[lkasdorf]

Please take a look at my blog here:
http://barncattechnology.blogspot.com

At the end of the first post I pose questions- how much Z travel should I design for on this machine, given its rail design. I need to construct riser blocks and I need to decide how much Z axis travel will be practical.

Any advice would be great.
Thanks-
Lynn Kasdorf

[aarggh]

You've got some nice hardware there Lynn, but the z in the current configuration is not very useful except for engraving of thin materials. You ideally need another higher rail, to spread the distance apart for your z axis, and a clearance of around 3 inches really is at the very least desirable. I would consider mandatory for any use. 4 inches below the lowest point is better, but ensure you allow enough height for tooling, and accessing the cutters with materials under the spindle.

Can you raise the x axis higher in the gantry, and maybe fit a supported round rail along the top, with an upside-down "L" plate to then mount your z axis on?

The forces from any decent machining or routing will cause massive amounts of flex and twist otherwise. You should be able to push reasonably hard on the axis and not have any detectable movement. As under load this will be very apparent. Also, do you have any bracing under your table as the rails are in a bit from the end, and you'll likely find machining side to side the ends will not end up machined the same depth as the middle section. Although this of course depends entirely on what you plan to machine.

cheers, Ian

[handlewanker]

Hi, lay down the work envelope dimensions you will not exceed under any circumstances and redesign the Z axis to have a longer travel to cover it......anything outside the work envelope is just exceeding the design criteria, and like hauling 1 ton rocks in a VW with stronger springs, it ain't advisable to try it.

This would entail going for longer rails and a longer ballscrew for the Z, but be advised any length increase in the Z travel is also a need, as you proposed, to raise the side support columns, but at the same time the longer Z axis will hang down further and impose more radial leverage on the crossbeam, which should be widened to cater for this effect......the list could go on.

It would appear that you want/need to do milling, hence the need for the increase in the crossbeam clearance, but if it is only to clear thicker materials while still having the same/existing Z axis travel, raising the columns will give you this, but you probably won't get all the way down to the thin stuff on the table, unless you anticipate this and use an extension holder in your collet chuck.

Raising the side columns only without any change to the Z axis travel can give you a simple solution as long as you use the extension approach for thick and thin jobs.......milling would not be an option, with extended holders, if any at all with the short ones.
Ian.

[lkasdorf]

I have started to machine 2" riser blocks. I've updated the blog with info and pics.

This will give me Z clearance of ~3 7/16". I'll plan on 4" -5" travel max on my Z mechanism.

The overall work envelope will be 24X, 12Y, >3Z. If I need more in Z, I could make taller risers in the future, but I'll be compromising rigidity the taller I make it.

barncattech blog

After this is machine is done, I have a full size Bridgeport clone CNC project to begin on. So, that will be the machine for serious metal machining. It has ball screws for X, Y and quill and big DC servos. It just needs servo drives. But that is another story.