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Thread: Making a CNC rotary table
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22nd Feb 2017, 06:24 PM #1Most Valued Member
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Making a CNC rotary table
I have a vertex rotary table like this one R006 | HV-6 Rotary Table | For Sale Sydney Brisbane Melbourne Perth | Buy Workshop Equipment & Machinery online at machineryhouse.com.au that doesn't get used so I figured I could either sell it or turn it into an electronically controlled table. I don't know why, but an electronically controlled table has always appealed to me instead of counting revolutions etc on my conventional indexing head. I have a Hercus dividing head that is missing some plates so I'll sell that one on. The one dividing plate I do have for it is abysmal, and it looks like they just eyeballed the hole locations. Given how much those genuine dividing heads sell for, I'll make up some accurate plates for the new owner and figured that task would be a good excuse for this project.
First up is to strip the Vertex and decide how I will mount the stepper. I'm going to drive it with a NEMA 23 motor 2.8A per phase stepper. i won't drive it at full power however, maybe 2.2 A per phase. Hopefully that will be enough.
There is considerable head scratching involved in mounting the motor. Unfortunately as the photo shows the plain bearing is outboard of the rotary table, and that will make for quite a clumsy install in my opinion.
Vertex Bushing.jpg
More to follow.
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22nd Feb 2017, 06:42 PM #2Philomath in training
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Interesting project Pete.
One of the reasons for the long snout is mounting division plates, and it looks like that shaft is mounted on an eccentric so the worm can be disengaged from the worm wheel. Given that you are electrifying it, neither of those two options are likely to be needed so is it worth while shortening that whole lot to make the motor mounting easier?
Michael
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22nd Feb 2017, 06:43 PM #3Most Valued Member
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Will you be coupling the motor direct or from a belt. If direct, I think MEW has an article on a similar set up, haven't got the latest one here, it's out on loan ATM, which I think has it in, powered by Aurdino I think it was.
What sort of dollars will you be asking for the Hercus dividing head?? Could be interested.
KrynTo grow old is mandatory, growing up is optional.
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22nd Feb 2017, 07:29 PM #4Most Valued Member
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Michael I pulled the whole lot apart and shortening it really wouldn't be a viable option. I like to have an "out" in case it doesn't work, and the out is to put it back the way it was from new and sell it on ebay as a barely used rotary table I'd have to cut the shaft and even then it wouldn't have much support. It's not a great design to be honest, no roller bearings anywhere, just plain bearings.
Kryn, funny you should mention that MEW article, as I was staring at this for ages, offering up the motor and deciding which way to go with it. I finally sketched up a design and was drawing it up in CAD when I happened to see that article you mentioned. Not only was it an article, it was on the cover! The good news was the idea I'd come up with was almost identical. I would have seen it before when i got the mag, and just forgot about it but maybe it was implanted in my brain without me being conscious of it. Who knows, but the two ideas were almost carbon copies, and was good news as it meant if it had been done before it should work. I have no fear of blatantly copying somebody else's idea, but always give credit if I'm aware, so I'll say I copied MEW in the motor mount.
Here's the raw stock I used for the two flanges at either end. They were scraps I'd sawn off a uni beam or lintel. I can't recall the project but it was about 10 mm thick and about the right size.
Coupling stock.jpg
After cleaning it up on the surface grinder I bored the flange to take a sleeve to couple the two flanges. I did it on the mill instead of the lathe so I could do it in one setup and drill the other holes too.
The Wohlhaupter doing what it does best, boring and facing the flange. It finished up being a couple of tenths of a millimetre over size. No biggie, but it issed me off just the same. Not sure what happened there and can only imagine I had the auto-trigger set fractionally off. I faced the other one and then bored it conventionally for the final couple of passes, just to maintain my sanity.
Coupling boring:facing.jpg
This is the other end and is bolted to the original Vertex ... I don't know what it would be called ... "flange" I suppose? I found there were 3 cap screw holes available, perfect for my application. I did this on the lathe.
Coupling 1.jpg
This is the piece that couples the two together. The line on it is just cosmetic and is as a result of bumping it back concentric with a roller bearing I have mounted in a tool holder. It does a great job and will get things extremely concentric. It went out slightly as a result of drilling the bore. It is quite a large stickout and the drill was enough to knock it out slightly. I could polish it up, but it will be painted anyway so isn't a factor. The cermet inserts I use leave a magnificent finish, and on most turning work you wouldn't even see that mark.
Coupling Shaft.jpg
Here's the completed coupling parts ready to be assembled.
Coupling parts.jpg
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22nd Feb 2017, 07:44 PM #5Most Valued Member
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Oh sorry, this was the bore I was referring to. You can see the 0.2 mm it's over ... just kidding. The Wohlhapter does a good job but takes 6 mm tool steel instead of what's more common for me 1/4". I can either drop them on the surface grinder and take them down to 6 mm, but also have a few 6 mm pieces here too. I am happy with the grind on the tool and the finish it leaves.
Coupling bore.jpg
Here's the completed motor mount ready for paint. I finished up bonding them, as I didn't want any distortion from welding. All the clearances etc were reasonably close and I could envision this all going to hell in a handbag and binding if it became distorted. In hindsight if I were to do it again I think I'd TIG braze it. The bonding should be ok, and I don't expect it to drop on my toe any time soon, but it also means I can't powdercoat it and will need to painted (as powdercoating requires 200+ C). It's not worth setting up to spray such a weeny part. I guess it will be hammer finish for him A shame as I have some texture powder I think would have matched the Vertex pretty well. Never mind. I gave the square motor mount a kiss with the grinder just to 100% sure it was parallel to the other end. It was pretty good as it was, but it doesn't take too long just to be sure.
Coupling complete.jpg
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22nd Feb 2017, 09:40 PM #6Most Valued Member
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Ok, well this is the completed motor mount. I can't say I'm crazy about that paint, but it probably looks better in the flesh compared to the photo.
Coupling Painted.jpg
The Vertex shaft is 12 mm and the motor I'm using is 1/4". Spring couplings that size are available but they're rather large so I bored out one that was smaller on both ends. I bored them reasonably accurately as I didn't want to introduce any concentricity here. It's probably not going to matter for this application, but may as well be done correctly. The coupling is a nice fit to both shafts. I initially made a steel solid coupling, but have now gone with this.
Motor Coupling.jpg
Here's the end result with the motor mounted. The stepper will stick out from the table but is the precise height of the table, so it shouldn't foul anything. If it does I'll have to take the motor apart and grind down the housing a poofteenth. I expect it to be out in air anyway. One thing I forgot to mention was the original shaft was hardened, so making it shorter just wasn't viable without a complete rebuild and redesign of the whole table. Given the amount of work that would involve I figure I can live with it.
Motor Mounted.jpg
This is the enclosure I have for it and I don't like it at all. If anyone could suggest anything better please let me know. I decided to have the power supply for this all within the one enclosure, however when the power supply showed up it's larger than the listing said. The power supply should be 110 mm long and it's more like 170ish. A PIA as it doesn't seem to fit anything. Apparently you don't get much for 11 bucks these days!
I just whizzed gown to Jaycar and this is all I could come up with. Maybe a diecast one would look better if I powdercoated it? I always find panels and enclosures the trickiest part of these types of projects, as they can make the difference between something that looks good and amateur-hour!
Enclosure.jpg
I'm probably going to have to leave it here for the moment anyway, so plenty of opportunity to stare out into space and scratch my butt as I figure out what I will do about this. The power supply only needs to be 12V 5A as I'll run 2.2A per phase on the stepper. The Arduino and display draw virtually nothing. I could have a seperate power supply I guess, but they're more expensive. Hmmm, not sure. I don't like what I have anyway, and it will likely boomerang back where it came from. I won't feel guilty given the asking price of them!
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22nd Feb 2017, 09:57 PM #7Banned
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22nd Feb 2017, 10:02 PM #8Most Valued Member
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22nd Feb 2017, 10:52 PM #9Product designer retired
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Pete F, is NEMA 23 going to be strong enough especially if you need to mill a radial slot?
Just a thought.
Ken
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22nd Feb 2017, 11:41 PM #10Most Valued Member
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23rd Feb 2017, 08:02 AM #11Most Valued Member
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Ken this is designed as a rotary indexing table, not a 4th axis, so it's not intended to be used while cutting. Think of it like an indexing head with an infinite number of indexing plates, including our old favourite, a 127 Having said that, I tried a motor in the table and I can stall it but only by grabbing the table with both hands. The worm is 90:1 so I'm guessing the force to get it to stall would be similar to that required to force a cutter through material ie if you needed to turn the handle with 2 hands. I have another Aciera table I would use to cut slots, but if needed I think this would be ok for that type of work anyway.
I used Loctite bearing retainer to bond the parts. It's high strength and I made the parts with a high amount of surface area. The downside is I don't think it will tolerate powdercoating temps. It would likely reverse but probably at reduced strength and I didn't want to reinvent that wheel, hence the bodge hammer finish.
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23rd Feb 2017, 09:47 AM #12Most Valued Member
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I have been looking into doing this for a while, and i did discover one thing of major note, while a lot of stepper drivers brag about microstepping, its not as useful as you imagine, as stepper motors can ONLY stop on full steps, which means your actual resolution is just how many steps the motor can make (for most nema 23 motors that is 200 or 1.8 deg per step) once that goes through the 90:1 reduction its pretty small, I think 0.2 deg per step, but still notable if you needed to do something prime or really odd division, I am designing mine with 2:1 belt drive to get that increment down to 0.1 degrees to be a bit more useful.
Regards - Ralph
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23rd Feb 2017, 09:53 AM #13
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23rd Feb 2017, 11:48 AM #14
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23rd Feb 2017, 05:10 PM #15Most Valued Member
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Most stepper drivers will allow half or 1/4, 1/8, 1/16 steps too. However anything less than 1/2 steps are not really practical and even 1/2 steps will reduce the stepper torque but not an issue for Pete since hes only using it for indexing. 1/2 steps produces 36000 steps per revolution in a 90:1 RT. More than enough for most applications...
Simon
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