My 2nd version of a 2.5D CNC milling machine

[tribbles]

I've now started the second version of my 2.5D CNC milling machine (many thanks to Gary's advice on parts) - I've got 10 days to build it (holiday from work). The basics are designed, but there's a lot of flexible design involved (i.e. "make it up as I go along" :) ).

I'll be (hopefully) updating my website every evening with the activities of the day.

http://www.tribbeck.com/steel/stlcutter2/

[bikepete]

As a newbie I hesitate to weigh in but are you sure one block either side of the router on the Z will be sufficient? Looks like a fairly heavy unit and four blocks total would much better resist the torque of its weight hanging out the front, let aside any cutting forces. If you want to stick with one each side to retain travel then maybe the double-length ones would be a good idea e.g. these?

[tribbles]

Thanks for the comments - it was something I considered, and I still may - I've arranged the ball screw nut quite a bit lower than the two blocks, so that adds some stability. There's some space below which can take another pair of blocks if I find there's some play.

[Lee Roberts]

Nice to see you are using the supported rail for the z-axis Jason, i'v also used the same for my second machine:

[pavlo]

Why have all that travel on the Z axis? If you are working with the router raised by more than a couple of inches the bottom end of the linear rails will clash with the work piece. I'm a newbie at this and have yet to build my Z axis so maybe I'm wrong, perhaps one of the more experienced guys will give their thoughts?

[Lee Roberts]

Hi pavlo,

Well I have given allot of thinking, after the z axis is complete I will have about 170mm of travel. When you look at the different length cutters and so on it’s really best to have about 100mm of travel so you can accommodate different lengths, you also need to think about how far the collet holder will hang out of the bottom.

The other main reason is that the supported rail is only fixed at 150mm intervals, so yes we could cut the rails/travel down but then we would also need to machine the rails with new fixing points (drill, tap).

Given the choice of + 70mm extra vs. the work and loss of cutting everything down I went for having extra travel.

If I was to bring the lengths down I would be wasting money on the Rail, Ball screws and time spent building. I went with a pre machined ball screw for this z axis and that is 400mm long, the design I have gone with allows me to keep the full length of the ball screw and the rails, now if at any point I need to machine a tall part I also have the travel to do so.

Its better to have it, then not. Even if you may never use it !

[pavlo]

Thanks for the reply Lee but I was referring to tribbles build blog. Your one makes sense to me

[Lee Roberts]

Why not use some of these and pocket the carriers (plates) to get the rails as close together as possible? Archimedes had it right ;)

For me price, £32.20 per bearing block ? How dare you :surprised:

[tribbles]

pavlo:

I think I've got about 230mm of travel (will need to measure it properly tomorrow when I work out how high it needs to go).

It'll be cutting 100mm tall foam to start off with (using a 100mm long tool), so that's the minimum movement I wanted; however, I may be using cutting heads with different lengths, so I wanted the option of going between 40mm and 100mm long cutting heads, which means 160mm travel. I've got the option of even longer tools if I find more suitable ones at a later date.

As Lee said, it's better to have too much than too little (although I don't have the full length of travel for the ballscrew [at this moment in time]).

Kip:

My original plans were to use profile rail for all of the axes, but I didn't want to spend "flipping great wodges of cash" Although I did want to spend more than the minimal amount I wanted on the first version.

The router isn't that heavy (with its base-plate, it's about 6.3Kg; without it I've no idea since I don't have a set of scales in the workshop), and the width of the whole Z-axis mechanism isn't that important (the rails are 1600mm long, the Z-carrier is 160mm wide, so movement is a maximum of 1440mm; 1200mm is the minimum I waned).

The X-axis will be using rails (with a pair of carriages on each side), but that's mainly because the Y-axis mechanism is very heavy (I can see an aluminium version being created at some point in time).

Oh, and I quite liked your thought of a train-wreck - why the edit?

Lee:

I think mine's a bit more "agricultural" than yours (which isn't surprising as it's being built in a workshop where they make crop sprayers).

[templecorran]

Sure is agricultural! :clap:

I'm looking at your X axis drive arrangement and wonder if the z carridge will bind in the rails. You have a turning moment there with the screw at the top and the cutter at the bottom, the point of rotation will be somewhere in between the X rails.

When I redid my rockcliff in alu angle I had a load of trouble with bearing blocks binding with the smallest possible movement in the assy. I still have trouble with the Y axis table (fixed gantry version) when I remove the upper part of my table with the T slots in.

I think you might have a problem with all that space between the uprights of the Z carridge letting the assy flex. To prevent that, you might want to make a bracing plate to stiffen up the four corners of the rectangle formed by the bearing blocks. And while you're at it, put the X drive nut in there too.

Any way. Thanks for reading my 2 cents worth. I hope it isn't needed. :whistling:

John
:geek: