Ski Builders Forum

hi everybody!
i am new to this forum so please excuse any stupid newbie questions & errors.
I put this post in bigkam's 'k.n.k' - topic as well, hope this is ok.

i am looking at buying my own cnc, no time to build one myself although i will miss the fun of designing my own.
I will probably get a BZT-PFU2515-PX, look at bzt-cnc.de in their webshop, am not allowed to post the whole link yet.

no my wallet doesn't say big mf on it i will make a small second business out of building custom snowboards and skis and use it for some other projects as well, so rather spend some more and do it right from the start.
last tuesday i drove up to northern germany from switzerland to have a look at the factory and machines. they didn't have my model completed and operable as it's a new model, but i could have a look at the finished frame without engines and ctrls, it all seemed of excellent quality, very well built and designed.
The salesperson then showed me another just finished router, similar to the one above but smaller (1500x100mm ), a little lighter and on the longitudinal axis the servos were not mounted on the nut, driving the nut instead of the screw, but on the ballscrew( 16mm), as in e.g. kam's knk-roter.
I was very surprised that the machine made a substantial amount of friction noise (with router switched of) and the ballscrews were resonating tremendously (amplitudes of their own diameter i guess) at higher speeds.
the salesperson told me the machine had just been finished and wasn't yet perfectly set up and greased. regarding resonance he said by having the servos driving the nut with fixed ballscrews this problem would be mostly solved as it was mainly due to the type of construction.
not sure if I should fully believe him, as I said he was a salesman, not an engineer or service person.

here my question: I haven't yet used a cnc and had considered cnc machines to be very quiet due do to the ball bearings throughout the machine? I thought of a zzzzzii..zzzziiii. sound;)
But it was more like kkrrrr...krrrrr ;(
Or is friction noise something normal?
Or does a new machine need some time to set up properly and be sort of 'broken in' like a new board or pair of skis?

I haven't yet used one so please forgive my greenhorn status.
thanks for your help folks, some quick feedback will be highly appreciated as they have 3 months of delivery time and i need to get going soon.

andi

ps: thanks everybody and especially you guys at skibuilder's for the vast amount of input. without you i wouldn't even have considered my company feasable.
you guys rock!
I will let you know and give some input back when planning is finished and my 'factory' is up and running!

Hey andi,

It's my opinion that a CNC machine (when all parts are aligned and lubed properly) should move around quite smoothly when the router is not running. Servo motors can tolerate a bit more vibration than stepper motors can (steppers will lose steps if they are subjected to too much vibration, and thus lose their place in the cutting program). Also, lead screws should not vibrate or wobble at expected operating speeds. I certainly wouldn't purchase a new machine that wobbled, moaned, or groaned... all of which will only get worse over time. It's not all that difficult to build a machine that moves smoothly, so I would sure want to make sure that the machine builder has the basic skills and ability to make such a machine. Also, I'd recommend that you make sure that there is good after purchase support for the machine that you end up buying. If you can't fix the machine yourself when it breaks down, availability of tech help and spare parts is crucial in getting your machine back on line.

Good luck,

G-man

thanks g-man,

just ordered yesterday after watching a couple of competitor's videos on the net. They all seemed to make similar noise, so it wasn't that bad after all.

Regarding resonance, according to some folks on the cnczone forum this should be eliminated by driving the nut not the screw as it will be on my machine.
That's what the people at bzt said as well. The one they showed me had the screw driven and had resonated mostly at the maximum rapids (16m/min).
So after looking around for months, in the end it seemed to me like the best deal anyway; the components seem to be excellent, the frame is made of steel, i am getting servos etc and I made sure that support is good.

If there's any excess friction etc, i suppose that, as you said, it will be due to set up, alignment or software.
As I had said, the machine they showed me was an older model, but brandnew and hadn't been set up properly yet, not a very smart move of the salesperson though to show me that one;)
Anyway I will see if my decision was right when the machine will be delivered in about 10 weeks..........

cheers!

andi
ps: my press got inspired by yours quite a bit, thanks, I will post some pics when it's finished.