Sounds like a well thought out plan :cheers:
Sounds like a well thought out plan :cheers:
I, just my personal opinion....it's easier and better to mill in a lathe with live tooling than to turn on a mill, router etc.
Attempting to convert a mill etc to do turning with multiple tooling is a complication at best.
I can understand the desire to do all machining operations with one machine....that's a do all machine...…. but it does take a lot of complication to get there.
I would imagine if you mounted a 3 jaw chuck directly in the spindle with the work piece pointing down and nested the various tools pointing up on the table you could do turning by using the Z axis and milling using the spindle as the main holding feature all in one go.
A servo driven 4th axis.....no need for a brake..... on the table then does the drilling and milling bit.....just thinking beyond the box......I think this has been done before somewhere if I remember.
Ian.
Yes, I've considered all options. In my specific case, I think i have the best solution. Putting work in the vertical spindle won't work for me for many reasons. First of all i want my vertical spindle to keep at least 15k rpm capability for fast work in aluminum, preferably 24k. Would be pretty hard to have a spindle capable of turning at low rpm as well as 24k. Also I want 5c holding with enough depth for getting multiple parts out of a long piece of stock. Also I want capability for turning longer tail stock supported work. None of this works with work in the vertical spindle.Quote:
Originally Posted by handlewanker
As for milling in a live tooling lathe, sure, if I had a live tooling lathe, but I don't. Even if i could afford to buy, or build one, I don't have the space. My main limitation is room for machines. If I had plenty of room, the simplest solution would have just been to build a much cheaper harmonic drive 4th axis with a much smaller servo and then just build a separate cnc lathe that wouldn't need servo drive. I just don't have the room for it. Even if I did have the room for it and the money for 2 separate machines, the configuration I've come up with is gonna be more efficient for what I want to do, which is small scale production on very specific rc helicopter parts. With my horizontal servo driven mill turn, I'll be able to complete many parts start to finish in a single op which includes turning, index milling, parting off. If i add
the pneumatic closer, potentially multiple parts without stopping. If I was doing only one off prototype parts, it probably would be more simple to separate the 4th axis and lathe, but that's not what I'm doing. I've done a lot of thinking on various parts I'll be working on and the gang tooling configuration I've come up with will work for many of my parts with zero tool changes. Getting all this figured out has definitely been complicated, but once it's together and setup, code written, it will be very efficient at making multiple parts. More so than the other options mentioned.
I can definitely understand where you're coming from though. For one off work, combining machines together will most likely makes things slower and more complicated. Separate lathe and mill with 4th is much easier to deal with for setup and cam, but for small scale production, I think my configuration has a big advantage, especially since I don't have room for multiple machines
Hi, I quite agree with your choice...….. if it works out OK it'll be quite neat.
The long job part is one thing you would gain advantage from a 4th and servo drive with a through hole.
I see you are opting for 5C collets...…..one problem with 5C is that it needs to have exact size collets for the material holding and a draw tube too tightened from the end which makes the 4th spindle diam and bearings a bit on the large size.
I think I would go the ER40 collet option....25mm diam material size is handy..... as it has a squeeze down factor of a mm and so can cater for raw material diams a few thou undersize.....I've never found any bar stock in cold rolled to be an exact size.
My personal preference for the 4th I'm building is an 80mm diam 3 jaw chuck with an option for a 125mm 4 jaw chuck too......the main reason is the large through diam.
One problem with those chucks is they are rated at max 4,000 rpm but as I won't be doing any turning for me it won't be a problem.
Ian.
5c has its ups and downs for sure. Like you mentioned, it needs exact collet sizes, although it seems to have enough give to handle standard stock sizes. They are supposed to handle +/-5 thou. One advantage of 5c over er is that they can grip onto short parts right at the nose. Er collets collapse at both the front and rear so if you try to grip something right in the nose, it will collapse at the back and not grip correctly. 5c is also nice because it's extremely versatile. Any attachment you can think of with 5c on the back of it. Expanding mandrels, large step chucks, 3,4,6 jaw chucks, flat fixture plates, emergency collets, list goes on, including a 5c-er40 attachment which i will most definately have for gripping any size I want. Bit more run out in the 5c-er40 attachment vs just an er40 chuck, but not much. The draw tube is also something that adds pretty huge capability once investing in a pneumatic closer. A bar puller attachment is simple to add, then you can crank out continuous parts unattended, as many that will fit in the bar stock.Quote:
Originally Posted by handlewanker
Well, all you say is quite true....I'm coming from the armchair engineer of old angle and am a veritable newcomer to CNC machining with a degree from the school of KISS....…….although I have a CNC mill it's not for production and mainly from the learning side.....oldies need their toys to keep their marbles clicking.
I'll stick with the simple 3 jaw chuck option as I think it will suffice for what I intend to do.
BTW....with all that servo drive and coupling in line with the 4th spindle, where can you fit a powered draw tube for the 5C.....by my reckoning you won't get much bar length if the servo is directly in line behind the 4th...…..would it not be a better option to drive from the side with an offset and a timing belt etc?...….. much as I dislike timing belt drives.
Even then I cannot imagine a longish bar of steel, say 20mm diam, sticking unsupported out of the 4th spindle end and revolving at a couple of thousand rpm with a turning operation...…...turret lathes have a bar feeder to feed and steady the long bar outside of the spindle.
Ian.
Yep, you are correct on all counts. Pneumatic draw tube doesn't work with the direct coupler. Also I am limited to about 12in bar stock.Quote:
Originally Posted by handlewanker
Basically here's my plan, I'll run it for now with direct coupler. Advantages are it was cheap and will give the best accuracy and rigidity with downside of 12 in max stock and no pneumatic closer. The pneumatic closer is another pretty large investment that I'm not ready for at the moment. 800 bucks for the cheap one, more like 1200 for the one i should get. Keeping that in mind, without the pneumatic closer there were basically no downsides to running direct coupling for now. Since I have to manually actuate drawtube anyway, it's also not a big deal to add bar stock more often. The direct coupler was built out of pieces of stock i already had aside from a 25 dollar plate of 3/4 mic6 I'm using for the base. So it was a pretty small expense to take the temporary direct coupling path. Also i like to experiment and see how different methods work. Once I get a feel for this mill turn setup and decide I want to invest in full automation, ill switch over to the dual idler 5mgt setup. At that point ill be able to complete multiple parts out of longer stock without stopping. The max length of unsupported stock without whipping is something I'm also really curious about, but I imagine it can't be that hard to build some kind of bearing support structure to stabilize longer bars with different attachments for different stock diameters.
Another thing I considered is that it will be easier to build a proper dual idler 5mgt setup if I already have a functional lathe. With the direct coupling setup, I'll be able to turn the needed parts for the belted setup like idlers exactly how i want them, the posts for mounting them on, the adapter for the pnematic closer, etc. All stuff that will need turning for proper accuracy.
At this point I'm not sure if thats exactly how it will play out. I have dreams of a much more serious machine. Dual opposing spindles on independent ballscrews capable of part transfers and a b axis head capable of machining on the faces of those transferred parts. Also something larger than the pass through of 5c. 3j or 16c would be amazing. Insanely expensive to buy spindles like this. In the back of my mind I'm wondering if my machine can be adapted for turning and grinding these larger spindles. Maybe, maybe not. Basically I'm trying to slowly upgrade my machine in different steps that give it capability of upgrading itself or building new machines.
All in good time as they say.....the longest journey starts with the first step.....or, it won't happen today and it won't happen tomorrow but it will happen...….how many times have I tried to practice that philosophy....LOL.
Ian.
Well dammit, looks like im abandoning some more parts i made lol. My dunham pneumatic closer showed up on ebay for about half price so I grabbed it up. Going straight to full automation. That means I have to let go of the direct coupling idea and go with the dual idler 5mgt setup. I guess in the end it's less wasted time and money. I can integrate all the pneumatics cleanly. The unit will have a single air line coming in that splits to 2 adjustable regulators, then a 4 way solenoid for the closer and a 2 way for the brake. Independent pressure adjusting for both. Back to cad I go. One thing I did realize is that I can just reassemble the original big belt design for turning any parts i need for the 5mgt setup with closer. It worked fine, just too much backlash for precision indexing, but it turn some parts no problem.
For the idlers I'm kind of wondering if it would be easiest to just use 2 big bearings stacked together. I'm thinking 40mm od, either 12 or 14mm wide double stacked for 24 or 28mm wide idler. No need for flanges since they will be right up close to the flanged 5mgt pulleys.
Nothing wrong with stacking bearings like that for idlers. Sound like a good plan.
Hi, provided they're sealed radial bearings there should be no problem.....just don't make them a force fit on the shaft.....perhaps a simple circlip to hold them snug will suffice...………..that makes easy assembly/disassemble when the need arises.
You might make them a fixed entity with the shaft they're mounted bolted against a slotted hole on the backplate face without having to user a swing arm and spring etc as once tensioned they won't need to be resilient.
There has been a school of though that a jockey wheel tensioner pressing against the back of the belt hastens belt wear due to the back flexing as it goes around the pulleys etc
I would think that if you just had the belt across 2 pulleys and tensioned them tight that would give you more than enough drive...…….. the extra tooth engagement of a back flexing belt is hardly measurable.
However, if you have a very small pulley on the servo then perhaps the belt back bending to get more tooth contact is necessary...……...testing will prove otherwise.
At any rate, the effect of the tight belt will put a big load on the servo motor spindle bearings so that is something to consider in the equation......a breakdown in the servo motor due to bearing failure is a major disaster.
I think a design that had a separate bearing in the backplate that the servo motor spindle poked through would take all the tension off of the servo motor spindle...……...but that would only work if the servo motor was fixed and you had an idler/s on a slotted mount to do the tensioning.
At best you would get 1:6 reduction with pulleys of 10 teeth on the servo and 60 teeth on the 4th spindle.
As you have considered the direct drive with servo at 1:1 perhaps a bigger pulley for 1:4 reduction etc on the servo, while giving less reduction, would not need an idler as you have greater wrap around and more teeth in contact.
Ian.
I'll be sticking with 1:1 ratio with the belt. As I figured out earlier, I need to give 8 to 1 electrical ratio to get 3k rpm within 500khz which brings my resolution down to .04 degree step, but those full steps will land exactly on binary indexing, 90, 180, 45, etc., so there's really no need to gear it down. I can also quickly change the electric gearing and steps per unit for more resolution with lower rpm limit when I need to hob gears or anything else that requires higher resolution. As good as .005 degree per step with 325rpm.Quote:
Originally Posted by handlewanker
I agree that the idlers aren't going to significantly improve my accuracy and rigidity, especially since I'll be using a brake with indexing, but I do see a couple other advantages. First if all with no idlers, the tension of the belt is going straight to radial load on the servo and spindle bearings. With 2 idlers pulled in close to eachother almost touching, the direction of the tension is directed inward, cutting down the radial load on the shafts by a huge amount, nearly eliminated. Another advantage is cutting down on any possible vibrations from unsupported belt. With the dual idlers, there is almost zero unsupported belt. Also much easier to set tension with the servo and spindle being fixed.
I argued against the idlers before, but now I'm seeing the advantages.
I plan to do it with the slots like you mentioned. There will actually be dual plates that capture the idlers, slots in both plates to allow adjustment of the idler positions. The dual plates will extend all the way over to the servo, so I do also gave the option of using the bearing support for the end of the servo shaft.
My original belt setup had the servo right next to the spindle with both shafts pointing in same direction. This worked and was nice and compact, but after spending some time modeling different gang tooling setups, it will open up a lot more options if the servo isn't next to the spindle. Much better if the spindle is in front by itself with clearance on both sides. The new setup will have the servo in back with shaft pointing opposite direction. You would thing that would make a really awkward configuration that takes up a lot of space, but now that I'm adding the pneumatic closer, it's basically the same footprint, the servo just sits next to the closer in back instead of next to the spindle in front. I'm gonna do some modeling this weekend and get it all layed out.