[LongRat]

If you don't need the accuracy then the last thing you should do is spend a fortune on components to get it!
I've got a CNC 4th axis on my home machine, which is simply a Vertex rotary table with a stepper motor on it. Works absolutely fine. The limiting factor with the backlash is that if you set the worm up for no slack at one point, somewhere else around the rotation the system will bind. There is a lot to be said for 'running in' the system. Just adjust as well as possible, and then set the table rotating continuously for half an hour or so. My system is really smooth after a few hours' use now. For a trunnion set up, you can't afford to have enough slack in the system that it will start vibrating in the backlash and cause finish problems. I think you should be able to get away with it though.

[MichaelGolden]

Hey guys, got the electronics last week. Just a little update getting everything together in my spare time.

If theres any problem with the backlash I can always go another route. I'm just not to keen on spending too much on this little toy right now. One step at a time. Lets try it out and see what happens.

I decided to get into hobby machining a year ago. I should give props to all you guys with build logs and youtube videos before me. Its helped a lot. Going to be an awesome year.

Mike

Attachment 221810

[lsfoils]

Greetings,
Worms and wheels are problematic... running them in works, to a degree, for those that are already very close. I would recommend against using any lapping compound as the wheel or worm can be permanently loaded with the compound and things will wear out quickly.

Bought a small rotab and found the wheel was out considerably. Took it apart and realized the worm was very close to 8 tpi. + or - just a tiny bit. The wheel was cast iron. So I made 2 worms on my lathe (no modular function on that machine for worm gears) and cut 2 duplicates for the worm gear/shaft out of SS 304; 8tpi, 29 degree included angle. Then I gashed one new worm gear at an angle offset from the shaft's center axis to make cutting teeth using a 60 degree dovetail cutter. I loaded up this new hob into the rotary table and set the backlash to near zero. Instead of using a stepper, I hooked onto it with my cordless drill. After maybe 30 seconds, I could hear the drill's motor smoothly running for the full rotation of the table. I readjusted the lash ring on the table and did it again. I think it took 3 cycles to get the worm to run clean. Wish I'd taken pictures. Anyway, if you use this method, be sure you take the table completely apart and clean it! I found quite a pile of shavings inside (surprising amount!) and you'll want to make sure all the bearings and bearing surfaces are clean. The teeth on the worm wheel looked perfect. There is still a tiny bit of backlash in the unit. Has to be to turn. But it works for what I do. Hope this helps. -Doug

[LongRat]

Nice method lsfoils.
Mike, while your CNC parts look nice on the bench, I am more impressed by you desktop wallpaper. Love it!

[TJones79]

Doug - this method sounds nice I might have to use it myself as I've had some problems with the worm wearing out too quickly.
Mike - your parts look nice. Glad you're making progress

[MichaelGolden]

lsfoils, that's some very useful information. Thanks for sharing your technique.

Haha, im glad you like it Longrat. I figured someone would appreciate it.

Thanks guys, its a fun little project. I just finished the initial shape of the chip guard. Next would be the drip tray/coolant, limit switches and zero backlash couplings. I ordered 1 zero backlash coupling from automation technologies and im glad I only got 1 because its not long enough to reach across the z axis shaft. So I'll probably cut a few all from scratch. We'll see how it goes..

I'd also like to recommend this little tachometer display from http://macpod.net/misc/sx2_tachomete...ter_kit_v2.php Its cheap and super easy to plug in. I cut a rectangle where the original "power" light sits on the housing. Works great!

Here's a pic anyway
Attachment 224114

[MichaelGolden]

Here's the very first part cut on the machine. I've never had the pleasure of using a cnc mill before so its all part of the learning curve. Here's my take on the limit switch housing. I got the idea from mduckett's thread http://www.cnczone.com/forums/bencht...version-7.html The springs are out of a cheap pen and wound down a bit smaller. I cut down a 1/4" bolt and drilled 1/8" and 5/32" holes. The push pins work well. The 3/8" brass rod is spun down to 0.12" and about 0.612" long. I've attached a file for the housing if anyone wants to use the measurements. I'm not sure how well it will actually work with the mill yet but we will find out!

Attachment 225412Attachment 225414Attachment 225416

[TOTALLYRC]

Feels great to make your first part on a new machine.
Keep going, you won't believe what you will now make just because you can.

Mike

[Fastest1]

Your own personal metal cutting robot. It is just fascinating to watch and do. Congratulations.

[hanermo]

I suggest you will need about 100x more steps, to make it work in metal for 5 axis.

This will become obvious to you once you get it working.
You dont need a lot of accuracy, necessarily, you need linearity and repeatability.
As well as rigidity.

The error budget stacks up fast. You multiple every axis´ error with each other.
Thus a 0.01 degree angular error (x1), at 100 mm radius == 0.01745 mm.

So, multiply x1 with x2 in microns == 17.45 x 17.45 = 304 microns. Or 0.3 mm.
(Now add backlash at 0.01 degrees only (unlikely), and its +/- 0.3 mm in true position.

Now multpily with linear errors on x, y and z, at say 3 microns each.
3 x 3 x 3 = 9 ; x 304 = 2740 microns.

2.740 mm.

You are unlikely to get 3 microns ACCURACY on x, y or z unless you use engineering components.

[arizonavideo]

Sure, so you should give up now before you have any FUN!

Your first part looks good, your bench is way too clean, try some spry coolant to fix that.

A blower will get the chips out of the way better but then your bench will have to give up some of that clean look.

Have fun

[LongRat]

That's a good looking first part.

[MichaelGolden]

Spray coolant is coming! For now I have some WD40 lol

I understand the backlash issue becoming more and more of a problem. Still something to decide upon. I really like diy stuff. Anyone had any success with hypocycloid reducers?

Made some new motor couplers out of puck board I had laying around to replace the rubber ones. Made 3 junk ones with the backlash I had until I got it to fit nice and snug. Then made 3 good ones! It seems to help. I haven't taken an accurate measurement of the backlash yet.

I have an extra tilting column base and took some cuts into it this weekend. Going to see if I can mount the stepper motor underneath the column. Seeing as how I will be adding a riser block for added z travel. It will save me a lot of space in the front (7 inches!) which will make room on my bench for an extended base.

It seemed to cut the cast iron relatively well. Snugged everything up. 2 flute 1/2" bit @ .04" deep 520-590rpm @4.5ipm 40% step over.

I will be looking into some upgrades for the gibs. I have been reading about some guys going with lineal bearings. I've also been thinking about replacing the z axis spring because it gets way too close to the work in some situations..

Here's some pics!

[rs4race]

Assuming your using mach, if you get a chance to measure the backlash mach will compensate for it. I havent really cut anything out since I put in the backlash numbers, but testing on the indicator is a lot better now that its compensating. It seems that it would be best to eliminate it mechanically, and also that you can only eliminate so much before you have to pay significantly.

I look forward to seeing your project come along. I was thinking about eventually converting my g0704 to 4 or 5 axis so I will be keeping an eye out here for tips.

[MichaelGolden]

So back to the low cost worm gear approach for a moment.

When I started assessing what size of work I would be doing. Such as the use of a 5 inch chuck... Needing a 6 inch rotary table... And gearing components. It was really adding up and pushing the limits of the little machine.

It was clear to add a spacer under the column to gain more z travel. (I'm laser cutting them from 3/4" steel.)

At first I thought a 5" chuck would only really need its radius of motion along the y axis. Which seems reasonable only being around 2.5", which the little machine is capable of. So I thought I would sketch up some measurements to get a better feel for the actual dimensions of the machine.

At first I was imagining the A axis table to be as long as the rotary table + stepper motor. But the assembly ends up being ridiculously long and difficult to balance on the table. The phase II rotary table I have is too heavy to be placed on the end of the x axis table. And I had previously imagined cutting the trunnion table housing from aluminum to save on space and weight. But I have a different idea.

The location of the stepper/servo motor attaching to the table is an issue. Even with expensive components. Theres just not very much room. And do I really need 360 degrees of tilt? I can have close to that, at the same time having a better balanced and easy to assemble/disassemble machine.

In the photo you can see the shaft sticking out of the rotary table and its range of motion around the center axis of the table. But if you map its range of motion you can choose any un-used area to mount the bearing support arm while keeping everything very close to the center of the table.

Required for this attempt would be the construction of the bearing support arm and a steel plate for the table to sit on. It would be a nice way to test the performance of the worm gears before deciding to pay for expensive components or choose to build everything from scratch.

[neilw20]

Assuming your using mach, if you get a chance to measure the backlash mach will compensate for it. I havent really cut anything out since I put in the backlash numbers, but testing on the indicator is a lot better now that its compensating. It seems that it would be best to eliminate it mechanically, and also that you can only eliminate so much before you have to pay significantly.

I look forward to seeing your project come along. I was thinking about eventually converting my g0704 to 4 or 5 axis so I will be keeping an eye out here for tips.

I refer you to post #5
http://www.cnczone.com/forums/bencht...ml#post1406234

Good luck with any compensation above 3 axis. It is broken, after weeks of testing, and I could not make it work on a 5 axis machine.

[MichaelGolden]

Here's a little progress update. Started work on the drip tray. Column spacers are cut. A bit of grinding and drilling to fit it together from here.

Also, I ordered a 50:1 harmonic drive for the A axis.

Some pics!

[MichaelGolden]

Alright dissected everything again and now its coming together. Ready to fit and extend the y axis. I'll have to order a new ballscrew. Got aluminum for machining some 4th axis stuff. Couple things left to do and I can start fiddling with 5th axis.

Here's some more pics

[MichaelGolden]

Little update

After shimming the extended base down I welded it to the steel it rests on. I have 1/2" bolts holding the rest of it down where the mounts allow. I was thinking about braze welding the cast iron together as a more permanent solution. I'm still waiting for the longer c1 ballscrew in the mail to arrive so I can put everything back together and start drilling holes into the rest of the components.

I was about to make a stepper motor mount from a solid piece of aluminum for my rotary table. And quickly decided it would be easier to test it out by welding some flanges to a piece of pipe. I decided to machine the whole thing down because it looks nicer.

[MichaelGolden]

I got a used harmonic drive off ebay for a decent price. Seems to work just fine. I'm making an aluminum housing for it and the stepper motor. It will bolt to the steel mounting body. Allowing me to upgrade to a better drive in the future, if I need.

These tapered roller bearings are actually wheel bearings that I snagged from work that are in excellent condition. The harmonic drive will directly turn a shaft. The shaft is a machined 1" bolt that is applying preload between the wheel bearing and another bearing housed inside a machined 2" piece of pipe.

I know it may not be incredibly accurate with the worm driven 5th axis backlash issues. But this is the absolute best way to learn, without forking out a ton of money into something you're unsure of. I use what I can get my hands on for little to no cost. I've already learnt so much just by thinking about how it all gets put together.

Here's the two rough cad drawings of the main dimensions.

I'll post some more pictures as I go.