Second MDF machine

[spalm]

Well I thought it was about time to post what I have been playing with for the last couple of months. I had a lot of CAD to learn. It seemed to pay off. It was slow, but I now know how to model a machine. Thanks to all who helped.

I’ll post a bunch of pictures of my dabbling. I was just prototyping in MDF and planned to switch to Baltic Birch ply for the real machine (you can see the sheets of ply in the background in some of the pictures) but I am so pleased with the results in MDF that I might just go with what I got. The results really rock!

It is basically a torsion box design of the JRGO machine (thank you JGRO for your design). Same dimensions, but I just turned the machine inside out and put the bearings in compression pressing in against the black pipe. (This is nothing new, see Ger21’s machine and several others) The bearing adjustment blocks work great. I did some tests for parallelism by marking the four extreme corners with a pen on the Z axis and then measuring the diagonals and it is dead on. Flex is not detectable with my initial testing. I still need to add the second skin to the bottom of the X (long) axis, but I want to drill and install a bunch of T-nuts for hold-downs first.

The design is held together with just 8 T-nuts on the gantry: 4 on the upper torsion box and 4 on the bottom box of the gantry. 4 T-nuts for each of the bearing blocks supply adjustment and 2 T-nuts lock each bearing block in place. (No tapping!) This is the first time I have used T-nuts (they seem kind of cheesy, but I must admit they work well in this application).

I had planned on using Igus round slides for the Z until I read some of the recent posts. So I don’t quite know what to do. Anyone have suggestions?

I have accumulated ½ inch by 8 two start Acme rod, Dumpster’s lead nuts, thrust and standard bearings, lock collars, Belleville washers, and motor couplers. (Plan to re-use the Hobbycnc drivers and 200 oz steppers) But I have not arrived at a solution for the drives yet. Now that I have the XY done, I plan to work on this and the Z.

I am so happy with the design so far I can’t decide on whether to use the dancing banana or the sheep.

Thank you all for your help (this place is the best),
Steve.

[zoltan]

Hi Steve,

Do you have any plans of your machine?

Thank you.

Zoltan

[DieGuy]

very nice indeed!

[spalm]

Hey Zoltan,
Yes I do have plans, but the Z axis and the drive screws are not complete. So not sure if you want them in this state.

[zoltan]

Hi Steve,

It is OK even if they are not complete. When you have the Z axis and leadscrews you can share. In the meantime I can build the other parts.

Thank you,

Zoltan

[mvaughn]

Steve,

Your machine is incredible. I was just thinking about how to design a machine that uses torsion boxes to support for the X axis bearings.

I would like to know your opinion on how much stiffness and rigidity has been gained by supporting your X axis pipes compared to the unsupported pipe on the original JGRO design?

Keep those pics coming.

[spalm]

Zoltan, I plan to supply plans but some things changed in the shop compared to the original design. Things like the bottom of the gantry does not line up with the bottom of the box, and the torsion supports changed in shape. The leadscrew mounting determines the holes so I think I should wait. I am using Inventor for CAD and any change in one of the small parts ripples into the total design and drives the constraint manager crazy (or maybe it’s just my CAD skills).

Mvaughn, support was the one of the main reason for the redesign. Also it is much easier to align. Those four screws really work. This puppy is solid, still need to do more testing and if it doesn’t perform, I’ll redesign it again. This project has totally consumed me.

Steve

[spalm]

Ok, I did some more testing. I started by tightening the bearings to make sure that all the slop was taken into account. Then I clamped a square to the Y axis and moved it around to test for level. The right side was over a 1/8 inch shorter than the left. I think this is because the right gantry wall is flexed from the pressure. By tightening the top set of the bearing adjusters and loosening the bottom, I was able to completely correct for this by causing the bearings to ride more on top of the pipe (see picture). It is now dead on across the width of the table.

The same tests on the long length of the table was never a problem. Flex is not noticeable at all (even though the long pipe is also half inch).

I wanted to take a movie of the ruler just skimming the entire top but thought it would be too nerdy.

I am really liking this…

Steve

[lurch]

Great rework of a classic starter design. Simple, well thought out improvements...nice, great for beginners! I like it...tell us how it performs, and more pictures please.....

[mvaughn]

Originally Posted by spalm I wanted to take a movie of the ruler just skimming the entire top but thought it would be too nerdy.

I don't think it would be nerdy at all! Everyone on this site has a little nerd in them anyway, we build CNC machines as a hobby.

[spalm]

Just some random thoughts. Anything to keep me from documenting this design.

To make the X axis pipe supports for the large torsion box, I started by cutting a sheet to 19 ½ inches and then ripping it to make the eleven 2 ½ inch strips. This made sure that they were all exactly the same size. Then I used a jig on my router table to add the curve for the pipe. By using a pattern cutter bit (with a bearing on the bottom of the bit) I inserted a strip in the jig, routed it, flipped it over, routed it again, flipped it end for end, routed it, flipped it again and routed it. This way I was assured that cutout was in the center and all the pieces were the same.

Lurch, thanks. That was my intention.

I am now thinking about using two rods and delrin slides for the Z using a jig to drill the holes. Any thoughts or a source for these rods or smooth pipes. Maybe half inch by 12 inches?

Steve

[mvaughn]

I was under the impression that you cut all your parts with your first machine. It's impressive to see that you made it so accurately by hand.

Here is a link to some 1/2 inch drill rod that you can use for your z-axis. I've used drill rod like this for all the axis's on my machine and it works very well. A little 600 grit wet sanding will polish the drill rod up very easily.

1/2 inch drill rod