4th axis

[Runner4404spd]

has anyone done a home made 4th axis conversion for these mills? i am looking for something with an 8 table, but there are few different types of models out there. ideally i would like zero backlash. one of the rotary table models i have seen has a gear drive and the other worm drive. are there particular brands that are better than others for this application? i understand the work drive should be adjustable to minimize backlash, is this the one to use? and which brand has this option?

[Cruiser]

Runner,
This is a cheap china 8" I got a while back and have been working with for a while. I did this thing twice, this is as it is right now and I like it so far. Before, I had the motor directly mounted on end of shaft and it was too long for traveling in the confines of machine. All I have to do now is to make a cover to keep krap from belt and to redo the wires. The wires work as is but I can't run them close to each other or I loose all function with the drive. I really need to cut them off and start from scratch with twisted pairs or something so I can run them in one bundle but I don't know yet if that will be enough.
As for Zero backlash, I have found that it is all in the setting of the worm. The worm is on an accentric and can be rotated into the gear for lash control and then a little stop set is run into stop for same. I found that they are not as quality controlled as I'd like but they are functional. Mine had some binds in the gear mesh, shaft bushings etc. which needed touch up, can't do anything about binds in worm tho except wait for them to smooth out in use. I am using a large servo that I got from Keling and It don't mind the binding at all within reason. If set too tight initially it can and will stall the drive out but that falls into how tight the lash is set. The backlash as mine is setup right now is so miniscule that it is quite ignorable and with use I thing it will get better.
I modified the end of the worm shaft and the concentric by shortening the concentric and machining the shaft then boring a pocket for a roller bearing that I had. This took a lot of wiggle out of the shaft and allowed me to set it up with some preload on the bearing to hold shaft in one position within the concentric.
I have had thoughts of using an indexer already setup with a chuck instead of this thing but didn't. If I get a few bucks ahead someday, I still may give it a try. Maybe my included pics will help with your idea's.
Don

[Runner4404spd]

i was planning on running mine with a servo and have toyed with the idea of mounting the encoder to the actual table either internally or with a shaft protruding. that would ultimately get rid of the back lash issue i think. i was looking at grizzly online and they have some gear driven rotary tables that they claim are like yausa brand. i've heard of yausa but really can the knock off be good?

[Cruiser]

Runner
I don't think that putting the encoder in another spot will do what you want. I left mine on the servo motor as it comes that way. My reasoning is that the motor is going to be spinning a lot more than the rotory and thus give a better resolution output. As for brands of rotables, I suspect that the main differance is the name applied per contract and that they are mostly made by the same chinese company.

[Runner4404spd]

i bought motors from keling and they don't have encoders on them yet. thats why i was thinking of adding a small shaft and installing the encoder onto the table directly. think of it as attaching the encoder onto the screw like the mill is. this way it really doesn't matter if there is alot of backlash between the table and the motor. ideally you want to minimize backlash but i think this would add a more precise control of the table.

[BobWarfield]

Runner, lots of folks have built 4th axes like Cruiser. But they're gonna have backlash or be finicky to adjust. If you want something better, look for a deal on a harmonic drive and then use that backlash free gearbox to drive your axis without any other gearing. It'll be more work to build, but it'll eliminate the backlash without the drawbacks.

Best,

BW

[Runner4404spd]

Bob,

i had a harmonic drive at one point in time. my worry about it was 1 it was a stepper driven one, and two i don't know enough about them. can the drive handle cutting forces? how do you mount a chuck or something else to it? if i have to build something like this i was thinking of a belt drive unit with some bearings supporting an open hole spacer. that way i can machine a 5c mount into the tube and just build a drawtube and a closer mechanism. in the short term i was hoping for less of a project as i'm limited on time.

[BobWarfield]

Quick and easy is slap a stepper on a regular rotary table.

The Harmonic should take the forces fine, but you will have to basically build the 4th axis from scratch, or adapt something. I've seen people adapt lathe spindles from small lathes and spindexers, both with good success. Of course the spindexer will be set up for 5C collets.

If it was me, I'd bore a big hunk of aluminum for some bronze bearing inserts and then line bore those. It doesn't need high speeds, it just wants to be stout. Eventually I'll whip up something like that.

Thought I had bought 2 Harmonic Drives and the outfit flaked. Said they didn't have them. You're not supposed to list on eBay unless you have the inventory, but of course they cheated. Watch out for the guys that show a picture of a warehouse on the listing.

Cheers,

BW

[dsdmax]

Gentleman - please excuse my ignorance as i am VERY new to this hobby .. still havent purchased a machine but did pickup Alibre CAD and working pretty well with that... my goal is to have the design process out of the way went i eventually get my machine so i can immediate start making chips.

Back to my question - why build a 4-axis? IH offers one? Its it the expensive of the available options, challenge to build one or quality of the product offering?

Just trying to understand the motivation of this thread.

[Runner4404spd]

I built my IH mill from a kit and didn't buy a finished product. also the 4th axis that is being sold is stepper driven. while i agree that this is ok as a stepper should work just fine. i have all my servos connected to an e stop so if one fails to reach position the whole machine faults. its a safety failsafe i built in using the gecko drive schematics. so far it works really well. i've had it stop a few times during the tuning process. so i would like my rotary to be servo driven. also yes there is some challenge to building it yourself. ultimately i don't have a huge need for it, but i would like to have one to tinker with, so i don't want to spend alot of money on it. also this will be a precursor to a five axis add on i want to build.

[Cruiser]

Runner,
I think that most of the "Backlash" issues are with motors too small that fault when the worm is engaged under tension. If it is loosened up to get motion for the small motor then you will have backlash. What I find is that my big servo will drive the worm engagement with enough tension to eliminate the backlash, but, If they have any out of square bushings within then there will be erratic binding, this is what i found. If your motor is big enough then it should be fine. If I remember correct mine is 1200 oz" and I'm glad I got a little greedy with motor size. I had to do some modifying of the worm drive components, but could not fix everything so still have one bind but it is getting less noticeable as it wears in. I have it adjusted to as near zero lash as I can get and I've made moves of .02 deg and it moves the indicator. Just how tight do you want yours ?

[Runner4404spd]

I think i will buy a wholesale tools model and then take it home, take it apart and inspect it. i agree there needs to be someway of adjusting the worm to minimize backlash. if there isn't then there is no point in even trying to mod the rotary into a 4th axis. also if i can move .2° and have it register then i think that will be good enough. ultimately i won't know until i get it actually built and making some parts.

like i said ideally this will lead to a 5th axis project. i notice either grizzly or enco had 2 axis rotary tables. again the goal would be servo drive and encoder feedback.

after i build my rotary i plan on getting onecnc xr3 4th axis software. i already have the 3 axis mill and 2 axis lathe software and like them both alot. could do without the cad part of the software as i find it tedious compared to solidworks.