Newbie - X Lead Screw, best position?.

[Mark Snape]

Could someone mind having a look at my design for the x-motion of a
CNC Router and pass any comments, please.

I want the weight of the gantry to lie directly above the rails, but whats
the best arrangement or position for the X Lead Screw?.

Many Thanks in advance for any comments.

Best Regards,
Mark.

[ahren]

Where are your bearings for the screw going to be? It isn't clear from the picture. And why are you going with a belt reduction? Are you using a servo motor? If you're using a stepper motor, I would go with a direct connection and a high lead screw to avoid whip.

If you're planning on using 8020 extrusion, you might check out my components (which are compatible with the 15 series) to give you some ideas.

Ahren
www.cncrouterparts.com

[Mark Snape]

Many Thanks Ahren for your reply.

Where are your bearings for the screw going to be? It isn't clear from the picture.And why are you going with a belt reduction?

The drawings is based on the data-cut design of Chris Luebke for from which i has purchased the plans, that design uses a belt drive reduction.

Are you using a servo motor?

No, i'm looking at using 450oz steppers on each of the screws.
(looking at a screw length of some 661/2" and 20mm diameter )

If you're using a stepper motor, I would go with a direct connection and a high lead screw to avoid whip.
Thanks for that advise, i'll alter accordingly.
do you think i need to thicken up the screw diameter and is it worth
adopting 1/16 microstepping rather than 1/8?.

Cheers,
Mark.

[ahren]

Mark,
How large is your machine? That is really the determining factor in how large of a screw you need. I've seen machines up to 5' x 3' built with 1/2-10 multi-start ACME, and my parts are designed to work with this size screw. There are free plans available for download on my website if you want to see another way of doing things.

As for microstepping, 1/8 vs. 1/10 vs 1/16 doesn't matter a whole lot. The point of microstepping is really to provide smoother motion. It also can provide increased resolution to an extent, but you shouldn't rely on it for this. Within a given step, microsteps are not that repeatable in terms of positioning.

Best regards,

Ahren
www.cncrouterparts.com

[Mark Snape]

Thanks Ahren.

Mark,
How large is your machine?
I'm looking at a size of approx, 74" x 55" in total withy a cutting area of
74" x 33" when allowing for the loss in router carriage width.

That is really the determining factor in how large of a screw you need. I've seen machines up to 5' x 3' built with 1/2-10 multi-start ACME, and my parts are designed to work with this size screw. There are free plans available for download on my website if you want to see another way of doing things.

As for microstepping, 1/8 vs. 1/10 vs 1/16 doesn't matter a whole lot. The point of microstepping is really to provide smoother motion. It also can provide increased resolution to an extent, but you shouldn't rely on it for this. Within a given step, microsteps are not that repeatable in terms of positioning.
Understood

Best regards,
Once again thanks for answering my question.
Cheers,
Mark.
Ahren

[Mark Snape]

PS.

Sorry have just checked and the x-cutting area is more like 60" i'd forgot that
the bed size all be larger to allow for the gantry.

[Riceburner98]

Let me know if you find the 1/2" cast tooling plate in that large a size for less than a couple thousand $! LOL Are you covering the entire base with it? I need a pretty big piece (not that big though!) for my machine and even at that size it's hellishly expensive... The 3'x4' 1/4" plate (not tooling plate) I need is already around $300.. I guess "expensive" is all relative though... I figured if you're using those ball bearing type rails it would be to keep the cost down, but the 3060 extrusion there is $$$$$$ as well.. The "cheap" / surplus 40 in. pieces on eBay I got were $70 each, I can't imagine how much a piece that long's going to cost..

[Mark Snape]

Thanks Riceburner98 for your comments ( sort of! ).

i guess i'm just starting to find out why accuracy and precision cost!.

But have a heart as i have got the Data-Cut plans from Chris and am not
a mechanical engineer by trade. So, guess i won't be using toolplate after
all ( Unless if win the UK Lottery soon! ).

I'll have a look around CNCZONE for an alternative.

Mark.

[Riceburner98]

Just saying, if anyone knows a cheap(er) place to get it, please let us all know! I want to use it, but dang it's expensive... As for the 8020, my boss built a huge CNC router at a place he used to work, and used a 6' piece of 6030 for the gantry which cost somewhere around $500 + shipping.. I knew the stuff was big, but when my 40" pieces came in the mail.... Wow. That stuff is big. I think it's 7lbs per foot as well.

[Mark Snape]

Thanks Riceburner98.