Step 5: Gantry Side Assembly
1x Gantry Side Left
1x Gantry Side Right
8x modified 5/16” washers
8x 3/8 V-groove bearings
8x 3/8” washers
8x 3/8” nut
3/8” x 2” hex bolt
4x 8mm skate bearings
4x 5/16” x 1 ¼” hex bolt
4x 5/16” washer
8x ¼” washer
4x 5/16” nut
2x ¼” cross nut
2x ¼” x 1 ½” hex bolt
To build the gantry we will start with the sides that run along the Y rails. In this step we’ll see how amazing the v-groove bearings are and how easily they make the assembly process.
The gantry sides are similar but with differences between left and right for the idler bearing counter bores and limit switch counter bores. The limit switch counter bores are on the outside of the ends when installed and the idler bearing counter bores are on the inside. The features for the stepper motor mount are repeated on both side so that the stepper is reversible should you want to install it on the other side for whatever reason.
5.1 The 3/8” V-groove bearings are installed using the hardware shown in photo #3 with the 3/8” washer on the outside and a modified 5/16” washer on the inside. A modified 5/16” washer is a 5/16” washer bored to an ID of 3/8”. This is done because a regular 3/8” washer will rub against both the inner and outer races of the bearing but the OD of the 5/16” washer is such that only the inner race is supported allowing the bearing to spin. Tighten the top bearings securely but keep the bottom ones loose for now. The bolts should be tight enough that the bearings won’t shift under a reasonable amount of force, but don’t tighten them up so tight that the washers crush the plywood beneath them. The consequences of this are outlined in Note 2 later on.
5.2 Next item to install is the 8mm idler bearings for the timing belt. These have a 5/16” washer on the inside in the counter bore, and two ¼” washers on the outside to provide the required standoff. ¼” washers are used for the same reason as the modified 5/16” washers for the v-groove bearings. Photos #4,5,6,7 shows the setup.
5.3 The v-groove bearings can now be tightened against the rails. Start by sliding the bearings over the rails (Photo #9), hopefully you followed the note in step 4.4 and held off from putting on the belt supports, if not, remove one per side to get the bearings over the rails. The top bearings are already tightened so only the four bottom ones required attention. I don’t have any pictures of this step as it requires both hands to do. For each set of top and bottom bearings, squeeze the bearings together with your fingers while tightening the bolt. I wrapped the bearings in a towel as you’ll want to squeeze them together as tight as possible but they have rather sharp edges. Once you have completed this step for both bearings per side you should be able to grab the gantry side and twist it every which way without any noticeable play (hold down the rail when you test this as they should still be loose; we’ll get to tightening them up at the end of this step).
Up to this point everything should have gone together smoothly as long as the holes have been drilled within 1/16” of their indicated positions which should be do-able even with hand tools (its been designed to be forgiving like that).
There is a chance that you won’t be able to get enough separation between the bearings to get them on the aluminum flat if the holes haven’t been located within the specified tolerance. If this happens, re-tighten the top bearings making them sit as high up in the holes as possible and retry the assembly. If this still doesn’t solve the problem the bottom holes will have to be re-bored to a larger size. These holes haven’t been given the same amount of wiggle room as the others to keep as much material as possible under the washers to prevent crushing.
I have not mentioned aligning the gantry side to the vertical during this step (when I say vertical I mean when viewed from the side. With the bearings tight around the rail the gantry side will automatically align itself to be vertical to the base when viewed from the front. If it is not, the most likely culprit would be a washer that has crushed the plywood around it from tightening the bolt far too much. If this has happened you should remake the gantry side as it will be close to impossible to get all the bearings lined up in the same plane.) If the top bearing holes are drilled in line with each other and the bolts are registered on the same face (top or bottom of the hole) then the gantry side will sit within a degree or two from vertical. Any misalignment (angular and height above the base) will be taken up in the connection of the gantry side with the gantry assembly. Having this flexibility in the design later on allows for you to focus on getting one pair of bearings tight around the rail at a time instead of worrying about multiple things at once.
5.4 The last item for the gantry sides are the limit switch “bumpers” that trigger the limit switches. Shown in Photos #10 & 11 they only go on the side the limit switches are on and can be modified in length by using a different length of hex bolt. Tighten these by hand until the end of the bolt bottoms out on the plywood pushing against the cross nut. Do not use a wrench on these as you can easily over tighten and crush the plywood. The belt supports can finally be installed as per step 4.4 so go ahead and put them on now.