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| smfr:
[Moved from homemodelenginemachinist.com] I've started work on a set of Stuart No. 4 castings that I was lucky to pick up on eBay: It has the crank as a casting, which I guess means that it's an older set? As far as I know, all the parts are present. I also have a casting kit for the reverse gear. |
| smfr:
[Moved from homemodelenginemachinist.com] Step 1! The boxbed: This is just basic squaring up on the milling machine, though space on my milling table is limited so clamping gets slightly interesting: There's a shim under the lowest corner to stop it rocking. Once the underside is done, we flip it over and mill the top side flat: Here I have to move clamps around, because I don't have enough travel. Note the 'L' on the lowest corner (found on the surface plate with a height gauge), so I know what height to start the cutter at. I was hoping one of the "No. 4" imprints on the castings remains on the final model, but I suspect they all get cut off. |
| smfr:
[Moved from homemodelenginemachinist.com] Next up, the soleplate. Again I had to get creative with clamping due to limited table space: Note the stacked clamps! It's suboptimal because the whole thing could swivel around the one bolt, but the rotational forces are minimal when just trimming the bottom. Once the bottom was flat, I flipped it over and went over the top surface, then cut the bearing slots. Here I messed up slightly: rather than center the slots on the entire casting, I started by centering them on the bearing bosses, but then found that those bosses are not centered, so I had to correct slightly. The slots are a bit oversize, but it's not an issue as I just cut the bearings to fit. While it was clamped down, I also drilled and spotfaced the holes for the corner bolts. The plan doesn't show the spotfacing, but it's certainly required for the nuts to sit flat. In the photo above I've completed one bottom bearing, making it a snug fit to the slot. Here's the other bearing being squared up: I swear this gunmetal squirms under the cutter. I was pretty sure I'd cut the slots on these bearings within a thou or so, but the slot ended up about 2.5 thou too narrow. I took these to final size by filing, since I wanted them to be a snug fit to the soleplate. |
| smfr:
[Moved from homemodelenginemachinist.com] The top bearings are a little more tricky. First I cleaned up the lower surface in the 4-jaw: I then glued the two together, planning to turn the bosses. However, I realized that I had no true surface I could use to ensure that the join was aligned the turning axis, and in the center. So after some application of heat to undo the Superglue, I used a chuck spider in the 4-jaw to put a small flat on top of each bearing, with the bearings having the same thickness: and then I could glue them together again: The boss is then a simple turning job: I also drilled a small hold down the center to I had a reference to re-center when I flipped it around. However, even with the best of plans... At some point in the hole drilling, the Superglue gave way and the two sides separated. >:( Also, look at that hole! It's all over the place, and (I think) not just after separation: After some futzing around trying to get the halves aligned properly, I attached them together with solder this time, and was able to complete the other side, and open up the hole to 1/4": I'm wondering how to ensure that things are lined up when I drill and ream the hole to size. My plan is something like this: 1. Sweat the two lower bearings together and drill to 1/4", so that both upper and lower bearings have 1/4" holes in roughly the right spot. Separate the halves. 2. Sweat the tops and bottoms together in pairs, aligning the holes 3. Drill to 27/64" 4. Drill and tap the soleplate for the hold-down bolts, and bolt the bearings down 5. Ream in place with a spiral 7/16" reamer Does that sound reasonable? |
| smfr:
[Moved from homemodelenginemachinist.com] Not too much progress over the past week. I think I've got as far as I can with the bearings until I receive the 7/16" spiral reamer I got on Ebay. Here's where I'm at: The upper bearings were separated, then spot-faced with a 7/16" end mill and drilled. I have yet to tidy up the ends, but know that I'll use the rounding table, and pivot around the opposite bolt hole. I still need to sweat the two lower bearings together to start the hole. Then I think I'll sweat uppers and lowers together and clean up the hole, then put them in the sole plate to see if things line up. I have a feeling that if I drill and ream them in place in the sole plate, the lower bearing is going to be oversize or misaligned. Maybe I'll do a dry-run or two at a smaller diameter to see how things work out. |
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