dual drive x-axis?

[fasteddy]

Hi Hiltonsteve..

Thanks for the advice... To answer some of your questions... I want it as accurate as I can get it using the cheapest, nastiest materials I can get my hands on.. from what I have seen on the net, if you get the design right then a mortgage is not necessary to make a reasonable CNC.. This is why I am picking everyone's grey matter on design and sourcing of electrics..

i intend, once this machine is built, to make the next one on it.. Will be using a lot more ally on the next one so if I can get the prototype rigid and sturdy enough, this should not be a problem... Might even just upgrade the prototype using the prototype..! Its all a bit of an experiment, will be using a lot of the suck it and see methodology..

As for leadscrew, have found Marchant Dice (ebay) do a 16mm x 4mm pitch trapezoidal one that seems cheap enough, although I am not sure about getting the ends machined, might look at knocking up a couple of weldable reducers.. Also got to locate cheap nuts for this thread...

I agree that expanding the gantry sides and extending the bearing rails will eliminate a lot of yaw, but I am trying to utilize as much of the work area as possible, also with a 48" y-axis, the potential for yaw while machining at the extreme ends of the y-axis is increased..

Really try to utilize design as much as possible to avoid having to win the lottery for this one.. More expensive materials, ballscrews, motors etc will overcome most of these problems, but cost is a big issue at the moment.. If the first one comes out ok, I will no doubt put more funds into the next one.. But for now, cheeeeeap!!!!

Am using angle ally and skate bearings for the runners...

[fasteddy]

Thanks Kip..

Will modify my design to put the additions tracks (under the bed, see my posted cad pic) closer to the gantry edges... I was originally thinking to spread the load a bit, but your comments make more sense...

[John S]

As for leadscrew, have found Marchant Dice (ebay) do a 16mm x 4mm pitch trapezoidal one that seems cheap enough, although I am not sure about getting the ends machined, might look at knocking up a couple of weldable reducers.. Also got to locate cheap nuts for this thread...

.

Doesn't he do the nuts ?

[fasteddy]

At a price John, not a nice one either.... Would be cheaper to buy a tap a go visit my mate and his lathe....!

[HiltonSteve]

At a price John, not a nice one either.... Would be cheaper to buy a tap a go visit my mate and his lathe....!

If you speak to Michael nice I am sure he would knock some nuts up for you. I think he has got a 10 x 4 tap not the 16 x 4 that you are looking at but why not drop down to 10 x 4 trapezoidal screws to save a bit of money, especially if they are temporary and you are going to upgrade the screws to ballscrews later, will be speaking to him in a bit so I will give him a nudge for you.

[Tom]

Hello Fasteddy,

It sounds like your build's very similar to mine.

I don't want to badmouth Marchant Dice needlessly, and Kevin may still come through with the goods, but i'm struggling to find out what the state of my (overdue) order is.

Anyway, best of luck with your build. I'll update on the leadscrews when I hear more...

[Ross77]

I agree that you should definatly get on and build it, probably learn more in the process. good luck.

May have retract my statement about cable stretch being low...
Had a look around today and seems that 1m of 3mm dia. stainless cable will stretch 0.5mm under a 200N load (20Kg ,not much if cuting Al and a heavy gantry)....:geek:

May be start a new tread If anyone is intested in following this topic up? Im not used to designing things that move! traditional to keep structures stationary. There must be a way to get cheap and accurate control of CNC machines........

[Ross77]

Somebody is going to have some fun calculating it all up! not me though :lol:


I'm a great believer in horses for courses....Milling machines for milling routers for routing......Now engravings a different thing.....It never ends does it :(

I hear you, I wouldnt ever use anything but ballscrews. But I like a challenge and am happy to do the math.

Would the SS cable stretch the same every time? What if it was already tensioned (stretched) ? What if the antistretchyness of the cable was more than the chiploadedness?

Yes the stretch is a product of the load (hookes law not mine) The bit that i dont understand is that if the cable is pre-tensioned and then a load is apllied, is this always an additional load (and therefore more elongation) as the cable is in an elastic state or is only a factor if it is greater than the preload stress?

if its the later then problem solved, if not can you use plastic design on moving parts?.........

[Ross77]

Somebody is going to have some fun calculating it all up! not me though :lol:


I'm a great believer in horses for courses....Milling machines for milling routers for routing......Now engravings a different thing.....It never ends does it :(

I hear you, I wouldnt ever use anything but ballscrews. But I like a challenge and am happy to do the math.

Would the SS cable stretch the same every time? What if it was already tensioned (stretched) ? What if the antistretchyness of the cable was more than the chiploadedness?

Yes the stretch is a product of the load (hookes law not mine) The bit that i dont understand is that if the cable is pre-tensioned and then a load is apllied, is this always an additional load (and therefore more elongation) as the cable is in an elastic state or is only a factor if it is greater than the preload stress?

[Ross77]

Easy...
got another week of college work yet and my brain is still in geek mode

Oi! stop thinking and make something...good, bad, indifferent just make it :D

Collets and ER32 chuck arrived today, so getting there....