How to Select a 4TH Axis

[kolias]

I used to be in love with the Yanks next door Craig but this is gone since about 4 years ago however we all must agree that when it comes to buy anything the Yanks have everything! So I better stay where I am.

Not quite clear on this yet but are you saying any servo needs a NEMA motor to get going?

And why DMM is asking about the NEMA dimensions? If the servo and NEMA are matched why do I care for the rest?

[joeavaerage]

Hi,

Not quite clear on this yet but are you saying any servo needs a NEMA motor to get going?

No. A servo is just a motor, a somewhat specialized motor, but none the less just a motor. It may have been built to a standard size like NEMA23.
The motor would still work if it were a few mm bigger or a few mm smaller but it would not sell nearly as well because all the machines out there have been made
for a standard sized motor. If the servo blows up in your printing press for instance you want to be able to ring up and get another, you don't even really care if its from
the same manufacturer, just as long as it fits in the hole and works.

And why DMM is asking about the NEMA dimensions? If the servo and NEMA are matched why do I care for the rest?

I suspect that DMM have some standard NEMA sizes and some metric sizes. If you are trying to repair an existing machine then you want to choose the right
one. If you are building from scratch, then it does not matter.

Craig

[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.

[kolias]

DMM came back and said they have nothing like a chuck or similar to mount on the motor. Do you have any ideas Craig how/what I can do to mount on the servo shaft something to hold my work piece?

[joeavaerage]

Hi,

Do you have any ideas Craig how/what I can do to mount on the servo shaft something to hold my work piece?

You can't mount a chuck direct onto the servo shaft. Firstly the servo shaft could spin to thousands of rpm and you are not going to do that with a fourth axis chuck.
Second issue is that the bearings of the servo are just ball bearings and don't have anything like the capacity to handle loads that you would expect of the chuck shaft.

That is why I used the servo reducers from Atlanta Drives, they have big output shaft bearings....I don't have to design and build the chuck shaft bearing arrangement.

The third thing is that a 400W servo rated at 3000 rpm has a torque of only 1.27Nm....that's pretty modest. You'll want 20Nm or more to reliably hold and rotate a workpiece
with authority against cutting loads, so you want something like twenty-fold torque multiplication. That in turn suggests either harmonic drive, cycloidal drive or worm drive.
Some of the low lash gear reducers coming out of China might be a worthy consideration. They tend to have lash of about 15 arc min, which is only fair it must be said,
but they are favorably priced compared to a <2 arc min Apex gearbox say.

https://www.ebay.com/itm/33424922714...3ABFBMsIuKqMhh

This listing, for a 20:1 gearbox has a 50 arcmin lh which is not great, but at $50USD.....it's pretty bloody good value. There are many hundreds of listings on Ebay for these things
ranging right up to Apex quality, take your pick.

I have bought many linear motion parts (ballscrews, linear guides etc) from this company, I suggest you check it out. Buying secondhand may mean that you can buy Apex for the same money you buy NoName Chinese
new.

https://www.ebay.com/str/industrialp...cat=4322458011

I bought my worm drive servo reducers off Ebay. This is a search for Atlanta Drives servo reducers:

https://www.ebay.com/sch/i.html?_fro...ducer&_sacat=0
Some are really expensive but some a very fairly priced. Sorry I bought the best value one about three weeks ago! It's sitting on my bench at work waiting for me to make a trunnion table
and a C axis platter for it.

Craig

[joeavaerage]

Hi,
what about this one:

https://www.ebay.com/itm/20230179089...Bk9SR_jAzqnIYQ

Its new (old stock), 19.5:1 reduction, 58 series which is big and chunky (no trouble with bearings) with <2 arc min lash. Just trying to work out what size it is from the part number,
I think it's 63mm, that is the distance from the center of the worm gear to the center of the driven gear which makes it identical to my fourth axis gearbox pictured earlier in this thread.
If that is the case it probably weighs about the same, say 10kg. At $149 USD it's pretty good value.

Its in Michigan. Packed lunch, life jacket and a quick swim across the Lake and you could pick it up in person!

Craig

[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,
if you start looking for Atlanta servo reducers this will be handy to decipher part numbers:

https://www.atlantadrives.com/part.htm

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]

A very nice job you did there Craig in your adaptor but for me I think I’m heading to a dead end. I have no capabilities to do such a job neither the knowledge to search and find the right parts to mate the servo to a gearbox and then to a chuck. The more I think about it I came to the conclusion that a servo is not a good idea for me especially when I can spend about $300 and get a complete assembly with a 6:1 NEMA motor like I posted earlier.

When I asked DMM about a quote, I was thinking that I will get a complete assembly like servo, gearbox and chuck and all I had to do get a power supply unit for the required DC volts and I’m done. I will wait to see the price from DMM and then I will decide but I’m sure I will not go for it.

[joeavaerage]

Hi,
but, I thought you already had a three axis CNC machine?. That is what I used to make the internal spline, the shaft coupling and keyway and the servo to gearbox adaptor plate,
so you already have what you need.

When I asked DMM about a quote, I was thinking that I will get a complete assembly like servo, gearbox and chuck

NO, definitely not. I would expect the servo, drive and cables to be in the region of $450USD, that's no gearbox, no chuck, just the working servo alone.

especially when I can spend about $300 and get a complete assembly with a 6:1 NEMA motor like I posted earlier.

Yes, I understand. That set-up is cheaper than I would expect to pay for the servo. Hell, I just paid $600NZD to get a gearbox into New Zealand....and that's just
the gearbox. So, yes, bang for your buck that little fourth axis you posted earlier is very much more budget friendly.

As I have stated before my machine has to machine steel.....and that is another ball game. The little fourth axis you are considering would just be a joke, and a costly ($300)
joke at that, for my intended purposes. My fourth axis cost about $1800NZD ($1130USD) plus my time. I didn't come here 'to copulate with arachnids'...no I most certainly did not!

Craig

[kolias]

Yes I do have a 3 axis cnc but it’s not for machining brass/metal and although it could do the job however I’m not a machinist and you need the knowhow to do what you do. As I mentioned my hobby is to BUILD the cnc and not to work on them.

I think the smart thing to do is to go for one of them not only for the money just because I have no need for anything more powerful.

That’s my point Craig, I wouldn’t even dream to work on steel although I would have liked to learn if I was younger. You have the experience to do what you like and you spend this kind of money to enjoy your work.

[Al_The_Man]

What “skewed rotor” means?

BTW a Skewed rotor means that the armature winding lamination are skewed instead of being straight which gives it a much smother rotation at low RPM's, IOW Servo rated.
It also is important to have the ability to add an encoder, if it does not already have it.
The one shown has the rear shaft for possible hollows shaft encoder add on.

[Al_The_Man]

One problem with worm & pinion GB's is there is traditionally backlash present.
The best solution that I have used in the past is planetary type..
One issue has been that it is hard to find them in a right angle configuration, but Automation Direct looks like they have them.
https://www.automationdirect.com/adc...rs/right_angle

[joeavaerage]

Hi Al,
yes worm drives do have backlash and commonly more than well made and designed planetary gearboxes.

You'll see in this thread I have been advocating Atlanta Drives servo reducers. The 58, HP (High Performance) series has a manufacturers spec of < 2arc min lash and the
98, HT (High Torque) series has a lash of <1 arc min, easily the match of even the best planetary gearboxes like Apex.

I have a 58 series 19.5:1 for my fourth axis. I cant feel any lash and have not been able to measure it either. I have just taken delivery of a 98 series 6.75:1 gearbox for a fifth axis,
at <1 arc min lash I cant feel that either!

Craig

[kolias]

I have now the cost from DMM for one complete assembly which includes:

400W motor 640-DST Model
DYN2 servo drive
DPGS-60-S1-10-14-00 Gearbox (10:1 or 5:1 same price)
Four cables (I can make my own but its suggested to get the cables and cut as needed to suite my layout since I need each cable special ends)
PSU 48VDC, 8A (approx. cost)
Total USD$809.00
Plus shipping and taxes will come to about CAD$1,700
Plus I have to add the cost of a chuck most likely it wlll easily go over CAD$2,000

It’s a wonderful set but too expensive for just a hobby CNC. Right now I dont know which way to go but I have the time to think about it

[kolias]

My alternative delivery included in CAD$ is this link

https://www.amazon.ca/gp/product/B08...DM55UG43X&th=1

[joeavaerage]

Hi,
that's too expensive, there are better choices. The 400W Delta kit (servo, servo drive and cables) is $398USD. I think DMM are just piling the costs on.
And whats the deal with the doubling in price in shipping and taxes? DMM is Canadian....are you trying to tell me it costs $900CAD to ship a servo/gearbox etc,
maybe 15kg from one part of Canada to the other? Hell, I paid $150USD to get a servo kit (8kg) from Hong Kong to New Zealand, and that's a three day service and its
9700kms!!!

Craig

[ardenum2]

that price doesn't feel right, smells like a scam. The kind you see on aliexpress, part costs $300 shipping another $300, fools you into believing the part is cheap but on the inside the part costs $550 and shipping $50.

Shipping should be zero in this case and the internets says sales tax caps at %15 in Canada?

For that kind of price you can get used direct drive rotary tables from ebay or new from the more honest chinese vendors