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  1. #21
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    Default Re: 7 Axis Swiss Mill-Turn (DIY)

    Wow! I would love to have a machine like this.... Thanks for posting.

    Robert



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    Default Re: 7 Axis Swiss Mill-Turn (DIY)

    Quote Originally Posted by embraced View Post
    The spindle: limitations? Precision, quality, matched angular contact bearings cost hundreds by themselves. plus then the taper (ISO30?) machining, heat treating and grinding, plus (presumably) pneumatic drawbar arrangement seems awfully expensive - my business is in manufacturing commercial machinery for processing MRI gradient coils, so I've been around. I'd love to know how you were able to keep the cost so low on the spindle specifically.

    Thanks,

    Lindsay
    I think he does not have a pneumatic drawbar but also he most likely made the spindle himself. Bearing most likely are not abec7 high precision matched but maybe like abec5 matched set that could be had for like $100-$200.
    I wonder if his spindle is even heat treated and ground. Or even you can buy a 30taper spindle from tormach for like $600. Or if you get their r8 spindle you could even add their pneumatic drawbar.



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    Default Re: 7 Axis Swiss Mill-Turn (DIY)

    I would love to see a video of this thing running a boring bar through some steel.



  4. #24

    Default Re: 7 Axis Swiss Mill-Turn (DIY)

    Arrrrrg I just typed out a 10 paragraph post addressing all of your questions and comments in detail, only to have it deleted because this website glitched when I was uploading a photo of stuff. It just makes the screen greyed out indefinitely when I try to link a photo.



  5. #25
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    Default Re: 7 Axis Swiss Mill-Turn (DIY)

    yup. type in word and copy pasta



  6. #26

    Default Re: 7 Axis Swiss Mill-Turn (DIY)

    jgwentworth and Hackish,

    I've tested several 3d printer boards; Smoothieboard with 5 steppers, Azteeg x3 pro with 8 steppers, and the production version machine will most likely use the Duet board with up to 12 steppers.
    3d printer boards also have other inputs and outputs, like lots of thermistors for temperature, heater outputs than can be used for air cylinder and solenoids, display screens, sd cards, lots of limit switches ect.

    Embraced and Ianagos,

    The spindles on this mill turn center use P5 grade (ABEC 5 equivalent) 15 degree angular contacts with indicators on the outer races.
    I picked bearing sizes such that they are also compatible with deep groove bearings and even tapered roller bearings.
    This is for forward compatibility, and it gives people the option of replacing bearings cheaply if something bad happens to the originals (at the cost of a couple tenths of runout).
    The bearings fit with a very light press fit on the shafts, no play allowed. The housings are blocks of solid 6061 aluminum with close tolerances. This eliminates the slight loss of rigidity from bolting a spindle cartridge into place.

    Neither spindle is hardened or ground on the prototype. The big headstock spindle started as a DOM tube with thick walls and a 2 inch bore. There is no need for this thing to be hardened.
    The milling spindle started as a solid 2.25" bar of 4140 pre-hard. Since both the taper and the bearing shaft was turned in one chucking, the concentricity of the assembled thing is excellent.
    On the production version, the spindles will be made in a CNC lathe with a large collet nose. If the spindles can be turned with tight enough tolerances, grinding won't be needed.
    For heat treating, I'm still uncertain. They could be roughed, through hardened, then ground. Or they could be ferritic nitrocarburized for a hard, rustproof skin without warping. Or they could even be PVD/CVD coated.

    BTW, the cost of the milling spindle head was about 200 dollars for the prototype. That's for the spindle headstock, spindle tube, P5 bearings, and BLDC motor combined.
    Runout at the tool tip is under 0.001", I can't measure any more accurately with the limited tools I have right now. I expect the production machine will range from 0.0002 to 0.0006" at the tool tip .

    Onto the "drawbar" and ATC mechanism. The drawbar on the prototype is literally just an M12 socket head cap screw. The bottom of the socket head sits on a roller thrust bearing sandwich.
    The production version will have an ultra low friction coating on the threads. With BT30 tool holders, there is no need for pull studs. The drawbar threads directly into the tool holder.
    5 foot-pounds on the socket head generates approximately 900 pounds of clamping force between the spindle taper and the tool holder, which is much more than adequate.
    There is no risk of the tool holder coming out during milling operations, and no pull stud to fatigue.



    The cross section below is a bit outdated, and it doesn't show the mechanism for stopping the drawbar relative to the spindle, but this should give you a general idea of what the inside looks like:




    Notice in the cross section photo that there is a spring and stop mechanism around the draw bar. This allows the drawbar to be pushed up by the tool holder before it engages with the threads.
    It's kind of hard to explain in words here, but the spindle ATC works by threading and unthreading tool holders into the spindle taper using the milling motor itself.
    This is inherently slower than an air cylinder and bellevile stack, but it's ultra compact and cheap in comparison. It also allows for 10 second manual tool changes without power or air.


    I know I'm forgetting something that I wrote in my first long response, but it got deleted and I can't remember it now.....

    Questions? Comments? Criticism? Let me know!

    Attached Thumbnails Attached Thumbnails 7 Axis Swiss Mill-Turn (DIY)-milling-spindle-cross-section-prototype2-jpg  
    Last edited by Generic Default; 03-05-2018 at 09:54 PM.


  7. #27
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    Default Re: 7 Axis Swiss Mill-Turn (DIY)

    I think it's very interesting and the machine looks very sexy. I remain unconvinced about the abilities of the machine on anything but the softest of metal. I'm not in any way trying to bust your balls, and I am not a professional machinist nor engineer. I ran a race car fab shop for a number of years, and based on my experience working with different types of metal I have difficulty picturing this thing doing anything that requires rigidity. I would love to see a video taking a reasonable cut with a boring bar on some steel.



  8. #28
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    Default Re: 7 Axis Swiss Mill-Turn (DIY)

    I certainly don't want to take away from Generic Default's impressive work here, but...

    Quote Originally Posted by hackish View Post
    I think it's very interesting and the machine looks very sexy. I remain unconvinced about the abilities of the machine on anything but the softest of metal. I'm not in any way trying to bust your balls, and I am not a professional machinist nor engineer. I ran a race car fab shop for a number of years, and based on my experience working with different types of metal I have difficulty picturing this thing doing anything that requires rigidity. I would love to see a video taking a reasonable cut with a boring bar on some steel.
    I absolutely agree with this, and I'm an engineer who's done machine design in a few industries.

    The thing I'd be most concerned about is long term reliability, but the lack of hard numbers on capacity reinforces my suspicion that this isn't going to be taking serious cuts in anything. Saying that the spindle has larger bearings than a Bridgeport is the kind of thing that makes me question the amount of engineering that went into the design in the first place. Larger bearings can't compensate for the overall lack of rigidity in the machine, and aluminum is a poor choice for a small machine where every pound of mass is a plus.

    At the right price point (under $5k), I'd probably be willing to try one out once people had trialed it through its teething period. I definitely have aluminum parts that could benefit from the mill-turn setup.



  9. #29

    Default Re: 7 Axis Swiss Mill-Turn (DIY)

    Sadly the only boring bars I have right now are those cheap little Chinese brazed carbide box of 9 types things, complete junk. They don't even have a relief angle. Definitely can't take any heavy cuts in steel with them.

    Pariel, I went with aluminum for quite a few reasons. As shown in the video, the machine weighs about 560 pounds. If I had made this from cast iron or steel, it would be 1600 pounds and would require a special table or stand. Plus I wouldn't be able to move it without a forklift. The individual components would weigh several hundred pounds. The large bearings are there to ensure that there is no flex at the rotational axes. I'm of the mindset that overkill doesn't hurt; if anything, it reduces the possible points of failure.

    The weakest points on this prototype machine are where the motor shafts couple to the pulleys. Since the motors are 6384 outrunners, the motor shaft is 8mm with a length of ~90mm from the point where the shaft couples to the rotor to the point where torque is transmitted via set screw or plum coupler to the pulley.
    This 8 x ~90mm steel shaft doesn't have the torsional rigidity I want. It's easy to fix with a larger shaft or by driving the pulley from the motor bell near the connection (which will be done on the production machine) but on this prototype, the spindle motor torsion is the weak point.

    "but the lack of hard numbers on capacity reinforces my suspicion"
    What kind of hard numbers do you want? I've been hesitant to list things like max turning length or diameter because it depends on what chuck/collet nose is on the faceplate, and the 4:1 ratio ect. I also don't want to be one of those people who lists the accuracy of the machine as the minimum theoretical micro-stepping resolution. Numbers like this are reminiscent of the way digital cameras are thought of by average consumers, where the megapixel number is seen as the only thing that matters.



  10. #30
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    Default Re: 7 Axis Swiss Mill-Turn (DIY)

    I totally missed what you meant by Swiss style on my first read through of this. On a Swiss machine I'm used to seeing a stationary bushing that the workpiece comes in and out of. Not used to seeing the actual spindle at all.
    On second look I realized you meant a lathe where the spindle moves in Z. I can certainly see why you went this route for a mill-turn machine. Putting 4 axes of movement all on the milling column would be ugly.
    Going full Swiss on this, adding a stationary rest would probably help quite a bit for long workpieces, though I guess no more really than adding a follow rest on a traditional lathe.



  11. #31
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    Default Re: 7 Axis Swiss Mill-Turn (DIY)

    Quote Originally Posted by Generic Default View Post
    Pariel, I went with aluminum for quite a few reasons. As shown in the video, the machine weighs about 560 pounds. If I had made this from cast iron or steel, it would be 1600 pounds and would require a special table or stand. Plus I wouldn't be able to move it without a forklift. The individual components would weigh several hundred pounds.
    Weight in a machine tool is a *good* thing. Yes, it makes it hard to move. The weights you're talking about are pretty standard for the larger benchtop mills, small knee mills, 12x36 lathes, etc. which many hobbyists have in their garages and basements. In addition, the vibration dampening characteristics of cast iron when compared to aluminum are probably valuable even in a machine this small.

    The large bearings are there to ensure that there is no flex at the rotational axes. I'm of the mindset that overkill doesn't hurt; if anything, it reduces the possible points of failure.
    I'm an engineer, my job is to optimize. An overly large bearing is expense that could be used elsewhere on the machine, and in either case doesn't make up for the lack of rigidity elsewhere.

    What kind of hard numbers do you want? I've been hesitant to list things like max turning length or diameter because it depends on what chuck/collet nose is on the faceplate, and the 4:1 ratio ect. I also don't want to be one of those people who lists the accuracy of the machine as the minimum theoretical micro-stepping resolution. Numbers like this are reminiscent of the way digital cameras are thought of by average consumers, where the megapixel number is seen as the only thing that matters.
    Real life speeds, feeds to calculate MRRs.

    Measurements of repeatable tolerances.

    Longevity of the PTFE on anodized aluminum boxways.

    It's an impressive piece of hardware, especially for one person to come up with, but I'm not convinced it's a product that's ready to compete on the open market. Frankly, I think Kickstarter functions as a crutch when it comes to differentiating products that can't last, and I would definitely not buy a machine tool through KS. Other people sitting more tightly in the hobby end of the spectrum may disagree, although I don't think you'll be able to price this machine low enough to focus primarily on hobbyists. When it comes to a highly custom machine tool like this, the other question is whether your company will be around to sell parts in five years (or preferably 10 or 20). Until you have enough installed capacity to convince serious businesses of your longevity, that will be a struggle -- just look at some of the FADAL guys attempt to relaunch as FADEC.



  12. #32

    Default Re: 7 Axis Swiss Mill-Turn (DIY)

    Some newer Swiss machines have the option to be a "chucker", where there is no guide bushing at all. This is one of those machines. I do have a design for a guide bushing block on this machine, but I couldn't do it with the 2k budget on this prototype. It's functionally the same as a following rest on a normal lathe.

    I also have a simple tailstock ready to make as well. Since the headstock slides along Z, the tailstock must slide with it to support a part between centers. One way to do this is with a motorized tailstock that's synchronized with the headstock, easy to do with stepper motors. The other is to connect the tailstock to the headstock with a link rod and quick-connect shaft collar or set screw system. This method would be fast and easy for long parts between centers. The length capacity is about 9 to 12 inches depending on what's mounted to the faceplate.

    EDIT for Pariel;

    Feeds and Speeds- Max linear speed on this machine with steppers is fairly slow, I haven't been able to go above 120 IPM without intermittent stalling. With ODrive servos, 500 IPM is the practical limit.
    Repeatability is well within 0.001", check the indicator GIF a few pages back. I'm sure the tool tip offsets would be compromised by more than this amount if the machine is not in a temperature stable room.
    The hard anodize on the boxways is in the range of 65 rockwell C. The pads between the sliding plates and the boxways are plain acetal for now; I'll be using PTFE filled delrin for the production version. Igus has a similar product, they are claiming upwards of 100km of travel before the plastic part needs to be replaced. These small plastic pads are about an eighth of an inch thick, around 2 square inches each. Couple dollars to replace, takes ~5 minutes. For obvious reasons I haven't been able to do long term wear tests yet.

    On the business/kickstarter side of things, the long term plan is to establish a small product line at a low price with unmatched metal cutting capability in the category. The limiting factor here is that residential power outlets can't put out more than about 2 or 3 horsepower, so that is the hard limit for continuous MMR. The initial Kickstarter will have a simple 3 axis variant available for under 2k with rigid tapping standard. The biggest selling point (I think) is the incredible value in the low price range compared to import machines. I'm hoping people will realize this when the kickstarter goes live.

    Last edited by Generic Default; 03-06-2018 at 06:17 PM.


  13. #33
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    Default Re: 7 Axis Swiss Mill-Turn (DIY)

    Max linear speed on this machine with steppers is fairly slow, I haven't been able to go above 120 IPM without intermittent stalling. With ODrive servos, 500 IPM is the practical limit.
    Speeds and feeds refers to cutting (hence getting MRR from it).

    Repeatability is well within 0.001", check the indicator GIF a few pages back. I'm sure the tool tip offsets would be compromised by more than this amount if the machine is not in a temperature stable room.
    All you're showing there is really backlash, that's not actually even positioning repeatability. More importantly, it's not showing part tolerance, which is going to be a function of deflection in the machine structure, vibration, and any drift in your system.

    Igus has a similar product, they are claiming upwards of 100km of travel before the plastic part needs to be replaced. These small plastic pads are about an eighth of an inch thick, around 2 square inches each. Couple dollars to replace, takes ~5 minutes. For obvious reasons I haven't been able to do long term wear tests yet.
    I assume you're talking about their Drylin series? Those aren't for use in machine tools, they're for automation. Deflection and wear in both are going to be a huge factor in repeatability as mentioned above.

    To compare your design to linear rails: ball bearing linear slides usually require lubrication (not replacement) every 100km. The wear rate you're talking about means you're setting up the machine to require nearly constant maintenance to hold your design tolerance.

    On the business/kickstarter side of things, the long term plan is to establish a small product line at a low price with unmatched metal cutting capability in the category. The limiting factor here is that residential power outlets can't put out more than about 2 or 3 horsepower, so that is the hard limit for continuous MMR.
    I can't disagree with that if you're just going to target low-budget consumers, this machine is certainly not capable of taking cuts that would use 2 HP at this point.

    The initial Kickstarter will have a simple 3 axis variant available for under 2k with rigid tapping standard. The biggest selling point (I think) is the incredible value in the low price range compared to import machines. I'm hoping people will realize this when the kickstarter goes live.
    I don't think you can hit that $2k number. Realize that machine tools that sell for $2k through importers like Grizzly can be had from China for $500-700. Have you gotten quotes from your suppliers for materials and services (especially stuff like hardening and anodizing the huge rails)? Have you priced out your own time to do machining, assembly, packing for shipping, and shipping costs? Have you identified another servo supplier in case ODrive has quality issues, can't satisfy demand, etc.? Have you priced out the overhead costs to actually manufacture it? Have you figured out how many machines you can supply without hiring on more help, and priced in those employees for when you will?

    This isn't intended to dissuade you from making a machine, but to point out the holes in your plan that will prevent you from forming a company that can run profitably.

    I think you'll find that it is very hard to sell any machine in the <$2k (or for that matter, <$5k) range, and that hobbyists in particular are a very limited market. Either way, it doesn't sound like this machine is likely to be something that any production shop or prosumer hobbyist is going to be interested in, given its limitations.



  14. #34
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    Default Re: 7 Axis Swiss Mill-Turn (DIY)

    https://www.tormach.com/document_dir...tml?doc_id=943

    The spec sheet on the Tormach 440 may be misleading but perhaps they use something similar for ways? If the above link doesn't work...

    Way Surfaces: Low friction PTFE-filled, Acetyl bonded sliding surface




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    Default Re: 7 Axis Swiss Mill-Turn (DIY)

    Quote Originally Posted by cmelo View Post
    https://www.tormach.com/document_dir...tml?doc_id=943

    The spec sheet on the Tormach 440 may be misleading but perhaps they use something similar for ways? If the above link doesn't work...
    They use turcite on cast iron ways..



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    Default Re: 7 Axis Swiss Mill-Turn (DIY)

    Quote Originally Posted by ianagos View Post
    They use turcite on cast iron ways..
    Right, and Turcite is acetal based and the OP is using acetal. So I'm assuming it's similar as far as how they'll wear. Or, a change from plain acetal to Turcite would be a simple swap. Disregarding the difference between riding on aluminum vs. cast iron.



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    Default Re: 7 Axis Swiss Mill-Turn (DIY)

    Quote Originally Posted by cmelo View Post
    Right, and Turcite is acetal based and the OP is using acetal. So I'm assuming it's similar as far as how they'll wear. Or, a change from plain acetal to Turcite would be a simple swap. Disregarding the difference between riding on aluminum vs. cast iron.
    I doubt aluminum will act the same as cast iron in this application. I think overall it’s a decent design but I just don’t see the market. Anybody who needs such a machine would go look for a used mill turn machine. That will have a bar puller or even feeder, full flood coolant, and an atc. People act like moving machinery is so difficult but it’s really not. A lot can be done in a garage too. I’d say a worn out industrial machine will probably hold the tolerances this would after a good cleaning of course. Plus this is an investment with no longevity. This was never built to last it’s built to a price point.

    I’m not dogging the creator and I think his idea is awsome. I just think there’s a bit more refining to do like ballscrews, an enclosure, and maybe iron ways

    Also spindle bearings that he said cost less than $100(he said the whole spindle and motor cost sub $200) aren’t gonna hold the greatest tolerances. The bearings for my fadals ballscrews cost like $85.



  18. #38
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    Default Re: 7 Axis Swiss Mill-Turn (DIY)

    How does the lathe spindle transition between indexed/simultaneous 5 axis moves and turning speeds? What kind of gearboxes are you using for the rotary axes?

    I think the parts and bearings are properly sized for the ways this machine will be used. It looks like a much better Pocket NC Company .

    The problems will be cost and limited market. CNC is hard, and CAM for a 7 axis machine is even harder. I'd pay maybe 3k for something like this but its hard to justify much more for what is essentially a hobby machine.



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    Default Re: 7 Axis Swiss Mill-Turn (DIY)

    Quote Originally Posted by ianagos View Post
    I doubt aluminum will act the same as cast iron in this application. I think overall it’s a decent design but I just don’t see the market. Anybody who needs such a machine would go look for a used mill turn machine. That will have a bar puller or even feeder, full flood coolant, and an atc. People act like moving machinery is so difficult but it’s really not. A lot can be done in a garage too. I’d say a worn out industrial machine will probably hold the tolerances this would after a good cleaning of course. Plus this is an investment with no longevity. This was never built to last it’s built to a price point.

    I’m not dogging the creator and I think his idea is awsome. I just think there’s a bit more refining to do like ballscrews, an enclosure, and maybe iron ways

    Also spindle bearings that he said cost less than $100(he said the whole spindle and motor cost sub $200) aren’t gonna hold the greatest tolerances. The bearings for my fadals ballscrews cost like $85.
    All great points and likely valuable to the OP. For myself and likely others I was more interested in satisfying curiosities about the build/design and their legitimacy in satisfying a certain price point. I'm not in the market for a machine like this, however, I do like the idea of the mostly aluminum design and keeping costs as low as possible at least for a DIY/personal machine. Like something I might make for myself, let's say strictly for fun. I think there's a lot of good ideas flowing from this thread.



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    Default Re: 7 Axis Swiss Mill-Turn (DIY)

    Quote Originally Posted by ianagos View Post
    I’m not dogging the creator and I think his idea is awsome. I just think there’s a bit more refining to do like ballscrews, an enclosure, and maybe iron ways

    Also spindle bearings that he said cost less than $100(he said the whole spindle and motor cost sub $200) aren’t gonna hold the greatest tolerances. The bearings for my fadals ballscrews cost like $85.
    I think the GIFs make this machine look a lot bigger than it is. I'm visualizing something along the lines of a 7 axis Sherline here. Those steppers are almost certainly Nema17s or smaller, and the spindle motor looks like a hobby brushless. Is the bed even 16" long? All the choices look quite rational in that context.



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