8x4 Wall Mounted; Upright ply cutter

[JAZZCNC]

Ok well here's my 2 cents.!

I completely agree with Boyan(Silyavski) and get what he's saying completely. (Thou I don't agree with some of the OTT building happening which he as IMO done but that's another issue and is IMO others do and will disagree)
I also Know Matt and get exactly what he's done. Which IMO He's hit the nail on the head and I applaud him for building a machine to do exactly what it says on the tin, which is Chomping thru ply wood.

Now the thing that bothers me here comes from experience speaking and helping others and knowing how people see an react to build threads.?
Newbies don't see this machine was built for low level purpose(even thou it was stated at beginning) or will realise this machine is limited in accurecy.!!
They just see a machine built quickly and with limited budget and tools and think that it's easy.! . . .Only after getting far into the build or finishing do they realise there is a little more to it than just throwing some steel together. End result is at best they are dissapointed in the results as it's not what they thought it would be or worse doesn't work and they give up.!!

Unfortunatly building any machine with decent accurecy levels does take some effort and expense which is what Boyan was saying and 100% correctly IMO.
Now I've shouted loud enough for the "Techno Crap" and OTT building to be curbed and some degree of sanity and common sense to applied. But there are occasions like this one where thru NO ONES fault the waters get muddied.!!

I'm in NO WAY having a dig at Matt or the machine because it's done and is doing exactly what it was built to do.!!. . But New builders and lurkers I feel need to be aware that this machine is limited in accurecy so if taking this route don't expact high accurecy you see on some other machines.

Matt as Done a great JOB in the short time but there's a reason.?? . . . . .He's ADDICTED TO CNC and got OCD. (join the club)

[Earle]

Jazz, Exactly he managed to build a machine 'that was fit for purpose', although like with all things lessons are learnt on the way.

For god's sake lets put this to bed, if someone wants to build a machine that is aerospace accurate and do it over a couple of years then 'yipppe I ay'

earle

[EddyCurrent]

Edit: written before Earle's last post but posted after it.

Not that it matters but here's what I think.
If you look at Matt's first build log; http://www.mycncuk.com/threads/5174-...6501#post36501
you will see he has been through the techno crap stages like everyone else. Now he's in a position to make it look easy becasue of that experience and the other builds he did.
But New builders and lurkers I feel you need to be aware that this machine was build by someone who made it look easy, not because he cut out the techno crap but because he was experienced.

[JAZZCNC]

But New builders and lurkers I feel you need to be aware that this machine was build by someone who made it look easy, not because he cut out the techno crap but because he was experienced.

NO it was made to look easy because he has experienced just enough to know how much Crap to cut so could achieve the intended purpose.!!

One other point I'd like to make is that this quick build and getting away with lesser accurecy build level was largely due to components used like round linear rails and normally prohibitly expansive rotating ballnuts.!!. . It would be a very differant story if profiled linear rails and conventional ballnut had been used.

Again I'll Say it for clarity I'm Not having a Dig at Matt (or anyone really) in anyway shape or form he's done a great job. Just stated what I wrote for sake of others as usual.!

[charlieuk]

Whats the advantage/disadvantage of rotating the ball nut rather than the screw? why did you choose to do it this way? Are there any more pictures of how you did it

[JAZZCNC]

Whats the advantage/disadvantage of rotating the ball nut rather than the screw? why did you choose to do it this way? Are there any more pictures of how you did it

The advantages are that only the ballnut is rotating so you don't get screw whip that can be common on long screws. Also the rotating mass is much less so smaller motors/drives can be used, alsoon a lesser note there's some speed advantage.

Problem or should say disadvantage with them is the cost if you try to buy the real thing.? They are silly money. This design is Jonathans and they where made by him just search the forum for rotating ballnut and you'll see he's posted the design.

While DIY you still need to be pretty well tooled up and know your way around a lathe and able to work to good tolerences and still there is a cost involved compared to normal setup that IMO negates the cost saving of being able to use smaller motors/drives.
So the real advantage IMO is that you take away the risk of whip/resonance etc that comes with long screws. I'd certainly use it over other means like R&P for long machines but you do need to be proficeint with a lathe and engineering. Farming the work out to a engineering company would not cost effective as well IMO as there is a fair amount of time involved to make these.

[charlieuk]

Cheers jazz I will look into it more but like you say probably not cost effective unless you have a good lathe to hand

[Jonathan]

Just to be clear, the rotating nut concept doesn't eliminate the problem of the screw resonating, it just raises the resonant frequency so you can go faster. The main reason the resonant frequency is raised is it enables you to mount the ends of the ball-screw more rigidly than with bearings, so for it to work well you need to make good strong mounts for both ends or the screw, with some adjustment in them to help with alignment.

The negative side is that to do a sufficiently accurate job of machining the mounts requires some care, so they take a long time to machine - at least with the equipment I have.