MendelMax build: Y table
Time to move onto the Y-table. A huge X-Y build area is one of the big advantages of the MendelMax, so this is a fun process.
Now stick these bushings-in-their-holders onto their Y-rods (two per rod). Fasten the rods to the sides of the Y-rod holders using printed clamps secured with M5 screws, screwing them into M5 nuts in the built-in nut holders. I found that screws longer than 10 mm helped here, so I pulled out some 16 mm long M5 screws that work perfectly.
The actual Y-table itself will really vary from machine to machine. Heated build platform choices, bushing choices, basic structure, etc. I’m going to go with a fairly conventional approach of a bottom plate of MDF that the bushing holders and belts are attached to, which itself is attached to an MDF print bed. I’m not using a heated build platform, but this setup gives me the flexibility to add one in the future by simply attaching it to the print bed.
I cut a 290 mm x 290 mm square of MDF to serve as the print bed and a 290 mm x 100 mm rectangle to serve as the bottom sheet. Now, my MendelMax is 40 mm wider than the “standard” size so all the lengths here reflect that. If you’re building a standard-sized machine, the print bed should be more like 250 x 290 and the bottom sheet should be 250 x 100. Measure your machine to make sure the dimensions make sense.
Now you need to drill holes in the bottom sheet to attach the bushing holders. Take the bushing holders you already attached to the rods and press them against the bottom sheet, moving the sheet until you have it positioned right. Then use a pencil and blacken the MDF visible through the screw holes in the bushing holders. Then go off and drill those holes to accommodate M3 screws.
Attach this drilled bottom sheet to your bushing holders and tighten the holders down:
Slide the carriage along the rods and push it sharply and see if its momentum continues the movement for a bit. If it doesn’t, then the bushings are binding somewhere and you’ll need to slightly reposition the holders. I found that enlarging or extending the drilled holes using a dremel tool allowed enough wiggle room that I could position the holders in such a way that there was no binding. Once you have this done, tighten the holders down in their new positions. Again make sure the carriage slides smoothly and keeps moving a bit after you stop pushing. If not, then continue this process of slightly repositioning the bushing holders until you get it perfect. You really want the Y-table to be as close to frictionless as you can manage.
Now we need to drill holes at the corners of this bottom sheet where it will connect to the actual print bed. I like to remove the bottom sheet, duct tape it to the print bed, and drill both at the same time so I can be sure the holes will line up:
Now’s the time to mark on your bottom sheet where to drill holes for the belt clamps. You want the belt clamps to be directly in front of the motor and idler pulleys when the carriage is slid all the way up or down the rods. I like to place the actual clamps in place and use a pencil to blacken the MDF visible through their holes. It’s not a disaster if they’re not perfectly centered since you can simply slide the motor and idler mounts along their extrusions to center them with wherever you put the belt clamps.
After drilling the holes, attach the belt clamps and their nut holders on the other side with washers and M3 screws that are at least 20 mm long:
Now you want to attach the bottom sheet to the print bed. There are several schools of thought on the best way to accomplish this, but I’m going with the tried-and-true screws-and-springs method. The upside to this method is that leveling the bed is incredibly easy, but the downside is that if you have weak springs, the bed can wobble and vibrate as the bottom sheet slides along the rods at high speed. To alleviate this, and to work around the fact that I didn’t have anything super-powerful in my big box ‘o springs, I used three of them for each 45mm long M3 screw:
Fasten the bottom sheet to the print bed with M3 nuts and washers. Don’t worry about tightening them all the way down or leveling it yet; we’ll do that later. Once you do, with all those springs, there’s so much tension that the print bed will be rock solid! Here’s what your completed bed should look like:
Now let’s deal with the Y-axis motor and idler mounts. I used a spare M8 bolt I had lying around for the idler, but you could easily use a 50 mm length of M8 threaded rod. Put two 608 bearings on your rod with washers on either side and tighten it down with M8 nuts. The dual 608 bearings are important because they prevent each other from wobbling. A single 608 bearing will eventually wobble and make the belt collide with the side of the idler mount.
Center the idler mechanism so that the bearings are right in front of the carriage’s belt clamp and tighten down the M5 nuts holding it to the extrusions. Note: this is the older-style idler mount; your idler may be the newer improvement made by AlephObjects, in which case it will function exactly the same way but look like this:
Time for the motor mount. Attach the motor with M3 screws that are 10-12 mm long and two washers. Then attach your motor pulley; I’m using metal ones from Misumi which are pricy but nice. Like with the idler, move the mount to center the motor pulley at the belt clamp on the bottom sheet and then tighten it down.
Almost done! Now comes the final step: attaching the belt. This part is a little tricky without access to the underside of the machine, so I balanced it on two kitchen table chairs to allow me to work from below.
You’ll want to take one end of your belt (I’m using 2mm GT2 belts) and fasten it to the idler-side belt clamp by loosening the clamp, inserting the belt, and tightening it back up again. Then thread the belt around the idler:
Now do the same on the motor side. Take the loose end of the belt, loop it around the motor pulley, attach it to the clamp on the other side. Pull it as tight as you can! You can cut off the loose ends to prevent the rest of the belt from flopping around. Here’s what it looks like on the bottom:
And from the top:
Slide the table around and let your imagination go wild as you think of all the 280 mm long objects you’ll soon be able to print! Next up: the extruder.