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IndustryArena Forum > Other Machines > PCB milling > Which bits to use for PCB milling?
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  1. #61
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    Re: Which bits to use for PCB milling?

    Hi zqrlsm,
    Jesper, Roger and I have been talking about etching circuit boards with really thick copper layers.
    I have PCB blank with 0.42mm (0.0165 inch)copper layers. Ordinary V tools are no good for this
    thick copper stuff.

    For that you need small diameter endmills, I use 0.5mm (and on occasion 0.4mm) endmills. The trouble
    is that they are very fragile and your milling technique needs to be spot on. Additionally carbide endmills
    are cheaper the smaller they get until about 3mm, smaller than that they start costing more.

    Jesper was contemplating using 0.2mm endmills, that's 8 thou!!!.....but I think he is coming to the conclusion
    that it is too ambitious for hobby use.

    I have successfully made surface mount boards with this heavy copper with SOIC outlines of 0.6mm between
    pads. Amongst the things I have to do to achieve it is use flood cooling. It might sound weird to most people
    using isolation routing but flood cooling was the last piece of the jigsaw I needed to make these boards.

    Craig

  2. #62
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    Re: Which bits to use for PCB milling?

    Hi Jesper,
    looking on the PCB Materials website nothing useful in 6/6 oz half a dozen choices including a couple of polyimide boards in 5/5 oz
    and some useful 7/7 oz as well.

    Craig
    Attached Thumbnails Attached Thumbnails 5oz5oz.png   7oz7oz.jpg  

  3. #63
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    Re: Which bits to use for PCB milling?

    Hi Craig ... I am just considering what to do ... Will get back shortly ;-)

    Cheers,

    Jesper

  4. #64
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    Re: Which bits to use for PCB milling?

    Quote Originally Posted by evalon View Post
    Hi both .. Just a brief reply as the evening is closing in ...

    @A_Camera: Thanks for posting & linking to your video. IMHO it looks quite good the aluminum you have milled. I also took a look at your youtube video list and noticed the difference between your Z-axis spindle assembly #1 and #2. And I guess that a major part of my issues are related to a Z-axis spindle that is neither sufficiently rigid nor has the weight in the right places (and maybe the router motor). Regarding your link to Jula I couldn't sign up as it appears that one has to be from Sweden - right? When signing up there is no option for other countries ...

    Jesper
    Hi,
    I don't know what you mean by Z spindle assembly #1 and #2. I had 2 spindle motors, the first one was a DC motor and the second one is the one I am using now, which is a 1.5kW brushless motor driven by a Bosch inverter. I broke the first fixture and had a temporary fix, but that lasted only a few weeks, until I received a new one.

    Regarding the link, I don't know if you can register from Denmark for their web shop, but there is a large Jula shop just after the bridge (Svågertorp), so depending on where in Denmark you live, it might be nearer than you think... if you decide to visit the shop phone them to check that they actually have the items you are looking for because they don't always have everything in every shop.

  5. #65
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    Re: Which bits to use for PCB milling?

    Hi all,

    I did some more tests today and I must admit that I am a bit put off by the results. And I am not sure I can make this CNC be as rigid as I would like it to be. So I am considering something else and to this end have a question: The various linear bearings typically are called "15", "20", "25" or the like from many different manufacturers, indicating the linear bearing's width as far as I can see. Do you know if it will be possible to buy e.g. block carriages from one manufacturer - and if the e.g. "20" size is the same - and then use linear rails from another manufacturer? It is slowly and unpleasantly dawning on me that rigidity & weight are key parameters.

    Although not myself so cheerful nevertheless a good day to you,

    Jesper

    P.S.: @A_camera: It won't be feasible with Jula as I live on the entirely opposite side of Denmark - some 300 kms from Copenhagen. And somehow I must have seen a different Z-axis video on youtube - describing how the user made a new z-axis fixture. So it happens

  6. #66
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    Re: Which bits to use for PCB milling?

    Hi Jesper,
    yes officially a size 15 car from one manufacturer will fit on size 15 rail from another.....don't do it.

    I assume you are talking the 'square' rail type? It is by far the most rigid but also the most expensive type.
    What you need to look for is that it has four rows of recirculating balls. I will dig up the model code
    for the THK cars that have the four rows and you would select those or another manufacturers direct equivalent.

    I use 15mm rails and cars from Bosch Rexroth. I bought them second hand, they are way out of my price range when new.
    I got them from Korea off a trader there and whom over a period of a couple of years bought several thousand dollars worth of
    stuff.

    https://www.ebay.com/str/industrialpartsshop

    this is an example of the stuff he sells:
    https://www.ebay.com/itm/THK-HSR20R2...sAAOSw8w1X5x8m
    $250us for 20mm (that's seriously strong/rigid) heavy duty rail/cars from THK, one of the premier manufacturers.

    If you want to but new then look at Hiwin, a Taiwanese manufacturer. Note that if you go to Aliexpress or the likes there will be any number
    of Hiwin lookalikes with the same part numbers and everything, buy with care.

    Craig

  7. #67
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    Re: Which bits to use for PCB milling?

    Hi Jesper,
    the manufacturers of these rails and cars have over a period of years invested tens or maybe hundreds of millions of dollars building
    superbly accurate machinery, grinding machines, heat treating equipment and so on. When we buy these expensive components what we
    are doing is buying a 'slice of all that production excellence' so we can bolt it into our machine without us having to make such a huge investment.

    Therefore any compromise that reduces the potential accuracy and rigidity of the components make a complete mockery of the high price
    paid for the parts. For this reason I would not recommend mixing components from different manufacturers in one rail or even one axis.

    The link I posted earlier featured THK rails and cars, the cars are of the HSR series. The HSR series is the heavy duty model of choice from THK.
    All of the manufacturers have equivalent models but it is by no means easy to determine if a particular car has the superb properties of the HSR
    series. For instance each manufacturer has models with two rows of recirculating balls, one on each side as opposed to two on each side,
    also called 4 point of contact, and such cars have dynamic load less than 1/4 of their similar looking cousins.

    My own experience is that second hand units have proven to be very good and approximately 1/4 that of new. Extensive research on each
    of the models is required. THK, NSK, IKO, Bosch Rexroth and Hiwin are likely to be the most abundantly stocked brands and it is worthwhile
    studying the catalogues of each to identify the genuinely good models from the merely adequate.
    Craig

  8. #68
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    Re: Which bits to use for PCB milling?

    Hello again Craig ... I intended this to be a brief message but I can see that it has grown ... I'd like to start out by saying that what you have posted in your previous two posts are very interesting to me. So thanks for posting this information

    One thing I do know though is that I won't have the time or energy to dig deep into how to design a second-to-none CNC. The reasons for this are two-fold: First it is not my main focus area (it is audio electronics) and second I mainly need a CNC in order for me to make things. That said contemplating (and feeling my mood) in relation to the CNC I have now bought - and which most likely won't work as expected - I know that I will have to arrive at a quite better solution this (the next) time.

    To this end: Any chance you will be fine with posting a picture of your CNC (or sending it in a PM)? It would be helpful for me to see what a well-functioning CNC looks like and how the design priorities appear to have been balanced.

    Also I found it very positive to read that you have used 15 mm rails. It potentially makes a design process less costly although I understand that your rails/cars are not any run of the mill.

    In any case this morning I made a search for rails/cars on ebay Germany and the most common types actually are from THK and Bosch Rexroth. There also is a seller who has a set of 14 cars from Hiwin (20mms ) up for auction:

    https://www.ebay.de/itm/Hiwin-F%C3%B...59.m1431.l2649

    Of course I don't know what the selling price will end up being but if I bought these it would cover all my "car" needs and then I would "just" have to find some 20 mm rails. However, these appear to NOT be up for auction so frequently. So unless you say that some other rails would work well with Hiwin I would be cautious here. A question comes up in this context: Are such linear rails reasonably simple to cut? I have access to a metal saw and thus could buy a longer rail that could be cut in two.

    Other options are these:

    https://www.ebay.de/itm/15-300mm-Lin...YAAOSwFxtbK3As ... 15mm HSR types BUT from a Chinese manufacturer called Vevor. Would be perfect though as they also sell some longer versions. And delivery is from Germany. ... Can I ask you what you think about it?

    https://www.ebay.de/itm/Linearfuhrun...kAAOSwdrlbc082 ... Bosch Rexroth 25mm but likely not the best type car.

    https://www.ebay.de/itm/1-Satz-25er-...kAAOSwQWFahWwj ... Bosch Rexroth 25mm, best type car (I think), but only two cars. If this would be sufficient it might be used as a Z-axis.


    If I could find an additional appr. 42 cm length 15 mm rail + cars then this combination could also be quite interesting:

    https://www.ebay.de/itm/THK-SR15W2UU...4d73%7Ciid%3A1 (y-axis)

    https://www.ebay.de/itm/2-st-THK-HRW...k/142912091922 (And then maybe this for a Z-axis)


    For a structural design I may have access to some 15 mm thickness 5457 aluminum plates that are cast aluminum. Do you think these would be sufficient for the structure of a quality CNC (x-axis, z-axis, possibly y-axis)?

    You also asked me which router I use. And I use a Kress 6990E going from 8000-24000 rpm and with collets of 3.175, 6, and 8mm. Eurohals 43mm mount. 900 watts. As it is I don't think the bearings on this router are very precise but it is virtually new so probably as good as this design allows. For a start I'd prefer to bring this router into a new design. The stepper motors are Nema 23 270 oz types driven by DM542s with a plentiful power supply.

    In one of your previous posts you also linked to some PCBs from PCBmaterialworld. As it is I need the base material thickness to be quite precisely 0.2 - 0.25 mms - one option here I have come to think of is to contact with a PCB manufacturer and have them make a laminate to my specifications but without etching etc. I think this may not be too costly - and I could buy them again & again if this need arises.

    If you got this far then thanks for reading and for any assistance ... I'd also like to say that in the days to come I have to focus more on my normal "day-work" so I likely won't be able to investigate/reply in much length ... but I will be looking into the auctions on ebay - and if you think some of the links above (maybe the THK or Vevor linear rails?) are good they could be an option ...

    Cheers from up north,

    Jesper

  9. #69
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    Re: Which bits to use for PCB milling?

    hi Jesper,
    Are such linear rails reasonably simple to cut? I have access to a metal saw and thus could buy a longer rail that could be cut in two.
    The steel rails are hard and very tough, you can cut them with a grinding disc only.

    Those Hiwin cars look good but I think 38 Euro is too expensive. You could buy the rails and cars cheaper from China even including
    shipping and tax.

    If you insist on buying European be prepared to pay a lot extra.

    For a structural design I may have access to some 15 mm thickness 5457 aluminum plates that are cast aluminum. Do you think these would be sufficient for the structure of a quality CNC (x-axis, z-axis, possibly y-axis)?
    depending on the design they sound good, you really need a T section or Box section to achieve rigidity, what you have proposed is strong but
    strength is NOT the same as rigidity.

    I have come to think of is to contact with a PCB manufacturer and have them make a laminate to my specifications but without etching etc
    I'm sure they would be delighted to entertain your query, for a minimum order of 1000 square feet say!!!

    Craig

  10. #70
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    Re: Which bits to use for PCB milling?

    Hi,
    those SR15 and HWR links are a poor chioce, I think you'll find they are two row cars, a lot of money
    but not really good enough. You want HSR cars.

    You need to decide whether you want 'adequate' or 'good'

    Craig

  11. #71
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    Re: Which bits to use for PCB milling?

    Hi Craig

    Thanks again for commenting.

    You need to decide whether you want 'adequate' or 'good'
    ... I think you are right here. Unfortunately I don't have a good practical reference allowing me to assess what "good" versus "adequate" quality milling looks like - nor what the full implications of going either way may be in terms of:


    - the ability to find good parts second-hand
    - price level
    - the complexity of design, materials and build (including the need for flood cooling, MQL etc.).


    Thus I am trying to navigate just as I best may in a field that is new to me - and where admittedly my financial resources are limited. Not least now where some of them are tied in a machine that likely won't work as I expected it to.

    On the other hand I am aware that you have a quite uncompromising and quality oriented approach to this - including what I perceive to be a good experience of what is needed to achieve a very good CNC milling quality.

    Hmmm ... Would a place to "meet" "quality-wise" be to search for block/rail solutions in the THK HSR15 series? I've made a search on the supplier you linked to the other day (dy-global) and he has some THK HSR15 offers that are also price-wise accessible to me. Also since he offers free international shipping I could buy the parts successively and e.g. start out by modifying my current CNC until it works as I would like it to. Should I then at a later point in time decide to go the "full monty" I can transfer these THK parts to a new and better machine. Would be fine with me ...

    A place to start could be this:

    X-axis

    https://www.ebay.com/itm/THK-NNB-HSR...AAAOSwldZbDh4X ... to be used for an X-axis. These are new! .... OR these used

    https://www.ebay.com/itm/THK-Used-HS...cAAOSw-VtbD303

    If using the latter then one of the rails could be cut into two Z-axis rails - if I can find a couple of additional HSR15R2UU cars (or a suitable replacement - any ideas here?)

    Y-axis

    https://www.ebay.com/itm/LM-Guide-TH...gAAOSwPhdU4sVd

    Z-axis

    https://www.ebay.com/itm/THK-HSR15AQ...MAAOSwcLxYMkwf ... OR this one ...

    https://www.ebay.de/itm/1-Satz-25er-...kAAOSwQWFahWwj ... notice that there are only two cars but "25" size and according to Bosch-Rexroth a very good quality https://www.boschrexroth.com/en/xc/p...at=LT&o=portal )

    Can I ask you what you think of these options? Except maybe for the Bosch selection they are all THK HSR types as far as I can see.

    Cheers,

    Jesper

  12. #72
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    Re: Which bits to use for PCB milling?

    Hi Jesper,
    I've looked through those links and any and all of them are good.

    My comment about adequate/good was a reference to the parts that you had linked to. It may not have been apparent to you but they were of lesser quality
    than this latest batch of links. The price of the lesser performing units is about 2/3 of the much better units that you are now looking at.

    The first units (SR & HRW) are 'adequate' whereas the HSR units you are looking at currently are 'good'. They are more expensive but not dramatically so.
    It would appear that you have done some intensive reading of various catalogues and are now starting to pick the good ones from the merely adequate ones.
    I have to agree I think dy-global's prices and extensive inventory is very valuable and may help you as much as the site helped me.

    You have stated that your first passion is audio electronics. It would be very easy to invest large sums in your CNC machine and leave little left for your
    main interest. I think that its worthwhile to take some time before committing to any purchase that you may balance it with other commitments and desires.
    My first interest was, and to a certain extent still is, RF electronics. I wanted a mill for circuit boards. I thought that if I was going to do that I would make the mill
    capable of machining metals, steel in particular. In so doing, without me being aware of it, my hobby changed from RF electronics to CNC.

    In the sense that both are learning curves they are both valuable as hobbies, 'learning' being the prime benefit of any hobby in my estimation.

    The principle determinant whether you are a CNC enthusiast or whether you have a CNC to advance your real hobby, audio electronics, is rigidity.
    If your intention is to make boards for your audio work then a simple/cheap/low rigidity router, even a Chinese one would probably be adequate.
    If however you want to do a good job in easy metals like aluminum, brass and copper then a marked increase in rigidity and cost is required. The cheap
    Chinese routers are pretty marginal for that work. If you want to mill steel then gantry type routers are not really want you want. You need to look to
    something like a small bed mill. My mill is such a design. Then downside is that the cost and complexity have taken me some way from my original
    intention.

    Another thought that you may have to balance is that if you decide for instance that you want/need components a,b and c for your machine but can't afford
    item d then you've spent a lot on a,b and c but NOT got the advantage you hoped for because of the lack of item d.

    In my case what happened was I had spent significant money on linear rails/cars, 5 phase steppers with low lash planetary gearboxes, C5 ground ballscrews,
    direct offline highvoltage stepper drivers, made cast iron beds for each axis and a slick German made high speed spindle. All that hardware amounts to something
    like $5000. But I found, much to my disgust, that I still could not really mill steel, the spindle, while really nice, is high speed/low torque, whereas I needed high
    torque/low speed for steel. My item d.....I had spent all that time and money and not quite there yet. It took another 18 months before I 'bit the bullet'
    and made another spindle for my machine, another $2000.

    Thus it pays to stand back a bit and plan, in general terms, a budget that sees the project through to completeion. I had expected to spend similar money to that
    I might have spent buying a complete machine but end up with something better. I did end up with something very satisfying, all my own work, but it cost a lot
    more than I thought when I started. I've learnt plenty on the way so I feel OK with it but if you have a definite/limited budget it would be upsetting.

    Craig

  13. #73
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    Re: Which bits to use for PCB milling?

    Hi again Craig,

    Hmmm ... your previous post treads many paths as I read it. Both practical and some thoughts about priorities in life and not least hobbies. It made me think yesterday and - in being practical here - what I can say is this:

    About priorities

    - I know quite well my direction in this and additional to what I have written - audio electronics - my use for a CNC is overall "audio related", i.e. also the parts that include transducers, enclosures etc. However, I won't be making e.g. loudspeaker drive units. Thus I am as sure as I can be that steel or stainless steel won't be focus fields for me. Materials to work with will be - as I have written - copper (not just PCBs), brass, aluminum, possibly bronze - and then wood and some plastics. But I guess that wood and plastics are the least demanding so I have not included these materials in my previous post as a "need to be able to do". Should I some day need materials made in steel or stainless steel I would contact a workshop that can work with these materials.

    - What I mainly need is a high precision machine for quite small sizes: I.e. no more than 200 x 250 x 50 mm cubic. What matters most here is that the Z-axis can make leveled surfaces - if possible down to 1-5 um precision over the full size (200 x 250 mm. Absolute precision is not that important but relative precision, i.e. a level surface, is). I will do likely 85% of all work within this size frame and - most importantly - this is where I will be milling metals. Mostly, and most importantly, copper and copper alloys. High milling speeds are not that important. Precision is much more important and typically depths into the material will be no more than 5 mms.

    However, for the last 15% of my work I need a machine that is capable of doing larger sizes - preferably up to 360 mm in the x-axis direction and then up to 500 mms in the y-axis direction. BUT ... if it is a gantry machine the y-axis material length can be longer as the material can be moved. Thus, my main need is to have this 360 mm x-axis work area - and then preferably up to 100 mms in the Z-axis plane. The practical work area therefore can be x, y, z: 360 x 300 x 100 mm. (an additional 100mm y-axis for fastening). ... And if there can be a practical way to move the Z-axis spindle holder e.g. 50 mm up & down then the Z-axis movement length can be kept to 50 mm iff this heightens the precision.

    About economy

    My funds undoubtedly are really limited so I have to make the CNC mill structure myself (here concluding that my current CNC will not work) - something I would guess that I likely can. I have access to a genuine steel NC mill - that is numerical control but not CNC. And I have access to a metal workshop.

    My limited funds also means that I will have to buy wisely - i.e. "best buys" - or make choices that lead me outside of the traditional product/purchase field (new/expensive brands). By saying the latter I also mean that if someone somewhere has found a way to design e.g. a high precision spindle that is not very expensive then this may/might be for me. Or similar approaches in other areas. Again with a reasonable amount of time spent. I notice here that both you and Roger have designed your spindles yourself, however, it is my impression that these are high torque spindles more than high speed spindles, right? In any case: The spindle/router I have now I may either sell or - initially - bring to a new design. But my funds are indeed limited here so a wise choice has to be made - remember here that milling speed is not a high priority.

    What I have

    I think the stepper motors (nema 23, 270 oz), the drivers (DM542), and the PSUs are quite good. 4 pcs stepper motors so can be used for a gantry machine (2 y-axes), or one drive below the milling plate. I won't mind replacing e.g. one of the stepper motors with a higher torque version e.g. for a high weight Z-axis. The drivers can deliver 4.2A and are driven from 38 VDC if I remember correctly.

    I can do 3D drawing and so it should be feasible to draw up a CNC mill to these specifications. FYI I have attached an example of a mill I drew up some months ago.

    What I learned yesterday
    It would appear that you have done some intensive reading of various catalogues and are now starting to pick the good ones from the merely adequate ones.
    Well, actually I had not read any datasheets but given that you appear to have insights into this field I decided to give dy-global another look. And having read your post I decided to study the datasheet for the HSR cars and the Bosch-Rexroth car that I linked to. And I found that two HSR15 cars placed closely together essentially have better load characteristics (static moment) than just one of the HQ Bosch-Rexroth cars of "25" size (the one I linked to). Also that there is approximately a 2x difference going from HSR15 to HSR20 to HSR25 etc.

    I also took a look at cast iron and "machine steel" items on ebay and they do indeed look very, very rigid - and heavy.

    What I am thinking

    If possible I would like to make a new smaller & very precise CNC mil. Work area 360 x 300 x 50/100 mm - within the confines of my budget. Considering that milling speed is not that important I reckon the main challenge will be the spindle's cost (unless a creative solution can be found here). I might start with the router I have and then replace it when budget allows.

    I reckon that the most important characteristic of a CNC is that the strength, rigidity & weight basically is localized exactly where the cutting bit meets the material. Thus, a weighty, rigid and precise Z-axis is key. Also that the milling plate is rigid. With this in mind I am thinking that maybe a spindle holding plate of steel or iron may be better than an aluminum plate. That said, I have access to e.g. a 20 mm thickness aluminum plate, or a 15mm plate from cast aluminum.

    For the z-axis maybe an HSR20 or HSR25 size may be better (IF at all available at reasonable cost)

    My limitations
    Time & money.

    The time constraint likely means that I will have to go "a known way", i.e. make assessments & decisions that do not require too much of my time or attention. This is a real constraint, unfortunately.

    It also means that the machine needs be ready in a not too distant future.


    Where I suggest starting

    If tjhere's any chance I can ask you to evaluate 3D drawings I make I would start out by making a 3D drawing of a CNC mill the size I have outlined. I would base it on the HSR15 parts - possibly with a larger one for the Z-axis spindle mount, if available. And 12 or 15 mm ball screws - as you suggest. Main supplier dy-global. I reckon the machine would be either gantry or bed mill - if a bed mill can accept up to 500 mm lengths in one direction (here precision is less important). What do you think about this? The main aim would be a small precision machine - and likely a replaceable spindle, unless a creative solution here can be found.


    Well, whewww! ... many words. Thanks for reading, Craig - I hope you got through in reasonably good shape ... And I would appreciate if you will give me some feedback on this ...

    Cheers from up north,

    Jesper
    Attached Thumbnails Attached Thumbnails CNC-1.jpg   CNC-2.jpg  

  14. #74
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    Re: Which bits to use for PCB milling?

    here that both you and Roger have designed your spindles yourself, however, it is my impression that these are high torque spindles more than high speed spindles, right
    Yes, my spindle is a low speed high torque unit. Industrial DC brushed motors can take a lot of abuse and generate very high torque.
    But no, I did not actually design my spindle, I just stripped it right down and then rebuilt it.

    The size you are suggesting, 360 x 300 x 100 mm, is actually quite large. Many commercial production machines are smaller, although they are likely to have a bigger Z travel - maybe 150 mm.

    Now for the bad news. The design you have is, well, not good enough for a mill. The base is far too light for a mill, although it might be OK for a light router. The vertical arms up the sides will deflect and vibrate badly. If you want to machine metals, you need to go up in mass and rigidity by a factor of at least 4x, although I would prefer 10x. Sorry to be so depressing, but ...

    Cheers
    Roger

  15. #75
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    Re: Which bits to use for PCB milling?

    Hi Roger ... Thanks again for your feedback. Just to clarify: The machine I included pictures of is one I drew a couple of months ago ... Today I would not make it not least because I would expect the vertical arms to be insufficient.

    But 4x to 10x .. are you here considering that I am talking about slow milling speeds and removing thin layers in the Z-direction?

    (Cheers) Jesper

  16. #76
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    Re: Which bits to use for PCB milling?

    Hi Jesper,
    I think you are getting close to setting the main parameters of your design.

    You need a machine rigid enough to do brass, aluminum etc but is not required to do steel. This suggests to me that a substantially
    built gantry mill would be a good choice.

    Bed mills are appropriate for high rigidity machines but require very large sections of either cast iron and/or aluminum. The axis beds need
    extensive machining to make them useful. The cost of the materials and the time and not inconsiderable cost of all the tooling required to machine
    it count against a bed mill design for you. If however you have 15-20mm aluminum plate you could make a useful gantry mill from that.

    Retain your existing steppers and drives.

    The major and expensive items are:

    1) SPINDLE. If you have a Kress router it makes sense to carry on with it. Were you to replace it you'd want something with angular contact bearings.
    I'm not a fan of Chinese made stuff but have to concede that the high speed (24000 rpm) asynchronous spindle motors with VFDs
    offered by Chinese manufacturers are just too price compelling to ignore. Provided your design allows the room and strength to fit such a spindle in
    future you should be good.

    2) BALLSCREWS. 12mm is too small, you should be looking at 16mm or better yet 20mm. Remember that the main bearing block will have to contain the axial
    forces of the axis to which it is attached. The next thing you have to decide is whether you want 'ground' or 'rolled' screws. A rolled screw will
    commonly be C7 grade, ie 50um in 300mm whereas ground screws start at C5, 18um in 300mm, and go upwards in accuracy and price up to
    C1. The highest grades are made to order so I doubt you'll go there. A rolled C7 screw 20mm in diameter 500mm long with bearing blocks
    might cost $150 new. The same sized screw but C5 ground will cost you $1500 new. Ground screws are roughly ten times the price of rolled
    screws. If you want the accuracy of ground screws then buying second hand is the only reasonable way to do so. I got four C5 20mm (5mm pitch)
    450mm long with bearing blocks for $150US each plus shipping. My mill was essentially designed around these items. Rolled screws on the other
    hand are very much cheaper and readily available. With such a wide selection you will almost assuredly find the size you require whereas the ground
    screws you take what you can get.

    3)LINEAR RAILS/CARS. You have already been investigating those. The best rigidity is achieved by two rails placed parallel to each other with two cars on each rail
    and the axis bed/gantry/spindle attached to the four contact points. If you rely on a single car to mount your spindle than any flex in that car on its
    rail will result in flexure of your spindle, it represents a poor design. Provided your design uses matched rails/cars with sufficient separation then 15mm
    rails are adequate. By all means use 20 or 25mm sizes if they are available but generally they cost considerably more and the extra strength is not
    required. A good design with 15mm rails will be rigid enough for your purposes.

    I would start by deciding what ballscrews you want and/or can get. They are expensive and yet they represent the ultimate in what can be accurately achieved.
    If going for ground screws then what's available will dictate the size of the machine to a large degree.

    The next step is as Roger has suggested to decide whether you do a gantry type router or whether you do a bed mill design. I'm thinking a well built gantry design
    is most likely. If you want better results then a bed mill is the way to go.

    Craig

  17. #77
    Join Date
    Jul 2012
    Posts
    89

    Re: Which bits to use for PCB milling?

    Hi Craig ... Once more thanks for your very helpful and detailed feedback. I'll be off for the weekend now but will get back on Monday. Likely things may clarify at least somewhat over the weekend.

    Wishing you both a pleasant weekend

    Jesper

  18. #78
    Join Date
    Apr 2018
    Posts
    11

    Re: Which bits to use for PCB milling?

    Just thought I'd post here quickly on a success.

    I've recently had to go sub-200 micron detail in a circuit, where the spacing between component legs can be from 0.4mm to 0.8mm and the biggest pads are spaced at 1.0mm, The 0.8mm is through-hole too. Just to make it difficult. Generally, Thats about the tolerance limit of my milling process, but I tried a 30degree 0.1mm triangular bit...

    The results were incredible. Clean cuts close to 0.1mm across the board. Solder tins and flows right up to them perfectly. I acidentally sanded some circuit material from the PCB and thought it was still there as the clean lines were still in the base material.

    Here's a pic ( I'm also really starting to understand the value of a good microscope and am using an Andonstar ADSM201 with a 1080P capture card ) - For reference, the through-holes are 0.4mm dia. Spacing of holes is 0.8mm.




    The bits seemed kind of new, so I wasn't sure how they'd work, but so far I'm pretty happy with the results. 11000 RPM brushless spindle, 6 inches/minute feed, on a 6040, using FreePCB, FlatCAM and Autoleveller. Manual change of bit to drill.

  19. #79
    Join Date
    Jun 2010
    Posts
    4252

    Re: Which bits to use for PCB milling?

    Hi evalon

    Yep, all things considered.

    Have a look at the specs for commercial machines. Sure, they are more than you want, but the specs will be educational.
    Then have a look in the epoxy-granite stream here at CNCZ and see how they talk about weight and stiffness.
    Milling any metal is worlds different from routing wood and engraving PCBs. For a mill, weight and stiffness are king.

    As a rule of thumb, if you want to reliably mill to within 0.1 mm, you really need a machine good to 0.03 mm, although I would prefer 0.01 mm. Yep, an order of magnitude better. Imho.

    Cheers
    Roger

  20. #80
    Join Date
    Nov 2012
    Posts
    1267

    Re: Which bits to use for PCB milling?

    The cuts look pretty good! The only thing I would do different is clear some unused copper between the traces to make soldering easier.

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