Rotary Axis

[rodm]

A mate called in tonight and dropped this on my bench. It is a zero backlash 5 inch chuck with 50:1 reduction.
The parts were mine and I have had them for a couple of years but lacked the intestinal fortitude to put them together as I just kept seeing problems.
I am over the moon with what he has done and this will replace the smaller 4th axis I have on the mill.
The gear reduction is through a ball reducer and then further reduced through toothed pulleys. There is a bearing in the front to support the chuck. All I have to do is fit a plate on the bottom to lift it so the jaws clear the table - and eventually make a tailstock.

[rodm]

Here is the 4th axis on my mill which has a zero backlash Harmonic Drive direct coupled to an 80mm three jaw. This one will be moved to 6B4 and I will have to design in extra Z axis travel on that machine. I have a tailstock from a Seig lathe that matches this and has an MT1 bore.

Before anyone asks about the progress on 6B4 I have been out of action since January so nothing has been coming out of my shed. Hopefully that will change soon.

I have a Chinese origin 4th axis which is also an 80mm chuck and has timing belt reduction only. That is out on loan so when it returns I will post a photo to show another example of a 4th axis. The backlash on that is quite acceptable for a gantry router but not as good as the ball reducer or harmonic drives.

[wheelinround]

Rod thats a real nice set up similar to what I have been checking out (as said over on Chris's thread)

One I found yesterday now this has real possibillities.

[ame=http://www.youtube.com/watch?v=w0-tXDEvAqg&feature=results_main&playnext=1&list=PLD289AC5358593DAC]New CNC Trunnion Table can be 4th or 5th Axis made by HTS - YouTube[/ame]

[wheelinround]

For the wood CNC I found this a while back

[ame=http://www.youtube.com/watch?v=O3d0fueNr30&feature=related]5 axis cnc routed Pineapple file - YouTube[/ame]

[rodm]

Hi Wheelinround,
The first one is Hoss's X2 freak and there is a long build thread over on the zone about this machine. He has done it all to this machine and has continued on to other builds. The trunion table is good but limited to 180 degrees for cutting.

The main issue with more than 4 axes is generating machine code to cut jobs. I am not aware of any decent afforable software to run a 5 or 6 axis machine. That may have changed as it must have been at least four years ago that I has a serious look into it.

[RayG]

Hi Rod,

Congratulations on your new 4th axis, looks pretty solid and with that 50 to 1 gearing should have no shortage of torque for any number of jobs.

I like the construction, very well thought out and executed.

A couple of questions...
What sort of mounting plate are you thinking of, flat plate with slots to match T-slots in the table on the mill?

Also what sort of bearings were used?, I'm guessing AC to cope with axial loading, did you go for precision bearings?

I was thinking of converting a vertex rotary table, but this approach has some definite advantages.

Nice job

Regards
Ray

PS, if you could get up to a few hundred rpm and the spindle is solid enough, you could run it as a cnc lathe...

[rodm]

Hi Ray,
The original assembly had the front plate and bearing on it - an ebay purchase. I assume it is a taper roller or AC but never pulled it down. It is firm with no detectable radial or end play.

I will attach this to a full length 20mm ally plate incorporating a tailstock slide. I am toying with mounting the tailstock on linear rails rather than slotting the ally plate. Locking the tailstock is my biggest problem as I do not want to load the trucks by pulling it down to the plate. Hope I am making sense and if there are any ideas on this I would be grateful for the input.
The plate will have four holes, 2 each end to pick up the tee slots for mounting on the mill. Might even drop an additional set of holes in the middle of the plate.
Set up on the mill should be easier as I can dial in a test bar held between the chuck and tailstock.

With a 5 inch chuck it makes the assembly quite high and not suitable for a gantry router but still workable for a mill with plenty of Z axis travel.

The Vertex rotary is a good choice. You can use them vertical and horizontal if you design the motor connection accordingly. Backlash can be eliminated through the worm drive and they have plenty of weight in them which is always good for machining. Mounting a chuck on them gets a bit tricky and you might need a chuck you can bolt through the face or a smaller chuck that you have enough rim on the backplate to use tee slots on the outside. I think Ozmestore has chucks and mountings specifically for rotaries or you might be miles ahead than me on this already. I tend to type as I think these things through so excuse my ramblings.

[RayG]

Hi Rod,

Just thinking aloud... (must be contagious.. )

The tailstock and chuck mounting is probably best referenced to the most accurate surface on the mill which would be the table ( once it's trammed ) ...

What about just making both ends mount on the table t-slots, with a bit of luck the tailstock center will be within range of the chuck center.. if head room is an issue, then that would also give you more Z But, on the downside, setup time would be longer than just having everything setup on a plate that you can drop on in a few minutes... I guess it's a trade off...

The one I've used with the rotary table is adjustable ( over a limited range) it looks a bit like this..



Regards
Ray

[rodm]

Hi Ray,
I agree about referencing to the table. Unfortunately it is being mounted on an X3 with a T slot length in the table of 470mm. I can't extend too far outside the table as it will hit the enclosure. If you look at the photo you can see I am stuck between a rock and hard place for mounting this = it will be a compromise.

I am leaning towards a mounting plate and overhanging each end so I can get a reasonable turning length. I have one of those rotary table tailstocks so I will try to find it tomorrow and see if it takes up less space than the C2 lathe tailstock. I would only be able to mount a centre in the tailstock anyway so won't be worried about loosing other tailstock tooling capabilities
.
Good news is I got it wired up tonight and got 10,000 velocity and 1500 acceleration (I think that is degrees per minute). Not fast enough for turning but quick enough to keep up with the feeds of the X3. The gear reduction is 30 to 1 which is a little low but it seems to hold well under power. Doing the cals at 10,000 that is 27 RPM and 833 RPM for the stepper so may be on the high side for realiability.

[Perfect Pens]

Rod,

I am watching with interest, as I too am looking to fit a 4th Axis to my Mechmate, just not sure which way to go? I was thinking something like what you have or a modified wood lathe might do the job. Any idea as too the pro's and con's ?
Which ever way I go, it will need to be removable from my CnC table. Any ideas as too where I might find such a beast ??

Cheers
Tony.

[SawDustSniffer]

ive got a 34 nema 1600 on a 20:1 gear box im willing to part with


12.8mm gearbox shaft with key
14.7mm stepper shaft with 1 flat side
4 wire 1600oz/in stepper motor
20:1 planetary Gearbox
also a stepper driver too suit(7amp 220volt max ) probably need a 240 to 110ac transformer , 220volts is a bit high for the motor ( driver is 110ac-220ac in )

it weighs a lot

its properly got enough toque to destroy my t slot if jambed while in use

[rodm]

Hi Tony,
Here are my thoughts (ramblings) on a 4th axis.
To do all from straight spindles to spirals and engraved cylinders you need fairly decent gear reduction. You want the drive motor to be able to hold your chuck against cutting forces remembering there will be a lever effect with large diameter jobs. You also want a decent resolution so the easiest path is gearing your motor down and I would recommend between 40:1 to 100:1. If you do the calcs then 40:1 comes out at 0.05 of a degree resolution on full steps and 100:1 comes out on 0.02 degree on full steps. Forget micro steps as that only has relevance for moving and not holding position. Servos are a better choice for a 4th axis as they will spin a lot faster so compensate for gear reduction and they hold resolution better than a stepper.

There is no point running a 4th axis with that resolution if you have backlash in the drive. I am being pedantic here. You will not get 40:1 reduction through teethed belts unless you run double reduction and even then you are inviting backlash through flex in the belts.
Best way to do this is through a gear drive. Harmonic drives are by far the best as they have multiple teeth in mesh at ony one time, then ball drives then planetary gear. Cost of these drives is expensive so be prepared for that. Rather than prattle on with this just ask if you want to know more.

The wood lathe headstock is a reasonable starting point because there are lots of chucks and accessories made for these already. You will have to work out how you are going to drive it and will probably need a lathe to make those parts. You can cut any plates on your Mechmate.

You can aslo lash up something like my mate did for me but there is a lot of work in that and he has a King Rich mill, European lathe and commercial CNC machine to play with.
The problem area is the front bearing supporting the chuck and working out a backplate for the chuck. Easy if you have the gear and knowledge but difficult for the less experienced and machine deprived of the group.

To give you an idea of cost I paid something like $600 for the Harmonic 4th axis and the components on the ball reducer 4th axis would have been around $250 including the chuck. If it was me again I would buy one of the 4th axis that Chris pointed to coming out of China. I know it would be nice to have a larger chuck on those but there are ways around that.

I also have a Chinese 4th axis I got with a 3020 machine and while not perfect they work OK. When I get that back I will remake a few bits to tidy it up.

Some points to consider are height of your gantry and Z axis travel will have to match your 4th axis.- keep motors and drive flat with table so you have no vertical projections to snag on the gantry. Think about tailstock to match centre height of chuck and ability to slide along axis and fine adjustment for holding work. You could index the 4th axis on you table with pins to locate it for setting up.

I am not sure if I have helped you with my lengthy ramblings but it might make you ponder a bit more and only you know your capabilites and what you are willing to part with for this project.

[Perfect Pens]

Rod,

Thanks for your detailed info much appreciated, i think I need to get my head around what I am going to use it for to determine what I actually need. So my Oriental Motor will not be any good Rod from what you are saying and I should be looking to change that to a servo is that correct?
I am a believer in doing it right the first time though and not skimping as I am sure you know that tends to cost more in the long run.
I think I need to do a bit more investigating, and very keen to get it happening.

What sort of size material would I be able to turn using one of those Ebay ones Rod, they appear to quite small ?

Cheers Rod

Tony.

[rodm]

Hi Tony,
The ebay ones won't hold much (63mm) but you can come up with spigots or drive centres to extend that range. I imagine you would be able to do ally, wood and composite materials using a decent variable speed spindle.

They are not ideal and the one I have needs a bit of re-working to make it better but for the price I accept their quality.

Steppers will work Ok but they are not fast. What you do is change your cutting strategy from rounding to moving along the axis that way you are not limited when roughing to the speed of the rotary. Eventually you will have wrap around the rotary and that is when you go get a cuppa. If time is money then think about a servo drive.

One obvious thing I haven't covered is what Ray is doing and get a 6 inch rotary axis and attached a motor to that. I have helped do a couple of these and they work very well but the cost of the rotary, chuck and backing plate puts you past the Chinese ones. From memory they have about a 90:1 reduction.

[Perfect Pens]

Thanks again Rod,

I will check out what Ray is doing also. I don't mind the cost so much its just getting something that is going to do the job and last doing it. I guess the other thing is quickness in cutting and what works better.

I have a bit more homework to do yet I think.

Cheers
Tony.