[suspension]

Hi Pete,

Looks like the spreadsheet is missing. I will read the HIWIN doc as well. Just went through the TOC and looks like it has lots of info.
Also, size of the machine would be around 580 mm X 250 mm X 450 mm.

Thanks

[peteeng]

Hmmm - here it is - Peter that's the working envelope? X580 Y250 and Z450?

[suspension]

Due to cost, faster rpm, easier ATC implementation, etc I am thinking of using a motorized ISO30 spindle instead of a servo driven Bt30 spindle. I really like to understand any disadvantages of This approach. Can threads be tapered with a non servo spidnle? Any other benefits of servo spindle?

[ardenum2]

Due to cost, faster rpm, easier ATC implementation, etc I am thinking of using a motorized ISO30 spindle instead of a servo driven Bt30 spindle. I really like to understand any disadvantages of This approach. Can threads be tapered with a non servo spidnle? Any other benefits of servo spindle?

different machining strategy, >18000 rpm, 2 or 3 flute endmill max. Thread milling instead of tapping, can be single flute or multi flute thread milling. Overall easier to achieve required stiffness. Check datron machining to get an idea of what you want to achieve.

https://www.youtube.com/watch?v=cDTpeLyU2TQ

[joeavaerage]

Hi,

In addition, I was researching TBI motion (I think they are Taiwanese) and gives pretty good accuracy of 18/3000 for Rolled C5 at 46USD per meter. (https://www.tuli-shop.com/tbi-motion...-scr-1604-f-c5).
C3 is much more expensive at around 193 per meter. (https://www.tuli-shop.com/tbi-motion...-scr-0801-g-c3).
I have seen elsewhere in the forum someone recommending this brand. The total cost will be higher when end machining, bearings, ball-nut are added however.

Do you think those prices are credible? I don't. Your money....your choice.

Craig

[ardenum2]

you have a few choices when it comes to ballscrews:

1.get brandname thk, nsk, etc and pay a grand for each ballscrew
2.get patient and get the above secondhand from ebay and tune your frame to whatever size and length you'll get, usually from https://www.ebay.com/sch/i.html?_dkr..._nkw=ballscrew
3. get cheap chinese c3's from aliexpress and hope for the best.

a good price for 2nd and 3rd would be $200-300 per ballscrew. Pay attention to the size you probably want 20 or 25 diameter ballscrews. These are usually listed as 2005, 2010, 2505, 2510. The first two numbers are the diameter the second two are the pitch.

You haven't mentioned but are you sending the castings to be machined at a company?

[pippin88]

Hi,
the minimum size of the ballscrew is that size required to preclude 'whipping' where the ballscrew spins that fast that it start getting out of line. There are some calculations floating around
that attempt to quantify it, but generally speaking the longer the ballscrew the bigger its diameter must be in order to avoid whipping. A related matter is the pitch of the screw. A fine pitch screw
will have to spin fast to meet your max velocity requirement and be more prone to whipping than a coarse pitch screw. The downside is that a coarse pitch screw requires more torque to achieve
the same acceleration and cutting force.

The maximum size ballscrew is that you can afford, and afford to buy a big enough servo to accelerate it. I've seen some guys thinking 'hey I'll get 36mm or 40mm ballscrews because they're so stiff,
only to find they need a 3 kW servo to spin them.

I have taken the approach that a fine pitch screw maybe a little slower but have greater cutting force authority......and so I have gone for 32mm diameter 5mm pitch screws. They are 648mm long
and will not whip at any realistic speed. In fact I spin them up to 5000rpm which give me a rapid traverse of 25m/min. The 32mm diameter means that they are stiff and accurate but require
decent servos to spin them, again I selected 750W.

Others favor course pitched screws, say 10mm or even 20mm. They argue that the screw need spin very much slower to get the required speed, and gearing could be used at need to increase
the torque of the servo to offset the greater torque demand for cutting forces and acceleration.

It is somewhat a matter of style.

The essential point is that the servo, any gearing, and the ballscrew must match the machine. If you think servos are expensive then you have not checked out the ground C5 and C3 grade screws.
One of the other contributors to this thread is of the opinion that some of the cheap Chinese made screws advertised as C3 and C5 grade while being less than a tenth of the price of the industry leaders like
THK, NSK, Bosch Rexroth etc. It is very seductive to believe that such high quality screws can be had at such bargain prices....but I disbelieve, I think is a case of the Chinese lying yet again.

Bear in mind that quality ballscrews are the absolute heart of any linear motion control system like a CNC. The better the ballscrews the better the result, and C5 and C3 screws (genuine) are worth way WAY more
than the servo that drives them. May I suggest you start doing your research on ballscrews now....they are commonly the most expensive piece of the whole puzzle.

C7 screws are rolled and have a linear accuracy of 50um/300mm. That sounds good but they can and do have cyclic error, and is uncontrolled but can easily exceed 35um/rev. If you are targeting 0.1mm
accuracy then these are ok. If you want 0.01mm accuracy they will not be up to it.

C5 and C3 are, and traditionally have been, made by grinding, and are mega expensive. A C5 screw is about 18um/300mm, which is better, but the real kicker is the cyclic which is 8um/rev.
C3's are better again, about 12um/300mm and 6um/rev. So both C5's and C3's are desired and required if you want accuracies of 0.01mm.

If a C7 screw, say 25mm diameter and 1000mm long is $100, a C5 25mm diameter and 1000mm long from THK or NSK will be over $1000, and C3's even more again.
If we as hobbyists could find C5 and C3 screws we could make much better machines, and I would advise caution before believing the advertising hype. Quality costs. BS is cheap.

I got my screws (ground C5's double nut, called BNFN by THK, 32mm diameter, 648mm long, 5mm pitch with two FK25 support bearings) secondhand from Korea. When I got them they still had the
original test certs....like they'd never been used, although they were advertised as second hand. I got three sets (screws/nuts/supports) for $1000USD including shipping to New Zealand.
Had I bought new they would have cost in excess of $2500 each. In short I could not have afforded to build my machine WITHOUT being able to get these absolutely superb screws at such a price.
I got new old stock THK linear rails and cars from the same company.

Once I secured these components (ballscrews and linear rails) I then designed my machine. I designed it to take advantage of what I could get second hand......I did not design my machine and then
try to find the really expensive and hard to find bits, I did the reverse.

https://www.ebay.com/str/industrialp....m47492.l74602

This place 'would put a horn on a jelly fish'.

Craig

Ball screw manufacturers also recommend a maximum speed based on diameter (not related to length / whip). I believe this is due to the surface speed of the balls as they travel.

It is often called the Dm.N value or Dn value.

https://www.steinmeyer.com/en/techno...mits/dn-value/

RPM x nominal diameter = DN
Need to keep DN below recommended value (varies, usually 50,000 to 120,000 depending on ball nut type)

e.g. 3000rpm x 20mm screw = 60,000

[suspension]

different machining strategy, >18000 rpm, 2 or 3 flute endmill max. Thread milling instead of tapping, can be single flute or multi flute thread milling. Overall easier to achieve required stiffness. Check datron machining to get an idea of what you want to achieve.

https://www.youtube.com/watch?v=cDTpeLyU2TQ

Thanks, so thread milling is good enough (or better). Any other benefits of a servo for the spindle that you can think of?
I have almost decided now with ISO30 and motorized spindle unless there are other advantages with a servo spindle.

[joeavaerage]

Hi,
I have two spindles, one is 800W@ 24000 rpm, and the other is a servo driven spindle of 1.8kW 6.1Nm (cont) @3500rpm.

I use the servo spindle for larger tools in steel and stainless, but mostly I use the 24000rpm spindle. If I used the servo spindle an hour or two a month my
24000rpm spindle gets used 40 hours or more.

To cut steel you need low speed but high torque and that is the exact opposite of high speed spindles. You have to decide what sort of work you are going to do
and get the appropriate spindle....or as I do, have two spindles.

If you have really deep pockets you can buy a 12000rpm or 15000rpm spindle but also has enough torque to drive bigger tools in steel but you'll pay not so much thousands
but ten or twenty thousand and need three phase....not really hobby stuff.

Craig

[suspension]

Much of my milling would be for hobby projects in Aluminium, but some semi-professional work is also possible. In any case, based on the information I have now, I can stick with a non servo spindle for now and later maybe add a servo based one if need arises.

I am yet to finalize the ballscrews. I asked TBI motion about authorized sellers. Even Digikey and RS seem to stock their stuff they don't seem to stock parts I am looking for. Lets see if https://www.tuli-shop.com is a genuine seller.

Regarding motorized ATC spindles, I see two major verities in aliexpress. A cylindrical type such as this and a boxed type one like this. Does any one know if these target different use cases?

[ardenum2]

Much of my milling would be for hobby projects in Aluminium, but some semi-professional work is also possible. In any case, based on the information I have now, I can stick with a non servo spindle for now and later maybe add a servo based one if need arises.

I am yet to finalize the ballscrews. I asked TBI motion about authorized sellers. Even Digikey and RS seem to stock their stuff they don't seem to stock parts I am looking for. Lets see if https://www.tuli-shop.com is a genuine seller.

Regarding motorized ATC spindles, I see two major verities in aliexpress. A cylindrical type such as this and a boxed type one like this. Does any one know if these target different use cases?

first one is watercooled so it's quiet second is air cooled so it's loud.

[joeavaerage]

Hi,
water cooled spindles are more tolerant of running at part speeds. That is the one shortcoming of these asynchronous spindles you are advised NOT to run them slower than half their
rated speed.

I see also that the listings you have linked to are between 5.7kW and 9kW. That is three phase territory....do you have three phase supply at your location?

Craig

[suspension]

Hi,
water cooled spindles are more tolerant of running at part speeds. That is the one shortcoming of these asynchronous spindles you are advised NOT to run them slower than half their
rated speed.

I see also that the listings you have linked to are between 5.7kW and 9kW. That is three phase territory....do you have three phase supply at your location?

Craig

I guess this spindle speed requirement is not applicable for water cooled ones?

As per power, the links I posted are just to get an idea about the difference. But my location anyway has 3-phase power.

[ardenum2]

I guess this spindle speed requirement is not applicable for water cooled ones?

a 24000RPM spindle is usually rated as 18000-24000RPM and that's fine because even for steel you don't drop down to x000's or x00's like you would with a belt drive.

Any other benefits of a servo for the spindle that you can think of?

Material removal with a belt drive will be higher than with a motorized spindle even if you use a 3000RPM or 6000RPM servo and not a 12000RPM dedicated spindle motor. If the only reason you're going motorized is for the ATC, you can just as well remove the dongs from a bt30 cartridge and run it like that.

It's all about frame stiffness, if its stiff enough go with a belt driven bt30, if it's not as stiff go with a motorized.

[suspension]

To select ball screws, I need to finalize machine size. I already have 15mm HIWIN linear carriages (HGW15CAZ0H) and HGR15RH linear rails.
These are 15mm which is half the size used in Stef's machine.

I bought these to build a pick-n-place machine for electronics, but later decided them to be an overkill. I really want to use them for this CNC build instead.
.
To see if these can support the weight of the machine, I did a calculation for nominal life (for Y axis) based on the formulae given in this HIWIN manual (Section 1-4, equation 1-2). I assumed total weigh of the X axis +T-slot table + work piece + etc to be 200Kg.
This gives 1348200 Kilo meters as nominal life approximately. Assuming 500 mm long Y travel, this amounts to running 427 years without any stopping if a full travel takes only 5 seconds. I did not accommodate environmental factors (equation 1-4).

This looks too good to be true given that if did a calculation for 30mm, this would probably give me million years. I double checked the calculation few times, getting the same answer. I appreciate if some one could take a look at this also if possible.

I did the above calculation to Y axis as it is the one that has the larger load out of X and Y. If this can withstand Y, then same can obviously withstand X.

For Z I think the calculation should be more complected due to moment created by Spindle weight. It was not clear from the manual on how to accommodate these moments in calculation of nominal life.

If above calculation is correct, I feel it is absolutely ok to go ahead with these 15mm rails/carriage.

[peteeng]

Hi Sus - The three main calcs for a bearing are its static strength (ie the one event load at which it gets damaged) its dynamic life ie the cycles it takes to fatigue and in the case of a linear bearing how far it can travel before it drops out of tolerance. The 15mm bearing can support 2.4 tonnes static and as you have calculated will have a long life in usual service. So in this regard they will be fine. I've done the same and decided to use 20mm as they match the ballscrew dims better. I see you have Z0 bearings. Ideally you should use high preload bearings for a mill. This minimises hysteresis (see page 9) and gives the cars better shock loading capability. In my first router I used Z0 and found they got a bit wobbly after 800hrs of use. I have since used medium preloads and found they are good. The preload is controlled by the size of the balls installed in the car. The balls are designed to wear first. Once they wear you can get new balls so then you can specify the medium or heavy size balls (page 28) In regard to moments the static rated moment is for a single car. Once placed into an assembly an individual car sees vectored forces not moments. See page 6. So the moment rating does not factor in... If you use a car by itself then these are useful. Peter

In my experience with a couple of routers the cars closest to the tool get hammered first (typically bottom ones on Z axis, they cop all the impact loads) so if you have the opportunity to put "better" bearings there do so.

[joeavaerage]

Hi,

I guess this spindle speed requirement is not applicable for water cooled ones?

Water cooled spindles are more 'tolerant', but that does not mean that they like running at part speeds either. I would be happier to run a water cooled spindle at 1/2 speed than air cooled, but would
still be dubious about running at 1/4 speed, water cooled or not.

You may have seen that many an industrial VMC has a spindles of 20kW, 25kW and more. Its less about absorbing all that power but rather that at part speeds to spindle still has the required
torque to cut steel.

For instance lets take a 20kW 15000rpm spindle, just as a ballpark.
rated torque =20,000 /(15000 x 2.PI/60 )
=12.7Nm

Which is good but not over the top. At part speeds the torque will be about the same, ie 12Nm. Note that these big spindles often have very good overload characteristics, so while it might
be 12Nm rated it will happily do 48Nm for short periods of time. The point being is that a big spindle has the torque and can therefore be used for cutting operations that require high
torque, ie steel/stainless etc and yet still have enough speed to do aluminum and other soft materials......so one spindle does the lot which is highly desirable.

Unfortunately these spindles are hopeless for us, they cost tens of thousands and weigh hundreds of kg's.....definitely not hobby stuff.

My first machine, a mini-mill was essentially a C frame type and I used BoschRexroth 15mm linear rails and cars (second hand from my favorite shop in Korea) and they were superb. I matched those
with 20mm dimeter 5mm pitch Koruda ground C5's (second hand from the same place). They were superb also....I used and used and used that little machine for seven and a half years.
The 15mm rails will limit the rigidity you can achieve so chose the screws, style of construction and construction materials to maximise what you have. No need to go overboard say on an outsize ballscrew
if the rails are the limiting factor. On the other hand you cannot afford to compromise on the construction or construction materials unless the compromise is AT LEAST AS GOOD as the rails.

Craig

[ardenum2]

Check lichuan servomotors, there's a guy on mycncuk that goes by the name jazzcnc, he makes a living building routers using lichuan servos and steppers and says he never had any issues with them. You can contact him directly at Home | JazzCNC

I'm linking 2 product lines 23bit 600W 60mm frame and 23bit 750W 80mm frame.
https://lichuanmotor.en.alibaba.com/...motor_kit.html
https://lichuanmotor.en.alibaba.com/...motor_kit.html

The prices are without tax and customs.

[suspension]

The balls are designed to wear first. Once they wear you can get new balls so then you can specify the medium or heavy size balls (page 28)

Does this mean I can still use the Z0, let the balls wear out and then fill with new larger balls for medium pre-load? I could not see and instructions on how to do that in the manual however.

In regard to moments the static rated moment is for a single car. Once placed into an assembly an individual car sees vectored forces not moments. See page 6. So the moment rating does not factor in... If you use a car by itself then these are useful. Peter

Thanks for clarifying. I missed this completely.

In my experience with a couple of routers the cars closest to the tool get hammered first (typically bottom ones on Z axis, they cop all the impact loads) so if you have the opportunity to put "better" bearings there do so.

Thanks for the tip. I only have 4 linear carriages (others are smaller, so wont work with this machine). I can use them for X and buy new ones for Y and Z. I will make sure to buy better ones there. I am planning 20mm for Z and 15/20mm for Y both medium pre-loaded.

[suspension]

Hi,



Water cooled spindles are more 'tolerant', but that does not mean that they like running at part speeds either. I would be happier to run a water cooled spindle at 1/2 speed than air cooled, but would
still be dubious about running at 1/4 speed, water cooled or not.

You may have seen that many an industrial VMC has a spindles of 20kW, 25kW and more. Its less about absorbing all that power but rather that at part speeds to spindle still has the required
torque to cut steel.

For instance lets take a 20kW 15000rpm spindle, just as a ballpark.
rated torque =20,000 /(15000 x 2.PI/60 )
=12.7Nm

Which is good but not over the top. At part speeds the torque will be about the same, ie 12Nm. Note that these big spindles often have very good overload characteristics, so while it might
be 12Nm rated it will happily do 48Nm for short periods of time. The point being is that a big spindle has the torque and can therefore be used for cutting operations that require high
torque, ie steel/stainless etc and yet still have enough speed to do aluminum and other soft materials......so one spindle does the lot which is highly desirable.

Unfortunately these spindles are hopeless for us, they cost tens of thousands and weigh hundreds of kg's.....definitely not hobby stuff.

My first machine, a mini-mill was essentially a C frame type and I used BoschRexroth 15mm linear rails and cars (second hand from my favorite shop in Korea) and they were superb. I matched those
with 20mm dimeter 5mm pitch Koruda ground C5's (second hand from the same place). They were superb also....I used and used and used that little machine for seven and a half years.
The 15mm rails will limit the rigidity you can achieve so chose the screws, style of construction and construction materials to maximise what you have. No need to go overboard say on an outsize ballscrew
if the rails are the limiting factor. On the other hand you cannot afford to compromise on the construction or construction materials unless the compromise is AT LEAST AS GOOD as the rails.

Craig

Understood the point about spindle speed. I guess I really do not need to go that slow. I can live with a water cooled one for now at-least.

Regarding the ballscrew/linear bearings - With your advice I am trying to finalize the ball screws first. If my existing linear rails are not adequate for the machine size that can be supported by these ball-screws, I will buy new ones. (Yes I can consider making a bigger machine to fully utilize ball screws).

I sent a message to that korean shop and asked if he can give some guarantees about accuracy/backslash. He said it difficult to give such a guarantee. (understandable). Did you check the accuracy of the parts you ordered from him?
As an alternative he recommended this: https://www.ebay.com/itm/192722054580
What are your thoughts on the price? I can use this same one for all three axis.

Also, I contacted TBI motion and asked whether this supplier (https://www.tuli-shop.com/) is an authorized distributor/re-seller and they said no
I asked for a quotation from TBI directly. Lets see how it goes.