2nd Build – 62 x 30 R&P

[Phil B]

After I got some wiring issues resolved, I finally got the machine running. I did go ahead and switch back the Ahrens Z nut so this is pretty much a stock design on the linear motion components. I built the Y with the rack on top and since running it, see no reason to switch it to the back of the gantry as drawn on my original design. This was is easier and works well so why bother.

I’m still awaiting my spindle clamp. Aside from that and few little do-dads and whatnot, the chassis is complete and I’m about ready to start the detailed checkouts and alignments. After that I’ll work on some side issues such as sweepers, home switches and similar things.

I’m currently running my modified hobbycnc board with the settings as follows:
XY = 400ipm, 10 accel, 1/8 step
Z = 120ipm, 10 accel, 1/4 step

It seems to run reliably at those speeds, if I push up to 600ipm I can get some stalling, the speeds I’m using now are fine for me. When running the break in wizard, I’ll occasionally hear a “pop” like a gear going back into the rack, don’t know what that is yet. Overall, I’m pretty happy with how the machine is running at this point.

[Phil B]

When I first assembled my machine I found it to be out of square by about 0.1” or so. I tried to get into square first by homing it in and then by shims, neither of which worked to my satisfaction.

I eventually discovered that there is a down side to building such a stiff frame, if it ain’t square to begin with, it’s about impossible to rack in into square. I eventually found out for sure that I could rack my frame by about +/-0.05” using homing, not quite enough and even then it put a lot of stress into the frame.

I tried this several different ways, the one that got really close was when I loosened the trucks to allow the frame to pivot on them. At that point I cracked a bearing and decided to go back to the drawing board so to speak.

I decided to reengineer the gantry uprights so I could rack more easily. Previously, I was basically trying to move the A axis in an arc and the trucks, rail, and frame protested every time. With the new design I will be racking as a parallelogram instead of an arc which doesn’t induce stress into the frame.
Here is a picture of the new design:





I cut one of the gantry uprights to make a 6” riser because the 8020 is easy to work with. The 6” isn’t quite enough so under that is another 2” riser block made of hardwood. The wood riser bolts to the 8020 riser through the truck plate. The gantry beam is attached to the 8020 riser via two 3/8 x 8 carriage bolts on each side. The hardest part of all this was drilling 4 half inch holes in the gantry. The 3/8” carriage bolts fit into the 8020 with only minimal grinding on the head and shank by the way.

With this, I’m able to loosen four nuts and rack the gantry into square very easily. Once Square, it stays that way. Although it will be harder to change the gantry height now, I like the design better, it’s visually smaller as well.

[zool]

The hardwood block looks nice, however, wouldn't you be better off with some 8020 or a piece of steel in there?

The base for my Shop Droid was going to be wood, but I spoke to a structural engineer and promptly changed my mind. It is all 8020 now. Rather than plywood or MDF for the table top, the table top will be Silestone with MDF spoil board on top of that.

Kitchen countertops and quartz bathroom surfaces by Silestone

Only so much can be hid with hide glue....

[Phil B]

The block could have been 8020 or some metal piece but in this case I doubt there would be any measurable difference in strength. If I were doing this from scratch I most likely would have engineered this riser block out. I could have mounted the 8020 shown vertically instead (and thus no wood riser) but I specifically wanted the slots running as shown.

As for the “base” being wood, I believe this is far stronger than probably all the metal strut bases you typically see, there is zero deflection / movement in it. The laminations the rail are attached to is a different story I’ll grant you. Those are pretty strong, If I had some 1.5 x 6 steel tube laying around I would have used it instead.

[mnerobi15]

Get a decent builder or architect to have a look. It could be VERY serious so you need an expert check it out.

The insurance people were not helpful as it could cost them a load of cash, please get an expert to give you their opinion.

[Phil B]

Here is a picture of the sweepers I came up with for the X axis, these only do the top of the rail. It's basically a vertical wood block with small Velcro pads attached to the bottom. The end grain of the wood was sealed with super glue just to ensure a good bond for the Velcro. The pads do a good job of keeping most of the dust from getting to the bearings.

I tried several different materials from brushes of all sorts to plastic, rubber, etc, these seem to outperform everything else I tried. I also plan to install a deflector shield which will prevent much of the debris from even getting to the rail.