[joeavaerage]

Hi,
I have to post a retraction, it would appear that the early LGH cars are two row, not four row. The diagram shows one groove, but then so does the diagram for the four row cars,
so the diagram is not conclusive in itself.

I cannot find an old catalog that specifies it but I have come to believe that my assertion that the LGH cars are good is mistaken. I would commend Ardenum's comment that you get four row
cars. The gold standard is four row rollers rather than balls, but they are really expensive. I used four row (Bosch Rexroth) ball cars in my first mini-mill and four row (THK) ball cars in my new build mill.
In both cases neither proved the 'weak link'. Certainly I would like rollers....but then I'd like Porsche rather than my Mazda too!.

Craig.

[suspension]

Hi,


In any event linear rails and cars are expensive new, but still very VERY much less than ground C5 and C3 ballscrews. If you can get good ballscrews, say new old stock, but bought
new linear rails/cars that would still be a good deal.



Craig

I actually considered that already and found that these two can work for Y and Z. (As I have reduced the travels to 400 X 300 X 380).

https://www.ebay.com/itm/20243348559...temCondition=3
https://www.ebay.com/itm/20420716231...temCondition=3

However the model numbers are not printed so I asked the seller if the drawing is accurate as it say preloaded and precision.
Lets see what he says.

Regarding the pitch, I will try to stick to 5mm. If I go with 10mm, will have a reduction mechanism so I can still use my selected 1KW servos.

[joeavaerage]

Hi,
Those screws also look superb. I rather think the 36mm diameter one is getting too large.

Remember the rotational inertia of a screw goes as the fourth power of diameter. So if a 32mm screw 1m long has a first moment of J, then a 36mm diameter screw of 1m long
will have a fist moment of 1.6J, ie the fist moment has increased not quite doubled. I would stick to 32mm if possible.

1kW servos could be coupled directly to 10mm pitch screws, it's a bit of 'six of one and half a dozen of the other' situation, although I think reduction would be mandatory if you were going for
36mm diameter screws. The previous calculations show just how sensitive the momentum equation is to the ballscrew diameter.

I think reducing the target travels is wise.....it brings so many more components into the mix for consideration and reduces the overall expenditure dramatically.
My machine has travels of 350mm x 350mm x 350mm and I find that entirely adequate. That is not to say I would not like more......but this is what I could afford and find good parts
for. That is enough.

Craig

[pippin88]

Hi,
I personally favor the 5mm pitch screws, you get greater thrust and therefore cutting authority, with a smaller servo. These 5mm pitch screws have max travel of 540mm, and probably 520mm
as a practical maximum.

The 8mm pitch screws have 580mm travel max and a practical max travel of say 560mm. Being 8mm pitch probably indicates that you should go up one size in servos, from say 750W to
900W or 1kW.

The 10mm pitch screws have 660mm and 589mm max travel respectively and a practical max travel of 640mm and 570mm. Being 10mm pitch will likely require 1.5kW servos to retain
the acceleration and thrust authority.

Its a classic case where if you want more travel then it costs. I can get a 750W Delta servo kit (servo, drive, cables) for $438USD + shipping whereas a 2kW Delta servo kit costs $895USD +shipping.

Pay your money and take your pick.

Craig

Craig,

Or 10mm pitch screws with 2:1 belt reduction.
Same torque/ thrust as 5mm screws with direct drive.
But screws spin at lower rpm for same linear travel speed.

Ball screw speed is limited by critical speed (whip) and by maximum ball speed (dm.n value). Often the Dm.n value is the real limiter.
E.g. a common maximum value for Dm.n is 70,000. Example using 25mm screw - 70,000 / 25 = 2800 maximum rpm.
Worse with 32mm screw. 70,000 / 32 = 2187.5rpm

Some screws (often more expensive, sometimes prioritising speed rather than rigidity or preload) will have higher Dm.n values, up to 120,000 or above. Highest I've seen mentioned are 160,000-200,000 but these are special order from manufacturer.

[joeavaerage]

Hi pippin,
these screw are 32mm in diameter ranging from 650 mm to 930mm long, they are not going to whip ....ever. My 32 mm screws are 650mm long and I can and do spin them at 5000rpm. With 5mm pitch that results in
25m/min rapids.......way WAY WAY faster than I need. In practice I find 7.5m/min to 15m/in to be adequate and that equates to 1500rpm to 3000rpm. Second issue is that at 3000rpm it takes less than two
seconds for my all of my axes to accelerate to speed, traverse the 350mm length of the axis and decelerate again. How often do you do that? Not often, 90% of a toolpath is stooging around at 1000mm/min or whatever the tool
can handle.

E.g. a common maximum value for Dm.n is 70,000. Example using 25mm screw - 70,000 / 25 = 2800 maximum rpm.
Worse with 32mm screw. 70,000 / 32 = 2187.5rpm

If you were operating at max or near max speed then maybe these guidelines are useful. For my machine it operates at a small fraction of that guideline 99.9% of the time. Quite
frankly I completely ignore it....it just not relevant to a hobby machine operating at such low 'duty cycle'.

Or 10mm pitch screws with 2:1 belt reduction.
Same torque/ thrust as 5mm screws with direct drive.

Correct, but why would you shag around with belt reduction when you can just direct couple them? Choose the correct screw and the correct servo and direct coupling is a snap. With these screws (32mm diameter) and
a 1kW servo direct coupling is a breeze. The 10mm pitch means somewhat less thrust.......125kg/Nm vs 62.5kg/Nm, but not a show stopper. If you can be bothered to arrange a belt reduction, then have at it.

Craig

[ardenum2]

just get the steinmeyer ones, they are well known over here, if the sizes fit you.

[suspension]

just get the steinmeyer ones, they are well known over here, if the sizes fit you.

Most probably this is the path I will have to take. Thanks for confirming.
I see that you provided a link to a chinese supplier. Have you used their linear rails/bearings before?

[ardenum2]

Most probably this is the path I will have to take. Thanks for confirming.
I see that you provided a link to a chinese supplier. Have you used their linear rails/bearings before?

I haven't but the prices are very appealing, they sell hiwin and rexroth too, for hiwins roller carriages size 25, the ones I need, the price ends up being $40 with tax and customs, that's half the price if I ordered directly from hiwin. If you're hesitant just get either RG or CG series directly from hiwin, skip the HG's. They sell stuff through their official website. Just have to login first to see the prices.

[pippin88]

BST Automation can now get Hiwin RG (Roller) rails.
I just got a set through them.

(Couple of years ago when I asked, they were not selling the RG series).

[pippin88]

just get the steinmeyer ones, they are well known over here, if the sizes fit you.

I asked Automation Overstock for a shipping quote to get some of those Steinmeyer but they next responded

[joeavaerage]

Hi pippin,
If you have the cash keep trying. The prices for those screws is exceptionally good. If I had spare cash I would entirely probably get some myself.

NZ Post offer a service where in effect they give you a post box in the US, so a US supplier only has to ship to Orgeon...and that they can do easily and cheaply. Once it arrives in
Oregon then NZ Post handles the international shipping and GST. Its not cheap exactly, but its reliable and relieves the US supplier of international shipping which many are loath to do.

Is it possible an Aussie company offers the same sort of service?

Craig

[suspension]

Hi pippin,
If you have the cash keep trying. The prices for those screws is exceptionally good. If I had spare cash I would entirely probably get some myself.

NZ Post offer a service where in effect they give you a post box in the US, so a US supplier only has to ship to Orgeon...and that they can do easily and cheaply. Once it arrives in
Oregon then NZ Post handles the international shipping and GST. Its not cheap exactly, but its reliable and relieves the US supplier of international shipping which many are loath to do.

Is it possible an Aussie company offers the same sort of service?

Craig

Have you tried ocean freight forwarders? They are cheap as they calculate cost based on volume. I use them all the time to import stuff.
But most probably you will have to go and do the custom clearance.

[suspension]

BST Automation can now get Hiwin RG (Roller) rails.
I just got a set through them.

(Couple of years ago when I asked, they were not selling the RG series).

How can we know if they sell genuine HIWIN? This is the problem I am facing with most of the chinese suppliers.

[pippin88]

How can we know if they sell genuine HIWIN? This is the problem I am facing with most of the chinese suppliers.

The sets I've bought from BST match the Hiwin catalogues / website pictures perfectly. They perform very well, with very smooth motion.

I have seen suspect ones online where the colours are wrong, etched text / model numbers are wrong.
Often sold by stores without much feedback or not open for long.

And reputation - search BST Automation here / online and you will find a lot of happy customers. I doubt they could maintain that selling fakes.

[pippin88]

Hi pippin,
If you have the cash keep trying. The prices for those screws is exceptionally good. If I had spare cash I would entirely probably get some myself.

NZ Post offer a service where in effect they give you a post box in the US, so a US supplier only has to ship to Orgeon...and that they can do easily and cheaply. Once it arrives in
Oregon then NZ Post handles the international shipping and GST. Its not cheap exactly, but its reliable and relieves the US supplier of international shipping which many are loath to do.

Is it possible an Aussie company offers the same sort of service?

Craig

Craig,

I have used a similar service in the past. Forgot about that option.
I will look into it thanks

(Though I need two screws with 800 effective travel, which Automation Overstock don't have an ideal option for)

[ardenum2]

BST Automation can now get Hiwin RG (Roller) rails.
I just got a set through them.

(Couple of years ago when I asked, they were not selling the RG series).

link? what was the price per carriage ?

[joeavaerage]

Hi pippin,
the 800mm travel sure thins out the field. These links are from the shop I've used quite a number of times before in Korea. In most cases he ships (Fedex) for free.
No harm in looking.

Craig

https://www.ebay.com/itm/20367977638...MAAOSwFrFhfl5A

https://www.ebay.com/itm/19345726069...4AAOSw6DtYShrk

https://www.ebay.com/itm/22480841593...cAAOSwUSth8VUC

https://www.ebay.com/itm/22407426999...4AAOSwfgNfB8tE

[joeavaerage]

Hi pippin,
the last time I dealt with him we dealt direct without Ebay intervening, saved commission etc. I paid $1000USD for three second hand (near new) THK 32mm BNFN 5mm pitch C5 screws with six FK25 support
bearings and including Fedex to New Zealand....bargain!!....didn't have to pay any GST either.

Craig

[pippin88]

Craig, thanks. I've spent more than a couple of hours digging through dy_global listings in the last month or so. Unfortunately have not found quite what I'm looking for. Either only 1 available when I need two, or great accuracy but no preload etc.
I scored a precision granite frame to use as my machine base - this has set the size of certain things and enforced a moving gantry design (thus needing two 800mm travel screws).

[pippin88]

link? what was the price per carriage ?

They are not listed, just message Fred via BST Automation on aliexpress.

I got 30mm roller rails
RG30-680mm 2pcs
RGH30HA-ZA 4pcs
USD490.00 including shipping by Fedex.