Been a day or three. Warning, big long slog ahead. Go grab a cuppa...
I've given up on finding a machine shop to deal with this recalcitrant rocker box. I even drove 50 friggin' miles to a place up in St Jo, only to have 'em hem and haw... and finally say
"well maybe 4- 500 bucks... hard to say." Funny, weren't hard at all for me to say no.
So while I was busy doing Sue's basement buildout, I pondered... then pondered some more.... from somewhere deep down in the 72 yr old grey matter a plan started takin' shape... several, actually.
First thing I need to do was find out if me an' Mr Atlas were on the same page when it comes to making small-ish bushings. Happy to report we are. Used some 6061T6 solid, which has a fair bit more bearing strength than your average casting ally, and turned to 14.5mm ID and 17.5mm OD.
So here's the plan... Take the oval shaped 15mm hole in the box and take it out to 17mm, then press in the bushings and ream to 15mm. I decided against buying steel bushing for 2 reasons. Main reason is the expansion rate of the aluminum box vs the much slower rate of the steel bush. There's a real danger of the bush getting loose enough to spin if the box expands to much too fast... in which case we are right back at totally screwed. Best to stick with like materials.
Second, buying a bush takes away my flexibility.... ID and OD are set in
stone steel. Making my own allows me to first measure the hole and then turn a bush to fit it. Seems... at least in my mind, that turning a bush to fit a hole will be much easier than drilling a hole to match the bush. If I get the hole just ever so slightly too big, I'm fucked. On the other hand, if I turn a bush down too small, I shitcan it and start over.
Back to the plan...
Dug in the scrap and found some plate that's about 10ga ( just over an eighth inch thick). Cut 4 pieces around 6X10" Welded two of 'em together.
Took those, clamped a third sheet on 'em and cut holes at the corners.
Ran 3/8" bolts up through the bottom and tightened in place.
Enlarged the holes slightly on the upper sheet so I had a little wiggle room for positioning.
Underneath the bottom I welded on some angle and runners so it'll mount and slide on the lathe ways.
The double angled piece by my thumb is what locks it to the ways. I can adjust the tension on it to remove any play and still allow it to slide. I also added a simplified version of gibs at the 4 corners to be able to remove any and all play. Spoiler alert... worked a treat!
Took the 4th sheet, cut the corners off and drilled 6 holes through it and the 3rd sheet.
There's 6 holes because I wanted to be able to cut both holes on one side if the need arises.... only 4 will be used for any given combination. To get the rocker box (remember that thing?
) to set square on the top plate, I tuned 4 1.5" stand-off bushings.
Making all the holes a little on the loose side now allows me full freedom of movement in space. I can adjust for up/down, tilt fore/aft, tilt left/right and left/right of the lathe centerline.
Next I took 3 of the 4 end caps , ground 'em flat and welded what was left of the screwdriver slot closed.
Faced 'em down flat and drilled a dimple in 2 of 'em. As a guess, the dimple is about 5 thou" across.
I cut 2 flats on 'em to get a wrench on. These screw back into place on the box. Then I can chuck dead centers up in both the chuck and tailstock.
I took the 3rd cap and drilled and tapped for a 1/4" 20 bolt.
Found a bolt about 6" long, cut the head off and screwed it into the cap.
So here's how it all works...
First I set the fixture (I'll call it that for lack of a better word) on the lathe then adjust the lock and gibs until there no free play in any axis except sliding back and forth.
Then I screw the dimpled caps place, install dead centers on both ends and then spend a shitload of time getting getting the dead centers and box end cap dimples to fall exactly in the same place. Remember I said the dimples are about .005" across? That means as long as the centers fall inside the dimples, my misalignment is less than 5 thou".... that is more than close enough for this task.
After that I remove the dimpled caps and screw the cap/bolt in the starboard side and chuck that up in the tailstock. Now I can use the tailstock wheel to slide my whole contraption back and forth across the bed.
You can see in the next pic that I tried a 17mm end mill first. The astute among you will also notice that's not an XS1B rocker box. Ya din't think I'd try the first cut on that did ya?
I picked up two 17mm bits cause they're Chinese and dirt cheap. Neither made a good hole.... which is what you expect for bits that cost $6.99 each. I didn't measure, but my 17mm ream would just slide in and out of the holes... they cut way too big.
I had also picked up a 16.5mm drill bit. The problem with it was the point. It has to be flat and not pointed so it could cut all the way to the bottom of the hole. No worries, disc sander made quick work of the point.
And the winner is..... the drill bit. Cut a nice clean 16.5mm hole purty as you please.
You can also see in the pic above that I'd already driven the ball bearing out of the oil passage. Once the bushing's in place, I'll need to re-drill that passageway.
Next I needed to finish the hole out to 17mm with the ream. Same problem with the ream, it won't reach all the way to the bottom of the hole. Gave it the same treatment as the drill bit.
And lo and behold, we now have a finished 17mm hole ready for a bushing.
I wasn't gonna write this post until it was completely done, but I've come here, hat in hand to ask a question of you machinist guru's out there. The hole is exactly 16.99mm. So what OD size do you guys want to see on the bushing for a "press fit?" I asked google and AI and got different answers. What do you folk that do this for a living recommend??
Yeah.... maybe not done with this box yet, but making and pressing in bushings is well within my wheelhouse. I'm confident the rest will go pretty smoothly.
Never say die.
