CNC Router V1.0 (For Cutting Multiple Materials)

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Originally Posted by biketrialsdave

Thanks Jazz! I had thought of something similar but was afraid monting the ballscrew like that would cause problems. Is the general idea of the gantry sides to keep them as short as possible? Well not the sides, but the distance between the top and bottom profile carriages on the X axis?

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Yes if you want the best possible strength then you want short stubby sides but this is only really required if you want to cut hard materials most of the time. Gantry height just needs to be high enough to provide support to the Y/Z axis and resist Twisting/flexing. With this design the height of the gantry supports and takes the full load of the Z axis bearings with just the ballscrew and motor above the gantry.
The red machine in the pictures is twin ballscrew driven and this cuts aluminium no problem with resoanable quality of finish but it's not designed to do this all the time and it would eventually take it's toll on the machine, where has with woods etc it will happily cut 24/7.

With regards to the ballscrew at the rear then IME it hardly makes any difference unless wanting to cut hard materials with deep DOC. Which in this case then you'd want a stronger gantry design. For all wood and lighter aluminium use then it's no problem at all, if it was I wouldn't be using this design.!

To be honest if your wanting to cut all materials then you have to lose something somewhere. If you build for cutting the hardest materials then you need strength and weight, this comes at the cost of speed unless you increase the strength of motors etc and this costs cash.
This is wasteful if your only ever going to cut hard materials 5% of the time. So IMO you get a much better machine if you target the main use and design for the optimum doing this.! . . . Jack of all trades works but truely is master of none and you have to accept this other wise you'll be sadly dissapointed.!

Finally feeling like I may be going in the right direction now! (*awaits comments saying I'm not* =P).

There's just enough room to mount the X axis motor on the inside of the gantry.


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Won't need that top piece it's only adding weight and expense.

Thought you might of said that! Now removed.

I am looking to mount the motor on the inside of the gantry but I'm going to need a long motor shaft or a pulley with a long hub length to get through the 20mm plate and out the other side with enough length. Any suggestions?

It looks as if it will be easier to mount the X axis motor on the outside of the gantry plate (See below). If I wanted to mount it on the inside and still use the FK bearing block then the shaft would be too short to mount a pulley.

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I am now looking at the Y axis ballscrew mounts in a little more detail. In the screenshot below how is the bearing mount attached to the steel box section? (Does anyone have a link to this build thread btw?)

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I assume that there's another piece of welded steel plate on the end of the box section? As below?

Attachment 12855

While I am on the subject of the "end plate", I assume some sort of adjustment will need to be built in to allow movement in the Z axis as if I use the epoxy method on the box section then it's going to add some height?

Dave

Yet more questions... this time about welding and distortion.

What is the best technique to use to minimize distortion? I assume I should tack weld each side of the box section before doing full fillet welds? Do I need to do any kind of stress relief to the joint after? I am only practicing at the moment. Picked up an Evolution Rage 3-S to cut some box section and purchased an auto darkening helmet =)

I've also ordered one of these, which I hope will help:

Attachment 12874

Dave

Hi Dave,

Yea tack it all up in sections keeping any eye out for square, once your happy fill them in, alternate the areas your working on so they have time to cool down while you work another area, it's the heat build up your trying to avoid.

If you can clamp stuff down so it's less likely to move or distort, if you want to get really into it, do some googling on preheating, Jody over at http://www.weldingtipsandtricks.com has a pretty comprehensive website and youtube channel.

Where did you get the jig from?

.Me

Speaking as a pretty second-rate welder, I found it really useful to build the bulk of the frame using just one spot of weld at each joint. I then used a series of Spanish windlasses, sash cramps, etc, to pull it all square before going round and building up the welds. Diagonal bracing followed. I cut all the box section as accurately as I could using an angle grinder in a cheap stand but it wasn't perfect. Your cutoff saw might do better. And if it goes pear-shaped (literally!) then there's always the angle grinder to cut the weld to start again - another reason not to weld too much before you're happy with the shape. The great thing about welding is that for something like this, it is very forgiving. I cut one piece on the wrong side of the line, but built back up with weld and ground back to dimension...

Good tips! Hopefully I will get some time over the weekend to practice with my new tools :) Still got a LOT of design work to do...I'm thinking of moving away from the FF blocks + aluminium plate for the Y axis and maybe just using steel channel (or angle) welded to the box section and mounting BK blocks to it? One of my biggest concerns for the whole project is actually drilling accurate/straight holes! I have a pillar drill but it is pretty useless as there is a lot of slop in the chuck.

This is the jig I bought, got to be worth a punt at £21!:

http://www.ebay.co.uk/itm/1114096787...84.m1497.l2648

Cheers Dave.