I haven't had much free time lately, so this has been the first time I've been able to tinker with the old Rockford drill in about three weeks. This bit has been one of the last holdups, though, and it's damn near time to start putting it all back together.
Anyway, here was the problem:
This is the spot on the right side of the column where the upper table-lift screw support went. Sometime back in the machine's long history (only about 100 years) something happened, and that upper support was knocked off or broke loose. This left a nasty hole in the column, about one-fifth of the column's diameter. I didn't like either the weak point, or the fact the screw mount had to be band-aided. (They ground a couple of ratty carriage bolts into a "T" shape, chiselled the hole wider, and used those in place of the stock bolts.)
Now, the problem is, cast iron is not easy to weld. Look at it sideways, and it'll crack. Get it too hot, and it'll crack. Let it cool too fast, and it'll crack. Use the wrong rod, and it'll crack. Use the wrong rod and it'll draw carbon out of the iron, giving you a file-hard weld you can't even drill, let alone tap.
I am by no means an expert welding cast iron. I'd done it once before, a good many years ago, and that was just to plug the hole in an old exhaust manifold after I'd taken the heat-crossover flapper out. I think I used stainless rod.
I looked around on the 'net and got a great deal of heavily conflicting information. Some said "it's easy!" while others said "forget it!" Some said it's easy to stick weld, just use high-nickel rod, preheat, and let it cool slow. Others said don't bother with the preheat, and heck, I used 7018. Others said braze it, still more said no way, make a plate and bolt it. Some said no matter what I do, it's going to crack and fail, leave it alone. Others said the same thing, and suggested an epoxy patch.
Even the Lincoln, Miller and Airgas boards couldn't come to a consensus.
I'd originally planned on brazing it. Braze has the best track record of success, and as long as you let it cool slow, the brass has enough "give" to take up any expansion or contraction without causing a crack.
It's a big piece to braze, though, and I worried about the heat conducting through to the babbitt bearings for the main shaft, which would probably melt at 350 to 400 degrees.
I eventually hit on "Muggy Weld", a stick electrode hyped as about the best thing going for cast welding. It was horrifically expensive at $63 with shipping, for just half a pound- a grand total of seven rods. That's nine dollars a rod!
Just so you don't have to skip to the end, the Muggy rod worked, but only barely, and the welds themselves cracked with alarming regularity. But I get ahead of myself...
To start, I had to grind out the broken section. As I was doing so, I found what I believe to be an inclusion of casting sand- so the support broke off, I think, because the casting was extremely weak there. Most of the holes for bolts on this drill- both through-holes and tapped holes- were cast in, not drilled in. And the column is itself hollow, and has some structure inside for the wheel that guides the counterweight chain.
So when it was cast, there were "cores"- molded sand blocks that when the iron is poured, form the internal voids and passages. Think the runners of an intake manifold.
Anyway, I suspect that there was an error of some sort with the column core mold where it joined the internal brace core, and the cores that were to form the lift-screw bolt holes. This flaw produced an inclusion- instead of almost 1/2" thick solid iron, there were two layers of slightly-less-than-1/4" iron, with a thick layer of core sand in between.
The outer layer probably peeled off when the screw mount was hit (or was yanked on by an enthusiastic user) and some of the inner layer was probably chiselled away to make room for the replacement bolts. (I saw signs of either grinding or chipping.)
After the grinding was done, I had a fairly smooth hole to patch:
Unfortunately, that's just it; it was a hole, not just a crack. I needed to find something to fill the gap, besides $100-a-pound welding rod. I scoured my junkpiles and found an old sewer pipe flange, that not only had a section about the same diameter as the column (so the curvature would be the same) but had about the same section thickness.
And you guys wonder why I save junk.
A quick- for liberal values of "quick"- trip through the bandsaw, a trim with a cutoff wheel, and a great deal of "adjusting" with a great big bench grinder, I had me a plug:
The welding itself was entirely too exciting and involved using up a months allotment of vocabulary. As I said above, the welds themselves had an alarming tendency to crack- This was, in part, I'm sure, due to the dual seams. Had it been a single groove or crack, I suspect I'd have had little difficulty.
But I had to weld, grind out, weld again, grind out again, and so on, using up my extremely limited supply of rod. I eventually decided to forgo the preheat altogether, and let the thing cool down to about 100 degrees. Between that and doing very short beads- and peening/chipping heavily, as they recommend- I finally stitched it all together.
With one full rod remaining.
I do not yet know if I "succeded". Given it's propensity to crack- fortunately apparently only the welds cracked, and not the casting- I suspect that only the top layer of weld is solid, and that most of the inner... maybe as much as half, probably has at least some small, hairline cracks.
If I could access the back of the weld, and had another half-pound of rod, I'm sure I could fix even that, but obviously that's not going to happen.
So I hope for two things: One, that I didn't make the problem worse, by adding stress with the patch that may lead to future cracking under drilling loads (or worse, have the whole top half of the press come popping off and fall onto the floor) and two that the patch has restored at least some of the strength lost with the missing original metal.
If I'm lucky, this badboy will last another hundred years.
![[linked image]](http://www.docsmachine.com/machineshop/castweld1.jpg)
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