Putting on the brakes - Veles Macedonia

[Borko]

Hi to all you great guys,

I'm Borko from Macedonia. The access to this great forum begun couple of years ago with google-ing two magic words "DIY" and "CNC".
That was viral.
A lot of sites for hobby DIY, MDF made, ALU made.... but nothing like this.
The dream begun, I was biten. I got the virus into me.

I've read dosen of threads and decision has been made.Yes I'm gonna make it.

I think this will be a long journey, I want to enjoy, and ofcourse I'll need all your support.

[Borko]

I want to start with Gerald's "kitchen project" is it Ok?.
I'm good with mechanics but not as well in electronics.
In meanwhile I found some "I" profiles on a junk yard 3m long. I'll attach some photos when I learn how to

[Borko]

Apologies to everyone, now I look at my thread title and it seems that I say hello only to Balkan forum members. It is a written mistake. I meant HELLO from Balkan peninsula where Macedonia is located.

Thanks

[Borko]

Here are some pics of my future beams.

[lonestaral]

Hello and welcome.

[IMMark]

Best of luck on your build!
Mark

[servant74]

Getting started is the hardest part, or so the big boys tell me ;-)

[Borko]

Thank you guys for your support and welcome.
My plan for(working) table size is 2450 x 2100. I'm limited in X direction by X - beams. I've got it from junkyard, (very sturdy and straight "I" cross section 180 x 75 mm, immediately caught my eye). They are little bit rusty but angle grinder will do the job.
Paid 40$ a piece.

[Borko]

Plan to get quote considering step motors,drivers...from this supplier:
www.driver-motor.com (China)

1. Steppers 86HS9801
2. DM856 Fully digital stepping drivers
3. Timing pulleys for reduction ratio 3:1 per axis
4. Spindle, water cooled, 2.2 KW

For Z-axis plan to use ball screw with NEMA 23 stepper (57HS6403).

Does it seem to be Ok ? What do you think ?

[darren salyer]

Why the decision to use ball screw on the Z? I've seen several builds do this.

[servant74]

Several reasons, some more valid than others: reduce backlash, smooth operation under load, relative ease of installation, etc. My favorite is: because the owner wants it.

[KenC]

This owner wants it

NEMA 23 stepper for Z is a bad idea.
The saving is insignificant. (what is 20~50 USD compare to the total USD4000 that you are going to spend)
I like to use same motor for all axis.

[Fox]

I agree with Ken. Same motor.

[Borko]

Thanks to all of you for the discussion for Z-axes.
Ken I didn't mean to save 30-35 bucks on motor. This planning was only for constructive reasons I got in my head.

Darren in this case, gravity(weight of everything that z-axis will care) will have no affect to stepper holding torque - gas strut.

Yes Jack, the backlash will be null, especially if we consider the weight of spindle (maybe bigger in the future) and to reduce maintenance.
I'll plan to use ball screw with 5mm pitch.

The spider design is ingenious we must admit, the machine either, but a little spice I hope, wouldn't bother to Gerald.

Ok Fox, let it be NEMA34 for Z-Axis, I'll sleep well without thinking NEMA23 is under dimensioned for the loads.

[Borko]

What do you think about these VFD and spindle on eBay?
Any experience?

http://www.ebay.com/itm/2-2KW-WATER-...item27d3017e8b

[danilom]

Good as any other chinese spindle and vfd (all look the same) , brings joy to any Mechmater when cutting.

Dependant on what you want to do , 5mm pitch on ballscrew will severely limit your Z axis feedrate especially if using LPT or higher microstep. And 5mm vs 10mm would not give you any more precision.

1.1Nm nema23 57HS6403 is not in any way up to the task for the Z axis motor, 57HS2410 with 2.8Nm might but why take the chance...

[pblackburn]

How much precision are you looking for...most use 200 step/rev with a 10 microstep. If one revolution is 10mm then per step is 0.005mm of travel the 10mm and 0.0025mm per step for the 5mm. The main factor is what type of speed in rapid you wish to run. A lot of people in other forums put the 1605 ballscrew on Milling Machines. Higher accuracy is required but most mills only travel around 5000 mm\min (approx 200IPM) in rapid. A router, the rapids are with a DIY build, is between 7600-30000 mm\min (300-1200IPM) depending on design factors. So you will be turning the 1605 ballscrew so fast you may have distortion. As Danilo stated, not much gain with a 5mm pitch vs the 10mm on a router. You will need to find the balance between the speed you are comfortable with and the accuracy and precision you wish to have. Unfortunately these do not play well with each other in the cost end of things, however, you can build a machine to do what you require without a pile of expense. In other words, you don't need a high end servo driving 25mm ballscrew with a minute pitch and encoder feedback controls either.

A NEMA 23 stepper in my opinion will be too undersized for the axes. You need to calculate out your load potential. You will see it clear as day. The NEMA 34 gets away with it with reduction quite easily.

My last bit of advice is to read until you understand most before locking down on any decision. A little delay now will make a more satisfying build later. The guys in this forum are not only helpful and experienced. They will not lead you astray. Without them, I would not have my machine up and running.

Good Luck

[Borko]

Ok, I understand the difference. I wouldn't gain much in precision but lose in speed. We are talking about 0.0025 mm vs 0.005mm.You're right. It doesn't matter to what I'm gonna deal with.

I have to choose between 5,10,20 mm pitch size. I'll go with the middle one.( 5 mm will slow the machine, 20 will decrease the precision and ballscrew diameter is to high 31mm, so 10 is the best match).

Danilo, I'm gonna use NEMA 34 for z-axis with 10mm pitch ballscrew.

Thanks Pete for your wide explanation to have the things more clear.

Guys, your experience is priceless.

[Fox]

There's this thing with accuracy crunching numbers; it's all theory.
If you are going hunting for numbers 0.0025 mm vs 0.005mm in your Mechmate build, you are over-reacting. Your machine frame, and certainly your MDF bed, are going to move way more then that.
Even profesional massive CNC systems in big companies have a very hard time of doing that accuracy.

[Borko]

I grind the X - Beams from rust, and did the measurement. I've got non parallel flanges to both beams. It's along the beams. Any idea how to resolve this? It's too much for shims. The beams are very straight, and massive too.

[smreish]

I would flip the beam if one edge really is flat and use the flat side up.
Then, I would custom cut or shim/grind the leg attachment points to make the top lie in plane.

On my #5, I had the similar problem with my C-channel and "tipped" the channel inward to get the edge flat in plane with the y - car. This caused the bed to be like : /_____\, but the top edges were flat and plumb.
....may not be the best solution, but it worked.

[KenC]

Shimming will sort things out, if you feel bad with a thicj shim pack, just remove some of the shims & replace them with thick washer.
Its old beam afterall, must compromise a little.

[Borko]

Thanks for your recommendations. It could help a lot, but I'm not happy with thick shims. I came to this in my mind.. What do you think?

[Borko]

Pics size so small. I meant to grind channel 1mm width / 5 mm depth with few passes of 1mm grinder disk, and then to apply a force to the top of the beam. End closing plates welded to the beams will fix it.

[pblackburn]

I would turn them upside down like Sean said

[KenC]

I would tilt/align the I beam & use the straightest face possible.
You only need one straight face.

[DocTanner]

I would use an automotive body filler to create a flat smooth surface.

[gorantec]

Hello and welcome.
Добредојде Борко

[Borko]

Thanks gorantec.

Blagodaram Goran.

[MetalHead]

Ditto on what Sean said.