New build mini Mill

[joeavaerage]

Hi,
my Z axis motor at the current time has to pick up about 50kg, and will eventually be required to pick up about 100kg when I get around to an ATC
spindle and 3kW servo motor to drive it. I elected to get one servo wit a brake rather than bother with a counterweight.

As it turns out I use 32mm diameter ground ballscrews and the large diameter screws by far and away dominate the inertia equation...NOT the axis mass at all.
I know its counter intuitive but the axis mass is only about 5%-10% of the total inertia with the ballscrews themselves contributing 80% and the servo armature another 10%.
This might surprise and that's why it makes sense to do the calculations BEFORE you commit to buy. My ballscrews are 5mm pitch and even without a brake do not slump
when de-powered. They might when I build a new spindle, but as the brake cost about $100USD premium over a plain servo I got it...so I'm ready for it no matter what happens.

Craig

[mactec54]

A little upgrade on the drawins. Added counter weight steel box with 20mm walls, which i will fill with Lead, it will fit around 80k of lead. The working table will be with m16 holes since i dont have T slot table.

You could mill the T-Slots once you have it built if you have enough table travel, threaded holes can be a pain if you don't plug the unused holes

Using a counter weight can take the load off the Z axis drive motor and Ballscrew

[StrawberryBoi]

Thanks everyone for your comments. So I will buy dmm or delta motors with high PPR. About the ballscrews I will see how my ballscrews will operate and if I'm not satisfied with the result i will change them to ground ballscrews.

My Z axis will be around 150kg, is 750w servo with a brake enough for it, cuz I see it is cheaper to buy a motor with a brake instead of making counterweight.

Any words about the design? How do you find it. Should I change anything there.

The design looks really beefy. I'd love to see how this holds up in FEA and in RL for stiffness. I imagine you could probably reduce a lot of metal mass if you cared too, but if it's not an issue at all then you can keep the beef so to speak.

[Vilyoo]

The design looks really beefy. I'd love to see how this holds up in FEA and in RL for stiffness. I imagine you could probably reduce a lot of metal mass if you cared too, but if it's not an issue at all then you can keep the beef so to speak.

Since I'm using fusion360 free version I can't simulate strength test. It is only in the payed version. Is there any other way to simulate it?

I'll consider buying new ground ballscrews and keep those I bought for another project. What is the best place to buy? Direct from hiwin or thk site?

i found this:
https://www.hiwin.cz/en/products/bal...nd-ball-screws
32mm with 5mm pitch, what do you think?

[mactec54]

Since I'm using fusion360 free version I can't simulate strength test. It is only in the payed version. Is there any other way to simulate it?

I'll consider buying new ground ballscrews and keep those I bought for another project. What is the best place to buy? Direct from hiwin or thk site?

i found this:
https://www.hiwin.cz/en/products/bal...nd-ball-screws
32mm with 5mm pitch, what do you think?

The P5 is the normal for mills if you can afford the P3 get them

[StrawberryBoi]

automation4less.com I think? They sell Hiwin rails and cars.

[mactec54]

automation4less.com I think? They sell Hiwin rails and cars.

They do sometimes have Ballscrews as well

[joeavaerage]

Hi,
I have bought secondhand ground (C5s and C3s) from this crew at a fraction of new price. In fact the 32mm THK BNFN screws in my new build mill came form here,
and I would swear they are new, they may have been fitted but I don't think used. I also bought new old stock THK linear rails and cars from the same place.

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

Naturally you may have to modify your design around what is available, but I think you'll find the prices are that compelling that you'll be prepared to do so.

Craig

[Vilyoo]

The owner of this website automation4less.com has banned the country or region your IP address is in (BG) from accessing this website.
Maybe they dont like us (bulgarians)

One option for now is Single flanged nut DIN 69051 from Hiwin Ground ballscrew, i talked to them and they said they dont have double nut for this ballscrew. Is it fine with a single nut? i will choose 32mm with 5mm pitch P3 or P5..
https://www.hiwin.cz/bg/produktsija/...-nut-din-69051

[Vilyoo]

Ive just talked to Hiwin supplier in Bulgaria and he told me that https://www.hiwin.cz/en/products/bal...-acc-din-69051
this is good enough for my project. He offered me 2505 ballscrew C5 for 280 Euro per metre with a single nut.

What is your opinion?

[joeavaerage]

Hi,
as I said earlier I used 32mm diameter screws in my project, largely because they were available as a complete set and quality etc. What I did not realise is just how SUBSTANTIAL
they are, really an overkill for my machine.

The rotational inertia of a rotating ballscrew increases as the fourth power of diameter and consequently my 32mm ballscrews represent 80% of the inertia, yes that's right 80%.!!!
You'd think the 115kg cast iron axis bed would dominate the inertia, it doesn't....not even close, its about 5% of the total inertia. Be very careful about specifying either heavy or large diameter
rotating components in your design otherwise you will find that you need huge servos just to spin the rotating parts.

I should have used 25mm ballscrews at most. The 32mm ones work fine but the inertia limits my acceleration to 0.25g using rated torque of the servos, whereas I could have had about 0.7g
with 25mm screws, it makes such a huge difference.

Craig

[StrawberryBoi]

As for the nut, single or double you want zero backlash. Depending on the design of the particular nut, it can require two for zero backlash or just one. That's the important thing to confirm.

[mactec54]

As for the nut, single or double you want zero backlash. Depending on the design of the particular nut, it can require two for zero backlash or just one. That's the important thing to confirm.

This is a small machine he is building and a double Ballnut can be a problem with Axis travel

Most Ground Ballscrews C3 /C5 have a single Ballnut that is preloaded

Rolled Ballscrews there is more need for a double Ballnut

[Vilyoo]

I really want to get grounded ballscrews but the Bulgarian Agent from Hiwin told me that C3 Grounded ballscrew (2505)with a single nut costs 800euro per metre (with a nut indcluded and machine ends) with a double ball nut he said 1100 euro. Those prices are above my budget. Do you think that price is normal?

[StrawberryBoi]

The C7 pricing is readily available, I think I'd have to RFQ for a C3 which will be a lot more expensive.

[StrawberryBoi]

I really want to get grounded ballscrews but the Bulgarian Agent from Hiwin told me that C3 Grounded ballscrew with a single nut costs 800euro per metre (with a nut indcluded and machine ends) with a double ball nut he said 1100 euro. Those prices are above my budget. Do you think that price is normal?

Can you give us the exact part number for the order? I can RFQ it and get pricing from Hiwin US and see if there is a difference.

[Vilyoo]

Can you give us the exact part number for the order? I can RFQ it and get pricing from Hiwin US and see if there is a difference.

https://www.hiwin.cz/en/products/bal...-nut-din-69051 2505
we have talked about this ballscrew in private message

[StrawberryBoi]

Hiwin is listing the 32mm OD at 2m for $500USD on alibaba. No information on the nut, may not include it.

[mactec54]

The C7 pricing is readily available, I think I'd have to RFQ for a C3 which will be a lot more expensive.

C7 is not suitable for a mill that you want to have a reasonable accuracy

[StrawberryBoi]

GBS-R25-5K4-FSC-A-1000-1129-0.008 is what you are asking about, that's the screw and the nut with the end bearing blocks.

I put in an RFQ to see how it compares for you.