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  1. #81
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    Default Re: Which bits to use for PCB milling?

    @Roger:

    Yep, all things considered.
    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.
    My goodness ... I just took a look at a couple of the granite mill threads I could find here at cnczone. And I have to admit that it humbles me ... probably better early than later and now more a feeling or "state" than acknowledged and work-able in thoughts and thinking. However, one thought that comes up is if it would be a good solution to include some kind of epoxy/granite into a design. E.g. a "constrained layer" assembly of maybe a steel/aluminum plate and then a cast epoxy granite plate ... I reckon it would really reduce the vibrations of the mill (of course depending on how it is done), right?

    @Craig: Thank you once more for elaborating and explaining. You are really, really saving me a lot of time and likely suboptimal choices! Thanks, Craig ... One question to your post above: When you mention the ground screws you bought I get the impression that those were not bought from dy-global. If this is the case do you then have a suggestion for a good vendor of ball screws?

    I will draw up a crude sketch of a CNC machine today and post it later in the day. Am somewhat inspired by the bed mill type but will see if I (with my current knowledge ) can make it work out ...

    @C-O-D: I never got to give you a feedback on this comment of yours earlier in the thread, but here it is:

    Well, I can tell you the first thing that would happen: you will buy a preheater and the most powerful soldering iron you can find.
    I think you are right, however, as it is I already have a 90w weller soldering iron, a heatbed, and a 700w desoldering station. Hope it is enough - and an additional benefit to giving heat to thick PCBs may be that I may also otherwise appreciate the extra heat now that autumn and winter is approaching here in Denmark

    Cheers to you all,

    Jesper



  2. #82
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    Default Re: Which bits to use for PCB milling?

    Hi Jesper,

    When you mention the ground screws you bought I get the impression that those were not bought from dy-global
    You are correct, I got them off a guy in Malaysia, he had a swag of them so I got four. I don't have a goto supplier, ground ballscrews are
    rare and precious, you take what you can find when you can find them.

    Craig



  3. #83
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    Default Re: Which bits to use for PCB milling?

    Mass and thickness . . .
    all very good.

    Be warned: I incline towards the precision end of things. For a router that might be a bit over the top - but for making PCBs for modern fine-pitch chips, not so much. You end up needing the precision - until you eventually go photo-etch.

    Cheers
    Roger



  4. #84
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    Default Re: Which bits to use for PCB milling?

    Hi all,

    So I have been drawing for some hours now on a design that came to inspire me: I reckon it is sort of a bed mill although - well, one never knows ... I don't know the exact criteria for a bed mill. But I hope I can ask you to take a look and gently comment ;-)

    I have attached a couple of pictures of the mill so that it can be seen from two angles. A couple of comments:

    * It is a sketch as I prefer to clarify the basic design before going into details.
    * The usable movement is x,y,z: 250 x 200 x 120 mms. And then if larger items are to be worked on then they must be moved.
    * The dark grey plates are made of 40mm steel. The light grey rectangular rods are made from 50x30 mm aluminum.
    * Except for the vertical distance of the cars on the Z-axis the spacing between the cars (maximum distance between the distant edges of the cars) is either 200 or 250 mms. The vertical spacing between the z-axis cars is 180 mms. All rails are HSR15 rails & cars.
    * The brownish cube are epoxy granite as described in this post:

    https://www.cnczone.com/forums/epoxy...ml#post1996146

    The framework at the back of the mill is to be filled with this epoxy granite as well.

    * I don't yet know how much work is involved in making such a mill nor what the cost is so there are at least these two reservations in terms of actually making it.

    That said my guess is that it can be really rigid, and also well damped due to the epoxy granite fillings.


    Can I ask you what you think about this? One thought I have had myself is if the HSR15 rails+bearings will survive such a placement in the long term if they are not covered ... ?

    Cheers & thanks,

    Jesper

    Attached Thumbnails Attached Thumbnails Which bits to use for PCB milling?-mill_v4-jpg   Which bits to use for PCB milling?-mill_v3-jpg   Which bits to use for PCB milling?-mill_v2-jpg  


  5. #85
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    Default Re: Which bits to use for PCB milling?

    Hi Jesper,
    that diagram is very much the basic structure of just about all vertical machining centers. Depending on construction you can make it as rigid as
    you require.

    My mill is very similar to this. I got some big cast iron weights that had been used in an elevator from the scrap yard and I made the beds out of solid
    cast iron. As it turns out the cast iron in the weights was poor but it did work out OK but it took a lot of milling. I also used a solid 80mm x80mm X500
    piece of steel as the vertical structure rather than the aluminum frame, it was a piece of surplus from work......the price was good....free!

    May I suggest that you have more Z travel, as much as X or Y at least. Once you build it you will want a vice or other clamping arrangements in addition
    to a spoil board for PCBs and the vertical travel is essential. The spacings between rails and cars all sound about right. In the event what you can actually do will
    in large part be determined by the components you can get. If you buy new then you can get whatever dimensions you want, if buying second hand,
    particularly ground ballscrews then you will be constrained by availability.

    My mill has travels 180mm x 180mm x 180mm. The ballscrews have a somewhat greater travel and I should have been a bit more patient about getting
    the rails and cars, I could have had greater travels with longer rails. All of the rails/cars I used are 15mm. They have proven adequate. Mine are likewise
    exposed and probably not long for this world! A lot of design and precision manufacture of shielding and screening goes into industrial machines to ensure
    maximum machine life. You and I are not really likely to wear this stuff out as hobbyists.

    Given that you are in Europe you may have more luck than I when trying to find cast iron, it is preferred over aluminum, particularly vibration damping.
    I was looking for approximately 250mm x 100mm continuous cast sections, and there are a couple of companies worldwide who do so. The freight
    to New Zealand was just out of reach. I found that the local foundry was an expensive option also. Since that time however I have made the acquaintance
    of a very experienced foundryman who can do up to 65kg of iron in a hit. If I were to do this again I would get the beds cast to order. I would make the patterns
    still.

    All in all you are looking at a substantial machine requiring hard to get top quality parts and materials and many hundreds of hours in the design and making.
    It rather sounds that you are making the transition to 'CNC Enthusiast' from 'Audio Buff'?

    Craig



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    Default Re: Which bits to use for PCB milling?

    Hi Craig ... Thanks once more for your feedback - & good to hear that my drawings were not that far off.

    Hmmm ... Can I ask you a very practical question? As it is I may have access to a variety of steel or iron and one of my criteria is that this mill should be easily transportable, i.e. if steel is used it needs to be easy to disassemble. Here I am thinking of using rectangular cross-section steel bars connected to eachother with bolts. I have attached a "just crude" illustration showing three such bars running in parallel.

    If this is a feasible approach I will have to drill quite some holes in steel/iron and here I may need some drills that are suited for this purpose - and preferably last very well as I prefer to not replace tools too often. Any chance I can ask you to say which drill type may be suitable for this purpose? I reckon that M5 or M6 should be feasible sizes. Maybe it is something drillman (or preferably for a beginning) carbidechiu carries? (carbidechiu: https://www.ebay.com/str/carbidechiu...p2047675.l2563 )

    Also, in this context, I have been wondering how you attached the steel base to your HSR15 cars? As far as I can see the versions dy-global have available are all with threaded holes for the car mounting ... Thus the bolts need to be mounted from the top - i.e. through the steel base - which would lead to some rather long Ø3.5 holes. Or maybe you drilled larger diameter holes for the major part of the way through the steel base and then just ~ Ø3.5 for the last centimeter or so? Probably is an easier way of doing it ...

    May I suggest that you have more Z travel, as much as X or Y at least.
    Sounds like a good idea. I will consider it!

    All in all you are looking at a substantial machine requiring hard to get top quality parts and materials and many hundreds of hours in the design and making.
    It rather sounds that you are making the transition to 'CNC Enthusiast' from 'Audio Buff'?
    :rainfro: ... Well, time still is a real constraint as is economy ... Fortunately my CAD program IMHO is very easy to use and get good results with in a short time span ... Also I hope that choosing time-conscious solutions and planning ahead may get me a good way through the actual build process. BTW: Did you know that some years ago there was a test with the aim of building a house (a normal house) in the shortest possible time? To my memory - with planning etc. - they were able to complete the house in about 30 minutes ... likely now with wallpapers etc. but all be major and major/minor structures. Impressive I would say ... a digression ...

    And then I would prefer to do as little milling as practically possible as this is something that may take both time and is not immediately available "in my backyard" so to say. I would aim for milling mainly on the surfaces that need be level i.e. the surfaces where the rails are mounted and the surfaces where the various structural parts go together. Hope this may work ...

    What I hope to achieve making this mill is to go from a "not really satisfied CNC owner/user" to a "quite satisfied CNC owner/user" - also knowing that this CNC can do "most" anything (maybe also mill tungsten ...??)

    Cheers,

    Jesper

    Attached Thumbnails Attached Thumbnails Which bits to use for PCB milling?-rods-jpg  
    Last edited by evalon; 09-18-2018 at 03:08 AM.


  7. #87
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    Default Re: Which bits to use for PCB milling?

    Ooups .. A P.S:

    I reckon that sooner or later I will be needing something like this:

    https://www.ebay.de/itm/0-01mm-Unive...gAAOSwETJaDkEP

    Likely in a better quality though ... To this end: Is there something to look out for here? I would like it to be easily mountable in the CNC spindle collet so that I can move it across surfaces with the CNC. Any ideas?

    Cheers,

    Jesper



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    Default Re: Which bits to use for PCB milling?

    Hi Jesper,
    my mill has three cast iron beds, one for each axis, all the same length and width, 200 x 450. They weigh probably 30kg each.
    Yes I can disassemble my machine but its too damned heavy to be called portable in practice.

    The linear rails attach to the beds with 4mm cap screws, 4mm being standard for 15mm linear guide, you will not be able to drill them out, the linear rail
    is too hard to drill. The flanged cars have 5mm threads and so yes the screws pass through the upper component to the car underneath. 5mm threads are standard
    for the 15 size cars. You can get cars with a 5mm clearance hole that allows you to pass the screw upwards through the car flange. The norm that you
    will find in the secondhand market is threaded however.

    If you are drilling mild steel and/or cast iron there is no need for flash drills, good readily available HSS drills are fine. You can sharpen them as need arises,
    grinding carbide is not nearly as easy. Likewise HSS taps are perfectly fine. After milling my axis beds I had a machine shop grind them in their surface
    grinder so that the rails and base of the bed a parallel within the tolerance of the grinding machine. The machine of the company I go to has about 2um
    difference over 450mm, good enough for me, in fact hard for me to even measure!

    Craig



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    Default Re: Which bits to use for PCB milling?

    Hola Craig ... thanks for clarifying. And now reading your last post it is finally clear to me what the "beds" you have been talking about are .. Probably quite obvious to someone familiar with CNC terminology but I have just had this question simmering in my mind: "What exactly are these "beds""? Now it is clear (I hope - )

    And the weight ... I can't help thinking of the extreme difference there is between the items I will be milling - typically small items and removing small amounts of material in copper - and then the weight and strength needed in the machinery for this to happen. My, my ...

    The machine of the company I go to has about 2um difference over 450mm, good enough for me, in fact hard for me to even measure!
    Well that sounds indeed precise. I will see what is available in my area ...

    Have a good day in NZ

    Jesper



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    Default Re: Which bits to use for PCB milling?

    Hi Jesper,
    remember my design goal was to be able to mill steel with reasonable facility. The rigidity required to do
    so is an order of magnitude again on what you require. Additionally the beds are the stiffness of the machine,
    they do not sit in a frame to hold them straight, they must therefore be of reasonable thickness and with cast iron
    that means heavy. Heavy is not in itself a design goal, but rather a consequence of the rigidity required.

    Craig



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    Default Re: Which bits to use for PCB milling?

    Hi,
    by the way my go to brand for quality measuring gear is Mitutoyo.

    The Chinese made stuff is not as good but it is a fraction of the price. If I'm buying something that I anticipate using all the
    time like calipers and dial gauge I hang out until I can afford Mitutoyo, for more casually used stuff Chinese is good.

    Craig



  12. #92
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    Default Re: Which bits to use for PCB milling?

    Hi again ... Thanks for following up ... If I can ask another quite practical question: How do you prevent your Z-axis from dropping down when powering off the driver to this axis? With these weights I would guess that it would just rotate the ball screw and "hammer" into the milling plate ...

    Cheers,

    Jesper



  13. #93
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    Default Re: Which bits to use for PCB milling?

    Hi,
    the Z axis consists of cast iron bed (bolted to the upright) with the rails mounted on that. Thus the moving weight of the Z axis consists
    of the steel plate sitting attached to the four linear cars, on the plate is an extension, approx. 150mm that holds the spindle.
    Total moving weight even counting my high torque servo driven spindle is probably about 15kg.


    The ballscrew is 20mm diameter, 5mm pitch. The Vexta 23 size stepper goes through a 10:1 low lash (2 arc min) planetary gearbox. The combination
    of the ballscrew and the gearbox mean that even unpowered the axis does not drop.

    It is a worthy question, many machines have a brake on the Z axis servo to prevent the Z axis from dropping when de-powered. I suspect that in absence
    of the reduction gearbox my Z axis would have sufficient weight to cause a problem when de-powered.

    Craig



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    Default Re: Which bits to use for PCB milling?

    Thanks Craig ...

    The Vexta 23 size stepper goes through a 10:1 low lash (2 arc min) planetary gearbox.
    I suppose the main purpose of this is to improve the precision of the stepper motor so as to allow for very minute variations of the Z-axis per step, right? If so then it may also be interesting to me - would you have a name for such a gearbox that I can search for? I found this on dy-global but the price is too high so if you know of a good alternative:

    https://www.ebay.com/itm/SPG-SPIF115...QAAOSwoudW3ksK

    Cheers,

    Jesper



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    Default Re: Which bits to use for PCB milling?

    Hi Jesper,
    the Vexta steppers are five phase which are 500 steps per revolution. The increased number of poles allows a better approximation
    to sinusoidal flux and can rotate faster without loss of torque relative to two phase steppers. The 10:1 gearbox takes the natural 0.720
    per step to 0.0720 per step or 5000 steps per revolution. A very useful gain in resolution without microstepping. The gearing increases the torque
    output, the steppers themselves are only about 80-90 oz in but the output shaft of the gearbox is 705 oz in.

    You might think all of these are advantages, 25 times the resolution of two phase steppers (without microstepping),faster speed without torque loss, vastly
    increased output torque, so what about the disadvantages? Firstly the cost of the greaboxes is high, if I bought new Apex reducers of this size they are about
    $400US each. The Vexta steppers themselves are specialist steppers and cost double-triple what you might pay for a similar sized two phase stepper.
    I use Vexta direct off-line drivers, even second hand over $150US each.

    Then there is speed....or rather lack of it. Despite five phase steppers being smoother and faster than two phase steppers the gear reduction is 10 to 1.
    I run my steppers quite happily at 2400 rpm, and that is at less than max current, without even a hint of loosing steps. At the output shaft that equates to
    240 rpm, with 5mm pitch ballscrews that is 1200mm/min. Pretty slow. On the up side the axis thrust is over 6kN, its got the grunt to push the tool into
    the material and rip your hand off if you are dumb enough to stick it in there!

    Overall I paid about $200 for each stepper and gearbox and $150 for each driver. It has given me a smooth and powerful axis drive solution albeit
    fairly slow. When I was researching and buying these things I was very new to it. At that time, about six years ago, there were fewer cheap AC servos.
    Consequently these steppers looked like pretty good value although second hand. Today I am much more aware of what's available combined with the
    marked increase in AC servo products getting to market that if I were doing it again I would go with AC servos not steppers.

    In some respects it stems from my decision to make my machine capable of milling steel. It has meant that I have required specialized and/or expensive
    parts, components and materials throughout. These steppers/gearboxes/drives are an example, I chose them to have the thrust and resolution that
    I wanted....and it costs! I don't regret it but would advise someone starting out to do some careful consideration/balancing at the 'what do I want' stage,
    its very easy to as I did, 'I want this, that and the other thing', only to find that the costs have blown out.

    Craig



  16. #96
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    Default Re: Which bits to use for PCB milling?

    Hi,
    this is the current version of what I have, note that the gearbox has more backlash than my ones, but none the less would be happy
    with these units, and be even happier if I could afford them!!!!

    https://catalog.orientalmotor.com/it.../pke566ac-ps10

    Craig



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    Default Re: Which bits to use for PCB milling?

    Good morning Craig ... & thanks again for being so forthcoming in sharing your experiences in choosing & designing your CNC. I know I have said it before - but it's really helpful

    Reading your two posts above I am thinking that it sounds as if your machine overall is very balanced/smooth working yet powerful. It also makes me wonder if the fact that you are using planetary gears with a 10:1 ratio allows for less overall vibration while milling - as I reckon the normal step angles in a stepper motor somehow translates into small vibrations being transferred to the end mill. Again likely depending on the overall mass/vibration damping qualities of the moveable system which I guess will dampen this to some extent.

    Considering things, however, I think I will stay with my current stepper/driver solution and then optimize the strength, rigidity and low-vibration qualities of the structural frame. This way I know that the basic CNC is fine and the I may eventually add better steppers/AC servos if I find that this becomes feasible.

    I do, however, need to find a solution to the "drop-heavy" risk of the Z-axis spindle mount. Doing an internet search I found this tip:



    He basically shorts one of the coils on the stepper motor when the driver power is off - apparently it is enough to prevent the Z-axis from dropping. If so then it is indeed a very straightforward solution as it basically can be handled with just the DPDT relay connected to the stepper motor coil (which is what he suggests).

    Regarding the actual material for building the CNC frame I have searched for suppliers of cast iron in Denmark (and a bit in Germany) and it appears that there are some companies selling these goods. Right now I am considering building the entire frame from 20*40 mm cast iron rectangular rods (GG-25). The benefits of doing so appear to be many:

    * the price is accessible I think - ~ USD2 per kilo for these surplus goods rods.

    * I basically can design and build all parts exactly to the sizes I wish to. And place the weight where I see it most useful. I may also build it so that it can relatively easily be taken apart.

    * Using an epoxy glue and filler the vibration level of the machine may likely be very low.

    * Machineability may be very straightforward as the main work process will be sawing the rods ... The way I think about the design I don't even have to consider precise rectangulars angles in the sawing process. And comparatively few holes to drill.

    * Additionally a bit of surface milling and grinding (or the like) for the linear rail mount surfaces. To be done by someone specialized in this.

    All in all I think/hope the design concept is coming together () ... Some process for me - but again very much assisted by you & others here ...


    Two parts that I do think I still need to find are:

    - couplings between the ball screws (specific words to search for? Something to take into consideration?)
    - end stop contacts. I suppose these may be fine:

    https://www.aliexpress.com/item/6pcs...ceBeautifyAB=0

    And then, in time, there is the spindle motor. Reading yours and Roger's posts and comments about this I reckon that a high(er) torque, low TIR version may be desired ... but this may come in due time.

    Wishing you/people here a pleasant day ...

    Jesper



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    Default Re: Which bits to use for PCB milling?

    Hi Jesper,
    my understanding is that you hope to cut cast iron bars and make a lattice by bolting/threading?

    Are you sure that will provide the rigidity you require? It will come down to the design of the bolted connections.

    Have you considered a RHS, say 50 X 50 X 5 welded steel frame. There was an article where a crew made such
    machine and filled the sections afterwards with cement to reduce vibrations, it worked pretty well.

    You would ideally post weld stress relieve the completed structure. Surely there is a foundry in your region with
    a heat treatment oven that could do it for you.

    Epoxy granite is a great idea....have you tried it? I would experiment before I committed to the cost of
    materials and moulds before I did so. My experience of casting in Epoxy is that without the right (expensive)
    grade of Epoxy you are going to have MAJOR exotherm problems.....I did until I bought, at great expense,
    a casting Epoxy.

    I would rather concentrate on a structural design, materials and fabrication process that provided a rigid structure
    without additions like Epoxy granite.

    Craig



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    Default Re: Which bits to use for PCB milling?

    Hey Craig,

    my understanding is that you hope to cut cast iron bars and make a lattice by bolting/threading?
    Yes & no ... I intend to glue the better part of the structure together and then afterwards fill them with the epoxy/granite molding blend. These "blocks" will then be screwed together with bolts & nuts.

    Epoxy granite is a great idea....have you tried it? I would experiment before I committed to the cost of
    materials and moulds before I did so. My experience of casting in Epoxy is that without the right (expensive)
    grade of Epoxy you are going to have MAJOR exotherm problems.....I did until I bought, at great expense,
    a casting Epoxy.
    There's always the possibility of a surprise here.... But I have contact with a person who a.o.t. sells to the Danish Wind Turbine industry (e.g. Vestas) and who has extensive knowledge of epoxies and other glue types. I intend to ask him what may be a feasible solution. Also - from reading another thread on the subject here on CNCZone it seems that the amount of epoxy to be used volume-wise is about 1/6 the volume of the epoxy/granite mixture combined. Also I expect the epoxy to not have very large volumes in isolation so I would assume that the large surfaces and the heat conductivity of the interspersed iron/granite together may lead away the epoxy's exotherm heat generation.

    In any case: I may also have access to some 50x50 mm & 60x60 mm rectangular bars, also cast iron. I could glue these together so that e.g. 4 of them made up the Z-axis vertical supporting structure - a 100x100 cross section area. Or two 60x60mm glued together to make a 120x60mm structure (thick material in the y-axis?).

    Alternatively I have access to a 100x100 mm "normal steel" rectangular bar that I could have cut to length for the purpose. Either of these probably would be easier (and also heavier ) to do but the weight would be more than about 40 kgs. I'm simply not sure I can lift this .... I'm a "runner type" body build so lightweight and adroit but just limitedly "strong" in a traditional sense ... But what would you choose from a strength/damping point of view? The price difference is limited.

    I think that for the actual plates that hold the items to be milled, and the plate that holds the spindle I will choose the cast iron 20x40 rods and glue them together with a suitable high strength epoxy. This would give high strength, some damping due to some constrained layer effect, and high weight where the vibrations are generated.

    And then - not to repeat myself but just to make sure this is of less importance:

    - couplings between the ball screws and the steppers (specific words to search for? Something to take into consideration?)
    Would you say that there is anything in particular to look out for here ... Or can I just use any coupling?

    Cheers,

    Jesper


    A P.S.: If I can ask you to just - in short is fine - to give a feedback on the "structure options" and the coupling choice I think it would be simpler if I draw up a 3D drawing of the structure including assembly bolts and then post it here so that we have a common reference. This likely will take a couple of days ...

    Jesper



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    Default Re: Which bits to use for PCB milling?

    Epoxy granite would be good.

    I have two commercial made PCB routers, by Lenz, they weigh 1200kg each because they have "torsion box" type construction made from cast iron. Each machine has two 60,000 rpm spindles in order to cut two PCB at a time. The spindles are 1.1KW, model Precise SC53. These spindles are "direct chucking", the collet is part of the spindle and they pick up a bare tool. Each spindle has 9 tools to choose from, the collet is air driven, the spindles are water cooled.

    The machines are moving bed, the gantry is cast aluminium and substantial.

    I believe spindle runout is less than 3 micron.

    This gives an idea of what was considered necessary by Lenz.

    I'm currently replacing the electronics on these machines with Machdrives BRA double encoder servo drives, it will probably take me a month to get around to it, but I can do some tests on thick PCB then.



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Which bits to use for PCB milling?

Which bits to use for PCB milling?