1st Build, Second machine

[m.marino]

Okay folks,

Starting the design and materials work on a new CNC Mill. Reasons are the current kit that I use does not have a long enough table, or Z travel, and a few other issues. So instead of trying to improve on what I have (though I will be doing that as well in the process); looking at building from base.

Size looking at is an X between 750mm to 1.5m, an Y of 500mm, Z of 150 - 175mm and adding an A with the ability to handle between 100 - 125mm dia. max.

Currently looking to go with profile rails for the guides. drive will be by either ballscrews or trapezoid screws (down to cost and how tight I can get tolerances for the work I am doing).

Looking at move over to a control spindle from the Kress I use on the current set up.

Structure is an area that I am still looking at as extruded has good points as does box frame. Also doing design work and as things move will be posting the designs up and then as things move into real pieces will be adding those as well.

On the router currently in use will be raising the Z and converting to anti backlash nuts on all three axi' which means a rebuild of the Y and Z. The X axis will just need a mounting bracket milled and taped for it to be converted.

I will be asking questions along the way as while I have learned alot there is always more to learn.

Michael

[m.marino]

And Life marches in....

While working on the design for the new machine, I am having to improve the current machine do to production requirements. Sooooooo......... I have a couple of questions. The machine I am working on improving on is a Marchant Dice A3 Trapezoidal screw driven model. I am working on improving the rigidity and milling speed. I am looking at a dumpsterCNC anti-backlash nut for the 12mm X axis and would like folks opinions on that idea. Drawing up a mounting bracket in ViaCAD v8 and wondering if 6mm (or 1/4") thick alli' will be thick enough to transfer the force down to the cross brace. Main reason for going this route is that while business is picking up I really need to be a bit tight on the expenses side of things (which is why upgrading this unit has become first priority instead of second).

I will post a jpeg of the drawing in a bit and could use any input you folks want to give.

Thanks ahead of time and hope to pay it back or forward sometime soon.

Michael

[m_c]

Any chance of that drawing?

And did you mean to say X-axis for the 6mm plate, as in the process of trying to figure out where the plate is going, I found your old thread where you say the X-axis is a 16mm screw...

[m.marino]

Any chance of that drawing?

And did you mean to say X-axis for the 6mm plate, as in the process of trying to figure out where the plate is going, I found your old thread where you say the X-axis is a 16mm screw...

m_c,

Still working on the drawing (need to get product work done so drawing is going to be a bit). What I am looking at is using the 12mm Trapezoid screw that is on the mill and fitting on of DumpsterCNC's anti-Backlash nuts on it. Using a piece of angle Alli' that is approx' 6mm thick and taping the holes on the flange to 5mm (they come at 4.39mm) and then adding a lock washer and nut on backside of that. bolting it to the cross member that moves the X axis via four bolts clamped into the rails of the alli' extrusion. This should give enough strength to hold it in place and still stay inside the 40mm of space I have to work with.

I am working with ViaCAD v8 and new to it. So some of it is taking a bit to learn as I am drawing it. Good part is being able to put in threading on the holes and build the spring for the anti-backlash nut.

Well hope that explains things a bit better.

Side note switched the steppers to parallel from series as getting the new 3A boards from Roy at DIYCNC. I am suprised at the speed increase even at 2.5A (max the current driver boards can put out). Looking forward to the 3A boards and the enclosure kit for my BOB. Which will help in dust control and tidy things up a bit.

Michael

[m_c]

Given the cutting forces involved, I'd say the angle should be sufficient. Even if it does flex, I'd suspect any flex would be less than backlash in the existing nut.
However, if flex does become a problem, provided there is enough room, you could add a couple triangular pieces to brace the angle, using countersunk screws on the underside it can still be bolted onto the cross brace.

Other option would be to get a mount machined from a bit solid bar.
I'd offer to help with any machining, but I'm of on a fortnights holiday in 10days, and already have a queue of jobs I'm needing to do before I go!

[m.marino]

m_c,

Thanks for the offer and I might take you up on it after you get back from the holidays. As right now swamped in getting product done and designing 4 new combs for chromatic harmonicas (different makes and reed count) cover sets plus variation for 6 different chromatic models, plus I have have clients work in bound that I need to have everything ready for and then add building concertinas to ship to folks as demo's and to see response in sales. Let's just say the days are busy and long (but I like them that way or I get bored and depressed, better to have things to do).

Folks,

Would 12mm thick alli' with precession rails (Hiwin type) 15-20mm be strong enough for a Y axis of 410mm (current machine) 600mm (project machine). Looking at bolting it to the uprights for the gantry as don't have access to welding equipment and from what I can figure 3-4 bolts per side should be strong enough (spaced to spread the load) looking at having having 100mm between centres on the rails with a 12mm Trapezoid or 10mm ballscrew (depending on what I can afford at the time) driving the Z body on it. Z would have 150mm travel and looks to be 15mm precession rails with a ballscrew. The Z would be 150mm wide to help decrease some of the torque forces, even though that will decrease my available travel in Y (the trade off is worth it to me). Any and all opinions would be welcomed even.

Michael.

[m_c]

12mm alli is pretty substantial, and I'd hazard a guess it would be fine, but I'm sure others will have a better idea than me!

Regarding the rails, I was actually reading about them the other day (can't remember if it was on HSM, CNCZone, or the Mach Forum!), and the general consensus is most hobby builds are majorly over engineered, as there was some big commercial machine running 15mm rails for the long axis. The only reason I was reading about them, is I've got plans for a new machine bubbling away in my mind, and linear rails are featuring.

[Jonathan]

Regarding the rails, I was actually reading about them the other day (can't remember if it was on HSM, CNCZone, or the Mach Forum!), and the general consensus is most hobby builds are majorly over engineered, as there was some big commercial machine running 15mm rails for the long axis. The only reason I was reading about them, is I've got plans for a new machine bubbling away in my mind, and linear rails are featuring.

Looks like we've been reading the same things. I agree that if you calculate based on the load ratings they seem plenty strong enough...I'm going to use them on my machine unless some >15mm turn up cheap on eBay. I think that's the reason most people use bigger, because it's what was available at the time on eBay.
You may need to watch out for the moment ratings, though for the size of your machine it should be fine, just space the rails out on each axis as far as you can.

(That's a bit vague I know, I can give some numbers/examples if required)

[m.marino]

Jonathan are talking to m_c or me on the rail spacing issue? Also you what would you charge to mill the bracket we are talking about for me? Well back to working on the drawing and setting things up as need be.

Michael

[Jonathan]

Jonathan are talking to m_c or me on the rail spacing issue?

I was talking in general really. On the axis the Z-axis is attached to in particular (Y in your case), the further apart the bearings are the lower the force on each when cutting and (to a lesser extent) accelerating. If you take moments in the X-Z plane then it's pretty obvious why...

Also you what would you charge to mill the bracket we are talking about for me? Well back to working on the drawing

I'm not so sure what's required. I can let you know when you've done the drawing...