[kolias]

I have a 3 axis table CNC mill about 4’x3’ with a 800W water cooled spindle all made with 3/8” and 1/2" thick aluminum plate/flat bars. It’s for a hobby use and I would like to install a 4TH axis.

I do have the space to put the 4TH axis on the side of the table and modify the spindle to go over it. I will prefer to drive this axis with a stepper motor and it will be used to mill aluminum and wood.

I see quite a few alternatives on the web but since I never used one before what would be the least complicated setup?

Thanks

[joeavaerage]

Hi,
I made one. This gearbox has some true grit. Its safe maximum load is 400Nm, that's the limiting strength of the gear teeth and a rated load of 125Nm (output shaft) at 4000rpm (input)
I did have a stepper on it, but the stepper was inclined to miss steps but worse was slow so I put a 750W Delta B2 series servo on it, the one pictured.
The servo is rated at 3000rpm and with the 19.5:1 worm reduction I get 153.8 rpm. I rounded it down to 150rpm in Mach.

Craig

[kolias]

That’s a nice unit you got there Craig but you have the knowledge and equipment to make such a unit but for a beginner do you have a suggestion for a smaller unit?

Besides that I never used a 4TH axis it looks like that I have to learn much more like servo motors and how to go about programming the 4TH axis to work on my cnc. Would the motor on this link be a good start?

https://www.automationtechnologiesin...o-kit/kl-5056h

My cnc has 3 axis, 4 stepper motors and works. Would I be able to connect a servo motor to my current BOB on the B axis or I need an extra BOB?

That’s a lot of difficult questions but to keep going I must have the answers and besides after I figure out and understand the physical questions I must figure out how to produce the g-code to get the B axis working

Thanks

[kolias]

If I need 220VAC to run servos it means I can’t buy one! And neither I want to have a transformer!. I think we discussed this subject a while back, although I can run 220VAC from my control panel to my workshop to do so it means I have to brake ceiling/walls gyprock or run exposed conduits on top of the walls/ceiling which the wife hates. Had I know this 25 years ago when I bought my house and completely renovate it myself then it would have been a piece of cake but then I didn’t even know what a cnc means!

I also understand and appreciate the value of a good servo but often times we must do what needs to be done. Like it’s wonderful to drive a Ferrari but a VW will do the same job but not as fast neither as comfy.

Now back to reality it means I must stick to steppers and for my hobby projects RPM’s is not important as long as it “turns”.

You amaze me Craig with the knowledge you have in this field and I thank you for your time and well written explanation. It’s true I used steppers before many times but I bought them as a kit from an outlet in USA which included everything to run a cnc (steppers, drivers, BOB, PSU etc.). Now I will try to buy the same kit from AliExpress or similar and they have the option of close loop steppers etc. and that’s why I asked the question.

[kolias]

Sorry mate I guess what DMM replied was confusing to someone like me who has never seen a servo.

“We have a NEMA23 motor with 540oz-in torque, this is our 400W motor with attached dimensions (57N-DHT). We also have a 200W motor with 270oz-in torque but the dimension is not exactly NEMA23, its close, also attached is dimension for this 200W motor (620-DST).”

The way I read the above from DMM is talking about a NEMA23 motor. Perhaps he should have said “…. our servo 400W is NEMA23 size…..”

So now with your last reply I understand a servo doesn’t need a NEMA motor to run and I’m happy with that.

From the drawings he sent me the 400W is 117.5mm long by 60 square and the 200W is 94 long by 60 square, a big difference between the two. Depending on the price difference I will go for the 400W.

[joeavaerage]

Hi,
this is my first foray into a rotary axis and so I have no more knowledge than you. What I did know and always aimed for was that my machine would cut steel and stainless
and that in turn demands rigidity, ergo the gearbox you see.

This gearbox is a 63mm size, that is to say the distance between the centreline of the worm gear and the centreline of the driven gear is 63mm. The same company, Atlanta Drives,
do one size smaller, a 50mm gearbox. The one pictured is a 58 series, that is heavy duty and <2 arc min backlash. They do another higher spec series, the 98 High Torque series
with <1 arc min backlash. These gearboxes are well represented on Ebay at anywhere from fair prices to expensive. It costs nothing to look.

As I posted I found a stepper to be a bit slow and inclined to miss steps. This stepper came off my previous mini-mill and so really is just too small for the job. I have used Delta servos
before and that's why I chose them again. With the gear reduction that means the chuck can do 150rpm, which in turn means that rotary toolpaths don't take an age to execute.
A stepper would have worked but result in about 25rpm output speed, which would cause rotary tool paths to drag on and on.

What motor you use on a fourth axis, or fifth come to that, is down to budget verses performance just like any of your other axes.

I have bought a subscription to Fusions Machining Extensions. The introductory offer was $1200USD/year reduced from the normal price of $1600USD/year, and that's over and above
the $545USD/year for the basic Fusion subscription. Fusion + Machining Extensions is, as I found, about the cheapest way to get continuous four and five axis. You are right to be
concerned with how to generate toolpaths.

You can write some simple toolpaths by hand, but its slow and tedious.

You might like to investigate Deskproto. Its is a cost effective way of generating continuous four axis toolpaths. It does indexing five axis only.

Craig

[kolias]

Many thanks Craig for the help,

Now I understand the advantage of higher RPM, no one will like to use 25RPM.

I knew CAM software are expensive but didn’t know by how much, they are too expensive for my needs. I have been fortunate in the past because a friend works in a machine shop close by and I can have access to a desktop with MastercamX5 which I used in the past and learned enough on my own to do basic toolpaths. I have to check to see if MastercamX5 can do a toolpath for a 4TH axis but the Deskproto you suggested looks promising. They have a free version for hobbyist but I couldn’t find out what “free” means. I will download what they have and eventually will find out.

[joeavaerage]

Hi,

Now I understand the advantage of higher RPM, no one will like to use 25RPM.

It means that you have one slow axis and so the whole machine slows down to match it. There are a few tricks that can improve cycle times with a slow fourth axis but they
all lessen finish. 150rpm is much better, its still not blindingly fast but it is highly useable.

I saw that Deskproto was $250USD for non-commercial use, and that is pretty fair value.

Its when you come simultaneous four and five axis is where the money goes. If you have access to Mastercam then do whatever is required to retain it....boxes of beer, plates of date scones,
whatever. If you have to buy simultaneous four and fve axis you'll weep.

Craig

[kolias]

I know transformers aren’t evil Craig (BTW I think they aren’t called transformers when you go from 220VAC to 110VAC) but the problem is that I still have to drag a 220VAC cable to my garage to feed the transformer to get the 110VAC or if I leave the transformer close to the panel still have to drag a 110VAC to the garage (that’s where I have the space for the cnc).

Thinking ahead I just realized that it will also be more difficult to sell a cnc which requires 220VAC because most houses do not have 220VAC available in a garage. All my previous machines were sold to people with a garage like mine except one went into an artisans shop where 220VAC was available.

[joeavaerage]

Hi,
I'm not sure what you're talking about. What voltage do you have in your workshop? If you need or want 220VAC (or 230VAC or 240VAC) to run specific device in your workshop then a transformer
to take your available input supply to the required output voltage, say 220VAC is required. No big deal, they are moderately costly but thereafter do well for decades.
The transformer can be in or on or near your machine, it does not need to be in the distribution panel.

A transformer is a still a transformer whether the voltage is increasing or decreasing.

I have said time and again that given that you don't have 220VAC (or 230VAC or 240VAC) in your shop direct then use the DYN2 drives. They require 70VDC, or thereabouts. So if you have
110VAC (or 115VAC or 120VAC) in your shop you just hook a power supply to it and viola....you have 70VDC to run your servos. If you choose your power supply wisely then it will run on
either 110VAC OR 220VAC, and that would make it compatible everywhere, a useful sales point. What's the bet if you equipped your machine with servos you'll not want to sell it!

I presume you use a power supply for your steppers? That same power supply could be used for servos. Having said that IF you do buy servos then you would be very poor idea
to give them anything less than the manufacturers recommends. As I've said before if you pay big money for servos don't throw any performance away by saving a few dollars on the power supply.

This is the sort of thing I had in mind:

https://www.antekinc.com/ps-15n70-15...-power-supply/

This thing kicks arse! 70VDC rock steady day in day out, 200% overload for minutes at a time. It can be wired to run on 115VAC or 230VAC, and we are NOT going to get hung up on a few volts either way
are we? With this power supply you could run four or five 200W or maybe even 400W servos and it wouldn't break a sweat.

Craig

[kolias]

Can you give me your opinion Craig on the attached kit?

What the ratio 100:1 and 50:1 means?

I’m not saying I will buy this kit but it will give me an idea what to look for. This kit is from Amazon.CA and the price is in CDN$

Thanks

[joeavaerage]

Hi,
the 50:1 and the 100:1 is the gear reduction of the harmonic drive.

A 50:1 harmonic drive powered by a stepper doing 500rpm will have a 10 rpm output, ie pretty slow.
A 100:1 harmonic drive powered by a stepper doing 500rpm will have a 5rpm output, even slower.

Harmonic drives are good because they have (theoretically) zero lash, but the typical gear reductions are 50:1 and 100:1 which are excessive for a fourth axis. Those reductions are better for a
robot arm that you expect to rotate +180 degrees and -180 degrees rather that rotate continuously. Such a large reductions will mean that even a small stepper will have great torque authority over the
chuck which is good of course. All in all,I'd say that unit looks pretty good just [Uslow[/U]. You could swap out the stepper for a servo doing 3000rpm and at 50:1 that would be 60rpm at the output, which would be useful.

Craig

[kolias]

Sorry Craig, I misunderstood.

That will work but now we come to the total cost of a 4TH axis with a servo.

$230 for the transformer + Shipping from USA to Canada approx. 70 = 300
Approx. cost for a servo 400 + Shipping = 470
Approx. cost for a gear box 500 + Shipping which I don’t know the cost
Total approx. USD$1280 = CAD$1721, say CAD$1800
Duties and taxes for the above to enter Canada are not included in the above but I will estimate them to be close to CAD$150

So we are talking to increase my cost by about 2000 – 2500 if we add the aluminum pcs I need to mount the 4TH axis, wiring and what not. That is a lot and it will be a hard sell. I’m not say no but will have to think about it.

[kolias]

Well Craig I think I go from one surprise to another. First I thought DMM will supply the chuck and also I thought they will supply the gearbox. Now it seem that’s not true. And all this happens because I have no experience with the servos.

Thanks to you again I learn! I hope I can find one of these gear boxes to fit the servo’s shaft.

Lets first see what is the price DMM offers and after we can decide about the gear boxes.

BTW are any more surprises? I mean is there anything more I need to have my bloody fourth axis complete? lol

Just noticed your last reply….Craig you are a devil..think I will swim across the lake in the middle of the winter lol. Sound good but first have to think if the shaft will fit into this gearbox

Many thanks

[joeavaerage]

Hi,
that's right....its winter there, I keep forgetting, being peak of summer here. Still a swim across Lake Michigan in summer would still be an serious ask!

The reality is that it most unlikely you'll find a servo that matches a gearbox perfectly. Whats most likely is that you might find a 23 size gearbox and so
it will match a 23 size servo, but the shaft sizes may not be perfect. Tough...you just adapt them together.

For instance the input to Atlanta Drives worm reducers are splined shafts. So you have to find a spline adaptor.....not easy or cheap. I made mine.
I have attached a pic for the model I drafted for the internal spline to match the input shaft, and the second pic is the toolpath. Just to give you some
context the bore is about 20mm. The tool I used is 1.5mm in diameter but 12mm long, so a very long and skinny tool. It took about three attempts
before I got both the model and toolpath parameters correct, or at least good enough that the tool survived! Eventually I ended up with a very nice fitting
internal spline made out of brass, brass being such a nice machining material for this sort of thing.

I did a similar thing on the other end for the servo shaft and keyway. The whole point about a CNC mill is that you can make parts, so that is what I did
rather than write to Atlanta Drives and buy one.

Craig

[joeavaerage]

Hi,
for instance the Atlanta Drive gearbox I linked to on Ebay is 63mm, that is the same size as mine but it has a size '6' flange, whatever '6' means. So you'd have to make an adaptor plate if you were going
to try to fit a 23 size motor. In my case I had a size '5' flange and had to make an adaptor plate to fit the 80mm servo I used. Again this is the perfect use for a CNC machine....no buying parts that
you can make yourself.

Craig

[kolias]

Thanks for the education Craig, much appreciated.

Are most of the stepper motors doing 500rpm?

Yes I could change the stepper with a servo but the problem will be if the servo shaft will fit. If not I’m not equipped to do what is required. An alternative will be to ask if they can switch the stepper for a servo before I buy but I doubt they can do it.

However I found a servo motor kit on this link.

https://www.automationtechnologiesin...a23-dual-shaft

What “skewed rotor” means?

I noticed the shaft is 1/4" and all the NEMA 23 motors I have now are also 1/4" shaft. So perhaps if all NEMA 23 motors are 1/4" shaft I may take the chance and get the harmonic drive kit I mentioned earlier and replace the stepper motor.

Are the specs on this servo any good?

Many thanks again

[joeavaerage]

Hi,

Are most of the stepper motors doing 500rpm?

Depending on the stepper no most will go faster.

If you have a low inductance stepper, say <1.5mH and a high voltage driver it might get to 1000rpm or even 1500rpm before stalling, but most steppers
are good to about 500rpm or so.

However I found a servo motor kit on this link.

No, you don't want that sort of thing. Its just a DC motor, then you have to add a driver, encoder etc......don't go there. If you are going to spend big money make sure you get
a great result.

This is what you want, if you want servos at all, 400W motor, drive and cables, the drive is 230VAC direct off-line eat any stepper ever made:

https://www.fasttobuy.com/220v-127nm...ol_p28069.html

Craig

[ardenum2]

What “skewed rotor” means?

it means it runs smoother, most modern motors are like this, expect frameless motors that you can buy relatively cheap on aliexpress which use permanent magnets still tend to be 'straight' but for pm's it doesn't matter that much because of their native synchronous nature.

the motors in the picture look like 1990's tech, you'd probably be better off with a modern closed looped stepper than this.

[kolias]

it means it runs smoother, most modern motors are like this, expect frameless motors that you can buy relatively cheap on aliexpress which use permanent magnets still tend to be 'straight' but for pm's it doesn't matter that much because of their native synchronous nature. the motors in the picture look like 1990's tech, you'd probably be better off with a modern closed looped stepper than this.

Thank you for your time