Fabricated parts required:
1x Gantry Assembly
1x X rail Top
1x X rail Bottom
6x ¼” x 2 ¼” hex bolt
6x ¼” washer
6x ¼” cross nut
8x 8-32 x 1 ¼” machine screw
8x 8-32 nut
16x #8 washer
Once you’ve built the Gantry assembly you’ve already finished the hardest part of this step. The squareness and stiffness of the machine depends on how square the gantry assembly ends are. Take the time to double check these before proceeding.
6.1 Take the gantry assembly and loosely attach it with the ¼” bolts and cross nuts (6 of each) using a ¼” washer underneath the bolt head. Photos #1,2&3 show all the bits and pieces.
6.2 With the gantry assembly loosely in place, tighten the three 8-32 machine screws on one of the Y rails to lock it in place. Try to get the rail so that the bolts are roughly centered in their holes and the rail is parallel to the base side.
6.3 With one of the rails locked down, tighten the three ¼” hex bolts on that side. While you tighten the bolts, hold a square up to the front face of the gantry assembly to keep it square to the base and line up the bottom to be around 4″ from the base (Photo #7). The actual distance you can get from the base surface will depend on the how the v-grove bearings were installed but shouldn’t be out by more than an eighth of an inch. The height isn’t terribly important but being square to the base is, focus on that when tightening the bolts.
6.4 You can now tighten the three ¼” hex bolts on the other side. Tighten the bolts evenly not one at once keeping an eye on how the gantry assembly comes together with the gantry side. Similar problems may be encountered as covered by Note 1 of Step 5. If everything goes together nicely there will be no gaps as in Photo #6 when the bolts are tightened loosely. Four issues in alignment could be encountered:
1) A gap anywhere and with the rails parallel to one another and the gantry sides vertical when viewed from the front is a sign that the gantry assembly sides aren’t square and flat.
2) A gap at the top bolt and with the gantry side leaning outwards when viewed from the front is a sign that the rails aren’t able to distance themselves far enough apart.
3) A gap at the bottom bolt and with the gantry side leaning inwards when viewed from the front is a sign that the rails aren’t able to distance themselves close enough together.
4) A gap at the middle/ back bolt and with the rails not parallel to one another when viewed from above is a sign that the gantry assembly ends aren’t square.
Issues 1 & 4 require modifications to the gantry assembly. Issues 2&3 may be resolved by adjusting the rail that was tightened down in step 6.2 In the case of #2, loosen the rail and retighten as far out as possible, or as far in as possible in the case of #3. Should this adjustment not be enough measure the distance between holes in the base and the length of the gantry assembly; drill the holes in the base larger to give more flexibility or reduce the length of the gantry assembly as required.
6.5 Once the gantry assembly is square and all six bolts are tightened, slide the gantry (now the gantry sides and gantry assembly are all attached I will simply refer to it as the gantry) to one end of the base. Side it back and forth an inch or two to make sure the rail has moved to the proper distance from the other rail and everything is smooth. Once you’re happy with it tighten the 8-32 machine screw on that end to tighten the second rail. Slide the gantry down to the other end and repeat the process of sliding the gantry back and forth. Tighten the middle machine screw and then the end one.
At this point both Y rails should be secured to the base, the front face of the gantry square to the base and the gantry free to slide the length of the rails with no play nor binding.
This process has come across as laborious and tedious but I had no problems assembling things on the first go which took under five minutes. Hopefully my success will be repeatable and if not the details provided will be enough to trouble shoot any problems.
6.6 Moving on to the X axis rails, attach the aluminum flats using washers on both sides and tightening finger tight. I put together a quick height gauge using a square of scrap of wood and a C-clamp to position the lower rail (Photo #10). Clamp the wood to a height that supports the aluminum rail with 1/8″ clearance from the bottom of the Gantry (required to give the V-groove bearings room to seat). With the rail supported on the wood at one end, tighten the end machine screw. When tightening, try to keep the rail level, more on this in a second. Move to the other side and support the bottom rail on the wood and tighten.
If the rail was perfectly level after you tightened the first screw you will be done, however, if there was any misalignment, the rail would have rotated around the screw that was tightened first when you adjusted it at the other end and will not be even along its length. Go back and forth leveling it out, slowly honing in on making it snug against the wood block along the whole length. This took me 2-3 iterations to achieve. Make sure the wood block doesn’t shift while doing this! Really I should have used two C-clamps to hold it in place to stop it sliding down.
Take your time on this step to get it right. If the rail isn’t a consistent height along its length, your cutting tool will not run at a consistent height over the work piece. Once things are set up right, tighten the two inner bolts.
6.7 Once you’re happy with the bottom rail, set the top rail parallel to the bottom. The bottom rail is our datum and the top rail needs to be a consistent distance apart. If the distance isn’t consistent, the trolley will be smooth running without play in the middle, will have excessive play on one end and will bind on the other. I used a pair of digital calipers locked to the required length as a measuring tool. These are not necessary and are overkill, a trammel or a ruler with two pieces of wood clamped to it similar to that used previously will be more than adequate for the task. As usual, position the upper surface of the rail to be 1/8″ inches clear of the top of the gantry to provide clearance for the V-groove bearing. The distance between rails is just shy of 5 ¼” (Note: I am doing a terrible job of measuring the distance in Photo #11, the edges of the rails should be an equal distance from the tips of the calipers). Adjust the height of the rail as in step 6.6 until consistent along the entire length.