how do you start machining a long shaft?
i know somewhere this was thoroughly covered, but i have not hit upon the correct search terms to find it (at least, to not end up with 100+ results). if someone recalls the thread, you can just tell me to look there.
i have a 3" OD x 24" long steel rod. if has some surface rust on it. all this talk of cannons got me thinking this piece of steel would make a nice cannon project. so what is the sequence of steps to give me a starting point? do i just plop it into a steady rest with the light rust on it and drill the end for a live center, and then use the center to hold the shaft while i machine a small band to run the steady on for actual machining?
i have never used a live (or dead) center or steady rest.
On big shafts you tend to get a center in the end, do a light scratch cut for the steady neer the far end and center of the lathes longitudinal travel, Polish it with emory, hit it with grease and if its big like 6"-12" add coolent and still grease the scratch cut where you trued it up and thats where you mount the steady rest. depending on the job you might do a few steady rest truing cuts.
than you face it best you can. true up the center suck a bullnose in the center and cut till the middle of the lathes travel up to the steady. onces its dead nuts move the steady behind the cross slide, get it set, greased and collent pump on it and cut all the way to the chuck.
Its lots of work but cuts that take 40 minutes are a machinist gravy job. just like keyways in 20 foot shafts on a horizontal mill. Thats fun, it dont get better than that.
I never turned anything longer than 16 feet. It was fun threading the end of that long ol prick.
Do you have a follow rest? They are made for long "rounding up" cuts like that. Once you get a clean diameter you can set up with the steady rest. One thing. Drill and bore the bore early in the game then maching the rest of the cannon to the bore. What about trunnions?
Trunnions he says, whats that. Well, I'll tell you those two trunnions will be the devil in the brew but they can be done quite nicely.
I did a cannon barrel with a 3" bore one time. It was made of bearing grade steel. It had been setting in the shop for months when I started there and that was the first job the boss gave me. I had a set of plans for the barrel dimensions as it was a full scale cannon. The customer was a Civil War reenactor and had a carriage and caisson built. He had a fortune in it but he has a fortune anyway.
We welded the trunnions in it and I made a breech plug that screwed in and then was welded. When it was finished the barrel looked just like the real thing.
He fires it at reenactments. He has fired it at the Perryville Ky battlefield.
It's only ink and paper
Forrest's question about trunnions is a good one. The workholding is a lot easier when the OD is straight than after it has some taper in it. Ask me how I know Den
That sounds like the general plan. When starting a cannon barrel, I drill for the trunnions before turning the OD profile of the barrel. I usually do the bore first, then drill almost to the bore.
There are a couple of ways to attach the trunnions, Jerry Howell's method of using a fine thread socket head capscrew to hold the saddle and then pressing a cap on the screw head for the trunnion works best for me for a smaller barrel.
This is a 6" barrel I did using that method;
The trunnions on this 6" long barrel were bored into the barrel with an endmill.
that's why i didn't even want to mention what i was going to do, but figured it might influence how i should do it. can i change the title of this thread to "how do you start machining a cannon barrel and locate the trunnion holes?"
since i see no stopping this train, i may as well hop aboard. so how deep do these trunnion holes need to be, and is there any problem welding them in place on a 20" steel cannon? is silver soldering them a better idea? i have found many drawings of various cannons, but they are mainly bore diameters and external dimensions. i have no firm ideas on how to attach the trunnions.
You can press them in and then weld them for the radius but I would bore the barrel and turn the OD before I bored the pocket for the trunnions. Only put them in far enough to hold them while welding. You can do the weld for the radius where the trunnions mate up to the barrel.
I didn't have any trouble doing the trunnion pockets after the barrel was tapered, it just took some thinking and setup time.
You'll need at least a three pass weld on the trunnions.
It's only ink and paper
Many ways to skin a cat. Here's a process I used at one shop a couple decades ago for starting long shafts (for scale reference, these shafts were about 8" o.d. and 9' long).
Use a center square and mark at least two lines at some kind of intersecting angle to each other. I'd usually mark 3 or 4 so I could average it out. Whatever method you use to find and mark the center should be OK.
Carefully center punch to establish a divot on that center spot. Then really smack a nice, deep center divot with a beefy center punch and big ol' hammer.
Use an older, kind of beat up but working live center, support the shaft by pressing the live center heartily into the divot you made with the center punch.
Since the tail end is now supported somewhat, you can now spin it and lightly turn a band on the shaft to support it with the steady rest. Obviously you don't want to spin things scary fast and you need to have a really healthy divot from that center punching maneuver, but not as much as you'd think if you haven't done this before. Anyway, once the band is turned, get the steady rest on it so you can face and center drill the end properly.
Now you have a properly dressed and prepped end to support from your better live center. Home free!
This is a bit of back & forth, but the shafts we started with were pretty egged and rough. It still only took ten minutes or so to do, and we had a gantry crane to lift all that heavy stuff which you probably won't need for a 3" shaft.