a hole, but again this is with a manual machine where the pantograph follower is following a pattern but it does make a difference.


    Col.
     
    Last edited: 5 October 2020
  13. Boyblunder

    Boyblunder Western Thunderer

    Thanks for more advice. I've ordered a set of D cutters that should arrive by the end of the month thanks Giles, they don't seem to be available in the UK. Until you posted the link I thought D cutters and V cutters were the same thing. By chance 6 of the spring lever Omron switches are already in stock for an unbuilt signal lever frame so I'm good to go, some pictures will be useful Simon. Thanks again Colin. I'm going to do some more practice with Fusion 360 and check that the G-code it produces matches the advice, if not I know how to reverse it manually. Candle / GRBL Control both provide simulations of the tool paths so no tools will be harmed while playing.
    Robin
     
    AdeMoore likes this.
  14. Giles

    Giles Western Thunderer

    I've just been making some outside cranks (0-14) from 1.6mm brass. These were done in their entirety with an 0.8mm cutter, at 0.2mm depth of cut and 0.5mm/sec pass speed. I suspect the loads on the machine frame are very low during this process.

    [​IMG]2020-10-05_04-58-56 by giles favell, on Flickr

    [​IMG]2020-10-05_04-56-38 by giles favell, on Flickr
     
  15. Giles

    Giles Western Thunderer

    Note in the top picture that the crank are still held in position by two small tabs on the left, preventing disaster. They are easily pinged out with a small screwdriver. Each crank has a machining time of 5 1/2 minutes
     
  16. simond

    simond Western Thunderer

    Limit switches... there are two on top of the X carriage, which contact the trunnions at each end of travel, and a third switch on the side to capture Z-max.

    image.jpg

    These are connected thus, hopefully you can follow the colours despite the rather dull photos, for which I apologise.

    image.jpg

    The final switch is on the Y axis which gives Y-min.

    image.jpg

    A further view of X-max (left, this is the rear) and X-min

    image.jpg

    Hope it helps, shout up if you need anything!

    atb
    Simon
     
    AdeMoore, Boyblunder and Dog Star like this.
  17. eastsidepilot

    eastsidepilot Western Thunderer

    I also leave small tabs when cutting very fine thin parts that could be liable to move such as cab window frames and beading etc. I release them with a plunge cut on sheet metal.

    Col.
     
    AdeMoore and Boyblunder like this.
  18. simond

    simond Western Thunderer